Resource allocation method in wireless communication system and node performing same

Abstract

According to one aspect of the present disclosure, there is provided a method performed by a first node in a wireless communication system, comprising: transmitting a first request message, the first request message comprising related information of at least one distribution unit (DU) and / or related information of at least one base station related to a mobility LTM configuration request triggered by Layer 1 / Layer 2; receiving a first response message, wherein the first response message comprises LTM random access channel (RACH) configuration information associated with the at least one DU and / or the at least one base station; and sending a second request message, wherein the second request message comprises at least one of the following information: the information of the to-be-released DU, the information of the to-be-released base station, the information of the to-be-released cell, the information of the cell receiving the LTM configuration request, the information of the DU receiving the LTM configuration request, and the information of the base station receiving the LTM configuration request.

Description

Technical Field

[0001] The present disclosure relates to wireless communication technology, and in particular to a resource allocation method for a UE in a mobility situation and various nodes for executing the resource allocation method. Background Art

[0002] To meet the increased demand for wireless data communication services since the deployment of 4G communication systems, efforts have been made to develop improved 5G or quasi-5G communication systems. Therefore, 5G or quasi-5G communication systems are also referred to as "beyond 4G networks" or "post-LTE systems."

[0003] Wireless communication is one of the most successful innovations in modern history. The number of wireless communication service subscribers recently surpassed 5 billion and continues to grow rapidly. Demand for wireless data services is rapidly increasing due to the growing popularity of smartphones and other mobile data devices (e.g., tablets, laptops, netbooks, e-book readers, and machine-type devices) among consumers and businesses. Improving radio interface efficiency and coverage is crucial to meeting this rapid growth and supporting new applications and deployments.

[0004] To reduce service interruption delays during UE mobility, Rel-18 is currently developing specifications for L1 / L2 Triggered Mobility (LTM). This process involves the gNB-DU determining the target cell and issuing a mobility command to the UE based on Layer 1 (Layer 1) measurement reports reported by the UE. Compared to conventional handovers based on Layer 3 measurement reports, LTMs deliver mobility commands more quickly, as L3 measurement reports are derived from linear averaging of Layer 1 measurements. These commands are then received more quickly by the UE via the gNB-DU's Layer 2 MAC CE. Furthermore, RACH-less access procedures can be used for UE access, further reducing service interruption delays during mobility. Summary of the Invention

[0005] According to one aspect of the present disclosure, there is provided a method performed by a first node in a wireless communication system, including: sending a first request message, the first request message including relevant information of at least one distributed unit (DU) and / or relevant information of at least one base station related to a layer 1 / layer 2 triggered mobility LTM configuration request; receiving a first response message, the first response message including LTM random access channel (RACH) configuration information associated with at least one DU and / or at least one base station; sending a second request message, the second request message including at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, information of the cell accepting the LTM configuration request, information of the DU accepting the LTM configuration request, information of the base station accepting the LTM configuration request.

[0006] According to an exemplary embodiment, the method may further include receiving a second response message, the second response message including RACH configurations allocated for other DUs or base stations except for the DU or base station to be released.

[0007] According to an exemplary embodiment, the first request message may further include at least one of the following information related to the LTM configuration request: LTM information request indication, LTM trigger indication, LTM configuration ID of a candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM channel state information (CSI) resource configuration, LTM configuration ID mapping list, list of multiple target secondary next-generation radio access network (S-NG-RAN) nodes, target S-NG-RAN node ID, recommended candidate primary secondary cell (PSCell) information.

[0008] According to an exemplary embodiment, the first response message may further include at least one of the following information: low-layer radio resource control (RRC) configuration generated for a candidate cell or candidate PSCell accepting the LTM configuration request, synchronization signal and physical broadcast channel block (SSB) configuration, new radio physical cell identity (NR PCI) information of the candidate cell, LTM reference configuration, indication of complete LTM configuration, LTM CSI report configuration, wherein the low-layer RRC configuration includes a transmission configuration indication status configuration (TCI) list.

[0009] According to an exemplary embodiment, the second request message may further include at least one of the following information: LTM trigger indication, LTM configuration ID of a candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM CSI resource configuration, LTM configuration ID mapping list, LTM CSI report configuration generated for a candidate cell or candidate PSCell accepting the LTM configuration request, TCI list, SSB configuration, and NR PCI information of the candidate cell.

[0010] According to an exemplary embodiment, the method may further include receiving a second response message, which may include RACH configuration information allocated for other DUs or base stations other than the DU or base station to be released.

[0011] According to an exemplary embodiment, the second response message may further include at least one of the following information: low-layer RRC configuration, SSB configuration, NR PCI information of a candidate cell, LTM reference configuration, indication of LTM complete configuration, LTM CSI report configuration generated for a candidate cell or a candidate PSCell that accepts the LTM configuration request, wherein the low-layer RRC configuration includes a transmission configuration indication status configuration TCI list.

[0012] According to an exemplary embodiment, the method may further include receiving a third request message, which includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released; and sending a fourth request message, which includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, indication information of RACH configuration release for at least one DU or base station to be released.

[0013] According to an exemplary embodiment, the relevant information of the DU or the relevant information of the base station may include at least one of the following: the identifier of the DU, the mapping identifier of the DU, the mapping index of the DU, the identifier of the base station, the mapping identifier of the base station, the mapping index of the base station. According to an exemplary embodiment, the base station may include a master base station and / or a secondary base station.

[0014] According to an exemplary embodiment, the relevant information of the DU or the relevant information of the base station may include at least one of the following: the identifier of the gNB-DU, the mapping identifier of the gNB-DU, the mapping index of the gNB-DU, the identifier of the NG-RAN node, the mapping identifier of the NG-RAN node, the mapping index of the NG-RAN node.

[0015] According to an exemplary embodiment, when the DU is a secondary node SN gNB-DU, or when the base station is an S-NG-RAN node, the relevant information of the DU or the relevant information of the base station may include at least one of the following: the identifier of the SN gNB-DU, the mapping identifier of the SN gNB-DU, the mapping index of the SN gNB-DU, the identifier of the S-NG-RAN node, the mapping identifier of the S-NG-RAN node, the mapping index of the S-NG-RAN node.

[0016] According to an exemplary embodiment, when the DU is the master node MN gNB-DU, or when the base station is the next-generation radio access network master node M-NG-RAN node, the relevant information of the DU or the relevant information of the base station may include at least one of the following: the identifier of the MN gNB-DU, the mapping identifier of the MN gNB-DU, the mapping index of the MN gNB-DU, the identifier of the M-NG-RAN node, the mapping identifier of the M-NG-RAN node, the mapping index of the M-NG-RAN node.

[0017] According to an exemplary embodiment, the method may further include receiving a message related to the timing advance (TA) value, where the message related to the timing advance (TA) value includes at least one of the following: the identifier of the source DU, the mapping identifier of the source DU, the mapping index of the source DU, the identifier of the source base station, the mapping identifier of the source base station, the mapping index of the source base station, the timing advance group identifier pointer (Tag ID Pointer). According to an exemplary embodiment, the source base station may include a source master base station and / or a source secondary base station.

[0018] According to an exemplary embodiment, the message related to the timing advance (TA) value may include at least one of the following: the identifier of the source gNB-DU, the mapping identifier of the source gNB-DU, the mapping index of the source gNB-DU, the identifier of the NG-RAN node, the mapping identifier of the NG-RAN node, the mapping index of the NG-RAN node, the timing advance group identifier pointer (Tag ID Pointer).

[0019] According to an exemplary embodiment, when the source gNB-DU is the SN gNB-DU, or when the NG-RAN node is the S-NG-RAN node, the message related to the timing advance (TA) value may include at least one of the following: the identifier of the SN gNB-DU, the mapping identifier of the SN gNB-DU, the mapping index of the SN gNB-DU, the identifier of the S-NG-RAN node, the mapping identifier of the S-NG-RAN node, the mapping index of the S-NG-RAN node, the identifier of the M-NG-RAN node to which the S-NG-RAN node belongs, the mapping identifier of the M-NG-RAN node, the index of the M-NG-RAN node, the timing advance group identifier pointer (Tag ID Pointer).

[0020] According to an exemplary embodiment, in the case where the gNB-DU is a MN gNB-DU or the NG-RAN node is a M-NG-RAN node, a message related to the Timing Advance (TA) value may include at least one of the following: the identifier of the MN gNB-DU, the mapping identifier of the MN gNB-DU, the mapping index of the MN gNB-DU, the identifier of the M-NG-RAN node, the mapping identifier of the M-NG-RAN node, the mapping index of the M-NG-RAN node, and the Timing Advance Group Identifier Pointer (Tag ID Pointer).

[0021] According to an exemplary embodiment, the first request message may include at least one of a UE context establishment request, a UE context modification request, a handover request, an S-Node addition request, an S-Node modification request, and an S-Node change request message. According to an exemplary embodiment, the first response message may include at least one of a UE context establishment response, a UE context modification response, a handover request confirmation, an S-Node addition request confirmation, and an S-Node modification request confirmation. According to an exemplary embodiment, the second request message may include at least one of a UE context modification request, a handover request, and an S-Node modification request. According to an exemplary embodiment, at least one of the first request message, the first response message, and the second request message may be a message between the first node and the DU (e.g., an F1 Application Protocol F1ap message) or a message between the first node and the base station (e.g., an Xn Application Protocol Xnap message).

[0022] According to an exemplary embodiment, the third request message may include at least one of a UE context release request, a UE context modification requirement, and a conditional handover cancellation. According to an exemplary embodiment, the fourth request message may include at least one of a UE context release command, a UE context modification request, and a handover cancellation. According to an exemplary embodiment, at least one of the third request message and the fourth request message may be a message between the first node and the DU (e.g., an F1 Application Protocol F1ap message) or a message between the first node and the base station (e.g., an Xn Application Protocol Xnap message).

[0023] According to an exemplary embodiment, the method may further include: in the case where it is determined that the UE is to perform a cell handover, sending a Long-Term Measurement (LTM) cell handover notification, the LTM cell handover notification including the ID of the target cell or the target PSCell for which the LTM handover is to be performed and / or the TCI state ID (including the combined or downlink TCI state ID and the uplink TCI state ID), and including the valid TA value information of other candidate cells or candidate PSCs. According to an exemplary embodiment, the LTM cell handover notification may be sent via an Xnap message.

[0024] According to another aspect of the present disclosure, there is provided a method performed by a second node in a wireless communication system, including: receiving a first request message, the first request message including relevant information of at least one distributed unit (DU) and / or relevant information of at least one base station related to a layer 1 / layer 2-triggered mobility LTM configuration request; sending a first response message, the first response message including LTM random access channel (RACH) configuration information associated with at least one DU and / or at least one base station; and receiving a second request message, the second request message including at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, information of the cell accepting the LTM configuration request, information of the DU accepting the LTM configuration request, information of the base station accepting the LTM configuration request.

[0025] According to an exemplary embodiment, the first request message may further include at least one of the following information related to the LTM configuration request: LTM information request indication, LTM trigger indication, LTM configuration ID of a candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM channel state information (CSI) resource configuration, LTM configuration ID mapping list, list of multiple target secondary next-generation radio access network (S-NG-RAN) nodes, target S-NG-RAN node ID, recommended candidate primary secondary cell (PSCell) information.

[0026] According to an exemplary embodiment, the first response message may further include at least one of the following information: low-layer radio resource control (RRC) configuration generated for a candidate cell or candidate PSCell accepting the LTM configuration request, synchronization signal and physical broadcast channel block (SSB) configuration, new radio physical cell identity (NR PCI) information of the candidate cell, LTM reference configuration, indication of complete LTM configuration, LTM CSI report configuration, wherein the low-layer RRC configuration includes a transmission configuration indication (TCI) state configuration list.

[0027] According to an exemplary embodiment, the second request message may further include at least one of the following information: LTM trigger indication, LTM configuration ID of a candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM CSI resource configuration, LTM configuration ID mapping list, LTM CSI report configuration generated for a candidate cell or candidate PSCell accepting the LTM configuration request, TCI state configuration list, SSB configuration, and NR PCI information of the candidate cell.

[0028] According to an exemplary embodiment, the method may further include sending a second response message, the second response message may include RACH configuration information allocated for other DUs or base stations except the DU or base station to be released.

[0029] According to an exemplary embodiment, the second response message may further include at least one of the following information: low-layer RRC configuration generated for a candidate cell or a candidate PSCell that accepts the LTM configuration request, SSB configuration, NR PCI information of the candidate cell, LTM reference configuration, indication of complete LTM configuration, LTM CSI report configuration, wherein the low-layer RRC configuration includes a transmission configuration indication status configuration TCI list.

[0030] According to an exemplary embodiment, when the second request message includes at least one of the following: information of a cell that accepts the LTM configuration request, information of a DU that accepts the LTM configuration request, information of a base station that accepts the LTM configuration request, the method further includes: determining at least one of information of a cell to be released, information of a DU to be released, information of a base station to be released based on the second request message and pre-configured information, the pre-configured information including information of at least one candidate cell and information of a DU and / or a base station associated with the at least one candidate cell; and performing a release for the RACH configuration of at least one DU or base station to be released.

[0031] According to an exemplary embodiment, the method may further include: sending a third request message, the third request message including at least one of the following: information of a DU to be released, information of a base station to be released, information of a cell to be released.

[0032] According to an exemplary embodiment, the method may further include: receiving a fourth request message, the fourth request message including at least one of the following: information of a DU to be released, information of a base station to be released, information of a cell to be released, indication information of a release of the RACH configuration for at least one DU or base station to be released; and performing a release for the RACH configuration of at least one DU or base station to be released.

[0033] According to an exemplary embodiment, the relevant information of the DU or the relevant information of the base station may include at least one of the following: identifier of the DU, mapping identifier of the DU, mapping index of the DU, identifier of the base station, mapping identifier of the base station, mapping index of the base station. According to an exemplary embodiment, the base station may include a primary base station and / or a secondary base station.

[0034] According to an exemplary embodiment, the relevant information of the DU or the relevant information of the base station may include at least one of the following: identifier of the gNB-DU, mapping identifier of the gNB-DU, mapping index of the gNB-DU, identifier of the NG-RAN node, mapping identifier of the NG-RAN node, mapping index of the NG-RAN node.

[0035] According to an exemplary embodiment, when the DU is a secondary node SN gNB-DU or the base station is an S-NG-RAN node, the relevant information of the DU or the relevant information of the base station may include at least one of the following: the identifier of the SN gNB-DU, the mapping identifier of the SN gNB-DU, the mapping index of the SN gNB-DU, the identifier of the S-NG-RAN node, the mapping identifier of the S-NG-RAN node, and the mapping index of the S-NG-RAN node.

[0036] According to an exemplary embodiment, when the DU is a master node MN gNB-DU or the base station is a next-generation radio access network master node M-NG-RAN node, the relevant information of the DU or the relevant information of the base station may include at least one of the following: the identifier of the MN gNB-DU, the mapping identifier of the MN gNB-DU, the mapping index of the MN gNB-DU, the identifier of the M-NG-RAN node, the mapping identifier of the M-NG-RAN node, and the mapping index of the M-NG-RAN node.

[0037] According to an exemplary embodiment, the method may further include sending a message related to a timing advance (TA) value. The message related to the timing advance (TA) value may include at least one of the following: the identifier of the source DU, the mapping identifier of the source DU, the mapping index of the source DU, the identifier of the source base station, the mapping identifier of the source base station, the mapping index of the source base station, and a timing advance group identifier pointer (Tag ID Pointer). According to an exemplary embodiment, the source base station may include a source master base station and / or a source secondary base station.

[0038] According to an exemplary embodiment, the message related to the timing advance (TA) value may include at least one of the following: the identifier of the source gNB-DU, the mapping identifier of the source gNB-DU, the mapping index of the source gNB-DU, the identifier of the NG-RAN node, the mapping identifier of the NG-RAN node, the mapping index of the NG-RAN node, and a timing advance group identifier pointer (Tag ID Pointer).

[0039] According to an exemplary embodiment, when the source gNB-DU is an SN gNB-DU or the NG-RAN node is an S-NG-RAN node, the message related to the timing advance (TA) value may include at least one of the following: the identifier of the SN gNB-DU, the mapping identifier of the SN gNB-DU, the mapping index of the SN gNB-DU, the identifier of the S-NG-RAN node, the mapping identifier of the S-NG-RAN node, the mapping index of the S-NG-RAN node, the identifier of the M-NG-RAN node to which the S-NG-RAN node belongs, the mapping identifier of the M-NG-RAN node, the index of the M-NG-RAN node, and a timing advance group identifier pointer (Tag ID Pointer).

[0040] According to an exemplary embodiment, in the case where the gNB-DU is the MN gNB-DU, or the NG-RAN node is the M-NG-RAN node, the message related to the Timing Advance (TA) value may include at least one of the following: the identifier of the MN gNB-DU, the mapping identifier of the MN gNB-DU, the mapping index of the MN gNB-DU, the identifier of the M-NG-RAN node, the mapping identifier of the M-NG-RAN node, the mapping index of the M-NG-RAN node, the Timing Advance Group Identifier Pointer (Tag ID Pointer).

[0041] According to an exemplary embodiment, the first request message may include at least one of a UE context establishment request, a UE context modification request, a handover request, an S-Node addition request, an S-Node modification request, and an S-Node change request message. According to an exemplary embodiment, the first response message may include at least one of a UE context establishment response, a UE context modification response, a handover request confirmation, an S-Node addition request confirmation, and an S-Node modification request confirmation. According to an exemplary embodiment, the second request message may include at least one of a UE context modification request, a handover request, and an S-Node modification request. According to an exemplary embodiment, at least one of the first request message, the first response message, and the second request message may be a message between the first node and the DU (e.g., an F1 Application Protocol (F1ap) message) or a message between the first node and the base station (e.g., an Xn Application Protocol (Xnap) message).

[0042] According to an exemplary embodiment, the third request message may include at least one of a UE context release request, a UE context modification requirement, and a conditional handover cancellation, where the third request message may be a message between the first node and the DU (e.g., an F1ap message) or a message between the first node and the base station (e.g., an Xnap message).

[0043] According to an exemplary embodiment, the fourth request message may include at least one of a UE context release command, a UE context modification request, and a handover cancellation, where at least one of the fourth request messages may be an F1ap message or an Xnap message.

[0044] According to an exemplary embodiment, the method may further include: receiving a Long-Term Mobility (LTM) cell handover notification when it is determined that the UE is to perform a cell handover, the LTM cell handover notification including the ID of the target cell or target Primary Secondary Cell (PSCell) for which the LTM handover is to be performed and / or the TCI state ID (including combined or downlink TCI state ID, and uplink TCI state ID), and including valid TA value information of other candidate cells or candidate PSCs. According to an exemplary embodiment, the LTM cell handover notification is forwarded via an Xnap message.

[0045] According to another aspect of the present disclosure, there is provided a method performed by a User Equipment (UE) in a wireless communication system, including: sending a layer 3 measurement report to a source Distributed Unit (DU), wherein the layer 3 measurement report is sent by the source DU to a first node, a first request message is sent by the first node, the first request message including relevant information of at least one DU and / or relevant information of at least one base station related to a layer 1 / layer 2 triggered mobility Long-Term Mobility (LTM) configuration request; a first response message is received by the first node, the first response message including LTM Random Access Channel (RACH) configuration information associated with at least one DU and / or at least one base station; a second request message is sent by the first node, the second request message including at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, information of the cell that accepts the LTM configuration request, information of the DU that accepts the LTM configuration request, information of the base station that accepts the LTM configuration request; and receiving a Radio Resource Control (RRC) reconfiguration message sent by the source DU.

[0046] According to an exemplary embodiment, the RRC reconfiguration message includes an addition, or modification, or release operation related to the LTM Random Access Channel (RACH) configuration information.

[0047] According to an exemplary embodiment, the LTM Random Access Channel (RACH) configuration information includes the LTM Random Access Channel (RACH) configuration information for each accepted LTM candidate cell associated with the at least one DU and / or the at least one base station, or includes the LTM Random Access Channel (RACH) configuration information for each accepted LTM candidate cell associated with a list of LTM candidate cells configured under the at least one DU and / or the at least one base station.

[0048] According to an exemplary embodiment, the first request message further includes at least one of the following information related to the LTM configuration request: LTM information request indication, LTM trigger indication, LTM configuration ID of the candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM Channel State Information (CSI) resource configuration, LTM configuration ID mapping list, list of multiple target base stations, target base station ID, recommended candidate Primary Secondary Cell (PSCell) information.

[0049] According to an exemplary embodiment, the first response message further includes at least one of the following information: low-layer radio resource control (RRC) configuration generated for a candidate cell or a candidate PSCell that accepts the LTM configuration request, synchronization signal and physical broadcast channel block (SSB) configuration, new radio physical cell identity (NR PCI) information of the candidate cell, LTM reference configuration, indication of complete LTM configuration, LTM CSI report configuration, wherein the low-layer RRC configuration includes a transmission configuration indication (TCI) state configuration list.

[0050] According to an exemplary embodiment, the second request message further includes at least one of the following information: LTM trigger indication, LTM modification indication, LTM configuration ID of the candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM CSI resource configuration, LTM configuration ID mapping list, LTM CSI report configuration generated for a candidate cell or a candidate PSCell that accepts the LTM configuration request, transmission configuration indication (TCI) state configuration list, SSB configuration, and NR PCI information of the candidate cell.

[0051] According to an exemplary embodiment, the third request message is received by the first node, and the third request message includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released.

[0052] According to an exemplary embodiment, the fourth request message is sent by the first node, and the fourth request message includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, indication information of RACH configuration release for at least one DU or base station to be released.

[0053] According to an exemplary embodiment, the relevant information of the DU or the relevant information of the base station includes at least one of the following: identification of the DU, mapping identification of the DU, mapping index of the DU, identification of the base station, mapping identification of the base station, mapping index of the base station. According to an exemplary embodiment, the base station may include a primary base station and / or a secondary base station.

[0054] According to an exemplary embodiment, a message related to the timing advance (TA) value is received by the first node, and the message related to the timing advance (TA) value includes at least one of the following: identification of the source DU, mapping identification of the source DU, mapping index of the source DU, identification of the source base station, mapping identification of the source base station, mapping index of the source base station, timing advance group identification pointer (Tag IDPointer). According to an exemplary embodiment, the source base station may include a source primary base station and / or a source secondary base station.

[0055] According to an exemplary embodiment, the first request message includes at least one of a UE context establishment request, a UE context modification request, a handover request, an S-Node addition request, an S-Node modification request, and an S-Node change request message. According to an exemplary embodiment, the first response message includes at least one of a UE context establishment response, a UE context modification response, a handover request confirmation, an S-Node addition request confirmation, and an S-Node modification request confirmation. According to an exemplary embodiment, the second request message includes at least one of a UE context modification request, a handover request, and an S-Node modification request.

[0056] According to an exemplary embodiment, the third request message includes at least one of a UE context release request, a UE context modification requirement, and a conditional handover cancellation. According to an exemplary embodiment, the fourth request message includes at least one of a UE context release command, a UE context modification request, and a handover cancellation.

[0057] According to an exemplary embodiment, in the case where the UE is determined to perform a cell handover, the LTM cell handover notification is sent by the first node. The LTM cell handover notification includes the ID of the target cell or target PSCell for which the LTM handover will be performed and / or the TCI status ID (including the combined or downlink TCI status ID, and the uplink TCI status ID), and includes valid TA value information of other candidate cells or candidate PSCs. According to other aspects of the present disclosure, a first node, a second node, and a UE for performing the above method are also disclosed. According to other aspects of the present disclosure, a computer-readable storage medium is also disclosed, which stores computer-executable instructions. When the computer-executable instructions are executed by a processor, the processor executes the method performed by the first node, the second node, or the UE as described above.

[0058] According to the embodiments of the present disclosure, it is possible to avoid the occurrence of LTM failures or anomalies in multiple scenarios where LTM occurs (for example, the nodes to which the source cell and the target cell belong can be under the same gNB-DU, or under different gNB-DUs but the same gNB-CU, or under different gNB-CUs). BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is an exemplary system architecture evolved according to the system architecture of the present disclosure.

[0060] Figure 2 is an exemplary system architecture according to various embodiments of the present disclosure.

[0061] Figure 3 is a flowchart of the LTM process in the prior art.

[0062] Figures 4-1 to 4-2It is a flowchart of the LTM process in the same CU different DU scenario according to an exemplary embodiment of the present disclosure.

[0063] Figures 5a-1 to 5a-3 Figures 4 and 5b are flowcharts of the LTM process in different CU scenarios according to an exemplary embodiment of the present disclosure.

[0064] Figures 6-1 to 6-3 It is a flowchart of the LTM process in the same MN different SN scenario in dual connectivity according to an exemplary embodiment of the present disclosure.

[0065] Figure 7 It is an embodiment where L3 handover occurs in the case of the configuration of LTM for the same CU different DU (Intra-CU Inter-DU).

[0066] Figure 8 It is an embodiment where the L3 handover process occurs in the case of the LTM configuration between different CUs (Inter-CU / gNB).

[0067] Figure 9 It is an embodiment where in the scenario of NR-DC, in the case of the inter-CU (inter-SN) LTM (SN change without MN change) configuration between different CUs triggered by the source S-NG-RAN node (source SN or S-SN), the S-SN triggers the L3 SN change process.

[0068] Figure 10 It is an embodiment where in the scenario of NR-DC, in the inter-CU (or inter-SN) LTM (SN change without MN change) process between different CUs triggered by the MN or the source S-NG-RAN node (source SN or S-SN).

[0069] Figure 11 It shows a flowchart of a method executed by a first node in a wireless communication system according to an exemplary embodiment of the present application.

[0070] Figure 12 It shows a flowchart of a method executed by a second node in a wireless communication system according to an exemplary embodiment of the present application.

[0071] Figure 13 It shows an exemplary structure applicable to each node of the present disclosure. Detailed implementation manners

[0072] The accompanying drawings discussed below and the various embodiments used to describe the principles of the present disclosure are for illustration only and should not be construed in any way as limiting the scope of the present disclosure. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any appropriately arranged system or device.

[0073] Figure 1 is an exemplary system architecture 1000 of System Architecture Evolution (SAE). The User Equipment (UE) 1001 is a terminal device used to receive data. The Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 1002 is a radio access network, which includes macro base stations (eNodeB / NodeB) that provide access to the wireless network interface for the UE. The Mobility Management Entity (MME) 1003 is responsible for managing the mobility context, session context, and security information of the UE. The Services Gateway (SGW) 1004 mainly provides user plane functions, and the MME 1003 and SGW 1004 may be in the same physical entity. The Packet Data Network Gateway (PGW) 1005 is responsible for functions such as charging and lawful interception, and may also be in the same physical entity as the SGW 1004. The Policy and Charging Rule Function (PCRF) 1006 provides Quality of Service (QoS) policies and charging guidelines. The Serving General Packet Radio Service (GPRS) Support Node (SGSN) 1008 is a network node device in the Universal Mobile Telecommunications System (UMTS) that provides routing for data transmission. The Home Subscriber Server (HSS) 1009 is the home subscription subsystem of the UE, responsible for protecting user information including the current location of the user equipment, the address of the serving node, user security information, and the packet data context of the user equipment.

[0074] Figure 2Exemplary system architecture 2000 according to various embodiments of the present disclosure. Other embodiments of the system architecture 2000 can be used without departing from the scope of the present disclosure. UE 2001 is a terminal device for receiving data. Next Generation-Radio Access Network (NG-RAN) 2002 is a radio access network, which includes base stations (gNB or eNB connected to the 5th Generation (5G) core network 5GC, and the eNB connected to 5GC is also called ng-gNB) that provide access to the wireless network interface for the UE. Access and Mobility Management Function (AMF) 2003 is responsible for managing the mobility context and security information of the UE. User Plane Function (UPF) 2004 mainly provides the functions of the user plane. Session Management Function (SMF) 2005 is responsible for session management. Data Network (DN) 2006 includes services such as those of the operator, access to the Internet, and third-party services.

[0075] For the convenience of description, the following are the dedicated names and explanations involved in the description of the embodiments of the present disclosure:

[0076] 1. LTM (L1 / L2 Triggered Mobility): Layer 1 / Layer 2 Triggered Mobility

[0077] 2. CFRA (Contention Free Random Access): Contention Free Random Access

[0078] 3. CSI (Channel State Information): Channel State Information

[0079] 4. CGI (Cell Global ID): Cell Global ID

[0080] 5. RLF (Radio Link Failure): Radio Link Failure

[0081] 6. AMF (Access and Mobility Management Function): Access and Mobility Management Function, which is a network element of the 5G core network and is responsible for 5G base station access and mobility management. The 5G base station is connected to the AMF through the NG-C interface.

[0082] 7. NG-RAN (New Generation Radio Access Network) Node: The next-generation radio access network node, e.g., a 5G base station, including gNB or ng-eNB.

[0083] 8. gNB (next Generation Node B): The next-generation base station node, e.g., a 5G NR (New Radio) base station.

[0084] 9. gNB-DU (Distributed Unit): The distributed unit of gNB. gNB-DU has functions such as the Radio Link Control (RLC) protocol, the Medium Access Control (MAC) protocol, and the Physical Layer (PHY) protocol.

[0085] 10. gNB-CU (Central Unit): The central unit of gNB. gNB-CU has functions such as the Radio Resource Control (RRC), the Service Data Adaptation Protocol (SDAP), and the Packet Data Convergence Protocol (PDCP).

[0086] 11. NR-DC (NR-NR Dual Connectivity): New Radio - New Radio dual connectivity, i.e., the next-generation radio access network dual connectivity.

[0087] 12. MN (Master Node): The master node.

[0088] 13. SN (Secondary Node): The secondary node.

[0089] 14. SCG (Secondary Cell Group): The secondary cell group. In the next-generation radio access network dual connectivity, it is the group of serving cells associated with the secondary node, including the primary cell SpCell (PSCell) of the secondary cell group, and optionally including one or more secondary cells SCell.

[0090] 15. PSCell (SpCell of a secondary cell group): The primary secondary cell, i.e., the primary cell in the secondary cell group.

[0091] 16. MCG (Master Cell Group): The master cell group, in the next-generation wireless access network dual-connection, is a group of serving cells associated with the master node, including the primary cell (PCell) of the master cell group, and optionally including one or more secondary cells (SCells).

[0092] 17. PCell (SpCell of a master cell group): The primary cell in the master cell group.

[0093] 18. SpCell (primary cell of a master or secondary cell group): The primary cell, that is, the primary cell in the master cell group or the secondary cell group.

[0094] 19. SpCell (Special Cell): The special cell, that is, the primary cell serving the UE, the primary cell in the master cell group or the secondary cell group.

[0095] 20. Tag ID Pointer (Timing Advance Group ID Pointer): The timing advance group identification pointer, that is, the tag-Id-ptr (Pointer) information defined in the TCI-UL-State IE or TCI-State IE in TS 38.331. The tag-Id-ptr indicates the TAG associated with or applied to the TCI state of the serving cell or cell. The value n0 indicates that the TAG associated with the TCI state of the cell or cell is represented by the tag-Id (Timing Advance Group ID), and the value n1 indicates that the TAG associated with the TCI state of the cell or cell is represented by the tag2-Id. The tag-Id represents the TAG associated with the TCI state set of the cell or cell.

[0096] It should be understood that the message names in this disclosure are only examples, and other names can be adopted. The information to be transmitted between interfaces can be defined in the form of a new message alone, or in the form of adding a new information element (IE) to an existing message in the existing corresponding interface specification.

[0097] The exemplary embodiments of the present disclosure will be further described below with reference to the accompanying drawings.

[0098] The text and drawings of the present disclosure are provided only as examples to assist in understanding the present disclosure. They should not be construed as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, it will be apparent to those skilled in the art based on the content disclosed herein that changes can be made to the illustrated embodiments and examples without departing from the scope of the present disclosure.

[0099] For the LTM process, the UE accesses another target cell from the source cell in the LTM manner. From the perspective of configuring the UE, the network-side configuration of LTM and the corresponding configured resources may change during the preparation phase, and how to cope with this change is a problem that needs to be solved.

[0100] Furthermore, considering the scenarios where the UE undergoes LTM, more scenarios need to be supported. For example, the nodes to which the source cell and the target cell belong may be under the same gNB-DU, or under different gNB-DUs but the same gNB-CU, or may be under different gNB-CUs (i.e., different base stations), and for the scenario of different gNB-CUs, it may be under different primary base stations or different secondary base stations in dual connection. This application proposes a configuration solution for the above-mentioned multiple scenarios and improves the technical points that may have defects in the existing configuration solutions.

[0101] Figure 3 It is a flowchart of an exemplary LTM process according to the present disclosure. To illustrate the failure scenarios that may occur during the LTM execution process, the normal LTM process is first introduced. Figure 3 The process represented shows the scenario where the UE moves from one gNB-DU to another gNB-DU under the same gNB-CU during NR LTM. The process is as follows:

[0102] 1. L3 measurement control and reporting

[0103] In one embodiment, the UE sends a Measurement Report (measurement report) message (the L3 measurement results are reported in this message) to the source gNB-DU, which contains the measurement values of neighboring cells. The source gNB-DU sends a UL RRCMESSAGE TRANSFER (uplink radio resource control message transfer) message to pass the received Measurement Report message to the gNB-CU.

[0104] 2. The gNB-CU decides to initiate LTM configuration.

[0105] 3. The gNB-CU sends a UE CONTEXT SETUP REQUEST message to the candidate gNB-DU, which contains at least one of the following information: a candidate cell ID, the LTM configuration ID of the candidate cell, a mapping list of LTM configuration IDs, and CSI resource configuration. The gNB-CU indicates the source gNB-DU ID and requests physical random access channel (PRACH) resources from the candidate gNB-DU. The gNB-CU may request the candidate gNB-DU to provide low layer configurations to generate a reference configuration.

[0106] 4. If the candidate gNB-DU accepts the LTM configuration request, it will respond with a UE CONTEXT SETUP RESPONSE message, which includes at least one of the following: low layer RRC configurations generated for the accepted target candidate cell (e.g., Transmission Configuration Indication (TCI) state configuration and Random Access Channel (RACH) configuration) and CSI report configuration.

[0107] 5. The gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU, including at least one of the following: CSI report configuration, TCI state configuration, and RACH configuration of the accepted target candidate cell in other gNB-DUs that have been collected.

[0108] 6. The source gNB-DU sends a UE CONTEXT MODIFICATION RESPONSE message as a response. This message may include the CSI report configuration generated for the prepared candidate cell.

[0109] 7. The gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the candidate gNB-DU, which contains at least one of the following: CSI report configuration, TCI state configuration, RACH configuration, and LTM configuration ID of the candidate cell in other candidate gNB-DUs. The gNB-CU may also provide the candidate gNB-DU with a reference configuration for the low layer part. The gNB-CU may also provide the candidate gNB-DU with an updated CSI resource configuration. As a possibility, the candidate cell may be the same cell as the source cell.

[0110] 8. The candidate gNB-DU sends a UE context modification response message as a response, including the updated low-layer configuration. The response sent by the candidate gNB-DU may also include the updated CSI report configuration.

[0111] 9. The gNB-CU sends a Downlink RRC Message Transfer message to the source gNB-DU, which contains the generated RRC Reconfiguration message with the LTM configuration.

[0112] 10. The source gNB-DU forwards the received RRC Reconfiguration message to the UE.

[0113] 11. The UE sends an RRC Reconfiguration Complete message to the source gNB-DU.

[0114] 12. The source gNB-DU forwards the RRC Reconfiguration Complete message to the gNB-CU via an Uplink RRC Message Transfer message.

[0115] 13. Early synchronization is performed to obtain an early Timing Advance (TA) value.

[0116] 14-15. The candidate gNB-DU sends at least one of the following to the source gNB-DU via DU-CU TA INFORMATION TRANSFER and CU-DU TA INFORMATION TRANSFER messages: TA value information, and associated CFRA resource information, candidate cell ID, and source gNB-DU ID. Among them, the source gNB-DU ID may be omitted in the CU-DU TA INFORMATION TRANSFER message.

[0117] 16. The UE sends a layer 1 measurement report to the source gNB-DU.

[0118] 17. The source gNB-DU decides to perform an LTM cell handover to a candidate target cell.

[0119] 18. The source gNB-DU sends a Cell Switch command to the UE.

[0120] 19. The source gNB-DU sends a DU-CU CELL SWITCH NOTIFICATION message to the gNB-CU, indicating that a cell switch command has been initiated to the UE. The DU-CU cell switch notification includes the target cell ID and / or the TCI status ID (including the combined or downlink TCI status ID, and the uplink TCI status ID), and includes valid TA value information for other candidate cells.

[0121] 20. The gNB-CU sends the target cell ID and / or the TCI status ID (including the combined or downlink TCI status ID, and the uplink TCI status ID), and includes valid TA value information for other candidate cells to the target gNB-DU through a CU-DU CELL SWITCH NOTIFICATION.

[0122] 21. The target gNB-DU detects that the UE has successfully accessed (based on the rach-less or rach-based access procedure).

[0123] 22. The target gNB-DU sends an ACCESS SUCCESS message to the gNB-CU and carries the target cell ID.

[0124] 23. The UE sends an RRCReconfigurationComplete message to the target gNB-DU.

[0125] 24. The target gNB-DU forwards the RRC reconfiguration complete message to the gNB-CU through an UL RRC MESSAGE TRANSFER message.

[0126] 25. The gNB-CU may send a UE CONTEXT RELEASE COMMAND message to the source gNB-DU to release the resources and configurations of the prepared cells (including the source cell).

[0127] 26. The source gNB-DU sends a UE CONTEXT RELEASE COMPLETE message to the gNB-CU as a response.

[0128] Figures 4-1 to 4-2(hereinafter collectively referred to as Figure 4) is an exemplary embodiment according to the present disclosure for the LTM process between different gNB-DUs of the same gNB-CU. The LTM process includes a one-time LTM handover process and a subsequent LTM process. The one-time LTM handover process means that after completing a single LTM handover process, the resources of the source cell and other unselected candidate cells are released on both the UE side and the network side. The subsequent LTM process means that when the UE undergoes an LTM process and switches from the source cell to the target cell, the configurations of other candidate cells are still retained on both the UE side and the network side. Optionally, if the source cell is a candidate cell for subsequent LTM, the above "other candidate cells" also include the source cell that is a candidate cell for subsequent LTM. In this way, without RRC reconfiguration, the UE reports the L1 measurement report of the candidate cell to the gNB-DU currently serving the UE according to the pre-configured LTM CSI report configuration for each candidate cell. After receiving the L1 measurement report, the gNB-DU can continue to trigger the LTM handover process to cause the UE to switch from the currently serving cell to another candidate cell. In this way, within the configured candidate cell list, the UE can undergo subsequent LTM handover processes without RRC reconfiguration.

[0129] In the LTM process between different gNB-DUs of the same gNB-CU, the RACH configuration for candidate cells is allocated for each gNB-DU. The advantage of this is the efficient utilization of PRACH resources. The PRACH resources allocated to each gNB-DU can serve multiple UEs under the gNB-DU because these UEs under the same gNB-DU may be configured for LTM for the same candidate cell. When the UE undergoes an LTM handover to a target cell under subsequent LTM configuration, if this cell belongs to another gNB-DU, the UE switches to a target gNB-DU. Under the new serving gNB-DU, the UE may also trigger an early TA acquisition process, that is, process 13 in the flow of Figure 4. This process includes that after the UE receives the PDCCH order instruction sent by the gNB-DU of the current serving UE, it sends a random access request first message to the candidate cell using the random access resource configuration indicated in the instruction. The random access resource configuration indicated in the instruction is specified, for example, by parameters such as the random access preamble index, synchronization signal, and physical broadcast channel (PBCH) block index (SSB index, synchronization signal / PBCH block index), and the PRACH occasion mask index. After receiving the random access request first message, the candidate cell calculates the timing advance (TA) value between the UE and the candidate cell. The candidate gNB-DU then sends the TA value and auxiliary information to the source gNB-DU, that is, the gNB-DU of the current serving UE, through processes 14-15. In Figure 3In procedure 3, the UE CONTEXT SETUP REQUEST message sent by the gNB-CU to the candidate gNB-DU contains a source gNB-DU ID and requests Physical Random Access Channel (PRACH) resources from the candidate gNB-DU. If only a one-time LTM handover procedure is supported, it is feasible to carry only one source gNB-DU ID because only the source gNB-DU needs to command the UE to perform the early TA acquisition procedure. However, if subsequent LTM procedures are to be supported, then each candidate cell needs to pre-allocate PRACH resources for each other candidate gNB-DU. Because when the UE accesses the target gNB-DU to which the target cell belongs, the corresponding target gNB-DU can use the PRACH resources of a certain candidate cell pre-allocated to this gNB-DU to command the UE to perform the early TA acquisition procedure for this candidate cell.

[0130] Therefore, according to an exemplary embodiment of the present application, it is possible to consider enhancing Figure 3 the partial procedures shown. Procedures 1 to 26 shown in FIG. 4 are similar to Figure 3 procedures 1 to 26 of Figure 3 which will not be described again in the following description. The embodiment of FIG. 4 enhances

[0131] the partial procedures in the embodiment of

[0132] - Optionally, a list of candidate gNB-DU IDs containing each other candidate gNB-DU ID can be directly carried. This list contains the source gNB-DU ID and other candidate gNB-DU IDs, indicating that the candidate cell needs to allocate PRACH resources for each gNB-DU configured for subsequent LTM.

[0133] - Optionally, if the gNB-CU does not want to carry the clear-text gNB-DU ID list, the gNB-CU can also, based on the implementation, map each candidate gNB-DU to a certain mapping ID or index or identifier. Then, a list containing the mapping ID or index or identifier (LTM gNB-DU Mapping ID / Index / identifier) of the LTM gNB-DU is sent to the candidate gNB-DU to request the candidate cell to configure for subsequent LTM, and PRACH resources are allocated for the mapping ID or index or identifier of each LTM gNB-DU.

[0134] Correspondingly, in process 4, the candidate gNB-DU accepts the LTM configuration request and sends a UE CONTEXT SETUP RESPONSE message as a response, which includes a list of RACH configurations of the target candidate cells that accept the LTM configuration request. Hereinafter, the candidate cell that accepts the LTM configuration request is also referred to as the "accepted candidate cell".

[0135] - Optionally, this list contains the PRACH resources allocated by the candidate cell for each requested gNB-DU ID.

[0136] - Optionally, if the gNB-CU provides a mapping ID or index or identifier, correspondingly, this list contains the PRACH resources allocated by the candidate cell for the mapping ID or index or identifier of each requested LTM gNB-DU (one mapped ID or index or identifier corresponds to one gNB-DU ID).

[0137] If the gNB-CU needs to configure the source gNB-DU as a candidate gNB-DU for subsequent LTM, then in process 5, the gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU, including the RACH configurations of the target candidate cells that have accepted the LTM configuration request in other gNB-DUs collected, and at the same time requests PRACH resources from the source gNB-DU.

[0138] - Optionally, a candidate gNB-DU ID list containing each other candidate gNB-DU ID can be directly carried. This list contains other candidate gNB-DU IDs, indicating that each candidate gNB-DU that requires the source cell or other candidate cells under the source gNB-DU to allocate PRACH resources for subsequent LTM configuration.

[0139] - Optionally, if the gNB-CU does not want to carry the list of plaintext gNB-DU IDs, the gNB-CU can also, based on the implementation, map each candidate gNB-DU to a certain mapping identifier / index / identifier, and send a list containing the mapping identifier / index / identifier (LTM gNB-DU Mapping ID / Index / identifier) of the LTM gNB-DU to the candidate gNB-DU, to request the source cell or other candidate cells under the source gNB-DU to allocate PRACH resources for each mapping identifier / index / identifier, so as to facilitate subsequent LTM configuration.

[0140] The process in which the gNB-CU configures the source gNB-DU as a candidate gNB-DU for subsequent LTM can occur between process 2 and process 5. Correspondingly, in process 6, the source gNB-DU sends a UE CONTEXT MODIFICATION RESPONSE message as a response. This message includes a list of RACH configurations of the accepted target candidate cells (which may include the source cell or other candidate cells under the source gNB-DU).

[0141] - Optionally, this list contains the PRACH resources allocated by the source cell or other candidate cells under the source gNB-DU for each requested gNB-DU ID.

[0142] - Optionally, if the gNB-CU provides a mapping identifier / index / identifier, correspondingly, this list contains the PRACH resources allocated by the source cell or other candidate cells under the source gNB-DU for each requested mapping identifier / index / identifier of the LTM gNB-DU (one mapping identifier / index / identifier corresponds to one gNB-DU ID).

[0143] In this way, for each gNB-DU for subsequent LTM configuration, including each candidate gNB-DU and the source gNB-DU, the gNB-CU obtains the RACH configurations allocated by each candidate cell for different gNB-DUs. Then, the gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to each of the other candidate gNB-DUs, notifying each gNB-DU of the RACH configurations allocated by the target candidate cells that have accepted the LTM configuration request among the other gNB-DUs for this gNB-DU.

[0144] Then, the source gNB-DU sends a PDCCH command instruction to the UE, commanding the UE to send a first random access request message to the candidate cell using the random access resource configuration indicated in the instruction. Among them, the random access resource configuration indicated in the instruction is specified, for example, by parameters such as the random access preamble index, the synchronization signal / PBCH block index, and the PRACH occasion mask index. After receiving the first random access request message, the candidate cell calculates the timing advance (TA) value between the UE and the candidate cell. Then, the candidate gNB-DU sends the TA value and auxiliary information to the source gNB-DU, that is, the gNB-DU currently serving the UE, through procedures 14-15.

[0145] - Optionally, if the RACH configuration is allocated based on the gNB-DU ID provided by the gNB-CU, when sending the TA value and auxiliary information to the gNB-CU in procedure 14, the source gNB-DU ID needs to be carried and sent to the gNB-CU so that the gNB-CU can continue to forward the corresponding TA information to the specified gNB-DU ID.

[0146] - Optionally, if the RACH configuration is allocated based on the LTM gNB-DU mapping identifier / index / identifier provided by the gNB-CU, when sending the TA value and auxiliary information to the gNB-CU in procedure 14, the indicated mapping identifier / index / identifier needs to be carried and sent to the gNB-CU. Then, the gNB-CU can know the gNB-DU ID corresponding to this LTM gNB-DU mapping identifier / index / identifier through the mapping relationship, so that the gNB-CU can continue to forward the corresponding TA information to the corresponding gNB-DU ID.

[0147] The message for the above procedure 14 contains at least one of the following multiple pieces of information:

[0148] DU-CU TA Information Transfer

[0149] TA Information List

[0150] >TA Information Item IEs

[0151] >>Candiate Cell ID

[0152] >>TA Value

[0153] >> Preamble Index

[0154] >> Random Access - Radio Network Temporary Indentifier, RA - RNTI

[0155] >> Source gNB - DU ID

[0156] >> LTM gNB - DU Mapping ID / Index / identifier, which maps a gNB - DU ID, such as the Source gNB - DU ID

[0157] >> Tag (Timing Advance Group) ID Pointer, which contains the tag - Id - ptr information defined in the TCI - UL - State IE or TCI - State IE in TS38.331.

[0158] In one embodiment, for the different PRACH resources allocated for a candidate cell for one or more LTM gNB - DUs, or the manifestation form of the RACH configuration information, it can be that one LTM gNB - DU ID corresponds to one PRACH resource, or RACH configuration information, or Early UL Sync Configuration information. It can also be to separately present the configuration information common to all LTM gNB - DUs among these configuration information, and then present the different configuration information corresponding to different LTM gNB - DUs (such as the Preamble Index List). In short, the idea embodied is that the candidate cell allocates different PRACH resources, or RACH configuration information, or Early UL Sync Configuration information for each LTM gNB - DU, and all are within the protection scope of the present invention.

[0159] When the gNB-CU receives the L3 measurement report reported by the UE, it can determine which gNB-DU under this gNB-CU the candidate cell belongs to through the cell ID information. When the gNB-CU determines the configured cell for LTM, in the UE CONTEXT SETUP REQUEST message sent by the gNB-CU to the candidate gNB-DU in Procedure 3, a list of candidate gNB-DU IDs corresponding to each candidate cell for LTM configuration or a list of mapping identifiers / indexes / identifiers will be carried. Then, the candidate gNB-DU prepares the corresponding resources for the candidate cells that accept the LTM configuration request and responds to the gNB-CU through the UE CONTEXT SETUP RESPONSE message. Assume that some candidate gNB-DUs do not have candidate cells that are accepted, that is, for each of these candidate cells, the candidate gNB-DU rejects the UE context setup request procedure of the gNB-CU. As shown in Figure 4 regarding the UE context setup procedure between the gNB-CU and the candidate gNB-DU2, if the candidate gNB-DU2 rejects the request of the gNB-CU, a UE CONTEXT SETUP FAILURE message will be sent as a response in Procedure 4-02; otherwise, a UE CONTEXT SETUP RESPONSE message will be sent as a response in Procedure 4-01. In the case of UE context setup failure, the RACH configuration prepared for the candidate cells accepted during the previous UE context setup procedure between the gNB-CU and other candidate gNB-DUs by this gNB-DU does not need to be retained and needs to be released. If not released, it will cause waste of PRACH resources for these candidate cells (such as preamble index resources). Regarding which candidate gNB-DU rejects the UE context setup request of the gNB-CU, only the gNB-CU knows. The gNB-CU can notify other candidate gNB-DUs (including the source gNB-DU) through the UE CONTEXT MODIFICATION REQUEST message carrying the LTMCells to be Released List IE which resources prepared for which LTM candidate cells need to be released. However, for the RACH configuration prepared by the candidate gNB-DU for the candidate cells, the gNB-DU receiving the UE context modification request cannot determine which candidate gNB-DU has released and is no longer in the LTM candidate gNB-DU list based on the release information of the LTM candidate cells carried therein.As shown in the process of Figure 4, after the gNB-CU interacts with each candidate gNB-DU and the source gNB-DU, and after process 6, assuming that one candidate cell on each gNB-DU is accepted as an LTM candidate cell, the gNB-CU can obtain the RACH configuration list for each candidate cell accepted as an LTM candidate cell for each gNB-DU, for example, as follows:

[0160] Early Sync Information List

[0161] Cell ID0 (Cell ID0, the source cell of the source gNB-DU0)

[0162] > RACH configuration for candidate gNB-DU ID1

[0163] > RACH configuration for candidate gNB-DU ID2

[0164] Cell ID1 (Cell ID1, the source cell of the source gNB-DU1)

[0165] > RACH configuration for source gNB-DU ID0

[0166] > RACH configuration for candidate gNB-DU ID2

[0167] Cell ID2 (Cell ID2, the source cell of the source gNB-DU2)

[0168] [[ID=2,7]]> RACH configuration for source gNB-DU ID0

[0169] > RACH configuration for candidate gNB-DU ID1<,

[0170] Then, in process 7, the gNB-CU notifies each candidate gNB-DU of the RACH configuration information prepared for this gNB-DU by other candidate cells through the UE CONTEXT MODIFICATION REQUEST message.

[0171] For example, the gNB-CU notifies the source gNB-DU of the following RACH configuration information:

[0172] Early Sync Information List

[0173] > Early Sync Information Item IEs

[0174] >>Cell ID (Cell ID, Candidate Cell ID1 or Candidate Cell ID2)

[0175] >>RACH Configuration

[0176] For example, gNB-CU notifies candidate gNB-DU1 of the following RACH configuration information:

[0177] Early Sync Information List

[0178] >Early Sync Information Item IEs

[0179] >>Cell ID (Cell ID, Source Cell ID0 or Candidate Cell ID2)

[0180] >>RACH Configuration

[0181] For example, gNB-CU notifies candidate gNB-DU2 of the following RACH configuration information:

[0182] Early Sync Information List

[0183] >Early Sync Information Item IEs

[0184] >>Cell ID (Cell ID, Source Cell ID0 or Candidate Cell ID1)

[0185] >>RACH Configuration

[0186] As shown in Figure 4, during the UE context establishment process for candidate Cell ID2 between gNB-CU and candidate gNB-DU2, if candidate gNB-DU2 rejects the request from gNB-CU and sends a UE context setup failure (UE CONTEXT SETUP FAILURE) message as a response. In this case, candidate gNB-DU2 is actually excluded from the LTM candidate gNB-DU list. If the source cell ID0 and candidate cell ID1 have prepared RACH configurations for candidate gNB-DU, the RACH configurations prepared for candidate gNB-DU need to be released. In this case, it is not sufficient for other candidate gNB-DUs (including the source gNB-DU) to only know that LTM Cell ID2 will be released because the source gNB-DU and candidate gNB-DU1 cannot determine that candidate gNB-DU2 will be released through the to-be-released LTM cell list IE. Only gNB-CU knows which candidate cells are on each gNB-DU, which candidate cells are released, and whether all candidate cells on a certain candidate gNB-DU are released.

[0187] Optional solution 1: Let each gNB-DU (including the source gNB-DU and / or candidate gNB-DU) be able to determine which candidate gNB-DU has released all its candidate cells, that is, the candidate gNB-DU has been released, through the received to-be-released LTM cell list IE information. For example, the F1ap message can be enhanced so that each gNB-DU knows which candidate cells each other candidate gNB-DU (optionally including the source gNB-DU) has, or the information indicating which candidate cell (optionally including the source cell) belongs to the corresponding gNB-DU ID needs to be known to each gNB-DU (including the source gNB-DU and / or candidate gNB-DU). Therefore, during the LTM resource preparation process, the UE context setup request (UE CONTEXT SETUP REQUEST) message or UE context modification request (UE CONTEXT MODIFICATION REQUEST) message sent by gNB-CU to the candidate gNB-DU (optionally including the source gNB-DU) can carry a list of information including one or more of the following:

[0188] - Each LTM candidate cell ID (represented by cell ID or NR CGI);

[0189] - LTM gNB-DU ID information (represented by gNB-DU ID, indicating the gNB-DU to which the LTM candidate cell belongs).

[0190] Optionally, based on the LTM Configuration ID Mapping List IE, add the indication information of the gNB-DU ID to which the LTM cell ID belongs:

[0191] - LTM Configuration ID Mapping List

[0192] > Configuration ID Mapping Item IEs

[0193] >> LTM Cell ID (which can be represented by the NR CGI)

[0194] >> LTM Configuration ID

[0195] >> LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU information to which the LTM cell corresponding to the LTM cell ID belongs)

[0196] Figure 4 shows an exemplary LTM cell release process 400. Among them, the gNB-CU determines that all LTM candidate cells in the gNB-DU2 need to be released based on the received UE CONTEXT SETUP FAILURE message. Therefore, other candidate cell releases are required for the RACH configuration prepared by the candidate gNB-DU2 before. Alternatively, optionally, when all candidate cells need to be released after the gNB-DU2 is configured, the gNB-DU2 can send a UE CONTEXT RELEASE REQUEST message to the gNB-CU in process 401. This message can include a list of LTM cells to be released. The gNB-CU can send a UE CONTEXT MODIFICATION REQUEST message to the gNB-DU0 and gNB-DU1 in process 402. This UE CONTEXT MODIFICATION REQUEST message can carry a list of information, including one or more of the above-described information.

[0197] Optionally, the gNB-CU may also send a UE CONTEXT RELEASE COMMAND message to the gNB-DU2 in procedure 403, carrying the list of LTM cells to be released, and commanding the gNB-DU2 to release the RACH configuration of the LTM cells to be released. After the release is completed, the gNB-DU2 sends a UE CONTEXT RELEASE COMPLETA message in procedure 404.

[0198] If the LTM configuration ID mapping list IE is included in the UE context establishment request message, the gNB-DU shall consider it as the mapping information of the LTM candidate cells. If the LTM gNB-DU ID is included in the LTM configuration ID mapping list IE, the gNB-DU will consider the gNB-DU information corresponding to each LTM candidate cell (i.e., the gNB-DU shall know the gNB-DU information corresponding to each LTM candidate cell, and optionally, the gNB-DU shall know the LTM candidate cell information on each other candidate gNB-DU). Subsequently, if a list cell of LTM cells to be released (i.e., the list IE of LTM cells to be released) is received from the gNB-CU, the gNB-DU can determine that a certain candidate gNB-DU will be released, and the behavior of releasing the previously prepared (or allocated) RACH configuration corresponding to this candidate gNB-DU is required.

[0199] Optionally, for the gNB-CU and each candidate gNB-DU, among the candidate gNB-DUs where the UE context setup request process (UE CONTEXT SETUP REQUEST) occurs first, the accepted LTM candidate cells prepare (or allocate) RACH configurations for other candidate gNB-DUs (some candidate gNB-DUs may not have undergone the UE context setup process yet and will undergo the UE context setup process subsequently). If later, the LTM candidate cells on other candidate gNB-DUs do not accept the LTM configuration request during the UE context setup request process (i.e., the gNB-DU replies to the gNB-CU with a UE context setup failure message), or if the LTM candidate cells on other candidate gNB-DUs accept the LTM configuration but later, for example, an LTM candidate cell release is triggered by the gNB-CU or the candidate gNB-DU, the gNB-DU performs a comparison and analysis after combining the list of LTM cells to be released cell (list of LTM cells to be released IE) received from the gNB-CU and / or the updated LTM configuration ID mapping list IE received from the gNB-CU. The gNB-DU can determine whether the candidate gNB-DU to which the LTM release cell belongs is released and whether it is necessary to release the corresponding previously prepared (or allocated) RACH configuration. If all the LTM candidate cells on a certain candidate gNB-DU are released, that is, this candidate gNB-DU is released, then release the RACH configuration previously prepared (or allocated) for this candidate gNB-DU by the LTM candidate cells that have accepted the LTM configuration request.

[0200] Corresponding to the embodiment of FIG. 4, optionally, if the LTM gNB-DU ID to which the corresponding LTM cell ID belongs is included in the LTM configuration ID mapping list IE (included in the UE CONTEXT SETUP REQUEST message), the gNB-DU will consider the gNB-DU information corresponding to each LTM candidate cell for comparison and analysis after receiving the updated LTM configuration ID mapping list IE (including the LTM gNB-DU ID) through the UE context modification request (UE CONTEXT MODIFICATION REQUEST) message subsequently. Thus, the gNB-DU can determine that a certain candidate gNB-DU is released and the action of releasing the previously prepared (or allocated) RACH configuration corresponding to this candidate gNB-DU is required.

[0201] For the embodiment corresponding to FIG. 4, optionally, if the gNB-DU receives an updated LTM configuration ID mapping list IE (including the LTM gNB-DU ID IE) through a UE CONTEXT MODIFICATION REQUEST message, or if the LTM gNB-DU ID is included in the LTM configuration ID mapping list IE (included in the UE CONTEXT MODIFICATION REQUEST message), the gNB-DU will consider the gNB-DU information corresponding to each LTM candidate cell for comparison and analysis with the LTM configuration ID mapping list IE in the UE CONTEXT SETUP REQUEST received in process 3 before. Thus, the gNB-DU can determine that a certain candidate gNB-DU is released and the behavior of releasing the RACH configuration previously prepared (or allocated) for this candidate gNB-DU is required.

[0202] When the candidate gNB-DU (which may include the source gNB-DU) receives the information of the LTM cell list to be released IE sent by the gNB-CU (such as Cell2 is released), or after receiving the updated LTM cell ID and the corresponding list information of the belonging gNB-DU ID and comparing it with the previous information, it can determine which LTM cells are released and whether all the candidate cells on a certain candidate gNB-DU are released (such as candidate gNB-DU2 is released). At this time, the RACH configuration previously allocated to the candidate cells on the candidate gNB-DU for candidate gNB-DU2 needs to be released, and the RACH configuration allocated to this candidate gNB-DU for the indicated released candidate cell (Cell2) also needs to be released.

[0203] Optional solution 2: The gNB-CU carries a new indication IE to notify other candidate gNB-DUs (optionally, which may include the source gNB-DU) which candidate gNB-DU has no accepted LTM candidate cells, that is, the entire gNB-DU has rejected the UE context setup request of the gNB-CU. According to an exemplary embodiment, one or more of the following information may be carried in the UE CONTEXT MODIFICATION REQUEST message in process 7:

[0204] - LTM Cells to be Released List

[0205] > LTM Cells to be Released Item IEs

[0206] >>LTM Cell ID

[0207] >>LTM gNB-DU ID (Indicated by the gNB-DU ID, which indicates the gNB-DU corresponding to the released LTM cell. When all candidate cells on the gNB-DU corresponding to the released LTM cell are released, that is, this candidate gNB-DU is released, the gNB-DU ID information is carried to other candidate gNB-DUs (including the source gNB-DU) to indicate that the gNB-DU indicated by this gNB-DU ID is released, and it is expected that the candidate cells on other candidate gNB-DUs and / or the source gNB-DU release the RACH configuration allocated for this gNB-DU ID, that is, the PRACH resource or the early synchronization information)

[0208] - LTM gNB-DUs to be Released List (indicating that the RACH configuration corresponding to the corresponding gNB-DU ID is to be released)

[0209] > LTM gNB-DUs to be Released Item IEs

[0210] >>LTM gNB-DU ID (Indicated by the gNB-DU ID, which indicates the information of the gNB-DU to be released, that is, there are no candidate cells on this candidate gNB-DU that accept the LTM configuration request, or all candidate cells on this candidate gNB-DU are released. In this case, the RACH configuration allocated for this gNB-DU ID by other candidate cells that accept the LTM configuration request needs to be released)

[0211] - RACH Configuration to be Released List (indicating that the RACH configuration corresponding to the corresponding gNB-DU ID is to be released)

[0212] > RACH Configuration to be Released Item IEs

[0213] >>LTM gNB-DU ID (Indicated by the gNB-DU ID, which indicates the information of the gNB-DU to be released, that is, there are no candidate cells on this candidate gNB-DU that accept the LTM configuration request, or all candidate cells on this candidate gNB-DU are released. In this case, the RACH configuration allocated for this gNB-DU ID by other candidate cells that accept the LTM configuration request needs to be released)

[0214] - List of Mapping IDs / Indexs / identifiers of LTM gNB-DU to be Released (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released List. If the RACH configuration for a candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU provided by the gNB-CU, this IE can indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0215] > IE of Mapping IDs / Indexs / identifiers of LTM gNB-DU to be Released (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0216] >> Mapping ID / Index / identifier of LTM gNB-DU (LTM gNB-DU Mapping ID / Index / identifier)

[0217] In one embodiment, optionally, if the List of LTM gNB-DU to be Released IE is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the RACH configuration allocated for the candidate cell that accepts the LTM configuration request for the gNB-DU ID indicated in the List of LTM gNB-DU to be Released IE. If the UE context establishment process between the gNB-CU and a certain candidate gNB-DU fails, it is possible to include the List of LTM gNB-DU to be Released IE in the UE CONTEXT MODIFICATION REQUEST message sent to other gNB-DUs to indicate that other gNB-DUs release the RACH configuration allocated for the candidate cell that accepts the LTM configuration request for the gNB-DU ID indicated in the List of LTM gNB-DU to be Released IE.

[0218] In this example, after receiving the indication from the gNB-CU, the source gNB-DU releases the RACH configuration allocated for the candidate gNB-DU ID2 by the source Cell ID0, and at the same time releases the RACH configuration allocated to the source gNB-DU by the candidate cell Cell ID2. When the candidate gNB-DU1 receives the indication from the gNB-CU, it releases the RACH configuration allocated for the candidate gNB-DU ID2 by the candidate Cell ID1, and at the same time releases the RACH configuration allocated to the candidate gNB-DU ID1 by the candidate cell Cell ID2.

[0219] Alternative Solution 3: Since there is always a sequence in the UE context establishment process between the gNB-CU and each candidate gNB-DU, the following situation may occur: The LTM candidate cell that accepts the LTM configuration request may have allocated RACH configurations in advance for all candidate gNB-DUs that are uncertain whether to accept the LTM configuration request. Subsequently, due to the failure of the UE context establishment process of a certain candidate gNB-DU, the gNB-CU needs to notify the gNB-DU corresponding to the candidate cell that has accepted the LTM configuration request to release the RACH configurations allocated for the candidate gNB-DU that rejects the LTM configuration request. To avoid this situation, it can be considered that in the UE context establishment request process (Process 3 in the embodiment of Figure 4) between the initial gNB-CU and each candidate gNB-DU, the request for early synchronization information is not carried out. Instead, after the gNB-CU and all candidate gNB-DUs have completed the UE context establishment process, the gNB-CU sends a UE context modification request (UE CONTEXT MODIFICATION REQUEST) message of Process 7 to the candidate gNB-DUs of those candidate cells that have accepted the LTM configuration request, requesting the allocation of RACH configurations for each other candidate gNB-DU that accepts the LTM configuration request. This solution is applicable to the initial LTM resource configuration preparation stage. For the case where the candidate cell that accepts the LTM configuration request has already allocated RACH configurations for each other candidate gNB-DU that accepts the LTM configuration request, if subsequent releases of the LTM candidate cell or candidate gNB-DU may be triggered by the gNB-CU or candidate gNB-DU, it is still necessary to use Alternative Solution 1 or Alternative Solution 2 to release the RACH configurations already allocated by the candidate cell that accepts the LTM configuration request for the candidate gNB-DU that has not undergone the release.

[0220] Another scenario is that in the initial LTM preparation stage, if there is an LTM candidate cell in the candidate gNB-DUs that has accepted the LTM configuration request, and the network has completed or not performed the RRC reconfiguration of the UE, but subsequently, due to some other situations, the gNB-CU or candidate gNB-DU decides to release the previously accepted LTM candidate cell. In this way, the LTM configuration needs to be updated.

[0221] For example, an exemplary LTM cell release process 400 is shown in FIG. 4. In process 401, the gNB-CU receives a UE context release request message sent by the gNB-DU2 to the gNB-CU. This message may include a list of LTM cells to be released. Alternatively, the gNB-CU decides to trigger process 403 to send a UE context release command message to the gNB-DU2, which may carry the list of LTM cells to be released. If it is determined that all LTM candidate cells in the gNB-DU2 are to be released, the release of candidate cells on other candidate gNB-DUs and / or the source gNB-DU for the RACH configuration prepared for the candidate gNB-DU2 is required. The gNB-CU may send a UE context modification request message to the gNB-DU0 and gNB-DU1 in process 402. The UE context modification request message carries one or more of the following information:

[0222] - LTM Cells to be Released List

[0223] > LTM Cells to be Released Item IEs

[0224] >> LTM Cell ID

[0225] >> LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU corresponding to the released LTM cell. When all candidate cells on the gNB-DU corresponding to the released LTM cell are released, that is, this candidate gNB-DU is released, the gNB-DU ID information is carried to indicate to other candidate gNB-DUs (including the source gNB-DU) that the gNB-DU indicated by this gNB-DU ID is released, and it is expected that the candidate cells on other candidate gNB-DUs and / or the source gNB-DU are released for the RACH configuration allocated for this gNB-DU ID, that is, the PRACH resource or early synchronization information)

[0226] - LTM gNB-DUs to be Released List (indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0227] >LTM gNB-DU Items to be Released IE (LTM gNB-DUs to be Released Item IEs)

[0228] >>LTM gNB-DU ID

[0229] - List of RACH Configurations to be Released (indicating that the RACH configurations corresponding to the gNB-DU ID are to be released)

[0230] >RACH Configuration to be Released IE (RACH Configuration to be Released Item IEs)

[0231] >>LTM gNB-DU ID

[0232] - List of LTM gNB-DU Mapping IDs / Indexs / identifiers to be Released (if the RACH configuration for a candidate cell is assigned based on the mapping ID / index / identifier corresponding to each gNB-DU provided by the gNB-CU, this IE can indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0233] >LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IE (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0234] >>LTM gNB-DU Mapping ID / Index / identifier (LTM gNB-DU Mapping ID / Index / identifier)

[0235] Optionally, the gNB-CU sends a UE CONTEXT RELEASE COMMAND message to gNB-DU2 in procedure 403, carrying the list of LTM cells to be released, and commands gNB-DU2 to release the RACH configurations of the LTM cells to be released. After the release is completed, gNB-DU2 sends a UE CONTEXT RELEASE COMPLETE message in procedure 404.

[0236] For example, the gNB-CU may carry the list information of LTM cells to be released in a UE CONTEXT MODIFICATION REQUEST message to notify each of the other candidate gNB-DUs to release the RACH configuration previously allocated to this candidate gNB-DU for the candidate cells to be released. In the case where a certain candidate gNB-DU is released, the RACH configurations prepared by other candidate cells for this gNB-DU also need to be released. However, the gNB-DU cannot determine whether a candidate gNB-DU is to be released through the list of LTM cells to be released IE. Only the gNB-CU can determine which candidate gNB-DU has released all the LTM candidate cells that have previously accepted the LTM configuration request, such that the entire gNB-DU is released and thus needs to be excluded from the list of LTM candidate gNB-DUs. Therefore, the gNB-CU needs to carry a new indication IE to notify other candidate gNB-DUs (optionally, including the source gNB-DU) of the gNB-DU information to be released. Therefore, during the LTM cell release process, the gNB-CU may carry one or more of the following information in a UE CONTEXT MODIFICATION REQUEST message:

[0237] - LTM Cells to be Released List

[0238] > LTM Cells to be Released Item IEs

[0239] >> LTM Cell ID

[0240] >> LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU corresponding to the LTM cell to be released. When all candidate cells on the gNB-DU corresponding to the LTM cell to be released are released, that is, this candidate gNB-DU is released, carry this gNB-DU ID information to other candidate gNB-DUs (including the source gNB-DU) to indicate that the gNB-DU indicated by this gNB-DU ID is released, and expect the candidate cells on other candidate gNB-DUs and / or the source gNB-DU to release the RACH configuration allocated to this gNB-DU ID, that is, the PRACH resource or early synchronization information)

[0241] - LTM gNB-DUs to be Released List (indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0242] >LTM gNB-DU Items to be Released IE (LTM gNB-DUs to be Released Item IEs)

[0243] >>LTM gNB-DU ID

[0244] - List of RACH Configurations to be Released (indicating that the RACH configurations corresponding to the gNB-DU ID are to be released)

[0245] >RACH Configuration to be Released Item IE (RACH Configuration to be Released Item IEs)

[0246] >>LTM gNB-DU ID

[0247] - List of LTM gNB-DU Mapping IDs / Indexs / identifiers to be Released (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released List. If the RACH configuration for a candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU provided by the gNB-CU, this IE can indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0248] >LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IE (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0249] >>LTM gNB-DU Mapping ID / Index / identifier (LTM gNB-DU Mapping ID / Index / identifier)

[0250] When the source gNB-DU receives an indication from the gNB-CU, it releases the RACH configurations allocated to the candidate gNB-DU ID for the source cell or other candidate cells on the source gNB-DU. At the same time, it releases the RACH configurations allocated to the candidate gNB-DU indicated in the list of LTM cells to be released for the source gNB-DU. When other candidate gNB-DUs receive an indication from the gNB-CU, they release the RACH configurations allocated to the candidate gNB-DU ID for the candidate cells on this candidate gNB-DU. At the same time, they release the RACH configurations allocated to the candidate gNB-DU indicated in the list of LTM cells to be released for this candidate gNB-DU.

[0251] Alternative Solution 4: Since the RACH configuration for each candidate cell is allocated based on each candidate gNB-DU, during the LTM preparation phase, the gNB-CU, based on the L3 measurement report, for each candidate cell, the gNB-CU requests resources from the corresponding candidate gNB-DU for each candidate cell through a separate UE context establishment process, and at the same time requests the early synchronization RACH configuration, and carries an LTM gNB-DU List (including all candidate gNB-DU IDs), requesting the candidate cell to allocate the RACH configuration for each LTM gNB-DU. If subsequent failures occur during the UE context establishment request process for all candidate cells on a certain candidate gNB-DU (such as DU2), that is, there are no accepted candidate cells on this candidate gNB-DU, that is, it is no longer a candidate gNB-DU for LTM, or a certain candidate gNB-DU (such as DU2) is released due to other reasons later (all candidate cells on this candidate gNB-DU may be released due to overload), and it is excluded from the candidate LTM gNB-DU list, that is, it does not belong to the candidate LTM gNB-DU anymore. In this case, for the RACH resources prepared for this gNB-DU (DU2) that failed or was released during LTM preparation for the candidate cells on other candidate gNB-DUs, they need to be released. The gNB-CU can request the RACH configuration again through the UE context modification request process, and carry an updated LTM gNB-DU List information, which does not include the gNB-DU (DU2) that failed or was released during LTM preparation, so that the candidate cells on other candidate gNB-DUs release the RACH configuration previously allocated for this gNB-DU2. At the same time, it may be necessary to update the allocation of the RACH configuration for other candidate gNB-DUs. If updated, the gNB-CU needs to redistribute it to each candidate gNB-DU again.

[0252] In one embodiment, optionally, if the LTM gNB-DU list IE to be released is included in the UE context modification request (UE CONTEXT MODIFICATION REQUEST) message, the gNB-DU shall, if supported, release the RACH configuration allocated for the candidate cell that accepts the LTM configuration request for the gNB-DU ID indicated in the LTM gNB-DU list IE to be released. Or rather, if the LTM gNB-DU list IE to be released is included in the UE context modification request (UE CONTEXT MODIFICATION REQUEST) message, the gNB-DU shall, if supported, release the RACH configuration allocated for the candidate cell that accepts the LTM configuration request for the gNB-DU corresponding to the gNB-DU ID included in the LTM gNB-DU list IE to be released.

[0253] In one embodiment, optionally, if the LTM gNB-DU list IE to be released is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the RACH configuration assigned to the candidate cell that has accepted the LTM configuration request for the gNB-DU ID indicated in the LTM gNB-DU list IE to be released. Or, if the LTM gNB-DU list IE to be released is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the RACH configuration assigned to the candidate cell that has accepted the LTM configuration request for the gNB-DU corresponding to the gNB-DU ID included in the LTM gNB-DU list IE to be released.

[0254] In one embodiment, optionally, if the LTM gNB-DU ID IE is included in the LTMCells to be Released List IE, which is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the RACH configuration or the early uplink synchronization configuration or the PRACH resources (including one or more preamble indexes) assigned to the LTM candidate cell for the gNB-DU indicated by this LTM gNB-DU ID.

[0255] In one embodiment, optionally, if the LTM configuration ID mapping list IE is included in the UE context setup request (UE CONTEXT SETUP REQUEST) or UE context modification request (UE CONTEXT MODIFICATION REQUEST) message, the gNB-DU shall consider it as the mapping information of the LTM candidate cell. If the LTM gNB-DU ID is included in the LTM configuration ID mapping list IE to indicate the gNB-DU information to which each LTM candidate cell belongs, the gNB-DU will consider the gNB-DU information corresponding to each LTM candidate cell (that is, the gNB-DU shall know the gNB-DU information corresponding to each LTM candidate cell. Optionally, the gNB-DU shall know which LTM candidate cell information exists on each other candidate gNB-DU). Subsequently, if the LTM cell list to be released (i.e., the LTM cell list IE) is received from the gNB-CU, the gNB-DU can determine which candidate gNB-DU will be released and the behavior of releasing the RACH configuration previously prepared (or allocated) for this candidate gNB-DU by the candidate cell that will receive the LTM configuration request.

[0256] Correspondingly, after the network side completes the release of the LTM cell resources, the gNB-CU needs to update the UE-side configuration through the RRC reconfiguration message.

[0257] In one embodiment, as Figure 4-2 In, regarding the trigger of LTM, the source gNB-DU sends a DU-CU cell switch notification (DU-CU CELL SWITCH NOTIFICATION) message to the gNB-CU through procedure 19, indicating that a cell switch command has been sent to the UE. The source gNB-DU can send the valid TA information to the target gNB-DU through the gNB-CU. In this way, it is avoided that the target gNB-DU performs the TA acquisition process based on the PDCCH command again for other LTM candidate cells. When the target gNB-DU triggers LTM subsequently, it can use the valid TA value of the corresponding LTM target cell. The DU-CU cell switch notification message contains one or more of the following information:

[0258] - Target cell ID (represented by Cell ID or NR CGI)

[0259] - TCI state ID (TCI State ID, corresponding to the CandidateTCI-StatesIdIE defined in TS 38.331)

[0260] - LTM cell switch information (LTM Cell Switch Information)

[0261] ■ Joint or DL TCI State ID (corresponding to the TCI-StateId IE defined in TS 38.331)

[0262] ■ UL TCI State ID (corresponding to the TCI-UL-StateId IE defined in TS 38.331)

[0263] - TA Information List (including one or more candidate cell IDs and corresponding valid TA values, and possible valid time information)

[0264] ■ Candidate cell ID (represented by Cell ID or NR CGI)

[0265] ■ TA Value (indicating the valid TA value of the candidate cell, passed to the target gNB or target gNB-DU for use)

[0266] ■ Tag (Timing Advance Group) ID Pointer (containing the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS38.331. For a candidate cell that is a MIMO cell, there may be operations with multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. Which TAG the TA calculated by the candidate cell is for needs to be told to the new source gNB-DU (the candidate gNB-DU becomes the source gNB-DU for subsequent LTM after being accessed by the UE). In this way, when the source gNB-DU triggers LTM, according to the L1 measurement report, it selects a certain TCI state on a certain candidate cell to determine which TA corresponding to the TAG should be used, and then sends it to the UE through the LTM cell handover command MAC CE)

[0267] ■ TA valid timer

[0268] Then the gNB-CU forwards the above information to the target gNB-DU (which becomes the new source gNB-DU after the UE access). The gNB-CU sends the CU-DU CELL SWITCH NOTIFICATION to the target gNB-DU through procedure 20. The CU-DU cell handover notification message contains one or more of the following information:

[0269] - Target cell ID (represented by Cell ID or NR CGI)

[0270] - TCI state ID (TCI State ID, corresponding to the CandidateTCI-StatesIdIE defined in TS 38.331)

[0271] - LTM cell switch information

[0272] ■ Joint or DL TCI state ID (corresponding to the TCI-StateId IE defined in TS 38.331)

[0273] ■ UL TCI state ID (corresponding to the TCI-UL-StateIdIE defined in TS 38.331)

[0274] - TA information list (contains one or more candidate cell IDs and their corresponding valid TA values, and possibly valid time information)

[0275] ■ Candidate cell ID (represented by Cell ID or NR CGI)

[0276] ■ TA value (TA Value, indicating the valid TA value of the candidate cell, passed to the target gNB or target gNB-DU for use)

[0277] ■ Timing Advance Group ID Pointer (Tag(Timing Advance Group)ID Pointer, contains the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS38.331. For a candidate cell that is a MIMO cell, there may be multiple TRPs

[0278] (Transmit / Receive Point) operations, so at most 2 different TAGs can be configured, and each TCI state is associated with a TAG. Which TAG the TA calculated by the candidate cell is for needs to be told to the new source gNB-DU (the target gNB-DU becomes the source gNB-DU for subsequent LTM when accessed by the UE). In this way, when the source gNB-DU triggers LTM, based on the L1 measurement report, it selects a certain TCI state on a certain candidate cell to determine which TA corresponding to the TAG should be used, and then sends it to the UE through the LTM cell switch command MAC CE)

[0279] ■TA Value Valid Timer

[0280] Figures 5a-1 to 5a-3 (hereinafter collectively referred to as Figure 5a) is the LTM process between different gNB-CUs according to an exemplary embodiment of the present application. Since the source gNB-CU can only determine which cell under which adjacent NG-RAN node the adjacent cell belongs to through the received L3 measurement report message. If the adjacent NG-RAN node is a base station with a separated architecture of gNB-CU and gNB-DU, the source gNB-CU cannot determine which gNB-DU the adjacent cell belongs to. In this case, the source gNB-CU or the source NG-RAN node can only determine which adjacent NG-RAN node the UE-reported adjacent cell belongs to, or which gNB-CU in which adjacent NG-RAN node (a separated architecture NG-RAN node can only have one gNB-CU).

[0281] In order for the gNB-CU to determine which gNB-DU the adjacent cell belongs to under the adjacent NG-RAN node through the L3 measurement report message (if the adjacent NG-RAN node has a separated architecture of gNB-CU and gNB-DU), according to an optional solution, the Xnap interface specification process can be enhanced to optionally include the gNB-DU ID information of the belonging cell in the interactive cell information. For example, it can be considered to add an optional sub-IE: gNB-DU ID in one or more of the following IEs to indicate the gNB-DU ID information of the cell to which this cell belongs.

[0282] >Served Cell Information NR

[0283] >Neighbour Information NR

[0284] >Neighbour Information E-UTRA

[0285] During the process of Xn interface establishment (XN SETUP) or NG-RAN node configuration update (NG-RAN NODE CONFIGURATION UPDATE) between two adjacent NG-RAN nodes or gNB-CUs, the Served Cell Information NR is exchanged, and the Neighbour Information NR or Neighbour Information E-UTRA is also exchanged. Optionally, if the corresponding cell indicates the gNB-DU ID it belongs to, then in the case where the NG-RAN node has a separated architecture of gNB-CU and gNB-DU, the gNB-CU can know which gNB-DU under the adjacent NG-RAN node the adjacent cell belongs to.

[0286] Figure 5bThe Xn interface establishment process between two adjacent NG-RAN nodes or gNB-CUs is shown. In each NG-RAN node, an F1 connection can be established between the gNB-CU and the gNB-DU through procedures 5001 and 5002. In procedure 5001, the gNB-DU sends an F1 establishment request (F1SETUP REQUEST) message to the gNB CU; in procedure 5002, the gNB-CU sends an F1 establishment response (F1 SETUP RESPONSE) message to the gNB-DU. For the NG-RAN node where the gNB-CU and the gNB-DU have established a connection, in procedure 5003, the NG-RAN node 1 or the gNB-CU therein sends an Xn establishment request (XNSETUP REQUEST) message to the NG-RAN node 2 or the gNB-CU therein. In procedure 5004, the NG-RAN node 2 or the gNB-CU therein sends an Xn establishment response (XN SETUP RESPONSE) message to the NG-RAN node 1 or the gNB-CU therein. Optionally, in procedure 5005, the gNB-DU performs configuration update and sends a gNG-DU configuration update (GNB-DU CONFIGURATION UPDATE) message to the gNB-CU; in procedure 5006, the gNB-CU sends a gNB-DU configuration update acknowledgement (GNB-DU CONFIGURATION UPDATEACKNOWLEDGE) message to the gNB-DU. In procedure 5007, for the NG-RAN node 1 where the configuration update has been performed between the gNB-CU and the gNB-DU, the NG-RAN node 1 or the gNB-CU therein sends a NG-RAN node configuration update (NG-RAN NODE CONFIGURATION UPDATE) message to the NG-RAN node 2 or the gNB-CU therein. In procedure 5008, the NG-RAN node 2 or the gNB-CU therein sends a NG-RAN node configuration update acknowledgement (NG-RAN NODECONFIGURATION UPDATE ACKNOWLEDGE) message to the NG-RAN node 1 or the gNB-CU therein. As Figure 5b shown, the gNB-DU ID information of the corresponding serving NR cell and the gNB-DU ID information of the NR neighboring cell can be carried in the Xn establishment request (XN SETUPREQUEST) or Xn establishment response (XN SETUP RESPONSE) message, or in the NG-RAN node configuration update (NG-RANNODE CONFIGURATION UPDATE) message.

[0287] Regarding the procedures of different gNB-CU LTMs, for the manner of PRACH resource allocation for candidate cells, if it is allocated based on each candidate cell or based on the UE, it will result in significant resource occupancy and waste. To save the use of PRACH resources for candidate cells, optionally, it can be considered to allocate based on the NG-RAN node (each NG-RAN node is represented by a Global NG-RANNode ID, which can include a Global gNB ID or a Global ng-eNB ID). Additionally, optionally, it can be considered to allocate based on the gNB-DU (each gNB-DU is represented by a gNB-DU ID and the belonging gNB ID).

[0288] Figure 5a shows the LTM procedure between different gNB-CUs according to an exemplary embodiment of the present application. The procedures between the involved gNB-CUs or between NG-RAN nodes can be applicable to other possible scenarios. For example, in the scenario where the LTM (inter-MN LTM) occurs between master nodes (MNs) and the secondary node (SN) changes or remains unchanged (with or without SN change). If the NG-RAN node is not an architecture where gNB-CU and gNB-DU are separated, the corresponding F1 interface messages and procedures are not involved in this disclosure.

[0289] The following describes each procedure shown in Figure 5a.

[0290] In the following procedure descriptions, the NG-RAN nodes involved can include gNBs or ng-eNBs. The corresponding source NG-RAN nodes can include source gNBs or source ng-eNBs, and the corresponding candidate NG-RAN nodes can include candidate gNBs or candidate ng-eNBs; for the NG-RAN node ID, it can be represented by the NG-RAN node global ID (Global NG-RAN Node ID), and this Global NG-RAN Node ID can include a Global gNB ID or a Global ng-eNB ID.

[0291] Procedure 501: The UE directly sends an L3 measurement report to the source NG-RAN node, or if the source NG-RAN node is an architecture where gNB-CU and gNB-DU are separated, the UE sends a MeasurementReport message reporting the L3 measurement result to the source gNB-DU, which contains the measurement values of neighboring cells. Then, the source gNB-DU sends an UL RRC MESSAGE TRANSFER message to pass the received measurement report message to the gNB-CU.

[0292] Procedure 502: The source NG-RAN node or the source gNB-CU receives the L3 measurement report reported by the UE and decides to perform LTM configuration.

[0293] Procedure 503: The source NG-RAN node (source gNB or source ng-eNB) or the source gNB-CU sends a HANDOVER REQUEST message or a new Xnap message (such as an LTM configuration request message or an LTM request message) to the candidate NG-RAN node (candidate gNB or candidate ng-eNB) or the candidate gNB-CU to which the candidate cell belongs for each candidate cell, including one or more of the following information:

[0294] - LTM trigger indication (LTM indication = initiation)

[0295] - Candidate cell ID (Cell ID or NR CGI)

[0296] - LTM configuration ID of the candidate cell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0297] - LTM configuration ID mapping list (LTM Configuration ID Mapping List, including the mapping relationship between each LTM cell ID (or NR CGI) and its corresponding LTM configuration ID (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331))

[0298] - LTM CSI resource configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0299] - Indication of LTM reference configuration request (LTM Reference Configuration Request, indicating that the source NG-RAN node requests the LTM reference configuration from the candidate NG-RAN node or the candidate gNB-CU)

[0300] - LTM Reference Configuration (including low-layer and / or high-layer reference configurations, optionally, may include the CellGroupConfig IE and / or CG-ConfigInfo IE defined in TS 38.331, where the CG-ConfigInfo IE contains ltm-ReferenceConfiguration information)

[0301] - Early Sync Information Request

[0302] - Request for RACH Configuration[[ID=*]]

[0303] ■ Optionally, if only one-shot LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, the source NG-RAN node ID can be carried, for example, the Global NG-RAN Node ID, which can contain the Global gNB ID or Global ng-eNB ID. This indicates that the source NG-RAN node or source gNB-CU requests PRACH resources from the candidate NG-RAN node or candidate gNB-CU based on the NG-RAN node for the early sync TA acquisition process.

[0304] ■ Optionally, to support subsequent LTM and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, a list of NG-RAN node IDs can be carried, for example, including the Global NG-RAN Node ID of each candidate NG-RAN node, where the Global NG-RAN Node ID can contain the Global gNB ID or Global ng-eNB ID. Or carry the LTM gNBs List, which contains each LTM gNB ID information represented by the Global gNB ID. This indicates that the source NG-RAN node or source gNB-CU requests PRACH resources from the candidate NG-RAN node or candidate gNB-CU based on each NG-RAN node for the early sync TA acquisition process.

[0305] ■ Optionally, if only one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, the source gNB-DU ID and the source NG-RAN node ID (for a base station with a split architecture, here it refers to the gNB ID), such as the NG-RAN node global ID, can be carried. This Global NG-RAN Node ID can include the Global gNB ID or Global ng-

[0306] eNB ID. It indicates that the source NG-RAN node or the source gNB-CU requests PRACH resources from the candidate NG-RAN node or the candidate gNB-CU based on the gNB-DU for the early synchronization TA acquisition process.

[0307] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate cell are allocated based on the gNB-DU, a list of gNB-DU IDs can be carried, and the NG-RAN node ID (for a base station with a split architecture, here it refers to the gNB ID) to which each gNB-DU ID belongs can be specified, for example, indicated by the NG-RAN node global ID. This Global NG-RAN Node ID can include the Global gNB ID or Global ng-eNB ID. It indicates that the source NG-RAN node or the source gNB-CU requests PRACH resources from the candidate NG-RAN node or the candidate gNB-CU for each gNB-DU for the early synchronization TA acquisition process.

[0308] ■ Optionally, if the source gNB-CU does not want to carry the plaintext source NG-RAN node ID and / or gNB-DU ID, or the list of NG-RAN node IDs and / or gNB-DU IDs, then the source gNB-CU can also map each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU (including the source gNB-DU) to a certain mapping identifier / index / identifier based on the implementation, and then pass the list of mapping identifiers / index / identifiers of the LTM NG-RAN node or LTM gNB-DU (the list of mapping identifiers / index / identifiers of the LTM NG-RAN node, or the list of mapping identifiers / index / identifiers of the LTM gNB-DU) to the candidate NG-RAN node or the candidate gNB-CU to request the candidate cell to allocate PRACH resources for each mapping identifier / index /

[0309] identifier.

[0310] Procedure 504: If the candidate NG-RAN node is an architecture with separated gNB-CU and gNB-DU, the candidate gNB-CU sends a UE context setup request (UE CONTEXT SETUP REQUEST) message to the gNB-DU to which the candidate cell belongs, including one or more of the following information:

[0311] - LTM trigger indication (LTM indicator = true)

[0312] - One candidate cell ID (Cell ID or NR CGI)

[0313] - LTM configuration ID of the candidate cell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0314] - LTM configuration ID mapping list (LTM Configuration ID Mapping List, including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID)

[0315] - LTM CSI resource configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0316] - Indication that the candidate gNB-CU requests the candidate gNB-DU to provide a lower layer configuration to generate a reference configuration (Request for Lower Layer Configuration)

[0317] - LTM reference configuration (LTM Reference Configuration, including the CellGroupConfig IE defined in TS 38.331)

[0318] - Early sync information request (Early Sync Information Request)

[0319] - Request indication for RACH configuration (Request for RACH Configuration).

[0320] ■ Optionally, if only one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, the source NG-RAN node ID can be carried, for example, the Global NG-RAN Node ID, which can include the Global gNB ID or the Global ng-eNB ID. This indicates that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the NG-RAN node.

[0321] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate cell are allocated based on the NG-RAN node, a list of NG-RAN node IDs can be carried, for example, including the Global NG-RAN Node ID of each candidate NG-RAN node, which can include the Global gNB ID or the Global ng-eNB ID. Or carry the LTM gNBs List, which contains the information of each LTM gNB ID, represented by the Global gNB ID. This indicates that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on each NG-RAN node.

[0322] ■ Optionally, if only one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, the source gNB-DU ID and the source NG-RAN node ID (for a split architecture base station, here it refers to the gNB ID), such as the Global NG-RAN Node ID, which can include the Global gNB ID or the Global ng-eNB ID, can be carried. This indicates that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the gNB-DU.

[0323] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate cell are allocated based on the gNB-DU, a list of gNB-DU IDs can be carried, and the NG-RAN node ID (for a split architecture base station, here it refers to the gNB ID) to which each gNB-DU ID belongs can be specified, for example, indicated by the Global NG-RAN Node ID, which can include the Global gNB ID or the Global ng-eNB ID. This indicates that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the gNB-DU.

[0324] Optionally, if the source NG-RAN node or source gNB-CU sends a mapping identifier or index or identifier for the source NG-RAN node ID and / or gNB-DU ID to the candidate NG-RAN node or candidate gNB-CU, or a list of mapping identifiers or indexes or identifiers of the LTM NG-RAN node (list of mapping identifiers / indexes / identifiers of the LTM NG-RAN node), or a list of mapping identifiers or indexes or identifiers of the LTM gNB-DU, then the candidate gNB-CU will pass the list of mapping identifiers or indexes or identifiers of the LTM NG-RAN node (list of mapping identifiers / indexes / identifiers of the LTM NG-RAN node, or list of mapping identifiers / indexes / identifiers of the LTM gNB-DU) to the candidate gNB-DU to request the candidate cell to allocate PRACH resources for each mapping identifier / index / identifier of the LTM NG-RAN node or gNB-DU.

[0325] Procedure 505: If the candidate gNB-DU accepts the LTM configuration request, it will send a UE context setup response (UECONTEXT SETUP RESPONSE) message to the candidate gNB-CU as a response, which may include one or more of the following information:

[0326] - A candidate cell ID (Cell ID or NR CGI)

[0327] - Low-layer RRC configuration generated for the target candidate cell that accepts the LTM configuration request, for example, a list of transmission configuration indication (TCI) state configurations (TCI States ConfigurationsList), as well as SSB configuration and NR PCI (Physical Cell Id) information of the candidate cell

[0328] - LTM reference configuration provided by the candidate gNB-DU (LTM Reference Configuration, including the CellGroupConfig IE defined in TS38.331)

[0329] - Indication of LTM complete configuration (LTM Complete Configuration Indicator, indicating whether the LTM configuration of the accepted candidate cell is a complete configuration)

[0330] - LTM CSI report configuration (contained in the CellGroupConfig IE defined in TS 38.331)

[0331] - Early Sync Information, including Early UL Sync Configuration or Early UL Sync Configuration for SUL (Supplementary Uplink) for supplementary uplink

[0332] - RACH configuration information (i.e., PRACH resources), including one or more RACH configuration information

[0333] ■ Optionally, it includes one RACH configuration information. That is, it includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for the source NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or the source gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0334] ■ Optionally, it includes one RACH configuration information. That is, it includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for the mapping identity / index / identifier of the source NG-RAN node or the source gNB-DU.

[0335] ■ Optionally, it includes a list of RACH configurations, multiple RACH configuration information. It includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for each candidate NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or each candidate gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0336] ■ Optionally, it includes a list of RACH configurations, multiple RACH configuration information. If the candidate gNB-CU provides the mapping identity or index or identifier of the LTM NG-RAN node, or the mapping identity or index or identifier of the LTM gNB-DU, correspondingly, this list includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for the mapping identity or index or identifier of each requested LTM NG-RAN node or gNB-DU.

[0337] Procedure 506: The candidate NG-RAN node (candidate gNB or candidate ng-eNB) or candidate gNB-CU sends a HANDOVER REQUEST ACKNOWLEDGE message or a new Xnap message (such as an LTM configuration request acknowledgement message or an LTM request acknowledgement message) to the source NG-RAN node (source gNB or source ng-eNB) or source gNB-CU for the requested candidate cell, which contains one or more of the following information:

[0338] - Candidate cell ID (Cell ID or NR CGI)

[0339] - Low-layer RRC configuration generated for the target candidate cell that accepts the LTM configuration request, for example, a list of Transmission Configuration Indication (TCI) state configurations (TCI States Configurations List, included in the LTM-TCI-Info IE defined in TS 38.331), as well as SSB configuration and NR PCI (Physical Cell Id) information of the candidate cell

[0340] - LTM reference configuration provided by the candidate NG-RAN node or candidate gNB-CU (LTM Reference Configuration, including low-layer and / or high-layer reference configurations, optionally, may include the CellGroupConfig IE and / or CG-ConfigInfo IE defined in TS 38.331, where the CG-ConfigInfo IE contains ltm-ReferenceConfiguration information)

[0341] - Indication of LTM complete configuration (LTM Complete Configuration Indicator, indicating whether the LTM configuration of the accepted candidate cell is a complete configuration)

[0342] - LTM CSI report configuration (included in the CellGroupConfig IE defined in TS 38.331)

[0343] - Early sync information (Early Sync Information), including early uplink sync configuration information of the candidate cell (Early UL Sync Configuration) or early uplink sync configuration information for supplementary uplink (Early UL Sync Configuration for SUL (Supplementary Uplink))

[0344] - TA assistance information, indicating that the TA value of the candidate cell is 0

[0345] - RACH configuration information (i.e., PRACH resources), including one or more RACH configuration information

[0346] ■ Optionally, it includes one RACH configuration information. That is, it includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for the source NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or the source gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0347] ■ Optionally, it includes one RACH configuration information. That is, it includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for the mapping identifier / index / identifier of the source NG-RAN node or source gNB-DU.

[0348] ■ Optionally, it includes a list of RACH configurations, multiple RACH configuration information. It includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for each candidate NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-

[0349] eNB ID)) or each candidate gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0350] ■ Optionally, it includes a list of RACH configurations, multiple RACH configuration information. If the candidate gNB-CU provides the mapping identifier or index or identifier of the LTM NG-RAN node, or the mapping identifier or index or identifier of the LTM gNB-DU, correspondingly, this list includes the RACH configuration information allocated for the candidate cell (represented by Cell ID or NR CGI) for the mapping identifier or index or identifier of each requested LTM NG-RAN node or gNB-DU.

[0351] For different PRACH resources, RACH configuration information, or Early UL SyncConfiguration information allocated to a candidate cell for one or more LTM gNB-DUs or LTM gNBs in procedure 505, 506, or 509, it may include one or more of the following information:

[0352] - RACH Configuration (contained in the EarlyUL-SyncConfig IE defined in TS 38.331, representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs or LTM gNBs. Different parts of the PRACH resources are shown by the following LTM gNB-DU list information or LTM gNB list information)

[0353] - LTM gNB-DUs List (containing one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0354] ■ LTM gNB-DU ID (indicated by gNB-DU ID)

[0355] ■ LTM gNB ID (indicated by Global gNB ID, used to represent the gNB information associated with the gNB-DU indicated by gNB-DU ID)

[0356] ■ Preamble Index List (containing one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB-DU ID)

[0357] - LTM gNBs List (containing one or more LTM gNB IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0358] ■ LTM gNB ID (indicated by Global gNB ID)

[0359] ■ Preamble Index List (containing one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB ID)

[0360] Procedure 507: If the source NG-RAN node is an architecture with separated gNB-CU and gNB-DU, the source gNB-CU may continue to allocate the corresponding RACH configuration to the source gNB-DU based on the RACH configuration implemented for each candidate cell assigned to this NG-RAN node. For example, if only one or more UEs under one source gNB-DU under the source gNB-CU initiate LTM configuration for the same candidate cell, then the RACH configuration of this candidate cell based on the NG-RAN node may be allocated to this gNB-DU; if multiple UEs under different source gNB-DUs initiate LTM configuration for the same candidate cell, then a subset of the RACH configuration of this candidate cell based on the NG-RAN node may be allocated to different gNB-DUs. In short, how the gNB-CU reallocates the RACH configuration to the gNB-DU is based on the implementation of the gNB-CU. If the RACH configuration of the candidate cell is allocated based on the gNB-DU, the source gNB-CU continues to forward the corresponding RACH configuration information to the corresponding candidate gNB-DU (including the source gNB-DU).

[0361] Procedure 508: The source gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU, which contains one or more of the following information:

[0362] - A candidate cell ID (Cell ID or NR CGI, which can be the source cell or other candidate cells under the source gNB-DU, and each candidate cell uses a separate UE context modification process)

[0363] - LTM trigger indication (LTM indicator = true)

[0364] - LTM configuration ID of the candidate cell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0365] - LTM configuration ID mapping list (LTM Configuration ID Mapping List, including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID)

[0366] - LTM CSI resource configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0367] - The source gNB-CU requests the source gNB-DU to provide an indication for generating a reference configuration of the lower layer configuration (Request for Lower Layer Configuration)

[0368] - LTM Reference Configuration (including the CellGroupConfig IE defined in TS 38.331)

[0369] - The CSI report configuration, the list of TCI state configurations, the SSB configuration, and the NR PCI information of the target candidate cells in other candidate NG-RAN nodes or candidate gNB-CUs that have accepted the LTM configuration request

[0370] - Early Sync Information List, containing the early uplink synchronization configuration information (Early UL SyncConfiguration) or the early uplink synchronization configuration information for supplementary uplink (Early UL Sync Configuration for SUL) of each candidate cell (represented by Cell ID or NR CGI) that has accepted the LTM configuration request

[0371] - TA Assistance Information, indicating that the TA value of the candidate cell is 0

[0372] - RACH configuration list, which is the early uplink synchronization configuration information. Optionally, it contains a subset or the whole set of RACH configuration information assigned to the belonging NG-RAN node for each candidate cell, or contains the RACH configuration information assigned to the belonging gNB-DU for each candidate cell. It can contain one or more of the following information:

[0373] ■ Candidate cell ID (represented by Cell ID or NR CGI)

[0374] ■ RACH configuration information (RACH Configuration) (contained in the EarlyUL-SyncConfig IE defined in TS 38.331, representing the common part of the PRACH resources of the candidate cell assigned to different LTM gNB-DUs, and the different parts of the PRACH resources are shown by the following list information of LTM gNB-DUs)

[0375] ■ LTM gNB-DU List (containing one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0376] ◆ LTM gNB-DU ID (indicated by gNB-DU ID)

[0377] ◆ LTM gNB ID (indicated by Global gNB ID, used to represent the gNB information associated with the gNB-DU indicated by gNB-DU ID)

[0378] ◆ Preamble Index List (containing one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB-DU ID)

[0379] - Early Sync Information Request

[0380] - Request for RACH Configuration

[0381] ■ Optionally, to support subsequent LTM and the PRACH resources of candidate cells are allocated based on the NG-RAN node, a list of NG-RAN node IDs can be carried, for example, including the Global NG-RAN Node ID of each candidate NG-RAN node, and this Global NG-RAN Node ID can contain Global gNB ID or Global ng-eNB ID. Or carry the LTM gNBs List, which contains the information of each LTM gNB ID, represented by Global gNB ID. It indicates that the source gNB-CU requests PRACH resources from the source gNB-DU based on each NG-RAN node.

[0382] ■ Optionally, to support subsequent LTM and the PRACH resources of candidate cells are allocated based on the gNB-DU, a list of gNB-DU IDs can be carried, and the NG-RAN node ID (for a split architecture base station, here it refers to gNB ID) to which each gNB-DU ID belongs is specified, for example, indicated by the Global NG-RAN Node ID, and this Global NG-RAN Node ID can contain Global gNB ID or Global ng-eNB ID. It indicates that the source gNB-CU requests PRACH resources from the source gNB-DU based on the gNB-DU.

[0383] ■ Optionally, if the source gNB-CU does not want to carry the cleartext candidate NG-RAN node ID and / or candidate gNB-DU ID, or the list of NG-RAN node IDs and / or list of gNB-DU IDs, then the source gNB-CU can also map each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU (including the source gNB-DU) to a certain mapping identifier / index / identifier based on the implementation, and then pass the list of mapping identifiers or indexes or identifiers of the LTM NG-RAN nodes or LTM gNB-DUs (the list of mapping identifiers / indexes / identifiers of the LTM NG-RAN nodes, or the list of mapping identifiers / indexes / identifiers of the LTM gNB-DUs) to the source gNB-DU to request the source cell or other candidate cells to allocate PRACH resources for each mapping identifier or index or identifier.

[0384] Procedure 509: If the source gNB-DU accepts the LTM configuration request, it sends a UE CONTEXT MODIFICATION RESPONSE message as a response. The message includes one or more of the following information:

[0385] - A candidate cell ID (Cell ID or NR CGI, which can include the source cell or other candidate cells under the source gNB-DU, and each candidate cell uses a separate UE context modification procedure)

[0386] - The low-layer RRC configuration generated for the target candidate cell that accepts the LTM configuration request, for example, the Transmission Configuration Indication (TCI) state configuration list (TCI States ConfigurationsList), as well as the SSB configuration and the NR PCI (Physical Cell Id) information of the candidate cell

[0387] - The LTM reference configuration provided by the source gNB-DU

[0388] - The indication of the LTM complete configuration

[0389] - The LTM CSI report configuration (contained in the CellGroupConfig IE defined in TS 38.331)

[0390] - Early Sync Information, including Early UL Sync Configuration or Early UL Sync Configuration for SUL of supplementary uplink carrier

[0391] - List of RACH configuration information (i.e., PRACH resources), including multiple RACH configuration information

[0392] ■ Optionally, it includes RACH configuration information allocated for each candidate NG-RAN node (indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) or each candidate gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) by candidate cells (including the source cell or other candidate cells under the source gNB-DU, represented by Cell ID or NR CGI).

[0393] ■ Optionally, if the source gNB-CU provides the mapping identifier or index or identifier of the LTM NG-RAN node, or the mapping identifier or index or identifier of the LTM gNB-DU, correspondingly, this list includes RACH configuration information allocated for the mapping identifier or index or identifier of each requested LTM NG-RAN node or gNB-DU by candidate cells (including the source cell or other candidate cells under the source gNB-DU, represented by Cell ID or NR CGI).

[0394] Procedure 510: To support subsequent LTM, the source NG-RAN node (source gNB or source ng-eNB) or source gNB-CU collects the LTM configuration information of all candidate cells that accept the LTM request and needs to convey it to each other candidate NG-RAN node (candidate gNB or candidate ng-eNB) or candidate gNB-CU. Then the source NG-RAN node (source gNB or source ng-eNB) or source gNB-CU sends the configuration information of other candidate cells that accept the LTM configuration to other candidate NG-RAN nodes (candidate gNB or candidate ng-eNB) or candidate gNB-CU through the Xn interface message. Optionally, a new Xnap message (such as the LTM configuration modification request message, LTM modification request message, or handover modification request message) can be defined, or the handover request message can be used to transmit this information. This message includes one or more of the following information:

[0395] - LTM modification or update indication (LTM indication = modification or update)

[0396] - A candidate cell ID (Cell ID or NR CGI)

[0397] - The LTM configuration ID of the candidate cell (LTM Configuration ID, corresponding to the LTM - CandidateId IE defined in TS 38.331)

[0398] - The source gNB - CU provides an updated LTM configuration ID mapping list (LTM Configuration ID MappingList, including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID). Optionally, after receiving the updated LTM configuration ID mapping list, the candidate gNB - CU compares it with that received in procedure 503, from which it can be determined which cells have not become LTM candidate cells for accepting the LTM configuration request. Since each candidate gNB - CU can determine which candidate NG - RAN node the candidate cell belongs to through the NR CGI information of the candidate cell, it can be determined which NG - RAN node or gNB - CU cannot be used as an LTM candidate NG - RAN node or candidate gNB - CU, and then release the RACH configuration previously allocated for this candidate NG - RAN node ID for the candidate cells configured on this candidate gNB - CU.

[0399] - The RRC configurations generated by the target candidate cells that have accepted the LTM configuration request among other candidate NG - RAN nodes collected, for example, including a Transmission Channel Indication (TCI) state configuration list (TCI States Configurations List, included in the LTM - TCI - Info IE defined in TS 38.331), as well as the SSB configuration and the NR PCI information of the candidate cell.

[0400] - The LTM reference configuration provided by the source gNB - CU (LTM Reference Configuration, including the reference configuration of the lower layer and / or higher layer, optionally, may include the CellGroupConfig IE and / or CG - ConfigInfo IE defined in TS 38.331, where the CG - ConfigInfo IE contains ltm - ReferenceConfiguration information)

[0401] - Indicator of LTM Complete Configuration (LTM Complete Configuration Indicator)

[0402] - LTM CSI Report Configuration (including the CellGroupConfig IE defined in TS 38.331)

[0403] - Updated LTM CSI Resource Configuration provided by the source gNB-CU (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS38.331)

[0404] - Early Sync Information List, including the Early UL SyncConfiguration or the Early UL Sync Configuration for SUL (supplementary uplink) of each candidate cell (represented by Cell ID or NR CGI) that has accepted the LTM configuration request

[0405] - TA Assistance Information, indicating that the TA value of the candidate cell is the 0-RACH configuration information list (i.e., PRACH resources), which is the Early UL Sync Configuration information

[0406] Contains multiple RACH configuration information

[0407] ■ Optionally, it contains the RACH configuration information assigned to each candidate cell (represented by Cell ID or NR CGI) that has accepted the LTM configuration request for the current candidate NG-RAN node, or for each candidate gNB-DU under the current candidate gNB-CU (indicated by gNB-DUID). It can contain one or more of the following information:

[0408] ◆ Candidate cell ID (represented by Cell ID or NR CGI)

[0409] ◆ RACH Configuration (RACH Configuration) (including the EarlyUL-SyncConfig IE defined in TS 38.331, representing the common part of the PRACH resources assigned to different LTM gNB-DUs or LTM gNBs of the candidate cell, and the different parts of the PRACH resources are shown by the following LTM gNB-DU list information)

[0410] gNB-DU or LTM gNB

[0411] ◆LTM gNB-DU List (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0412] ●LTM gNB-DU ID (indicated by gNB-DU ID)

[0413] ●LTM gNB ID (indicated by Global gNB ID, used to represent the gNB information associated with the gNB-DU indicated by gNB-DU ID)

[0414] ●Preamble Index List (including one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB-DU ID)

[0415] ◆LTM gNB List (including one or more LTM gNB IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0416] ●LTM gNB ID (indicated by Global gNB ID)

[0417] ●Preamble Index List (including one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB ID)

[0418] -LTM Cells to be Released List (including information of multiple cells to be released, indicating the cells to be released by Cell ID or LTM candidate cells that have not been accepted by other candidate NG-RAN nodes or candidate gNB-CUs)

[0419] -LTM Cell ID (indicated by Cell ID or NR CGI, indicating the cell to be released)

[0420] - List of LTM NG-RAN Nodes to be Released (LTM NG-RAN nodes to be Released List, which contains information of multiple NG-RAN nodes to be released. The NG-RAN nodes to be released (gNB or ng-eNB) are indicated by the global ID of the NG-RAN node (i.e., Global gNB ID or Global ng-eNBID). If a rejection occurs during the previous request process for all candidate cells on this candidate NG-RAN node (such as process 506-2 and process 505-2), then this candidate NG-RAN node is excluded from the candidate node list).

[0421] Therefore, the RACH configurations previously allocated to this candidate NG-RAN node by other candidate cells and the source cell need to be released.

[0422] - LTM NG-RAN Node ID (represented by the global ID of the NG-RAN node (i.e., Global gNB ID or Global ng-eNBID), indicating the NG-RAN node (gNB or ng-eNB) to be released)

[0423] - List of LTM gNB-DUs to be Released (LTM gNB-DUs to be Released List), which contains information of gNB-DUs to be released. The gNB-DU to be released can be indicated by the gNB-DU ID, and the global ID of the NG-RAN node (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs can also be indicated. Assume that the RACH configuration of the candidate cell is allocated based on the gNB-DU, and if a rejection occurs during the previous request process for all candidate cells on this candidate gNB-DU (such as process 505-2), that is, this candidate gNB-DU is excluded from the candidate node list. Therefore, for this candidate gNB-DU, the RACH configurations previously allocated to this candidate gNB-DU by other candidate cells and the source cell need to be released.

[0424] - LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU to be released)

[0425] - List of mapping identifiers / indexes / identifiers of the LTM NG-RAN node or gNB-DU to be released.

[0426] If the source gNB-CU or the source NG-RAN node requests the candidate cell to allocate PRACH resources by implementing a correspondence between each candidate NG-RAN node (including the source NG-RAN node) or candidate gNB-DU and a certain mapping identifier / index / identifier, the source gNB-CU or the source NG-RAN node may notify the candidate gNB-CU or candidate NG-RAN node of the list of mapping identifiers / indexes / identifiers to be released, so as to instruct the candidate gNB-CU or candidate NG-RAN node to release the PRACH resources allocated to the candidate NG-RAN node or candidate gNB-DU corresponding to the mapping identifier / index /

[0427] identifier of the LTM NG-RAN node or gNB-DU for the candidate cell.

[0428] - The mapping identifier / index / identifier of the LTM NG-RAN node or gNB-DU (LTM NG-

[0429] RAN node / gNB-DU Mapping ID / Index / identifier, corresponding to the NG-

[0430] RAN node or gNB-DU to be released)

[0431] Procedure 511: Similar to Procedure 507, if the candidate NG-RAN node is an architecture where the gNB-CU and gNB-DU are separated, the candidate gNB-CU may continue to allocate the corresponding RACH configuration to the candidate gNB-DU based on the RACH configuration allocated to this NG-RAN node for each other candidate cell. For example, if there is only one candidate gNB-DU under the candidate gNB-CU, then this RACH configuration based on the NG-RAN node can be all allocated to this gNB-DU; if there are different candidate gNB-DUs, then different subsets of this RACH configuration based on the NG-RAN node can be allocated to different gNB-DUs. If the RACH configuration of the candidate cell is allocated based on the gNB-DU, the candidate gNB-CU continues to forward the corresponding RACH configuration information to the corresponding candidate gNB-DU.

[0432] Procedure 512: The candidate gNB-CU sends a UE context modification request (UE CONTEXT MODIFICATION REQUEST) message to the candidate gNB-DU, which contains one or more of the following information:

[0433] - A candidate cell ID (Cell ID or NR CGI)

[0434] - LTM Configuration ID of the candidate cell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0435] -Updated LTM Configuration ID Mapping List (including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID)

[0436] - Updated LTM CSI resource configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0437] - The CSI reporting configuration, TCI status configuration list, SSB configuration and NR PCI information of the target candidate cells of other candidate NG-RAN nodes that have accepted the LTM configuration request, as well as the collected information.

[0438] -LTM Reference Configuration (LTM Reference Configuration, the reference configuration of the low-level part,

[0439] Including CellGroupConfig IE defined in TS 38.331)

[0440] -Early Sync Information List, which contains the information for each accepted

[0441] Early UL Sync Configuration information of the candidate cell (indicated by Cell ID or NR CGI) for the LTM configuration request or Early UL Sync Configuration for SUL

[0442] -TA Assistance Information, indicating that the candidate cell's TA value is 0 - RACH configuration list, i.e., early uplink synchronization configuration information. Optionally, it contains a subset or full set of RACH configuration information assigned to the NG-RAN node for each candidate cell (Cell ID or NR CGI), or the RACH configuration information assigned to the gNB-DU for each candidate cell. It can include one or more of the following information:

[0443] ■ Candidate Cell ID (represented by Cell ID or NR CGI)

[0444] ■ RACH Configuration Information (RACH Configuration) (contained in the EarlyUL-SyncConfig IE defined in TS 38.331, representing the common part of the PRACH resources allocated to different LTM gNB-DUs by the candidate cell. Different parts of the PRACH resources are shown using the following LTM gNB-DU list information)

[0445] ■ LTM gNB-DU List (LTM gNB-DUs List) (contains one or more LTM gNB-DU IDs and the corresponding allocated PRACH resources, such as Preamble Index List)

[0446] ◆ LTM gNB-DU ID (indicated by gNB-DU ID)

[0447] ◆ LTM gNB ID (indicated by Global gNB ID, representing the gNB information associated with the gNB-DU indicated by the gNB-DU ID)

[0448] ◆ Preamble Index List (contains one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB-DU ID)

[0449] - LTM Cells to be Released List (contains information about multiple cells to be released, indicating the cells to be released by Cell ID or LTM candidate cells that have not been accepted by other candidate NG-RAN nodes or candidate gNB-CUs)

[0450] - LTM Cell ID (represented by Cell ID or NR CGI, indicating the cell to be released)

[0451] - LTM NG-RAN nodes to be Released List (which contains information of multiple NG-RAN nodes to be released, and indicates the NG-RAN nodes (gNB or ng-eNB) to be released through the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNBID)). Assume that the RACH configuration of the candidate cell is allocated based on the NG-RAN node. Optionally, if the LTM NG-RAN nodes to be Released List is received in procedure 510, or the LTM cells to be Released List is received in procedure 510, or the updated LTM configuration ID mapping list is received in procedure 510, the candidate gNB-CU can determine which candidate NG-RAN node is to be released, that is, this candidate NG-RAN node is excluded from the candidate node list. Therefore, for this candidate NG-RAN node, the RACH configuration previously allocated to this candidate NG-RAN node for the candidate cells configured on this gNB-DU needs to be released.

[0452] - LTM NG-RAN node ID (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the NG-RAN node (gNB or ng-eNB) to be released, and used to indicate that the RACH configuration previously allocated to this candidate NG-RAN node for the candidate cells configured on the candidate gNB-DU needs to be released)

[0453] - LTM gNB-DUs to be Released List, which contains information of the gNB-DUs to be released, can indicate the gNB-DU to be released through the gNB-DU ID, and can also indicate the NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs. Assume that the RACH configuration of the candidate cell is allocated based on the gNB-DU, and the LTM gNB-DUs to be Released List is received in the previous procedure 510.

[0454] - LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU to be released)

[0455] - List of mapping identifiers / indexes / identifiers of the LTM NG-RAN node or gNB-DU to be released. If the candidate gNB-CU or candidate NG-RAN node receives a list of mapping identifiers / indexes / identifiers of the LTM NG-RAN node or gNB-DU to be released from the source gNB-CU or source NG-RAN node, the candidate gNB-CU may notify the candidate gNB-DU to which the candidate cell belongs, indicating the release of the PRACH resources allocated to the candidate NG-RAN node or candidate gNB-DU corresponding to the mapping identifier / index / identifier.

[0456] - Mapping identifier / index / identifier of the LTM NG-RAN node or gNB-DU (LTM NG-

[0457] RAN node / gNB-DU Mapping ID / Index / identifier), corresponding to the NG-

[0458] RAN node or gNB-DU to be released)

[0459] When the candidate gNB-DU receives the ID of the NG-RAN node to be released (i.e., Global gNB ID or Global ng-eNB ID) or gNB-DU ID, or receives the mapping identifier / index / identifier information of the NG-RAN node or gNB-DU to be released, the RACH configuration allocated to this NG-RAN node ID or gNB-DU ID, or mapping identifier / index / identifier, for the candidate cell on the candidate gNB-DU needs to be released.

[0460] Procedure 513: The candidate gNB-DU sends a UE context modification response message as a response, including the updated low-layer configuration of the candidate cell. The response sent by the candidate gNB-DU may also include the updated CSI report configuration.

[0461] Procedure 514: The candidate gNB or candidate gNB-CU sends a HANDOVER REQUEST ACKNOWLEDGE message to the source gNB or source gNB-CU for the candidate cell. Optionally, a new Xnap message (e.g., LTM configuration modification request acknowledgement message, LTM modification request acknowledgement message, or handover modification request acknowledgement message) can be defined, which includes the updated LTM configuration of the candidate cell and may also include the updated CSI report configuration.

[0462] Procedure 515: For other candidate NG-RAN nodes, similar procedures 510 to 514 also occur, where the source NG-RAN node or source gNB-CU transfers the configuration information of the relevant LTM to other candidate NG-RAN nodes or candidate gNB-CUs, as well as possible updates to the LTM configuration information.

[0463] An exemplary LTM cell release procedure 500 is shown in Figure 5a. In this case, when gNB-DU2 needs to release its candidate cells, it sends a UE context modification requirement (UE CONTEXT MODIFICATION REQUIRED) or UE context release request (UE CONTEXT RELEASE REQUEST) message to gNB-CU2 in procedure 551, carrying a list of the LTM cells to be released. Or the release procedure of the LTM cell or LTM gNB-DU initiated by the candidate gNB-CU2 through a UE context modification request (UE CONTEXT MODIFICATION REQUEST) or UE context release command (UE CONTEXT RELEASE COMMAND) message. Or the situation where all LTM candidate cells on the candidate gNB-CU2 have been released. Then, the candidate gNB-CU2 can send a conditional handover cancel (CONDITIONAL HANDOVER CANCEL) message, or a newly defined Xnap message (such as an LTM cancel message, an LTM configuration cancel message) to the source gNB-CU0 in procedure 553, carrying a list of the LTM cells to be released and / or a list of the LTM gNB-DUs to be released. The message may include one or more of the following information:

[0464] - List of LTM cells to be released (LTM Cells to be Released List)

[0465] > LTM cell to be released item IE (LTM Cells to be Released Item IEs)

[0466] >> LTM cell ID (indicated by Cell ID or NR CGI)

[0467] - List of LTM gNB-DUs to be released (LTM gNB-DUs to be Released List, indicating that the LTM configuration for the corresponding gNB-DU ID is to be released)

[0468] > LTM gNB-DU to be released item IE (LTM gNB-DUs to be Released Item IEs)

[0469] >>LTM gNB-DU ID (Indicated by gNB-DU ID)

[0470] Based on the received conditional handover cancellation or newly defined Xnap message, the source gNB-CU0 can determine whether all cells in the candidate gNB-CU2 or the candidate NG-RAN node are released, or whether all cells under a certain gNB-DU are released. When all or some cells in the candidate gNB-CU2 or the candidate NG-RAN node or all or some cells under a certain gNB-DU are released, the source gNB-CU0 sends a UE context modification request (UECONTEXT MODIFICATION REQUEST) message to the source gNB-DU in procedure 555. This UE context modification request message may include one or more of the following information:

[0471] - List of LTM cells to be released

[0472] > LTM cell to be released item IE

[0473] >> LTM Cell ID (Indicated by Cell ID or NR CGI)

[0474] - List of LTM gNB-DUs to be released (indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0475] > LTM gNB-DU to be released item IE

[0476] >> LTM gNB-DU ID (Indicated by gNB-DU ID)

[0477] >> LTM gNB ID (Indicating the gNB to which the LTM gNB-DU is associated, indicated by Global gNB ID)

[0478] - List of LTM gNBs to be released (indicating that the LTM configuration of the gNB node corresponding to the corresponding gNB ID is to be released)

[0479] > LTM gNB to be released item IE

[0480] >>LTM gNB ID (indicated by Global gNB ID) - List of RACH configurations to be released (indicating that the RACH configurations corresponding to the Global gNB ID or gNB-DU ID are to be released)

[0481] >RACH Configuration to be Released Item IEs

[0482] >>LTM gNB-DU ID (indicated by gNB-DU ID)

[0483] >>LTM gNB ID (indicating the gNB node to be released or the gNB node to which the LTM gNB-DU is associated, indicated by Global gNB ID)

[0484] - List of LTM gNB-DU Mapping IDs / Indexs / identifiers to be released (if the RACH configuration for a candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU provided by the gNB-CU, this IE can indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0485] >LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs

[0486] >>LTM gNB-DU Mapping ID / Index / identifier

[0487] After the source gNB-DU receives this information, if the RACH configuration of the candidate cell is allocated based on the gNB-CU or the NG-RAN node (gNB or ng-eNB), the candidate cell on the source gNB-DU needs to release the previously allocated RACH configuration (i.e., PRACH resources, such as the Preamble Index List) for the gNB node indicated by the Global gNB ID. If the RACH configuration of the candidate cell is allocated based on the gNB-DU, the candidate cell on the source gNB-DU needs to release the previously allocated RACH configuration (i.e., PRACH resources, such as the Preamble Index List) for the gNB-DU node under the gNB indicated by the gNB-DUID and the corresponding Global gNB ID. After the source gNB-DU receives the information of the released LTM cell, at the same time, it also releases the RACH configuration previously allocated to the source gNB-DU by these LTM cells. Then, in procedure 556, the source gNB-DU sends a UE CONTEXT MODIFICATION RESPONSE message to the source gNB-CU.

[0488] For the release of the LTM candidate cell, the candidate gNB-DU or the candidate gNB, after the source gNB or the source gNB-CU obtains this information, needs to notify other candidate gNBs or candidate gNB-CUs to update the configuration. In procedure 557, the source gNB or the source gNB-CU sends a HANDOVER CANCEL message or a newly defined Xnap message (such as an LTM cancellation message, an LTM configuration cancellation message) to the candidate gNB-CU1. This message can carry the list of LTM cells to be released, the list of LTM NG-RAN nodes to be released, and / or the list of LTM gNB-DUs to be released. The message can include one or more of the following information:

[0489] - List of LTM Cells to be Released

[0490] > LTM Cells to be Released Item IEs

[0491] >> LTM Cell ID (indicated by Cell ID or NR CGI)

[0492] - List of LTM gNB-DUs to be Released (indicating that the LTM configuration for the corresponding gNB-DU ID is to be released)

[0493] >IEs of LTM gNB-DU Items to be Released

[0494] >>LTM gNB-DU ID (Indicated by gNB-DU ID)

[0495] >>LTM gNB ID (Indicates the serving gNB associated with the LTM gNB-DU, indicated by Global gNB ID)

[0496] - LTM gNBs to be Released List (Indicates that the LTM configuration of the gNB node corresponding to the corresponding gNB ID is to be released)

[0497] >IEs of LTM gNB Items to be Released

[0498] >>LTM gNB ID (Indicated by Global gNB ID)

[0499] Based on the received HANDOVER CANCEL message or newly defined Xnap messages (such as LTM Cancel message, LTM Configuration Cancel message), candidate gNB-CU1 sends a UE CONTEXT MODIFICATION REQUEST message to candidate gNB-DU1 in procedure 558. The message includes one or more of the following information:

[0500] - LTM Cells to be Released List

[0501] >IEs of LTM Cells to be Released Items

[0502] >>LTM Cell ID (LTM Cell ID, indicated by Cell ID or NR CGI)

[0503] - LTM gNB-DUs to be Released List (Indicates that the RACH configuration corresponding to the corresponding gNB-DU ID is to be released)

[0504] >IEs of LTM gNB-DU Items to be Released

[0505] >>LTM gNB-DU ID (Indicated by gNB-DU ID)

[0506] >>LTM gNB ID (Indicating the serving gNB associated with the LTM gNB-DU, indicated by Global gNB ID)

[0507] - List of LTM gNBs to be Released (Specifying that the LTM configuration of the gNB node corresponding to the gNB ID is to be released)

[0508] > LTM gNBs to be Released Item IEs

[0509] >>LTM gNB ID (Indicated by Global gNB ID)

[0510] Similarly, after receiving this information, if the RACH configuration of the candidate cell is allocated based on the gNB-CU or the NG-RAN node (gNB or ng-eNB), the candidate cell on the candidate gNB-DU needs to release the previously allocated RACH configuration (i.e., PRACH resources, such as Preamble Index List) for the gNB node indicated by the Global gNB ID. If the RACH configuration of the candidate cell is allocated based on the gNB-DU, the candidate cell on the candidate gNB-DU needs to release the previously allocated RACH configuration (i.e., PRACH resources, such as Preamble Index List) for the gNB-DU node under the serving gNB indicated by the gNB-DU ID and the corresponding Global gNB ID. After receiving the information on the released LTM cells, the candidate gNB-DU also releases the RACH configuration previously allocated to this candidate gNB-DU for these LTM cells, and then sends a response to the candidate gNB-CU. The candidate gNB-CU receives the UE CONTEXT MODIFICATION RESPONSE message from the candidate gNB-DU1 in procedure 559.

[0511] Optionally, gNB-CU2 may also send a UE context release command (UE CONTEXT RELEASE COMMAND) message to gNB-DU2 in procedure 560, carrying the list of LTM cells to be released, and commanding gNB-DU2 to release the RACH configuration of the LTM cells to be released. After the release is completed, gNB-DU2 sends a UE context release complete (UE CONTEXT RELEASE COMPLETA) message in procedure 561.

[0512] Procedure 516: When the network side has completed the LTM-related configuration, the RRC reconfiguration process of the UE needs to be performed. The source gNB-CU sends a downlink RRC message transfer (DL RRC MESSAGE TRANSFER) message to the source gNB-DU, which contains the generated RRC reconfiguration (RRC Reconfiguration) message with the LTM configuration.

[0513] Procedure 517: The source gNB-DU forwards the received RRC reconfiguration message to the UE.

[0514] Procedure 518: The UE sends an RRC reconfiguration complete (RRC Reconfiguration Complete) message to the source gNB-DU.

[0515] Procedure 519: The source gNB-DU forwards the RRC reconfiguration complete message to the gNB-CU through an uplink RRC message transfer (UL RRC MESSAGE TRANSFER) message. Next, optionally, the source gNB may trigger early data forwarding to other candidate gNBs.

[0516] Procedure 520: Early synchronization is performed to obtain an early timing advance (Timing Advance, TA) value. This process includes the UE sending a first random access request message to the candidate cell using the random access resource configuration indicated in the instruction after receiving a PDCCH order instruction sent by the gNB-DU serving the current UE. The random access resource configuration indicated in the instruction is specified, for example, by parameters such as the random access preamble index (Random Access Preamble index), the synchronization signal / PBCH block index (SSB index), and the PRACH occasion mask index (PRACH occasion Mask index). After receiving the first random access request message, the candidate cell calculates the timing advance (Timing Advance, TA) value between the UE and the candidate cell.

[0517] Process 521: The candidate gNB-DU sends the TA value and associated information to the candidate gNB-CU via a non-UE-associated DU-CU TA Information Transfer (DU-CU TAINFORMATION TRANSFER) message, which includes one or more of the following information:

[0518] -TA Information List (TA values may differ for different candidate cells for the same UE, and for the same candidate cell for different UEs)

[0519] -Candidate cell ID (Cell ID or NR CGI)

[0520] -TA value

[0521] -Preamble Index

[0522] -Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0523] - Source NG-RAN node ID information (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)). This allows the candidate gNB-DU to determine which NG-RAN node (gNB or ng-eNB) the UE is currently located under based on the PRACH resources (e.g., Preamble Index) sent by the UE. Because PRACH resource allocation for candidate cells is based on NG-RAN node allocation, different PRACH resources are allocated for different NG-RAN node IDs. This information is carried to indicate to the candidate gNB-CU that TA-related information should be forwarded to the indicated NG-RAN node.

[0524] - Source gNB-DU ID information (expressed as gNB-DU ID) and the NG-RAN node ID to which it belongs (through the NG-RAN node global ID (i.e. Global gNB ID or Global ng-eNB ID)

[0525] Indication), the candidate gNB-DU can thus determine which NG-RAN node and gNB-DU the UE is currently located under through the PRACH resources sent by the UE. Because the PRACH resource allocation of the candidate cell is based on gNB-DU allocation, different gNB-DU IDs are allocated different PRACH resources. This information is carried to indicate to the candidate gNB-CU whether to continue to send the indicated NG-

[0526] The RAN node forwards the TA-related information and then forwards the TA-related information to the indicated gNB-DU.

[0527] - The mapping identity / index / identifier information of the LTM NG-RAN node or gNB-DU, which is mapped to the source NG-RAN node ID or source gNB-DU. If the candidate gNB-DU is the PRACH resource allocated for the mapping identity / index / identifier, the PRACH resource sent by the UE can determine which mapping identity / index / identifier it is.

[0528] - Timing Advance Group Identity Pointer (Tag (Timing Advance Group) ID Pointer, containing the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS 38.331. For a candidate cell that is a MIMO cell, there may be operations of multiple Transmit / Receive Points (TRPs), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. It is necessary to tell the source gNB or source gNB-DU which TAG the TA calculated by the candidate cell is for. In this way, when the source gNB or source gNB-DU triggers LTM, according to the L1 measurement report, select a certain TCI state on a certain candidate cell to determine which TA corresponding to the TAG should be used, and then send it to the UE through the LTM cell handover command MAC CE).

[0529] Procedure 522: Then the candidate NG-RAN node or candidate gNB-CU forwards the TA-related information (optionally, the candidate gNB-CU can determine which NG-RAN node or gNB-CU it corresponds to through the LTM NG-RAN node Mapping ID or Index or information) to the corresponding source NG-RAN node (source gNB or source ng-eNB) or source gNB-CU through the newly defined Xnap information not associated with the UE (such as TA information transmission), which includes one or more of the following information:

[0530] - TA Information List (The TA values for the same UE may be different for different candidate cells, and the TA values for different UEs may also be different for the same candidate cell)

[0531] - Candidate Cell ID (Cell ID or NR CGI)

[0532] - TA value

[0533] - Preamble Index

[0534] - Random Access - Radio Network Temporary Identifier (RA - RNTI)

[0535] - Source gNB - DU ID information (represented by gNB - DU ID). Thus, the candidate gNB - DU can determine, through the PRACH resource (e.g., Preamble Index) sent by the UE, under which gNB - DU of which NG - RAN node (gNB or ng - eNB) the UE is currently located. Because the allocation of PRACH resources for candidate cells is based on the gNB - DU allocation, different gNB - DU IDs allocate different PRACH resources. Carry this information to indicate to the source gNB - CU to continue forwarding TA - related information to the indicated source gNB - DU.

[0536] - Mapping identity / index / identifier information of the LTM gNB - DU, mapped to the source gNB - DU. If the candidate gNB - DU is allocated PRACH resources for the mapping identity / index / identifier, the PRACH resource sent by the UE can determine which mapping identity / index / identifier it is.

[0537] - Timing Advance Group ID Pointer (Tag (Timing Advance Group) ID Pointer, containing the tag - Id - ptr information defined in the TCI - UL - State IE or TCI - State IE in TS 38.331. For a candidate cell that is a MIMO cell, there may be operations with multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG).

[0538] Which TAG the TA calculated by the candidate cell is for needs to be told to the source gNB or source gNB - DU. Thus, when the source gNB or source gNB - DU triggers LTM, according to the L1 measurement report, selecting a certain TCI state on a certain candidate cell can determine which TA corresponding to the TAG should be used, and then send it to the UE through the LTM cell handover command MAC CE).

[0539] Process 523: After the source gNB-CU receives the relevant TA information, it proceeds to allocate the corresponding RACH configuration to the source gNB-DU based on the RACH configuration assigned to the NG-RAN node for each candidate cell, as implemented in process 507. The source gNB-CU uses the TA-related information to determine which source gNB-DU to forward the traffic to (the source NG-RAN node may have different UEs associated with different source gNB-DUs initiating LTM for the same candidate cell). Optionally, if the source gNB-CU receives the indicated source gNB-DU ID or the mapping identifier / index / identifier of the LTM gNB-DU in process 522, it proceeds to forward the relevant TA information to the corresponding source gNB-DU.

[0540] Process 524: The source gNB-CU sends the TA value information, associated CFRA resource information (preamble index and RA-RNTI), candidate cell ID, and timing advance group identifier pointer (Tag ID Pointer) to the corresponding source gNB-DU via a non-UE-associated CU-DU TA Information Transfer (CU-DU TA INFORMATIONTRANSFER) message.

[0541] Process 525: The UE sends a Layer 1 measurement report to the source gNB-DU.

[0542] Process 526: The source gNB-DU decides to perform LTM cell handover to a candidate target cell.

[0543] Process 527: The source gNB-DU sends a Cell Switch Command to the UE.

[0544] Process 528: The source gNB-DU sends a DU-CU CELL SWITCH NOTIFICATION message to the gNB-CU, indicating that a cell handover command has been initiated for the UE. The DU-CU CELL SWITCH NOTIFICATION message includes the target cell ID and TCI state ID (including the joint or downlink TCI state ID and the uplink TCI state ID), as well as the TA information list (which contains valid TA values for one or more candidate cells, the timing advance group identifier (Tag ID Pointer), and possible validity period information, which is passed by the source gNB-DU to the target gNB-DU via the source gNB-CU and the target gNB-CU). Optionally, the source gNB may trigger late data forwarding to the target gNB.

[0545] Procedure 529: The source NG-RAN node or the source gNB-CU forwards the LTM cell switch notification (LTM CELLSWITCH NOTIFICATION) to the target NG-RAN node or the target gNB-CU (the NG-RAN node or gNB-CU to which the target cell belongs) through an existing or newly defined Xnap message, which contains one or more of the following information:

[0546] - Target cell ID (represented by Cell ID or NR CGI)

[0547] - TCI state ID (TCI State ID, corresponding to the CandidateTCI-StatesIdIE defined in TS 38.331)

[0548] - LTM cell switch information (LTM Cell Switch Information)

[0549] ■ Joint or DL TCI state ID (Joint or DL TCI State ID, corresponding to the TCI-StateId IE defined in TS 38.331)

[0550] ■ UL TCI state ID (UL TCI State ID, corresponding to the TCI-UL-StateIdIE defined in TS 38.331)

[0551] - TA information list (TA Information List) (including one or more candidate cell IDs and corresponding valid TA values, and possible validity time information)

[0552] ■ Candidate cell ID (represented by Cell ID or NR CGI)

[0553] ■ TA value (TA Value, indicating the valid TA value of the candidate cell, passed to the target gNB or target gNB-DU for use)

[0554] ■ Timing Advance Group Identification Pointer (Tag (Timing Advance Group) ID Pointer, containing the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS38.331. For a candidate cell that is a MIMO cell, there may be operations with multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. It is necessary to tell the source gNB or source gNB-DU (the candidate gNB or candidate gNB-DU becomes the source gNB or source gNB-DU for subsequent LTM after being accessed by the UE) which TAG the TA calculated by the candidate cell is for. In this way, when the source gNB or source gNB-DU triggers LTM, based on the L1 measurement report, it selects a certain TCI state on a certain candidate cell to determine which TA corresponding to the TAG should be used, and then sends it to the UE through the LTM cell handover command MAC CE)

[0555] ■ TA value validity time (TA valid timer)

[0556] Procedure 530: The target gNB-CU sends the target cell ID and TCI state ID (including combined or downlink TCI state ID, and uplink TCI state ID), as well as a list of TA information (including valid TA values of one or more candidate cells, Timing Advance Group Identification Pointer (Tag ID Pointer), and possible validity time information) to the target gNB-DU through the CU-DU CELL SWITCH NOTIFICATION.

[0557] Procedure 531: The target gNB-DU detects the successful access of the UE (based on the rach-less or rach-based access procedure).

[0558] Procedure 532: The target gNB-DU sends an ACCESS SUCCESS message to the gNB-CU and carries the target cell ID.

[0559] Procedure 533: The UE sends an RRC Reconfiguration Complete message to the target gNB-DU.

[0560] Procedure 534: The target gNB-DU forwards the RRC Reconfiguration Complete message to the gNB-CU through the UL RRC MESSAGE TRANSFER message.

[0561] Procedure 535: The target gNB-CU sends a HANDOVER SUCCESS message to the source gNB-CU and carries the target cell ID. Next, optionally, the source gNB may trigger late data forwarding to the target gNB. After the target gNB and the core network complete the path conversion process, early data forwarding may be performed to other candidate gNBs.

[0562] For subsequent LTM procedures, optionally, the source NG-RAN node or the source gNB-CU sends a HANDOVER SUCCESS message to other candidate gNB-CUs or other candidate NG-RAN nodes and carries the target cell ID (represented by Cell ID or NR CGI), notifying other candidate gNB-CUs or other candidate NG-RAN nodes of the target cell information for the UE's LTM access. From the target cell ID information, the candidate gNB-CU or the candidate NG-RAN node can determine the target NG-RAN node, i.e., the NG-RAN node currently serving the UE.

[0563] Procedure 536: For subsequent LTM procedures, when the UE accesses the target cell, at this time the target cell becomes the source cell serving the UE for the next LTM procedure, and other candidate cells and the source cell that previously served the UE both become candidate cells. Similar procedures 520 - 536 may partially or fully occur cyclically in each LTM procedure.

[0564] If only one-time LTM procedure is supported, then procedures 536 - 537 will not occur. When the source NG-RAN node or the source gNB-CU receives the HANDOVER SUCCESS message, it will notify other candidate NG-RAN nodes or candidate gNB-CUs through a HANDOVER CANCEL Xnap message or a newly defined Xnap message (such as an LTM cancellation message, an LTM configuration cancellation message), release the resources of other prepared LTM candidate cells and the UE context, and the source NG-RAN node or the source gNB-CU releases the resources of the source cell and the UE context.

[0565] Regarding the configuration of LTM candidate cells, it is possible to release the configured LTM candidate cells after or before the RRC reconfiguration of the UE is completed. Correspondingly, the RACH configuration allocated to the candidate cells also needs to be released. If all candidate cells on the candidate gNB-DU or the candidate NG-RAN node are released, correspondingly, the RACH configuration allocated to other candidate cells for this candidate gNB-DU or candidate NG-RAN node needs to be released. The following describes this situation.

[0566] During the LTM cell release process shown in Figure 5a, if the candidate gNB-DU triggers the candidate cell release process, the list of LTM candidate cells to be released is carried in the UE CONTEXT MODIFICATION REQUIRED or UE CONTEXT RELEASE REQUEST message to notify the candidate gNB-CU which LTM candidate cells have been released; if the candidate gNB-CU triggers the candidate cell release process, the list of LTM candidate cells to be released is carried in the UE CONTEXT MODIFICATION REQUEST or UE CONTEXT RELEASE COMMAND message to notify the candidate gNB-DU which LTM candidate cells have been released. Then, the candidate gNB-CU or the candidate NG-RAN node needs to forward the list information of the LTM candidate cells to be released to the source gNB-CU or the source NG-RAN node through the Xnap message. Optionally, the CONDITIONAL HANDOVER CANCEL message or a newly defined Xnap message (such as the LTM cancellation message, the LTM configuration cancellation message) can be considered. The Xnap message carries one or more of the following information:

[0567] - LTM Cells to be Released List, which contains information of one or more cells to be released, and the cells to be released are indicated by Cell ID.

[0568] - LTM Cell ID (indicated by Cell ID or NR CGI, indicating the cell to be released)

[0569] - LTM NG-RAN (gNB or ng-eNB) nodes to be Released List, which contains information of the NG-RAN nodes (gNB or ng-eNB) to be released, and the NG-RAN nodes (gNB or ng-eNB) to be released are indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID).

[0570] - LTM NG-RAN node ID (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the NG-RAN node (gNB or ng-eNB) to be released)

[0571] - List of LTM gNB-DUs to be Released, which contains candidate gNB-DU information to be released and indicates the gNB-DU to be released by the gNB-DU ID. Optionally, the NG-RAN node ID to which the gNB-DU ID belongs can be indicated, represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID).

[0572] - LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU to be released)

[0573] - List of mapping identities / indexes / identifiers of the LTM NG-RAN node / gNB-DU to be released. If the source gNB-CU or the source NG-RAN node requests the candidate cell to allocate PRACH resources by implementing the correspondence between each candidate NG-RAN node (including the source NG-RAN node) or candidate gNB-DU and a certain mapping identity / index / identifier. The source gNB-CU or the source NG-RAN node can notify the candidate gNB-CU or the candidate NG-RAN node of the list of mapping identities / indexes / identifiers of the LTM NG-RAN node / gNB-DU to be released, in order to indicate to the candidate gNB-

[0574] CU or the candidate NG-RAN node to release the PRACH resources allocated by the candidate cell to the candidate NG-RAN node or gNB-DU corresponding to this mapping identity / index / identifier.

[0575] - Mapping identity / index / identifier of the LTM NG-RAN node or gNB-DU (LTM NG-

[0576] RAN node / gNB-DU Mapping ID / Index / identifier, corresponding to the NG-

[0577] RAN node or gNB-DU to be released).

[0578] In one embodiment, optionally, if the list of LTM cells to be released IE is included in the CONDITIONAL HANDOVER CANCEL message, the source NG-RAN node shall consider releasing the resources reserved only by the cells identified by the included NG-RAN CGI or NR CGI.

[0579] When the source gNB-CU or the source NG-RAN node receives the list information of LTM cells to be released sent by the candidate gNB-CU or the candidate NG-RAN node, it can determine whether all candidate cells on the candidate gNB-CU or the candidate NG-RAN node have been released, or whether all candidate cells on a certain candidate gNB-DU have been released. Optionally, notify the source gNB-DU through the UE CONTEXT MODIFICATION REQUEST message, and the message carries one or more of the following information:

[0580] - LTM Cells to be Released List (containing information of one or more cells to be released, and the cells to be released are indicated by Cell ID)

[0581] - LTM Cell ID (indicated by Cell ID or NR CGI, indicating the cell to be released)

[0582] - LTM NG-RAN nodes (gNB or ng-eNB) to be Released List

[0583] (gNBs or ng-eNBs) containing information of one or more NG-RAN nodes (gNB or ng-eNB) to be released, and the NG-RAN nodes (gNB or ng-eNB) to be released are indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)

[0584] RAN node (gNB or ng-eNB))

[0585] eNB))

[0586] - LTM NG-RAN node ID (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the NG-RAN node (gNB or ng-eNB) to be released)

[0587] - LTM gNB-DUs to be Released List (containing information of the gNB-DU to be released, and the gNB-DU to be released is indicated by the gNB-DU ID, and the NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs is also indicated.)

[0588] - LTM gNB-DU ID (represented by gNB-DU ID, indicating the gNB-DU to be released)

[0589] - List of LTM mapping identities / indexes / identifiers to be released. If the source gNB-CU or the source NG-RAN node, based on the implementation, maps each candidate NG-RAN node (including the source NG-

[0590] RAN node) or candidate gNB-DU to a certain mapping identity / index / identifier, and then passes the list containing the mapping identity or index or identifier to the candidate NG-RAN node or candidate gNB-CU to request the candidate cell to allocate PRACH resources for each mapping identity or index or identifier, the source gNB-CU shall specify the mapping identity / index / identifier corresponding to the candidate NG-

[0591] RAN node or candidate gNB-DU to be released.

[0592] - Mapping identity / index / identifier of the LTM NG-RAN node or gNB-DU (LTM NG-

[0593] RAN node / gNB-DU Mapping ID / Index / identifier), corresponding to the NG-

[0594] RAN node or gNB-DU to be released.

[0595] After the source gNB-DU receives the NG-RAN node ID and / or gNB-DU ID (or the corresponding mapping identity / index / identifier) or LTM cell ID to be released, the RACH configuration allocated for this NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID), or gNB-DU ID, or the corresponding mapping identity / index / identifier for the source cell or other candidate cells on the source gNB-DU needs to be released. The RACH configuration allocated for the released LTM cell also needs to be released.

[0596] When the source gNB-CU or the source NG-RAN node receives the list information of LTM cells to be released sent by the candidate gNB-CU or the candidate NG-RAN node, optionally, it can determine whether all candidate cells on the candidate gNB-CU or the candidate NG-RAN node have been released, or whether all candidate cells on a certain candidate gNB-DU have been released. Optionally, the source gNB-CU or the source NG-RAN node receives the list information of LTM NG-RAN nodes / gNB-DUs to be released sent by the candidate gNB-CU or the candidate NG-RAN node. The source gNB-CU or the source NG-RAN node needs to forward the list information of LTM cells to be released and other information to other candidate gNB-CUs or candidate NG-RAN nodes through the Xnap message. Optionally, the enhanced HANDOVER CANCEL message or a newly defined Xnap message (such as the LTM cancellation message, the LTM configuration cancellation message) can be considered. The Xnap message carries one or more of the following information:

[0597] - List of LTM Cells to be Released (containing information of one or more cells to be released, and the cells to be released are indicated by Cell ID)

[0598] - LTM Cell ID (indicated by Cell ID or NR CGI, indicating the cell to be released)

[0599] - List of LTM NG-RAN nodes (gNB or ng-eNB) to be Released (LTM NG-RAN nodes

[0600] (gNBs or ng-eNBs) to be Released List, containing information of one or more NG-

[0601] RAN nodes (gNB or ng-eNB), and the NG-RAN nodes (gNB or ng-

[0602] eNB) to be released are indicated by the NG-RAN node global ID (i.e., Global gNB ID or Globalng-eNB ID)

[0603] - LTM NG-RAN node ID (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNBID), indicating the NG-RAN node (gNB or ng-eNB) to be released)

[0604] - List of LTM gNB-DUs to be Released, which contains the information of gNB-DUs to be released, indicates the gNB-DU to be released by the gNB-DU ID, and indicates the NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs.

[0605] - LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU to be released)

[0606] - List of mapping identifiers / indexes / identifiers of the LTM NG-RAN node / gNB-DU to be released. If the source gNB-CU or the source NG-RAN node requests the candidate cell to allocate PRACH resources by implementing the correspondence between each candidate NG-RAN node (including the source NG-RAN node) or candidate gNB-DU and a certain mapping identifier / index / identifier. The source gNB-CU or the source NG-RAN node can notify the candidate gNB-CU or the candidate NG-RAN node of the list of mapping identifiers / indexes / identifiers of the LTM to be released, so as to indicate to the candidate gNB-CU or the candidate NG-RAN node to release the PRACH resources allocated by the candidate cell to the candidate NG-RAN node or gNB-DU corresponding to this mapping identifier / index / identifier.

[0607] - Mapping identifier / index / identifier of the LTM NG-RAN node or gNB-DU (LTM NG-

[0608] RAN node / gNB-DU Mapping ID / Index / identifier, corresponding to the NG-

[0609] RAN node or gNB-DU to be released).

[0610] In one embodiment, optionally, if the list of LTM cells to be released IE is included in the HANDOVERCANCEL message, the target NG-RAN node shall consider that the source NG-RAN node only cancels the handover related to the candidate cells identified by the included NG-RAN CGI or NR CGI, and cancels the signaling connection associated with the UE that is the same as the source NG-RAN node UE XnAP ID IE, if included, also identified by the target NG-RAN node UE XnAP ID IE.

[0611] In one embodiment, optionally, if the list of LTM NG-RAN nodes to be released IE is included in the HANDOVER CANCEL message, the target NG-RAN node shall, if supported, release the RACH configuration allocated for the configured LTM candidate cells for the indicated NG-RAN node ID (represented by the NG-RAN node global ID and included in the list of LTM NG-RAN nodes to be released IE).

[0612] In one embodiment, optionally, if the list of LTM gNB-DU to be released IE is included in the HANDOVER CANCEL message, the target NG-RAN node shall, if supported, release the RACH configuration allocated for the configured candidate cells for the indicated gNB-DU ID (included in the list of LTM gNB-DU to be released IE).

[0613] When the candidate gNB-CU or candidate NG-RAN node receives the list of LTM cells to be released information sent by the source gNB-CU or source NG-RAN node, optionally, it can determine whether all candidate cells on a certain NG-RAN node have been released, and optionally, it can determine whether all candidate cells on the gNB-DU of a certain NG-RAN node have been released. Since the cell and neighboring cell information of each node can be known between two gNB-CUs or NG-RAN nodes through the Xn establishment process or the NG-RAN configuration update process, and at the same time, it can be determined which NG-RAN node has configured which candidate cells through the configured list of LTM candidate cells; or, it can be determined through the list of LTM NG-RAN nodes to be released, the list of LTM gNB-DU to be released, or the corresponding list of LTM mapping identifiers / indexes / identifiers sent by the source NG-RAN node or source gNB-CU. Optionally, then the candidate gNB-CU notifies the candidate gNB-DU through the UE CONTEXT MODIFICATION REQUEST message, and this message can carry one or more of the following information:

[0614] - List of LTM Cells to be Released (including information of one or more cells to be released, and the cells to be released are indicated by Cell ID)

[0615] - LTM Cell ID (represented by Cell ID or NR CGI, indicating the cell to be released)

[0616] - List of LTM NG-RAN nodes (gNB or ng-eNB) to be released

[0617] (gNBs or ng-eNBs) to be Released List, which contains one or more NG-RAN nodes (gNB or ng-eNB) information to be released.

[0618] RAN node (gNB or ng-eNB) information, and the NG-RAN node (gNB or ng-eNB) to be released is indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID).

[0619] eNB))

[0620] - LTM NG-RAN node ID (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the NG-RAN node (gNB or ng-eNB) to be released)

[0621] - LTM gNB-DU List to be Released, which contains one or more gNB-DU information to be released. The gNB-DU to be released is indicated by the gNB-DU ID, and the NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs is also indicated.

[0622] DU, and indicates the NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs)

[0623] - LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU to be released)

[0624] - List of mapping identities / indexes / identifiers of the LTM NG-RAN node / gNB-DU to be released. If the candidate gNB-CU or candidate NG-RAN node receives the list of mapping identities / indexes / identifiers of the LTM NG-RAN node / gNB-DU to be released from the source gNB-CU or source NG-RAN node, the candidate gNB-CU can notify the candidate gNB-DU belonging to the candidate cell, specifying to release the PRACH resources of the candidate NG-RAN node or gNB-DU corresponding to the mapping identity / index / identifier.

[0625] - Mapping identity / index / identifier of the LTM NG-RAN node or gNB-DU (LTM NG-

[0626] RAN node / gNB-DU Mapping ID / Index / identifier, corresponding to the NG-

[0627] RAN node or gNB-DU.

[0628] When the candidate gNB-DU receives the NG-RAN node ID for release and / or the candidate gNB-DU ID (or the corresponding mapping identifier / index / identifier) and / or the LTM cell ID, the RACH configuration allocated for the candidate cell on the candidate gNB-DU for this NG-RAN node ID or gNB-DU ID or mapping identifier / index / identifier needs to be released. The RACH configuration allocated for the LTM cell to be released needs to be released.

[0629] Optionally, in one embodiment, if the list of LTM NG-RAN nodes to be released IE is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the RACH configuration allocated for the configured candidate cell for the indicated NG-RAN node ID (represented by the NG-RAN node global ID and included in the list of LTM NG-RAN nodes to be released IE).

[0630] Optionally, in one embodiment, if the list of LTM gNB-DUs to be released IE is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the RACH configuration allocated for the configured candidate cell for the indicated gNB-DU ID (included in the list of LTM gNB-DUs to be released IE).

[0631] If the LTM cell release process occurs after the initial RRC reconfiguration of the UE has been completed, then after the network side completes the corresponding LTM cell release, it is also necessary to reconfigure the UE with RRC again.

[0632] In one embodiment, regarding the different PRACH resources allocated for a candidate cell to one or more LTM gNB-DUs or LTM gNBs, or the manifestation form of RACH configuration information, it can be that one LTM gNB-DU ID or one LTM gNB ID corresponds to one PRACH resource, or RACH configuration information, or Early UL Sync Configuration information. It can also be to separately present the configuration information common to all LTM gNB-DUs or LTM gNBs among these configuration information, and then present the different configuration information (such as Preamble Index List) corresponding to different LTM gNB-DUs or different LTM gNBs. In short, the idea embodied is that the candidate cell allocates different PRACH resources, or RACH configuration information, or Early UL Sync Configuration information for each LTM gNB-DU or LTM gNB, and all are within the protection scope of this invention.

[0633] In one embodiment, regarding the release of LTM candidate cells, or the release of all LTM candidate cells on a candidate gNB-DU, that is, the release of the LTM gNB-DU, and the release of all LTM candidate cells on an NG-RAN node (gNB or ng-eNB), for the transmission of this information in the above embodiments, such as a candidate NG-RAN node (gNB or ng-eNB) notifying the source NG-RAN node (gNB or ng-eNB), and the source NG-RAN node (gNB or ng-eNB) notifying other candidate NG-RAN nodes (gNB or ng-eNB), and the name of this information transmitted between the gNB-CU and gNB-DU of a gNB involving a split architecture can be:

[0634] - LTM Cells to be Released List or LTM Cells to be Cancelled List

[0635] ■ LTM Cell ID (represented by Cell ID or NR CGI, indicating the cell to be released or cancelled)

[0636] - List of LTM NG-RAN nodes (gNB or ng-eNB) to be Released or Cancelled (LTM NG-RAN nodes (gNBs or ng-eNBs) to be Released List or LTM NG-RAN nodes (gNBs or ng-eNBs) to be Cancelled List)

[0637] ■ LTM NG-RAN Node ID, represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the NG-RAN node (gNB or ng-eNB) to be released or cancelled

[0638] - List of LTM gNB-DUs to be Released or Cancelled (LTM gNB-DUs to be Released List or LTM gNB-DUs to be Cancelled List)

[0639] ■ LTM gNB-DU ID, represented by the gNB-DU ID, indicating the gNB-DU to be released or cancelled

[0640] In one embodiment, optionally, if the LTM Information Request IE is included in the HANDOVER REQUEST message, the target NG-RAN node shall consider that the request pertains to the LTM of the candidate cell indicated by the included Target Cell Global ID IE, and shall include the LTM Information Acknowledge IE in the HANDOVER REQUEST ACKNOWLEDGE message.

[0641] In one embodiment, optionally, if the LTM Information Modification Request IE is included in the HANDOVER MODIFICATION REQUEST message, the target NG-RAN node shall consider that the request pertains to the LTM of the candidate cell indicated by the included Target Cell Global ID IE, and shall include the LTM Information Modification Acknowledge IE in the HANDOVER MODIFICATION REQUEST ACKNOWLEDGE message.

[0642] In one embodiment, optionally, if the LTM Reference Configuration Request IE set to "Request" is included in the LTM Information Request IE in the HANDOVER REQUEST message, the target NG-RAN node shall provide a reference configuration for LTM if supported.

[0643] In one embodiment, optionally, if the LTM Configuration ID Mapping List IE is included in the HANDOVER REQUEST message, the target NG-RAN node, if supported, shall consider it as mapping information for LTM candidate cells.

[0644] In one embodiment, optionally, if the LTM Configuration ID Mapping List IE is included in the HANDOVER MODIFICATION REQUEST message, the target NG-RAN node, if supported, shall consider it as mapping information for LTM candidate cells.

[0645] In one embodiment, optionally, if the target NG-RAN node applies a complete configuration for a specific target cell, e.g., as part of LTM preparation, it shall notify the source NG-RAN node by including the LTM Complete Configuration Indicator IE set to "Complete" in the LTM Information Confirmation IE included in the HANDOVER REQUEST CONFIRM message.

[0646] In one embodiment, optionally, if the Early Sync Information Request IE is included in the HANDOVER REQUEST message, the target NG-RAN node, if supported, shall include the Early UL Sync Configuration for early TA acquisition (early UL sync) and / or the Early UL Sync Configuration for SUL in the Early Sync Information IE in the HANDOVER REQUEST CONFIRM message.

[0647] In one embodiment, optionally, if early synchronization information IE is included in the handover request confirmation message, the source NG-RAN node shall, if supported, consider it as the early synchronization information generated from the candidate cell accepted from the candidate NG-RAN nodes.

[0648] In one embodiment, optionally, if CSI Resource Configuration is included in the LTM information request IE in the handover request message, the target NG-RAN node shall, if supported, use it to generate the LTM CSI report configuration for the requested LTM candidate cells (included in the CellGroupConfig IE, in the handover command message in the transparent container IE from the target NG-RAN node to the source NG-RAN node).

[0649] In one embodiment, optionally, if CSI Resource Configuration is included in the LTM information modification request IE in the handover modification request message, the target NG-RAN node shall, if supported, use it to generate the LTM CSI report configuration for the requested LTM candidate cells (included in the CellGroupConfig IE, in the handover command message in the transparent container IE from the target NG-RAN node to the source NG-RAN node).

[0650] In one embodiment, optionally, if the early synchronization information list IE is included in the handover modification request message, the target NG-RAN node shall, if supported, use it in accordance with the provisions of TS 38.300.

[0651] In one embodiment, optionally, if the LTM Cells to be Released / Cancelled List IE to be released or cancelled is included in the handover modification request message, the target NG-RAN node shall, if supported, release the candidate cells configured in the list.

[0652] In one embodiment, optionally, if the LTM gNB-DU list IE to be released or cancelled is included in the handover modification (HANDOVER MODIFICATION REQUEST) message, the target NG-RAN node shall, if supported, release the RACH configuration or the early uplink synchronization configuration allocated for the gNB-DU ID (corresponding gNB-DU) indicated in the LTM gNB-DU list IE to be released or cancelled for the LTM candidate cells.

[0653] In one embodiment, optionally, if the list IE of LTM NG-RAN nodes to be released or cancelled is included in the HANDOVER MODIFICATION REQUEST message, the target NG-RAN node shall, if supported, release the RACH configuration or early uplink synchronization configuration allocated for the Global NG-RAN NodeID (corresponding NG-RAN node) indicated in the list IE of LTM NG-RAN nodes to be released or cancelled for the LTM candidate cell.

[0654] In one embodiment, optionally, if the list IE of LTM gNBs to be released or cancelled is included in the HANDOVER MODIFICATION REQUEST message, the target gNB node shall, if supported, release the RACH configuration or early uplink synchronization configuration allocated for the Global gNB ID (corresponding gNB) indicated in the list IE of LTM gNBs to be released or cancelled for the LTM candidate cell.

[0655] Figures 6-1 to 6-3 (Collectively referred to as Figure 6 below) is an embodiment of the inter-CU (inter-SN) LTM (SN change without MN change) process triggered by the source S-NG-RAN node (source SN or S-SN) or MN in the NR-DC scenario, that is, the UE performs LTM between different CUs (different SNs), where the MN remains unchanged and the SN changes. Optionally, if the M-NG-RAN node or S-NG-RAN node is not an architecture with separated gNB-CU and gNB-DU, the corresponding F1 interface messages and processes are not involved in this disclosure. For the LTM cell handover command triggered by the S-SN (or the gNB-DU of the S-SN), it is necessary to transmit the configuration information of each LTM PSCell cell (including but not limited to CSI report configuration, TCI state configuration, RACH configuration, and LTM configuration ID information, etc.) to each candidate SN (including the source SN) or the gNB-DU of the candidate SN (including the gNB-DU of the source SN), and transmit the TA-related information of the UE for the candidate primary and secondary cells (PSCell) to the source SN or the gNB-DU of the source SN. For the LTM cell handover command triggered by the MN (or the gNB-DU of the MN), it is necessary to transmit the configuration information of each LTM cell to the MN (or the gNB-DU of the MN), and transmit the TA-related information of the UE for the candidate PSCell to the MN or the gNB-DU of the MN.

[0656] The following describes each process shown in Figure 6.

[0657] The NG-RAN nodes involved in the following process descriptions, such as the M-NG-RAN node (MN) or the S-NG-RAN node (SN), may include gNB or ng-eNB; for the NG-RAN nodes of the split architecture, they include gNB-CU and gNB-DU. The NG-RAN node ID can be represented by the Global NG-RAN Node ID, and the Global NG-RAN Node ID can include the Global gNB ID or the Global ng-eNB ID.

[0658] Procedure 601: For the scenario of inter-SN LTM triggered by the SN, the UE can directly send the L3 measurement report of the adjacent PSCell to the source S-NG-RAN node (when SRB3 exists). If the source S-NG-RAN node is of the split architecture of gNB-CU and gNB-DU, the UE can send an L3 measurement report message to the gNB-CU through the source gNB-DU. Alternatively, the UE can forward the L3 measurement report of the PSCell to the S-SN through the MN (when SRB1 exists). Or, for the scenario of inter-SN LTM triggered by the MN, the UE can directly send the L3 measurement report of the PSCell to the MN. If the MN node is of the split architecture of gNB-CU and gNB-DU, it is sent from the gNB-DU to the gNB-CU of the MN.

[0659] Procedure 602: The source S-NG-RAN node or the source SN gNB-CU receives the L3 measurement report of the PSCell reported by the UE and triggers the LTM configuration decision. Optionally, the MN receives the L3 measurement report of the PSCell of the UE and triggers the LTM configuration decision. Only one of them is taken. If the MN triggers the LTM configuration decision, Procedure 603 will be ignored.

[0660] Procedure 603: The source S-NG-RAN node or the source SN gNB-CU initiates a request for Inter-CU or inter-SN LTM to the MN, and sends an S-NODE CHANGE REQUIRED message to the MN, which includes one or more of the following information:

[0661] - LTM Information Required

[0662] - Multiple Target S-NG-RAN node List

[0663] - Each Target S-NG-RAN node ID (represented by the NG-RAN node Global ID (Global gNB ID or Global ng-eNB ID))

[0664] - LTM Trigger Indication (LTM Indicator = true or initiation)

[0665] - Maximum Number of PSCells To Prepare

[0666] - Estimated Arrival Probability (indicating the probability of the UE accessing the Target S-NG-RAN node)

[0667]

[0668] - S-NG-RAN node to M-NG-RAN node Container (containing the CG-Config message defined in TS 38.331, which includes ltm-ReferenceConfigurationSCG and the frequency points, PCI, and L3 measurement reports of each recommended candidate PSCell)

[0669]

[0670] - LTM Configuration ID Mapping List (including the mapping relationship between the cell ID (or NR CGI) of each LTM PSCell and its corresponding LTM Configuration ID (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331))

[0671]

[0672] - Early Sync Information Request

[0673] - Request for RACH Configuration

[0674] ​​​■ Optionally, if only one-time LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, the source S-NG-RAN node ID (indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) can be carried, indicating that the S-SN requests PRACH resources based on the NG-RAN node for the early synchronization TA acquisition process.

[0675] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a list of target S-NG-RAN node IDs (each target S-NG-RAN node ID is indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) can be carried, indicating that the S-SN requests PRACH resources based on each S-NG-RAN node for the early synchronization TA acquisition process.

[0676] ■ Optionally, if only one-time LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the S-SN, the gNB-DU ID of the S-SN and the S-NG-RAN node ID (indicated by the NG-RAN node global ID (for a base station with a split architecture, here it refers to the gNB ID)) can be carried, indicating that the S-SN requests PRACH resources based on the gNB-DU of the S-SN for the early synchronization TA acquisition process.

[0677] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a list of gNB-DU IDs can be carried, and each gNB-DU ID indicates the S-NG-RAN node ID to which it belongs (indicated by the NG-RAN node global ID (for a base station with a split architecture, here it refers to the gNB ID)), indicating that the S-SN requests PRACH resources based on the gNB-DU of each candidate SN (including the gNB-DU of the S-SN) for the early synchronization TA acquisition process.

[0678] Optionally, if the S-SN does not want to carry the plaintext S-NG-RAN node ID and / or S-SN gNB-DU ID, or the list of S-NG-RAN node IDs and / or the list of SN gNB-DU IDs, the S-SN can also map each candidate S-NG-RAN node (including the source S-NG-RAN node) or each candidate SN gNB-DU (including the source SN gNB-DU) to a mapping identifier / index / identifier based on the implementation, and then pass the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN node or LTM SN gNB-DU (the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN node, or the list of mapping identifiers / index / identifiers of the LTM SN gNB-DU) to the MN to request the candidate PSCell to allocate PRACH resources for each mapping identifier / index / identifier.

[0679] Procedure 604: The MN initiates the SN addition procedure to each different candidate SN, sending an S-NODE addition request (S-NODE ADDITION REQUEST) message to the candidate SN, which contains one or more of the following information:

[0680] - LTM information request

[0681] - LTM trigger indication (LTM indication = initiation / true)

[0682] - Multiple target S-NG-RAN node list

[0683] - Each target S-NG-RAN node ID (Target S-NG-RAN node ID, represented by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID), recommended candidate target S-NG-RAN node information)

[0684] - Recommended candidate PSCell information (recommended candidate PSCell on each target S-NG-RAN node,

[0685] each PSCell is represented by Cell ID or NR CGI)

[0686] - LTM Configuration ID of the candidate PSCell (corresponding to the LTM-CandidateId IE defined in TS 38.331), including the LTM Configuration ID of each candidate PSCell on this candidate SN.

[0687] - LTM Configuration ID Mapping List, including the mapping relationship between each recommended LTM candidate PSCell ID and its corresponding LTM Configuration ID (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331).

[0688] - LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0689] - Indication of LTM Reference Configuration Request, indicating that the MN requests the LTM reference configuration from the candidate SN.

[0690] - LTM Reference Configuration (including the reference configuration of the lower layer and / or higher layer, including the CellGroupConfig IE and / or CG-

[0691] ConfigInfo message defined in TS 38.331)

[0692] - M-NG-RAN node to S-NG-RAN node Container (M-NG-RAN node to S-NG-

[0693] RAN node Container, containing the CG-ConfigInfo message defined in TS 38.331, which contains the ltm-ReferenceConfiguration information)

[0694] - Early Sync Information Request

[0695] - Request for RACH Configuration

[0696] ■ Optionally, if only one-shot LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, the source S-NG-RAN node ID (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) can be carried, indicating that the MN requests PRACH resources from the candidate SN or gNB-CU based on the S-NG-RAN node for the early synchronization TA acquisition process.

[0697] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a list of target S-NG-RAN node IDs (each target S-NG-RAN node ID is indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) can be carried, indicating that the MN requests PRACH resources from the candidate SN or gNB-CU based on each S-NG-RAN node for the early synchronization TA acquisition process.

[0698] ■ Optionally, if only one-shot LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the S-SN, the gNB-DU ID of the S-SN and the S-NG-RAN node ID (indicated by the NG-RAN node global ID (Global gNBID or Global ng-eNB ID)) can be carried, indicating that the MN requests PRACH resources from the candidate SN or gNB-CU based on the S-SN gNB-DU for the early synchronization TA acquisition process.

[0699] ■ Optionally, to support subsequent LTM and if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a list of gNB-DU IDs can be carried, each gNB-DU ID indicating the S-NG-RAN node ID to which it belongs (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)), indicating that the MN requests PRACH resources from the candidate SN or gNB-CU based on each gNB-DU of the candidate SN (including the gNB-DU of the S-SN) for the early synchronization TA acquisition process.

[0700] ■ Optionally, if the MN does not want to carry the plaintext source S-NG-RAN node ID and / or S-SN gNB-DU ID, or the list of S-NG-RAN node IDs and / or SN gNB-DU IDs, the S-SN or MN can also, based on the implementation, map each candidate S-NG-RAN node (including the source S-NG-RAN node) or each candidate SN's gNB-DU (including the source SN's gNB-DU) to a certain mapping identifier / index / identifier, and then pass the list of mapping identifiers / index / identifiers containing the LTM S-NG-RAN node or LTM SN gNB-DU (the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN node, or the list of mapping identifiers / index / identifiers of the LTM SN gNB-DU) to the candidate SN or gNB-CU to request the candidate PSCell to allocate PRACH resources for each mapping identifier / index / identifier.

[0701] ■ Optionally, if the PRACH resources of the candidate PSCell are allocated based on the M-NG-RAN node, the M-NG-RAN node ID (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) can be carried, indicating that the MN requests PRACH resources from the candidate SN or gNB-CU based on the M-NG-RAN node for the early synchronization TA acquisition process.

[0702] ■ Optionally, if the PRACH resources of the candidate PSCell are allocated based on the MN's gNB-DU (if the MN is in an architecture where the gNB-CU and gNB-DU are separated), an MN gNB-DU ID can be carried, represented by the gNB-DU ID, and the M-NG-RAN node ID to which the gNB-DU ID belongs (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) can be specified, indicating that the MN requests PRACH resources from the candidate SN or gNB-CU based on the MN's gNB-DU (possibly multiple UEs on the MN initiate the SN LTM request process for the same candidate PSCell on different gNB-DUs) for the early synchronization TA acquisition process.

[0703] ■ Optionally, if the MN does not want to carry the plaintext M-NG-RAN node ID and / or MN gNB-DU ID, the MN can also, based on the implementation, map the M-NG-RAN node or the MN's gNB-DU to a certain mapping identifier / index / identifier, and then send the mapping identifier / index / identifier to the candidate SN or gNB-CU to request the candidate PSCell to allocate PRACH resources for the mapping identifier / index / identifier.

[0704] Procedure 605: If the candidate S-NG-RAN node is an architecture where the gNB-CU and gNB-DU are separated, the candidate gNB-CU initiates a UE context establishment procedure for each candidate PSCell to the candidate gNB-DU, and sends a UE context establishment request (UECONTEXT SETUP REQUEST) message, which contains one or more of the following information:

[0705] - LTM trigger indication (LTM indicator = true)

[0706] - A candidate PSCell ID (Cell ID or NR CGI)

[0707] - LTM configuration ID of the candidate PSCell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0708] - LTM configuration ID mapping list (LTM Configuration ID Mapping List, including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID)

[0709] - LTM CSI resource configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0710] - Indication that the candidate gNB-CU requests the candidate gNB-DU to provide a lower layer configuration to generate a reference configuration (Request for Lower Layer Configuration)

[0711] - LTM reference configuration (LTM Reference Configuration, including the CellGroupConfig IE defined in TS 38.331)

[0712] -Early Sync Information Request

[0713] -Request for RACH Configuration

[0714] ■Optionally, if only one-time LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, the source S-NG-RAN node ID and the associated M-NG-RAN node ID (both indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) may be carried to indicate that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the S-NG-RAN node.

[0715] ■Optionally, to support subsequent LTM, and with PRACH resources allocated based on the S-NG-RAN node for the candidate PSCell, a list of target S-NG-RAN node IDs (including the source S-NG-RAN node ID, with each S-NG-RAN node ID indicating the associated M-NG-RAN node ID) may be carried (all indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNBID)), indicating that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU on a per-S-NG-RAN node basis.

[0716] ■Optionally, if only one-time LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the S-SN, the gNB-DU ID of the S-SN and the S-NG-RAN node ID and the associated M-NG-RAN node ID (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) may be carried to indicate that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the S-SN.

[0717] ■Optionally, to support subsequent LTM, and with PRACH resources of the candidate PSCell based on the gNB-DU allocation of the candidate SN, a list of gNB-DU IDs may be carried, where each gNB-DU ID indicates the S-NG-RAN node ID and the associated M-NG-RAN node ID (via the NG-RAN node global ID (Global gNB ID or Global ng-

[0718] (eNB ID) indication), indicating that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the candidate SN's gNB-DU.

[0719] ■ Optionally, if what the MN sends to the candidate gNB-CU is a mapping identifier / index / identifier for the source S-NG-RAN node ID and / or S-SNgNB-DU ID, or a list of mapping identifiers / index / identifiers for the LTM S-NG-RAN node (list of mapping identifiers / index / identifiers for the LTM S-NG-RAN node), or a list of mapping identifiers / index / identifiers for the LTM SN gNB-DU, then the candidate gNB-CU passes the list of mapping identifiers / index / identifiers for the LTM S-NG-RAN node (list of mapping identifiers / index / identifiers for the LTM S-NG-RAN node, or list of mapping identifiers / index / identifiers for the LTM SN gNB-DU) to the candidate gNB-DU to request the candidate PSCell to allocate PRACH resources for each mapping identifier / index / identifier of the LTM S-NG-RAN node or SN gNB-DU.

[0720] ■ Optionally, if the PRACH resources of the candidate PSCell are allocated based on the M-NG-RAN node, the M-NG-RAN node ID can be carried (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)), indicating that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the M-NG-RAN node for the early synchronization TA acquisition process.

[0721] ■ Optionally, if the PRACH resources of the candidate PSCell are allocated based on the MN's gNB-DU (if the MN is an architecture where the gNB-CU and gNB-DU are separated), a MN gNB-DU ID can be carried, represented by the gNB-DU ID, and the M-NG-RAN node ID to which the gNB-DU ID belongs is specified (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)), indicating that the candidate gNB-CU requests PRACH resources from the candidate gNB-DU based on the MN's gNB-DU (it is possible that multiple UEs on different MNs initiate the SN LTM request process for the same candidate PSCell on different gNB-DUs) for the early synchronization TA acquisition process.

[0722] Optionally, if the MN does not want to carry the plaintext M-NG-RAN node ID and / or MN gNB-DU ID, the MN can also map the M-NG-RAN node or the MN's gNB-DU to a certain mapping identifier / index / identifier based on the implementation, and then send the mapping identifier / index / identifier to the candidate SN or gNB-CU. Then, the candidate gNB-CU requests the candidate gNB-DU to allocate PRACH resources for the candidate PSCell based on the mapping identifier / index / identifier.

[0723] Procedure 606: If the candidate gNB-DU accepts the LTM configuration request for the candidate PSCell, it will respond with a UE CONTEXT SETUP RESPONSE message to the candidate gNB-CU, including one or more of the following information:

[0724] - A candidate PSCell ID (Cell ID or NR CGI)

[0725] - Low-layer RRC configuration generated for the accepted target candidate PSCell (e.g., a list of Transmission Configuration Indication (TCI) state configurations, as well as SSB configuration and NR PCI information of the candidate PSCell)

[0726] - LTM reference configuration provided by the candidate gNB-DU (LTM Reference Configuration, including the CellGroupConfig IE defined in TS38.331)

[0727] - Indicator of LTM complete configuration (LTM Complete Configuration Indicator), indicating whether the LTM configuration of the accepted candidate PSCell is a complete configuration.

[0728] - CSI report configuration (contained in the CellGroupConfig IE defined in TS 38.331)

[0729] - Early sync information, including Early UL Sync Configuration or Early UL Sync Configuration for SUL (Supplementary Uplink) for supplementary uplink

[0730] - RACH configuration information (i.e., PRACH resources), including one or more RACH configuration information

[0731] ■ Optionally, it includes one RACH configuration information. That is, it includes the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) for the source S-NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or the source SN gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0732] ■ Optionally, it includes one RACH configuration information. That is, it includes the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) for the mapping identifier / index / identifier of the source S-NG-RAN node or the source SN gNB-DU.

[0733] ■ Optionally, it includes a list of RACH configurations, multiple RACH configuration information. It includes the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) for each candidate S-NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or each candidate SN gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0734] ■ Optionally, it includes a list of RACH configurations, multiple RACH configuration information. If the candidate gNB-CU provides the mapping identifier or index or identifier of the LTM S-NG-RAN node, or the mapping identifier or index or identifier of the LTM SN gNB-DU, correspondingly, this list includes the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) for the mapping identifier or index or identifier of each requested LTM S-NG-RAN node or SN gNB-DU.

[0735] - Optionally, it includes a RACH configuration information. That is, it includes the RACH configuration information allocated by a candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) for an M-NG-RAN node (optionally indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) or for an MN gNB-DU (optionally indicated by the gNB-DU ID and the NG-RAN node global ID of the affiliated MN, i.e., Global gNB ID or Global ng-eNB ID).

[0736] - Optionally, it includes a RACH configuration information. That is, it includes the RACH configuration information allocated by a candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) for the mapping identifier or index or identifier of an M-NG-RAN node or an MN gNB-DU.

[0737] Procedure 607: The candidate SN sends an S-NODE ADDITION REQUEST ACKNOWLEDGE message to the MN, which includes one or more of the following information:

[0738] - A list of candidate PSCell IDs (representing the list of candidate PSCs accepted on this candidate SN, each PSCell represented by Cell ID or NR CGI)

[0739] - The RRC configuration generated for each accepted target candidate PSCell (for example, it includes a list of Transmission Channel Indication (TCI) state configurations (TCI States Configurations List, included in the LTM-TCI-Info IE defined in TS 38.331), as well as the SSB configuration and the NR PCI information of the candidate PSCell).

[0740] - The S-NG-RAN node to M-NG-RAN node Container (including the CG-Config message defined in TS 38.331, which includes the ltm-ReferenceConfigurationSCG)

[0741] - Reference configuration provided by candidate SN or candidate SN gNB-CU (LTM Reference Configuration, including the CG-Config message defined in TS 38.331, which includes ltm-ReferenceConfigurationSCG)

[0742] - Indicator of LTM complete configuration (LTM Complete Configuration Indicator, indicating whether the LTM configuration of each accepted candidate PSCell is a complete configuration)

[0743] - CSI report configuration (included in the CellGroupConfig IE defined in TS 38.331) (indicating the LTM CSI report configuration generated by each accepted candidate PSCell)

[0744] - Early sync information, including the early uplink sync configuration information (Early UL SyncConfiguration) or the early uplink sync configuration information for supplementary uplink (Early UL Sync Configuration for SUL (Supplementary Uplink)) of the candidate cell PSCell (represented by Cell ID or NR CGI) that has accepted the LTM configuration request

[0745] - TA assistance information, indicating that the TA value of the candidate cell PSCell is 0

[0746] - RACH configuration information (i.e., PRACH resources), including one or more RACH configuration information

[0747] ■ Optionally, it includes a list of RACH configuration information. That is, it includes the RACH configuration information allocated for each accepted candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) on the candidate SN for the source S-NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or the source SN gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)).

[0748] Optionally, it includes a list of RACH configuration information. That is, it includes the RACH configuration information assigned to the mapping identifier / index / identifier of each accepted candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) on the candidate SN for the source S-NG-RAN node or the source SN gNB-DU.

[0749] Optionally, it includes a list of RACH configurations, multiple RACH configuration information. It includes the RACH configuration information assigned to each accepted candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) on the candidate SN for each candidate S-NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or each candidate SN gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID) of the candidate SN to which it belongs).

[0750] Optionally, it includes a list of RACH configurations, multiple RACH configuration information. It includes the RACH configuration information assigned to each accepted candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) on the candidate SN for the mapping identifier / index / identifier of the LTM S-NG-RAN node or the mapping identifier / index / identifier of the LTM SN gNB-DU.

[0751] Optionally, it includes a list of RACH configuration information. That is, it includes the RACH configuration information assigned to each accepted candidate PSCell (PSCell ID, represented by Cell ID or NR CGI) on the candidate SN for the M-NG-RAN node (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)) or the MN gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID) of the MN to which it belongs).

[0752] Optionally, it includes a list of RACH configuration information. That is, it includes the RACH configuration information assigned to the mapping identifier / index / identifier of each accepted candidate PSCell (PSCell represented by Cell ID or NR CGI) on the candidate SN for the M-NG-RAN node or the MN gNB-DU.

[0753] Procedure 608: The MN transmits the relevant received LTM configuration information of the candidate PSCells to the source S-NG-RAN node or the source SN gNB-CU, and may initiate a request to the S-SN to use the source PSCell or other PSCells on the S-SN as candidate PSCells. Optionally, the MN sends an S-NODE modification request (S-NODE MODIFICATION REQUEST) message to the S-SN, which contains one or more of the following information:

[0754] - LTM Information Request

[0755] - LTM indication = initiation / true

[0756] - Multiple Target S-NG-RAN node List (the list of candidate S-NG-RAN nodes that receive the LTM configuration request)

[0757] - Target S-NG-RAN node ID (represented by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) for each target S-NG-RAN node

[0758] - Candidate PSCell ID that receives the LTM configuration request on each target S-NG-RAN node (each PSCell is represented by Cell ID or NR CGI)

[0759] - LTM Configuration ID of the candidate PSCells (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331), including the LTM configuration IDs of each candidate PSCell (including the source PSCell and other candidate PSCells) on this S-SN.

[0760] - LTM Configuration ID Mapping List, including the mapping relationship between each LTM candidate PSCellID and its corresponding LTM Configuration ID (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331).

[0761] - LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0762] - Indication of LTM Reference Configuration Request, indicating the MN to request the LTM reference configuration from the source S-NG-RAN node or the source SN gNB-CU.

[0763] - LTM Reference Configuration (including the CellGroupConfig IE and / or CG-ConfigInfo message defined in TS 38.331)

[0764] - M-NG-RAN node to S-NG-RAN node Container (containing the CG-ConfigInfo message defined in TS 38.331, which contains the ltm-ReferenceConfiguration information)

[0765] - RRC configuration generated by the target candidate PSCell that accepts the LTM configuration request on other candidate SNs collected (for example, including the Transmission Channel Indication (TCI) state configuration list (TCIStates Configurations List, included in the LTM-TCI-Info IE defined in TS 38.331), as well as the SSB configuration and the NR PCI information of the candidate PSCell.

[0766] - Indication of LTM Complete Configuration, indicating whether the LTM configuration of each candidate PSCell that accepts the LTM configuration request is a complete configuration.

[0767] - CSI Report Configuration (included in the CellGroupConfig IE defined in TS 38.331), indicating the LTM CSI report configuration generated by each candidate PSCell that accepts the LTM configuration request.

[0768] - Early Sync Information Request

[0769] - Request for RACH Configuration

[0770] ■ Optionally, to support subsequent LTM and for the PRACH resources of the candidate PSCell to be allocated based on the target S-NG-RAN node, a list of target S-NG-RAN node IDs (each target S-NG-RAN node is indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) may be carried, indicating that the MN requests PRACH resources from the source SN for each S-NG-RAN node for the early synchronization TA acquisition process.

[0771] ■ Optionally, to support subsequent LTM and for the PRACH resources of the candidate PSCell to be allocated based on the gNB-DU of the candidate SN, a list of gNB-DU IDs may be carried, and each gNB-DU ID indicates the S-NG-RAN node ID to which it belongs (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)), indicating that the MN requests PRACH resources from the source SN for the gNB-DU of each candidate SN for the early synchronization TA acquisition process.

[0772] ■ Optionally, if the MN does not want to carry the plaintext list of S-NG-RAN node IDs and / or the list of SN gNB-DU IDs, the MN can also map each candidate S-NG-RAN node or the gNB-DU of each candidate SN to a certain mapping identifier / index / identifier based on the implementation, and then pass the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN node or the LTM SN gNB-DU (the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN node, or the list of mapping identifiers / index / identifiers of the LTM SN gNB-DU) to the source SN or the source SN gNB-CU to request the candidate PSCell to allocate PRACH resources for each mapping identifier / index / identifier.

[0773] ■ Optionally, if the PRACH resources of the candidate PSCell are allocated based on the M-NG-RAN node, the M-NG-RAN node ID (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) may be carried, indicating that the MN requests PRACH resources from the source SN or the gNB-CU of the source SN for the M-NG-RAN node for the early synchronization TA acquisition process.

[0774] ■ Optionally, if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the MN (if the MN is an architecture where the gNB-CU and gNB-DU are separated), an MN gNB-DU ID can be carried, denoted by the gNB-DU ID. Optionally, the M-NG-RAN node ID to which the gNB-DU ID belongs can be specified (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNBID)), indicating that the MN requests PRACH resources from the source SN or the gNB-CU of the source SN based on the gNB-DU of the MN (possibly multiple UEs on the MN initiate the SN LTM request process for the same candidate PSCell on different gNB-DUs) for the early synchronization TA acquisition process.

[0775] ■ Optionally, if the MN does not want to carry the plaintext M-NG-RAN node ID and / or MN gNB-DU ID, the MN can also, based on the implementation, map the M-NG-RAN node or the gNB-DU of the MN to a certain mapping identifier / index / identifier, and then pass the mapping identifier / index / identifier to the source SN or the gNB-CU of the source SN to request the candidate PSCell to allocate PRACH resources for the mapping identifier / index / identifier.

[0776] - Early Sync Information, including the early uplink synchronization configuration information (Early UL SyncConfiguration) or the early uplink synchronization configuration information for supplementary uplink (Early UL Sync Configuration for SUL (Supplementary Uplink)) of each candidate cell PSCell (denoted by Cell ID or NR CGI) that has accepted the LTM configuration request.

[0777] - TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0778] - RACH configuration information (i.e., PRACH resources), including one or more RACH configuration information

[0779] Optionally, it includes a list of RACH configuration information, which includes one or more RACH configuration information. That is, it includes the RACH configuration information assigned to the source S-NG-RAN node (indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) or the gNB-DU of the source SN (indicated by the gNB-DU ID and the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) for each candidate PSCell (the PSCell is represented by Cell ID or NR CGI) that accepts the LTM configuration request.

[0780] Optionally, it includes a list of RACH configuration information, which includes one or more RACH configuration information. That is, it includes the RACH configuration information assigned to the mapping identifier / index / identifier of the source S-NG-RAN node or the gNB-DU of the source SN for each candidate PSCell (the PSCell ID is represented by Cell ID or NR CGI) that accepts the LTM configuration request.

[0781] Procedure 609: If the source S-NG-RAN node is an architecture with separated gNB-CU and gNB-DU, the gNB-CU of the source SN can continue to allocate the corresponding RACH configuration to the source gNB-DU based on the implementation of allocating the RACH configuration for each candidate PSCell to this S-NG-RAN node. For example, if one or more UEs under only one source gNB-DU under the gNB-CU of the source SN initiate the LTM configuration for the same candidate PSCell, then the RACH configuration of this candidate PSCell based on the S-NG-RAN node can be all allocated to this gNB-DU. If multiple UEs under different gNB-DUs on the source SN initiate the LTM configuration for the same candidate PSCell, then different subsets of the RACH configuration of this candidate PSCell based on this NG-RAN node can be allocated to different gNB-DUs. In short, how the SN gNB-CU reallocates the RACH configuration to the gNB-DU is based on the implementation of the gNB-CU. If the RACH configuration of the candidate PSCell is allocated based on the gNB-DU, the source SN gNB-CU continues to forward the corresponding RACH configuration information to the corresponding candidate gNB-DU (including the source gNB-DU).

[0782] Procedure 610: If the source S-NG-RAN node is an architecture with separated gNB-CU and gNB-DU, the source gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU, which contains one or more of the following information:

[0783] - A candidate PSCell ID (which can be the source cell or other candidate PSCs under the source gNB-DU, and each candidate PSCell uses a separate UE context modification procedure. Represented by Cell ID or NR CGI)

[0784] - LTM trigger indication (LTM indicator = true)

[0785] - LTM configuration ID of the candidate PSCell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0786] - LTM configuration ID mapping list (LTM Configuration ID Mapping List, including the mapping relationship between each LTM candidate PSCell ID and its corresponding LTM configuration ID)

[0787] - LTM CSI resource configuration (LTM-CSI-ResourceConfig IE, including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0788] - Indication that the source gNB-CU requests the source gNB-DU to provide lower layer configuration to generate a reference configuration (Request for Lower Layer Configuration)

[0789] - LTM reference configuration (LTM Reference Configuration, including the CellGroupConfig IE defined in TS 38.331)

[0790] - The CSI report configuration, TCI status configuration list of the accepted target candidate PSCs in other candidate S-NG-RAN nodes that have been collected, as well as the SSB configuration and NR PCI information of the candidate PSCs.

[0791] - Early Sync Information List, containing the Early UL Sync Configuration or Early UL Sync Configuration for SUL allocated to the candidate cell PSCell (represented by Cell ID or NR CGI) of each accepted LTM configuration request

[0792] - TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0793] - RACH Configuration List, optionally, containing a subset or the whole set of RACH configuration information allocated to the source S-NG-RAN node to which each candidate PSCell belongs, or containing the RACH configuration information allocated to the source gNB-DU for each candidate PSCell

[0794] - Early Sync Information Request

[0795] - Request for RACH Configuration

[0796] ■ Optionally, to support subsequent LTM and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a list of target S-NG-RAN node IDs (each S-NG-RAN node ID indicates the associated M-NG-RAN node ID, both indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)) can be carried, indicating that the source gNB-CU requests PRACH resources from the source gNB-DU based on each S-NG-RAN node

[0797] ■ Optionally, to support subsequent LTM and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a list of gNB-DU IDs can be carried, each gNB-DU ID indicating the S-NG-RAN node ID to which it belongs and the associated M-NG-RAN node ID (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-

[0798] eNB ID)), indicating that the source gNB-CU requests PRACH resources from the source gNB-DU based on the gNB-DU of the candidate SN

[0799] Optionally, if the source SN gNB-CU does not want to carry the clear-text candidate S-NG-RAN node ID and / or the gNB-DU ID of the candidate SN, or the list of S-NG-RAN node IDs and / or the list of gNB-DU IDs of the SNs, the source SN gNB-CU can also, based on the implementation, map each candidate S-NG-RAN node or the gNB-DU of each candidate SN to a certain mapping identifier / index / identifier, and then transmit a list of mapping identifiers / index / identifiers of the LTM S-NG-RAN nodes or LTM SN gNB-DUs (the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN nodes, or the list of mapping identifiers / index / identifiers of the LTM SN gNB-DUs) to the source gNB-DU to request the source PSCell or other candidate PSCs to allocate PRACH resources for each mapping identifier / index / identifier.

[0800] Optionally, if what the MN decides to send to the source gNB-CU is a list of mapping identifiers / index / identifiers of the LTM S-NG-RAN nodes (the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN nodes), or a list of mapping identifiers / index / identifiers of the LTM SN gNB-DUs, the source SN gNB-CU will transmit a list of mapping identifiers / index / identifiers of the LTM S-NG-RAN nodes (the list of mapping identifiers / index / identifiers of the LTM S-NG-RAN nodes, or the list of mapping identifiers / index / identifiers of the LTM SN gNB-DUs) to the gNB-DU of the source SN to request the source PSCell or candidate PSCs to allocate PRACH resources for each mapping identifier / index / identifier of each LTM S-NG-RAN node or SN gNB-DU.

[0801] Optionally, the PRACH resources of the candidate PSCell are allocated based on the M-NG-RAN node, and the M-NG-RAN node ID can be carried (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)), indicating that the source SN gNB-CU requests PRACH resources from the source gNB-DU based on the M-NG-RAN node for the early synchronization TA acquisition process.

[0802] ■ Optionally, the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the MN (if the MN is an architecture where the gNB-CU and gNB-DU are separated), which can carry a gNB-DU ID and indicate the M-NG-RAN node ID to which the gNB-DU ID belongs (indicated by the NG-RAN node global ID (Global gNB ID or Global ng-eNB ID)), indicating that the source SN gNB-CU requests PRACH resources from the source gNB-DU based on the gNB-DU of the MN (possibly different UEs of the source SN are associated with different MNs or different gNB-DUs on the same MN) for the early synchronization TA acquisition process.

[0803] ■ Optionally, if the MN does not want to carry the plaintext M-NG-RAN node ID and / or MN gNB-DU ID, the MN can also map the M-NG-RAN node or the gNB-DU of the MN to a certain mapping identifier / index / identifier based on the implementation, and then pass the mapping identifier / index / identifier to the source SN or gNB-CU, and the source gNB-CU requests the source gNB-DU to allocate PRACH resources for its source PSCell or candidate PSCell for the mapping identifier / index / identifier.

[0804] Procedure 611: If the source gNB-DU accepts the LTM configuration request for the source PSCell or other candidate PSCells, it sends a UE CONTEXT MODIFICATION RESPONSE message as a response. This message includes one or more of the following information:

[0805] - A candidate PSCell ID (Cell ID or NR CGI, which can include the source PSCell or other candidate PSCells under the source gNB-DU, and each candidate PSCell uses a separate UE context modification process)

[0806] - The low-layer RRC configuration generated for the accepted target candidate PSCell (e.g., a list of Transmission Configuration Indication (TCI) state configurations, as well as the SSB configuration and the NR PCI information of the candidate PSCell)

[0807] - The reference configuration provided by the source gNB-DU (LTM Reference Configuration, including the CellGroupConfig IE defined in TS 38.331)

[0808] -LTM Complete Configuration Indicator (indicates whether the LTM configuration of the accepted candidate PSCell is complete)

[0809] -CSI reporting configuration (contained in CellGroupConfig IE defined in TS 38.331)

[0810] -Early Sync Information, including Early UL Sync Configuration or Early UL Sync Configuration for SUL (Supplementary Uplink) allocated to each candidate cell PSCell (indicated by Cell ID or NR CGI) that has accepted the LTM configuration request

[0811] -RACH configuration information list (i.e. PRACH resources), including multiple RACH configuration information

[0812] ■Optionally, RACH configuration information allocated by candidate PSCells (including the source PSCell or other candidate PSCells under the source gNB-DU, indicated by Cell ID or NR CGI) for each candidate S-NG-RAN node (indicated by the NG-RAN node global ID (i.e., GlobalgNB ID or Global ng-eNB ID)) or the gNB-DU of each candidate SN (indicated by the gNB-DU ID and the NG-RAN node global ID (i.e., GlobalgNB ID or Global ng-eNB ID) of the SN to which it belongs).

[0813] ■Optionally, if the source gNB-CU provides an LTM S-NG-RAN node mapping identity or index or identifier, or an LTM SN gNB-DU mapping identity or index or identifier, then accordingly, this list contains the RACH configuration information assigned to the candidate PSCells (including the source PSCell or other candidate PSCells under the source gNB-DU, represented by Cell ID or NR CGI) for each requested LTM S-NG-RAN node or SN gNB-DU mapping identity / index / identifier.

[0814] Optionally, it includes a RACH configuration information. That is, it includes the RACH configuration information allocated for the candidate PSCell (which may include the source PSCell or other candidate PSCs under the source gNB-DU) (the PSCell is represented by Cell ID or NR CGI) for the M-NG-RAN node (optionally, it can be indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) or for the MNgNB-DU (optionally, it can be indicated by the gNB-DU ID and the NG-RAN node global ID of the affiliated MN, i.e., Global gNB ID or Global ng-eNB ID).

[0815] Optionally, it includes a RACH configuration information. That is, it includes the RACH configuration information allocated for the mapping identifier / index / identifier of the candidate PSCell (which may include the source PSCell or other candidate PSCs under the source gNB-DU) (the PSCell is represented by Cell ID or NR CGI) for the M-NG-RAN node or the MNgNB-DU.

[0816] Procedure 612: The source S-NG-RAN node or the source SN gNB-CU transmits the relevant LTM configuration information to the MN, and the source SN sends an S-NODE modification request acknowledgement (S-NODE MODIFICATION REQUEST ACKNOWLEDGE) message to the MN, which includes one or more of the following information:

[0817] - A list of candidate PSCell IDs (representing the list of candidate PSCs accepted on the source SN, including the source PSCell and, possibly, other candidate PSCs on the S-SN, each PSCell is represented by Cell ID or NR CGI)

[0818] - The RRC configuration generated by the target candidate PSCell accepted on the source SN (for example, it includes a list of transmission channel indication (TCI) state configurations (TCI States ConfigurationsList, included in the LTM-TCI-Info IE defined in TS 38.331), as well as the SSB configuration and the NR PCI information of the candidate PSCell).

[0819] - S-NG-RAN node to M-NG-RAN node Container (including the CG-Config message defined in TS 38.331, which includes ltm-ReferenceConfigurationSCG)

[0820] - Reference configuration provided by the source SN or source SN gNB-CU (LTM Reference Configuration, including the CG-Config message defined in TS38.331, which includes ltm-ReferenceConfigurationSCG)

[0821] - LTM Complete Configuration Indicator, indicating whether the LTM configuration of each accepted candidate PSCell is a complete configuration

[0822] - CSI report configuration (including the CellGroupConfig IE defined in TS 38.331) (indicating the generated LTM CSI report configuration of each accepted candidate PSCell)

[0823] - Early Sync Information, including the Early UL SyncConfiguration or Early UL Sync Configuration for SUL (Supplementary Uplink) assigned to each candidate cell PSCell (represented by Cell ID or NR CGI) of the accepted LTM configuration request

[0824] - TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0825] - List of RACH configuration information (i.e., PRACH resources), including multiple RACH configuration information

[0826] ■ Optionally, it includes RACH configuration information allocated for each candidate PSCell (including the source PSCell or other candidate PSCs under the S-SN, represented by CellID or NR CGI) for each candidate S-NG-RAN node (indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) or for each gNB-DU of the candidate SN (indicated by the gNB-DU ID and the NG-RAN node global ID of the affiliated SN, i.e., Global gNB ID or Global ng-eNB ID).

[0827] ■ Optionally, if the source gNB-CU provides an S-LTM NG-RAN node mapping identifier or index or identifier, or an LTM SN gNB-DU mapping identifier or index or identifier, correspondingly, this list includes RACH configuration information allocated for each candidate PSCell (including the source PSCell or other candidate PSCs under the S-SN, represented by Cell ID or NR CGI) for the mapping identifier / index / identifier of each requested LTM S-NG-RAN node or SN gNB-DU.

[0828] ■ Optionally, it includes a list of RACH configuration information. That is, it includes RACH configuration information allocated for each accepted candidate PSCell (which may include the source PSCell) (PSCell represented by Cell ID or NR CGI) on the source SN for the M-NG-RAN node (indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID) or for the MN gNB-DU (indicated by the gNB-DU ID and the NG-RAN node global ID of the affiliated MN, i.e., Global gNB ID or Global ng-eNB ID).

[0829] ■ Optionally, it includes a list of RACH configuration information. That is, it includes RACH configuration information allocated for each accepted candidate PSCell (which may include the source PSCell) (PSCell represented by Cell ID or NR CGI) on the source SN for the mapping identifier / index / identifier of the M-NG-RAN node or MN gNB-DU.

[0830] Procedure 613: The MN sends the configuration information of other accepted candidate PSCs to each other candidate S-NG-RAN node or SN gNB-CU. Optionally, these information can be transmitted by sending an S-NODE modification request (S-NODE MODIFICATION REQUEST) message. This message includes one or more of the following information:

[0831] - LTM modification or update indication (LTM indication = modification or update)

[0832] - Multiple Target S-NG-RAN node List (the list of accepted candidate S-NG-RAN nodes). Optionally, after receiving the list of other accepted target S-NG-RAN nodes, the candidate S-NG-RAN node or SN gNB-CU compares it with the recommended list of target S-NG-RAN nodes received in Procedure 604, and can determine that there is no information of the accepted candidate S-NG-RAN node, and then release the RACH configuration previously allocated for this candidate S-NG-RAN node ID for the configured LTM candidate PSCell.

[0833] - Each Target S-NG-RAN node ID (represented by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID)

[0834] - The list of accepted candidate PSCell IDs on each target S-NG-RAN node (which can include the source PSCell, and each PSCell is represented by Cell ID or NR CGI). Optionally, after receiving the LTM cell information accepted on other target S-NG-RAN nodes, the candidate S-NG-

[0835] RAN node or SN gNB-CU compares it with the recommended LTM candidate PSCell information received in Procedure 604, and can determine that there is no information of the accepted candidate LTM cell, and then can determine that there is no information of the accepted candidate S-NG-RAN node or no information of the accepted candidate SN gNB-DU, and then release the RACH configuration previously allocated for this candidate S-

[0836] NG-RAN node ID and / or SN gNB-DU ID for the configured LTM candidate PSCell.

[0837] - LTM Configuration ID of the candidate PSCell (corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0838] - Updated LTM Configuration ID Mapping List (LTM Configuration ID Mapping List,

[0839] including the mapping relationship between each accepted LTM cell ID and its corresponding LTM configuration ID). Optionally, after the candidate S-NG-RAN node or SN gNB-CU receives the LTM cell information accepted on other target S-NG-

[0840] RAN nodes, it compares it with the recommended LTM candidate PSCell information received in process 604 before. It can determine the unaccepted candidate LTM cell information, and then can determine the unaccepted candidate S-NG-RAN node information or unaccepted candidate SN gNB-DU information, and then release the RACH configuration previously allocated for this candidate S-NG-RAN node ID and / or SN gNB-DU ID for the configured LTM candidate PSCell.

[0841] - RRC configuration generated by the target candidate PSCell accepted on other accepted candidate SNs (optionally, may include the source SN) (for example, including the Transmission Channel Indication (TCI) state configuration list (TCI States Configurations List, included in the LTM-TCI-Info IE defined in TS 38.331), as well as the SSB configuration and the NR PCI information of the candidate PSCell.

[0842] - Indication of LTM Complete Configuration (LTM Complete Configuration Indicator, indicating whether the LTM configuration of each accepted candidate PSCell is a complete configuration)

[0843] - CSI report configuration (included in the CellGroupConfig IE defined in TS 38.331) (indicating the LTM CSI report configuration generated by each accepted candidate PSCell)

[0844] - Updated LTM CSI resource configuration provided by the MN (LTM-CSI-ResourceConfig IE,

[0845] including the ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331

[0846] - Early Sync Information, including the Early UL SyncConfiguration or the Early UL Sync Configuration for SUL (Supplementary Uplink) assigned to the PSCell (represented by Cell ID or NR CGI) of each candidate cell that has accepted the LTM configuration request

[0847] - TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0848] - List of RACH configuration information (i.e., PRACH resources), that is, Early UL Sync Configuration information. It contains multiple RACH configuration information

[0849] ■ Optionally, it contains a list of RACH configuration information, which includes multiple RACH configuration information, that is, the RACH configuration information assigned to the candidate PSCell (which may include the source PSCell, and the PSCell ID is represented by Cell ID or NR CGI) accepted on each other candidate SN for the current candidate S-NG-RAN node, or for each candidate gNB-DU (indicated by the gNB-DU ID) under the current candidate SN gNB-CU. It may contain one or more of the following information:

[0850] ◆ Candidate cell PSCell ID (represented by Cell ID or NR CGI)

[0851] ◆ RACH Configuration information (contained in the EarlyUL-SyncConfig IE defined in TS 38.331, representing the common part of the PRACH resources assigned by the candidate cell PSCell to different LTM gNB-DUs or LTM S-NG-RANs, and the different parts of the PRACH resources are shown by the following LTM gNB-DU list information)

[0852] part, and the different parts of the PRACH resources are shown by the following LTM gNB-DU list information)

[0853] ◆LTM gNB-DU List (containing one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0854] ●LTM gNB-DU ID (indicated by gNB-DU ID)

[0855] ●LTM S-NG-RAN ID (indicated by Global gNB ID, used to represent the S-NG-RAN information associated with the gNB-DU indicated by gNB-DU ID)

[0856] ●Preamble Index List (containing one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated gNB-DU ID)

[0857] ◆LTM S-NG-RAN List (containing one or more LTM S-NG-RAN IDs and the corresponding PRACH resources allocated, such as Preamble Index List)

[0858] ●LTM S-NG-RAN ID (indicated by Global gNB ID)

[0859] ●Preamble Index List (containing one or more Preamble Indexes, representing different parts of the PRACH resources allocated for the indicated S-NG-RAN ID)

[0860] ■Optionally, it contains a list of RACH configuration information, which includes multiple RACH configuration information, that is, the RACH configuration information allocated for the mapping identifier / index / identifier of each candidate PSCell accepted on each candidate SN (which may include the source PSCell, and the PSCell ID is represented by Cell ID or NR CGI) for the current candidate S-NG-RAN node or for each candidate gNB-DU under the current candidate SN gNB-CU.

[0861] - List of LTM S-NG-RAN Nodes to be Released (LTM S-NG-RAN nodes to be Released List, which contains information of multiple S-NG-RAN nodes to be released, and indicates the S-NG-RAN nodes to be released through the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID)). If a rejection occurs during all previous requests for all candidate PSCs on this candidate S-NG-RAN node, that is, this candidate S-NG-RAN node is excluded from the candidate node list, for this candidate S-NG-RAN node, the RACH configurations previously assigned to this candidate S-NG-RAN node by other candidate PSCs and the source PSC need to be released.

[0862] - LTM S-NG-RAN Node ID (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the candidate S-NG-RAN node to be released)

[0863] - List of LTM gNB-DUs to be Released (LTM gNB-DUs to be Released List), which contains information of gNB-DUs to be released, indicates the gNB-DU to be released through the gNB-DU ID, and can indicate the S-NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs. Assume that the RACH configuration of the candidate PSC is allocated based on the SN gNB-DU. If a rejection occurs during all previous requests for all candidate PSCs on this candidate SN gNB-DU, that is, this candidate SN gNB-DU is excluded from the candidate node list, for this candidate SN gNB-DU, the RACH configurations previously assigned to this candidate SN gNB-DU by other candidate PSCs and the source PSC need to be released.

[0864] - LTM gNB-DU ID and / S-NG-RAN Node ID (i.e., Global gNB ID or Global ng-eNB ID) (indicating the SN gNB-DU to be released)

[0865] - List of mapping identities / indexes / identifiers of the LTM S-NG-RAN nodes or SN gNB-DUs to be released. If the S-SN or MN requests the candidate PSCell to allocate PRACH resources by implementing the correspondence of each candidate S-NG-RAN node (including the source S-NG-RAN node) or candidate SN gNB-DU with a certain mapping identity / index / identifier. The MN can notify the candidate S-NG-RAN node of the list of mapping identities / indexes / identifiers to be released to indicate to the candidate S-NG-RAN node to release the PRACH resources allocated to the candidate S-NG-RAN node corresponding to this LTM S-NG-RAN node or SN gNB-DU mapping identity / index / identifier, or the candidate SN gNB-DU, for the candidate PSCell.

[0866] - LTM S-NG-RAN node or SN gNB-DU mapping identity / index / identifier (LTM S-NG-RAN node / SN gNB-DU Mapping ID / Index / identifier), corresponding to the S-NG-RAN node or SN gNB-DU to be released.

[0867] For the different PRACH resources, or RACH configuration information, or Early UL Sync Configuration information allocated by the candidate cell PSCell for one or more LTM gNB-DUs or LTM gNBs in procedures 606 or 607 or 611 or 612, and regarding the transfer of this information in procedures 608 or 613, it may include one or more of the following information: [[ID=⑧]]

[0868] [[ID=⑨]]- Candidate cell PSCell ID (represented by Cell ID or NR CGI) [[ID=⑩]] [[ID=⑪]]

[0869] [[ID=⑫]]- RACH configuration information (RACH Configuration) (contained in the EarlyUL-SyncConfig IE defined in TS 38.331, representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs or LTM S-NG-RANs, and the different parts of the PRACH resources are shown by the following LTM gNB-DU list information or LTM S-NG-RAN list information) [[ID=⑬]] [[ID=⑭]]

[0870] [[ID=⑮]]- LTM gNB-DU list (LTM gNB-DUs List) (containing one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, such as Preamble Index List) [[ID=⑯]]<00017⑦]] It should be noted that in the original text, there is an incorrect tag format in "[[ID=⑧]]

[0868] ", which is corrected to "

[0868] " in the translation. Also, the "⑦" in "[[ID=⑯]]<00017⑦]] " seems to be an error and is retained as is in the translation for now. If this is a specific format requirement, it may need to be adjusted according to the actual situation.

[0871] ■LTM gNB-DU ID (indicated by gNB-DU ID)

[0872] ■LTM M-NG-RAN or S-NG-RAN ID (indicated by Global gNB ID, used to represent the S-NG-RAN or M-NG-RAN information associated with the gNB-DU indicated by gNB-DU ID)

[0873] ■Preamble Index List (contains one or more Preamble Index, representing different parts in the PRACH resources allocated for the indicated gNB-DU ID)

[0874] -LTM S-NG-RAN list (LTM S-NG-RANs List) (contains one or more LTM S-NG-RAN IDs and the corresponding allocated PRACH resources, such as Preamble Index List)

[0875] ■LTM S-NG-RAN ID (indicated by Global gNB ID)

[0876] ■Preamble Index List (contains one or more Preamble Index, representing different parts in the PRACH resources allocated for the indicated S-NG-RAN ID)

[0877] In one embodiment, if MN or one of the candidate SNs triggers the release of the LTM candidate PSCell, optionally, the following one or more pieces of information can be carried using the S-NODE modification request message (S-NODE MODIFICATION REQUEST or S-NODE MODIFICATION REQUIRED):

[0878] -LTM PSCells to be Released List (contains information of multiple primary and secondary cells to be released, and the primary and secondary cells to be released are indicated by PSCell ID)

[0879] -LTM PSCell ID (represented by Cell ID or NR CGI, indicating the primary and secondary cells to be released)

[0880] In one embodiment, if MN or one of the candidate SNs triggers the process of SN release, that is, all the candidate PSCs on the candidate SN are released. Optionally, the S-NODE RELEASE REQUEST or S-NODE RELEASE REQUIRED message can be used to carry the above information.

[0881] Optionally, based on the released LTM PSCells information, the M-NG-RAN node can determine whether the candidate S-NG-RAN node or a certain gNB-DU under the candidate S-NG-RAN node has been released, and then notify each other candidate S-NG-RAN node and the source S-NG-RAN node about the LTM PSCell release information and / or LTM S-NG-RAN node release information and / or the list of LTM gNB-DUs to be released. Optionally, the S-NODE MODIFICATION REQUEST message or a newly defined XnAP (such as LTM PSCell Change Cancel) message can be used to carry one or more of the following information:

[0882] - The list of LTM primary and secondary cells to be released or cancelled (LTM PSCells to be Released List or LTM PSCells to be Cancelled List, containing information of one or more primary and secondary cells to be released, and the cells to be released are indicated by Cell ID)

[0883] - LTM PSCell ID (indicated by Cell ID or NR CGI, indicating the cell to be released)

[0884] - The list of LTM S-NG-RAN nodes to be released or cancelled (LTM S-NG-RAN nodes to be Released List or LTM S-NG-RAN nodes to be Cancelled List, containing information of one or more S-NG-RAN nodes to be released, and the S-NG-RAN nodes to be released are indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID))

[0885] - LTM S-NG-RAN node ID (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the S-NG-RAN node to be released)

[0886] - List of LTM gNB-DUs to be Released or Cancelled (LTM gNB-DUs to be Released List or LTM gNB-DUs to be Cancelled List) (including one or more gNB-DUs to be released -

[0887] DU information, indicating the gNB-DU to be released by the gNB-DU ID and indicating the S-NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs)

[0888] - LTM gNB-DU ID (represented by the gNB-DU ID, indicating the gNB-DU to be released under the candidate SN)

[0889] - LTM S-NG-RAN node ID (represented by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the candidate SN node to which the gNB-DU to be released belongs)

[0890] In one embodiment, optionally, if the list of LTM cells to be released IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall consider that the M-NG-RAN node cancels only the resources related to the candidate PSCell identified by the included NG-RAN CGI or NR CGI.

[0891] In one embodiment, optionally, if the list of LTM cells to be released IE is included in the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node shall consider that the S-NG-RAN node cancels only the resources related to the candidate PSCell identified by the included NG-RAN CGI or NR CGI.

[0892] In one embodiment, optionally, if the list of LTM S-NG-RAN nodes to be released IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, release the configured RACH configuration or PRACH resources or early uplink synchronization configuration assigned to the indicated S-NG-RAN node ID (represented by the NG-RAN node global ID and included in the list of LTM S-NG-RAN nodes to be released IE) for the LTM candidate PSCell.

[0893] In one embodiment, optionally, if the LTM gNB-DU list IE to be released is included in the S-NODE modification request (S-NODE MODIFICATION REQUEST) message, the S-NG-RAN node shall, if supported, release the configured LTM candidate PSCell's RACH configuration or PRACH resource or early uplink synchronization configuration assigned for the indicated gNB-DU ID (included in the LTM gNB-DU list IE to be released, and the gNB-DU under the S-NG-RAN node to be released is indicated by the NG-RAN node global ID and the gNB-DU ID).

[0894] Procedure 614: Similar to procedure 609, if the candidate S-NG-RAN node is an architecture where the gNB-CU and gNB-DU are separated, the candidate SN gNB-CU can continue to allocate the corresponding RACH configuration to the candidate SN gNB-DU based on the RACH configuration assigned to this S-NG-RAN node for each other candidate PSCell. For example, if there is only one candidate gNB-DU under the candidate SN gNB-CU, then this RACH configuration based on the S-NG-RAN node can be all allocated to this gNB-DU. If there are different candidate gNB-DUs, then different subsets of this RACH configuration based on the S-NG-RAN node can be allocated to different gNB-DUs. If the RACH configuration of the candidate PSCell is allocated based on the SN gNB-DU, the candidate SN gNB-CU continues to forward the corresponding RACH configuration information to the corresponding candidate gNB-DU.

[0895] Procedure 615: The candidate gNB-CU sends a UE context modification request (UE CONTEXT MODIFICATION REQUEST) message to the candidate gNB-DU, which includes one or more of the following information:

[0896] - A candidate PSCell ID (Cell ID or NR CGI)

[0897] - The LTM configuration ID of the candidate PSCell (LTM Configuration ID, corresponding to the LTM-CandidateId IE defined in TS 38.331)

[0898] - The LTM configuration ID mapping list (LTM Configuration ID Mapping List, including the mapping relationship between each accepted LTM cell ID and its corresponding LTM configuration ID)

[0899] - Updated LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0900] - List of CSI report configurations, TCI state configurations, SSB configurations, and NR PCI information of the accepted target candidate PSCs in other candidate S-NG-RAN nodes collected

[0901] - LTM Reference Configuration (the reference configuration of the lower layer, including CellGroupConfig IE defined in TS38.331)

[0902] - Early Sync Information List, containing early uplink synchronization configuration information (Early UL SyncConfiguration) or early uplink synchronization configuration information for supplementary uplink (Early UL Sync Configurationfor SUL) of each candidate cell (represented by Cell ID or NR CGI) that has accepted the LTM configuration request

[0903] - TA Assistance Information, indicating that the TA value of the candidate cell PSC is 0

[0904] - RACH configuration list, optionally, containing a subset or the whole set of RACH configuration information assigned to the belonging S-NG-RAN node for each candidate PSC (PSCell ID represented by Cell ID or NR CGI), or containing RACH configuration information assigned to the belonging SN gNB-DU for each candidate PSC

[0905] - List of LTM S-NG-RAN nodes to be Released (containing information of multiple S-NG-RAN nodes to be released, indicating the S-NG-RAN nodes to be released through the NG-RAN node global ID (i.e., Global gNB ID or Globalng-eNB ID)). Assuming that the RACH configuration of the candidate PSC is assigned based on the S-NG-RAN node, optionally, the list of S-NG-RAN nodes to be released is received in procedure 613

[0906] - LTM S-NG-RAN Node ID (indicated by the NG-RAN node global ID (i.e., Global gNB ID or Global ng-eNB ID), indicating the S-NG-RAN node to be released)

[0907] - List of LTM gNB-DUs to be Released (contains information of gNB-DUs to be released, indicates the gNB-DU to be released by the gNB-DU ID, and indicates the S-NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) to which the gNB-DU ID belongs). Assume that the RACH configuration of the candidate PSCell is allocated based on the SN gNB-DU. Optionally, the list of SN gNB-DUs to be released was received in the previous procedure 613.

[0908] - LTM gNB-DU ID and / S-NG-RAN node ID (i.e., Global gNB ID or Global ng-eNB ID) (indicating the SN gNB-DU to be released)

[0909] - List of mapping IDs / indexes / identifiers of the LTM S-NG-RAN node or SN gNB-DU to be released. If the candidate S-NG-RAN node receives a list of mapping IDs / indexes / identifiers of the LTM S-NG-RAN node or SN gNB-DU to be released from the MN, the candidate gNB-CU can notify the candidate gNB-DU, specifying to release the PRACH resources allocated for the candidate S-NG-RAN node or candidate SN gNB-DU corresponding to the mapping ID / index / identifier.

[0910] - Mapping ID / index / identifier of the LTM S-NG-RAN node or SN gNB-DU (LTM S-NG-RAN node / SN gNB-DU Mapping ID / Index / identifier, corresponding to the S-NG-RAN node or SN gNB-DU to be released)

[0911] When the candidate gNB-DU receives the S-NG-RAN node ID and / or SN gNB-DU ID for release, or receives the mapping ID / index / identifier information for release, the RACH configuration allocated for this S-NG-RAN node ID or SN gNB-DU ID or mapping ID / index / identifier on the candidate PSCell on the candidate gNB-DU needs to be released. The RACH configuration or PRACH resources or early uplink synchronization configuration allocated for the released LTM cell needs to be released.

[0912] In one embodiment, optionally, if the list of LTM S-NG-RAN nodes to be released is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the configured candidate PSCell's RACH configuration or PRACH resources or early uplink synchronization configuration allocated for the indicated S-NG-RAN node ID (represented by the NG-RAN node global ID and included in the list of LTM S-NG-RAN nodes to be released).

[0913] In one embodiment, optionally, if the list of LTM gNB-DU to be released is included in the UE CONTEXT MODIFICATION REQUEST message, the gNB-DU shall, if supported, release the configured candidate PSCell's RACH configuration or PRACH resources or early uplink synchronization configuration allocated for the indicated gNB-DU ID (represented by the NG-RAN node global ID and the gNB-DU ID for a candidate gNB-DU under a candidate SN and included in the list of LTM gNB-DU to be released).

[0914] Procedure 616: The candidate gNB-DU sends a UE context modification response message as a response, including the lower-layer configuration of the candidate cell PSCell update. The response sent by the candidate gNB-DU may also include the updated CSI report configuration.

[0915] Procedure 617: The candidate SN gNB-CU replies to the MN with an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message, which may include the LTM configuration of the candidate cell PSCell update and may also include the updated CSI report configuration.

[0916] Procedure 618: For other candidate S-NG-RAN nodes, similar procedures 613 to 617 also occur. The MN transfers the relevant LTM configuration information to other candidate SNs or candidate SN gNB-CUs, as well as possible updates to the LTM configuration information.

[0917] Procedure 619: When the network side has completed the LTM-related configuration, the RRC reconfiguration process of the UE needs to be performed. The MN sends an RRCReconfiguration message containing the generated LTM configuration to the UE.

[0918] Procedure 620: The UE sends an RRC Reconfiguration Complete message to the MN.

[0919] Procedure 621: The MN sends a S-NODE CHANGE CONFIRM message to the source SN (if the inter-SN LTM is triggered by the MN receiving the UE's L3 measurement report and Procedure 603 is ignored, then this Procedure 621 is also ignored), including the RRC Reconfiguration Complete message, which contains one or more of the following information:

[0920] - LTM Information Confirm

[0921] - Multiple Target S-NG-RAN node List

[0922] - Target S-NG-RAN node ID (represented by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID)

[0923] - Candidate PSCell List (including the list of accepted PSCells on each target S-NG-RAN node)

[0924] - Candidate PSCell ID (each PSCell ID is represented by Cell ID or NR CGI)

[0925] Procedure 622: Early synchronization is performed to obtain an early Timing Advance (TA) value. This procedure includes that after the UE receives a PDCCH order instruction sent by the serving MN or S-SN of the current serving UE, or the corresponding MN gNB-DU or S-SN gNB-DU, the UE sends a first random access request message to the candidate PSCell using the random access resource configuration indicated in the instruction. The random access resource configuration indicated in the instruction is specified, for example, by parameters such as the Random Access Preamble index, the Synchronization Signal / PBCH block index (SSB index), and the PRACH occasion Mask index. After receiving it, the candidate PSCell calculates the Timing Advance (TA) value between the UE and the candidate PSCell. If the PDCCH command (PDCCH order) instruction for the UE is triggered by the MN (or the gNB-DU of the MN), the TA value of the candidate PSCell needs to be finally transmitted from the candidate SN or the gNB-DU of the candidate SN to the MN (or the gNB-DU of the MN). If the PDCCH command (PDCCH order) instruction for the UE is triggered by the S-SN (or the source gNB-DU of the S-SN), the TA value of the candidate PSCell needs to be finally transmitted from the candidate SN or the gNB-DU of the candidate SN to the S-SN (or the source gNB-DU of the S-SN).

[0926] Procedure 623: The candidate gNB-DU sends the TA value and associated information to the candidate gNB-CU through a DU-CU TA INFORMATION TRANSFER message, which includes one or more of the following information:

[0927] - TA Information List (The TA values may be different for the same UE for different candidate PSCs, and may also be different for different UEs for the same candidate PSCell)

[0928] - Candidate PSCell ID (Cell ID or NR CGI)

[0929] - TA value

[0930] - Preamble Index

[0931] - Random Access - Radio Network Temporary Identifier (RA - RNTI)

[0932] - Source S - NG - RAN node ID information (NG - RAN node global ID, i.e., Global gNB ID or Global ng - eNB ID). The candidate gNB - DU can determine which S - NG - RAN node the UE is currently under by the PRACH resources sent by the UE. Because if the allocation of the PRACH resources of the candidate PSCell is based on the S - NG - RAN node, different S - NG - RAN node IDs allocate different PRACH resources. Carry this information to indicate to the candidate gNB - CU to continue forwarding TA - related information to the indicated S - NG - RAN node.

[0933] - Source SN gNB - DU ID information, and indicate the S - NG - RAN node ID to which it belongs (indicated by the NG -

[0934] RAN node global ID (i.e., Global gNB ID or Global ng - eNB ID)). The candidate

[0935] gNB - DU can determine which gNB - DU under which S -

[0936] NG - RAN node the UE is currently under by the PRACH resources sent by the UE. Because if the allocation of the PRACH resources of the candidate PSCell is based on the SN gNB - DU, different gNB - DU IDs allocate different PRACH resources. Carry this information to indicate to the candidate gNB - CU to continue forwarding TA - related information to the indicated S - NG - RAN node and the source SN gNB - DU.

[0937] - M - NG - RAN node ID information (NG - RAN node global ID, i.e., Global gNB ID or Global ng - eNB ID), optionally, indicate the M - NG - RAN node information associated with the S - NG - RAN node. This information can be carried to indicate to the candidate gNB - CU to first forward TA - related information to the indicated M - NG - RAN node, and then continue to forward TA - related information to the S - NG -

[0938] RAN node indicated by the S - NG - RAN node ID. Optionally, if the RACH configuration of the candidate PSCell is based on the M - NG - RAN node, this information can be carried to indicate to the candidate gNB - CU to continue to the indicated M -

[0939] The NG-RAN node forwards TA-related information.

[0940] - Information on the MN gNB-DU ID and the ID of the affiliated M-NG-RAN node (indicated by the NG-RAN node global ID, i.e., Global gNB ID or Global ng-eNB ID). If the RACH configuration of the candidate PSCell is allocated based on the MN gNB-DU, this information can be carried to indicate to the candidate gNB-CU to continue forwarding TA-related information to the indicated M-NG-RAN node, and then continue to forward the TA-related information to the corresponding MN gNB-DU according to the indicated MN gNB-DU ID.

[0941] - Mapping identification / index / identifier information of the LTM S-NG-RAN node or SN gNB-DU (mapped to the source S-NG-RAN node ID or the source SN gNB-DU). If the candidate gNB-DU is allocated PRACH resources for the mapping identification / index / identifier, the mapping identification / index / identifier can be determined from the PRACH resources sent by the UE.

[0942] - Mapping identification / index / identifier information of the LTM M-NG-RAN node or MN gNB-DU (mapped to the M-NG-RAN node ID or the MN gNB-DU). If the candidate gNB-DU is allocated PRACH resources for the mapping identification / index / identifier, the mapping identification / index / identifier can be determined from the PRACH resources sent by the UE.

[0943] - Timing Advance Group ID Pointer (Tag (Timing Advance Group) ID Pointer, containing the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS 38.331. For the candidate cell PSCell being a MIMO cell, there may be operations of multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. It is necessary to tell the source SN or the gNB-DU of the source SN (for the inter-SN LTM scenario triggered by the SN) or the MN or the gNB-DU of the MN (for the inter-SN LTM scenario triggered by the MN) which TAG the TA calculated by the candidate cell PSCell is for. Thus, the source SN or the source gNB-

[0944] When DU, or MN or the gNB-DU of MN triggers LTM, it selects a TCI state on a certain candidate cell PSCell according to the L1 measurement report to determine which TA corresponding to which TAG should be used, and then sends it to the UE through the LTM cell handover command MAC CE).

[0945] Procedure 624: The candidate S-NG-RAN node or the candidate gNB-CU forwards the TA-related information to the corresponding M-NG-RAN node through the received M-NG-RAN node ID information, or the mapping identifier / index / identifier information, using the existing message or the newly defined Xnap information (optionally, the message name can be TA Information Transfer or other names), which includes one or more of the following information:

[0946] - TA Information List (the TA values may be different for the same UE for different candidate PSCells, and may also be different for different UEs for the same candidate PSCell)

[0947] - Candidate PSCell ID (Cell ID or NR CGI)

[0948] - TA value

[0949] - Preamble Index

[0950] - Random Access-Radio Network Temporary Identifier (RA-RNTI)

[0951] - Source S-NG-RAN node ID information (NG-RAN node global ID, that is, Global gNB ID or Global ng-eNB ID), carrying this information to indicate to MN to continue forwarding the TA-related information to the indicated S-NG-RAN node.

[0952] - Source SN gNB-DU ID information and the affiliated S-NG-RAN node ID (indicated by the NG-RAN node global ID (that is, Global gNB ID or Global ng-eNB ID)), carrying this information to indicate to MN to continue forwarding the TA-related information to the indicated S-NG-RAN node, and then the source SN continues to forward the TA-related information to the corresponding gNB-DU according to the indicated SN gNB-DU ID.

[0953] - MN gNB-DU ID information. If the RACH configuration of the candidate PSCell is allocated based on the MN gNB-DU, this information can be carried to indicate to the MN to continue forwarding TA-related information to the gNB-DU corresponding to the MN gNB-DU ID.

[0954] - LTM S-NG-RAN node or SN gNB-DU mapping identifier / index / identifier information (mapped to the source S-NG-RAN node ID or the source SN gNB-DU). This information can be carried to indicate to the MN to continue forwarding TA-related information to the S-NG-RAN node mapped to the indicated mapping identifier / index / identifier.

[0955] - LTM MN gNB-DU mapping identifier / index / identifier information (mapped to the MN gNB-DU). This information can be carried to indicate to the MN to continue forwarding TA-related information to the MN gNB-DU mapped to the indicated mapping identifier / index / identifier.

[0956] - Timing Advance Group Identity Pointer (Tag (Timing Advance Group) ID Pointer, containing the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS 38.331. For the candidate cell PSCell being a MIMO cell, there may be operations with multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. Which TAG the TA calculated by the candidate cell PSCell is for needs to be told to the source SN or the gNB-DU of the source SN (for the inter-SN LTM scenario triggered by the SN) or the MN or the gNB-DU of the MN (for the inter-SN LTM scenario triggered by the MN). Thus, the source SN or the source gNB-DU, or the MN or the gNB-DU of the MN, when triggering LTM, can select a certain TCI state on a certain candidate cell PSCell according to the L1 measurement report to determine which TA corresponding to which TAG should be used, and then send it to the UE through the LTM cell change command MAC CE).

[0957] Procedure 625: The MN forwards TA-related information to the corresponding source S-NG-RAN node or source SN gNB-CU through an existing message or newly defined Xnap information (optional, the message name can be TA Information Transfer or other names), which contains one or more of the following information:

[0958] - TA Information List (The TA values may be different for the same UE with different candidate PSCs, and may also be different for different UEs with the same candidate PSC)

[0959] - Candidate PSCell ID (Cell ID or NR CGI)

[0960] - TA value

[0961] - Preamble Index

[0962] - Random Access - Radio Network Temporary Indentifier (RA - RNTI)

[0963] - Source gNB - DU ID information. Carry this information to indicate to the gNB - CU of the source SN to continue forwarding TA - related information to the indicated source gNB - DU.

[0964] - Mapping identity / index / identifier information of the LTM gNB - DU (mapped to the source gNB - DU). This information can be carried to indicate to the gNB - CU of the source SN to continue forwarding TA - related information to the source gNB -

[0965] DU mapped by the identity / index / identifier.

[0966] - Timing Advance Group ID Pointer (Tag (Timing Advance Group) ID Pointer, containing the tag - Id - ptr information defined in the TCI - UL - State IE or TCI - State IE in TS 38.331. For a candidate cell PSCell that is a MIMO cell, there may be operations with multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs can be configured, and each TCI state is associated with a TAG. Which TAG the TA calculated for the candidate cell PSCell is for needs to be told to the source SN or the gNB - DU of the source SN (for the inter - SN LTM scenario triggered by the SN). In this way, when the source SN or gNB - DU triggers LTM, based on the L1 measurement report, select a certain TCI state on a certain candidate cell PSCell to determine which TA corresponding to the TAG should be used, and then send it to the UE through the LTM cell change command MAC CE).

[0967] If the RACH configuration of the candidate PSCell is allocated based on the M-NG-RAN node or the MN gNB-DU, then the processes 625 to 627 regarding TA information transmission on the S-SN side are ignored. Then, after process 624, if the MN is an architecture with separated gNB-CU and gNB-DU, the gNB-CU of the MN continues to forward the TA-related information to the gNB-DU indicated by the MN gNB-DU ID information, or forwards the TA-related information to the MN gNB-DU ID that maps the identification / index / identifier mapping.

[0968] Process 626: When the source gNB-CU receives the relevant TA information, based on the implementation in process 609, the source gNB-CU continues to allocate the corresponding RACH configuration to the source gNB-DU based on the RACH configuration allocated to this NG-RAN node for each candidate PSCell. The source gNB-CU can determine which source gNB-DU needs to be forwarded through the TA-related information (under the source NG-RAN node, different UEs under different source gNB-DUs may initiate the LTM configuration for the same candidate PSCell). Optionally, if the source gNB-CU receives the indicated source gNB-DU ID information or the mapping identification / index / identifier information of the LTM gNB-DU in process 625, it continues to forward the relevant TA information to the corresponding source gNB-DU.

[0969] Process 627: The source gNB-CU sends the TA value information, the associated CFRA resource information (preamble index and RA-RNTI), the candidate PSCell ID, and the timing advance group identification pointer (Tag ID Pointer) to the corresponding source gNB-DU through the CU-DU TA INFORMATION TRANSFER message.

[0970] Process 628: For the inter-SN LTM request triggered by the S-SN, the UE sends a layer 1 measurement report to the gNB-DU of the source SN or the source S-SN. Optionally, for the inter-SN LTM request triggered by the MN, the UE can send a layer 1 measurement report to the MN, or the gNB-DU serving the UE under the MN.

[0971] Process 629: The source gNB-DU (optionally, it can be the source SN's, or the source gNB-DU serving the UE under the MN) decides to perform an LTM cell handover to a candidate target PSCell.

[0972] Procedure 630: The source gNB-DU (optional, which can be the source SN's, or the lower source gNB-DU of the MN) sends a Cell Switch Command to the UE. Optionally, the Cell Switch Command contains an indication to the UE that the cell type of access is the Primary Secondary Cell (PSCell) in the SCG, or in other words, it indicates that it is a cell switch command regarding the SCG, rather than a cell switch command for the MCG, so as to distinguish whether the cell type to which the UE is accessing in the current signaling is a cell in the MCG or the target cell under single connection.

[0973] Procedure 631: The source SN gNB-DU (or MN gNB-DU) sends a DU-CU CELL SWITCH NOTIFICATION message to the source SN gNB-CU (or MN gNB-CU), indicating that a cell switch command has been initiated to the UE. The DU-CU CELL SWITCH NOTIFICATION message includes the target cell PSCell ID and cell switch information (which includes the combined / downlink TCI state ID, and may include the uplink TCI state ID), as well as a list of TA information (which includes the valid TA values of one or more candidate cells PSCell, the Timing Advance Group Identity Pointer (Tag ID Pointer), and possibly the valid time information, which is passed by the source SN gNB-DU to the target SN gNB-DU through the source SN gNB-CU, MN, and the target SN gNB-CU for use).

[0974] Procedure 632: The source S-NG-RAN node or the source SN gNB-CU forwards the LTM Cell Switch Notification to the MN through an existing or newly defined Xnap message (optionally, the message name can be LTM CELL SWITCH NOTIFICATION or LTM PSCELL SWITCH NOTIFICATION), which includes one or more of the following information:

[0975] - The target cell ID or the target PSCell ID (represented by Cell ID or NR CGI)

[0976] - The TCI state ID (TCI State ID, corresponding to the CandidateTCI-StatesIdIE defined in TS 38.331)

[0977] - The LTM Cell Switch Information

[0978] ■ Joint or DL TCI State ID (corresponding to the TCI-StateId IE defined in TS 38.331)

[0979] ■ UL TCI State ID (corresponding to the TCI-UL-StateId IE defined in TS 38.331)

[0980] - TA Information List (containing one or more candidate cell PSCell IDs and corresponding valid TA values, and possibly valid time information)

[0981] ■ Candidate cell PSCell ID (represented by Cell ID or NR CGI)

[0982] ■ TA Value (indicating the valid TA value of the candidate cell PSCell, passed from the MN to the target SN or used by the target SN gNB-DU)

[0983] ■ Timing Advance Group ID Pointer (Tag(Timing Advance Group)ID Pointer, containing the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS38.331. For a candidate cell PSCell that is a MIMO cell, there may be operations with multiple TRPs (Transmit / Receive Point), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. Which TAG the TA calculated by the candidate cell PSCell is for needs to be told to the source SN or the source SN's gNB-DU (for the SN-triggered inter-SN LTM scenario) (the candidate SN gNB or the candidate SN's gNB-DU becomes the source SN gNB or the source SN's gNB-DU for subsequent LTM after being accessed by the UE) or the MN or the MN's gNB-DU (for the MN-triggered inter-SN LTM scenario), so that the source SN or the source gNB-DU, or the MN or the MN's gNB-DU, when triggering LTM, can select a TCI state on a certain candidate cell PSCell according to the L1 measurement report to determine which TAG's TA to use, and then send it to the UE through the LTM cell handover command MAC CE)

[0984] ■ TA valid timer

[0985] If the cell handover command is triggered by the MN or MN gNB-DU, and the MN gNB-DU sends a DU-CU CELL SWITCH NOTIFICATION message to the MN gNB-CU, then procedure 632 is ignored.

[0986] Procedure 633: The MN forwards the LTM cell handover notification to the target S-NG-RAN node or the target SN gNB-CU (the S-NG-RAN node or gNB-CU to which the target cell belongs) through an existing or newly defined Xnap message (optionally, the message name can be LTM CELL SWITCH NOTIFICATION or LTM PSCELL SWITCH NOTIFICATION), which contains one or more of the following information:

[0987] - Target cell ID or target PSCell ID (represented by Cell ID or NR CGI)

[0988] - TCI state ID (TCI State ID, corresponding to the CandidateTCI-StatesIdIE defined in TS 38.331)

[0989] - LTM cell handover information (LTM Cell Switch Information)

[0990] ■ Joint or DL TCI state ID (Joint or DL TCI State ID, corresponding to the TCI-StateId IE defined in TS 38.331)

[0991] ■ UL TCI state ID (UL TCI State ID, corresponding to the TCI-UL-StateIdIE defined in TS 38.331)

[0992] - TA information list (TA Information List) (containing one or more candidate cell PSCell IDs and their corresponding valid TA values, and possibly valid time information)

[0993] ■ Candidate cell PSCell ID (represented by Cell ID or NR CGI)

[0994] ■ TA value (TA Value, indicating the valid TA value of the candidate cell PSCell, passed to the target SN or target SN gNB-DU for use)

[0995] ■ Timing Advance Group Identification Pointer (Tag(Timing Advance Group)ID Pointer, which contains the tag-Id-ptr information defined in the TCI-UL-State IE or TCI-State IE in TS38.331. For the candidate cell PSCell which is a MIMO cell, there may be operations of multiple TRPs (Transmit / Receive Points), so at most 2 different TAGs are configured, and each TCI state is associated with a TAG. Which TAG the TA calculated by the candidate cell PSCell is for needs to be told to the source SN or the gNB-DU of the source SN (for the inter-SN LTM scenario triggered by the SN) (the candidate SN gNB or the gNB-DU of the candidate SN, when accessed by the UE, will be the source SN gNB or the gNB-DU of the source SN for subsequent LTM) or the MN or the gNB-DU of the MN (for the inter-SN LTM scenario triggered by the MN). In this way, the source SN or the source gNB-DU, or the MN or the gNB-DU of the MN, when triggering LTM, selects a certain TCI state on a certain candidate cell PSCell according to the L1 measurement report, can judge which TA corresponding to the TAG should be used, and then sends it to the UE through the LTM cell switch command MAC CE)

[0996] ■ TA value validity time (TA valid timer)

[0997] Procedure 634: The target S-NG-RAN node or SN gNB-CU sends the target cell PSCell ID and cell switch information (including the combined / downlink TCI state ID and possibly the uplink TCI state ID), and the TA information list (including the valid TA values of one or more candidate cell PSCs, the Timing Advance Group Identification Pointer (Tag ID Pointer), and possibly the valid time information) to the target gNB-DU through the CU-DU CELLSWITCH NOTIFICATION.

[0998] Procedure 635: The target gNB-DU detects the successful access of the UE (based on the rach-less or rach-based access procedure).

[0999] Procedure 636: The target gNB-DU sends an ACCESS SUCCESS message to the gNB-CU and carries the target cell ID.

[1000] Procedure 637: After the UE successfully accesses the target cell, it sends an RRC Reconfiguration Complete message to the MN, which carries the RRC Reconfiguration Complete message sent to the target S-NG-RAN node.

[1001] Procedure 638: The SN Reconfiguration Complete message (S-NODE RECONFIGURATION COMPLETE) sent by the MN to the target S-NG-RAN node, which carries the RRC Reconfiguration Complete sent to the target S-NG-RAN node.

[1002] Procedure 639: For subsequent LTM procedures, if the LTM cell handover command is triggered by the MN, when the MN learns that the UE has successfully accessed the target cell (which can be through Procedure 637), optionally, the MN sends an Xnap message to the source S-NG-RAN node or the source SN gNB-CU to notify that the LTM Inter-SN has been executed. Optionally, the following one or more pieces of information can be included in the S-NODE MODIFICATION REQUEST or XN-U ADDRESS INDICATION message:

[1003] - LTM Inter-SN Execution Notification (LTM Inter-SN Execution Notification = true), notifying the source SN that the LTM has been executed. The source SN stops sending downlink data to the UE, and then the source SN starts late data forwarding.

[1004] - Target cell ID (represented by Cell ID or NR CGI)

[1005] - Data forwarding information of the target NG-RAN node (optionally, it can be represented by Data Forwarding Info from target NG-RAN node, the data forwarding information of the target S-NG-RAN node based on PDU session or based on DRB)

[1006] Procedure 640: For subsequent LTM procedures, when the UE accesses the target PSCell, at this time the target PSCell becomes the source PSCell serving the UE for the next LTM procedure, and other candidate PSCs and the source PSCell that previously served the UE both become candidate PSCs. Similar procedures 622 - 639 may partially or fully occur cyclically in each LTM procedure.

[1007] If only a one-time LTM process is supported, process 640 will not occur. When the MN receives the message of process 637, it will trigger the S-NODE RELEASE process to release the resources of other prepared LTM candidate PSCs and the UE context to the source S-NG-RAN node and other candidate S-NG-RAN nodes, and release the resources of the source cell and the UE context.

[1008] In one embodiment, optionally, if the LTM Information Request IE is included in the S-NODE ADDITION REQUEST message, the S-NG-RAN node shall consider that this request is triggered for LTM preparation. If the S-NG-RAN node accepts the LTM preparation request, it shall include the LTM Information Acknowledge IE in the S-NODE ADDITION REQUEST ACKNOWLEDGE message.

[1009] In one embodiment, optionally, if the LTM Information Request IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall consider that this request is triggered for LTM preparation or modification. If the S-NG-RAN node accepts the LTM preparation or modification request, it shall include the LTM Information Acknowledge IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

[1010] In one embodiment, optionally, if the LTM Reference Configuration Request IE set to "Request" is included in the LTM Information Request IE in the S-NODE ADDITION REQUEST message, the S-NG-RAN node shall provide the SCG reference configuration for LTM if it is supported.

[1011] In one embodiment, optionally, if the LTM reference configuration request (LTM Reference Configuration Request) IE set to "Request" is included in the LTM information request (LTM Information Request) IE in the S-NODE modification request (S-NODE MODIFICATION REQUEST) message, the S-NG-RAN node shall provide the SCG reference configuration for LTM if supported.

[1012] In one embodiment, optionally, if the LTM configuration ID mapping list (LTM Configuration ID Mapping List) IE is included in the S-NODE addition request message, the S-NG-RAN node, if supported, shall regard it as the mapping information of the LTM candidate cell PSCell.

[1013] In one embodiment, optionally, if the LTM configuration ID mapping list (LTM Configuration ID Mapping List) IE is included in the S-NODE modification request (S-NODE MODIFICATION REQUEST) message, the S-NG-RAN node, if supported, shall regard it as the mapping information of the LTM candidate cell PSCell.

[1014] In one embodiment, optionally, if the early sync information request (Early Sync Information Request) IE is included in the S-NODE addition request message, the S-NG-RAN node, if supported, shall include the early UL sync configuration (Early UL Sync Configuration) for early TA acquisition (early UL sync) and / or the early UL sync configuration (Early UL Sync Configuration for SUL) IE for SUL in the early sync information (Early Sync Information) IE in the S-NODE addition request confirmation message.

[1015] In one embodiment, optionally, if the early sync information IE is included in the S-NODE addition request confirmation message, the M-NG-RAN node shall regard it as the early sync information generated from the candidate cell PSCell accepted from the candidate S-NG-RAN node if supported.

[1016] In one embodiment, optionally, if the Early Sync Information Request IE is included in the S-NODE modification request message, then the S-NG-RAN node, if supported, shall include in the Early Sync Information IE in the S-NODE modification request confirmation message the Early UL Sync Configuration for early TA acquisition (early UL synchronization) and / or the Early UL Sync Configuration for SUL IE.

[1017] In one embodiment, optionally, if the Early Sync Information IE is included in the S-NODE modification request confirmation message, the M-NG-RAN node, if supported, shall consider it as the early sync information generated from the candidate cell PSCell accepted from the candidate S-NG-RAN node.

[1018] In one embodiment, optionally, if the Early Sync Information List IE is included in the S-NODE modification request message, the S-NG-RAN node, if supported, shall utilize this early sync information as described in TS 37.340.

[1019] In one embodiment, optionally, if the CSI Resource Configuration is included in the LTM information request IE in the S-NODE addition request message, then the S-NG-RAN node, if supported, shall use it to generate the LTM CSI report configuration (included in the CellGroupConfig IE, in the CandidateList message in the transparent container IE from the S-NG-RAN node to the M-NG-RAN node) for the requested LTM candidate cell PSCell.

[1020] In one embodiment, optionally, if the CSI Resource Configuration is included in the LTM information request IE in the S-NODE modification request message, then the S-NG-RAN node, if supported, shall use it to generate the LTM CSI report configuration (included in the CellGroupConfig IE, in the CandidateList message in the transparent container IE from the S-NG-RAN node to the M-NG-RAN node) for the requested LTM candidate cell PSCell.

[1021] In one embodiment, optionally, if the S-NG-RAN node has applied a complete configuration for a specific target cell PSCell, for example, as part of the LTM preparation, the M-NG-RAN node shall be notified by including an LTM complete configuration indicator (LTM Complete Configuration Indicator) IE set to "complete" in the LTM information confirmation IE included in the S-NODE addition request confirmation message.

[1022] In one embodiment, optionally, if the S-NG-RAN node has applied a complete configuration for a specific target cell PSCell, for example, as part of the LTM preparation, the M-NG-RAN node shall be notified by including an LTM complete configuration indicator (LTM Complete Configuration Indicator) IE set to "complete" in the LTM information confirmation IE included in the S-NODE modification request confirmation message.

[1023] In one embodiment, optionally, if the LTM multi-target S-NG-RAN node list IE is included in the LTM information request IE included in the SN addition request message, the S-NG-RAN node, if supported, shall consider that the information belongs to the list of PSCs for other candidate SNs proposed for LTM preparation and operate as described in TS 37.340.

[1024] In one embodiment, optionally, if the LTM multi-target S-NG-RAN node list IE is included in the LTM information request IE included in the SN modification request message, the S-NG-RAN node, if supported, shall ...

Claims

1. A method performed by a first node in a wireless communication system, comprising: Sending a first request message, where the first request message includes relevant information of at least one distributed unit DU and / or relevant information of at least one base station related to a layer 1 / layer 2 triggered mobility LTM configuration request; receiving a first response message, the first response message including LTM random access channel (RACH) configuration information associated with the at least one DU and / or the at least one base station; Send a second request message, which includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, information of the cell that accepts the LTM configuration request, information of the DU that accepts the LTM configuration request, and information of the base station that accepts the LTM configuration request.

2. The method according to claim 1, wherein The first request message further includes at least one of the following information related to the LTM configuration request: an LTM information request indication, an LTM trigger indication, an LTM configuration ID of a candidate cell, an LTM reference configuration request indication, an LTM reference configuration, an LTM channel state information CSI resource configuration, an LTM configuration ID mapping list, a list of multiple target base stations, a target base station ID, and recommended candidate primary and secondary cell (PSCell) information; The first response message further includes at least one of the following information: a low-layer radio resource control RRC configuration generated for the candidate cell or candidate PSCell that accepts the LTM configuration request, a synchronization signal and physical broadcast channel block SSB configuration, a new radio physical cell identifier NR PCI information of the candidate cell, an LTM reference configuration, an indication of LTM full configuration, and an LTM CSI report configuration, wherein the low-layer RRC configuration includes a transmission configuration indication status configuration TCI list; and / or The second request message also includes at least one of the following information: LTM trigger indication, LTM modification indication, LTM configuration ID of the candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM CSI resource configuration, LTM configuration ID mapping list, LTM CSI report configuration generated for the candidate cell or candidate PSCell that accepts the LTM configuration request, transmission configuration indication status configuration TCI list, SSB configuration and NR PCI information of the candidate cell.

3. The method according to claim 1, further comprising: receiving a third request message, where the third request message includes at least one of the following: information of a DU to be released, information of a base station to be released, and information of a cell to be released; Send a fourth request message, where the fourth request message includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, and indication information of releasing the RACH configuration for at least one DU to be released or base station.

4. The method according to claim 1, wherein The relevant information of the DU or the relevant information of the base station includes at least one of the following: the identifier of the DU, the mapping identifier of the DU, the mapping index of the DU, the identifier of the base station, the mapping identifier of the base station, and the mapping index of the base station.

5. The method according to claim 1 , further comprising receiving a message related to a timing advance (TA) value, in, The message related to the timing advance TA value includes at least one of the following: the identifier of the source DU, the mapping identifier of the source DU, the mapping index of the source DU, the identifier of the source base station, the mapping identifier of the source base station, the mapping index of the source base station, and the timing advance group identifier pointer.

6. A method performed by a second node in a wireless communication system, comprising: receiving a first request message, wherein the first request message includes relevant information of at least one distributed unit DU and / or relevant information of at least one base station related to a layer 1 / layer 2 triggered mobility LTM configuration request; Sending a first response message, where the first response message includes LTM random access channel (RACH) configuration information associated with the at least one DU and / or the at least one base station; as well as Receive a second request message, which includes at least one of the following: information of the DU to be released, information of the base station to be released, information of the cell to be released, information of the cell that accepts the LTM configuration request, information of the DU that accepts the LTM configuration request, and information of the base station that accepts the LTM configuration request.

7. The method according to claim 6, wherein: The first request message further includes at least one of the following information related to the LTM configuration request: an LTM information request indication, an LTM trigger indication, an LTM configuration ID of a candidate cell, an LTM reference configuration request indication, an LTM reference configuration, an LTM channel state information CSI resource configuration, an LTM configuration ID mapping list, a list of multiple target base stations, a target base station ID, and recommended candidate primary and secondary cell (PSCell) information; The acceptance response message also includes at least one of the following information: a low-layer radio resource control RRC configuration generated for the candidate cell or candidate PSCell that accepts the LTM configuration request, a synchronization signal and physical broadcast channel block SSB configuration, a new radio physical cell identifier NR PCI information of the candidate cell, an LTM reference configuration, an indication of LTM full configuration, and an LTM CSI report configuration, wherein the low-layer RRC configuration includes a transmission configuration indication status configuration TCI list; and / or The second request message also includes at least one of the following information: LTM trigger indication, LTM modification indication, LTM configuration ID of the candidate cell, LTM reference configuration request indication, LTM reference configuration, LTM CSI resource configuration, LTM configuration ID mapping list, LTM CSI report configuration generated for the candidate cell or candidate PSCell that accepts the LTM configuration request, transmission configuration indication status configuration TCI list, SSB configuration and NR PCI information of the candidate cell.

8. The method according to claim 6, wherein: In the case where the second request message includes at least one of the following: information of a cell that accepts the LTM configuration request, information of a DU that accepts the LTM configuration request, information of a base station that accepts the LTM configuration request, The method further comprises: Determining, based on the second request message and pre-configured information, at least one of information about a cell to be released, information about a DU to be released, and information about a base station to be released, where the pre-configured information includes information about at least one candidate cell and information about a DU and / or base station associated with the at least one candidate cell; and The release is performed for at least one DU to be released or the RACH configuration of the base station.

9. The method according to claim 6, further comprising: Sending a third request message, where the third request message includes at least one of the following: information of the DU to be released, information of the base station to be released, and information of the cell to be released; receiving a fourth request message, the fourth request message including at least one of the following: information of a DU to be released, information of a base station to be released, information of a cell to be released, and indication information of releasing a RACH configuration for at least one DU to be released or base station; as well as The release is performed for at least one DU to be released or the RACH configuration of the base station.

10. The method according to claim 6, wherein: The relevant information of the DU or the relevant information of the base station includes at least one of the following: the identifier of the DU, the mapping identifier of the DU, the mapping index of the DU, the identifier of the base station, the mapping identifier of the base station, and the mapping index of the base station.

11. A method performed by a user equipment (UE) in a wireless communication system, comprising: Sending a layer 3 measurement report to a source distribution node DU, wherein the layer 3 measurement report is sent by the source DU to a first node, a first request message is sent by the first node, and the first request message includes relevant information of at least one DU and / or relevant information of at least one base station related to a layer 1 / layer 2 triggered mobility LTM configuration request; a first response message is received by the first node, and the first response message includes LTM random access channel RACH configuration information associated with the at least one DU and / or the at least one base station; a second request message is sent by the first node, and the second request message includes at least one of the following: information of a DU to be released, information of a base station to be released, information of a cell to be released, information of a cell that accepts the LTM configuration request, information of a DU that accepts the LTM configuration request, and information of a base station that accepts the LTM configuration request; and Receive a radio resource control (RRC) reconfiguration message sent by the source DU.

12. A first node in a wireless communication system, comprising: a transceiver configured to transmit and receive signals; and A processor is coupled to the transceiver and configured to execute the method according to any one of claims 1 to 5.

13. A second node in a wireless communication system, comprising: a transceiver configured to transmit and receive signals; and A processor is coupled to the transceiver and configured to perform the method according to any one of claims 6 to 10.

14. A user equipment (UE) in a wireless communication system, comprising: a transceiver configured to transmit and receive signals; and A processor is coupled to the transceiver and configured to execute the method according to claim 11. 15 . A computer-readable storage medium storing computer-executable instructions, wherein when the computer-executable instructions are executed by a processor, the processor executes the method according to claim 1 .

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