Methods and apparatus for resource allocation and node performing in a wireless communication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. According to an aspect of the present disclosure, a method performed by a first node in a wireless communication system is provided. The method comprises: transmitting a first request message, wherein the first request message comprises information on at least one distributed unit (DU) and / or information on at least one base station associated with a layer 1 / layer 2 triggered mobility (LTM) configuration request; 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 transmitting a second request message, wherein the second request message comprises at least one of: information on a to-be-released DU, information on a to-be-released base station, information on a to-be-released cell, information on a cell which accepted the LTM configuration request, information on a DU which accepted the LTM configuration request, and information on a base station which accepted the LTM configuration request.

Description

METHODS AND APPARATUS FOR RESOURCE ALLOCATION AND NODE PERFORMING IN A WIRELESS COMMUNICATION SYSTEM

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

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in “Sub 6GHz” bands such as 3.5GHz, but also in “Above 6GHz” bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The present disclosure relates to wireless communication systems and, more specifically, the present disclosure relates to resource allocation and node performing in a wireless communication system.

[0009] According to an aspect of the present disclosure, a method performed by a first node in a wireless communication system is provided. The method comprises: transmitting a first request message, wherein the first request message comprises information on at least one distributed unit (DU) and / or information on at least one base station associated with a layer 1 / layer 2 triggered mobility (LTM) configuration request; 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 transmitting a second request message, wherein the second request message comprises at least one of: information on a to-be-released DU, information on a to-be-released base station, information on a to-be-released cell, information on a cell which accepted the LTM configuration request, information on a DU which accepted the LTM configuration request, and information on a base station which accepted the LTM configuration request.

[0010] According to an exemplary embodiment, the method may further comprise: receiving a second response message, wherein the second response message comprises an RACH configuration allocated to a DU or base station other than the to-be-released DU or base station.

[0011] According to an exemplary embodiment, the first request message may further comprise at least one of: an LTM information request indication, an LTM triggering 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 a plurality of target secondary new generation radio access network nodes (S-NG-RAN nodes), a target S-NG-RAN node ID and recommended candidate primary secondary cell (PSCell) information that are associated with the LTM configuration request.

[0012] According to an exemplary embodiment, the first response message may further comprise at least one of: a lower-layer radio resource control (RRC) configuration generated for a candidate cell or candidate PSCell which accepted the LTM configuration request, a synchronization signal and physical broadcast channel block (SSB) configuration, new radio physical cell identifier (NR PCI) information of the candidate cell, the LTM reference configuration, an LTM complete configuration indicator and an LTM CSI report configuration, wherein the lower-layer RRC configuration comprises a transmission configuration indication (TCI) states configurations list.

[0013] According to an exemplary embodiment, the second request message may further comprise at least one of: the LTM triggering indication, the LTM configuration ID of the candidate cell, the LTM reference configuration request indication, the LTM reference configuration, the LTM CSI resource configuration, the LTM configuration ID mapping list, an LTM CSI report configuration generated for the candidate cell or candidate PSCell which accepted the LTM configuration request, the transmission configuration indication (TCI) states configurations list, the SSB configuration and the NR PCI information of the candidate cell.

[0014] According to an exemplary embodiment, the method may further comprise: receiving the second response message. The second response message may comprise RACH configuration information allocated to the DU or base station other than the to-be-released DU or base station.

[0015] According to an exemplary embodiment, the second response message may further comprise at least one of: the lower-layer RRC configuration generated for the candidate cell or candidate PSCell which accepted the LTM configuration request, the SSB configuration, the NR PCI information of the candidate cell, the LTM reference configuration, the LTM complete configuration indicator and the LTM CSI report configuration, wherein the lower-layer RRC configuration comprises the transmission configuration indication (TCI) states configurations list.

[0016] According to an exemplary embodiment, the method may further comprise: receiving a third request message, wherein the third request message comprises at least one of: the information on the to-be-released DU, the information on the to-be-released base station and the information on the to-be-released cell; and transmitting a fourth request message, wherein the fourth request message comprises at least one of: the information on the to-be-released DU, the information on the to-be-released base station, the information on the to-be-released cell, and release indication information for an RACH configuration of at least one to-be-released DU or base station.

[0017] According to an exemplary embodiment, the information on the DU or the information on the base station may comprise at least one of: an ID of the DU, a mapping ID of the DU, a mapping index of the DU, an ID of the base station, a mapping ID of the base station, and a mapping index of the base station. According to an exemplary embodiment, the base station may comprise a primary base station and / or secondary base station.

[0018] According to an exemplary embodiment, the information on the DU or the information on the base station may comprise at least one of: an ID of a gNB-DU, a mapping ID of the gNB-DU, a mapping index of the gNB-DU, an ID of an NG-RAN node, a mapping ID of the NG-RAN node, and a mapping index of the NG-RAN node.

[0019] 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 information on the DU or the information on the base station may comprise at least one of: an ID of the SN gNB-DU, a mapping ID of the SN gNB-DU, a mapping index of the SN gNB-DU, an ID of the S-NG-RAN node, a mapping ID of the S-NG-RAN node, and a mapping index of the S-NG-RAN node.

[0020] According to an exemplary embodiment, when the DU is a master node (MN) gNB-DU or the base station is a master new generation radio access network node (M-NG-RAN node), the information on the DU or the information on the base station may comprise at least one of: an ID of the MN gNB-DU, a mapping ID of the MN gNB-DU, a mapping index of the the MN gNB-DU, an ID of the M-NG-RAN node, a mapping ID of the M-NG-RAN node, and a mapping index of the M-NG-RAN node.

[0021] According to an exemplary embodiment, the method may further comprise: receiving a timing advance (TA) value related message. Here, the timing advance (TA) value related message comprises at least one of: an ID of a source DU, a mapping ID of the source DU, a mapping index of the source DU, an ID of a source base station, a mapping ID of the source base station, a mapping index of the source base station, and a timing advance group identity pointer (Tag ID Pointer). According to an exemplary embodiment, the source base station may comprise a source primary base station and / or source secondary base station.

[0022] According to an exemplary embodiment, the timing advance (TA) value related message may comprise at least one of: an ID of a source gNB-DU, a mapping ID of the source gNB-DU, a mapping index of the source gNB-DU, the ID of the NG-RAN node, the mapping ID of the NG-RAN node, the mapping index of the NG-RAN node, and the timing advance group identity pointer (Tag ID Pointer).

[0023] According to an exemplary embodiment, when the source gNB-DU is the SN gNB-DU or the NG-RAN node is the S-NG-RAN node, the timing advance (TA) value related message may comprise at least one of: the ID of the SN gNB-DU, the mapping ID of the SN gNB-DU, the mapping index of the SN gNB-DU, the ID of the S-NG-RAN node, the mapping ID of the S-NG-RAN node, the mapping index of the S-NG-RAN node, an ID of an M-NG-RAN node to which the S-NG-RAN node belongs, a mapping ID of the M-NG-RAN node, an index of the M-NG-RAN node, and the timing advance group identity pointer (Tag ID Pointer).

[0024] According to an exemplary embodiment, when the gNB-DU is the MN gNB-DU or the NG-RAN node is the M-NG-RAN node, the timing advance (TA) value related message may comprise at least one of: the ID of the MN gNB-DU, the mapping ID of the MN gNB-DU, the mapping index of the the MN gNB-DU, the ID of the M-NG-RAN node, the mapping ID of the M-NG-RAN node, the mapping index of the M-NG-RAN node, and the timing advance group identity pointer (Tag ID Pointer).

[0025] According to an exemplary embodiment, the first request message may comprise at least one of: a UE Context Setup Request message, a UE Context Modification Request message, a Handover Request message, an S-Node Addition Request message, an S-Node Modification Request message, and an S-Node Change Request message. According to an exemplary embodiment, the first response message may comprise at least one of: a UE Context Setup Response message, a UE Context Modification Response message, a Handover Request Acknowledge message, an S-Node Addition Request Acknowledge message, and an S-Node Modification Request Acknowledge message. According to an exemplary embodiment, the second request message may comprise at least one of: the UE Context Modification Request message, the Handover Request message, and the S-Node Modification Request message. 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 (e.g., an F1 application protocol (F1ap) message) between the first node and the DU or a message (e.g., an Xn application protocol (Xnap) message) between the first node and the base station.

[0026] According to an exemplary embodiment, the third request message may comprise at least one of: a UE context release request message, a UE Context Modification Required message, and a Conditional Handover Cancel message. According to an exemplary embodiment, the fourth request message may comprise at least one of: a UE Context Release Command message, the UE Context Modification Request message, and a Handover Cancel message. According to an exemplary embodiment, at least one of the third request message and the fourth request message may be a message (e.g., an F1 application protocol (F1ap) message) between the first node and the DU or a message (e.g., an Xn application protocol (Xnap) message) between the first node and the base station.

[0027] According to an exemplary embodiment, the method may further comprise: transmitting an LTM Cell Switch Notification in a situation where a decision that the UE is to perform cell switch is made. The LTM Cell Switch Notification comprises an ID and / or a TCI state ID (including a joint or downlink TCI state ID, and an uplink TCI state ID) of a target cell or target PSCell on which an LTM handover is to be performed, and comprises valid TA value information of another candidate cell or candidate PSCell. According to an exemplary embodiment, the LTM Cell Switch Notification may be transmited through an Xnap message.

[0028] According to another aspect of the present disclosure, a method performed by a second node in a wireless communication system is provided. The method comprises: receiving a first request message, wherein the first request message comprises information on at least one distributed unit (DU) and / or information on at least one base station associated with a layer 1 / layer 2 triggered mobility (LTM) configuration request; transmitting 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 receiving a second request message, wherein the second request message comprises at least one of: information on a to-be-released DU, information on a to-be-released base station, information on a to-be-released cell, information on a cell which accepted the LTM configuration request, information on a DU which accepted the LTM configuration request, and information on a base station which accepted the LTM configuration request.

[0029] According to an exemplary embodiment, the first request message may further comprise at least one of: an LTM information request indication, an LTM triggering 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 a plurality of target secondary new generation radio access network nodes (S-NG-RAN nodes), a target S-NG-RAN node ID and recommended candidate primary secondary cell (PSCell) information that are associated with the LTM configuration request.

[0030] According to an exemplary embodiment, the first response message may further comprise at least one of: a lower-layer radio resource control (RRC) configuration generated for a candidate cell or candidate PSCell which accepted the LTM configuration request, a synchronization signal and physical broadcast channel block (SSB) configuration, new radio physical cell identifier (NR PCI) information of the candidate cell, the LTM reference configuration, an LTM complete configuration indicator and an LTM CSI report configuration, wherein the lower-layer RRC configuration comprises a transmission configuration indication (TCI) states configurations list.

[0031] According to an exemplary embodiment, the second request message may further comprise at least one of: the LTM triggering indication, the LTM configuration ID of the candidate cell, the LTM reference configuration request indication, the LTM reference configuration, the LTM CSI resource configuration, the LTM configuration ID mapping list, an LTM CSI report configuration generated for the candidate cell or candidate PSCell which accepted the LTM configuration request, the transmission configuration indication (TCI) states configurations list, the SSB configuration and the NR PCI information of the candidate cell.

[0032] According to an exemplary embodiment, the method may further comprise: transmitting a second response message. The second response message may comprise RACH configuration information allocated to a DU or base station other than the to-be-released DU or base station.

[0033] According to an exemplary embodiment, the second response message may further comprise at least one of: the lower-layer RRC configuration generated for the candidate cell or candidate PSCell which accepted the LTM configuration request, the SSB configuration, the NR PCI information of the candidate cell, the LTM reference configuration, the LTM complete configuration indicator and the LTM CSI report configuration, wherein the lower-layer RRC configuration comprises the transmission configuration indication (TCI) states configurations list.

[0034] According to an exemplary embodiment, when the second request message comprises at least one of: the information on the cell which accepted the LTM configuration request, the information on the DU which accepted the LTM configuration request and the information on the base station which accepted the LTM configuration request, the method further comprises: determining at least one of the information on the to-be-released cell, the information on the to-be-released DU and the information on the to-be-released base station based on the second request message and pre-configured information, wherein the pre-configured information comprises information on at least one candidate cell and information on a DU and / or base station associated with the at least one candidate cell; and releasing an RACH configuration of at least one to-be-released DU or base station.

[0035] According to an exemplary embodiment, the method may further comprise: transmitting a third request message. The third request message comprises at least one of: the information on the to-be-released DU, the information on the to-be-released base station and the information on the to-be-released cell.

[0036] According to an exemplary embodiment, the method may further comprise: receiving a fourth request message. The fourth request message comprises at least one of: the information on the to-be-released DU, the information on the to-be-released base station, the information on the to-be-released cell, and release indication information for the RACH configuration of the at least one to-be-released DU or base station.

[0037] According to an exemplary embodiment, the information on the DU or the information on the base station may comprise at least one of: an ID of the DU, a mapping ID of the DU, a mapping index of the DU, an ID of the base station, a mapping ID of the base station, and a mapping index of the base station. According to an exemplary embodiment, the base station may comprise a primary base station and / or secondary base station.

[0038] According to an exemplary embodiment, the information on the DU or the information on the base station may comprise at least one of: an ID of a gNB-DU, a mapping ID of the gNB-DU, a mapping index of the gNB-DU, an ID of an NG-RAN node, a mapping ID of the NG-RAN node, and a mapping index of the NG-RAN node.

[0039] 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 information on the DU or the information on the base station may comprise at least one of: an ID of the SN gNB-DU, a mapping ID of the SN gNB-DU, a mapping index of the SN gNB-DU, an ID of the S-NG-RAN node, a mapping ID of the S-NG-RAN node, and a mapping index of the S-NG-RAN node.

[0040] According to an exemplary embodiment, when the DU is a master node (MN) gNB-DU or the base station is a master new generation radio access network node (M-NG-RAN node), the information on the DU or the information on the base station may comprise at least one of: an ID of the MN gNB-DU, a mapping ID of the MN gNB-DU, a mapping index of the the MN gNB-DU, an ID of the M-NG-RAN node, a mapping ID of the M-NG-RAN node, and a mapping index of the M-NG-RAN node.

[0041] According to an exemplary embodiment, the method may further comprise: transmitting a timing advance (TA) value related message. Here, the timing advance (TA) value related message comprises at least one of: an ID of a source DU, a mapping ID of the source DU, a mapping index of the source DU, an ID of a source base station, a mapping ID of the source base station, a mapping index of the source base station, and a timing advance group identity pointer (Tag ID Pointer). According to an exemplary embodiment, the source base station may comprise a source primary base station and / or source secondary base station.

[0042] According to an exemplary embodiment, the timing advance (TA) value related message may comprise at least one of: an ID of a source gNB-DU, a mapping ID of the source gNB-DU, a mapping index of the source gNB-DU, the ID of the NG-RAN node, the mapping ID of the NG-RAN node, the mapping index of the NG-RAN node, and the timing advance group identity pointer (Tag ID Pointer).

[0043] According to an exemplary embodiment, when the source gNB-DU is the SN gNB-DU or the NG-RAN node is the S-NG-RAN node, the timing advance (TA) value related message may comprise at least one of: the ID of the SN gNB-DU, the mapping ID of the SN gNB-DU, the mapping index of the SN gNB-DU, the ID of the S-NG-RAN node, the mapping ID of the S-NG-RAN node, the mapping index of the S-NG-RAN node, an ID of an M-NG-RAN node to which the S-NG-RAN node belongs, a mapping ID of the M-NG-RAN node, an index of the M-NG-RAN node, and the timing advance group identity pointer (Tag ID Pointer).

[0044] According to an exemplary embodiment, when the gNB-DU is the MN gNB-DU or the NG-RAN node is the M-NG-RAN node, the timing advance (TA) value related message may comprise at least one of: the ID of the MN gNB-DU, the mapping ID of the MN gNB-DU, the mapping index of the the MN gNB-DU, the ID of the M-NG-RAN node, the mapping ID of the M-NG-RAN node, the mapping index of the M-NG-RAN node, and the timing advance group identity pointer (Tag ID Pointer).

[0045] According to an exemplary embodiment, the first request message may comprise at least one of: a UE Context Setup Request message, a UE Context Modification Request message, a Handover Request message, an S-Node Addition Request message, an S-Node modification request message, and an S-Node Change Request message. According to an exemplary embodiment, the first response message may comprise at least one of: a UE Context Setup Response message, a UE Context Modification Response message, a Handover Request Acknowledge message, an S-Node Addition Request Acknowledge message, and an S-Node Modification Request Acknowledge message. According to an exemplary embodiment, the second request message may comprise at least one of: the UE Context Modification Request message, the Handover Request message, and the S-Node modification request message. 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 (e.g., an F1 application protocol (F1ap) message) between a first node and the DU or a message (e.g., an Xn application protocol (Xnap) message) between the first node and the base station.

[0046] According to an exemplary embodiment, the third request message may comprise at least one of: a UE context release request message, a UE Context Modification Required message, and a Conditional Handover Cancel message. Here, the third request message may be a message (e.g., an F1 application protocol (F1ap) message) between the first node and the DU or a message (e.g., an Xn application protocol (Xnap) message) between the first node and the base station.

[0047] According to an exemplary embodiment, the fourth request message may comprise at least one of: a UE Context Release Command message, the UE Context Modification Request message, and a Handover Cancel message. Here, the fourth request message may be an F1ap message or an Xnap message.

[0048] According to an exemplary embodiment, the method may further comprise: receiving an LTM Cell Switch Notification in a situation where a decision that the UE is to perform cell switch is made. The LTM Cell Switch Notification comprises an ID and / or a TCI state ID (including a joint or downlink TCI state ID, and an uplink TCI state ID) of a target cell or target PSCell on which an LTM handove is to be performed, and comprises valid TA value information of another candidate cell or candidate PSCell. According to an exemplary embodiment, the LTM Cell Switch Notification is forwarded through an Xnap message.

[0049] According to another aspect of the present disclosure, a method performed by a user equipment (UE) in a wireless communication system is provided. The method comprises: transmitting a layer 3 measurement report to a source distributed node (DU), wherein the layer 3 measurement report is transmited by the source DU to a first node, and a first request message is transmited by the first node, the first request message comprising information on at least one DU and / or information on at least one base station associated with a layer 1 / layer 2 triggered mobility (LTM) configuration request; a first response message is received by the first node, the first response message comprising LTM random access channel (RACH) configuration information associated with the at least one DU and / or the at least one base station; and a second request message is transmited by the first node, the second request message comprising at least one of: information on a to-be-released DU, information on a to-be-released base station, information on a to-be-released cell, information on a cell which accepted the LTM configuration request, information on a DU which accepted the LTM configuration request, and information on a base station which accepted the LTM configuration request; and receiving a radio resource control (RRC) Reconfiguration message transmited by the source DU.

[0050] According to an exemplary embodiment, the RRC Reconfiguration message comprises information on an addition, modification or release operation for the LTM random access channel (RACH) configuration information.

[0051] According to an exemplary embodiment, the LTM random access channel RACH configuration information comprises LTM random access channel (RACH) configuration information allocated by each LTM accepted candidate cell to the at least one DU and / or the at least one base station, or comprises LTM random access channel (RACH) configuration information allocated by each LTM accepted candidate cell to an LTM candidate cell list configured under the at least one DU and / or the at least one base station.

[0052] According to an exemplary embodiment, the first request message further comprises at least one of: an LTM information request indication, an LTM triggering 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 a plurality of target base stations, a target base station and recommended candidate primary secondary cell (PSCell) information that are associated with the LTM configuration request.

[0053] According to an exemplary embodiment, the first response message further comprises at least one of: a lower-layer radio resource control (RRC) configuration generated for a candidate cell or candidate PSCell which accepted the LTM configuration request, a synchronization signal and physical broadcast channel block (SSB) configuration, new radio physical cell identifier (NR PCI) information of the candidate cell, the LTM reference configuration, an LTM complete configuration indicator and an LTM CSI report configuration, wherein the lower-layer RRC configuration comprises a transmission configuration indication (TCI) states configurations list.

[0054] According to an exemplary embodiment, the second request message further comprises at least one of: the LTM triggering indication, an LTM modification indication, the LTM configuration ID of the candidate cell, the LTM reference configuration request indication, the LTM reference configuration, the LTM CSI resource configuration, the LTM configuration ID mapping list, an LTM CSI report configuration generated for the candidate cell or candidate PSCell which accepted the LTM configuration request, the transmission configuration indication (TCI) states configurations list, the SSB configuration and the NR PCI information of the candidate cell.

[0055] According to an exemplary embodiment, a third request message is received by the first node. The third request message comprises at least one of: the information on the to-be-released DU, the information on the to-be-released base station and the information on the to-be-released cell.

[0056] According to an exemplary embodiment, a fourth request message is transmited by the first node. The fourth request message comprises at least one of: the information on the to-be-released DU, the information on the to-be-released base station, the information on the to-be-released cell, and release indication information for an RACH configuration of at least one to-be-released DU or base station.

[0057] According to an exemplary embodiment, the information on the DU or the information on the base station may comprise at least one of: an ID of the DU, a mapping ID of the DU, a mapping index of the DU, an ID of the base station, a mapping ID of the base station, and a mapping index of the base station. According to an exemplary embodiment, the base station may comprise a primary base station and / or secondary base station.

[0058] According to an exemplary embodiment, a timing advance (TA) value related message is received by the first node. Here, the timing advance (TA) value related message comprises at least one of: an ID of a source DU, a mapping ID of the source DU, a mapping index of the source DU, an ID of a source base station, a mapping ID of the source base station, a mapping index of the source base station, and a timing advance group identity pointer (Tag ID Pointer). According to an exemplary embodiment, the source base station may comprise a source primary base station and / or source secondary base station.

[0059] According to an exemplary embodiment, the first request message comprises at least one of: a UE Context Setup Request message, a UE Context Modification Request message, a Handover Request message, an S-Node Addition Request message, an S-Node modification request message, and an S-Node Change Request message. According to an exemplary embodiment, the first response message comprises at least one of: a UE Context Setup Response message, a UE Context Modification Response message, a Handover Request Acknowledge message, an S-Node Addition Request Acknowledge message, and an S-Node Modification Request Acknowledge message. According to an exemplary embodiment, the second request message comprises at least one of: the UE Context Modification Request message, the Handover Request message, and the S-Node modification request message.

[0060] According to an exemplary embodiment, the third request message comprises at least one of: a UE context release request message, a UE Context Modification Required message, and a Conditional Handover Cancel message. According to an exemplary embodiment, the fourth request message comprises at least one of: a UE Context Release Command message, the UE Context Modification Request message, and a Handover Cancel message.

[0061] According to an exemplary embodiment, an LTM Cell Switch Notification is transmited by the first node in a situation where a decision that the UE is to perform cell switch is made. The LTM Cell Switch Notification comprises an ID and / or a TCI state ID (including a joint or downlink TCI state ID, and an uplink TCI state ID) of a target cell or target PSCell on which an LTM handover is to be performed, and comprises valid TA value information of another candidate cell or candidate PSCell. According to other aspects of the present disclosure, the first node, the second node and the UE that perform the above methods are further disclosed. According to another aspect of the present disclosure, a computer readable storage medium is further disclosed. The computer readable storage medium stores a computer executable instruction. When the computer executable instruction is executed by a processor, the processor performs the above method performed by the first node, the second node or the UE.

[0062] According to an exemplary embodiment, a method performed by a central unit (CU) in a wireless communication system, the method including receiving, from a source distributed unit (DU), a notification message for a cell switch, the notification message including tag identifier (ID) pointer information corresponding to a timing advance (TA) value, transmitting, to a target DU, the notification message for the cell switch.

[0063] According to an exemplary embodiment, a central unit (CU) in a wireless communication system, the CU comprising: a transceiver, and a controller coupled with the transceiver configured to: receive, from a source distributed unit (DU), a notification message for a cell switch, the notification message including tag identifier (ID) pointer information corresponding to a timing advance (TA) value transmit, to a target DU, the notification message for the cell switch.

[0064] According to the implementations of the present disclosure, the LTM failure or abnormality can be avoided in a plurality of scenarios where the LTM occurs (e.g., the nodes to which the source cell and the target cell belong may be under the same gNB-DU, under different gNB-DUs under the same gNB-CU, or under different gNB-CUs).

[0065] According to an embodiment of the disclosure, a wireless communication can be performed efficiently. Especially, a resource allocation and node performing in a wireless communication system can be performed efficiently.

[0066] FIG. 1 is an exemplary system architecture evolved according to a system architecture of the present disclosure;

[0067] FIG. 2 is an exemplary system architecture according to various embodiments of the present disclosure;

[0068] FIG. 3 is a flowchart of an LTM procedure in prior art;

[0069] FIG. 4A is a flowchars of an Intra-gNB-CU Inter-gNB-DU LTM procedure according to an exemplary embodiment of the present disclosure;

[0070] FIG. 4B is a flowchars of an Intra-gNB-CU Inter-gNB-DU LTM procedure according to an exemplary embodiment of the present disclosure;

[0071] FIG. 5A is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0072] FIG. 5B is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0073] FIG. 5C is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0074] FIG. 5D is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0075] FIG. 5E is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0076] FIG. 5F is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0077] FIG. 5G is a flowchart of an Inter-CU LTM procedure according to an exemplary embodiment of the present disclosure;

[0078] FIG. 6A is a flowchart of an LTM procedure between different SNs under the same MN in dual connectivity according to an exemplary embodiment of the present disclosure;

[0079] FIG. 6B is a flowchart of an LTM procedure between different SNs under the same MN in dual connectivity according to an exemplary embodiment of the present disclosure;

[0080] FIG. 6C is a flowchart of an LTM procedure between different SNs under the same MN in dual connectivity according to an exemplary embodiment of the present disclosure;

[0081] FIG. 6D is a flowchart of an LTM procedure between different SNs under the same MN in dual connectivity according to an exemplary embodiment of the present disclosure;

[0082] FIG. 6E is a flowchart of an LTM procedure between different SNs under the same MN in dual connectivity according to an exemplary embodiment of the present disclosure;

[0083] FIG. 7 is an embodiment of an L3 handover in a situation of an Intra-CU Inter-DU LTM configuration;

[0084] FIG. 8 is an embodiment of an L3 handover procedure in a situation of an Inter-CU / gNB LTM configuration;

[0085] FIG. 9 is an embodiment in which an S-SN triggers an SN change procedure of L3 in a situation of an inter-CU (between different CUs; inter-SN) LTM (SN change without MN change) configuration triggered by a source S-NG-RAN node (source SN or S-SN) in an NR-DC scenario;

[0086] FIG. 10 is an embodiment of an inter-CU (between different CUs; or inter-SN) LTM (SN change without MN change) procedure triggered by an MN or source S-NG-RAN node (source SN or S-SN) in an NR-DC scenario;

[0087] FIG. 11 is a flow block diagram of a method performed by a first node in a wireless communication system according to an exemplary embodiment of the present disclosure;

[0088] FIG. 12 is a flow block diagram of a method performed by a second node in a wireless communication system according to an exemplary embodiment of the present disclosure; and

[0089] FIG. 13 illustrates an exemplary structure of each node applicable to the present disclosure.

[0090] In order to meet an increasing demand for wireless data communication services since a deployment of 4G communication system, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called “beyond 4G network” or “post LTE system”.

[0091] Wireless communication is one of the most successful innovations in modern history. Recently, a number of subscribers of wireless communication services has exceeded 5 billion, and it continues growing rapidly. With the increasing popularity of smart phones and other mobile data devices (such as tablet computers, notebook computers, netbooks, e-book readers and machine-type devices) in consumers and enterprises, a demand for wireless data services is growing rapidly. In order to meet rapid growth of mobile data services and support new applications and deployments, it is very important to improve efficiency and coverage of wireless interfaces.

[0092] In order to reduce the interrupt latency of business service of a UE in a mobility procedure, Rel-18 is currently formulating specifications for L1 / L2 triggered mobility (LTM). The main process is that, based on the L1 (Layer 1) measurement report reported by the UE, the gNB-DU decides a target cell and transmits a mobility command to the UE. Compared with the previous handover procedure performed based on an L3 measurement report, since the L3 measurement report is obtained based on a reprocessing such as linear averaging on the L1 measurement, the handover based on the L1 measurement report can have a faster mobility command, and the UE can receive this command more quickly through the L2 MAC CE of the gNB-DU. In addition, for the access process of the UE, a procedure without a traditional RACH (random access channel) access (i.e., a rach-less procedure) can be applied, thereby further reducing the interrupt latency of business service of the UE in the mobility procedure.

[0093] The drawings discussed below and various embodiments for describing the principles of the present disclosure in this patent document are only for illustration and should not be interpreted as limiting the scope of the disclosure in any way. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any suitably arranged system or device.

[0094] Fig. 1 is an exemplary system architecture 100 of system architecture evolution (SAE). User equipment (UE) 101 is a terminal device for receiving data. An evolved universal terrestrial radio access network (E-UTRAN) 102 is a radio access network, which includes a macro base station (eNodeB / NodeB) that provides UE with interfaces to access the radio network. A mobility management entity (MME) 103 is responsible for managing mobility context, session context and security information of the UE. A serving gateway (SGW) 104 mainly provides functions of user plane, and the MME 103 and the SGW 104 may be in the same physical entity. A packet data network gateway (PGW) 105 is responsible for functions of charging, lawful interception, etc., and may be in the same physical entity as the SGW 104. A policy and charging rules function entity (PCRF) 106 provides quality of service (QoS) policies and charging criteria. A general packet radio service support node (SGSN) 108 is a network node device that provides routing for data transmission in a universal mobile telecommunications system (UMTS). A home subscriber server (HSS)109 is a home subsystem of the UE, and is responsible for protecting user information including a current location of the user equipment, an address of a serving node, user security information, and packet data context of the user equipment, etc.

[0095] Fig. 2 is an exemplary 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. User equipment (UE) 2001 is a terminal device for receiving data. A next generation radio access network (NG-RAN) 2002 is a radio access network, which includes a base station (a gNB or an eNB connected to 5G core network 5GC, and the eNB connected to the 5GC is also called ng-gNB) that provides UE with interfaces to access the radio network. An access control and mobility management function entity (AMF) 2003 is responsible for managing mobility context and security information of the UE. A user plane function entity (UPF) 2004 mainly provides functions of user plane. A session management function entity SMF 2005 is responsible for session management. A data network (DN) 2006 includes, for example, services of operators, access of Internet and service of third parties.

[0096] For the convenience of description, the special names involved in the following description of the embodiments of the present disclosure and their explanations are as follows:

[0097] 1. LTM (L1 / L2 Triggered Mobility): layer 1 / layer 2 triggered mobility

[0098] 2. CFRA: Contention Free Random Access

[0099] 3. CSI: Channel State Information

[0100] 4. CGI: Cell Global ID

[0101] 5. RLF: Radio Link Failure

[0102] 6. AMF: an access and mobility management function, which is a network element in a 5G core network and is responsible for the access and mobility management of a 5G base station. The 5G base station and the AMF are connected through an NG-C interface.

[0103] 7. NG-RAN node: a new generation radio access network node, for example, a 5G base station, including a gNB or an ng-eNB.

[0104] 8. gNB (next Generation Node B): a next generation base station node, for example, a 5G NR (New Radio) base station.

[0105] 9. gNB-DU: a gNB distributed unit, which has functions such as a radio link control (RLC) protocol, a medium access control (MAC) protocol and a physical layer (PHY) protocol.

[0106] 10. gNB-CU: a gNB central unit, which has functions such as a radio resource control (RRC) protocol, a service data adaptation protocol (SDAP) and a packet data convergence protocol (PDCP).

[0107] 11. NR-DC (NR-NR Dual Connectivity): a new radio-new radio dual connectivity (i.e., a next generation radio access network dual connectivity).

[0108] 12. MN: Master Node.

[0109] 13. SN: Secondary node.

[0110] 14. SCG: a secondary cell group, which is a group of serving cells associated with a secondary node in the next generation radio access network dual connectivity. The SCG includes the primary cell SpCell (PSCell) of the secondary cell group, and optically includes one or more secondary cells (SCell).

[0111] 15. PSCell: a primary secondary cell, i.e., the SpCell of a secondary cell group.

[0112] 16. MCG: a master cell group, which is a group of serving cells associated with a master node in the next generation radio access network dual connectivity. The MCG includes the primary cell SpCell (PCell) of the master cell group, and optically includes one or more secondary cells SCell.

[0113] 17. PCell: the SpCell of a master cell group.

[0114] 18. SpCell: a primary cell, i.e., the primary cell of a master cell group or a secondary cell group.

[0115] 19. SpCell: a special cell, i.e., a primary cell serving a UE (the primary cell of a master cell group or a secondary cell group).

[0116] 20. Tag ID Pointer: a timing advance group identity pointer, i.e., the tag-Id-ptr (Pointer) information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. The tag-Id-ptr indicates the TAG that is associated with or applied to a serving cell or the TCI state of this cell. value n0 means a serving cell or the TCI state of this serving cell associate with the TAG indicated by tag-Id, value n1 means a serving cell or the TCI state of this serving cell associated with the TAG indicated by tag2-Id. The tag-Id-ptr refers to the TAG associated with the serving cell or the TCI state set of this serving cell.

[0117] It should be understood that the message names in the present disclosure are examples only and other names may be adopted. The information may be transmitted between interfaces by using a newly defined message, or by adding a new information element (IE) into an existing message in an existing corresponding interface specification.

[0118] Exemplary embodiments of the present disclosure are further described below with reference to the accompanying drawings.

[0119] The text and drawings are provided as examples only to help understand the present disclosure. They should not be interpreted as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, based on the disclosure herein, it will be apparent to those skilled in the art that changes may be made to the illustrated embodiments and examples without departing from the scope of the present disclosure.

[0120] For an LTM procedure, the UE accesses from a source cell to another target cell by means of LTM. From the UE configuration, there may be a change in the LTM configuration and the correspondingly configured resource on the network side during a preparation phase. How to deal with this change is a problem to be solved.

[0121] Further, considering the scenario of the UE's LTM, more scenarios need to be supported. An an example, the node to which a source cell belongs and the node to which a target cell belongs may be under the same gNB-DU, under the same gNB-CU but under different gNB-DUs, or under different gNB-CUs (i.e., different base stations). As another example, the different gNB-CUs may be under different primary base stations or different secondary base stations in a dual connectivity. The present disclosure proposes a configuration scheme for the above scenarios and improves the existing configuration scheme.

[0122] FIG. 3 is a flowchart of an exemplary LTM procedure according to the present disclosure. To illustrate the failure scenario that may occur during execution of the LTM, a normal LTM procedure is first introduced. The procedure shown in FIG. 3 is a scenario where a UE moves from a gNB-DU to another gNB-DU under the same gNB-CU during NR LTM. The procedure is as follows:

[0123] 1. L3 Measurement Control and Report

[0124] In an embodiment, the UE transmits a Measurement Report message, in which an L3 measurement result is reported, to a source gNB-DU. The message includes the measurement value of a neighbour cell. The source gNB-DU transmits a UL RRC (uplink radio resource control) Message Transfer message and transfers the received Measurement Report message to the gNB-CU.

[0125] 2. The gNB-CU decides to initiate an LTM configuration.

[0126] 3. The gNB-CU transmits a UE Context Setup Request message to a candidate gNB-DU, which includes at least one of a candidate cell ID, an LTM configuration ID of a candidate cell, an LTM configuration ID mapping list and a CSI resource configuration. The gNB-CU indicates a source gNB-DU ID and requests a physical random access channel (PRACH) resource from the candidate gNB-DU. The gNB-CU may request the candidate gNB-DU to provide a lower-layer configuration to generate a reference configuration.

[0127] 4. If the candidate gNB-DU accepts an LTM configuration request, the candidate gNB-DU will transmit a UE Context Setup Response message as a response, including at least one of a lower-layer RRC configuration (e.g., a transmission configuration indication (TCI) states configurations and a random access channel (RACH) configuration) and a CSI report configuration, generated for a target candidate cell which accepted the LTM configuration request.

[0128] 5. The gNB-CU transmits a UE Context Modification Request message to the source gNB-DU, including at least one of the collected CSI report configuration, TCI states configurations and RACH configuration of a target candidate cell which accepted the LTM configuration request in other gNB-DUs.

[0129] 6. The source gNB-DU transmits a UE Context Modification Response message as a response. The message may include a CSI report configuration generated for a prepared candidate cell.

[0130] 7. The gNB-CU transmits a UE Context Modification Request message to the candidate gNB-DU, including at least one of the CSI report configuration, the TCI state configuration, the RACH configuration and the LTM configuration ID of a candidate cell in another candidate gNB-DU. The gNB-CU may further provide a reference configuration of a lower layer portion to the candidate gNB-DU. The gNB-CU may further provide an updated CSI resource configuration to the candidate gNB-DU. Optionally, the candidate cell and the source cell may be the same cell.

[0131] 8. The candidate gNB-DU transmits a UE Context Modification Response message as a response, including an updated lower-layer configuration. The response transmited by the candidate gNB-DU may further include an updated CSI report configuration.

[0132] 9. The gNB-CU transmits a downlink RRC (DL RRC) Message Transfer message to the source gNB-DU, including a generated RRC Reconfiguration (RRCReconfiguration) message having the LTM configuration.

[0133] 10. The source gNB-DU forwards the received RRC Reconfiguration message to the UE.

[0134] 11. The UE transmits an RRC Reconfiguration Complete (RRCReconfigurationComplete) message to the source gNB-DU.

[0135] 12. The source gNB-DU forwards the RRC Reconfiguration Complete message to the gNB-CU through an uplink RRC (UL RRC) Message Transfer message.

[0136] 13. Early synchronization is performed to obtain an early timing advance (TA) value.

[0137] 14-15. The candidate gNB-DU transmits at least one of TA value information, associated CFRA resource information, a candidate cell ID and the source gNB-DU ID to the source gNB-DU through a DU-CU TA Information Transfer message and a CU-DU TA Information Transfer message. Here, the source gNB-DU ID may be omitted in the CU-DU TA Information Transfer message.

[0138] 16. The UE transmits a layer 1 measurement report to the source gNB-DU.

[0139] 17. The source gNB-DU decides to perform LTM cell switch on a candidate target cell.

[0140] 18. The source gNB-DU transmits a Cell Switch Command to the UE.

[0141] 19. The source gNB-DU transmits a DU-CU Cell Switch Notification message to the gNB-CU, indicating that the Cell Switch Command is initiated to the UE. A DU-CU Cell Switch Notification includes a target cell ID and / or a TCI state ID (including a joint or downlink TCI state ID, and an uplink TCI state ID), and includes valid TA value information of another candidate cell.

[0142] 20. The gNB-CU transmits the target cell ID and / or the TCI state ID (including the joint or downlink TCI state ID, and the uplink TCI state ID) and the valid TA value information of the other candidate cell to the target gNB-DU through the CU-DU Cell Switch Notification.

[0143] 21. The target gNB-DU detects a successful access (a rach-less based or rach-based access procedure) of the UE.

[0144] 22. The target gNB-DU transmits an Access Success message (carrying a target cell ID) to the gNB-CU.

[0145] 23. The UE transmits an RRC Reconfiguration Complete (RRCReconfigurationComplete) message to the target gNB-DU.

[0146] 24. The target gNB-DU forwards the RRC Reconfiguration Complete message to the gNB-CU through an uplink RRC (UL RRC) Message Transfer message.

[0147] 25. The gNB-CU may transmit a UE Context Release Command message to the source gNB-DU to release the resource and configuration of the prepared cell (including the source cell).

[0148] 26. The source gNB-DU transmits a UE Context Release Complete message to the gNB-CU as a response.

[0149] FIGS. 4-1 to 4-2 (hereinafter collectively referred to as FIG. 4) are exemplary embodiments of an Intra-gNB-CU Inter-gNB-DU LTM procedure between different gNB-DUs under the same gNB-CU according to the present disclosure. The LTM procedure includes a one-time LTM handover procedure and a subsequent LTM procedure. The one-time LTM handover procedure refers to that, after one LTM handover procedure is completed, the resources of a source cell and other unselected candidate cells are released on the UE side and the network side. The subsequent LTM procedure refers to that, after the UE switches from the source cell to the target cell in one LTM procedure, the configurations of other candidate cells are still reserved on the UE side and the network side. Optionally, if the source cell is used as a candidate cell for the subsequent LTM, the “other candidate cell” mentioned above may also include the source cell used as a candidate cell for the subsequent LTM. In this way, when not performing an RRC reconfiguration, the UE is configured according to the LTM CSI report pre-configured by each candidate cell, and reports the L1 measurement report of the candidate cell to the gNB-DU currently serving the UE. Upon receiving the L1 measurement report, the gNB-DU may continue to trigger the LTM procedure to cause the UE to switch from the current serving cell to another candidate cell. Thus, the UE can perform a subsequent LTM procedure in the configured candidate cell list without performing the RRC reconfiguration.

[0150] In the LTM procedure between different gNB-DUs under the same gNB-CU, the RACH configuration for a candidate cell is allocated to each gNB-DU. This has the advantage that the PRACH resources are efficiently utilized, and the PRACH resource allocated to each gNB-DU may serve a plurality of UEs under the gNB-DU, since the UEs under the same gNB-DU may have an LTM configuration for the same candidate cell. When the UE switches to a target cell through one LTM under the configuration of the subsequent LTM, if the cell is under another gNB-DU, the UE switches to a target gNB-DU. The UE may trigger an early TA acquisition procedure (i.e. procedure 13 in the process in FIG. 4) under a new serving gNB-DU. This procedure includes a procedure that the UE transmits, after receiving a PDCCH order instruction transmited by the gNB-DU currently serving the UE, a first Random Access Request message to the candidate cell using a random access resource configuration indicated in the instruction. Here, the random access resource configuration indicated in the instruction is indicated by, for example, a random access preamble index, a synchronization signal and physical broadcast channel (PBCH) block index (SSB index, synchronization signal / PBCH block index), and a PRACH occasion mask index. After receiving a first Random Access Request message, the candidate cell calculates a timing advance (TA) value between the UE and the candidate cell. The candidate gNB-DU transmits the TA value and the assistance information to the source gNB-DU (i.e., the gNB-DU currently serving the UE) through procedures 14-15. In procedure 3 of FIG. 3, the UE Context Setup Request message transmited by the gNB-CU to the candidate gNB-DU includes a source gNB-DU ID, and the gNB-CU requests a physical random access channel (PRACH) resource from the candidate gNB-DU. If only the one-time LTM handover procedure is supported, it is feasible to carry only one source gNB-DU ID, because only the source gNB-DU is required to order the UE to perform the early TA acquisition procedure. However, if considering the situation that the subsequent LTM procedure is supported, each candidate cell needs to pre-allocate a PRACH resource to each of other candidate gNB-DUs. This is because, after the UE accesses the target gNB-DU to which the target cell belongs, the corresponding target gNB-DU may order the UE to perform the early TA acquisition procedure on a certain candidate cell of the present gNB-DU by using the PRACH resource pre-allocated to the candidate cell.

[0151] To this end, according to an exemplary embodiment of the present disclosure, some procedures in FIG. 3 may be enhanced. The procedures 1-26 shown in FIG. 4 are similar to those in FIG. 3. In the following description, the description for the same procedure will be omitted. Some of the procedures in the embodiment of FIG. 3 are enhanced in the embodiment of FIG. 4, as described below.

[0152] According to an exemplary embodiment of the present disclosure, t the UE Context Setup Request message transmited by the gNB-CU to the candidate gNB-DU in the procedure 3 is enhanced. For example, in the procedure 3 of FIG. 4, the gNB-CU transmits the UE Context Setup Request message to the candidate gNB-DU, when the gNB-CU requests a PRACH resource from the candidate gNB-DU,

[0153] -Optionally, a candidate gNB-DU ID list including gNB-DU IDs of all the other candidate gNB-DUs may be carried directly. This list includes a source gNB-DU ID and other candidate gNB-DUs' IDs, indicating that a candidate cell is required to allocate a PRACH resource to each gNB-DU performing a subsequent LTM configuration.

[0154] -Optionally, if the gNB-CU does not want to carry a plaintext gNB-DU ID list, the gNB-CU may alternatively associate each candidate gNB-DU with a certain mapping ID, index or identifier based on the implementation by means of mapping. Then, a list including the mapping ID, index or identifier of an LTM gNB-DU (LTM gNB-DU mapping ID / index / identifier) is transmited to the candidate gNB-DU to request the candidate cell to allocate a PRACH resource to the mapping ID, index or identifier of each LTM gNB-DU, to perform the the subsequent LTM configuration.

[0155] Accordingly, in procedure 4, the candidate gNB-DU accepts the LTM configuration request, and transmits a UE Context Setup Response message as a response, the message including the RACH configuration list of a target candidate cell which accepted the LTM configuration request. Hereinafter, a candidate cell which accepted the LTM configuration request is also referred to as a “candidate cell with acceptance.”

[0156] -Optionally, this list includes the PRACH resource allocated by the candidate cell to each requested gNB-DU ID.

[0157] -Optionally, if the gNB-CU provides a mapping ID, index or identifier, this list includes the PRACH resource allocated by the candidate cell to the mapping ID, index or identifier of each requested LTM gNB-DU (one mapping ID, index or identifier corresponding to one gNB-DU ID).

[0158] If the gNB-CU needs to configure the source gNB-DU as the candidate gNB-DU for the subsequent LTM, then in procedure 5, the gNB-CU transmits a UE Context Modification Request message to the source gNB-DU, the message including the collected RACH configuration of a target candidate cell which accepted the LTM configuration request in other gNB-DU. Meanwhile, the gNB-CU requests a PRACH resource from the source gNB-DU.

[0159] -Optionally, a candidate gNB-DU ID list including each other candidate gNB-DU ID may be carried directly. This list includes the other candidate gNB-DU ID, indicating that the source cell or another candidate cell under the source gNB-DU are required to allocate a PRACH resource to each candidate gNB-DU performing the subsequent LTM configuration.

[0160] -Optionally, if the gNB-CU does not want to carry the plaintext gNB-DU ID list, the gNB-CU may alternatively associate each candidate gNB-DU with a certain mapping ID / index / identifier based on the implementation by means of mapping, and transmit the list including the mapping ID / index / identifier of the LTM gNB-DU (LTM gNB-DU mapping ID / index / identifier) to the candidate gNB-DU to request the source cell or the other candidate cell under the source gNB-DU to allocate, for each mapping ID / index / identifier of each LTM gNB-DU, a PRACH resource so as to perform the the subsequent LTM configuration.

[0161] The procedure that the gNB-CU configures the source gNB-DU as the candidate gNB-DU for the subsequent LTM may occur between procedure 2 and procedure 5. Accordingly, in procedure 6, the source gNB-DU transmits a UE Context Modification Response message as a response. The message may include the RACH configuration list of the target candidate cell with acceptance.

[0162] -Optionally, this list includes the PRACH resource allocated by the source cell or the other candidate cell under the source gNB-DU to each requested gNB-DU ID.

[0163] -Optionally, if the gNB-CU provides a mapping ID / index / identifier, this list includes accordingly the PRACH resource allocated by the source cell or the other candidate cell under the source gNB-DU to the mapping ID / index / identifier of each requested LTM gNB-DU (one mapping ID / index / identifier corresponding to one gNB-DU ID).

[0164] In this way, for each gNB-DU (including each candidate gNB-DU and the source gNB-DU) for the subsequent LTM configuration, the gNB-CU obtains the RACH configuration allocated by each candidate cell to a different gNB-DU. Then, the gNB-CU respectively transmits a UE Context Modification Request message to other candidate gNB-DUs, notifying each gNB-DU of the collected RACH configuration allocated to this gNB-DU by the target candidate cell which accepted the LTM configuration request in another gNB-DU.

[0165] Then, the source gNB-DU transmits a PDCCH order instruction to the UE, to order the UE to transmit a first Random Access Request message to the candidate cell using a random access resource configuration indicated in the instruction. Here, the random access resource configuration indicated in the instruction is indicated by, for example, a random access preamble index, a synchronization signal / PBCH block index (SSB index), and a PRACH occasion mask index. After receiving the first Random Access Request message, the candidate cell calculates a timing advance (TA) value between the UE and the candidate cell. Then, the candidate gNB-DU transmits the TA value and the assistance information to the source gNB-DU (i.e., the gNB-DU currently serving the UE) through procedures 14-15.

[0166] - Optionally, in the situation where the RACH configuration is allocated based on the gNB-DU ID provided by the gNB-CU, when the TA value and the assistance information are transmited to the gNB-CU in procedure 14, the source gNB-DU ID is required to be carried to be transmited to the gNB-CU, such that the gNB-CU continues to forward the corresponding TA information to the indicated gNB-DU ID.

[0167] - Optionally, in the situation where the RACH configuration is allocated based on the LTM gNB-DU mapping ID / index / identifier provided by the gNB-CU, when the TA value and the assistance information are transmited to the gNB-CU in procedure 14, the indicated mapping ID / index / identifier is required to be carried to be transmited to the gNB-CU. Then, the gNB-CU can know the gNB-DU ID corresponding to this LTM gNB-DU mapping ID / index / identifier through the mapping relationship, such that the gNB-CU continues to forward the corresponding TA information to the corresponding gNB-DU ID.

[0168] The above message for procedure 14 at least includes one or more of the following information:

[0169] DU-CU TA Information Transfer

[0170] TA Information List

[0171] >TA Information Item IEs

[0172] >>Candiate Cell ID

[0173] >>TA Value

[0174] >>Preamble Index

[0175] >>Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0176] >>Source gNB-DU ID

[0177] >>LTM gNB-DU Mapping ID / Index / identifier, mapped to one gNB-DU ID such as the source gNB-DU ID

[0178] >>Timing Advance Group Identity Pointer (Tag ID Pointer), including tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331.

[0179] In an embodiment, the allocation of different PRACH resources or RACH configuration information by the candidate cell to one or more LTM gNB-DUs may refer to that one LTM gNB-DU ID corresponds to one PRACH resource, one piece of RACH configuration information, or one piece of early uplink synchronization (UL Sync) configuration information. Alternatively, the common configuration information to all LTM gNB-DUs in these configuration information may be shown separately, and the different configuration information (such as a Preamble Index List) corresponding to different LTM gNB-DUs is then shown. In short, the idea embodied is that the allocation of different PRACH resources, RACH configuration information or early UL Sync configuration information by the candidate cell to each LTM gNB-DU is within the scope of protection of the present disclosure.

[0180] When the L3 measurement report reported by the UE is received by the gNB-CU, the gNB-CU can determine, according to the ID information of the cell, which gNB-DU under this gNB-CU the candidate cell belongs to. When the gNB-CU decides the configuration cell for the LTM, the candidate gNB-DU ID list or mapping ID / index / identifier list corresponding to each candidate cell perofrming the LTM configuration may be carried in the UE Context Setup Request message transmited by the gNB-CU to the candidate gNB-DU in procedure 3. Then, the candidate gNB-DU prepares the resources for the candidate cells which accepted the LTM configuration request and transmits the UE Context Setup Response message to the gNB-CU as a response. It is assumed that, there is no candidate cell with acceptance in some candidate gNB-DU. That is, each candidate cell in a candidate gNB-DU rejects the UE Context Setup Request procedure of the gNB-CU. As shown in FIG. 4, for 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, the candidate gNB-DU2 will transmit a UE Context Setup Failure message as a response in procedure 4-02; otherwise, the candidate gNB-DU2 will transmit a UE Context Setup Response message as a response in procedure 4-01. In the situation of a UE context setup failure, the RACH configuration prepared for this gNB-DU by the candidate cell with acceptance in the UE context setup procedure previously performed between the gNB-CU and the other candidate gNB-DU no longer needs to be reserved, but needs to be released. If the RACH configuration is not released, it will cause a waste of PRACH resources (e.g., preamble index resources) of these candidate cells. Only the gNB-CU knows which candidate gNB-DU rejects the UE Context Setup Request of the gNB-CU. The gNB-CU may notify, by using the LTM cells to-be-released list (LTM Cells to be Released List) IE carried in the UE Context Modification Request message, the other candidate gNB-DUs (including the source gNB-DU) that the resources prepared for which LTM candidate cell need to be released. However, for the RACH configuration prepared by the candidate cell based on the candidate gNB-DU, the gNB-DU receiving the UE Context Modification Request cannot determine, according to the release information of the LTM candidate cell carried therein, which candidate gNB-DU is released and is no longer in the LTM candidate gNB-DUs list. As shown in the process in FIG. 4, when the interaction of the gNB-CU with each candidate gNB-DU and the source gNB-DU is completed, after procedure 6, assuming that one candidate cell on each gNB-DU is accepted as an LTM candidate cell, the gNB-CU may obtain the RACH configuration list of each candidate cell accepted as the LTM candidate cell for each gNB-DU, for example, as follows:

[0181] Early Synchronization (Sync) Information List

[0182] Cell ID0 (a source cell belonging to a source gNB-DU0)

[0183] >RACH Configuration for Candidate gNB-DU ID1

[0184] >RACH Configuration for Candidate gNB-DU ID2

[0185] Cell ID1 (a source cell belonging to a source gNB-DU1)

[0186] >RACH Configuration for Source gNB-DU ID0

[0187] >RACH Configuration for Candidate gNB-DU ID2

[0188] Cell ID2 (a source cell belonging to a source gNB-DU2)

[0189] >RACH Configuration for Source gNB-DU ID0

[0190] >RACH Configuration for Candidate gNB-DU ID1

[0191] Then, in procedure 7, the gNB-CU notifies, by using the UE Context Modification Request message, each candidate gNB-DU of the RACH configuration information prepared by the other candidate cell for this gNB-DU.

[0192] For example, the gNB-CU notifies the source gNB-DU of the following RACH configuration information:

[0193] Early Synchronization (Sync) Information List

[0194] >Early Synchronization (Sync) Information Item IEs

[0195] >>Cell ID (a candidate cell ID1 or a candidate cell ID2)

[0196] >>RACH Configuration

[0197] For example, the gNB-CU notifies the candidate gNB-DU1 of the following RACH configuration information:

[0198] Early Synchronization (Sync) Information List

[0199] >Early Synchronization (Sync) Information Item IEs

[0200] >>Cell ID (a source cell ID0 or the candidate cell ID2)

[0201] >>RACH Configuration

[0202] For example, the gNB-CU notifies the candidate gNB-DU2 of the following RACH configuration information:

[0203] Early Synchronization (Sync) Information List

[0204] >Early Synchronization (Sync) Information Item IEs

[0205] >>Cell ID (the source cell ID0 or the candidate cell ID1)

[0206] >>RACH Configuration

[0207] As shown in FIG. 4, in the UE context setup procedure for the candidate cell ID2 between the gNB-CU and the candidate gNB-DU2, if the candidate gNB-DU2 rejects the request of the gNB-CU and transmits the UE Context Setup Failure message as the response, the candidate gNB-DU2 is actually excluded from the LTM candidate gNB-DUs list. If the source cell ID0 and the candidate cell ID1 have prepared the RACH configuration for the candidate gNB-DU2, the RACH configuration prepared for the candidate gNB-DU2 needs to be released. In this situation, it is not enough for the other candidate gNB-DUs (including the source gNB-DU) to only know that the LTM Cell ID2 is to be released, because the source gNB-DU and the candidate gNB-DU1 cannot determine, according to the LTM Cells To-Be-Released List IE, that the candidate gNB-DU2 is to be released. Only the 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.

[0208] Alternative Scheme 1: Each gNB-DU (including the source gNB-DU and / or candidate gNB-DU) can determine, through the received LTM Cells to be Released List IE information, which candidate gNB-DU has all candidate cells released, that is, the candidate gNB-DU is released. For example, an F1ap message may be enhanced to make each gNB-DU know which candidate cells each of the other candidate gNB-DUs (optionally including the source gNB-DU) has, or the information that each 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, in the LTM resource preparation procedure, the UE Context Setup Request message or UE Context Modification Request message transmited by the gNB-CU to the candidate gNB-DU (optionally including the source gNB-DU) may carry a list of information, including one or more of the following information:

[0209] -Each LTM Candidate Cell ID (represented by a cell ID or NR CGI);

[0210] -LTM gNB-DU ID Information (represented by a gNB-DU ID, and indicating the gNB-DU to which the LTM candidate cell belongs).

[0211] Optionally, the gNB-DU ID indication information to which the LTM cell ID belongs is added on the basis of the LTM Configuration ID Mapping List IE:

[0212] -LTM Configuration ID Mapping List

[0213] >Configuration ID Mapping Item IEs

[0214] >>LTM Cell ID (which can be represented by an NR CGI)

[0215] >>LTM Configuration ID

[0216] >>LTM gNB-DU ID (represented by a gNB-DU ID, and indicating the information on the gNB-DU to which the LTM cell corresponding to the LTM cell ID belongs)

[0217] FIG. 4 shows an exemplary LTM cell release procedure 400, in which the gNB-CU determines, based on the received UE Context Setup Failure message, that all the LTM candidate cells in the gNB-DU2 are to be released, and therefore another candidate cell is required to release the RACH configuration previously prepared for the candidate gNB-DU2. Optionally, when there is a situation where all candidate cells of the gNB-DU2 need to be released after the configuration is completed, the gNB-DU2 may transmit a UE Context Release Request message to the gNB-CU in procedure 401. The message may include an LTM Cells to be Released List. The gNB-CU may transmit the UE Context Modification Request message to the gNB-DU0 and the gNB-DU1 in procedure 402. The UE Context Modification Request message may carry a list of information, including one or more of the information described above.

[0218] Optionally, the gNB-CU may transmit a UE Context Release Command message (carrying the LTM Cells to be Released List) to the gNB-DU2 in procedure 403, to instruct the gNB-DU2 to release the RACH configuration of a to-be-released LTM cell. After completing the release, the gNB-DU2 transmits a UE Context Release Complete message in procedure 404.

[0219] If the LTM Configuration ID Mapping List IE is included in the UE Context Setup Request message, the gNB-DU should consider the LTM Configuration ID Mapping List IE 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, the gNB-DU will consider the gNB-DU information corresponding to each LTM candidate cell (i.e., the gNB-DU should know the gNB-DU information corresponding to each LTM candidate cell, and alternatively, the gNB-DU should know which LTM candidate cell each of the other candidate gNB-DUs have thereon). If the LTM Cells to be Released List information element (i.e., the LTM Cells to be Released List IE) is received from the gNB-CU later, the gNB-DU can determine an action that a certain candidate gNB-DU is to be released and it is required to release the RACH configuration previously prepared for (or allocated to) this candidate gNB-DU.

[0220] Optionally, for the gNB-CU and each candidate gNB-DU, in the candidate gNB-DU on which the UE Context Setup Request procedure is first performed, the LTM candidate cell with acceptance prepares (or allocates) an RACH configuration for (or to) other candidate gNB-DUs (some of which may not have undergone the UE context setup procedure and will undergo the UE context setup procedure later). If later an LTM candidate cell on the other candidate gNB-DUs does not accept the LTM configuration request in the UE Context Setup Request procedure (i.e., the gNB-DU responses with UE Context Setup Failure information to the gNB-CU), or if an LTM candidate cell on the other candidate gNB-DUs accepts the LTM configuration but an LTM candidate cell release (for example, triggered by the gNB-CU or a candidate gNB-DU) occurs later, the gNB-DU compares and analyzes the LTM Cells to be Released List information element (i.e., the LTM Cells to be Released List IE) received from the gNB-CU and / or the updated LTM Configuration ID Mapping List IE received from the gNB-CU. Accordingly, the gNB-DU can determine whether the candidate gNB-DU to which an LTM released cell belongs is released and whether the corresponding RACH configuration prepared (or allocated) previously needs to be released. If all the LTM candidate cells on a certain candidate gNB-DU are released, that is, the candidate gNB-DU is released, the RACH configuration previously prepared for (or allocated to) this candidate gNB-DU by the LTM candidate cell which accepted the LTM configuration request is released.

[0221] In the embodiment corresponding to 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 the subsequent comparison and analysis performed after receiving the updated LTM Configuration ID Mapping List IE (including the LTM gNB-DU ID) through the UE Context Modification Request message. Thus, the gNB-DU can determine the action that the certain candidate gNB-DU is released and it is required to release the RACH configuration previously prepared for (or allocated to) this candidate gNB-DU.

[0222] In the embodiment corresponding to FIG. 4, optionally, if the gNB-DU receives the updated LTM Configuration ID Mapping List IE (including the LTM gNB-DU ID IE) in the 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 the comparison with the LTM Configuration ID Mapping List IE in the UE Context Setup Request previously received in procedure 3. Thus, the gNB-DU can determine the action that the certain candidate gNB-DU is released and it is required to release the RACH configuration previously prepared for (or allocated to) this candidate gNB-DU.

[0223] After receiving the LTM Cells to be Released List IE (for example, Cell2 being released) information transmited by the gNB-CU, or after receiving the updated LTM cell ID and the corresponding gNB-DU ID list information and comparing the updated LTM cell ID and the corresponding gNB-DU ID list information with the previous information, the candidate gNB-DU (which may include the source gNB-DU) can determine which LTM cells are released and whether there is a candidate gNB-DU on which all the candidate cells are released (for example, the candidate gNB-DU2 is released). At this time, the RACH configuration previously allocated to the candidate gNB-DU2 by the candidate cell on the candidate gNB-DU needs to be released, and at the same time, the RACH configuration allocated to this candidate gNB-DU by the indicated released candidate cell (Cell2) also needs to be released.

[0224] Alternative Scheme 2: The gNB-CU notifies, by carrying a new indication IE, other candidate gNB-DUs (which may optionally include the source gNB-DU) of which candidate gNB-DU has no LTM candidate cell with acceptance, that is, the entire gNB-DU rejects 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 procedure 7:

[0225] -To-be-released LTM Cells List (LTM Cells to be Released List)

[0226] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0227] >>LTM Cell ID

[0228] >>LTM gNB-DU ID (represented by a gNB-DU ID, and 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, 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 other candidate gNB-DUs and / or the candidate cells on the source gNB-DU release the RACH configuration (i.e., PRACH resources or early synchronization information) allocated to this gNB-DU ID)

[0229] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0230] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0231] >>LTM gNB-DU ID (represented by a gNB-DU ID, and indicating the to-be-released gNB-DU information (i.e., there is no candidate cell which accepted the LTM configuration request on this candidate gNB-DU, or all the candidate cells on this candidate gNB-DU are released, and in this situation, the RACH configuration allocated to this gNB-DU ID by other candidate cells which accepted the LTM configuration request needs to be released))

[0232] - RACH Configuration to be Released List (indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0233] >To-be-released RACH Configuration Item IEs (RACH Configuration to be Released Item IEs)

[0234] >>LTM gNB-DU ID (represented by a gNB-DU ID, and indicating the to-be-released gNB-DU information (i.e., there is no candidate cell which accepted the LTM configuration request on this candidate gNB-DU, or all the candidate cells on this candidate gNB-DU are released, and in this situation, the RACH configuration allocated to this gNB-DU ID by other candidate cells which accepted the LTM configuration request needs to be released))

[0235] -Mapping ID / Index / Identifier List of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released List, if the RACH configuration for the candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU and provided by the gNB-CU, this IE may indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0236] >Mapping ID / Index / Identifier Item IEs of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0237] >>Mapping ID / Index / Identifier of LTM gNB-DU (LTM gNB-DU Mapping ID / Index / identifier)

[0238] In an embodiment, optionally, if the LTM gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should, if supported, release the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the gNB-DU ID indicated in the LTM gNB-DUs to be Released List IE. If the UE context setup procedure between the gNB-CU and a certain candidate gNB-DU fails, it is possible to include the LTM gNB-DUs to be Released List IE in the UE Context Modification Request message transmited to another gNB-DU, to indicate that the other gNB-DU releases the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the gNB-DU ID indicated in the LTM gNB-DUs to be Released List IE.

[0239] In this example, after receiving the indication from the gNB-CU, the source gNB-DU releases the RACH configuration allocated by the source cell ID0 to the candidate gNB-DU ID2, and releases the RACH configuration allocated by the candidate cell ID2 to the source gNB-DU at the same time. When receiving the indication from the gNB-CU, the candidate gNB-DU1 releases the RACH configuration allocated by the candidate Cell ID1 to the candidate gNB-DU ID2, and releases the RACH configuration allocated by the candidate cell ID2 to the candidate gNB-DU ID1.

[0240] Alternative Scheme 3: Since the UE context setup procedures between the gNB-CU and candidate gNB-DUs are always performed in an order, the following situation may occur. The LTM candidate cell which accepted the LTM configuration request allocates an RACH configuration in advance to all candidate gNB-DUs of which the acceptance for the LTM configuration request is uncertain. Then, due to the failure of the UE context setup procedure of a certain candidate gNB-DU, the gNB-CU needs to notify the gNB-DU corresponding to the candidate cell which accepted the LTM configuration request to release the RACH configuration allocated to the candidate gNB-DU rejecting the LTM configuration request. In order to avoid this situation, it is possible to consider not requesting early synchronization information in the initial UE Context Setup Request procedure (procedure 3 in the embodiment of FIG. 4) between the gNB-CU and each candidate gNB-DU, but waiting until the gNB-CU and all candidate gNB-DUs complete the UE context setup procedures, and then the gNB-CU transmits the UE Context Modification Request message in procedure 7 to the candidate gNB-DU having the candidate cell that accepts the LTM configuration request, to request the allocation of RACH configuration for each of the other candidate gNB-DUs which accepted the LTM configuration request. This scheme is applicable to the initial LTM resource configuration preparation phase. For the situation where the candidate cell which accepted the LTM configuration request allocates the RACH configuration to each of the other candidate gNB-DUs which accepted the LTM configuration request, if the release of the LTM candidate cell or candidate gNB-DU that may be triggered by the gNB-CU or candidate gNB-DU occurs later, it is still required to use the alternative scheme 1 or 2 to release the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the candidate gNB-DU that has been released.

[0241] In another scenario, during the initial LTM preparation phase, there may be an LTM candidate cell which accepted the LTM configuration request in the candidate gNB-DU, and the network has completed or not performed the RRC Reconfiguration for the UE, but later, due to some other circumstances, the gNB-CU or the candidate gNB-DU decides to release the LTM candidate cell that previously accepts the LTM configuration request. In this case, the LTM configuration needs to be updated.

[0242] For example, FIG. 4 shows an exemplary LTM cell release procedure 400. Here, in procedure 401, the gNB-CU receives a UE Context Release Request message transmited by the gNB-DU2 to the gNB-CU. The message may include an LTM Cells to be Released List. Alternatively, the gNB-CU decides to trigger the procedure 403 to transmit a UE Context Release Command message (which may carry the LTM Cells to be Released List) to the gNB-DU2, and decides that all LTM candidate cells in the gNB-DU2 are to be released. Therefore, the other candidate gNB-DUs and / or the candidate cells on the source gNB-DU are required to release the RACH configuration prepared for the candidate gNB-DU2. The gNB-CU may transmit a UE Context Modification Request message to the gNB-DU0 and the gNB-DU1 in procedure 402. The UE Context Modification Request message carries one or more of the following information:

[0243] -To-be-released LTM Cells List (LTM Cells to be Released List)

[0244] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0245] >>LTM Cell ID

[0246] >>LTM gNB-DU ID (represented by a gNB-DU ID, and 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 other candidate gNB-DUs and / or the candidate cells on the source gNB-DU release the RACH configuration (i.e., PRACH resources or early synchronization information) allocated to this gNB-DU ID)

[0247] -To-be-released LTM gNB-DUs List (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0248] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0249] >>LTM gNB-DU ID

[0250] - RACH Configuration to be Released List (indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0251] >To-be-released RACH Configuration Item IEs (RACH Configuration to be Released Item IEs)

[0252] >>LTM gNB-DU ID

[0253] -Mapping ID / Index / Identifier List of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released List, if the RACH configuration for the candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU and provided by the gNB-CU, this IE may indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0254] >Mapping ID / Index / Identifier Item IEs of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0255] >>Mapping ID / Index / Identifier of LTM gNB-DU (LTM gNB-DU Mapping ID / Index / identifier)

[0256] Optionally, the gNB-CU transmits the UE Context Release Command message (carrying the LTM Cells to be Released List) to the gNB-DU2 in procedure 403, to instruct the gNB-DU2 to release the RACH configuration of a to-be-released LTM cell. After completing the release, the gNB-DU2 transmits a UE Context Release Complete message in procedure 404.

[0257] For example, the gNB-CU may notify, by using the UE Context Modification Request message carrying the LTM Cells to be Released List information, each of the other candidate gNB-DUs to release the RACH configuration previously allocated to this candidate gNB-DU for the to-be-released candidate cell. In the situation where a certain candidate gNB-DU is released, the RACH configuration previously prepared for this gNB-DU by other candidate cells also needs to be released. However, the gNB-DU cannot determine whether there is a candidate gNB-DU to be released through the LTM Cells to be Released List IE. Only the gNB-CU can determine whether a candidate gNB-DU has released all LTM candidate cells that previously accept the LTM configuration request, such that the entire gNB-DU is released and thus needs to be excluded from the LTM candidate gNB-DUs list. Therefore, the gNB-CU is required to carry a new indication IE to notify other candidate gNB-DUs (which optionally include the source gNB-DU) of the to-be-released gNB-DU information. Therefore, in the LTM cell release procedure, the gNB-CU may make the UE Context Modification Request message carry one or more of the following information:

[0258] -To-be-released LTM Cells List (LTM Cells to be Released List)

[0259] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0260] >>LTM Cell ID

[0261] >>LTM gNB-DU ID (represented by a gNB-DU ID, and 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 other candidate gNB-DUs and / or the candidate cells on the source gNB-DU release the RACH configuration (i.e., PRACH resources or early synchronization information) allocated to this gNB-DU ID)

[0262] -To-be-released LTM gNB-DUs List (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0263] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0264] >>LTM gNB-DU ID

[0265] - RACH Configuration to be Released List (indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0266] >To-be-released RACH Configuration Item IEs (RACH Configuration to be Released Item IEs)

[0267] >>LTM gNB-DU ID

[0268] -Mapping ID / Index / Identifier List of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released List, if the RACH configuration for the candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU and provided by the gNB-CU, this IE may indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0269] >Mapping ID / Index / Identifier Item IEs of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0270] >>Mapping ID / Index / Identifier of LTM gNB-DU (LTM gNB-DU Mapping ID / Index / identifier)

[0271] After receiving the indication from the gNB-CU, the source gNB-DU releases the RACH configuration allocated by the source cell or other candidate cells on the source gNB-CU to the to-be-released candidate gNB-DU ID, and releases the RACH configuration allocated to the source gNB-DU by the candidate cell indicated in the LTM Cells to be Released List information at the same time. When receiving the indication from the gNB-CU, the other candidate gNB-DUs release the RACH configuration allocated by the candidate cell on this candidate gNB-DU to the to-be-released candidate gNB-DU ID, and release the RACH configuration allocated to this candidate gNB-DU by the candidate cell indicated in the LTM Cells to be Released List information at the same time.

[0272] Alternative Scheme 4: Since the RACH configuration of each candidate cell is allocated based on each candidate gNB-DU, in the LTM preparation phase, for each candidate cell, the gNB-CU requests a resource from the corresponding candidate gNB-DU based on the L3 measurement report through a separate UE context setup procedure, requests an early synchronization RACH configuration at the same time, and requests the candidate cell to allocate an RACH configuration to each LTM gNB-DU by carrying an LTM gNB-DUs list (including all candidate gNB-DU IDs). If the UE Context Setup Request procedure for all the candidate cells on a certain candidate gNB-DU (e.g., DU2) subsequently fails (that is, there is no candidate cell with acceptance on this candidate gNB-DU, that is, this candidate gNB-DU is not an LTM candidate gNB-DU), or if a certain candidate gNB-DU (e.g., DU2) is subsequently released due to other reasons (all candidate cells on this candidate gNB-DU may be released due to overload) and is excluded from the candidate LTM gNB-DUs list (that is, this candidate gNB-DU does not belong to the candidate LTM gNB-DU), then the candidate cells on other candidate gNB-DUs need to release the RACH resources prepared for the gNB-DU (DU2) of which the LTM preparation fails or which is released. The gNB-CU may request the RACH configuration again through the UE Context Modification Request procedure, and updated LTM gNB-DUs list information may be carried therein. Here, the information does not include the gNB-DU (DU2) of which the LTM preparation fails or which is released. In this way, the candidate cells on the other candidate gNB-DUs release the RACH configuration previously allocated to this gNB-DU2. At the same time, the RACH configuration of the other candidate gNB-DUs may be updated and allocated. If the RACH configuration is updated, the gNB-CU is required to redistribute the RACH configuration to each candidate gNB-DU.

[0273] In an embodiment, optionally, if the LTM gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should, if supported, release the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the gNB-DU ID indicated in the LTM gNB-DUs to be Released List IE. In other words, if the LTM gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should, if supported, release the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the gNB-DU corresponding to the gNB-DU ID included in the LTM gNB-DUs to be Released List IE.

[0274] In an embodiment, optionally, if the LTM gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should, if supported, release the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the gNB-DU ID indicated in the LTM gNB-DUs to be Released List IE. In other words, if the LTM gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should, if supported, release the RACH configuration allocated by the candidate cell which accepted the LTM configuration request to the gNB-DU corresponding to the gNB-DU ID included in the LTM gNB-DUs to be Released List IE.

[0275] In an embodiment, optionally, if the LTM gNB-DU ID IE is included in the LTM Cells to be Released List (LTM Cells to be Released List) included in the UE Context Modification Request message, the gNB-DU should, if supported, release the RACH configuration, early uplink synchronization configuration or PRACH resource (including one or more preamble indexes) allocated by the candidate cell to the gNB-DU indicated by the LTM gNB-DU ID.

[0276] In an embodiment, optionally, if the LTM Configuration ID Mapping List IE is included in the UE Context Setup Request message or the UE Context Modification Request message, the gNB-DU should consider the LTM Configuration ID Mapping List IE 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, for indicating the gNB-DU information corresponding to each LTM candidate cell, the gNB-DU will consider the gNB-DU information corresponding to each LTM candidate cell (i.e., the gNB-DU should know the gNB-DU information corresponding to each LTM candidate cell, and optionally, the gNB-DU should know which LTM candidate cell is on each of the other candidate gNB-DUs). If the LTM Cells to be Released List information element (i.e., the LTM Cells to be Released List IE) is received from the gNB-CU later, the gNB-DU can determine an action that a certain candidate gNB-DU is to be released and it is required to release the RACH configuration previously prepared for (allocated to) this candidate gNB-DU by the candidate cell which accepted the LTM configuration request.

[0277] Accordingly, after the release of LTM cell resources is completed on the network side, the gNB-CU needs to update the configuration on the UE side through an RRC Reconfiguration message.

[0278] In an embodiment, as shown in FIG. 4-2, regarding the triggering of LTM, the source gNB-DU transmits a DU-CU Cell Switch Notification message to the gNB-CU in procedure 19, indicating that a Cell Switch Command is initiated to the UE. The source gNB-DU may transmit valid TA information to the target gNB-DU through the gNB-CU. In this way, the target gNB-DU does not need to perform the TA acquisition procedure on other LTM candidate cells again based on the PDCCH order. When a subsequent LTM is triggered, the target gNB-DU can use the valid TA value of the corresponding LTM target cell. The DU-CU Cell Switch Notification message includes one or more of the following information:

[0279] -Target Cell ID (represented by a cell ID or NR CGI)

[0280] -TCI State ID (corresponding to a CandidateTCI-StatesId IE defined in TS 38.331)

[0281] -LTM Cell Switch Information

[0282] >Joint or Downlink (DL) TCI State ID (corresponding to a TCI-StateId IE defined in TS 38.331)

[0283] >Uplink (UL) TCI State ID (corresponding to a TCI-UL-StateId IE defined in TS 38.331)

[0284] -TA Information List (including one or more candidate cell IDs and corresponding valid TA values, as well as possible valid time information)

[0285] >Candidate Cell ID (represented by a cell ID or NR CGI)

[0286] >TA Value (indicating the valid TA value of a candidate cell, and transferred to a target gNB or target gNB-DU for use)

[0287] >Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a new source gNB-DU (after a candidate gNB-DU is accessed by the UE, the candidate gNB-DU is the source gNB-DU for the subsequent LTM). In this case, when the LTM is triggered, the source gNB-DU selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0288] >TA Value Validation Time (TA valid timer)

[0289] Then, the gNB-CU forwards the above information to the target gNB-DU (which is used as the new source gNB-DU after being accessed by the UE). The gNB-CU transmits a CU-DU Cell Switch Notification to the target gNB-DU in procedure 20. The CU-DU Cell Switch Notification message includes one or more of the following information:

[0290] -Target Cell ID (represented by a cell ID or NR CGI)

[0291] -TCI State ID (corresponding to a CandidateTCI-StatesId IE defined in TS 38.331)

[0292] -LTM Cell Switch Information

[0293] >Joint or Downlink (DL) TCI State ID (corresponding to a TCI-StateId IE defined in TS 38.331)

[0294] >Uplink (UL) TCI State ID (corresponding to a TCI-UL-StateId IE defined in TS 38.331)

[0295] -TA Information List (including one or more candidate cell IDs and corresponding valid TA values, as well as possible valid time information)

[0296] >Candidate Cell ID (represented by a cell ID or NR CGI)

[0297] >TA Value (indicating the valid TA value of a candidate cell, and transferred to a target gNB or target gNB-DU for use)

[0298] >Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a new source gNB-DU (after a candidate gNB-DU is accessed by the UE, the candidate gNB-DU is the source gNB-DU for the subsequent LTM). In this case, when the LTM is triggered, the source gNB-DU selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0299] >TA Value Validation Time (TA valid timer)

[0300] FIGS. 5a-1 to 5a-3 (hereinafter collectively referred to as FIG. 5) are exemplary embodiments of an LTM procedure between different gNB-CUs according to the present disclosure. The source gNB-CU can only determine, according to a received L3 Measurement Report message, which neighbour NG-RAN node a neighbour cell is under. If the neighbour NG-RAN node refers to a base station that is in a gNB-CU and a gNB-DU split architecture, the source gNB-CU cannot determine which gNB-DU the neighbour cell is under. In this situation, the source gNB-CU or a source NG-RAN node can only determine which neighbour NG-RAN node the neighbour cell reported by the UE belongs to, or the gNB-CU of which neighbour NG-RAN node (one NG-RAN node as a split architecture can only have one gNB-CU).

[0301] In order to enable the gNB-CU to determine the neighbour cell is under which gNB-DU under a neighbour NG-RAN node (if the neighbour NG-RAN node is in a gNB-CU and gNB-DU split architecture ), according to an optional scheme, an Xnap interface specification procedure can be enhanced, such that the exchanged cell information can optionally include the gNB-DU ID information to which the cell belongs. For example, it is possible to consider adding a selectable sub-IE (gNB-DU ID) to one or more of the following IEs, the gNB-DU ID indicating the gNB-DU ID information to which this cell belongs.

[0302] >Served Cell Information NR

[0303] >Neighbour Cell Information NR (Neighbour Information NR)

[0304] >E-UTRA Neighbour Cell Information (Neighbour Information E-UTRA)

[0305] In an Xn interface setup (XN SETUP) procedure or the NG-RAN node configuration update procedure, two neighbour NG-RAN nodes or gNB-CUs will exchange served NR cell information (Served Cell Information NR) and exchange NR neighbour cell information (Neighbour Information NR) or E-UTRA neighbour cell information (Neighbour Information E-UTRA). Optionally, if the corresponding cell indicates the gNB-DU ID to which the cell belongs, then in the situation where the NG-RAN node is in a gNB-CU and gNB-DU split architecture, the gNB-CU can know the neighbour cell belongs to a cell under which gNB-DU under the neighbour NG-RAN node.

[0306] FIG. 5b shows an Xn interface setup procedure of two neighbour NG-RAN nodes or gNB-CUs will. 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 transmits an F1 Setup Request message to the gNB-DU. In procedure 5002, the gNB-CU transmits an F1 Setup Response message to the gNB-DU. For the NG-RAN node in which the connection between the gNB-CU and the gNB-DU is established, in procedure 5003, the NG-RAN node 1 or the gNB-CU therein transmits an XN Setup 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 transmits an 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 transmits a gNG-DU Configuration Update message to the gNB-CU. In procedure 5006, the gNB-CU transmits a gNB-DU Configuration Update Acknowledge message to the gNB-DU. In procedure 5007, for the NG-RAN node 1 in which the configuration update is performed between the gNB-CU and the gNB-DU, the NG-RAN node 1 or the gNB-CU therein transmits an 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 transmits an NG-RAN Node Configuration Update Acknowledge message to the NG-RAN node 1 or the gNB-CU therein. As shown in FIG. 5b, the gNB-DU ID information to which the corresponding served NR cell belongs and the gNB-DU ID information to which the NR neighbour cell belongs may be carried in the XN Setup Request message or XN Setup Response message, or in the NG-RAN Node Configuration Update message.

[0307] In the LTM procedure btween different gNB-CUs, for the PRACH resource allocation method of the candidate cell, the allocation is based on each candidate cell or based on the UE, it will cause large resource occupation and waste. In order to save the use of PRACH resources of the candidate cell, optionally, it is possible to consider the allocation performed based on the NG-RAN node (each NG-RAN node is represented by a galobal NG-RAN node ID, which may include a global gNB ID or a global ng-eNB ID). In addition, optionally, consider the allocation method performed based on the gNB-DU (each gNB-DU is represented by a gNB-DU ID and the gNB ID to which the gNB-DU ID belongs).

[0308] FIG. 5a illustrates an LTM procedure between different gNB-CUs according to an exemplary embodiment of the present disclosure. The involved procedure between the gNB-CUs or NG-RAN nodes may be applicable to other possible scenarios, for example, a scenario where a secondary node (SN) changes or remains unchanged (with or without an SN change) while the LTM (inter-MN LTM) occurs between master nodes (MN). If the NG-RAN node is not in a gNB-CU and a gNB-DU split architecture, the corresponding F1 interface message and procedure are not involved in the present disclosure.

[0309] The procedures shown in FIG. 5a are described below.

[0310] The NG-RAN node involved in the following description of the procedures may include a gNB or an ng-eNB, the corresponding source NG-RAN node may include a source gNB or a source ng-eNB, and the corresponding candidate NG-RAN node may include a candidate gNB or a candidate ng-eNB. An NG-RAN node ID may be represented by a global NG-RAN node ID, and the global NG-RAN node ID may include a global gNB ID or global ng-eNB ID.

[0311] Procedure 501: The UE directly transmits an L3 measurement report to the source NG-RAN node, or if the source NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the UE transmits, the source gNB-DU, a Measurement Report message for reporting an L3 measurement result. Here, the message include the measurement value of a neighbour cell. Then, the source gNB-DU transmits an uplink radio resource control (UL RRC) Message Transfer message to transfer the received Measurement Report message to the gNB-CU.

[0312] 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 an LTM configuration.

[0313] Procedure 503: For each candidate cell, the source NG-RAN node (the source gNB or the source ng-eNB) or the source gNB-CU respectively initiates a Handover Request message or a new Xnap message (e.g., an LTM Configuration Request message, or an LTM Request message) to the candidate NG-RAN node (candidate gNB or candidate ng-eNB) or candidate gNB-CU to which the candidate cell belongs. Here, the message includes one or more of the following information:

[0314] -LTM Triggering Indication (LTM indication = initiation)

[0315] -Candidate Cell ID (a cell ID or NR CGI)

[0316] -LTM Configuration ID of Candidate Cell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0317] -LTM Configuration ID Mapping List (including the mapping relationship between each LTM cell ID (or NR CGI) and its corresponding LTM configuration ID (corresponding to an LTM-CandidateId IE defined in TS 38.331))

[0318] -LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0319] -LTM Reference Configuration Request Indication (indicating that the source NG-RAN node requests an LTM reference configuration from the candidate NG-RAN node or the candidate gNB-CU)

[0320] -LTM Reference Configuration (which includes a lower-layer and / or high-layer reference configuration, and which may optionally include a CellGroupConfig IE and / or CG-ConfigInfo IE defined in TS 38.331, wherein the CG-ConfigInfo IE includes ltm-ReferenceConfiguration information)

[0321] -Early Synchronization (Sync) Information Request

[0322] -Request Indication for RACH Configuration (Request for RACH Configuration)

[0323] >Optionally, if only one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, a source NG-RAN node ID (e.g., a global NG-RAN node ID, which may include a global gNB ID or a global ng-eNB ID) may be carried, indicating that the source NG-RAN node or the source gNB-CU requests, based on the NG-RAN node, a PRACH resource from the candidate NG-RAN node or the candidate gNB-CU for an early synchronization TA acquisition procedure.

[0324] >Optionally, in order that subsequent LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, an NG-RAN node ID list (including, for example, the global NG-RAN node ID of each candidate NG-RAN node, which may include a global gNB ID or a global ng-eNB ID) may be carried, or an LTM gNBs list (including each piece of LTM gNB ID information, which is represented by a global gNB ID) may be carried, indicating that the source NG-RAN node or the source gNB-CU requests, based on each NG-RAN node, a PRACH resource from the candidate NG-RAN node or the candidate gNB-CU for the early synchronization TA acquisition procedure.

[0325] >Optionally, if only the one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, a source gNB-DU ID and a source NG-RAN node ID (referring to a gNB ID when the base station is in a gNB-CU and a gNB-DU split architecture, for example, the global NG-RAN node ID, which may include the global gNB ID or the global ng-eNB ID) may be carried, indicating that the source NG-RAN node or the source gNB-CU requests, based on the gNB-DU, a PRACH resource from the candidate NG-RAN node or the candidate gNB-CU for the early synchronization TA acquisition procedure.

[0326] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, a gNB-DU ID list (indicating the NG-RAN node ID (referring to a gNB ID when the base station is in a gNB-CU and a gNB-DU split architecture, for example, the NG-RAN node ID is indicated through the global NG-RAN node ID which may include the global gNB ID or the global ng-eNB ID) to which each gNB-DU ID belongs) may be carried, indicating that the source NG-RAN node or the source gNB-CU requests, based on each gNB-DU, a PRACH resource from the candidate NG-RAN node or the candidate gNB-CU for the early synchronization TA acquisition procedure.

[0327] >Optionally, if the source gNB-CU does not want to carry a plaintext source NG-RAN node ID and / or gNB-DU ID, or the NG-RAN node ID list and / or gNB-DU ID list, the source gNB-CU may alternatively associate each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU (including the source gNB-DU) with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit a list including the mapping ID / index / identifier of the LTM NG-RAN node or LTM gNB-DU (the mapping ID / index / identifier list of the LTM NG-RAN node or the mapping identifier / index / identifier list of the LTM gNB-DU) to the candidate NG-RAN node or the candidate gNB-CU, to request the candidate cell to allocate a PRACH resource to each mapping ID / index / identifier.

[0328] Procedure 504: If the candidate NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the candidate gNB-CU transmits a UE Context Setup Request message to the gNB-DU to which the candidate cell belongs. Here, the message includes one or more of the following information:

[0329] -LTM Triggering Indication (LTM Indicator = true)

[0330] - Candidate Cell ID (a cell ID or NR CGI)

[0331] -LTM Configuration ID of Candidate Cell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0332] -LTM Configuration ID Mapping List (including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID)

[0333] -LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0334] -Indication (Request for Lower Layer Configuration) that the candidate gNB-CU requests the candidate gNB-DU to provide a lower-layer configuration to generate a reference configuration

[0335] -LTM Reference Configuration (including a CellGroupConfig IE defined in TS 38.331)

[0336] -Early Synchronization (Sync) Information Request

[0337] -Request Indication for RACH Configuration (Request for RACH Configuration)

[0338] >Optionally, if only the one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, a source NG-RAN node ID (e.g., a global NG-RAN node ID, which may include a global gNB ID or a global ng-eNB ID)) may be carried, indicating that the candidate gNB-CU requests, based on the NG-RAN node, a PRACH resource from the candidate gNB-DU.

[0339] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, an NG-RAN node ID list (including, for example, the global NG-RAN node ID of each candidate NG-RAN node, which may include a global gNB ID or a global ng-eNB ID) may be carried, or an LTM gNBs list (including each piece of LTM gNB ID information, which is represented by a global gNB ID) may be carried, indicating that the candidate gNB-CU requests, based on each NG-RAN node, a PRACH resource from the candidate gNB-DU.

[0340] >Optionally, if only the one-time LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, a source gNB-DU ID and a source NG-RAN node ID (referring to a gNB ID when the base station is in a gNB-CU and a gNB-DU split architecture, for example, the global NG-RAN node ID, which may include the global gNB ID or the global ng-eNB ID) may be carried, indicating that the candidate gNB-CU requests, based on the gNB-DU, a PRACH resource from the candidate gNB-DU.

[0341] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, a gNB-DU ID list (indicating the NG-RAN node ID (referring to a gNB ID when the base station is in a gNB-CU and a gNB-DU split architecture, for example, the NG-RAN node ID is indicated through the global NG-RAN node ID which may include the global gNB ID or the global ng-eNB ID) to which each gNB-DU ID belongs) may be carried, indicating that the candidate gNB-CU requests, based on the gNB-DU, a PRACH resource from the candidate gNB-DU.

[0342] >Optionally, if the source NG-RAN node or the source gNB-CU transmits, to the candidate NG-RAN node or the candidate gNB-CU, a mapping ID, index or identifier with respect to the source NG-RAN node ID and / or gNB-DU ID, a mapping ID, index or identifier list of an LTM NG-RAN node (the mapping ID / index / identifier list of the LTM NG-RAN node), or a mapping ID, index or identifier list of an LTM gNB-DU, the candidate gNB-CU transmits a list including the mapping ID, index or identifier of the LTM NG-RAN node or LTM gNB-DU (the mapping ID / index / identifier list of the LTM NG-RAN node or the mapping identifier / index / identifier list of the LTM gNB-DU) to the candidate gNB-CU, to request the candidate cell to allocate a PRACH resource to the mapping ID / index / identifier of each LTM NG-RAN node or gNB-DU.

[0343] Procedure 505: If the candidate gNB-DU accepts an LTM configuration request, the candidate gNB-DU will transmit a UE Context Setup Response message as a response to the candidate gNB-CU. Here, the message may include one or more of the following information:

[0344] -Candidate Cell ID (cell ID or NR CGI)

[0345] -Lower-layer RRC Configuration generated for a target candidate cell which accepted the LTM configuration request (e.g., a transmission configuration indication (TCI) states configurations list), SSB Configuration and NR PCI (physical cell Id) Information of Candidate Cell

[0346] -LTM Reference Configuration (provided by the candidate gNB-DU, and including a CellGroupConfig IE defined in TS 38.331)

[0347] -LTM Complete Configuration Indicator (indicating whether the LTM configuration of the candidate cell with acceptance is a complete configuration)

[0348] -LTM CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331)

[0349] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL)

[0350] -RACH Configuration Information (i.e. PRACH Resources), including one or more pieces of RACH configuration information

[0351] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to the source NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the source gNB-DU (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0352] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to the mapping ID / index / identifier of the source NG-RAN node or the source gNB-DU is included.

[0353] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. The RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to each candidate NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or each candidate gNB-DU (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0354] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. If the candidate gNB-CU provides the mapping ID, index or identifier of the LTM NG-RAN node, or the mapping ID, index or identifier of the LTM gNB-DU, the list includes accordingly the RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to the mapping ID, index or identifier of each requested LTM NG-RAN node or gNB-DU.

[0355] Procedure 506: For the requested candidate cell, the candidate NG-RAN node (candidate gNB or candidate ng-eNB) or the candidate gNB-CU responses with a Handover Request Acknowledge message or a new Xnap message (e.g., an LTM Configuration Request Acknowledgement message, or an LTM Request Acknowledgement message) to the source NG-RAN node (the source gNB or the source ng-eNB) or the source gNB-CU. Here, the message includes one or more of the following information:

[0356] -Candidate Cell ID (cell ID or NR CGI)

[0357] -Lower-layer RRC Configuration generated for a target candidate cell which accepted the LTM configuration request (e.g., a transmission configuration indication (TCI) states configurations list included in an LTM-TCI-Info IE defined in TS 38.331), SSB Configuration and NR PCI (physical cell Id) Information of Candidate Cell

[0358] -LTM Reference Configuration (which is provided by the candidate NG-RAN node or candidate gNB-CU and includes a lower-layer and / or high-layer reference configuration, and which may optionally include a CellGroupConfig IE and / or CG-ConfigInfo IE defined in TS 38.331, the CG-ConfigInfo IE including ltm-ReferenceConfiguration information)

[0359] -LTM Complete Configuration Indicator (indicating whether the LTM configuration of the candidate cell with acceptance is a complete configuration)

[0360] -LTM CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331)

[0361] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) of the candidate cell

[0362] -TA Assistance Information, indicating that the TA value of the candidate cell is 0

[0363] -RACH Configuration Information (i.e. PRACH Resources), including one or more pieces of RACH configuration information

[0364] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to the source NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the source gNB-DU (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0365] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to the mapping ID / index / identifier of the source NG-RAN node or the source gNB-DU is included.

[0366] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. The RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to each candidate NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or each candidate gNB-DU (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0367] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. If the candidate gNB-CU provides the mapping ID, index or identifier of the LTM NG-RAN node, or the mapping ID, index or identifier of the LTM gNB-DU, the list includes accordingly the RACH configuration information allocated by the candidate cell (represented by the cell ID or NR CGI) to the mapping ID, index or identifier of each requested LTM NG-RAN node or gNB-DU.

[0368] The different PRACH resources, RACH configuration information or early uplink synchronization configuration information allocated by the candidate cell to one or more LTM gNB-DUs or LTM gNBs in procedure 505, 506 or 509 may include one or more of the following information:

[0369] -RACH Configuration information (included in an EarlyUL-SyncConfig IE defined in TS 38.331, and representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs or LTM gNBs, the different parts of the PRACH resources being represented using the following LTM gNB-DUs list information or LTM gNBs list information)

[0370] -LTM gNB-DUs List (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0371] >LTM gNB-DU ID (indicated by a gNB-DU ID)

[0372] >LTM gNB ID (indicated by a global gNB ID, and used to represent the gNB information associated with the gNB-DU indicated by the gNB-DU ID)

[0373] >Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB-DU ID)

[0374] -LTM gNBs List (including one or more LTM gNB IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0375] >LTM gNB ID (indicated by a global gNB ID)

[0376] >Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB ID)

[0377] Procedure 507: If the source NG-RAN node is in the gNB-CU and gNB-DU split architecture, the source gNB-CU may continue to allocate the corresponding RACH configuration to the source gNB-DU based on the implementation of the RACH configuration allocated by each candidate cell to this NG-RAN node. For example, if one or more UEs under only one source gNB-DU under the source gNB-CU initiate an LTM configuration to the same candidate cell, then all the NG-RAN node-based RACH configurations of this candidate cell can be allocated to this gNB-DU. If a plurality of UEs under different source gNB-DUs under the source gNB-CU initiate an LTM configuration to the same candidate cell, then a subset of the NG-RAN node-based RACH configurations of this candidate cell can be allocated to the 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).

[0378] Procedure 508: The source gNB-CU transmits a UE Context Modification Request message to the source gNB-DU. Here, the message includes one or more of the following information:

[0379] -Candidate Cell ID (a cell ID or NR CGI, which may refer to the source cell or another candidate cell under the source gNB-DU, each candidate cell using a separate UE context modification procedure)

[0380] -LTM Triggering Indication (LTM indicator = true)

[0381] -LTM Configuration ID of Candidate Cell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0382] -LTM Configuration ID Mapping List (including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID)

[0383] -LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0384] -Indication (Request for Lower Layer Configuration) that the source gNB-CU requests the source gNB-DU to provide a lower-layer configuration to generate a reference configuration

[0385] -LTM Reference Configuration (including a CellGroupConfig IE defined in TS 38.331)

[0386] -Collected CSI Report Configuration and TCI States Configurations List of Target Candidate Cell which accepted LTM Configuration Request in Other Candidate NG-RAN Node or Candidate gNB-CU, SSB Configuration and NR PCI Information of Candidate Cell

[0387] -Early Synchronization (Sync) Information List, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) allocated by each candidate cell (represented by a cell ID or NR CGI) which accepted the LTM configuration request

[0388] -TA Assistance Information, indicating that the TA value of the candidate cell is 0

[0389] -RACH Configuration List (i.e., early uplink synchronization configuration information), which optionally includes a subset or complete set of the RACH configuration information allocated by each candidate cell to the NG-RAN node to which the candidate cell belongs, or includes the RACH configuration information allocated by each candidate cell to the gNB-DU to which the candidate cell belongs, and which may include one or more of the following information:

[0390] >Candidate Cell ID (represented by a cell ID or NR CGI)

[0391] >RACH Configuration Information (included in an EarlyUL-SyncConfig IE defined in TS 38.331, and representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs, the different parts of the PRACH resources being represented using the following LTM gNB-DUs list information)

[0392] >LTM gNB-DUs list (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0393] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0394] >>LTM gNB ID (indicated by a global gNB ID, and used to represent the gNB information associated with the gNB-DU indicated by the gNB-DU ID)

[0395] >>Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB-DU ID)

[0396] -Early Synchronization (Sync) Information Request

[0397] -Request Indication for RACH Configuration (Request for RACH Configuration)

[0398] >Optionally, in order that subsequent LTM is supported and the PRACH resources of the candidate cell are allocated based on the NG-RAN node, an NG-RAN node ID list (including, for example, the global NG-RAN node ID of each candidate NG-RAN node, which may include a global gNB ID or a global ng-eNB ID) may be carried, or an LTM gNBs list (including each piece of LTM gNB ID information, which is represented by a global gNB ID) may be carried, indicating that the source gNB-CU requests, based on each NG-RAN node, a PRACH resource from the source gNB-DU.

[0399] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate cell are allocated based on the gNB-DU, a gNB-DU ID list (indicating the NG-RAN node ID (referring to a gNB ID when the base station is in a gNB-CU and a gNB-DU split architecture, for example, the NG-RAN node ID is indicated through the global NG-RAN node ID which may include the global gNB ID or the global ng-eNB ID) to which each gNB-DU ID belongs) may be carried, indicating that the source gNB-CU requests, based on the gNB-DU, a PRACH resource from the source gNB-DU.

[0400] >Optionally, if the source gNB-CU does not want to carry a plaintext candidate NG-RAN node ID and / or candidate gNB-DU ID, or the NG-RAN node ID list and / or gNB-DU ID list, the source gNB-CU may alternatively associate each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU (including the source gNB-DU) with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit a list including the mapping ID / index / identifier of the LTM NG-RAN node or LTM gNB-DU (the mapping ID / index / identifier list of the LTM NG-RAN node or the mapping identifier / index / identifier list of the LTM gNB-DU) to the source gNB-DU, to request the source cell or another candidate cell to allocate a PRACH resource to each mapping ID / index / identifier.

[0401] Procedure 509: If the source gNB-DU accepts the LTM configuration request, the source gNB-DU transmits a UE Context Modification Response message as a response. The message includes one or more of the following information:

[0402] -Candidate Cell ID (a cell ID or NR CGI, which may include the source cell or another candidate cell under the source gNB-DU, each candidate cell using a separate UE context modification procedure)

[0403] -Lower-layer RRC Configuration (e.g., a transmission configuration indication (TCI) states configurations list) generated for a target candidate cell which accepted the LTM configuration request, SSB Configuration and NR PCI (physical cell Id) Information of Candidate Cell

[0404] -LTM Reference Configuration (provided by the source gNB-DU)

[0405] -LTM Complete Configuration Indicator

[0406] -LTM CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331)

[0407] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplinkcarrier(Early UL Sync Configuration for SUL)

[0408] -RACH Configuration Information List (i.e. PRACH Resources), including a plurality of pieces of RACH configuration information

[0409] >Optionally, the RACH configuration information allocated by the candidate cell (including the source cell or the other candidate cell under the source gNB-DU, and represented by the cell ID or NR CGI) to each candidate NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or each candidate gNB-DU (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0410] >Optionally, if the source gNB-CU provides the mapping ID, index or identifier of the LTM NG-RAN node or the mapping ID, index or identifier of the LTM gNB-DU, the list includes accordingly the RACH configuration information allocated by the candidate cell (including the source cell or the other candidate cell under the source gNB-DU, and represented by the cell ID or NR CGI) to the mapping ID, index or identifier of each requested LTM NG-RAN node or gNB-DU.

[0411] Procedure 510: To support subsequent LTM, the LTM configuration information of all candidate cells which accepted the LTM request that is collected by the source NG-RAN node (source gNB or source ng-eNB) or source gNB-CU needs to be transmitted to each of other candidate NG-RAN nodes (candidate gNBs or candidate ng-eNBs) or candidate gNB-CUs. Then, the source NG-RAN node (source gNB or source ng-eNB) or the source gNB-CU transmits, through an Xn interface message, the configuration information of another candidate cell which accepted the LTM request to the other candidate NG-RAN nodes (candidate gNBs or candidate ng-eNBs) or candidate gNB-CUs. Optionally, a new Xnap message (e.g., an LTM Configuration Modification Request message, an LTM Modification Request message, or a Handover Modification Request message) can be defined, or a Handover Request message can be used to transfer the information. The message includes one or more of the following information:

[0412] -LTM Modification or Update Indication (LTM indication = modification or update)

[0413] -Candidate Cell ID (a cell ID or NR CGI)

[0414] -LTM Configuration ID of Candidate Cell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0415] -Updated LTM Configuration ID Mapping List (provided by the source gNB-CU, and including the mapping relationship between each LTM cell ID and its corresponding LTM configuration ID; optionally, the candidate gNB-CU compares, after receiving the updated LTM configuration ID mapping list, the updated LTM configuration ID mapping list with the list received in procedure 503, and thus can determine which cell has not become the LTM candidate cell that accepts 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 is possible to determine 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 to this candidate NG-RAN node ID by the candidate cell configured on this candidate gNB-CU.

[0416] -Collected RRC Configuration (generated by a target candidate cell which accepted the LTM configuration request in another candidate NG-RAN node, including, e.g., a transmission configuration indication (TCI) states configurations list, and included in an LTM-TCI-Info IE defined in TS 38.331), SSB Configuration and NR PCI (physical cell Id) Information of Candidate Cell

[0417] -LTM Reference Configuration (which is provided by the source gNB-CU and includes a lower-layer and / or high-layer reference configuration, and which may optionally include a CellGroupConfig IE and / or CG-ConfigInfo IE defined in TS 38.331, the CG-ConfigInfo IE including ltm-ReferenceConfiguration information)

[0418] -LTM Complete Configuration Indicator

[0419] -LTM CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331)

[0420] -Updated LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, provided by the source gNB-CU and including an ltm-CSI-ResourceConfigToAddModList IE IE defined in TS 38.331)

[0421] -Early Synchronization (Sync) Information List, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) of each candidate cell (represented by a cell ID or NR CGI) which accepted the LTM configuration request

[0422] -TA Assistance Information, indicating that the TA value of the candidate cell is 0

[0423] -RACH Configuration Information List (i.e. PRACH Resources), that is, early uplink synchronization configuration information, including a plurality of pieces of RACH configuration information

[0424] >Optionally, the RACH configuration information allocated by each of the other candidate cells (represented by a cell ID or NR CGI) which accepted the LTM configuration request to a current candidate NG-RAN node or to each candidate gNB-DU (indicated through a gNB-DU ID) under a current candidate gNB-CU is included. The RACH configuration information may include one or more of the following information:

[0425] >>Candidate Cell ID (represented by a cell ID or NR CGI)

[0426] >>RACH Configuration Information (included in an EarlyUL-SyncConfig IE defined in TS 38.331, and representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs or LTM gNBs, the different parts of the PRACH resources being represented using the following LTM gNB-DUs list or LTM gNBs List information)

[0427] >>LTM gNB-DUs list (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0428] >>>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0429] >>>LTM gNB ID (indicated by a global gNB ID, and used to represent the gNB information associated with the gNB-DU indicated by the gNB-DU ID)

[0430] >>>Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB-DU ID)

[0431] >>LTM gNBs List (including one or more LTM gNB IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0432] >>>LTM gNB ID (indicated by a global gNB ID)

[0433] >>>Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB ID)

[0434] -LTM Cells to be Released List (LTM Cells to be Released List, including the information on a plurality of to-be-released cells, where a to-be-released cell or an LTM candidate cell that is not accepted by other candidate NG-RAN nodes or candidate gNB-CUs is indicated through a Cell ID)

[0435] -LTM Cell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released cell)

[0436] -To-be-released LTM NG-RAN Node List (LTM NG-RAN nodes to be Released List, including the information on a plurality of to-be-released NG-RAN nodes, where a to-be-released NG-RAN node (gNB or ng-eNB) is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID)). If a rejection (e.g., procedure 506-2, and procedure 505-2) occurs in the previous request procedure for all candidate cells on this candidate NG-RAN node, this candidate NG-RAN node is excluded from the candidate node list. Therefore, the RACH configuration previously allocated to this candidate NG-RAN node by other candidate cells and the source cell needs to be released.

[0437] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., global gNB ID or global ng-eNB ID), and indicating a to-be-released candidate NG-RAN node (gNB or ng-eNB))

[0438] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, including the information on to-be-released gNB-DUs, where a to-be-released gNB-DU may be indicated through a gNB-DU ID which may indicate the NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs). It is assumed that the RACH configuration of the candidate PSCell is allocated based on the SN gNB-DU. If a rejection (e.g., procedure 505-2) occurs in the previous request procedure for all candidate cells on this candidate gNB-DU, that is, this candidate gNB-DU is excluded from the candidate node list, the RACH configuration previously allocated to this candidate gNB-DU by other candidate cells and the source cell needs to be released.

[0439] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a to-be-released gNB-DU)

[0440] -Mapping ID / Index / Identifier List of To-be-released LTM NG-RAN Node or gNB-DU. If the source gNB-CU or source NG-RAN node requests, by making each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU correspond to a certain mapping ID / index / identifier, the candidate cell to allocate a PRACH resource, the source gNB-CU or source NG-RAN node may notify the candidate gNB-CU or candidate NG-RAN node of a to-be-released mapping ID / index / identifier list, to indicate that the candidate gNB-CU or candidate NG-RAN node releases the PRACH resource allocated by the candidate cell to the candidate NG-RAN node or candidate gNB-DU corresponding to this LTM NG-RAN node or gNB-DU mapping ID / index / identifier.

[0441] >Mapping ID / Index / Identifier of LTM NG-RAN Node or gNB-DU (LTM NG-RAN node / gNB-DU Mapping ID / Index / identifier, correposnding to a to-be-released NG-RAN node or gNB-DU)

[0442] Procedure 511: Similar to procedure 507, if the candidate NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the candidate gNB-CU may continue to allocate the corresponding RACH configuration to the candidate gNB-DU based on the implementation of the RACH configuration allocated by each of the other candidate cells to this NG-RAN node. For example, if there is only one candidate gNB-DU under the candidate gNB-CU, then all the NG-RAN node-based RACH configurations can be allocated to this gNB-DU. If there are different candidate gNB-DUs under the candidate gNB-CU, then different subsets of the NG-RAN node-based RACH configurations can be allocated to the 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.

[0443] Procedure 512: The candidate gNB-CU transmits a UE Context Modification Request message to the candidate gNB-DU. Here, the message includes one or more of the following information:

[0444] -Candidate Cell ID (a Cell ID or NR CGI)

[0445] -LTM Configuration ID of Candidate Cell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0446] -Updated LTM Configuration ID Mapping List (including the mapping relationship between each LTM Cell ID and its corresponding LTM configuration ID)

[0447] -Updated LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0448] -Collected CSI Report Configuration and TCI States Configurations List of Target Candidate Cell which accepted LTM Configuration Request in Other Candidate NG-RAN Node, SSB Configuration and NR PCI Information of Candidate Cell

[0449] -LTM Reference Configuration (a reference configuration of a low layer portion, including a CellGroupConfig IE defined in TS 38.331)

[0450] -Early Synchronization (Sync) Information List, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) allocated by each candidate cell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0451] -TA Assistance Information, indicating that the TA value of the candidate cell is 0

[0452] -RACH Configuration List (i.e., early uplink synchronization configuration information), which optionally includes a subset or complete set of the RACH configuration information allocated by each candidate cell (a Cell ID or NR CGI) to the NG-RAN node to which the candidate cell belongs, or includes the RACH configuration information allocated by each candidate cell to the gNB-DU to which the candidate cell belongs, and which may include one or more of the following information:

[0453] >Candidate Cell ID (represented by a Cell ID or NR CGI)

[0454] >RACH Configuration Information (included in an EarlyUL-SyncConfig IE defined in TS 38.331, and representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs, the different parts of the PRACH resources being represented using the following LTM gNB-DUs list information)

[0455] >LTM gNB-DUs list (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0456] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0457] >>LTM gNB ID (indicated by a global gNB ID, and used to represent the gNB information associated with the gNB-DU indicated by the gNB-DU ID)

[0458] >>Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB-DU ID)

[0459] -LTM Cells to be Released List (LTM Cells to be Released List, including the information on a plurality of to-be-released cells, where a to-be-released cell or an LTM candidate cell that is not accepted by other candidate NG-RAN nodes or candidate gNB-CUs is indicated through a Cell ID)

[0460] >LTM Cell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released cell)

[0461] -To-be-released LTM NG-RAN Node List (LTM NG-RAN nodes to be Released List, including the information on a plurality of to-be-released NG-RAN nodes, where a to-be-released NG-RAN node (gNB or ng-eNB) is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID)). Assuming that the RACH configuration of the candidate cell is allocated based on the NG-RAN node, and optionally, a to-be-released LTM NG-RAN node list is received in procedure 510, an LTM Cells to be Released List is received in procedure 510, or an 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 by the candidate cell configured on this gNB-DU needs to be released.

[0462] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), indicating a to-be-released NG-RAN node (gNB or ng-eNB), and used to indicate that the RACH configuration previously allocated to this candidate NG-RAN node by the candidate cell configured on the candidate gNB-DU needs to be released)

[0463] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, including the information on to-be-released LTM gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID which may indicate the NG-RAN node (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs). It is assumed that the RACH configuration of the candidate cell is allocated based on the gNB-DU, and the to-be-released gNB-DUs list is received in the above procedure 510.

[0464] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a to-be-released gNB-DU)

[0465] -Mapping ID / Index / Identifier List of To-be-released LTM NG-RAN Node or gNB-DU (if the candidate gNB-CU or candidate NG-RAN node receives the mapping ID / index / identifier list of a to-be-released LTM NG-RAN node or gNB-DU 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 that the PRACH resource allocated to the candidate NG-RAN node or candidate gNB-DU corresponding to the mapping ID / index / identifier is to be released)

[0466] >Mapping ID / Index / Identifier of LTM NG-RAN Node or gNB-DU (LTM NG-RAN node / gNB-DU Mapping ID / Index / identifier, corresponding to a to-be-released NG-RAN node or gNB-DU)

[0467] After the candidate gNB-DU receives the to-be-released NG-RAN node ID (i.e. global gNB ID or global ng-eNB ID) or gNB-DU ID, or receives the mapping ID / index / identifier information on the to-be-released NG-RAN node or gNB-DU, the RACH configuration allocated to this NG-RAN node ID or gNB-DU ID or the mapping ID / index / identifier by the candidate cell on the candidate gNB-DU needs to be released.

[0468] Procedure 513: The candidate gNB-DU transmits a UE Context Modification Response message as a response, including the updated lower-layer configuration of the candidate cell. The response transmited by the candidate gNB-DU may further include the updated CSI report configuration.

[0469] Procedure 514: For the candidate cell, the candidate gNB or candidate gNB-CU responses with a Handover Request Acknowledge message to the source gNB or the source gNB-CU. Optionally, a new Xnap message (e.g., an LTM configuration Modification Request Acknowledge message, an LTM Modification Request Acknowledge message or a Handover Modification Request Acknowledge message) may be defined, which includes the updated LTM configuration of the candidate cell and may further include the updated CSI report configuration.

[0470] Procedure 515: For other candidate NG-RAN nodes, procedures similar to procedures 510-514 also occur. The source NG-RAN node or source gNB-CU transfers the relevant LTM configuration information and possible updates of the LTM configuration information to the other candidate NG-RAN nodes or candidate gNB-CUs.

[0471] FIG. 5a shows an exemplary LTM cell release procedure 500. Here, when the candidate cell of the gNB-DU2 needs to be released, the gNB-DU2 transmits a UE Context Modification Required message or UE Context Release Request message to the gNB-CU2 in procedure 551, carrying an LTM Cells to be Released List. Optionally, the candidate gNB-CU2 initiates an LTM cell release procedure or LTM gNB-DU release procedure by using the UE Context Modification Request message or a UE Context Release Command message. Optionally, all LTM candidate cells on the candidate gNB-CU2 are released. The candidate gNB-CU2 may then transmit a Conditional Handover Cancel message or a newly defined Xnap message (e.g., an LTM Cancel message, and an LTM Configuration Cancel message) to the source gNB-CU0 in procedure 553, carrying an LTM Cells to be Released List and / or a to-be-released LTM gNB-DUs list. The message may include one or more of the following information:

[0472] -LTM Cells to be Released List (LTM Cells to be Released List)

[0473] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0474] >>LTM Cell ID (indicated by a Cell ID or NR CGI)

[0475] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0476] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0477] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0478] Based on the received Conditional Handover Cancel message or newly defined Xnap message, the source gNB-CU0 can determine whether all cells in the candidate gNB-CU2 or candidate NG-RAN node are released, or all cells under a certain gNB-DU are released. When all or some of the cells in the candidate gNB-CU2 or candidate NG-RAN node or all or some of the cells under the certain gNB-DU are released, the source gNB-CU0 transmits a UE Context Modification Request message to the source gNB-DU in procedure 555. The UE Context Modification Request message may include one or more of the following information:

[0479] -LTM Cells to be Released List (LTM Cells to be Released List)

[0480] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0481] >>LTM Cell ID (indicated by a Cell ID or NR CGI)

[0482] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0483] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0484] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0485] >>LTM gNB ID (indicating a gNB to which the associated LTM gNB-DU belongs, and indicated by a global gNB ID)

[0486] -To-be-released LTM gNBs List (LTM gNBs to be Released List, indicating that the RACH configuration for the gNB node corresponding to a gNB ID is to be released)

[0487] >To-be-released LTM gNB Item IEs (LTM gNBs to be Released Item IEs)

[0488] >>LTM gNB ID (indicated by a global gNB ID)

[0489] -To-be-released RACH Configuration List (indicating that the RACH configuration for the corresponding global gNB ID or gNB-DU ID is to be released)

[0490] >To-be-released RACH Configuration Item IEs (RACH Configuration to be Released Item IEs)

[0491] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0492] >>LTM gNB ID (indicating a released gNB node or a gNB node to which the associated LTM gNB-DU belongs, and indicated by a global gNB ID)

[0493] -Mapping ID / Index / Identifier List of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released List, if the RACH configuration for the candidate cell is allocated based on the mapping ID / index / identifier corresponding to each gNB-DU and provided by the gNB-CU, this IE may indicate that the PRACH resources of the candidate gNB-DU corresponding to this mapping ID / index / identifier need to be released)

[0494] >Mapping ID / Index / Identifier Item IEs of To-be-released LTM gNB-DU (LTM gNB-DU Mapping IDs / Indexs / identifier to be Released Item IEs)

[0495] >>Mapping ID / Index / Identifier of LTM gNB-DU (LTM gNB-DU Mapping ID / Index / identifier)

[0496] After the source gNB-DU receives these information, if the RACH configuration of the candidate cell is allocated based on the gNB-CU or NG-RAN node (gNB or ng-eNB), the candidate cell on the source gNB-DU needs to perform a release operation on the RACH configuration (i.e., PRACH resources, e.g., a preamble index list) previously allocated to 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 perform a release operation on the RACH configuration (i.e., PRACH resources, e.g., a preamble index list) previously allocated to the gNB-DU ID and the gNB-DU node under the gNB indicated by the global gNB ID. After receiving the released LTM cell information, the source gNB-DU also performs a release operation on the RACH configuration previously allocated to the source gNB-DU by these LTM cells. Then, in procedure 556, the source gNB-DU transmits a UE Context Modification Response message to the source gNB-CU.

[0497] For the release of an LTM candidate cell, candidate gNB-DU or candidate gNB, after obtaining these information, the source gNB or source gNB-CU needs to notify other candidate gNBs or candidate gNB-CUs to update the configuration. In procedure 557, the source gNB or source gNB-CU transmits a Handover Cancel message or a newly defined Xnap message (e.g., an LTM Cancel message, and an LTM Configuration Cancel message) to the candidate gNB-CU1. The message may carry an LTM Cells to be Released List, a to-be-released LTM NG-RAN node list and / or a to-be-released LTM gNB-DUs list. The message may include one or more of the following information:

[0498] -LTM Cells to be Released List (LTM Cells to be Released List)

[0499] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0500] >>LTM Cell ID (indicated by a Cell ID or NR CGI)

[0501] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0502] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0503] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0504] >>LTM gNB ID (indicating a gNB to which the associated LTM gNB-DU belongs, and indicated by a global gNB ID)

[0505] -To-be-released LTM gNBs List (LTM gNBs to be Released List, indicating that the RACH configuration for the gNB node corresponding to a gNB ID is to be released)

[0506] >To-be-released LTM gNB Item IEs (LTM gNBs to be Released Item IEs)

[0507] >>LTM gNB ID (indicated by a global gNB ID)

[0508] Based on the received Handover Cancel message or newly defined Xnap message (e.g., the LTM Cancel message, and the LTM Configuration Cancel message), the candidate gNB-CU1 transmits a UE Context Modification Request message to the candidate gNB-DU1 in procedure 558. The message includes one or more of the following information:

[0509] -LTM Cells to be Released List (LTM Cells to be Released List)

[0510] >To-be-released LTM Cell Item IEs (LTM Cells to be Released Item IEs)

[0511] >>LTM Cell ID (indicated by a Cell ID or NR CGI)

[0512] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, indicating that the RACH configuration for the corresponding gNB-DU ID is to be released)

[0513] >To-be-released LTM gNB-DU Item IEs (LTM gNB-DUs to be Released Item IEs)

[0514] >>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0515] >>LTM gNB ID (indicating a gNB to which the associated LTM gNB-DU belongs, and indicated by a global gNB ID)

[0516] -To-be-released LTM gNBs List (LTM gNBs to be Released List, indicating that the RACH configuration for the gNB node corresponding to a gNB ID is to be released)

[0517] >To-be-released LTM gNB Item IEs (LTM gNBs to be Released Item IEs)

[0518] >>LTM gNB ID (indicated by a global gNB ID)

[0519] Similarly, after the candidate gNB-DU receives these information, if the RACH configuration of the candidate cell is allocated based on the gNB-CU or NG-RAN node (gNB or ng-eNB), the candidate cell on the candidate gNB-DU needs to perform a release operation on the RACH configuration (i.e., PRACH resources, e.g., a preamble index list) previously allocated to 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 perform a release operation on the RACH configuration (i.e., PRACH resources, e.g., a preamble index list) previously allocated to the gNB-DU ID and the gNB-DU node under the gNB indicated by the global gNB ID. After receiving the released LTM cell information, the candidate gNB-DU also performs a release operation on the RACH configuration previously allocated to the candidate gNB-DU by these LTM cells, and then replies to the candidate gNB-CU. The candidate gNB-CU receives a UE Context Modification Response message from the candidate gNB-DU1 in procedure 559.

[0520] Optionally, the gNB-CU2 may further transmit a UE Context Release Command message (carrying an LTM Cells to be Released List) to the gNB-DU2, to instruct the gNB-DU2 to release the RACH configuration of a to-be-released LTM cell. After completing the release, the gNB-DU2 transmits a UE Context Release Complete message in procedure 561.

[0521] Procedure 516: The RRC Reconfiguration procedure of the UE is required to be performed after the LTM-related configuration is completed on the network side. The source gNB-CU transmits a downlink (DL) RRC Message Transfer message to the source gNB-DU, the message including a generated RRC Reconfiguration message with an LTM configuration.

[0522] Procedure 517: The source gNB-DU forwards the received RRC Reconfiguration message to the UE.

[0523] Procedure 518: The UE transmits an RRC Reconfiguration Complete message to the source gNB-DU.

[0524] Procedure 519: The source gNB-DU forwards the RRC Reconfiguration Complete message to the gNB-CU through an uplink (UL) RRC Message Transfer message. Next, optionally, the source gNB may trigger early data forwarding to another candidate gNB.

[0525] Procedure 520: Early synchronization is performed to obtain an early timing advance (TA) value. This procedure includes a procedure that the UE transmits, after receiving a PDCCH order instruction transmited by the gNB-DU currently serving the UE, a first Random Access Request message to the candidate cell using a random access resource configuration indicated in the instruction. Here, the random access resource configuration indicated in the instruction is indicated by, for example, a random access preamble index, a synchronization signal / PBCH block index (SSB index), and a PRACH occasion mask index. After receiving the first Random Access Request message, the candidate cell calculates a timing advance (TA) value between the UE and the candidate cell.

[0526] Procedure 521: The candidate gNB-DU transmits the TA value and associated information to the candidate gNB-CU through a non-UE-associated DU-CU TA Information Transfer message, which includes one or more of the following information:

[0527] -TA Information List (the same UE may have different TA values for different candidate cells, and different UEs may have different TA values for the same candidate cell)

[0528] -Candidate Cell ID (a Cell ID or NR CGI)

[0529] -TA Value

[0530] -Preamble Index

[0531] -Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0532] -Source NG-RAN Node ID Information (represented by a global NG-RAN node ID (i.e. a global gNB ID or global ng-eNB ID)). Accordingly, the candidate gNB-DU can determine, through the PRACH resource (e.g. the preamble index) transmited by the UE, which NG-RAN node (gNB or ng-eNB) the UE is currently under. Since the allocation of PRACH resources by the candidate cell is based on the NG-RAN node, different PRACH resources are allocated to different NG-RAN node IDs. This information is carried to indicate that the candidate gNB-CU continues to forward the TA-related information to the indicated NG-RAN node.

[0533] -Source gNB-DU ID Information (represented by a gNB-DU ID and indicating the NG-RAN node ID (indicated through a global NG-RAN node ID (i.e. global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs). Accordingly, the candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which gNB-DU under which NG-RAN node the UE is currently under. Since the allocation of PRACH resources by the candidate cell is based on the gNB-DU, different PRACH resources are allocated to different gNB-DU IDs. This information is carried to indicate that the candidate gNB-CU continues to forward the TA-related information to the indicated NG-RAN node, and then forward the TA-related information to the indicated gNB-DU.

[0534] -Mapping ID / Index / Identifier Information of LTM NG-RAN node or gNB-DU, mapped to the source NG-RAN node ID or source gNB-DU. If the candidate gNB-DU allocates a PRACH resource to the mapping ID / index / identifier, the candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which mapping ID / index / identifier it is.

[0535] -Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a source gNB or source gNB-DU. In this case, when the LTM is triggered, the source gNB or source gNB-DU selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0536] Procedure 522: The candidate NG-RAN node or candidate gNB-CU then forwards the TA-related information to the corresponding source NG-RAN node (source gNB or source ng-eNB) or source gNB-CU through a newly defined Xnap message (e.g., TA INFORMATION TRANSFER) that is not associated with the UE (optionally, the candidate gNB-CU can determine, through the LTM NG-RAN node mapping ID, index or information, which NG-RAN node or gNB-CU the LTM NG-RAN node mapping ID, index or information corresponds to), which includes one or more of the following information:

[0537] -TA Information List (the same UE may have different TA values for different candidate cells, and different UEs may have different TA values for the same candidate cell)

[0538] -Candidate Cell ID (a Cell ID or NR CGI)

[0539] -TA Value

[0540] -Preamble Index

[0541] -Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0542] -Source gNB-DU ID Information (represented by a gNB-DU ID). Accordingly, the candidate gNB-DU can determine, through the PRACH resource (e.g., preamble index) transmited by the UE, which gNB-DU under which NG-RAN node (gNB or ng-eNB) the UE is currently under. Since the allocation of PRACH resources by the candidate cell is based on the gNB-DU, different PRACH resources are allocated to different gNB-DU IDs. This information is carried to indicate that the sourcegNB-CU continues to forward the TA-related information to the indicated source gNB-DU.

[0543] -Mapping ID / Index / Identifier Information of LTM gNB-DU, mapped to the source gNB-DU. If the candidate gNB-DU allocates a PRACH resource to the mapping ID / index / identifier, the candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which mapping ID / index / identifier it is.

[0544] -Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a source gNB or source gNB-DU. In this case, when the LTM is triggered, the source gNB or source gNB-DU selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0545] Procedure 523: After the source gNB-CU receives the relevant TA information, based on the implementation in procedure 507, the source gNB-CU continues to allocate the corresponding RACH configuration to the source gNB-DU based on the implementation of the RACH configuration allocated to this NG-RAN node by each candidate cell. The source gNB-CU can determine which source gNB-DU the source gNB-CU needs to forward the TA information to through the TA-associated information (different UEs under different source gNB-DUs under the source NG-RAN node may initiate an LTM configuration to the same candidate cell). Optionally, if the source gNB-CU receives the indicated source gNB-DU ID information or the mapping ID / index / identifier information of the LTM gNB-DU in procedure 522, the source gNB-CU continues to forward the relevant TA information to the corresponding source gNB-DU.

[0546] Procedure 524: The source gNB-CU transmits the TA value information, associated CFRA resource information (preamble index and RA-RNTI), a candidate Cell ID and a timing advance group identity pointer (Tag ID Pointer) to the corresponding source gNB-DU through a non-UE-associated CU-DU TA Information Transfer message.

[0547] Procedure 525: The UE transmits a layer 1 measurement report to the source gNB-DU.

[0548] Procedure 526: The source gNB-DU decides to perform LTM cell switch on a candidate target cell.

[0549] Procedure 527: The source gNB-DU transmits a Cell Switch Command to the UE.

[0550] Procedure 528: The source gNB-DU transmits a DU-CU Cell Switch Notification message to the gNB-CU, indicating that the Cell Switch Command is initiated to the UE. The DU-CU Cell Switch Notification message includes a target Cell ID and / or a TCI state ID (including a joint or downlink TCI state ID, and an uplink TCI state ID), and includes a TA information list (including valid TA values of one or more candidate cells, a timing advance group identity pointer (TAG ID Pointer), as well as possible valid time information, and transferred by the source gNB-DU through the source gNB-CU and the target gNB-CU to the target gNB-DU for use). Next, the source gNB may optionally trigger the late data forwarding to the target gNB.

[0551] Procedure 529: The source NG-RAN node or source gNB-CU forwards an LTM Cell Switch Notification to the target NG-RAN node or target gNB-CU (the NG-RAN node or gNB-CU to which the target cell belongs) through an existing or newly defined Xnap message (e.g., LTM CELL SWITCH NOTIFICATION), the notification including one or more of the following information:

[0552] -Target Cell ID (represented by a Cell ID or NR CGI)

[0553] -TCI State ID (corresponding to a CandidateTCI-StatesId IE defined in TS 38.331)

[0554] -LTM Cell Switch Information

[0555] >Joint or Downlink (DL) TCI State ID (corresponding to a TCI-StateId IE defined in TS 38.331)

[0556] >Uplink (UL) TCI State ID (corresponding to a TCI-UL-StateId IE defined in TS 38.331)

[0557] -TA Information List (including one or more candidate Cell IDs and corresponding valid TA values, as well as possible valid time information)

[0558] >Candidate Cell ID (represented by a Cell ID or NR CGI)

[0559] >TA Value (indicating the valid TA value of a candidate cell, and transferred to a target gNB or target gNB-DU for use)

[0560] >Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a new source gNB-DU (after a candidate gNB-DU is accessed by the UE, the candidate gNB-DU is the source gNB-DU for the subsequent LTM). In this case, when the LTM is triggered, the source gNB-DU selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0561] >TA Value Validation Time (TA valid timer)

[0562] Procedure 530: The target gNB-CU transmits a target Cell ID and / or a TCI state ID (including a joint or downlink TCI state ID, and an uplink TCI state ID) and a TA information list (including valid TA values of one or more candidate cells, a timing advance group identity pointer (TAG ID Pointer), as well as possible valid time information) to the target gNB-DU through a CU-DU Cell Switch Notification.

[0563] Procedure 531: The target gNB-DU detects the successful access of the UE (rach-less-based or rach-based access procedure).

[0564] Procedure 532: The target gNB-DU transmits an Access Success message (carrying a target Cell ID) to the gNB-CU.

[0565] Procedure 533: The UE transmits an RRC Reconfiguration Complete (RRCReconfigurationComplete) message to the target gNB-DU.

[0566] Procedure 534: The target gNB-DU forwards the RRC Reconfiguration Complete message to the gNB-CU through an uplink (UL) RRC Message Transfer message.

[0567] Procedure 535: The target gNB-CU transmits a Handover Success message (carrying the target Cell ID) to the source gNB-CU. Next, the source gNB may optionally trigger the late data forwarding to the target gNB. The target gNB may perform early data forwarding to other candidate gNBs after completing a path switching procedure with a core network .

[0568] For the subsequent LTM procedure, optionally, the source NG-RAN node or source gNB-CU transmits the Handover Success message (carrying the target Cell ID (represented by a Cell ID or NR CGI)) to other candidate gNB-CUs or other candidate NG-RAN nodes, to notify the other candidate gNB-CUs or the other candidate NG-RAN nodes of the information on the target cell to which the UE accesses through LTM. According to the target Cell ID information, the candidate gNB-CU or candidate NG-RAN node can determine the target NG-RAN node, that is, the NG-RAN node currently serving the UE.

[0569] Procedure 536: For the subsequent LTM procedure, when the UE accesses the target cell, the target cell becomes the source cell serving the UE for the next LTM procedure, and other candidate cells and the source cell previously serving the UE all become candidate cells. Similar procedures 520-536 may occur partially or completely in a loop in each LTM procedure.

[0570] If only one-time LTM procedure is supported, procedures 536-537 will not occur. After receiving the Handover Success message, the source NG-RAN node or source gNB-CU will notify, through a Handover Cancel Xnap message or a newly defined Xnap message (e.g., an LTM Cancel message, and an LTM Configuration Cancel message), the other candidate NG-RAN nodes or candidate gNB-CUs to release the resources of another prepared LTM candidate cell and the context of the UE, and the source NG-RAN node or source gNB-CU releases the resources of the source cell and the context of the UE.

[0571] For the configuration of an LTM candidate cell, after or before the RRC Reconfiguration for the UE is completed, the release of the configured LTM candidate cell may occur, and accordingly, the RACH configuration allocated by the candidate cells also needs to be released. If all candidate cells on the candidate gNB-DU or candidate NG-RAN node are released, and accordingly, the RACH configuration allocated by another candidate cell to this candidate gNB-DU or candidate NG-RAN node needs to be released. This situation is described below.

[0572] In the LTM cell release procedure shown in FIG. 5a, if the candidate gNB-DU triggers the candidate cell release procedure, the candidate gNB-DU will notify, by using the UE Context Modification Required message or UE Context Release Request message carrying the LTM Cells to be Released List, the candidate gNB-CU of which LTM candidate cell is released. If the candidate gNB-CU triggers the candidate cell release procedure, the candidate gNB-CU will notify, through the UE Context Modification Request message or UE Context Release Command message carrying the LTM Cells to be Released List, the candidate gNB-DU of which LTM candidate cell is released. Then, the candidate gNB-CU or the candidate NG-RAN node needs to forward the LTM Cells to be Released List infomraiton to the source gNB-CU or the source NG-RAN node through the Xnap message. Optionally, consider enhancing the Conditional Handover Cancel message or the newly defined Xnap message (e.g., the LTM Cancel message, and the LTM Configuration Cancel message). The Xnap message carries one or more of the following information:

[0573] -LTM Cells to be Released List (LTM Cells to be Released List, including the information on a plurality of to-be-released cells, where a to-be-released cell is indicated through a Cell ID)

[0574] -LTM Cell ID (represented by a Cell ID or NR CGI, indicating a to-be-released cell)

[0575] -To-be-released LTM NG-RAN (gNB or ng-eNB) List (LTM NG-RAN nodes (gNBs or ng-eNBs) to be Released List, including the information on to-be-released NG-RAN nodes (gNBs or ng-eNBs), where a to-be-released NG-RAN node (gNB or ng-eNB) is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID))

[0576] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released NG-RAN node (gNB or ng-eNB))

[0577] -To-be-released LTM gNB-DUs list (LTM gNB-DUs to be Released List, including the information on to-be-released LTM gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID which may optionally indicate the NG-RAN node ID (represented by the global NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID)) to which the gNB-DU ID belongs)

[0578] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a to-be-released gNB-DU)

[0579] -Mapping ID / Index / Identifier List of To-be-released LTM NG-RAN Node / gNB-DU (if the source gNB-CU or source NG-RAN node requests, by making each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU correspond to a certain mapping ID / index / identifier, the candidate cell to allocate a PRACH resource, the source gNB-CU or source NG-RAN node may notify the candidate gNB-CU or candidate NG-RAN node of a to-be-released LTM NG-RAN node / gNB-DU mapping ID / index / identifier list, to indicate that the candidate gNB-CU or candidate NG-RAN node releases the PRACH resource allocated by the candidate cell to the candidate NG-RAN node or candidate gNB-DU corresponding to the mapping ID / index / identifier)

[0580] >Mapping ID / Index / Identifier of LTM NG-RAN Node / gNB-DU (LTM NG-RAN node / gNB-DU Mapping ID / Index / identifier, correposnding to a to-be-released LTM NG-RAN node / gNB-DU)

[0581] In an embodiment, optionally, if the LTM Cells to be Released List IE is included in the Conditional Handover / LTM Cancel message, the source NG-RAN node should consider releasing only the resource reserved by the cell identified by the included NG-RAN CGI or NR CGI.

[0582] After receiving the LTM Cells to be Released List information transmited by the candidate gNB-CU or candidate NG-RAN node, the source gNB-CU or source NG-RAN node can determine whether all candidate cells on the candidate gNB-CU or candidate NG-RAN node are released, or all candidate cells on a certain candidate gNB-DU are released. Optionally, the source gNB-DU is notified through a UE Context Modification Request message, which carries one or more of the following information:

[0583] -LTM Cells to be Released List (LTM Cells to be Released List, including the information on one or more to-be-released cells, where a to-be-released cell is indicated through a Cell ID)

[0584] >LTM Cell ID (represented by a Cell ID or NR CGI, indicating a to-be-released cell)

[0585] -To-be-released LTM NG-RAN Node (gNB or ng-eNB) List (LTM NG-RAN nodes (gNBs or ng-eNBs) to be Released List, including the information on one or more to-be-released NG-RAN nodes (gNBs or ng-eNBs), where a to-be-released NG-RAN node (gNB or ng-eNB) is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID))

[0586] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released NG-RAN node (gNB or ng-eNB))

[0587] -To-be-released LTM gNB-DU List (LTM gNB-DUs to be Released List, including the information on to-be-released LTM gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID, indicating the NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs)

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

[0589] -To-be-released LTM Mapping ID / Index / Identifier List (if the source gNB-CU or source NG-RAN node requests, by making each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU correspond to a certain mapping ID / index / identifier and by transmitting a list including the mapping ID, index or identifier to the candidate NG-RAN node or the candidate gNB-CU, the candidate cell to allocate a PRACH resource to each mapping ID, index or identifier, the source gNB-CU only needs to indicate the mapping ID / index / identifier corresponding to a to-be-released candidate NG-RAN node or candidate gNB-DU)

[0590] >Mapping ID / Index / Identifier of LTM NG-RAN Node or gNB-DU (LTM NG-RAN node / gNB-DU Mapping ID / Index / identifier, correposnding to a to-be-released NG-RAN node / gNB-DU)

[0591] After the source gNB-DU receives the to-be-released NG-RAN node ID and / or gNB-DU ID (or the corresponding mapping ID / index / identifier) or LTM Cell ID, the RACH configuration allocated by the source cell or other candidate cells on the source gNB-DU to this NG-RAN node ID (i.e. global gNB ID or global ng-eNB ID), or gNB-DU ID, or the corresponding mapping ID / index / identifier needs to be released. The RACH configuration allocated to the released LTM cell also needs to be released.

[0592] After receiving the LTM Cells to be Released List information transmited by the candidate gNB-CU or candidate NG-RAN node, the source gNB-CU or source NG-RAN node can optionally determine whether all candidate cells on the candidate gNB-CU or candidate NG-RAN node are released, or all candidate cells on a certain candidate gNB-DU are released. Optionally, the source gNB-CU or source NG-RAN node receives the to-be-released NG-RAN node / gNB-DU list information transmited by the candidate gNB-CU or candidate NG-RAN node. The source gNB-CU or the source NG-RAN node needs to forward the LTM Cells to be Released List infomraiton and other information to the other candidate gNB-CU or candidate NG-RAN node through the Xnap message. Optionally, it is possible to consider enhancing the Handover Cancel message or the newly defined Xnap message (e.g., the LTM Cancel message, and the LTM Configuration Cancel message). The Xnap message carries one or more of the following information:

[0593] -LTM Cells to be Released List (LTM Cells to be Released List, including the information on one or more to-be-released cells, where a to-be-released cell is indicated through a Cell ID)

[0594] >LTM Cell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released cell)

[0595] -To-be-released LTM NG-RAN Node (gNB or ng-eNB) List (LTM NG-RAN nodes (gNBs or ng-eNBs) to be Released List, including the information on one or more to-be-released NG-RAN nodes (gNBs or ng-eNBs), where a to-be-released NG-RAN node (gNB or ng-eNB) is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID))

[0596] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released NG-RAN node (gNB or ng-eNB))

[0597] -To-be-released LTM gNB-DU List (LTM gNB-DUs to be Released List, including the information on to-be-released LTM gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID, indicating the NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs)

[0598] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a to-be-released gNB-DU)

[0599] -Mapping ID / Index / Identifier List of To-be-released LTM NG-RAN Node / gNB-DU (if the source gNB-CU or source NG-RAN node requests, by making each candidate NG-RAN node (including the source NG-RAN node) or each candidate gNB-DU correspond to a certain mapping ID / index / identifier, the candidate cell to allocate a PRACH resource, the source gNB-CU or source NG-RAN node may notify the candidate gNB-CU or candidate NG-RAN node of a to-be-released LTM mapping ID / index / identifier list, to indicate that the candidate gNB-CU or candidate NG-RAN node releases the PRACH resource allocated by the candidate cell to the candidate NG-RAN node or candidate gNB-DU corresponding to the mapping ID / index / identifier)

[0600] >Mapping ID / Index / Identifier of LTM NG-RAN Node / gNB-DU (LTM NG-RAN node / gNB-DU Mapping ID / Index / identifier, correposnding to a to-be-released LTM NG-RAN node / gNB-DU)

[0601] In an embodiment, optionally, if the LTM Cells to be Released List IE is included in the Handover Cancel message, the target NG-RAN node should consider that the source NG-RAN node cancels only the handover associated with the candidate cell identified by the NG-RAN CGI or NR CGI included therein, and cancel a UE associated signaling connection identified by a source NG-RAN node UE XnAP ID IE, which may also be identified by a target NG-RAN node UE XnAP ID IE if included.

[0602] In an embodiment, optionally, if the LTM NG-RAN nodes to be Released List IE is included in the Handover Cancel message, the target NG-RAN node should release, if supported, the RACH configuration allocated by the configured LTM candidate cell to the indicated NG-RAN node ID (represented by the global NG-RAN node ID, and included in the LTM NG-RAN nodes to be Released List IE).

[0603] In an embodiment, optionally, if the LTM gNB-DUs to be Released List IE is included in the Handover Cancel message, the target NG-RAN node should release, if supported, the RACH configuration allocated by the configured candidate cell to the indicated gNB-DU ID (included in the LTM gNB-DUs to be Released List IE).

[0604] After receiving the LTM Cells to be Released List information transmited by the source gNB-CU or source NG-RAN node, the candidate gNB-CU or candidate NG-RAN node can optionally determine whether all candidate cells on a certain NG-RAN node are released, and can optionally determine whether all candidate cells on a gNB-DU on a certain NG-RAN node are released. Since two gNB-CUs or NG-RAN nodes can know the information on a cell and neighbour cell at each node through the Xn Setup procedure or the NG-RAN Configuration Update procedure, and can determine, according to the configured LTM candidate cell list, which candidate cell which NG-RAN node is configured with; or can perform the determination through the to-be-released LTM NG-RAN node list, the to-be-released LTM gNB-DU list or the corresponding to-be-released LTM mapping ID / index / identifier list information transmited by the source NG-RAN node or source gNB-CU. Optionally, the candidate gNB-CU then notifies the candidate gNB-DU through a UE Context Modification Request message. The message may carry one or more of the following information:

[0605] -LTM Cells to be Released List (LTM Cells to be Released List, including the information on one or more to-be-released cells, where a to-be-released cell is indicated through a Cell ID)

[0606] >LTM Cell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released cell)

[0607] -To-be-released LTM NG-RAN Node (gNB or ng-eNB) List (LTM NG-RAN nodes (gNBs or ng-eNBs) to be Released List, including the information on one or more to-be-released NG-RAN nodes (gNBs or ng-eNBs), where a to-be-released NG-RAN node (gNB or ng-eNB) is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID))

[0608] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released NG-RAN node (gNB or ng-eNB))

[0609] -To-be-released LTM gNB-DU List (LTM gNB-DUs to be Released List, including the information on to-be-released LTM gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID, indicating the NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs)

[0610] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a to-be-released gNB-DU)

[0611] -Mapping ID / Index / Identifier List of To-be-released LTM NG-RAN Node / gNB-DU (if the candidate gNB-CU or candidate NG-RAN node receives a to-be-released LTM NG-RAN Node / gNB-DU mapping ID / index / identifier list 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, to indicate that the PRACH resource of the candidate NG-RAN node or candidate gNB-DU corresponding to the mapping ID / index / identifier is released)

[0612] >Mapping ID / Index / Identifier of LTM NG-RAN Node / gNB-DU (LTM NG-RAN node / gNB-DU Mapping ID / Index / identifier, correposnding to a to-be-released LTM NG-RAN node / gNB-DU)

[0613] After the candidate gNB-DU receives the to-be-released NG-RAN node ID, gNB-DU ID (or the corresponding mapping ID / index / identifier) and / or LTM Cell ID, the RACH configuration allocated by the candidate cell on the candidate gNB-DU to this NG-RAN node ID, or gNB-DU ID, or mapping ID / index / identifier needs to be released. The RACH configuration allocated by the to-be-released LTM cell needs to be released.

[0614] In an embodiment, optionally, if the NG-RAN nodes to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should release, if supported, the RACH configuration allocated by the configured candidate cell to the indicated NG-RAN node ID (represented by the global NG-RAN node ID, and included in the LTM NG-RAN nodes to be Released List IE).

[0615] In an embodiment, optionally, if the gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should release, if supported, the RACH configuration allocated by the configured candidate cell to the indicated gNB-DU ID (included in the LTM gNB-DUs to be Released List IE).

[0616] If the LTM cell release procedure is after an initial RRC reconfiguration of the UE is complete, the RRC reconfiguration of the UE shall be performed again after the corresponding LTM cell release is carried out by the network side.

[0617] In an embodiment, the allocation of different PRACH resources or RACH configuration information by the candidate cell to one or more LTM gNB-DUs or LTM gNBs may refer to that one LTM gNB-DU ID or one LTM gNB ID corresponds to one PRACH resource, one piece of RACH configuration information, or one piece of early uplink synchronization (UL Sync) configuration information, or may refer to that the common configuration information to all LTM gNB-DUs or LTM gNBs in these configuration information is shown separately, and the different configuration information (such as a preamble index list) corresponding to different LTM gNB-DUs or different LTM gNBs is then shown. In short, the idea embodied is that the allocation of different PRACH resources, RACH configuration information or early UL Sync configuration information by the candidate cell to each LTM gNB-DU or LTM gNB is within the scope of protection of the present disclosure.

[0618] In an embodiment, regarding the release of an LTM candidate cell, or the release of all LTM candidate cells on a candidate gNB-DU (i.e., the release of the LTM gNB-DU), and the release of all LTM candidate cells on an NG-RAN node (gNB or ng-eNB), the names of the information transferred (e.g., the 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 another candidate NG-RAN node (gNB or ng-eNB)) and the information transmitted between the gNB-CU and gNB-DU of the gNB as the split architecture in the above embodiments may be:

[0619] -To-be-released or To-be-cancelled LTM Cell List (LTM Cells to be Released List or LTM Cells to be Cancelled List)

[0620] >LTM Cell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released or to-be-cancelled cell)

[0621] -To-be-released or To-be-cancelled LTM NG-RAN Node (gNB or ng-eNB) List (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)

[0622] >LTM NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released or to-be-cancelled NG-RAN node (gNB or ng-eNB))

[0623] -To-be-released or To-be-cancelled LTM gNB-DU List (LTM gNB-DUs to be Released List or LTM gNB-DUs to be Cancelled List)

[0624] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a to-be-released or to-be-cancelled gNB-DU)

[0625] In an embodiment, optionally, if an LTM Information Request IE is included in a Handover Request message, the target NG-RAN node shall consider that the request concerns the LTM of the candidate cell indicated by the included Target Cell Global ID IE and shall include an LTM Information Acknowledge IE in a Handover Request Acknowledge message.

[0626] In an embodiment, optionally, if an LTM Information Modification Request IE is included in a Handover / LTM Modification Request message, the target NG-RAN node shall consider that the request concerns the LTM of the candidate cell indicated by the included Target Cell Global ID IE and shall include an LTM Information Modification Acknowledge IE in a Handover / LTM Modification Request Acknowledge message.

[0627] In an embodiment, optionally, if an 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, if supported, provide the reference configuration for the LTM.

[0628] In an embodiment, optionally, if an LTM Configuration ID Mapping List IE is included in the Handover Request message, the target NG-RAN node shall, if supported, consider this as the mapping information for the LTM candidate cell(s).

[0629] In an embodiment, optionally, if the LTM Configuration ID Mapping List IE is included in the Handover / LTM Modification Request message, the target NG-RAN node shall, if supported, consider this as the mapping information for the LTM candidate cell(s).

[0630] In an embodiment, optionally, if the target NG-RAN node applies a complete configuration to a specific target cell, e.g., as part of the LTM preparation, the source NG-RAN node should be notified by including an LTM Complete Configuration Indicator IE set to “complete” in the LTM Information Acknowledge IE included in the Handover Request Acknowledge message.

[0631] In an embodiment, optionally, if an Early Synchronization (Sync) Information Request IE is included in the Handover Request message, the target NG-RAN node shall, if supported, include an Early UL Synchronization (Sync) Configuration IE for an early TA acquisition and / or an Early UL Synchronization (Sync) Configuration IE for SUL in an Early Synchronization (Sync) Information IE in the Handover Request Acknowledge message.

[0632] In an embodiment, optionally, if the Early Synchronization Information IE is included in the Handover Request Acknowledge message, the source NG-RAN node shall, if supported, consider it as the generated early synchronization information from the accepted candidate cell in the candidate NG-RAN node.

[0633] In an embodiment, optionally, if a 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 an LTM CSI reporting configuration (included in a CellGroupConfig IE, the Handover Command message included in a target NG-RAN node to source NG-RAN node transparent container IE) for the requested LTM candidate cell.

[0634] In an embodiment, optionally, if the CSI resource configuration is included in the LTM Information Modification Request IE in the Handover / LTM Modification Request message, the target NG-RAN node shall, if supported, use it to generate the LTM CSI reporting configuration (included in a CellGroupConfig IE, the Handover Command message included in the target NG-RAN node to source NG-RAN node transparent container IE ) for the requested LTM candidate cell.

[0635] In an embodiment, optionally, if an Early Synchronization Information List IE is included in the Handover / LTM Modification Request message, the target NG-RAN node should use, if supported, the Early Synchronization Information List IE as specified in TS 38.300.

[0636] In an embodiment, optionally, if the LTM Cells to be Released / Cancelled List IE is included in the Handover / LTM Modification Request message, the target NG-RAN node shall, if supported, release the configured candidate cells in the list.

[0637] In an embodiment, optionally, if the LTM gNB-DUs to be Released or Cancelled List IE is included in the Handover / LTM Modification Request message, the target NG-RAN node should release, if supported, the RACH configuration or early uplink synchronization configuration allocated by the LTM candidate cell to the gNB-DU ID (corresponding gNB-DU) indicated in the gNB-DUs to be Released or Cancelled List IE.

[0638] In an embodiment, optionally, if an LTM NG-RAN nodes to be Released or Cancelled List IE is included in the Handover / LTM Modification Request message, the target NG-RAN node should release, if supported, the RACH configuration or early uplink synchronization configuration allocated by the LTM candidate cell to the global NG-RAN node ID (corresponding NG-RAN node) indicated in the LTM NG-RAN nodes to be Released or Cancelled List IE.

[0639] In an embodiment, optionally, if an LTM gNBs to be Released or Cancelled List IE is included in the Handover Modification Request message, the target NG-RAN node should release, if supported, the RACH configuration or early uplink synchronization configuration allocated by the LTM candidate cell to the global gNB ID (corresponding gNB) indicated in the LTM gNBs to be Released or Cancelled List IE.

[0640] FIGS. 6-1 to 6-3 (hereinafter collectively referred to as FIG. 6) are embodiments of an inter-CU (inter-SN) LTM (SN change without MN change) procedure triggered by a source S-NG-RAN node (a source SN or S-SN) or an MN in an NR-DC scenario. That is, a UE performs LTM between different CUs (different SNs), the MN does not change, and the SN changes. Optionally, if an M-NG-RAN node or the S-NG-RAN node is not in a gNB-CU and a gNB-DU split architecture, the corresponding F1 interface message and procedure are not involved in the present disclosure. For the LTM Cell Switch Command triggered by the S-SN (or the gNB-DU of the S-SN), it is required to transmit the configuration information of each LTM PSCell cell (including, but not limited to, a CSI report configuration, a TCI state configuration, an RACH configuration and LTM configuration ID information) 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 a candidate primary secondary cell (PSCell) to the source SN or the gNB-DU of the source SN. For the LTM Cell Switch Command triggered by the MN (or the gNB-DU of the MN), it is required 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).

[0641] The procedures shown in FIG 6 are described below.

[0642] The NG-RAN node (e.g., the M-NG-RAN node (MN) or S-NG-RAN node (SN)) involved in the following description of the procedures may include a gNB or ng-eNB. Moreover, for the NG-RAN node as a split architecture, the NG-RAN node includes a gNB-CU and a gNB-DU. An NG-RAN node ID may be represented by a global NG-RAN node ID, and the global NG-RAN node ID may include a global gNB ID or global ng-eNB ID.

[0643] Procedure 601: For the scenario of inter-SN LTM triggered by the SN, the UE may directly transmit an L3 measurement report of a neighbour PSCell to the source S-NG-RAN node (using the presence of an SRB3). If the source S-NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the UE may transmit an L3 Measurement Report message to the gNB-CU through the source gNB-DU. Optionally, the UE may forward the L3 measurement report of the PSCell to the S-SN through the MN (using the presence of an SRB1). Optionally, for the scenario of inter-SN LTM triggered by the MN, the UE may directly transmit the L3 measurement report of the PSCell to the MN. If the MN node is in a gNB-CU and a gNB-DU split architecture, the UE may transmit the L3 measurement report to the gNB-CU of the MN through the gNB-DU.

[0644] 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 an LTM configuration decision. Optionally, the MN receives the L3 measurement report of the PSCell reported by the UE, and triggers an LTM configuration decision. One of the two is selected. If the LTM configuration decision is triggered by the MN, Procedure 603 will be omitted.

[0645] Procedure 603: The source S-NG-RAN node or the source SN gNB-CU initiates an Inter-CU or inter-SN LTM request to the MN, and transmits an S-NODE Change Required message to the MN. Here, the message includes one or more of the following information:

[0646] -LTM Information Required

[0647] -List of Multiple Target S-NG-RAN Nodes

[0648] >Each Target S-NG-RAN Node ID (represented by a global NG-RAN node ID (global gNB ID or global ng-eNB ID))

[0649] -LTM Triggering Indication (LTM Indicator = true or initiation)

[0650] -Maximum Number of PSCells To Prepare

[0651] -Estimated Arrival Probability (indicating a probability that the UE accesses the target S-NG-RAN node)

[0652] -S-NG-RAN Node to M-NG-RAN Node Container (including a CG-Config message defined in TS 38.331, the message including ltm-ReferenceConfigurationSCG and including the frequency, PCI and L3 measurement report of each recommended candidate PSCell)

[0653] -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 (corresponding to an LTM-CandidateId IE defined in TS 38.331))

[0654] -Early Synchronization (Sync) Information Request

[0655] -RACH Configuration Request Indication (Request for RACH Configuration)

[0656] >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 through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) may be carried, indicating that the S-SN requests, based on the NG-RAN node, a PRACH resource for an early synchronization TA acquisition procedure.

[0657] >Optionally, in order that subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a target S-NG-RAN node ID list may be carried (each target S-NG-RAN node ID is indicated through the global NG-RAN node ID (i.e., global gNB ID or global ng-eNB ID)), indicating that the S-SN requests, based on each S-NG-RAN node, a PRACH resource for the early synchronization TA acquisition procedure.

[0658] >Optionally, if only the one-time LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the S-SN, gNB-DU ID of the S-SN and the source S-NG-RAN node ID (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) may be carried, indicating that the S-SN requests, based on the gNB-DU of the S-SN, a PRACH resource for the early synchronization TA acquisition procedure.

[0659] >Optionally, in order that subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a gNB-DU ID list may be carried (each gNB-DU ID indicates the S-NG-RAN node ID (indicated through the global NG-RAN node ID (referring to a gNB ID when the base station is in a gNB-CU and a gNB-DU split architecture) to which the gNB-DU ID belongs), indicating that the S-SN requests, based on the gNB-DU of each candidate SN (including the gNB-DU of the S-SN), a PRACH resource for the early synchronization TA acquisition procedure.

[0660] >Optionally, if the S-SN does not want to carry a plaintext S-NG-RAN node ID and / or S-SN gNB-DU ID, or the S-NG-RAN node ID list and / or SN gNB-DU ID list, the S-SN may alternatively associate 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) with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit a list including the mapping ID / index / identifier of the LTM S-NG-RAN node or LTM SN gNB-DU (the mapping ID / index / identifier list of the LTM S-NG-RAN node or the mapping identifier / index / identifier list of the LTM SN gNB-DU) to the MN, to request the candidate PSCell to allocate a PRACH resource to each mapping ID / index / identifier.

[0661] Procedure 604: The MN initiates an SN addition procedure to each different candidate SN, and transmits an S-NODE Addition Request message to the candidate SN. Here, the message includes one or more of the following information:

[0662] -LTM Information Request

[0663] -LTM Triggering Indication (LTM indication = initiation / true)

[0664] -List of Multiple Target S-NG-RAN Nodes

[0665] >Each Target S-NG-RAN Node ID (represented by a global NG-RAN node ID (global gNB ID or global ng-eNB ID), the information on a recommended candidate target S-NG-RAN node)

[0666] >Information on Recommended Candidate PSCell (the recommended candidate PSCell on each target S-NG-RAN node, each PSCell being represented by a Cell ID or NR CGI)

[0667] -LTM Configuration ID of the Candidate PSCell (corresponding to an LTM-CandidateId IE defined in TS 38.331), including the LTM configuration ID of each candidate PSCell on this candidate SN

[0668] -LTM Configuration ID Mapping List, including the mapping relationship between each recommended LTM candidate PSCell ID and its corresponding LTM configuration ID (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0669] -LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0670] -LTM Reference Configuration Request Indication, indicating that the MN requests an LTM reference configuration from the candidate SN

[0671] -LTM Reference Configuration (including a lower-layer and / or high-layer reference configuration, and including a CellGroupConfig IE and / or CG-ConfigInfo message defined in TS 38.331)

[0672] -M-NG-RAN Node to S-NG-RAN Node Container (including a CG-ConfigInfo message defined in TS 38.331, the message including ltm-ReferenceConfiguration information)

[0673] -Early Synchronization (Sync) Information Request

[0674] -Request Indication for RACH Configuration (Request for RACH Configuration)

[0675] >Optionally, if only the 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 through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) may be carried, indicating that the MN requests, based on the S-NG-RAN node, a PRACH resource from the candidate SN or gNB-CU for an early synchronization TA acquisition procedure.

[0676] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a target S-NG-RAN node ID list may be carried (each target S-NG-RAN node ID is indicated through the global NG-RAN node ID (i.e., global gNB ID or global ng-eNB ID)), indicating that the MN requests, based on each S-NG-RAN node, a PRACH resource from the candidate SN or gNB-CU for the early synchronization TA acquisition procedure.

[0677] >Optionally, if only the 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 through the global NG-RAN node ID (global gNB ID or global ng-eNB ID)) may be carried, indicating that the MN requests, based on the gNB-DU of the S-SN, a PRACH resource from the candidate SN or gNB-CU for the early synchronization TA acquisition procedure.

[0678] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a gNB-DU ID list may be carried (each gNB-DU ID indicates the S-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) to which the gNB-DU ID belongs, indicating that the MN requests, based on the gNB-DU of each candidate SN (including the gNB-DU of the S-SN), a PRACH resource from the candidate SN or gNB-CU for the early synchronization TA acquisition procedure.

[0679] >Optionally, if the MN does not want to carry a plaintext source S-NG-RAN node ID and / or S-SN gNB-DU ID, or an S-NG-RAN node ID list and / or SN gNB-DU ID list, the S-SN or MN may alternatively associate each candidate S-NG-RAN node (including the source S-NG-RAN node) or the gNB-DU of each candidate SN (including the gNB-DU of the source SN) with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit a list including the mapping ID / index / identifier of the LTM S-NG-RAN node or LTM SN gNB-DU (the mapping ID / index / identifier list of the LTM S-NG-RAN node or the mapping identifier / index / identifier list of the LTM SN gNB-DU) to the candidate SN or gNB-CU, to request the candidate PSCell to allocate a PRACH resource to each mapping ID / index / identifier.

[0680] >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 through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the MN requests, based on the M-NG-RAN node, a PRACH resource from the candidate SN or gNB-CU for the early synchronization TA acquisition procedure.

[0681] Optionally, if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the MN (if the MN is in a gNB-CU and a gNB-DU split architecture), an MN gNB-DU ID (represented by a gNB-DU ID, which may indicate the M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs) may be carried, indicating that the MN requests, based on the gNB-DU of the MN (it is possible that a plurality of UEs on the MN initiate an SN LTM request procedure with respect to the same candidate PSCell on different gNB-DUs), a PRACH resource from the candidate SN or gNB-CU for the early synchronization TA acquisition procedure.

[0682] Optionally, if the MN does not want to carry a plaintext M-NG-RAN node ID and / MN gNB-DU ID, the MN may alternatively associate the M-NG-RAN node or the gNB-DU of the MN with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit the mapping ID / index / identifier to the candidate SN or gNB-CU, to request the candidate PSCell to allocate the PRACH resources to the mapping ID / index / identifier.

[0683] Procedure 605: If the candidate S-NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the candidate gNB-CU initiates the UE Context Setup procedure with respect to each candidate PSCell to the candidate gNB-DU, and transmits a UE Context Setup Request message. Here, the message includes one or more of the following information:

[0684] -LTM Triggering Indication (LTM Indicator = true)

[0685] -Candidate PSCell ID (Cell ID or NR CGI)

[0686] -LTM Configuration ID of Candidate PSCell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0687] -LTM Configuration ID Mapping List (including the mapping relationship between each LTM Cell ID and its corresponding LTM configuration ID)

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

[0689] -Indication (Request for Lower Layer Configuration) that the candidate gNB-CU requests the candidate gNB-DU to provide a lower-layer configuration to generate a reference configuration

[0690] -LTM Reference Configuration (including a CellGroupConfig IE defined in TS 38.331)

[0691] -Early Synchronization (Sync) Information Request

[0692] -Request Indication for RACH Configuration (Request for RACH Configuration)

[0693] >Optionally, if only the 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 an associated M-NG-RAN node ID (both indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the candidate gNB-CU requests, based on the S-NG-RAN node, a PRACH resource from the candidate gNB-DU.

[0694] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a target S-NG-RAN node ID list (including the source S-NG-RAN node ID, each S-NG-RAN node ID indicating an associated M-NG-RAN node ID (the S-NG-RAN node ID and the associated M-NG-RAN node ID are both indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the candidate gNB-CU requests, based on each S-NG-RAN node, a PRACH resource from the candidate gNB-DU.

[0695] >Optionally, if only the 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, the S-NG-RAN node ID and an associated M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the candidate gNB-CU requests, based on the gNB-DU of the S-SN, a PRACH resource from the candidate gNB-DU.

[0696] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a gNB-DU ID list may be carried (each gNB-DU ID indicates the S-NG-RAN node ID to which the gNB-DU ID belongs and an associated M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)), indicating that the candidate gNB-CU requests, based on the gNB-DU of the candidate SN, a PRACH resource from the candidate gNB-DU.

[0697] >Optionally, if the MN transmits, to the candidate gNB-CU, a mapping ID / index / identifier with respect to the source S-NG-RAN node ID and / or S-SN gNB-DU ID, a mapping ID / index / identifier list of an LTM S-NG-RAN node (the mapping ID / index / identifier list of the LTM S-NG-RAN node), or a mapping ID / index / identifier list of an LTM SN gNB-DU, then the candidate gNB-CU transmits the LTM S-NG-RAN node mapping ID / index / identifier list (the mapping ID / index / identifier list of the LTM S-NG-RAN node or the mapping ID / index / identifier list of the LTM SN gNB-DU) to the candidate gNB-DU, to request the candidate PSCell to allocate a PRACH resource to the mapping ID / index / identifier of each LTM S-NG-RAN node or SN gNB-DU.

[0698] >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 through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the candidate gNB-CU requests, based on the M-NG-RAN node, a PRACH resource from the candidate gNB-DU for the early synchronization TA acquisition procedure.

[0699] >Optionally, if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the MN (if the MN is in a gNB-CU and a gNB-DU split architecture), an MN gNB-DU ID (represented by a gNB-DU ID, indicating the M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs) may be carried, indicating that the candidate gNB-CU requests, based on the gNB-DU of the MN (it is possible that a plurality of UEs on the MN initiate an SN LTM request procedure with respect to the same candidate PSCell on different gNB-DUs), a PRACH resource from the candidate SN or gNB-CU for the early synchronization TA acquisition procedure.

[0700] >Optionally, if the MN does not want to carry a plaintext M-NG-RAN node ID and / MN gNB-DU ID, the MN may alternatively associate the M-NG-RAN node or the gNB-DU of the MN with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit the mapping ID / index / identifier to the candidate SN or gNB-CU, and then, the candidate gNB-CU requests the candidate PSCell of the candidate gNB-DU to allocate a PRACH resource to the mapping ID / index / identifier.

[0701] Procedure 606: If the candidate gNB-DU accepts an LTM configuration request with respect to the candidate PSCell, the candidate gNB-DU will transmit a UE Context Setup Response message as a response to the candidate gNB-CU. Here, the message includes one or more of the following information:

[0702] -Candidate PSCell ID (Cell ID or NR CGI)

[0703] -Lower-layer RRC Configuration (e.g., a transmission configuration indication (TCI) states configurations list) generated for a target candidate PSCell with acceptance, SSB Configuration and NR PCI Information of Candidate PSCell

[0704] -LTM Reference Configuration (provided by the candidate gNB-DU, and including a CellGroupConfig IE defined in TS 38.331)

[0705] -LTM Complete Configuration Indicator, indicating whether the LTM configuration of the candidate PSCell with acceptance is a complete configuration

[0706] -CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331)

[0707] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL)

[0708] -RACH Configuration Information (i.e. PRACH Resources), including one or more pieces of RACH configuration information

[0709] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by a Cell ID or NR CGI) to the source S-NG-RAN node or the gNB-DU of the source SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0710] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) to the mapping ID / index / identifier of the source S-NG-RAN node or the source SN gNB-DU is included.

[0711] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. The RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) to each candidate S-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of each candidate SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0712] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. If the candidate gNB-CU provides the mapping ID, index or identifier of the LTM S-NG-RAN node, or the mapping ID, index or identifier of the LTM SN gNB-DU, the list includes accordingly the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) to the mapping ID, index or identifier of each requested LTM S-NG-RAN node or SN gNB-DU.

[0713] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) for the M-NG-RAN node (which may optionally be indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID))) or the gNB-DU of the MN (which may optionally be indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the MN to which the gNB-DU ID belongs) is included.

[0714] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) to the mapping ID, index or identifier of the M-NG-RAN node or the mapping ID, index or identifier of the gNB-DU of the MN is included.

[0715] Procedure 607: The candidate SN responses withan S-NODE Addition Request Acknowledge message to the MN. Here, the message includes one or more of the following information:

[0716] -Candidate PSCell ID List (representing a list of candidate PSCells with acceptance on this candidate SN, each PSCell being represented by a Cell ID or NR CGI)

[0717] -RRC Configuration (generated by a target candidate PSCell with acceptance, including, e.g., a transmission configuration indication (TCI) states configurations list, and included in an LTM-TCI-Info IE defined in TS 38.331), SSB Configuration and NR PCI Information of Candidate PSCell

[0718] -S-NG-RAN Node to M-NG-RAN Node Container (including a CG-Config message defined in TS 38.331, the message including ltm-ReferenceConfigurationSCG)

[0719] -Reference Configuration (LTM Reference Configuration, provided by the candidate SN or the gNB-CU of the candidate SN, and including a CG-Config message defined in TS 38.331, the message including ltm-ReferenceConfigurationSCG)

[0720] -LTM Complete Configuration Indicator, indicating whether the LTM configuration of each candidate PSCell with acceptance is a complete configuration

[0721] -CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331, and indicating the generated LTM CSI report configuration of each candidate PSCell with acceptance)

[0722] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) of a candidate cell PSCell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0723] -TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0724] -RACH Configuration Information (i.e. PRACH Resources), including one or more pieces of RACH configuration information

[0725] >Optionally, one RACH configuration information list is included. That is, the RACH configuration information allocated by each candidate PSCell (PSCell ID, represented by a Cell ID or NR CGI) with acceptance on the candidate SN to the source S-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of the source SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0726] >Optionally, one RACH configuration information list is included. That is, the RACH configuration information allocated by each candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) with acceptance on the candidate SN to the source S-NG-RAN node or the mapping ID / index / identifier of the gNB-DU of the source SN is included.

[0727] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. The RACH configuration information allocated by each candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) with acceptance on the candidate SN to each candidate S-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of each candidate SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the candidate SN to which the gNB-DU ID belongs) is included.

[0728] >Optionally, one RACH configuration list (a plurality of pieces of RACH configuration information) is included. The RACH configuration information allocated by each candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) with acceptance on the candidate SN to the mapping ID, index or identifier of the LTM S-NG-RAN node or the mapping ID, index or identifier of the gNB-DU of the LTM SN is included.

[0729] >Optionally, one RACH configuration information list is included. That is, the RACH configuration information allocated by each candidate PSCell (PSCell ID, represented by the Cell ID or NR CGI) with acceptance on the candidate SN to the source M-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of the MN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the MN to which the gNB-DU ID belongs) is included.

[0730] >Optionally, one RACH configuration information list is included. That is, the RACH configuration information allocated by each candidate PSCell (the PSCell is represented by the Cell ID or NR CGI) with acceptance on the candidate SN to the M-NG-RAN node or the mapping ID / index / identifier of the gNB-DU of the MN is included.

[0731] Procedure 608: The MN transmits the relevant LTM configuration information of the candidate PSCell with acceptance to the source S-NG-RAN node or source SN gNB-CU and may initiate, to the S-SN, a request to use the source PSCell or another PSCell on the S-SN as a candidate PSCell. Optionally, the MN transmits an S-NODE Modification Request message to the S-SN. Here, the message includes one or more of the following information:

[0732] -LTM Information Request

[0733] -LTM Triggering Indication (LTM indication = initiation / true)

[0734] -List of Multiple Target S-NG-RAN Nodes (a list of candidate S-NG-RAN nodes which accepted the LTM configuration request)

[0735] >Each Target S-NG-RAN Node ID (represented by a global NG-RAN node ID (global gNB ID or global ng-eNB ID))

[0736] >Candidate PSCell ID (which accepted the LTM configuration request on each target S-NG-RAN node, each PSCell being represented by a Cell ID or NR CGI)

[0737] -LTM Configuration ID of the Candidate PSCell (corresponding to an LTM-CandidateId IE defined in TS 38.331), including the LTM configuration ID of each candidate PSCell on this S-SN (including the source PSCell and the other candidate PSCell on the S-SN)

[0738] -LTM Configuration ID Mapping List, including the mapping relationship between each LTM candidate PSCellID and its corresponding LTM configuration ID (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0739] -LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0740] -LTM Reference Configuration Request Indication, indicating that the MN requests an LTM reference configuration from the source S-NG-RAN node or source SN gNB-CU

[0741] -LTM Reference Configuration (including a CellGroupConfig IE and / or CG-ConfigInfo message defined in TS 38.331)

[0742] -M-NG-RAN Node to S-NG-RAN Node Container (including a CG-ConfigInfo message defined in TS 38.331, the message including ltm-ReferenceConfiguration information)

[0743] -Collected RRC configuration (generated by the target candidate PSCell which accepted the LTM configuration request on another candidate SN, including, for example, a transmission channel indication (TCI) states configurations list (TCI States Configurations List), and included in an LTM-TCI-Info IE defined in TS 38.331), SSB configuration and NR PCI information of Candidate PSCell

[0744] -LTM Complete Configuration Indicator, indicating whether the LTM configuration of each candidate PSCell which accepted the LTM configuration request is a complete configuration

[0745] -CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331, and indicating the generated LTM CSI report configuration of each candidate PSCell which accepted the LTM configuration request)

[0746] -Early Synchronization (Sync) Information Request

[0747] -RACH Configuration Request Indication (Request for RACH Configuration)

[0748] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a target S-NG-RAN node ID list may be carried (each target S-NG-RAN node ID is indicated through the global NG-RAN node ID (global gNB ID or global ng-eNB ID)), indicating that the MN requests, based on each S-NG-RAN node, a PRACH resource from the source SN for the early synchronization TA acquisition procedure.

[0749] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a gNB-DU ID list may be carried (each gNB-DU ID indicates the S-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs), indicating that the MN requests, based on the gNB-DU of each candidate SN, a PRACH resource from the source SN for the early synchronization TA acquisition procedure.

[0750] >Optionally, if the MN does not want to carry a plaintext S-NG-RAN node ID list and / SN gNB-DU ID list, the MN may alternatively associate each candidate S-NG-RAN node or the gNB-DU of each candidate SN with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit a list including the mapping ID / index / identifier of the LTM S-NG-RAN node or LTM SN gNB-DU (a mapping ID / index / identifier list of the LTM S-NG-RAN node or a mapping ID / index / identifier list of the LTM SN gNB-DU) to the source SN or the gNB-CU of the source SN to request the candidate PSCell to allocate a PRACH resource to each mapping ID / index / identifier.

[0751] >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 through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the MN requests, based on the M-NG-RAN node, a PRACH resource from the source SN or the gNB-CU of the source SN for the early synchronization TA acquisition procedure.

[0752] >Optionally, if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the MN (if the MN is in a gNB-CU and a gNB-DU split architecture), an MN gNB-DU ID (represented by a gNB-DU ID, which may optionally indicate the M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs) may be carried, indicating that the MN requests, based on the gNB-DU of the MN (it is possible that a plurality of UEs on the MN initiate an SN LTM request procedure with respect to the same candidate PSCell on different gNB-DUs), a PRACH resource from the source SN or the gNB-CU of the source SN for the early synchronization TA acquisition procedure.

[0753] >Optionally, if the MN does not want to carry a plaintext M-NG-RAN node ID and / MN gNB-DU ID, the MN may alternatively associate the M-NG-RAN node or the gNB-DU of the MN with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit the mapping ID / index / identifier to the source SN or the gNB-CU of the source SN to request the candidate PSCell to allocate a PRACH resource to the mapping ID / index / identifier.

[0754] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) of each candidate cell PSCell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0755] -TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0756] -RACH Configuration Information (i.e. PRACH Resources), including one or more pieces of RACH configuration information

[0757] >Optionally, one RACH configuration information list is included, the list including one or more pieces of RACH configuration information. That is, the RACH configuration information allocated by each candidate PSCell (the PSCell being represented by a Cell ID or NR CGI) which accepted the LTM configuration request to the source S-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of the source SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) is included.

[0758] >Optionally, one RACH configuration information list is included, the list including one or more pieces of RACH configuration information. That is, the RACH configuration information allocated by each candidate PSCell (the PSCell ID being represented by a Cell ID or NR CGI) which accepted the LTM configuration request to the mapping ID / index / identifier of the source S-NG-RAN node or the gNB-DU of the source SN is included.

[0759] Procedure 609: If the source S-NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the gNB-CU of the source SN may continue to allocate the corresponding RACH configuration to the source gNB-DU based on the implementation of the RACH configuration allocated by 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 an LTM configuration to the same candidate PSCell, then all the S-NG-RAN node-based RACH configurations of this candidate PSCell can be allocated to this gNB-DU. If a plurality of UEs under different gNB-DUs on the source SN initiate an LTM configuration to the same candidate PSCell, then different subsets of the S-NG-RAN node-based RACH configurations of this candidate PSCell can be allocated to the 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).

[0760] Procedure 610: If the source S-NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the source gNB-CU transmits a UE Context Modification Request message to the source gNB-DU. Here, the message includes one or more of the following information:

[0761] -Candidate PSCell ID (referring to another candidate PSCell under the source cell or the source gNB-DU, and represented by a Cell ID or NR CGI, each candidate PSCell using a separate UE context modification procedure)

[0762] -LTM Triggering Indication (LTM indicator = true)

[0763] -LTM Configuration ID of Candidate PSCell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0764] -LTM Configuration ID Mapping list (including the mapping relationship between each LTM candidate PSCellID and its corresponding LTM configuration ID (corresponding to an LTM-CandidateId IE defined in TS 38.331))

[0765] -LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0766] -Indication (Request for Lower Layer Configuration) that the source gNB-CU requests the source gNB-DU to provide a lower-layer configuration to generate a reference configuration

[0767] -LTM Reference Configuration (including a CellGroupConfig IE defined in TS 38.331)

[0768] -Collected CSI Report Configuration and TCI States Configurations List of Target Candidate PSCell With Acceptance in Other Candidate S-NG-RAN Node, SSB Configuration and NR PCI Information of Candidate PSCell

[0769] -Early Synchronization (Sync) Information List, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) allocated by each candidate cell PSCell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0770] -TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0771] -RACH Configuration List (optionally including a subset or complete set of the RACH configuration information allocated by each candidate PSCell to the source S-NG-RAN node to which the candidate PSCell belongs, or including the RACH configuration information allocated by each candidate PSCell to the source gNB-DU to which the candidate PSCell belongs)

[0772] -Early Synchronization (Sync) Information Request

[0773] -Request Indication for RACH Configuration (Request for RACH Configuration)

[0774] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the S-NG-RAN node, a target S-NG-RAN node ID list may be carried (each S-NG-RAN node ID indicates an associated M-NG-RAN node ID, the S-NG-RAN node ID and the M-NG-RAN node ID both being indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)), indicating that the source gNB-CU requests, based on each S-NG-RAN node, a PRACH resource from the source gNB-DU.

[0775] >Optionally, in order that the subsequent LTM is supported and the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the candidate SN, a gNB-DU ID list may be carried (each gNB-DU ID indicates the S-NG-RAN node ID to which the gNB-DU ID belongs and an associated M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID))), indicating that the source gNB-CU requests, based on the gNB-DU of the candidate SN, a PRACH resource from the source gNB-DU.

[0776] >Optionally, if the gNB-CU of the source SN does not want to carry a plaintext candidate S-NG-RAN node ID and / or a plaintext gNB-DU ID of the candidate SN, or an S-NG-RAN node ID list and / or a gNB-DU ID list of the SN, the gNB-CU of the source SN may alternatively associate each candidate S-NG-RAN node or the gNB-DU of each candidate SN with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit a list including the mapping ID / index / identifier of the LTM S-NG-RAN node or LTM SN gNB-DU (a mapping ID / index / identifier list of the LTM S-NG-RAN node or a mapping identifier / index / identifier list of the LTM SN gNB-DU) to the source gNB-DU, to request the source PSCell or another candidate PSCell to allocate a PRACH resource to each mapping ID / index / identifier.

[0777] >Optionally, if the MN decides to transmit, to the source gNB-CU, an LTM S-NG-RAN node mapping ID / index / identifier list (the mapping ID / index / identifier list of the LTM S-NG-RAN node) or the mapping identifier / index / identifier list of the LTM SN gNB-DU, the source gNB-CU transmits the list including the mapping ID / index / identifier of the LTM S-NG-RAN node (the mapping ID / index / identifier list of the LTM S-NG-RAN node or the mapping identifier / index / identifier list of the LTM SN gNB-DU) to the source gNB-DU, to request the source PSCell or the other candidate PSCell to allocate a PRACH resource to the mapping ID / index / identifier of each LTM S-NG-RAN node or SN gNB-DU.

[0778] >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 through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID)) may be carried, indicating that the gNB-CU of the source SN requests, based on the M-NG-RAN node, a PRACH resource from the source gNB-DU for the early synchronization TA acquisition procedure.

[0779] >Optionally, if the PRACH resources of the candidate PSCell are allocated based on the gNB-DU of the MN (if the MN is in a gNB-CU and a gNB-DU split architecture), a gNB-DU ID (indicating the M-NG-RAN node ID (indicated through the global NG-RAN node ID (the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs) may be carried, indicating that the gNB-CU of the source SN requests, based on the gNB-DU of the MN (it is possible that a plurality of UEs on the MN initiate an SN LTM request procedure with respect to the same candidate PSCell on different gNB-DUs), a PRACH resource from the source gNB-DU for the early synchronization TA acquisition procedure.

[0780] >Optionally, if the MN does not want to carry a plaintext M-NG-RAN node ID and / MN gNB-DU ID, the MN may alternatively associate the M-NG-RAN node or the gNB-DU of the MN with a certain mapping ID / index / identifier based on the implementation by means of mapping, and then transmit the mapping ID / index / identifier to the source SN or gNB-CU, and then, the source gNB-CU requests the source PSCell or candidate PSCell of the source gNB-DU to allocate a PRACH resource to the mapping ID / index / identifier.

[0781] Procedure 611: If the source PSCell or the other candidate PSCell accepts the LTM configuration request, the source gNB-DU transmits a UE Context Modification Response message a response. Here, the message includes one or more of the following information:

[0782] -Candidate PSCell ID (Cell ID or NR CGI, which may include the source PSCell or another candidate PSCell under the source gNB-DU, each candidate PSCell using a separate UE context modification procedure)

[0783] -Lower-layer RRC Configuration (e.g., a transmission configuration indication (TCI) states configurations list) generated for a target candidate PSCell with acceptance, SSB Configuration and NR PCI Information of Candidate PSCell

[0784] -Reference Configuration (LTM Reference Configuration, provided by the source gNB-DU and including a CellGroupConfig IE defined in TS 38.331)

[0785] -LTM Complete Configuration Indicator (indicating whether the LTM configuration of the candidate PSCell with acceptance is a complete configuration)

[0786] -CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331)

[0787] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) allocated by each candidate cell PSCell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0788] -RACH Configuration Information List (i.e. PRACH Resources), including one or more pieces of RACH configuration information

[0789] >Optionally, the RACH configuration information allocated by the candidate PSCell (including the source PSCell or the other candidate PSCell under the source gNB-DU, and represented by the Cell ID or NR CGI) to each candidate S-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of each candidate SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the SN to which the gNB-DU ID belongs) is included.

[0790] >Optionally, if the source gNB-CU provides the mapping ID, index or identifier of the LTM S-NG-RAN node or the mapping ID, index or identifier of the LTM SN gNB-DU, the list includes accordingly the RACH configuration information allocated by the candidate PSCell (including the source PSCell or the other candidate PSCell under the source gNB-DU, and represented by the Cell ID or NR CGI) to the mapping ID, index or identifier of each requested LTM S-NG-RAN node or SN gNB-DU.

[0791] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate PSCell (which may include the source PSCell or the other candidate PSCell under the source gNB-DU, and is represented by the Cell ID or NR CGI) to the M-NG-RAN node (which may optionally be indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID))) or the gNB-DU of the MN (which may optionally be indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the MN to which the gNB-DU ID belongs) is included.

[0792] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by the candidate PSCell (which may include the source PSCell or the other candidate PSCell under the source gNB-DU, and is represented by the Cell ID or NR CGI) to the mapping ID / index / identifier of the M-NG-RAN node or the mapping ID / index / identifier of the gNB-DU of the MN is included.

[0793] Procedure 612: The source S-NG-RAN node or source SN gNB-CU transmits the relevant LTM configuration information to the MN, and the source SN transmits an S-NODE Modification Request Acknowledge message to the MN. Here, the message includes one or more of the following information:

[0794] -Candidate PSCell ID List (representing a list of candidate PSCells with acceptance on the source SN, the list including the source PSCell and other candidate PSCells on a possible S-SN, and each PSCell being represented by a Cell ID or NR CGI)

[0795] -RRC Configuration (generated by the target candidate PSCell with acceptance on the source SN, including, for example, a transmission channel indication (TCI) states configurations list (TCI States Configurations List, and included in an LTM-TCI-Info IE defined in TS 38.331), SSB Configuration and NR PCI Information of Candidate PSCell

[0796] -S-NG-RAN Node to M-NG-RAN Node Container (including a CG-Config message defined in TS 38.331, the message including ltm-ReferenceConfigurationSCG)

[0797] -Reference Configuration (LTM Reference Configuration, provided by the source SN or the gNB-CU of the source SN, and including a CG-Config message defined in TS 38.331, the message including ltm-ReferenceConfigurationSCG)

[0798] -LTM Complete Configuration Indicator (indicating whether the LTM configuration of each candidate PSCell with acceptance is a complete configuration)

[0799] -CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331, and indicating the generated LTM CSI report configuration of each candidate PSCell with acceptance)

[0800] -Early Synchronization (Sync) Information, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) allocated by each candidate cell PSCell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0801] -TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0802] -RACH Configuration Information List (i.e. PRACH Resources), including a plurality of pieces of RACH configuration information

[0803] >Optionally, the RACH configuration information allocated by the candidate PSCell (including the source PSCell or the other candidate PSCell under the S-SN, and represented by the Cell ID or NR CGI) to each candidate S-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID)) or the gNB-DU of each candidate SN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the SN to which the gNB-DU ID belongs) is included.

[0804] >Optionally, if the source gNB-CU provides the mapping ID, index or identifier of the LTM S-NG-RAN node or the mapping ID, index or identifier of the LTM SN gNB-DU, the list includes accordingly the RACH configuration information allocated by the candidate PSCell (including the source PSCell or the other candidate PSCell under the S-SN, and represented by the Cell ID or NR CGI) to the mapping ID, index or identifier of each requested LTM S-NG-RAN node or the SN gNB-DU.

[0805] >Optionally, one piece of RACH configuration information is included. That is, the RACH configuration information allocated by each candidate PSCell (which may include the source PSCell, and is represented by a Cell ID or NR CGI) with acceptance on the source SN to the M-NG-RAN node (indicated through the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID))) or the gNB-DU of the MN (indicated through the gNB-DU ID and the global NG-RAN node ID (i.e. the global gNB ID or global ng-eNB ID) of the MN to which the gNB-DU ID belongs) is included.

[0806] >Optionally, one RACH configuration information list is included. That is, the RACH configuration information allocated by each candidate PSCell (which may include the source PSCell, and is represented by the Cell ID or NR CGI) with acceptance on the source SN to the mapping ID / index / identifier of the M-NG-RAN node or the mapping ID / index / identifier of the gNB-DU of the MN is included.

[0807] Procedure 613: The MN transmits configuration information of another candidate PSCell with acceptance to each of other candidate S-NG-RAN nodes or the gNB-CU of each of other SNs. Optionally, the MN may transmit the information by transmitting the S-NODE Modification Request message. The message includes one or more of the following information:

[0808] -LTM Modification or Update Indication (LTM indication = modification or update)

[0809] -List of Multiple Target S-NG-RAN Nodes (a list of target S-NG-RAN nodes with acceptance; optionally, the candidate S-NG-RAN node or SN gNB-CU compares, after receiving a list of other target S-NG-RAN nodes with acceptance, the list with the recommended target S-NG-RAN node list previously received in procedure 604, and thus can determine the information on a candidate S-NG-RAN node with no acceptance, and then releases the RACH configuration previously allocated by the configured LTM candidate PSCell to this candidate S-NG-RAN node ID)

[0810] >Each Target S-NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID))

[0811] >ID List of Candidate PSCells for Accpetion on Each Target S-NG-RAN Node (the PSCells may include the source PSCell, and each PSCell is represented by a Cell ID or NR CGI; optionally, the candidate S-NG-RAN node or SN gNB-CU compares, after receiving the information on the LTM cell with acceptance on the other target S-NG-RAN node, the information with the information on the recommended LTM candidate PSCell previously received in procedure 604, and thus can determine the information on a candidate LTM cell with no acceptance and determine the information on a candidate S-NG-RAN node with no acceptance or the information on a candidate SN gNB-DU with no acceptance, and then releases the RACH configuration previously allocated by the configured LTM candidate PSCell to this candidate S-NG-RAN node ID and / or SN gNB-DU ID)

[0812] -LTM Configuration ID of the Candidate PSCell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0813] -Updated LTM Configuration ID Mapping List (including the mapping relationship between the ID of each LTM cell with acceptance and its corresponding LTM configuration ID; optionally, the candidate S-NG-RAN node or SN gNB-CU compares, after receiving the information on the LTM cell with acceptance on the other target S-NG-RAN node, the information with the information on the recommended LTM candidate PSCell previously received in procedure 604, and thus can determine the information on the candidate LTM cell with no acceptance and determine the information on the candidate S-NG-RAN node with no acceptance or the information on the candidate SN gNB-DU with no acceptance, and then releases the RACH configuration previously allocated by the configured LTM candidate PSCell to this candidate S-NG-RAN node ID and / or SN gNB-DU ID)

[0814] -RRC Configuration (generated by the target candidate PSCell with acceptance on another candidate SN with acceptance (which may optionally include the source SN), including, for example, a transmission channel indication (TCI) states configurations list (TCI States Configurations List, and included in an LTM-TCI-Info IE defined in TS 38.331), SSB Configuration and NR PCI Information of Candidate PSCell

[0815] -LTM Complete Configuration Indicator (indicating whether the LTM configuration of each candidate PSCell with acceptance is a complete configuration)

[0816] -CSI Report Configuration (included in a CellGroupConfig IE defined in TS 38.331, and indicating the generated LTM CSI report configuration of each candidate PSCell with acceptance)

[0817] -Updated LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, provided by the MN and including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0818] -Early Synchronization (Sync) Information List, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) allocated by each candidate cell PSCell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0819] -TA Assistance Information, indicating that the TA value of the candidate cell PSCell is 0

[0820] -RACH Configuration Information List (i.e., PRACH resources, i.e., early uplink synchronization configuration information), including a plurality of pieces of RACH configuration information:

[0821] >Optionally, one RACH configuration information list is included, the list including a plurality of pieces of RACH configuration information. That is, the RACH configuration information allocated by the candidate PSCell (which may include the source PSCell, the PSCell ID being represented by the Cell ID or NR CGI) with acceptance on each of the other candidate SNs to the current candidate S-NG-RAN node or to each candidate gNB-DU (indicated though the gNB-DU ID) under the current candidate SN gNB-CU is included. The information may include one or more of the following information:

[0822] >>Candidate Cell PSCell ID (represented by a Cell ID or NR CGI)

[0823] >>RACH Configuration Information (included in an EarlyUL-SyncConfig IE defined in TS 38.331, and representing the common part of the PRACH resources allocated by the candidate cell PSCell to different LTM gNB-DUs or LTM S-NG-RANs, the different parts of the PRACH resources being represented using the following LTM gNB-DU list information)

[0824] >>LTM gNB-DU List (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0825] >>>LTM gNB-DU ID (indicated by a gNB-DU ID)

[0826] >>>LTM S-NG-RAN ID (indicated by a global gNB ID, and used to represent the S-NG-RAN information associated with the gNB-DU indicated by the gNB-DU ID)

[0827] >>>Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB-DU ID)

[0828] >>LTM S-NG-RAN List (including one or more LTM S-NG-RAN IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0829] >>>LTM S-NG-RAN ID (indicated by a global gNB ID)

[0830] >>>Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated S-NG-RAN ID)

[0831] >Optionally, one RACH configuration information list is included, the list including a plurality of pieces of RACH configuration information. That is, the RACH configuration information allocated by the candidate PSCell (which may include the source PSCell, the PSCell ID being represented by the Cell ID or NR CGI) with acceptance on each candidate SN to the current candidate S-NG-RAN node or to the mapping ID / index / identifier of each candidate gNB-DU under the current candidate SN gNB-CU is included.

[0832] -LTM S-NG-RAN Nodes to be Released List (LTM S-NG-RAN Nodes to be Released List, including the information on a plurality of to-be-released S-NG-RAN nodes, where a to-be-released S-NG-RAN node is indicated through a global NG-RAN node ID (i.e., global gNB ID or global ng-eNB ID)). If a rejection occurs in the previous request procedure for all candidate PSCells on this candidate S-NG-RAN node, that is, this candidate S-NG-RAN node is excluded from the candidate node list, the RACH configuration previously allocated to this candidate S-NG-RAN node by other candidate PSCells and the source PSCell needs to be released.

[0833] >LTM S-NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., global gNB ID or global ng-eNB ID), and indicating a to-be-released candidate S-NG-RAN node)

[0834] -To-be-released LTM gNB-DU List (LTM gNB-DUs to be Released List, including the information on to-be-released gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID which may indicate the S-NG-RAN node ID (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs). It is assumed that the RACH configuration of the candidate PSCell is allocated based on the SN gNB-DU. If a rejection occurs in the previous request procedure for all candidate PSCells on this candidate SN gNB-DU, that is, this candidate SN gNB-DU is excluded from the candidate node list, the RACH configuration previously allocated to this candidate SN gNB-DU by other candidate PSCells and the source PSCell needs to be released.

[0835] >LTM gNB-DU ID and / S-NG-RAN Node ID (i.e., the global gNB ID or global ng-eNB ID), indicating a to-be-released SN gNB-DU

[0836] -Mapping ID / Index / Identifier List of To-be-released LTM S-NG-RAN Node or SN gNB-DU. If the S-SN or MN requests, by making each candidate S-NG-RAN node (including the source S-NG-RAN node) or each candidate SN gNB-DU correspond to a certain mapping ID / index / identifier, the candidate PScell to allocate a PRACH resource, the MN may notify the candidate S-NG-RAN node of a to-be-released mapping ID / index / identifier list, to indicate that the candidate S-NG-RAN node releases the PRACH resource allocated by the candidate PScell to the candidate S-NG-RAN node or candidate SN gNB-DU corresponding to this LTM S-NG-RAN node or SN gNB-DU mapping ID / index / identifier.

[0837] >Mapping ID / Index / Identifier of LTM S-NG-RAN Node or SN gNB-DU (LTM S-NG-RAN node / SN gNB-DU Mapping ID / Index / identifier, correposnding to a to-be-released S-NG-RAN node or SN gNB-DU)

[0838] For different PRACH resources, RACH configuration information or early uplink synchronization (UL Sync) configuration information allocated by the candidate cell PSCell to one or more LTM gNB-DUs or LTM gNBs in procedure 606, 607, 611 or 612, and the transmission of such information in procedure 608 or 613, the information may include one or more of the following information:

[0839] -Candidate Cell PSCell ID (represented by a Cell ID or NR CGI)

[0840] -RACH Configuration Information (included in an EarlyUL-SyncConfig IE defined in TS 38.331, and representing the common part of the PRACH resources allocated by the candidate cell to different LTM gNB-DUs or LTM S-NG-RANs, the different parts of the PRACH resources being represented using the following LTM gNB-DU list information or LTM S-NG-RAN list information)

[0841] -LTM gNB-DU List (including one or more LTM gNB-DU IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0842] >LTM gNB-DU ID (indicated by a gNB-DU ID)

[0843] >LTM M-NG-RAN or S-NG-RAN ID (indicated by a global gNB ID, and used to represent the S-NG-RAN or M-NG-RAN information associated with the gNB-DU indicated by the gNB-DU ID)

[0844] >Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated gNB-DU ID)

[0845] -LTM S-NG-RAN List (including one or more LTM S-NG-RAN IDs and the corresponding PRACH resources allocated, for example, a preamble index list)

[0846] >LTM S-NG-RAN ID (indicated by a global gNB ID)

[0847] >Preamble Index List (including one or more preamble indexes, and representing the different parts of the PRACH resources allocated to the indicated S-NG-RAN ID)

[0848] In an embodiment, if the MN or one of the candidate SNs triggers the release of the LTM candidate PSCell, optionally, an S-NODE Modification Request message (S-NODE MODIFICATION REQUEST or S-NODE MODIFICATION REQUIRED) may be used to carry one or more of the following information:

[0849] -To-be-released LTM Primary Secondary Cell List (LTM PSCells to be Released List, including the information on a plurality of to-be-released primary secondary cells, where a to-be-released primary secondary cell is indicated through a PSCell ID)

[0850] >LTM PSCell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released primary secondary cell

[0851] In an embodiment, if the MN or one of the candidate SNs triggers the release of the SN, that is, all candidate PSCells on the candidate SN are released, optionally, an S-NODE Release Request message (S-NODE Release Request or S-NODE Release Required) may be used to carry the above information.

[0852] Optionally, the M-NG-RAN node can determine, through the information on the released LTM PSCells, whether the candidate S-NG-RAN node or a certain gNB-DU under the candidate S-NG-RAN node is released, and then notify each of the other candidate S-NG-RAN nodes and the source S-NG-RAN node of the LTM PSCell release information, LTM S-NG-RAN node release information and / or the to-be-released LTM gNB-DU list. Optionally, an S-NODE Modification Request message or a newly defined XnAP (e.g., an LTM PSCell Change Cancel) message can be used to carry one or more of the following information:

[0853] -To-be-released or To-be-cancelled LTM Primary Secondary Cell List (LTM PSCells to be Released List or LTM PSCells to be Cancelled List, including the information on one or more to-be-released primary secondary cells, where a to-be-released cell is indicated through a Cell ID)

[0854] >LTM PSCell ID (represented by a Cell ID or NR CGI, and indicating a to-be-released cell)

[0855] -To-be-released or To-be-cancelled LTM S-NG-RAN Node List (LTM S-NG-RAN nodes to be Released List or LTM S-NG-RAN nodes to be Cancelled List, including the information on one or more to-be-released S-NG-RAN nodes, where a to-be-released S-NG-RAN node is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID))

[0856] >LTM S-NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released S-NG-RAN node)

[0857] -To-be-released or To-be-cancelled LTM gNB-DU List (LTM gNB-DUs to be Released List or LTM gNB-DUs to be Cancelled List, including the information on one or more to-be-released gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID which indicates the S-NG-RAN node (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs)

[0858] >LTM gNB-DU ID (represented by a gNB-DU ID, and indicating a released gNB-DU under a candidate SN)

[0859] >LTM S-NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating the candidate SN to which a to-be-released gNB-DU belongs)

[0860] In an embodiment, optionally, if an LTM Cells to be Released List IE is included in the S-NODE Modification Request message, the S-NG-RAN node should consider cancelling only the resource associated with the candidate PSCell identified by the included NG-RAN CGI or NR CGI.

[0861] In an embodiment, optionally, if the LTM Cells to be Released List IE is included in the S-NODE Modification Required message, the M-NG-RAN node should consider that the S-NG-RAN node cancels only the resource associated with the candidate PSCell identified by the included NG-RAN CGI or NR CGI.

[0862] In an embodiment, optionally, if an LTM S-NG-RAN Nodes to be Released List IE is included in the S-NODE Modification Request message, the S-NG-RAN node should release, if supported, the RACH configuration, PRACH resource or early uplink synchronization configuration allocated by the configured LTM candidate PScell to the indicated S-NG-RAN node ID (represented by the global NG-RAN node ID, and included in the LTM S-NG-RAN Nodes to be Released List IE).

[0863] In an embodiment, optionally, if an LTM gNB-DUs to be Released List IE is included in the S-NODE Modification Request message, the S-NG-RAN node should release, if supported, the RACH configuration, PRACH resource or early uplink synchronization configuration allocated by the configured LTM candidate PScell to the indicated gNB-DU ID (included in the LTM gNB-DUs to be Released List IE, where a gNB-DU under the to-be-released S-NG-RAN node is indicated through a global NG-RAN node ID and a gNB-DU ID).

[0864] Procedure 614: Similar to procedure 609, if the candidate S-NG-RAN node is in a gNB-CU and a gNB-DU split architecture, the candidate SN gNB-CU may continue to allocate the corresponding RACH configuration to the candidate SN gNB-DU based on the implementation of the RACH configuration allocated by each of the other candidate PScells to this S-NG-RAN node. For example, if there is only one candidate gNB-DU under the candidate SN gNB-CU, then all the S-NG-RAN node-based RACH configurations can be allocated to this gNB-DU. If there are different candidate gNB-DUs under the candidate SN gNB-CU, then different subsets of the S-NG-RAN node-based RACH configurations can be allocated to the 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.

[0865] Procedure 615: The candidate gNB-CU transmits a UE Context Modification Request message to the candidate gNB-DU. Here, the message includes one or more of the following information:

[0866] -Candidate PSCell ID (a Cell ID or NR CGI)

[0867] -LTM Configuration ID of Candidate PSCell (corresponding to an LTM-CandidateId IE defined in TS 38.331)

[0868] -LTM Configuration ID Mapping List (including the mapping relationship between the ID of each LTM cell with acceptance and its corresponding LTM configuration ID)

[0869] -Updated LTM CSI Resource Configuration (LTM-CSI-ResourceConfig IE, including an ltm-CSI-ResourceConfigToAddModList IE defined in TS 38.331)

[0870] -Collected CSI Report Configuration and TCI States Configurations List of Target Candidate PSCell with Acceptance in Other Candidate S-NG-RAN Node, SSB Configuration and NR PCI Information of Candidate Cell

[0871] -LTM Reference Configuration (a reference configuration of a low layer portion, including a CellGroupConfig IE defined in TS 38.331)

[0872] -Early Synchronization (Sync) Information List, including early uplink synchronization configuration information (Early UL Sync Configuration) or early uplink synchronization configuration information for an supplementary uplink (Early UL Sync Configuration for SUL) of each candidate cell (represented by a Cell ID or NR CGI) which accepted the LTM configuration request

[0873] -TA Assistance Information, indicating that the TA value of the candidate PSCell is 0

[0874] -RACH Configuration List (which optionally includes a subset or complete set of the RACH configuration information allocated by each candidate PSCell (a PSCell ID is represented by a Cell ID or NR CGI) to the S-NG-RAN node to which the candidate PSCell belongs, or includes the RACH configuration information allocated by each candidate PSCell to the SN gNB-DU to which the candidate PSCell belongs)

[0875] -LTM S-NG-RAN Nodes to be Released List (LTM S-NG-RAN nodes to be Released List, including the information on a plurality of to-be-released S-NG-RAN nodes, where a to-be-released S-NG-RAN node is indicated through a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID)). It is assumed that the RACH configuration of the candidate PSCell is allocated based on the S-NG-RAN node, and optionally, an LTM S-NG-RAN Nodes to be Released List is received in procedure 613.

[0876] >LTM S-NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID), and indicating a to-be-released S-NG-RAN node)

[0877] -To-be-released LTM gNB-DU List (LTM gNB-DUs to be Released List, including the information on to-be-released LTM gNB-DUs, where a to-be-released gNB-DU is indicated through a gNB-DU ID which indicates the S-NG-RAN node (i.e., the global gNB ID or global ng-eNB ID) to which the gNB-DU ID belongs). It is assumed that the RACH configuration of the candidate PSCell is allocated based on the SN gNB-DU, and optionally, the to-be-released SN gNB-DU list is received in the above procedure 613.

[0878] >LTM gNB-DU ID and / S-NG-RAN Node ID (i.e., a global gNB ID or global ng-eNB ID, indicating a to-be-released SN gNB-DU)

[0879] -Mapping ID / Index / Identifier List of To-be-released LTM S-NG-RAN Node or SN gNB-DU (if the candidate S-NG-RAN node receives the mapping ID / index / identifier list of a to-be-released LTM S-NG-RAN Node or SN gNB-DU from the MN, the candidate gNB-CU may notify the candidate gNB-DU, indicating that the PRACH resource allocated to the candidate S-NG-RAN node or candidate SN gNB-DU corresponding to the mapping ID / index / identifier is to be released)

[0880] >Mapping ID / Index / Identifier of LTM S-NG-RAN Node or SN gNB-DU (LTM S-NG-RAN node / SN gNB-DU Mapping ID / Index / identifier, corresponding to a to-be-released S-NG-RAN node or SN gNB-DU)

[0881] After the candidate gNB-DU receives the release related S-NG-RAN node ID and / or SN gNB-DU ID, or receives the release related mapping ID / index / identifier information, the RACH configuration allocated to this S-NG-RAN node ID or SN gNB-DU ID or the mapping ID / index / identifier by the candidate PSCell on the candidate gNB-DU needs to be released. The RACH configuration, PRACH resource or early uplink synchronization configuration allocated to the released LTM cell also needs to be released.

[0882] In an embodiment, optionally, if the LTM S-NG-RAN Nodes to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should release, if supported, the RACH configuration, PRACH resource or early uplink synchronization configuration allocated by the configured candidate PSCell to the indicated S-NG-RAN node ID (represented by the global NG-RAN node ID, and included in the LTM S-NG-RAN Nodes to be Released List IE).

[0883] In an embodiment, optionally, if the LTM gNB-DUs to be Released List IE is included in the UE Context Modification Request message, the gNB-DU should release, if supported, the RACH configuration, PRACH resource or early uplink synchronization configuration allocated by the configured candidate PSCell to the indicated gNB-DU ID (a candidate gNB-DU under a candidate SN is represented by the global NG-RAN node ID and the gNB-DU ID, and the gNB-DU ID is included in the LTM gNB-DU to be Released List IE).

[0884] Procedure 616: The candidate gNB-DU transmits a UE Context Modification Response message as a response, including the updated lower-layer configuration of the candidate cell PSCell. The response transmited by the candidate gNB-DU may further include the updated CSI report configuration.

[0885] Procedure 617: The candidate SN gNB-CU transmits an S-NODE Modification Request Acknowledge message as a response to the MN. Here, the message may include the updated lower-layer configuration of the candidate cell PSCell, and may further include the updated CSI report configuration.

[0886] Procedure 618: For other candidate S-NG-RAN nodes, procedures similar to procedures 613-617 also occur. The MN transfers the relevant LTM configuration information and possible updates of the LTM configuration information to the other candidate SNs or candidate SN gNB-CUs.

[0887] Procedure 619: The RRC Reconfiguration procedure of the UE is required to be performed after the LTM-related configuration is completed on the network side. The MN transmits a generated RRC Reconfiguration message (with an LTM configuration) to the UE.

[0888] Procedure 620: The UE transmits an RRC Reconfiguration Complete message to the MN.

[0889] Procedure 621: The MN transmits an S-NODE Change Confirm message to the source SN (if the inter-SN LTM is triggered by the MN receiving the L3 measurement report from the UE, procedure 603 is omitted, and this procedure 621 is also omitted), the message including the RRC Reconfiguration Complete message. The message includes one or more of the following information:

[0890] -LTM Information Confirm

[0891] -List of Multiple Target S-NG-RAN Nodes

[0892] >Target S-NG-RAN Node ID (represented by a global NG-RAN node ID (i.e., a global gNB ID or global ng-eNB ID))

[0893] >Candidate PSCell List (including a list of PSCells with acceptance on each target S-NG-RAN node)

[0894] >>Candidate PSCell ID (each PSCell ID is represented by a Cell ID or NR CGI)

[0895] Procedure 622: Early synchronization is performed to obtain an early timing advance (TA) value. This procedure includes a procedure that the UE transmits, after receiving a PDCCH order instruction transmited by the MN or S-SN currently serving the UE or the corresponding MN gNB-DU or S-SN gNB-DU, a first Random Access Request message to the candidate PSCell using a random access resource configuration indicated in the instruction. Here, the random access resource configuration indicated in the instruction is indicated by, for example, a random access preamble index, a synchronization signal / PBCH block index (SSB index), and a PRACH occasion mask index. After receiving the first Random Access Request message, the candidate PSCell calculates a timing advance (TA) value between the UE and the candidate PSCell. If the PDCCH order instruction is triggered by the MN (or the gNB-DU of the MN) to be transmited to the UE, 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 order instruction is triggered by the S-SN (or the source gNB-DU of the S-SN) to be transmited to the UE, 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).

[0896] Procedure 623: The candidate gNB-DU transmits 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:

[0897] -TA Information List (the same UE may have different TA values for different candidate PSCells, and different UEs may have different TA values for the same candidate PSCell)

[0898] -Candidate PSCell ID (a Cell ID or NR CGI)

[0899] -TA Value

[0900] -Preamble Index

[0901] -Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0902] -Source S-NG-RAN Node ID Information (represented by a global NG-RAN node ID (i.e. a global gNB ID or global ng-eNB ID)). The candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which S-NG-RAN node the UE is currently under. Since the allocation of PRACH resources by the candidate PSCell is based on the S-NG-RAN node, different PRACH resources are allocated to different S-NG-RAN node IDs. This information is carried to indicate that the candidate gNB-CU continues to forward the TA-related information to the indicated S-NG-RAN node.

[0903] -Source gNB-DU ID Information (indicating the S-NG-RAN node ID (indicated through a global NG-RAN node ID (i.e. global gNB ID or global ng-eNB ID)) to which the gNB-DU ID belongs). The candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which gNB-DU under which S-NG-RAN node the UE is currently under. Since the allocation of PRACH resources by the candidate PSCell is based on the SN gNB-DU, different PRACH resources are allocated to different gNB-DU IDs. This information is carried to indicate that the candidate gNB-CU continues to forward the TA-related information to the indicated S-NG-RAN node and source SN gNB-DU.

[0904] -M-NG-RAN Node ID Information (a global NG-RAN node ID (i.e. a global gNB ID or global ng-eNB ID), indicating optionally the M-NG-RAN node information associated with an S-NG-RAN node). This information may be carried to indicate that the candidate gNB-CU first forwards the TA-related information to the indicated M-NG-RAN node, and then continues to forward the TA-related information to the S-NG-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 may be carried to indicate that the candidate gNB-CU continues to forward the TA-related information to the indicated M-NG-RAN node.

[0905] -MN gNB-DU ID Information and M-NG-RAN node ID (to which the MN gNB-DU ID belongs) Information (indicated through a global NG-RAN node ID (i.e. global gNB ID or global ng-eNB ID)). If the RACH configuration of the candidate PSCell is based on the MN gNB-DU, this information may be carried to indicate that the candidate gNB-CU continues to forward the TA-related information to the indicated M-NG-RAN node, and then continues to forward the TA-related information to the corresponding MN gNB-DU according to the indicated MN gNB-DU ID.

[0906] -Mapping ID / Index / Identifier Information of LTM S-NG-RAN node or SN gNB-DU, mapped to the source S-NG-RAN node ID or source SN gNB-DU. If the candidate gNB-DU allocates a PRACH resource to the mapping ID / index / identifier, the candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which mapping ID / index / identifier it is.

[0907] -Mapping ID / Index / Identifier Information of LTM M-NG-RAN node or MN gNB-DU, mapped to the M-NG-RAN node ID or MN gNB-DU. If the candidate gNB-DU allocates a PRACH resource to the mapping ID / index / identifier, the candidate gNB-DU can determine, through the PRACH resource transmited by the UE, which mapping ID / index / identifier it is.

[0908] -Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a source SN or the gNB-DU of the source SN (for the inter-SN LTM scenario triggered by the SN) or to an MN or the gNB-DU of the MN (for the inter-SN LTM scenario triggered by the MN). In this case, when the LTM is triggered, the source SN or gNB-DU of the source SN or the MN or gNB-DU of the MN selects a certain TCI state on a certain candidate PSCell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0909] Procedure 624: The candidate S-NG-RAN node or candidate gNB-CU forwards, through the received M-NG-RAN node ID information or mapping ID / index / identifier information, the TA-related information to the corresponding M-NG-RAN node using the existing message or the newly defined Xnap information (alternatively, the message name can be TA Information Transfer or else), which includes one or more of the following information:

[0910] -TA Information List (the same UE may have different TA values for different candidate PSCells, and different UEs may have different TA values for the same candidate PSCell)

[0911] -Candidate PSCell ID (a Cell ID or NR CGI)

[0912] -TA Value

[0913] -Preamble Index

[0914] -Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0915] -Source S-NG-RAN Node ID Information (a global NG-RAN node ID (i.e. a global gNB ID or global ng-eNB ID)). This information is carried to indicate that the MN continues to forward the TA-related information to the indicated S-NG-RAN node.

[0916] -Source SN gNB-DU ID Information and S-NG-RAN node ID (to which the SN gNB-DU ID belongs, and indicated through a global NG-RAN node ID (i.e. global gNB ID or global ng-eNB ID)). This information is carried to indicate that the MN continues to forward 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.

[0917] -MN gNB-DU ID Information. If the RACH configuration of the candidate PSCell is based on the MN gNB-DU, this information may be carried to indicate that the MN continues to forward the TA-related information to the corresponding gNB-DU according to the MN gNB-DU ID.

[0918] -Mapping ID / Index / Identifier Information of LTM S-NG-RAN node or SN gNB-DU, mapped to the source S-NG-RAN node ID or source SN gNB-DU. This information may be carried to indicate that the MN continues to forward the TA-related information to the S-NG-RAN node to which the mapping ID / index / identifier is mapped.

[0919] -Mapping ID / Index / Identifier Information of LTM MN gNB-DU, mapped to the MN gNB-DU. This information may be carried to indicate that the MN continues to forward the TA-related information to the MN gNB-DU to which the mapping ID / index / identifier is mapped.

[0920] -Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a source SN or the gNB-DU of the source SN (for the inter-SN LTM scenario triggered by the SN) or to an MN or the gNB-DU of the MN (for the inter-SN LTM scenario triggered by the MN). In this case, when the LTM is triggered, the source SN or source gNB-DU or the MN or gNB-DU of the MN selects a certain TCI state on a certain candidate PSCell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0921] Procedure 625: The MN forwards the TA-related information to the corresponding source S-NG-RAN node or source SN SN gNB-CU through the existing message or the newly defined Xnap information (alternatively, the message name can be TA Information Transfer or else), which includes one or more of the following information:

[0922] -TA Information List (the same UE may have different TA values for different candidate PSCells, and different UEs may have different TA values for the same candidate PSCell)

[0923] -Candidate PSCell ID (a Cell ID or NR CGI)

[0924] -TA Value

[0925] -Preamble Index

[0926] -Random Access-Radio Network Temporary Indentifier (RA-RNTI)

[0927] -Source gNB-DU ID Information. This information is carried to indicate that the gNB-CU of the source SN continues to forward the TA-related information to the indicated source gNB-DU.

[0928] -Mapping ID / Index / Identifier Information of LTM gNB-DU, mapped to the source gNB-DU. This information may be carried to indicate that the source gNB-CU continues to forward the TA-related information to the source gNB-DU to which the mapping ID / index / identifier is mapped

[0929] -Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate cell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate cell is for is required to be told to a source SN or the gNB-DU of the source SN (for the inter-SN LTM scenario triggered by the SN). In this case, when the LTM is triggered, the source SN or source gNB-DU selects a certain TCI state on a certain candidate PSCell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0930] If the RACH configuration of the candidate PSCell is allocated based on the M-NG-RAN node or the MN gNB-DU, the procedures 625-627 associated with the transmission of TA information on the S-SN side are omitted. Then, after procedure 624, if the MN is in a gNB-CU and a gNB-DU split architecture, 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 to the MN gNB-DU ID to which the mapping ID / index / identifier is mapped.

[0931] Procedure 626: After receiving the relevant TA information, based on the implementation of procedure 609, the source gNB-CU continues to allocate the corresponding RACH configuration to the source gNB-DU based on the implementation of the RACH configuration allocated to this NG-RAN node by each candidate PSCell. The source gNB-CU can determine which source gNB-DU the TA-related information needs to be forwarded to through the TA-associated information (different UEs under different source gNB-DUs under the source NG-RAN node may initiate an LTM configuration to the same candidate PSCell). Optionally, if the source gNB-CU receives the indicated source gNB-DU ID information or the mapping ID / index / identifier information of the LTM gNB-DU in procedure 625, the source gNB-CU continues to forward the relevant TA information to the corresponding source gNB-DU.

[0932] Procedure 627: The source gNB-CU transmits the TA value information, associated CFRA resource information (preamble index and RA-RNTI), a candidate PSCell ID and a timing advance group identity pointer (Tag ID Pointer) to the corresponding source gNB-DU through a CU-DU TA Information Transfer message.

[0933] Procedure 628: For the inter-SN LTM request triggered by the S-SN, the UE transmits 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 may transmit the layer 1 measurement report to the MN or the gNB-DU serving the UE under the MN.

[0934] Procedure 629: The source gNB-DU (which may optionally refer to the source gNB-DU of the source SN or the source gNB-DU serving the UE under the MN) decides to perform LTM cell switch on a candidate target PSCell.

[0935] Procedure 630: The source gNB-DU (which may optionally refer to the source gNB-DU of the source SN or the source gNB-DU under the MN) transmits a Cell Switch Command to the UE. Optionally, the Cell Switch Command includes an indication to the UE (indicating that the type of the accessed cell is the primary secondary cell PSCell in the SCG, or indicating that the Cell Switch Command is a Cell Switch Command for the SCG, not for the MCG), to distinguish from the type of the cell accessed by the UE in the current signaling is the MCG cell or the target cell under a single connectivity.

[0936] Procedure 631: The source SN gNB-DU (or MN gNB-DU) transmits a DU-CU Cell Switch Notification message to the source SN gNB-CU (or MN gNB-CU), indicating that the Cell Switch Command is initiated to the UE. The DU-CU Cell Switch Notification message includes a target cell PSCell ID and cell switch information (which includes a joint / downlink TCI state ID, and may include an uplink TCI state ID), and includes a TA information list (including valid TA values of one or more candidate cells PSCells, a timing advance group identity pointer (TAG ID Pointer), as well as possible valid time information, and transferred by the source SN gNB-DU through the source SN gNB-CU, the MN and the target SN gNB-CU to the target SN gNB-DU for use).

[0937] Procedure 632: The source S-NG-RAN node or source SN gNB-CU forwards an LTM Cell Switch Notification to the MN through an existing or newly defined Xnap message (alternatively, the message name can be LTM Cell Switch Notification or LTM PSCell Switch Notification), the notification including one or more of the following information:

[0938] -Target Cell ID or Target PSCell ID (represented by a Cell ID or NR CGI)

[0939] -TCI State ID (corresponding to a CandidateTCI-StatesId IE defined in TS 38.331)

[0940] -LTM Cell Switch Information

[0941] >Joint or Downlink (DL) TCI State ID (corresponding to a TCI-StateId IE defined in TS 38.331)

[0942] >Uplink (UL) TCI State ID (corresponding to a TCI-UL-StateId IE defined in TS 38.331)

[0943] -TA Information List (including one or more candidate cell PSCell IDs and corresponding valid TA values, as well as possible valid time information)

[0944] >Candidate Cell PSCell ID (represented by a Cell ID or NR CGI)

[0945] >TA Value (indicating the valid TA value of a candidate cell PSCell, and transferred to a target SN or the gNB-DU of the target SN for use)

[0946] >Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate PSCell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate PSCell is for is required to be told to the source SN or the gNB-DU of the source SN (for the scenario of SN triggered inter-SN LTM) (after a candidate SN gNB or the gNB-DU of the candidate SN is accessed by the UE, the candidate SN gNB or the gNB-DU of the candidate SN is the source SN gNB or the gNB-DU of the source SN for the subsequent LTM), or told to the MN or the gNB-DU of the MN (for the scenario of MN triggered inter-SN LTM). In this case, when the LTM is triggered, the source SN or the source gNB-DU of the SN, or the MN or the gNB-DU of the MN selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0947] >TA Value Validation Time (TA valid timer)

[0948] If the MN or MN gNB-DU triggers the Cell Switch Command, and the MN gNB-DU transmits the DU-CU Cell Switch Notification message to the MN gNB-CU, procedure 632 will be omitted.

[0949] Procedure 633: The MN forwards an LTM Cell Switch Notification to the target S-NG-RAN node or target SN gNB-CU (the S-NG-RAN node or gNB-CU to which the target PSCell belongs) through an existing or newly defined Xnap message (alternatively, the message name can be LTM Cell Switch Notification or LTM PSCell Switch Notification), the notification including one or more of the following information:

[0950] -Target Cell ID or Target PSCell ID (represented by a Cell ID or NR CGI)

[0951] -TCI State ID (corresponding to a CandidateTCI-StatesId IE defined in TS 38.331)

[0952] -LTM Cell Switch Information

[0953] >Joint or Downlink (DL) TCI State ID (corresponding to a TCI-StateId IE defined in TS 38.331)

[0954] >Uplink (UL) TCI State ID (corresponding to a TCI-UL-StateId IE defined in TS 38.331)

[0955] -TA Information List (including one or more candidate cell PSCell IDs and corresponding valid TA values, as well as possible valid time information)

[0956] >Candidate Cell PSCell ID (represented by a Cell ID or NR CGI)

[0957] >TA Value (indicating the valid TA value of a candidate cell PSCell, and transferred to a target SN or the gNB-DU of the target SN for use)

[0958] >Timing Advance Group (TAG) Identity (ID) Pointer, including the tag-Id-ptr information defined by a TCI-UL-State IE or TCI-State IE in TS 38.331. When the candidate PSCell is a MIMO cell, there may be a multi-TRP (transmit / receive point) operation. In this case, at most 2 different TAGs are configured, and each TCI state is associated with one TAG. Which TAG the TA calculated by the candidate PSCell is for is required to be told to the source SN or the gNB-DU of the source SN (for the scenario of SN triggered inter-SN LTM) (after a candidate SN gNB or the gNB-DU of the candidate SN is accessed by the UE, the candidate SN gNB or the gNB-DU of the candidate SN is the source SN gNB or the gNB-DU of the source SN for the subsequent LTM), or told to the MN or the gNB-DU of the MN (for the scenario of MN triggered inter-SN LTM). In this case, when the LTM is triggered, the source SN or the source gNB-DU of SN, or the MN or the gNB-DU of the MN selects a certain TCI state on a certain candidate cell according to an L1 measurement report, and thus can determine the TA which TAG corresponds to should be used, and then transmits the TA to the UE through an LTM Cell Switch Command MAC CE.

[0959] >TA Value Validation Time (TA valid timer)

[0960] Procedure 634: The target S-NG-RAN node or SN gNB-CU transmits the target cell PSCell ID, cell switch information (which includes the joint / downlink TCI state ID, and may include the uplink TCI state ID), the TA information list (including the valid TA values of one or more candidate cells PSCells, the timing advance group identity pointer (TAG ID Pointer), as well as the possible valid time information) to the target gNB-DU through a CU-DU cell swith notification.

[0961] Procedure 635: The target gNB-DU detects the successful access of the UE (rach-less-based or rach-based access procedure).

[0962] Procedure 636: The target gNB-DU transmits an Access Success message (carrying a target Cell ID) to the gNB-CU.

[0963] Procedure 637: The UE transmits an RRC Reconfiguration Complete (RRCReconfigurationComplete) message to the MN after successfully accessing to the target cell.

[0964] Procedure 638: The MN transmits an SN Reconfiguration Complete message (S-NODE reconfiguration complete) to the target S-NG-RAN node, the message carrying the RRC Reconfiguration Complete transmited to the target S-NG-RAN node.

[0965] Procedure 639: For the subsequent LTM procedure, if the LTM Cell Switch Command is triggered by the MN, after learning that the UE has successfully accessed the target cell (possibly through procedure 637), the MN optionally transmits an Xnap message to the source S-NG-RAN node or the source SN gNB-CU to notify that the LTM Inter-SN is executed. Optionally, one or more of the following informat...

Claims

1.A method performed by a central unit (CU) in a wireless communication system, the method including:receiving, from a source distributed unit (DU), a notification message for a cell switch, the notification message including tag identifier (ID) pointer information corresponding to a timing advance (TA) valuetransmitting, to a target DU, the notification message for the cell switch.2.The method of claim 1, further comprising:transmitting, to a candidate base station, a handover request message including at least one of a target cell global ID, logical topology management (LTM) information request, early synchronization information request, an LTM reference configuration request indication, an LTM reference configuration, an LTM channel state information (CSI) resource configuration, or an LTM configuration ID mapping list; andas a response to the handover request message, receiving, from the candidate base station, a handover request acknowledge message including at least one of a transmission configuration indication (TCI) state configuration list, a list of the early synchronization information, the LTM reference configuration, the LTM CSI resource configuration.3.The method of claim 2, further comprising:transmitting, to the candidate base station, a update request message to update LTM configuration data; andas a response to the update request message, receiving, from the candidate base station, a update acknowledge message including at least one of an LTM reference configuration, or a CSI report configuration.4.The method of claim 2, further comprising:in case that a early TA acquisition procedure is triggered, receiving, from the candidate base station, a TA information transfer message including at least one of a TA value or information associated with the TA value.5.The method of claim 2, further comprising:in case that a cell switch is triggered, transmitting, to a target base station, a cell switch notification message including at least one of a target cell global ID, LTM cell switch information, a joint, a downlink (DL) TCI state ID, or a uplink (UL) TCI state ID.6.The method of claim 2, further comprising:in case that a LTM candidate cell is canceled, receiving, from the candidate base station, a LTM cancel message including at least one of a list of LTM cells to be released or a LTM cell ID.7.A central unit (CU) in a wireless communication system, the CU comprising:a transceiver, anda controller coupled with the transceiver configured to:receive, from a source distributed unit (DU), a notification message for a cell switch, the notification message including tag identifier (ID) pointer information corresponding to a timing advance (TA) valuetransmit, to a target DU, the notification message for the cell switch.8.The CU of claim 7, wherein the controller is further configured to:transmit, to a candidate base station, a handover request message including at least one of a target cell global ID, logical topology management (LTM) information request, early synchronization information request, an LTM reference configuration request indication, an LTM reference configuration, an LTM channel state information (CSI) resource configuration, or an LTM configuration ID mapping list; andas a response to the handover request message, receive, from the candidate base station, a handover request acknowledge message including at least one of a transmission configuration indication (TCI) state configuration list, a list of the early synchronization information, the LTM reference configuration, the LTM CSI resource configuration.9.The CU of claim 8, wherein the controller is further configured to:transmit, to the candidate base station, a update request message to update LTM configuration data; andas a response to the update request message, receive, from the candidate base station, a update acknowledge message including at least one of an LTM reference configuration, or a CSI report configuration.10.The CU of claim 8, wherein the controller is further configured to:in case that a early TA acquisition procedure is triggered, receive, from the candidate base station, a TA information transfer message including at least one of a TA value or information associated with the TA value.11.The CU of claim 8, wherein the controller is further configured to:in case that a cell switch is triggered, transmit, to a target base station, a cell switch notification message including at least one of a target cell global ID, LTM cell switch information, a joint, a downlink (DL) TCI state ID, or a uplink (UL) TCI state ID.12.The CU according to claim 8, wherein the controller is further configured to:in case that a LTM candidate cell is canceled, receive, from the candidate base station, a LTM cancel message including at least one of a list of LTM cells to be released or a LTM cell ID

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