Method and apparatus for UL synchronization and DL synchronization

Abstract

Embodiments of the present application relate to a method and apparatus for uplink (UL) synchronization and downlink (DL) synchronization in a lower layer-based mobility situation under a 3rd Generation Partnership Project (3GPP) 5G system or the like. In accordance with an embodiment of the present application, a candidate distributed unit (DU) of a base station (BS) includes a transceiver and a processor coupled to the transceiver; and the processor is configured to cause the candidate DU to: receive a request from a centralized unit (CU) of the BS, wherein the request includes identifier (ID) information for one or more candidate cells; and transmitting a response message to the CU based on the request, wherein the response message is associated with a cell handover procedure.

Description

Technical Field

[0001] Embodiments of the present application generally relate to wireless communication technology, and more particularly, to a method and apparatus for lower layer-based mobility with uplink (UL) synchronization and downlink (DL) synchronization before cell switching. Background Art

[0002] Wireless communication systems are widely deployed to provide various telecommunication services, such as telephony, video, data, messaging, broadcast, etc. Wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of wireless communication systems may include fourth generation (4G) systems (e.g., long term evolution (LTE) systems, advanced LTE (LTE-A) systems, or LTE-A Pro systems) and fifth generation (5G) systems, which may also be referred to as new radio (NR) systems.

[0003] Currently, details about UL synchronization and DL synchronization in lower layer based mobility have not been discussed in 3GPP 5G technology. Summary of the invention

[0004] Some embodiments of the present application provide a candidate distributed unit (DU) of a base station (BS). The candidate DU includes a transceiver and a processor coupled to the transceiver; and the processor is configured to cause the candidate DU to: receive a first request from a centralized unit (CU) of the BS, wherein the first request includes identifier (ID) information of one or more candidate cells; and transmit a response message to the CU based on the first request, wherein the response message is associated with a cell switching process.

[0005] In some embodiments of the present application, the response message includes at least one of the following: lower layer radio resource control (RRC) configuration information, which is associated with at least one candidate cell within the one or more candidate cells; random access channel (RACH) configuration information, which is used for a timing advance (TA) acquisition process performed by a user equipment (UE); a first indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; or a second indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the at least one candidate cell.

[0006] In an embodiment of the present application, TA acquisition or early TA acquisition means that the UE is expected to perform a TA acquisition process before a cell switching process. TA acquisition or early TA acquisition may be triggered by receiving an indication (e.g., a physical downlink control channel (PDCCH) command as downlink control information (DCI)) from a serving BS.

[0007] In some embodiments of the present application, the RACH configuration information includes at least one of the following: a random access (RA) preamble index; a synchronization signal / physical broadcast channel (SS / PBCH) index; or a RACH opportunity (RO).

[0008] In some embodiments of the present application, the RACH configuration information is included in a dedicated IE in the response message; or, the lower layer RRC configuration information is included in one or more IEs in the response message, and the RACH configuration information is merged into the one or more IEs.

[0009] In some embodiments of the present application, the RACH configuration information is included in the DU to CU RRC information IE included in the response message.

[0010] In some embodiments of the present application, the first request further includes at least one of the following: a third indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the candidate cell within the one or more candidate cells; or a fourth indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the candidate cell.

[0011] In some embodiments of the present application, the first request further includes at least one of the following: a fifth indication, which is used to indicate that the first request is for lower layer triggered mobility (LTM); ID information of the source DU of the BS; ID information of the UE; or ID information of the source cell of the UE.

[0012] In some embodiments of the present application, the processor is configured to enable the candidate DU to identify whether the at least one candidate cell and the first candidate cell within the one or more candidate cells have the same TA value for the UE based on the first request, and if the at least one candidate cell and the first candidate cell have the same TA value for the UE, then the response message further includes at least one of the following: a sixth indication, which is used to indicate whether the first TA value associated with the at least one candidate cell is the same as the second TA value associated with the first candidate cell; or ID information of the first candidate cell.

[0013] In some embodiments of the present application, the first request is received from the CU via the F1 interface, and the first request is a UE context establishment request message or a UE context modification request message; or the response message is transmitted to the CU via the F1 interface, and the response message is a UE context establishment response message or a UE context modification response message.

[0014] Some embodiments of the present application provide a centralized unit (CU) of a base station (BS). The CU includes a transceiver and a processor coupled to the transceiver; and the processor is configured to cause the CU to: transmit a first request to a candidate distributed unit (DU) of the BS, wherein the first request includes identifier (ID) information of one or more candidate cells; and receive a response message from the candidate DU, wherein the response message is associated with a cell switching process.

[0015] In some embodiments of the present application, the response message includes at least one of the following: lower layer radio resource control (RRC) configuration information, which is associated with at least one candidate cell within the one or more candidate cells; random access channel (RACH) configuration information, which is used for a timing advance (TA) acquisition process performed by a user equipment (UE); a first indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; or a second indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the at least one candidate cell.

[0016] In some embodiments of the present application, the processor is configured to cause the CU to transmit a first message to a source DU of the BS, the first message including the RRC configuration information associated with the at least one candidate cell, and the RRC configuration information including the lower layer RRC configuration information.

[0017] In some embodiments of the present application, the first message further includes first information, and the first information includes at least one of the following: a third indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; or a fourth indication, which is used to indicate whether the UE performs a DL synchronization operation before the cell switching process for the at least one candidate cell; or the RACH configuration information.

[0018] In some embodiments of the present application, the first information is included in the RRC configuration information in the first message or outside the RRC configuration information.

[0019] In some embodiments of the present application, the RACH configuration information includes at least one of the following: a random access (RA) preamble index; a synchronization signal / physical broadcast channel (SS / PBCH) index; or a RACH opportunity (RO).

[0020] In some embodiments of the present application, the RACH configuration information is included in a dedicated information element (IE) in the first message; or the first message includes one or more IEs, the IEs include the lower layer RRC configuration information, and the RACH configuration information is merged into the one or more IEs.

[0021] In some embodiments of the present application, the RACH configuration information is included in the CU to DU RRC information IE included in the first message.

[0022] In some embodiments of the present application, the first request is transmitted to the candidate DU via the first F1 interface, and the first request is a UE context establishment request message or a UE context modification request message; or the response message is received from the candidate DU via the first F1 interface, and the response message is a UE context establishment response message or a UE context modification response message; or the first message is transmitted to the source DU via the second F1 interface, and the first message is a DL RRC message transmission message or a UE context modification request message.

[0023] In some embodiments of the present application, at least one of the response message or the first message further includes at least one of the following: a fifth indication, which is used to indicate whether the first TA value associated with the at least one candidate cell is the same as the second TA value associated with the first candidate cell within the one or more candidate cells; or ID information of the first candidate cell.

[0024] In some embodiments of the present application, the processor is configured to cause the CU to receive the first request from a source DU of the BS.

[0025] In some embodiments of the present application, the first request further includes at least one of the following: a sixth indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the candidate cell within the one or more candidate cells; or a seventh indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the candidate cell.

[0026] In some embodiments of the present application, the first request further includes at least one of the following: an eighth indication, which is used to indicate that the first request is for lower layer triggered mobility (LTM); ID information of the source DU of the BS; ID information of the UE; or ID information of the source cell of the UE.

[0027] In some embodiments of the present application, the RACH configuration information is included in a dedicated information element (IE) in the response message; or, the lower layer RRC configuration information is included in one or more IEs in the response message, and the RACH configuration information is merged into the one or more IEs.

[0028] In some embodiments of the present application, the RACH configuration information is included in the DU to CU RRC information IE included in the response message.

[0029] Some embodiments of the present application provide a source distributed unit (DU) of a base station (BS). The source DU includes a transceiver and a processor coupled to the transceiver; and the processor is configured to cause the source DU to: receive a first message from a centralized unit (CU) of the BS, wherein the first message includes radio resource control (RRC) configuration information associated with at least one candidate cell related to a cell switching process; and transmit a second message including the RRC configuration information to a user equipment (UE).

[0030] In some embodiments of the present application, the first message further includes first information, and the first information includes at least one of the following: a first indication, which is used to indicate whether the UE performs timing advance (TA) acquisition before the cell switching process for the at least one candidate cell; or a second indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the at least one candidate cell; or random access channel (RACH) configuration information for the TA acquisition process performed by the UE.

[0031] In some embodiments of the present application, the first information is included in the RRC configuration information in the first message or outside the RRC configuration information.

[0032] In some embodiments of the present application, the RACH configuration information is included in a dedicated information element (IE) in the first message; or, the lower layer RRC configuration information is included in one or more IEs in the first message, and the RACH configuration information is merged into the one or more IEs.

[0033] In some embodiments of the present application, the RACH configuration information is included in the CU to DU RRC information IE included in the first message.

[0034] In some embodiments of the present application, at least one of the first message or the second message further includes at least one of the following: a third indication for indicating whether the first TA value associated with the at least one candidate cell is the same as the second TA value associated with the first candidate cell associated with the LTM; or ID information of the first candidate cell.

[0035] In some embodiments of the present application, before receiving the first message, the processor is configured to cause the source DU to transmit a first request to the CU for a random access channel (RACH) resource for requesting a timing advance (TA) acquisition process performed by the UE.

[0036] In some embodiments of the present application, the second message is an RRC reconfiguration message.

[0037] In some embodiments of the present application, the second message further includes at least one of the following: a fourth indication, which is used to indicate whether the UE performs a timing advance (TA) acquisition process before the cell switching process for the at least one candidate cell; a fifth indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the at least one candidate cell; or RACH configuration information for the TA acquisition process performed by the UE.

[0038] In some embodiments of the present application, the RACH configuration information includes at least one of the following: a random access (RA) preamble index; a synchronization signal / physical broadcast channel (SS / PBCH) index; or a RACH opportunity (RO).

[0039] In some embodiments of the present application, after transmitting the second message, the processor is configured to cause the source DU to transmit a sixth indication to indicate at least one of: performing a timing advance (TA) acquisition process; whether to create a dedicated medium access control (MAC) entity associated with the at least one candidate cell for the TA acquisition process performed by the UE; or performing a downlink (DL) synchronization operation to the at least one candidate cell.

[0040] In some embodiments of the present application, the sixth indication is included in the following: a physical downlink control channel (PDCCH) command; downlink control information (DCI); or a medium access control (MAC) control element (CE).

[0041] Some embodiments of the present application provide a user equipment (UE). The UE includes a transceiver and a processor coupled to the transceiver; and the processor is configured to enable the UE to: receive a first message from a source distributed unit (DU) of the (BS), wherein the first message includes radio resource control (RRC) configuration information associated with at least one candidate cell related to a cell switching process; and receive a first indication from the source DU to trigger a timing advance (TA) acquisition process or a downlink (DL) synchronization operation.

[0042] In some embodiments of the present application, the first message is an RRC reconfiguration message.

[0043] In some embodiments of the present application, the first message further includes at least one of the following: a second indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; a third indication, which is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the at least one candidate cell; or random access channel (RACH) configuration information for the TA acquisition process.

[0044] In some embodiments of the present application, the RACH configuration information includes at least one of the following: a random access (RA) preamble index; a synchronization signal / physical broadcast channel (SS / PBCH) index; or a RACH opportunity (RO).

[0045] In some embodiments of the present application, the first message further includes at least one of the following: a fourth indication, which is used to indicate whether the first TA value associated with the at least one candidate cell is the same as the second TA value associated with the first candidate cell associated with the LTM; or ID information of the first candidate cell.

[0046] In some embodiments of the present application, the processor is configured to cause the UE to start performing the DL synchronization operation to the at least one candidate cell after receiving the first message.

[0047] In some embodiments of the present application, the processor is configured to, after receiving the RRC configuration information associated with the at least one candidate cell, cause the UE to perform the TA acquisition process before the cell switching process.

[0048] In some embodiments of the present application, the processor is configured to enable the UE to perform the TA acquisition process based on a MAC entity of the UE or an RLC entity of the UE.

[0049] In some embodiments of the present application, the processor is configured to enable the UE to determine to create a dedicated medium access control (MAC) entity for the TA acquisition process based on one of the following: receiving a fifth indication from the source DU, and the fifth indication instructs the UE to create a MAC entity associated with the at least one candidate cell for the TA acquisition process; the index of the candidate distributed unit (DU) of the BS is different from the index of the source DU; or the index of the candidate cell group of the BS is different from the index of the source cell group of the BS.

[0050] In some embodiments of the present application, the fifth indication is included in the following: the first message; a physical downlink control channel (PDCCH) command; downlink control information (DCI); or a medium access control (MAC) control element (CE).

[0051] In some embodiments of the present application, in response to determining to create the dedicated MAC entity for the TA acquisition process, the processor is configured to cause the UE to perform at least one of the following: creating the MAC entity for the TA acquisition process; or creating a radio link control (RLC) entity associated with the at least one candidate cell for the TA acquisition process.

[0052] In some embodiments of the present application, at least one of the MAC entity or the RLC entity is created by the UE based on default configuration information configured to the UE, and wherein the processor is configured to cause the UE to release both the MAC entity and the RLC entity after acquiring a TA value associated with the at least one candidate cell through the TA acquisition process.

[0053] In some embodiments of the present application, at least one of the MAC entity or the RLC entity is created by the UE based on the RRC configuration information associated with the at least one candidate cell, and wherein the processor is configured to cause the UE to maintain at least one of the MAC entity or the RLC entity after acquiring a TA value related to the at least one candidate cell through the TA acquisition process.

[0054] In some embodiments of the present application, if the at least one candidate cell includes a second candidate cell and a third candidate cell, the processor is configured to enable the UE to: create at least one of a first MAC entity or a first RLC entity of the second candidate cell, and after obtaining a TA value related to the second candidate cell, maintain the at least one of the first MAC entity or the first RLC entity; and create at least one of a second MAC entity or a second RLC entity of the third candidate cell, and after obtaining a TA value related to the third candidate cell, maintain the at least one of the second MAC entity or the second RLC entity.

[0055] In some embodiments of the present application, the processor is configured to enable the UE to: receive a cell switching command associated with the third candidate cell from the source DU; and after switching from the source cell of the UE to the third candidate cell, maintain or release at least one of the first MAC entity or the first RLC entity.

[0056] Some embodiments of the present application provide a method performed by a candidate distributed unit (DU) of a base station (BS). The method includes: receiving a first request from a centralized unit (CU) of the BS, wherein the first request includes identifier (ID) information of one or more candidate cells; and transmitting a response message to the CU based on the first request, wherein the response message is associated with a cell switching process.

[0057] Some embodiments of the present application provide a method performed by a centralized unit (CU) of a base station (BS). The method includes: transmitting a first request to a candidate distributed unit (DU) of the BS, wherein the first request includes identifier (ID) information of one or more candidate cells; and receiving a response message from the candidate DU, wherein the response message is associated with a cell switching process.

[0058] Some embodiments of the present application provide a method performed by a source distributed unit (DU) of a base station (BS). The method includes: receiving a first message from a centralized unit (CU) of the BS, wherein the first message includes radio resource control (RRC) configuration information associated with at least one candidate cell related to a cell switching process; and transmitting a second message including the RRC configuration information to a user equipment (UE).

[0059] Some embodiments of the present application provide a method performed by a UE. The method includes: receiving a first message from a source distributed unit (DU) of the (BS), wherein the first message includes radio resource control (RRC) configuration information associated with at least one candidate cell related to a cell switching process; and receiving a first indication from the source DU to trigger a timing advance (TA) acquisition process or a downlink (DL) synchronization operation.

[0060] Some embodiments of the present application provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement the above method performed by a UE or a network node (e.g., a base station (BS), a CU, or a DU).

[0061] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to describe the manner in which the advantages and features of the present application can be obtained, the description of the present application is presented by reference to specific embodiments of the present application illustrated in the accompanying drawings. These drawings depict only example embodiments of the present application and therefore should not be considered limiting of its scope.

[0063] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present application.

[0064] Figure 2 A schematic diagram illustrating inter-cell layer 1 / layer 2 (L1 / L2) mobility according to some embodiments of the present application.

[0065] Figures 3 to 6 An exemplary flow chart associated with a cell switching process according to some embodiments of the present application is illustrated.

[0066] Figures 7 to 9 An exemplary flow chart illustrating a cell switching process according to some embodiments of the present application.

[0067] Fig.10 A block diagram illustrating an exemplary apparatus according to some embodiments of the present application. DETAILED DESCRIPTION

[0068] The detailed description of the accompanying drawings is intended as a description of the preferred embodiments of the present application and is not intended to represent the only form in which the present application can be practiced. It should be understood that the same or equivalent functions can be accomplished by different embodiments that are intended to be included in the spirit and scope of the present application.

[0069] Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided under specific network architectures and new service scenarios (e.g., 3GPP 5G, 3GPP LTE Release 8, etc.). It is considered that, with the development of network architectures and new service scenarios, all embodiments in the present application are also applicable to similar technical problems; and in addition, the terms described in the present application may change, which should not affect the principles of the present application.

[0070] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present application. Figure 1 , the wireless communication system 100 includes at least one base station (BS) 101 and at least one user equipment (UE) 102. Specifically, for the purpose of illustration, the wireless communication system 100 includes one BS 101 and two UEs 102 (e.g., UE 102a and UE 102b). Figure 1 Only a specific number of BSs and UEs are illustrated in FIG. 1 , but it is considered that in some other embodiments of the present application, the wireless communication system 100 may include more or less BSs and UEs.

[0071] The wireless communication system 100 is compatible with any type of network capable of sending and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a network based on time division multiple access (TDMA), a network based on code division multiple access (CDMA), a network based on orthogonal frequency division multiple access (OFDMA), an LTE network, a network based on 3GPP, a 3GPP5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0072] BS 101 may communicate with a core network (CN) node (not shown) (e.g., a mobility management entity (MME) or a serving gateway (S-GW), a mobility management function (AMF), or a user plane function (UPF), etc.) via an interface. A BS may also be referred to as an access point, an access terminal, a base station, a macro cell, a Node B, an enhanced Node B (eNB), a gNB, a home Node B, a relay node or a device, or described using other terms used in the art. In 5G NR, a BS may also be referred to as a RAN node or a network device. Each BS may serve several UEs within a service area, such as a cell or a cell sector, via a wireless communication link. For example, during a handover process for a UE, neighboring BSs may communicate with each other as needed.

[0073] UE 102 (e.g., UE 102a and UE 102b) should be understood as any type of terminal device, which may include a computing device, such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (e.g., a TV connected to the Internet), a set-top box, a game console, a security system (including a security camera), a car computer, a network device (e.g., a router, a switch and a modem), or the like. According to an embodiment of the present application, UE 102 may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identity module, a personal computer, a selective call receiver, or any other device capable of sending and receiving communication signals on a wireless network. In some embodiments, UE 102 may include a wearable device, such as a smart watch, a fitness bracelet, an optical head-mounted display, or the like. In addition, UE 102 may be referred to as a subscriber unit, a mobile device, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device, or described using other terms used in the art. UE 102 may communicate directly with BS 101 via uplink (UL) communication signals.

[0074] In 3GPP Release 18, support for inter-cell mobility based on Layer 1 / Layer 2 (L1 / L2) signaling has been discussed. Specifically, the UE may be provided with configurations from multiple cells in advance, and the BS (e.g., gNB) may switch the UE to a new cell using L1 / L2 signaling in consideration of receiving physical layer measurement results. According to the 3GPP standard document, a BS may be composed of a BS centralized unit (CU) and one or more BS distributed units (DU). The BS-CU and BS-DU are connected via the F1 interface, which is a logical interface. One BS-DU is connected to only one BS-CU.

[0075] Figure 2 A schematic diagram illustrating inter-cell layer 1 / layer 2 (L1 / L2) mobility according to some embodiments of the present application. Figure 2 As shown in FIG, the CU can communicate with two DUs (ie, DU1 or DU2) via the F1 interface. Figure 2 The CU in may implement the legacy mobility decision based on layer 3 (L3) measurement results. Figure 2 DU1 or DU2 in the L1 / L2 mobility decision can be implemented based on the physical layer measurement results.

[0076] Compared to the legacy L3 mobility, L1 / L2 mobility is considered faster with less processing delay and signaling delay. Figure 2CU shown in FIG. 4 makes mobility decisions based on received radio resource management (RRM) measurement reports. Unlike legacy L3 mobility, in L1 / L2 mobility, DUs (e.g., Figure 2 DU1 or DU2 shown in the figure makes mobility decisions based on physical layer measurements carried, for example, in channel state information (CSI) reports. In addition, in legacy L3 mobility, a handover command is sent from the SN CU to the UE via an RRC message, while in L1 / L2 mobility, a "handover" command is sent from the DU to the UE via L1 / L2 signaling (e.g., downlink control information (DCI) or medium access control (MAC) control element (CE)). The "handover" command in L1 / L2 mobility can be about cell activation or deactivation, for example, activating a new serving PCell while deactivating an old serving PCell.

[0077] At present, the problem of UL synchronization and DL synchronization in the case of lower layer-based mobility has not been solved. Embodiments of the present application are intended to solve such problems. For example, some embodiments of the present application study the initiation of a TA acquisition process, such as candidate DU-based initiation, source DU-based initiation, and CU-based initiation of a TA acquisition process. Some embodiments of the present application study a mechanism in which two candidate cells have the same TA value and the UE is not expected to be triggered twice by a PDCCH command. The mechanism is enhanced to support avoiding the acquisition of the same TA value. In an embodiment of the present application, TA acquisition or early TA acquisition means that the UE is expected to perform a TA acquisition process before a cell switching process. TA acquisition or early TA acquisition can be triggered by receiving an indication from a serving BS (e.g., a PDCCH command as a DCI).

[0078] Some embodiments of the present application study whether another protocol stack (e.g., MAC entity) should be created when the UE receives a PDCCH command and how to determine whether to create a MAC entity for RACH. Some embodiments of the present application enhance F1 signaling to support the network (e.g., candidate cell) to configure the DL synchronization operation of part of the candidate cell. Some embodiments of the present application study when the UE starts to perform the DL synchronization operation of part of the candidate cell.

[0079] Some embodiments of the present application may be applicable to the case of "lower layer triggered mobility" or "L1 / L2 triggered mobility", and the abbreviation of at least one of them may be "LTM". In the LTM case, the UE may access the serving BS (e.g., the serving gNB). The UE may report the layer 3 (L3) measurement results based on the configuration from the serving gNB. If the serving gNB (e.g., the CU of the serving gNB) decides to switch the UE to a candidate cell based on the measurement results, the serving gNB may request the target DU to prepare the configuration of one or more candidate cells. After receiving the candidate cell configuration from the target DU of the serving gNB, the serving gNB may transmit an RRC reconfiguration message including ID information of one or more candidate cells to the UE. For example, the CU may transmit the RRC reconfiguration message to the UE via the source DU of the serving gNB. The UE may transmit an RRC reconfiguration complete message to the serving gNB (e.g., the CU) via the source DU. The UE may ensure UL synchronization or DL ​​synchronization before receiving a cell switching command. For example, the UE may obtain or acquire a TA value via random access (RA) or preamble transmission. The UE may report Layer 1 (L1) measurements for dynamic switching purposes. The serving gNB (e.g., source DU) may transmit a cell switching command, such as a MAC CE or DCI. The UE may apply the RRC reconfiguration message and start a timer upon receiving the lower layer command.

[0080] Specifically, in the present application Figures 3 to 10 In the embodiments, both inter-DU mobility cases and intra-DU mobility cases are considered, for example, inter-gNB-DU LTM or intra-gNB-DU LTM. Inter-DU mobility means that the connection to the CU remains unchanged, while the UE may change from a source cell associated with a source DU to a target cell associated with a target DU due to mobility, and both the source DU and the target DU are managed by the CU. Intra-DU mobility means that the connection to the CU remains unchanged, while the UE may change from a source cell to a target cell associated with the same DU due to mobility. More details will be explained in the following text with reference to the accompanying drawings.

[0081] Figure 3 An exemplary flow chart associated with a cell switching process according to some embodiments of the present application is illustrated. Figure 3 The exemplary flowchart 300 in the embodiment of the present invention may be composed of a candidate DU (e.g., as in Figure 2 In some cases, the candidate DU may also be referred to as the target DU. Although described with respect to the candidate DU, it should be understood that other devices may be configured to perform similar Figure 3 The details described in all other embodiments of this application can be applied to Figure 3 In addition, in Figure 3 The details described in the embodiments may be applied to Figure 1 , 2 and all embodiments 4 to 10.

[0082] In exemplary flowchart 300, at operation 301, a candidate DU (e.g., Figure 2 DU1) can be obtained from the CU of the BS (e.g., Figure 2 The request may include ID information of one or more candidate cells.

[0083] In some embodiments, the request is received from the CU via the F1 interface. The request may be referred to as an F1 request message or the like. For example, the request may be a UE context establishment request message or a UE context modification request message. In some embodiments, the request is received by the CU from a source DU of the BS (e.g., Figure 2 DU2) shown and described in FIG. 1 is received and then transmitted to the candidate DU.

[0084] In such Figure 3 In operation 302, the candidate DU may transmit a response message associated with a cell switching process to the CU based on the request. In some embodiments, the candidate DU may determine whether to accept the request received in operation 301 and transmit the response message to the CU in response to determining to accept the request.

[0085] In some embodiments, in operation 302, a response message is transmitted to the CU via the F1 interface. The response message may be referred to as an F1 response message or the like. For example, the response message may be a UE context establishment response message or a UE context modification response message. Figure 7 and 8 Specific examples are described in the embodiments of the present invention.

[0086] In some embodiments, the response message in operation 302 includes at least one of the following:

[0087] (1) Lower layer RRC configuration information associated with at least one candidate cell among the one or more candidate cells. For example, the lower layer RRC configuration information may be referred to as “lower layer RRC configuration of LTM”, “L1 / L2

[0088] RRC configuration information", "RRC configuration of LTM", "LTM configuration information" or the like.

[0089] (2) By UE (for example, Figure 1301). The RACH configuration information may be referred to as "RACH configuration for TA acquisition" or the like. In some embodiments, the RACH configuration information includes at least one of: an RA preamble index; an SS / PBCH index; or an RO. In some embodiments, the candidate DU generates the RACH configuration information after receiving the request in operation 301.

[0090] (3) An indication (for simplicity, indicated as indication #1) for indicating whether the UE performs the TA acquisition procedure before the cell switching procedure for the at least one candidate cell. Indication #1 may be referred to as "early TA acquisition indication" or the like. Early TA acquisition means that the UE is expected to perform the TA acquisition procedure before the cell switching procedure.

[0091] (4) An indication for indicating whether the UE performs a DL synchronization operation before a cell switching procedure for the at least one candidate cell (denoted as indication #2 for simplicity). Indication #2 may be referred to as an "indication of early DL synchronization" or the like. Early DL synchronization means that the UE is expected to perform a DL synchronization operation before a cell switching procedure. Figure 7 Specific examples are described in the embodiments of the present invention.

[0092] In some embodiments, the lower layer RRC configuration information is included in one or more IEs in the response message, and the RACH configuration information is merged into the one or more IEs. In these embodiments, indication #1 may be included in the response message. If indication #1 is not included in the response message, the CU needs to read the container. If RACH resources for TA acquisition are included, the CU needs to transmit an indication of early TA acquisition and indicate the corresponding RACH resources (e.g., RACH configuration for TA acquisition) to the source DU.

[0093] In some other embodiments, the RACH configuration for TA acquisition is included in a dedicated IE in the response message. That is, the RACH configuration for TA acquisition is not merged into the lower layer RRC configuration of LTM. In these embodiments, if indication #1 is not included, the RACH configuration for TA acquisition as a separate IE in the response message can be used to implicitly indicate early TA acquisition, that is, the RACH configuration for TA acquisition can implicitly indicate that the UE is expected to perform the TA acquisition procedure before the cell switching procedure.

[0094] In an embodiment, the RACH configuration for TA acquisition is included in the "DU to CU RRC Information IE" included in the response message (as specified in the 3GPP standard document TS38.473). For example, the RACH configuration for TA acquisition may be included in the "DU to CU RRC Information IE" as a separate IE, for example, as a sub-IE of the "DU to CU RRC Information IE" of the response message. In another embodiment, the RACH configuration for TA acquisition is included in the response message as an IE other than the "DU to CU RRC Information IE" included in the response message, for example, as an IE in parallel with the "DU to CU RRC Information IE".

[0095] In some embodiments, the request received by the candidate DU in operation 301 further includes at least one of the following:

[0096] (1) An indication for indicating whether the UE performs the TA acquisition procedure before the cell switching procedure for a candidate cell within one or more candidate cells (denoted as indication #3 for simplicity). Indication #3 may be referred to as "early TA acquisition indication" or the like.

[0097] (2) An indication for indicating whether the UE performs a DL synchronization operation before a cell switching procedure for the candidate cell (for simplicity, indicated as indication #4). Indication #4 may be referred to as an "early DL synchronization indication".

[0098] or similar. Figure 7 Specific examples are described in the embodiments of the present invention.

[0099] In some embodiments, the request received by the candidate DU in operation 301 further includes at least one of the following:

[0100] (1) An indication indicating that the request is for LTM (for simplicity, indicated as indication #5). For example, indication #5 indicates that the request is for requesting RRC configuration of LTM.

[0101] (2) ID information of the source DU of the BS.

[0102] (3)UE ID information.

[0103] (4) ID information of the UE's source cell. Figure 8 Specific examples are described in the embodiments of the present invention.

[0104] In some embodiments, the candidate DU may identify, based on the request, whether at least one candidate cell and another candidate cell within the one or more candidate cells (denoted as candidate cell #1 for simplicity) have the same TA value for the UE. If the at least one candidate cell and candidate cell #1 have the same TA value for the UE, the response message further includes at least one of the following:

[0105] (1) An indication for indicating whether the TA value associated with the at least one candidate cell is the same as the TA value associated with candidate cell #1 (for simplicity, indicated as indication #6).

[0106] (2) ID information of candidate cell #1 For example, if the TA value associated with at least one candidate cell is the same as the TA value associated with candidate cell #1, the response message further includes the ID information of candidate cell #1.

[0107] As follows Figure 8 Specific examples are described in the embodiments of the present invention.

[0108] Figure 4 A further exemplary flow chart associated with a cell handover process according to some embodiments of the present application is illustrated. Figure 4 The exemplary flowchart 400 in the embodiment of the present invention may be performed by a CU (e.g., as in Figure 2 Although described with respect to a CU, it should be understood that other devices may be configured to perform similar Figure 4 The details described in all other embodiments of this application can be applied to Figure 4 In addition, in Figure 4 The details described in the embodiments may be applied to Figures 1 to 3 and all embodiments from 5 to 10.

[0109] In such Figure 4 In the exemplary flowchart 400 shown in FIG. 4 , in operation 401, a CU (e.g., Figure 2 CU shown and described in the figure) may provide candidate DUs (e.g., Figure 2 In some embodiments, the request is transmitted to the candidate DU via the F1 interface. For example, the request may be a UE context establishment request message or a UE context modification request message.

[0110] In some embodiments, the request transmitted by the CU in operation 401 further includes at least one of the following:

[0111] (1) an indication for indicating whether the UE performs the TA acquisition process before the cell switching process for the candidate cell in the one or more candidate cells, for example, an indication for early TA acquisition (for example, Figure 3 Instruction #3) described in the embodiments.

[0112] (2) an indication for indicating whether the UE performs a DL synchronization operation before a cell switching process for the candidate cell, for example, an indication for early DL synchronization (for example, Figure 3 Instruction #4) described in the embodiments.

[0113] As follows Figure 7 Specific examples are described in the embodiments of the present invention.

[0114] In some embodiments, the request transmitted by the CU in operation 401 further includes at least one of the following:

[0115] (1) An indication for indicating that the request is for lower layer triggered mobility (LTM) (e.g., Figure 3 Instruction #5) described in the embodiments;

[0116] (2) ID information of the source DU of the BS;

[0117] (3) UE ID information; or

[0118] (4) ID information of the UE's source cell. Figure 8 Specific examples are described in the embodiments of the present invention.

[0119] In some embodiments, the CU may receive, for example, from a source DU (eg, such as a Figure 2 DU2) shown and described in FIG. 4 receives the request and then transmits the request to the candidate DU in operation 401.

[0120] In such Figure 4 In operation 402 shown in FIG. 1 , the CU may receive a response message associated with a cell switching process from the candidate DU. In some embodiments, the response message is received via the F1 interface. For example, the response message is a UE context establishment response message or a UE context modification response message.

[0121] In some embodiments, the response message received by the CU in operation 402 includes at least one of the following:

[0122] (1) Lower layer RRC configuration information associated with at least one candidate cell within the one or more candidate cells, which may be referred to as “lower layer RRC configuration of LTM”, “L1 / L2 RRC configuration information of LTM”, “RRC configuration of LTM”, “LTM configuration information” or the like.

[0123] (2) By UE (for example, Figure 1 RACH configuration information for the TA acquisition process performed by the UE 102 shown and described in FIG. 1 , for example, “RACH configuration for TA acquisition”. In some embodiments, the RACH configuration information includes at least one of the following: a RA preamble index; a SS / PBCH index; or a RO.

[0124] (3) an indication for indicating whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell, for example, an indication for early TA acquisition (for example, Figure 3 Instruction #1) described in the embodiments.

[0125] (4) an indication for indicating whether the UE performs a DL synchronization operation before a cell switching process for the at least one candidate cell, for example, an indication for early DL synchronization (for example, Figure 3 Instruction #2) as described in the embodiment of Figure 7 Specific examples are described in the embodiments of the present invention.

[0126] In some embodiments, the RACH configuration information is included in a dedicated IE in the response message. In an embodiment, the RACH configuration information is included in a "DU to CU RRC Information IE" (as specified in 3GPP standard document TS38.473) included in the response message, for example, as a sub-IE of the "DU to CU RRC Information IE". In another embodiment, the RACH configuration information is included in the response message as an IE other than the "DU to CU RRC Information IE", for example, in parallel with the "DU to CU RRC Information IE".

[0127] In some other embodiments, the lower layer RRC configuration information is included in one or more IEs in the response message, and the RACH configuration information is combined into one or more IEs.

[0128] In some embodiments, the response message received by the CU in operation 402 further includes at least one of the following:

[0129] (1) used to indicate whether the TA value associated with the at least one candidate cell is consistent with another candidate cell in the one or more candidate cells (for example, Figure 3 The candidate unit #1) is associated with the same TA value as described in the embodiment, for example, Figure 3 Instruction #6 described in the embodiments of the present invention.

[0130] (2) ID information of another candidate cell, if the TA value associated with at least one candidate cell is the same as the TA value associated with another candidate cell. Figure 8 Specific examples are described in the embodiments of the present invention.

[0131] In some embodiments, the CU may send a signal to a source DU (eg, Figure 2 DU2) shown and described in FIG. 1 (denoted as message #1 for simplicity). Message #1 may include RRC configuration information associated with at least one candidate cell. For example, message #1 may include an RRC reconfiguration message, and the RRC reconfiguration message includes RRC configuration information. The RRC configuration information may include a lower layer RRC configuration of the LTM.

[0132] In some embodiments, message #1 is transmitted to the source DU via the F1 interface. For example, message #1 may be a DL RRC message transfer message or a UE context modification request message.

[0133] In some embodiments, message #1 further includes information (denoted as information #1 for simplicity) including at least one of the following:

[0134] (1) An indication for indicating whether the UE performs the TA acquisition procedure before the cell switching procedure for the at least one candidate cell (denoted as indication #7 for simplicity), for example, an indication for early TA acquisition.

[0135] (2) An indication for indicating whether the UE performs a DL synchronization operation before a cell switching procedure for the at least one candidate cell (denoted as indication #8 for simplicity), for example, an indication of early DL synchronization.

[0136] (3) RACH configuration information for the TA acquisition process performed by the UE. In some embodiments, the RACH configuration information includes at least one of the following: RA preamble index; SS / PBCH index; or RO. Figure 7 Specific examples are described in the embodiments of the present invention.

[0137] In some embodiments, information #1 may be included in or outside of RRC configuration information associated with at least one candidate cell in message #1.

[0138] In some embodiments, the RACH configuration information is included in a dedicated IE in message #1. In an embodiment, the RACH configuration information is included in the "CU to DU RRC Information IE" (as specified in 3GPP standard document TS38.473) included in message #1, for example, as a sub-IE of the "CU to DU RRC Information IE". In another embodiment, the RACH configuration information is included in the response message as an IE other than the "CU to DU RRC Information IE", for example, in parallel with the "CU to DU RRC Information IE".

[0139] In some other embodiments, message #1 includes one or more IEs including the lower layer RRC configuration information, and the RACH configuration information is incorporated into the one or more IEs within message #1.

[0140] In some embodiments, message #1 further includes at least one of the following:

[0141] (1) used to indicate whether the TA value associated with the at least one candidate cell is consistent with another candidate cell in the one or more candidate cells (for example, Figure 3 An indication (for simplicity, indicated as indication #9) having the same TA value associated with candidate unit #1) as described in the embodiment of the present invention.

[0142] (2) ID information of another candidate cell, if the TA value associated with at least one candidate cell is the same as the TA value associated with another candidate cell. Figure 8 Specific examples are described in the embodiments of the present invention.

[0143] Figure 5 Another exemplary flow chart associated with a cell switching process according to some embodiments of the present application is illustrated. Figure 5 The exemplary flowchart 500 in the embodiment of the present invention may be performed by a source DU (e.g., as in Figure 2 Although described with respect to a source DU, it should be understood that other devices may be configured to perform similar Figure 5 The details described in all other embodiments of this application can be applied to Figure 5 In addition, in Figure 5 The details described in the embodiments may be applied to Figures 1 to 4 and all embodiments 6 to 10.

[0144] In such Figure 5 In the exemplary flowchart 500 shown in FIG. 5 , in operation 501, a source DU (e.g., Figure 2 DU2) can be obtained from the CU of the BS (e.g., Figure 2 CU shown and described in Figure 4 Message #1 described in the embodiment of the present invention). The received message may include RRC configuration information associated with at least one candidate cell related to the cell switching process.

[0145] In some embodiments, the message received in operation 501 further includes at least one of the following information (e.g., Figure 4 The information #1) described in the embodiment of the present invention may be included in the RRC configuration information in the received message or in addition to the RRC configuration information:

[0146] (1) an indication for indicating whether the UE performs TA acquisition before a cell switching procedure for the at least one candidate cell, for example, an indication for early TA acquisition (for example, Figure 4 Instruction #7) described in the embodiments.

[0147] (2) an indication for indicating whether the UE performs a DL synchronization operation before a cell switching process for the at least one candidate cell, for example, an indication for early DL synchronization (for example, Figure 4 Instruction #8) described in the embodiments.

[0148] (3) RACH configuration information for the TA acquisition process performed by the UE. In some embodiments, the RACH configuration information includes at least one of the following: a RA preamble index; a SS / PBCH index; or a RO.

[0149] In some embodiments, the RACH configuration information is included in a dedicated IE in the message received in operation 501. In an embodiment, the RACH configuration information is included in a sub-IE of the "CU to DU RRC information IE". In another embodiment, the RACH configuration information is included in an IE other than the "CU to DU RRC information IE", for example, in parallel with the "CU to DU RRC information IE". In some other embodiments, the lower layer RRC configuration information is included in one or more IEs in the message received in operation 501, and the RACH configuration information is merged into one or more IEs.

[0150] In some embodiments, the message received in operation 501 further includes at least one of the following:

[0151] (1) indicating whether the TA value associated with the at least one candidate cell is the same as another candidate cell associated with the LTM (e.g., Figure 4 The candidate unit #1) is associated with the same TA value as described in the embodiment, for example, Figure 4 Instruction #9 described in the embodiments of the present invention.

[0152] (2) ID information of another candidate cell, if the TA value associated with at least one candidate cell is the same as the TA value associated with another candidate cell.

[0153] In some embodiments, before receiving the message in operation 501, the source DU may transmit a "request for RACH resources for requesting a TA acquisition procedure performed by the UE" to the CU.

[0154] In such Figure 5 In operation 502 shown in FIG. 1 , the source DU may send a signal to the UE (eg, Figure 1 UE 102 (shown and described in FIG. 1 ) transmits another message (denoted as message #2 for simplicity) including RRC configuration information. In some embodiments, message #2 is an RRC reconfiguration message.

[0155] In some embodiments, message #2 further includes at least one of the following:

[0156] (1) An indication for indicating whether the UE performs a TA acquisition procedure before a cell switching procedure for the at least one candidate cell (denoted as indication #10 for simplicity), for example, an indication for early TA acquisition.

[0157] (2) An indication for indicating whether the UE performs a DL synchronization operation before a cell switching procedure for the at least one candidate cell (denoted as indication #11 for simplicity), for example, an indication of early DL synchronization.

[0158] (3) RACH configuration information for the TA acquisition process performed by the UE. In some embodiments, the RACH configuration information includes at least one of the following: RA preamble index; SS / PBCH index; or RO. Figure 7 Specific examples are described in the embodiments of the present invention.

[0159] In some embodiments, message #2 may include at least one of the following:

[0160] (1) indicating whether the TA value associated with the at least one candidate cell is the same as another candidate cell associated with the LTM (e.g., Figure 4 An indication of the same TA value associated with candidate unit #1) as described in the embodiment (for simplicity, indicated as indication #12).

[0161] (2) ID information of another candidate cell, if the TA value associated with at least one candidate cell is the same as the TA value associated with another candidate cell. Figure 8 Specific examples are described in the embodiments of the present invention.

[0162] In some embodiments, after transmitting message #2, the source DU may transmit an indication (denoted as indication #13 for simplicity) to the UE, which may be included in a PDCCH order, DCI or MAC CE. Indication #13 may indicate at least one of the following:

[0163] (1) Execute the TA acquisition process;

[0164] (2) whether to create a dedicated MAC entity associated with at least one candidate cell for the TA acquisition procedure performed by the UE; or

[0165] (3) Perform DL synchronization operation to the at least one candidate cell. Figure 8 and 9 Specific examples are described in the embodiments of the present invention.

[0166] Figure 6 Another exemplary flow chart associated with a cell switching process according to some embodiments of the present application is described. Figure 6 The exemplary flowchart 600 in the embodiment of the present invention may be performed by a UE (e.g., as in Figure 1 Although described with respect to a UE, it should be understood that other devices may be configured to perform similar Figure 6 The details described in all other embodiments of this application can be applied to Figure 6 In addition, in Figure 6 The details described in the embodiments may be applied to Figures 1 to 5 and all embodiments of 7 to 10.

[0167] In such Figure 6 In the exemplary flowchart 600 shown in FIG. 6 , in operation 601, the UE may receive a source DU (e.g., Figure 2 DU2) receives a message as shown and described in the figure. The message may include RRC configuration information associated with at least one candidate cell related to the cell handover process. In some embodiments, the message is an RRC reconfiguration message.

[0168] In some embodiments, the message received by the UE in operation 601 further includes at least one of the following:

[0169] (1) an indication for indicating whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell, for example, an indication for early TA acquisition (for example, Figure 5 Instruction #10) described in the embodiments.

[0170] (2) an indication for indicating whether the UE performs a DL synchronization operation before a cell switching process for the at least one candidate cell, for example, an indication for early DL synchronization (for example, Figure 5 Instruction #11) described in the embodiments.

[0171] (3) RACH configuration information for TA acquisition process In some embodiments, the RACH configuration information includes at least one of the following: RA preamble index; SS / PBCH index; or RO.

[0172] In some embodiments, the message received by the UE in operation 601 further includes at least one of the following:

[0173] (1) indicating whether the TA value associated with the at least one candidate cell is the same as another candidate cell associated with the LTM (e.g., Figure 4 The candidate unit #1) is associated with the same TA value as described in the embodiment, for example, Figure 5 Instruction #12 described in the embodiments of the present invention.

[0174] (2) ID information of another candidate cell, if the TA value associated with at least one candidate cell is the same as the TA value associated with another candidate cell.

[0175] In such Figure 6 In operation 602, the UE may receive an indication (e.g., Figure 5 The indication #13 described in the embodiment of the present invention is used to trigger the TA acquisition process or DL ​​synchronization operation. The indication may be included in a PDCCH command, a DCI or a MAC CE.

[0176] In some embodiments, the UE may start performing a DL synchronization operation to at least one candidate cell after receiving the message in operation 601 .

[0177] In some embodiments, after receiving the RRC configuration information associated with the at least one candidate cell in the message in operation 601, the UE may perform the TA acquisition process before the cell switching process.

[0178] In some embodiments, the UE may perform the TA acquisition process based on a MAC entity of the UE or an RLC entity of the UE.

[0179] In some embodiments, the UE may determine to create a dedicated MAC entity for the TA acquisition process based on one of the following:

[0180] (1) receiving an indication from the source DU (e.g., Figure 5Instruction #13 described in the embodiment of the present invention). The instruction may instruct the UE to create a MAC entity associated with the at least one candidate cell for the TA acquisition process. In some embodiments, the instruction includes: a message received by the UE in operation 601;

[0181] PDCCH command; DCI; or MAC CE.

[0182] (2) The index of the candidate DU of the BS is different from the index of the source DU.

[0183] (3) The index of the candidate cell group of the BS is different from the index of the source cell group of the BS.

[0184] In some embodiments, in response to determining to create a dedicated MAC entity for the TA acquisition process, the UE may perform at least one of the following:

[0185] (1) creating the MAC entity for the TA acquisition process; or

[0186] (2) Creating an RLC entity associated with the at least one candidate cell for the TA acquisition process.

[0187] In some embodiments, the MAC entity and / or the RLC entity are created by the UE based on default configuration information configured to the UE.In an embodiment, after acquiring the TA value associated with the at least one candidate cell through a TA acquisition process, the UE may release both the MAC entity and the RLC entity.

[0188] In some other embodiments, the MAC entity and / or the RLC entity are created by the UE based on the RRC configuration information associated with the at least one candidate cell. In an embodiment, after acquiring the TA value associated with the at least one candidate cell through the TA acquisition process, the UE may maintain the MAC entity and / or the RLC entity.

[0189] In some embodiments, if at least one candidate cell includes two candidate cells, for example, candidate cell #2 and candidate cell #3, the UE may create a MAC entity and / or RLC entity of candidate cell #2, and after obtaining the TA value related to candidate cell #2, maintain the MAC entity and / or RLC entity of candidate cell #2; and the UE may create a MAC entity and / or RLC entity of candidate cell #3, and after obtaining the TA value related to candidate cell #3, maintain the MAC entity and / or RLC entity of candidate cell #3.

[0190] In an embodiment, the UE may receive a cell switching command associated with candidate cell #3 from the source DU. After switching from the source cell of the UE to candidate cell #3, the UE may maintain or release the MAC entity and / or RLC entity of candidate cell #2. Fig. 9 Specific examples are described in the embodiments of the present invention.

[0191] The following text describes Figures 3 to 6 A specific embodiment of the flowchart shown and described in any one of the foregoing. It should be understood by those skilled in the art that without departing from the spirit and scope of the present disclosure, Figures 7 to 9 The sequence of operations in any of the exemplary flowcharts 700, 800, and 900 in the example may be changed, and Figures 7 to 9 Some operations in any of the exemplary flowcharts 700, 800, and 900 in may be eliminated or modified.

[0192] Figure 7 An exemplary flow chart illustrating the execution of a cell switching process according to some embodiments of the present application. The details described in all other embodiments of the present application are applicable to Figure 7 The embodiments shown in .

[0193] like Figure 7 As shown in FIG. 7 , BS 705 is in a CU-DU architecture and includes CU 704, source DU 702, and candidate DU 703. Figure 7 In the embodiment of , the cell switching operation performed by UE 701 may refer to an intra-DU situation in which the source cell and the target cell are in the same DU, or to an inter-DU situation in which the source cell and the target cell are located at different DUs. Figure 7 The flowchart 700 shown in FIG. 7 only shows the cell switching operation in the inter-DU case for exemplary purposes. If the source DU 702 and the candidate DU 703 are the same DU, the flowchart 700 can also be applied to the intra-DU case.

[0194] In such Figure 7 In the exemplary flowchart 700 shown in FIG. 7 , in operation 711, UE 701 may access a serving BS (e.g., a gNB) and send a measurement report to the serving BS (e.g., BS 705). The serving BS may include a CU (e.g., a gNB-CU) and one or more DUs (e.g., a gNB-DU). The serving cell is associated with the CU and the DU. There is an F1 interface between the DU and the CU. For example, Figure 7 , BS 705 includes CU 704, source DU 702, and candidate DU 703. BS 705 may include one or more other candidate DUs ( Figure 7 not shown).

[0195] In some embodiments, UE 701 may send a measurement report to CU 704 via source DU 702. For example, UE 701 may send a measurement report containing measurement results of neighboring cells to source DU 702. Source DU 702 may send a UL RRC messaging message containing the measurement report to CU 704.

[0196] In operation 712 , the CU 704 may determine to initiate an L1 / L2-based inter-cell mobility configuration process, that is, make an L1 / L2-based inter-cell mobility configuration decision.

[0197] In operation 713, CU 704 may send a request for RACH resources for TA acquisition to candidate DU 703 via the F1 interface. The request may contain ID information of the candidate cell. In some embodiments, the candidate cell may also be referred to as a "target candidate cell" or the like. In the inter-DU case, the request may be a UE context establishment request message. In the intra-DU case, the request may be a UE context modification request message.

[0198] In some embodiments, the request in operation 713 may include at least one of the following:

[0199] (1) An indication for indicating whether the UE performs a TA acquisition procedure before a cell switching procedure for at least one candidate cell, for example, an indication for early TA acquisition (for example, Figure 3 Indication #3 described in the embodiment of FIG. 1 ). This indication is used to indicate whether at least one candidate cell requires early TA acquisition. Early TA acquisition means that the UE 701 is expected to perform TA acquisition before the cell switching process.

[0200] (2) an indication for indicating whether the UE performs a DL synchronization operation before a cell switching process for the at least one candidate cell, for example, an indication for early DL synchronization (for example, Figure 3 Indication #4 described in the embodiment of the present invention). This indication is used to indicate whether early DL synchronization is required for at least one candidate cell. Early DL synchronization means that it is expected that UE 701 performs a DL synchronization operation before the cell switching process.

[0201] Prior to operation 713, the source DU 702 may transmit a request for RACH resources for TA acquisition to the CU 704 via the F1 interface. The request is used to request the CU 704 to provide a configuration for TA acquisition of the UE 701, such as RACH configuration information indicating RACH resources for early TA acquisition. The request may contain ID information of the candidate cell. Then, in operation 713, the CU 704 may transmit an F1 request message to the candidate DU 703.

[0202] In operation 714, the candidate DU 703 may transmit a response message, i.e., an F1 response message, to the CU 704 via the F1 interface. In the inter-DU case, the F1 response message may be a UE context establishment response message. In the intra-DU case, the F1 response message may be a UE context modification response message. In some embodiments, after the candidate DU 703 decides to accept the request for LTM configuration in operation 713, the F1 response message is transmitted in operation 714.

[0203] In some embodiments, the F1 response message in operation 714 may include the lower layer RRC configuration of the target cell, which may be referred to as the "lower layer RRC configuration of the LTM", such as Figure 3 and 4 Described in.

[0204] In some embodiments, the F1 response message in operation 714 may include at least one of the following information, and for example, this information may be included in an RRCReconfiguration message:

[0205] (1) Early TA acquisition instructions (e.g. Figure 3 Indication #1) described in the embodiment of the present invention is used to indicate whether the candidate cell needs early TA acquisition. Early TA acquisition means that the UE 701 is expected to perform TA acquisition before the cell switching process.

[0206] (2) RACH configuration for TA acquisition, which may include at least one of the following:

[0207] a) RA preamble index.

[0208] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0209] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0210] (3) Indication of early DL synchronization (e.g. Figure 3 Indication #2) described in the embodiment of the present invention is used to indicate whether the candidate cell needs early DL synchronization. Early DL synchronization means that the UE 701 is expected to perform a DL synchronization operation before the cell switching process.

[0211] Regarding how to carry the above information for TA acquisition from the candidate DU 703 to the CU 704 in the F1 response message in operation 714, there may be the following three options, ie, Option A, Option B, and Option C, in different embodiments.

[0212] (1) Option A: The RACH configuration for TA acquisition is a separate IE included in the F1 response message in operation 714. That is, the RACH configuration for TA acquisition is not incorporated into the lower layer RRC configuration of the LTM in the F1 response message. For example, the RACH configuration for TA acquisition as a separate IE may be included in the "DU to CU RRC Information IE" (as specified in 3GPP standard document TS38.473) of the F1 response message in operation 714. In this option, if the indication of early TA acquisition is not included, the RACH configuration for TA acquisition as a separate IE may be used to implicitly indicate early TA acquisition.

[0213] (2) Option B: The RACH configuration for TA acquisition may be incorporated into the lower layer RRC configuration of the LTM included in the F1 response message in operation 714. In this way, an indication of early TA acquisition is required. If the indication of early TA acquisition is not included in the F1 response message, the CU 704 needs to read the container. If the RACH configuration for TA acquisition is included, the CU 704 needs to indicate the early TA acquisition and the corresponding RACH resources to the source DU 702.

[0214] (3) Option C: RACH configuration for TA acquisition is outside the "DU to CURRC Information IE" included in the F1 response message in operation 714. In this option, if the indication of early TA acquisition is not included, the RACH configuration for TA acquisition as a separate IE can be used to implicitly indicate early TA acquisition.

[0215] In operation 715, CU 704 may send an F1 message (e.g., Figure 4 The F1 message in operation 715 may be a DL RRC message transfer message or a UE context modification request message.

[0216] In some embodiments, the F1 message in operation 715 includes at least one of the following information (e.g., Figure 4 The information #1) described in the embodiment of the present invention, and for example, this information may be included in the RRCReconfiguration message in the F1 message:

[0217] (1) An indication of early TA acquisition for indicating whether the candidate cell needs early TA acquisition (e.g., Figure 4 Indication #7 described in the embodiment of FIG. 1 ). Early TA acquisition means that it is expected that UE 701 performs TA acquisition before the cell switching process.

[0218] (2) RACH configuration for TA acquisition, which may include at least one of the following:

[0219] a) RA preamble index.

[0220] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0221] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0222] (3) An early DL synchronization indication for indicating whether a candidate cell requires early DL synchronization (e.g., Figure 4 Early DL synchronization means that the UE 701 is expected to perform a DL synchronization operation before the cell switching process.

[0223] Regarding how to use the above information for TA acquisition in the F1 message in operation 715 (for example, as in Figure 4 The information #1) described in the embodiment of FIG. 1 is carried from CU 704 to source DU 702. In different embodiments, there may be three options, namely Option X, Option Y and Option Z.

[0224] (1) Option X: The RACH configuration for TA acquisition is a separate IE included in the F1 message in operation 715.

[0225] That is, the RACH configuration for TA acquisition is not incorporated into the lower layer RRC configuration of the LTM in the F1 message. For example, the RACH configuration for TA acquisition as a separate IE may be included in the "CU to DU RRC Information IE" (as specified in 3GPP standard document TS38.473) of the F1 message in operation 715. In this option, if the indication of early TA acquisition is not included, the RACH configuration for TA acquisition as a separate IE may be used to implicitly indicate early TA acquisition.

[0226] (2) Option Y: The RACH configuration for TA acquisition may be incorporated into the lower layer RRC configuration of the LTM included in the F1 message in operation 715. In this way, the indication of early TA acquisition, the preamble index and / or the time-frequency resource index may be listed in the F1 message.

[0227] (3) Option Z: RACH configuration for TA acquisition is outside the "CU to DU RRC Information IE" included in the F1 message in operation 715. In this option, if the indication of early TA acquisition is not included, the RACH configuration for TA acquisition as a separate IE may be used to implicitly indicate early TA acquisition.

[0228] In operation 716, the source DU 702 may send a message (eg, Figure 5 Message #2) described in the embodiment of the present invention is forwarded to UE 701. In some embodiments, the message in operation 716 may include the following information:

[0229] (1) An indication of early TA acquisition for indicating to UE 701 whether the candidate cell requires early TA acquisition (e.g., Figure 5 Instruction #10) described in the embodiments.

[0230] (2) RACH configuration for TA acquisition, which may include at least one of the following:

[0231] a) RA preamble index.

[0232] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0233] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0234] (3) An indication of early DL synchronization for indicating to UE 701 whether a candidate cell requires early DL synchronization (e.g., Figure 5 Instruction #11) described in the embodiments.

[0235] In some embodiments, once UE 701 receives the configuration of the target cell (eg, RRCReconfiguration message) in operation 716, UE 701 may start to perform DL synchronization operation to the target cell.

[0236] In operation 717, UE 701 may transmit an RRC response message to source DU 702. For example, the RRC response message may be an RRC reconfiguration complete message. In some embodiments, source DU 702 may forward the RRC reconfiguration complete message to CU 704 via an F1 message (e.g., a UL RRC message transfer message or a UE context modification response message).

[0237] In operation 718, the source DU 702 may transmit an indication to the UE 701 (e.g., Figure 5 In some embodiments, the indication may include a dedicated preamble and / or dedicated time-frequency domain resources, which are configured by the candidate DU 703.

[0238] In some embodiments, the source DU 702 may transmit an indication (e.g., Figure 5 Indication #13) described in the embodiment of the present invention is used to indicate whether UE 701 performs DL synchronization operation to the configured candidate cell. This indication may be included in an RRC message, a PDCCH command, a DCI or a MAC CE.

[0239] In operation 719A, the UE 701 may perform a TA acquisition procedure. In addition, in operation 719B, the UE 701 may send an L1 measurement result to the source DU 702.

[0240] In some embodiments, the TA acquisition process includes preamble transmission. In an embodiment, if a random access response (RAR) is included in the TA acquisition process, the UE 701 may obtain or acquire a TA value from the candidate cell. In another embodiment, if the RAR is not included in the TA acquisition process, the UE 701 may obtain or acquire a TA value from the source cell; the candidate cell receives a dedicated preamble and calculates the TA value; and then, the candidate cell may transmit the TA value and ID information of the corresponding candidate cell and the ID information of the UE 701 to the source DU 702 via the CU 704.

[0241] In operation 720, once the source DU 702 decides to perform LTM to the candidate target cell, that is, to perform a cell switching process to the candidate target cell, the source DU 702 may transmit a cell switching command (eg, a MAC CE including a candidate cell configuration index) to the UE 701 to trigger the cell switching process.

[0242] In operation 721, UE 701 may perform a cell handover procedure and synchronize to a candidate target cell, for example, perform UL synchronization and / or DL ​​synchronization operations to the candidate target cell.

[0243] Figure 8 A further exemplary flow chart illustrating a cell switching process according to some embodiments of the present application. Figure 8 The embodiments shown in .

[0244] like Figure 8 As shown in FIG. 8 , BS 805 is in a CU-DU architecture and includes CU 804, source DU 802, and candidate DU 803. Figure 8 In the embodiment of , the cell switching operation performed by UE 801 may refer to an intra-DU situation in which the source cell and the target cell are in the same DU, or to an inter-DU situation in which the source cell and the target cell are located at different DUs. Figure 8 The flowchart 800 shown in FIG. 8 only shows the cell switching operation in the inter-DU case for exemplary purposes. If the source DU 802 and the candidate DU 803 are the same DU, the flowchart 800 can also be applied to the intra-DU case.

[0245] In such Figure 8 In the exemplary flowchart 800 shown in FIG. 8 , in operation 811, UE 801 may access a serving BS (e.g., a gNB) and send a measurement report to the serving BS (e.g., BS 805). The serving BS may include a CU (e.g., a gNB-CU) and one or more DUs (e.g., a gNB-DU). The serving cell is associated with the CU and the DU. There is an F1 interface between the DU and the CU. For example, Figure 8 , BS 805 includes CU 804, source DU 802, and candidate DU 803. BS 805 may include one or more other candidate DUs ( Figure 8 not shown).

[0246] In some embodiments, UE 801 may send a measurement report containing measurement results of neighboring cells to source DU 802. Source DU 802 may send a UL RRC messaging message including the measurement report to CU 804.

[0247] In operation 812, the CU 804 may determine to initiate an L1 / L2-based inter-cell mobility configuration process, that is, make an L1 / L2-based inter-cell mobility configuration decision.

[0248] In operation 813, CU 804 may send a request for RACH resources acquired by the TA to the candidate DU 803 via the F1 interface, for example, an F1 request message. The F1 request message may contain ID information of the candidate cell and may also be referred to as a "request for LTM configuration" or the like. In the inter-DU case, the F1 request message may be a UE context establishment request message. In the intra-DU case, the F1 request message may be a UE context modification request message.

[0249] In some embodiments, the F1 request message in operation 813 may include at least one of the following:

[0250] (1) An indication for indicating whether the UE performs a TA acquisition procedure before a cell switching procedure for at least one candidate cell, for example, an indication for early TA acquisition (for example, Figure 3 Indication #3 described in the embodiment of FIG. 1 ). This indication is used to indicate whether the candidate cell needs early TA acquisition. Early TA acquisition means that the UE 801 is expected to perform a TA acquisition process before the cell switching process.

[0251] (2) RACH configuration for TA acquisition, which may include at least one of the following:

[0252] a) RA preamble index.

[0253] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0254] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0255] (3) an indication for indicating whether the UE performs a DL synchronization operation before a cell switching process for the at least one candidate cell, for example, an indication for early DL synchronization (for example, Figure 3 Indication #4 described in the embodiment of FIG. 1 ). This indication is used to indicate whether a candidate cell requires early DL synchronization. Early DL synchronization means that the UE 801 is expected to perform DL synchronization before the cell switching process.

[0256] Prior to operation 813, the source DU 802 may transmit a request for RACH resources for TA acquisition to the CU 804 via the F1 interface. The request is used to request the CU 804 to provide a configuration for the TA acquisition process of the UE 801, such as RACH configuration information indicating RACH resources for early TA acquisition. The request may contain ID information of the candidate cell. The request may also be referred to as a "request for LTM configuration" or the like. Then, in operation 813, the CU 804 may transmit a request message to the candidate DU 803.

[0257] In some embodiments, the request from source DU 802 to CU 804 may include at least one of the following information:

[0258] (1) An indication used to indicate that this F1 request message is used to request the RRC configuration of LTM (for example, Figure 3 Instruction #5) described in the embodiments.

[0259] (2) Candidate cell ID information used to indicate candidate cells configured by LTM.

[0260] (3) ID information of the source DU 802.

[0261] (4) ID information of UE 801 (eg, source CU / DU UE F1AP ID).

[0262] (5) ID information of the source cell of UE 801.

[0263] In some embodiments, source DU 802 may also send auxiliary information including, for example, an existing TA value to a target DU (eg, candidate DU 803 ) via CU 804 , so that the target DU may decide whether early TA acquisition is required or whether to reuse the existing TA value.

[0264] In operation 814, the candidate DU 803 may transmit a response message to the CU 804 via the F1 interface. In the inter-DU case, the F1 response message may be a UE context establishment response message. In the intra-DU case, the F1 response message may be a UE context modification response message. In some embodiments, after the candidate DU 803 decides to accept the request in operation 813, the F1 response message is transmitted in operation 814.

[0265] In some embodiments, the F1 response message in operation 814 includes the lower layer RRC configuration of the target cell, which may be referred to as the "lower layer RRC configuration of the LTM", such as Figure 3 and 4 Described in.

[0266] In some embodiments, the F1 response message in operation 814 includes at least one of the following information, and for example, this information may be included in an RRCReconfiguration message:

[0267] (1) Early TA acquisition instructions (e.g. Figure 3 Indication #1) described in the embodiment of the present invention is used to indicate whether the candidate cell needs early TA acquisition. Early TA acquisition means that the UE 801 is expected to perform a TA acquisition process before the cell switching process.

[0268] (2) RACH configuration for TA acquisition, which may include at least one of the following:

[0269] a) RA preamble index.

[0270] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0271] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0272] (3) Indication of early DL synchronization (e.g. Figure 3 Indication #2) described in the embodiment of the present invention is used to indicate whether a candidate cell requires early DL synchronization. Early DL synchronization means that the UE 801 is expected to perform DL synchronization before the cell switching process.

[0273] In some embodiments, before operation 814, the candidate DU 803 may identify whether the prepared candidate cell and another candidate cell have the same TA value for the same UE (e.g., UE 801), for example, based on the received ID information of UE 801 (e.g., source CU / DU UE F1AP ID) and the ID information of the source cell, or based on the received same request message. After identification, the F1 response message in operation 814 may include at least one of the following information:

[0274] (1) A TA value used to indicate that the prepared candidate cell is the same as another candidate cell (e.g. Figure 3 An indication of whether the TA value of the candidate cell #1) described in the embodiment of FIG. 1 is the same (for example, Figure 3 Instruction #6) is described in the embodiments.

[0275] (2) ID information of another candidate cell, if the TA value associated with this candidate cell is the same as the TA value associated with another candidate cell.

[0276] In operation 815, CU 804 may send an F1 message (e.g., Figure 4 The message #1) described in the embodiment of the present invention includes a generated RRCReconfiguration message with LTM configuration. This F1 message can be a DL RRC message transfer message or a UE context modification request message.

[0277] In some embodiments, the F1 message in operation 815 may include at least one of the following information (e.g., Figure 4 The information #1) described in the embodiment of the present invention, and for example, this information may be included in the RRCReconfiguration message in the F1 message:

[0278] (1) An indication of early TA acquisition for indicating whether the candidate cell needs early TA acquisition (e.g., Figure 4 Indication #7 described in the embodiment of FIG. 1 ). Early TA acquisition means that it is expected that UE 801 performs a TA acquisition procedure before a cell switching procedure.

[0279] (2) The RACH configuration for TA acquisition may include at least one of the following:

[0280] a) RA preamble index.

[0281] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0282] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0283] (3) An early DL synchronization indication for indicating whether a candidate cell requires early DL synchronization (e.g., Figure 4 Indication #8 described in the embodiment of FIG. 1 ). Early DL synchronization means that the UE 801 is expected to perform DL synchronization before the cell switching process.

[0284] In some embodiments, the F1 message in operation 815 includes at least one of the following information:

[0285] (1) An indication of whether the TA of the candidate cell is the same as that of another candidate cell (e.g. Figure 4 Instruction #9) described in the embodiments.

[0286] (2) ID information of another candidate cell, if the TA value associated with at least one candidate cell is the same as the TA value associated with another candidate cell.

[0287] In operation 816, the source DU 802 sends a message (eg, Figure 5 The message #2) described in the embodiment of the present invention is forwarded to UE 801. In some embodiments, the message in operation 816 may include at least one of the following information:

[0288] (1) An early TA acquisition indication for indicating to UE 801 whether the candidate cell requires early TA acquisition (e.g., Figure 5 Instruction #10) described in the embodiments.

[0289] (2) RACH configuration for TA acquisition, which may include at least one of the following:

[0290] a) RA preamble index.

[0291] b) SS / PBCH Index: This field may indicate the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission.

[0292] c) RO, which is a time-frequency domain resource used for preamble transmission. For example, the field "PRACH Mask Index" is used to indicate a RACH opportunity (RO) associated with the SS / PBCH indicated by the "SS / PBCH Index" for PRACH transmission.

[0293] (3) An indication of early DL synchronization for indicating to UE 801 whether a candidate cell requires early DL synchronization (e.g., Figure 5 Instruction #11) described in the embodiments.

[0294] In some embodiments, the message in operation 816 may include at least one of the following information.

[0295] (1) An indication of whether the TA value of a candidate cell is the same as the TA value of another candidate cell (e.g., Figure 5 Instruction #12) described in the embodiments.

[0296] (2) The ID of another candidate cell, if the TA value of the candidate cell is the same as the TA value of another candidate cell.

[0297] In operation 817, UE 801 may transmit an RRC response message to source DU 802. The RRC response message may be an RRC reconfiguration complete message. In some embodiments, source DU 802 may forward the RRC reconfiguration complete message to CU 804 via an F1 message (eg, UL RRC message transfer message or UE context modification response message).

[0298] In operation 818, once the source DU 802 decides to perform LTM to the candidate target cell, that is, to perform a cell switching process to the candidate target cell, the source DU 802 may transmit a cell switching command (eg, a MAC CE including a candidate cell configuration index) to the UE 801 to trigger the cell switching process.

[0299] In operation 819, UE 801 may perform a cell switching process and synchronize to the candidate target cell, for example, perform UL synchronization and / or DL ​​synchronization operations to the candidate target cell. In some embodiments, if UE 801 receives an indication of early TA acquisition in operation 816 (for example, Figure 5 In some embodiments, if the UE 801 receives an indication in operation 816 indicating whether the TA value of the candidate target cell is the same as the TA value of another candidate cell (e.g., Figure 5 If the UE 801 does not specify an indication #12 described in the embodiment of the present invention, then the UE 801 may use the TA value of another candidate cell in operation 819.

[0300] Fig. 9 Another exemplary flow chart illustrating the execution of a cell switching process according to some embodiments of the present application. The details described in all other embodiments of the present application may be applicable to Fig. 9 The embodiments shown in .

[0301] like Fig. 9 As shown in FIG. 1 , BS 905 is in a CU-DU architecture and includes CU 904, source DU 902, and candidate DU 903. Fig. 9 In the embodiment of , the cell change of UE 901 may refer to an intra-DU situation where the source cell and the target cell are in the same DU, or to an inter-DU situation where the source cell and the target cell are located at different DUs. Fig. 9 The flowchart 900 shown in FIG. 9 shows only the cell change in the inter-DU case for exemplary purposes. If the source DU 902 and the candidate DU 903 are the same DU, the flowchart 900 can be applied to the intra-DU case.

[0302] In such Fig. 9In the exemplary flowchart 900 shown in FIG. 1 , in operation 911, UE 901 may access a serving BS (e.g., a gNB) and send a measurement report to the serving BS (e.g., BS 905). The serving BS may include a CU (e.g., a gNB-CU) and one or more DUs (e.g., a gNB-DU). The serving cell is associated with the CU and the DU. There is an F1 interface between the DU and the CU. For example, Fig. 9 , BS 905 includes CU 904, source DU 902, and candidate DU 903. BS 905 may include one or more other candidate DUs ( Fig. 9 not shown).

[0303] In some embodiments, UE 901 may send a measurement report to CU 904 via source DU 902. For example, UE 901 may send a measurement report containing measurement results of neighboring cells to source DU 902. Source DU 902 may send a UL RRC messaging message containing the measurement report to CU 904.

[0304] In operation 912 , the CU 904 may transmit an RRCReconfiguration message associated with one or more candidate cells for LTM purposes to the UE 901 via the source DU 902 .

[0305] In some embodiments, CU 904 may determine to initiate an L1 / L2-based inter-cell mobility configuration process, i.e., make an L1 / L2-based inter-cell mobility configuration decision. CU 904 may receive an RRCReconfiguration message from a candidate cell (e.g., from a candidate DU 903) via an F1 interface. Then, CU 904 may forward the RRCReconfiguration message to UE 901 via source DU 902 in operation 912.

[0306] In operation 913, UE 901 may receive an indication (e.g., such as Figure 5 In some embodiments, the indication #13 described in the embodiment of the present invention is used to trigger the TA acquisition process to the candidate cell. In some embodiments, the indication is included in a PDCCH command, a DCI or a MAC CE. The indication may indicate at least one of the following to the UE 901:

[0307] (1) Execute the TA acquisition process;

[0308] (2) whether to create a dedicated MAC entity associated with at least one candidate cell for the TA acquisition process; or

[0309] (3) Perform DL synchronization operation to at least one candidate cell.

[0310] In operation 914, UE 901 may determine whether to create a dedicated MAC entity or a separate MAC entity for the TA acquisition process. There may be two options, option M and option N, in different embodiments.

[0311] (1) Option M: UE 901 determines to create or establish a dedicated or separate MAC entity of the candidate cell for the TA acquisition process. In addition, UE 901 may create or establish an RLC entity of the candidate cell.

[0312] a) UE 901 may create or establish a dedicated MAC entity and / or a dedicated RLC entity based on RRC configuration information associated with the candidate cell (eg, based on the configuration of the candidate cell including the DUID, DU index and / or cell group ID of the candidate cell).

[0313] b) In some embodiments, after acquiring the TA value associated with the candidate cell through the TA acquisition process, the UE 901 may maintain or release the dedicated MAC entity and / or the dedicated RLC entity.

[0314] c) In an embodiment, if there are two candidate cells, for example, candidate cell #2 and candidate cell #3, UE 901 may create a dedicated MAC entity and / or a dedicated RLC entity for candidate cell #2, and maintain the dedicated MAC entity and / or the dedicated RLC entity for candidate cell #2 after obtaining the TA value associated with candidate cell #2. UE 901 may create a dedicated MAC entity and / or a dedicated RLC entity for candidate cell #3, and maintain the dedicated MAC entity and / or the dedicated RLC entity for candidate cell #3 after obtaining the TA value associated with candidate cell #3. If UE 901 receives a cell switching command associated with candidate cell #3 from source DU 902 (for example, in operation 915 described below), then after switching from the source cell of UE 901 to candidate cell #3, UE 901 may maintain or release the MAC entity and / or the RLC entity for candidate cell #2.

[0315] d) The configuration of the MAC entity (or RLC entity) used for the TA acquisition process is different from the configuration of the candidate cell.

[0316] For example, UE 901 may create or establish a dedicated MAC entity and / or a dedicated MAC entity based on a default configuration configured to the UE.

[0317] Or a dedicated RLC entity. In an embodiment, after acquiring the TA value related to the candidate cell through the TA acquisition process, the UE 901 may release both the dedicated MAC entity and the dedicated RLC entity.

[0318] (2) Option N: No dedicated or separate MAC entity is required for the TA acquisition procedure. The UE 901 may perform the TA acquisition procedure based on the MAC entity of the UE (ie, the source MAC entity) or the RLC entity of the UE (ie, the source RLC entity).

[0319] In operation 915, once the source DU 902 decides to perform a cell switching process to a candidate target cell, the source DU 902 may transmit a cell switching command to the UE 901 to trigger the cell switching process. The cell switching command may be used to trigger the UE 901 to perform a TA acquisition process. In some embodiments, the cell switching command is included in a MAC CE including a candidate cell configuration index. In some other embodiments, the cell switching command is included in a DCI or RRC message.

[0320] In operation 916 , the UE 901 may perform a cell switching procedure and synchronize to the candidate target cell, for example, perform UL synchronization and / or DL ​​synchronization operations to the candidate target cell.

[0321] Fig.10 1 is a block diagram illustrating an exemplary device 1000 according to some embodiments of the present application. Fig.10 1000, the apparatus 1000 may include at least one processor 1006 and at least one transceiver 1002 coupled to the processor 1006. Although elements such as at least one transceiver 1002 and the processor 1006 are described in singular form in this figure, plural forms are contemplated unless limitation to the singular form is explicitly stated. In some embodiments of the present application, the transceiver 1002 may be divided into two devices, such as a receiving circuit system and a transmitting circuit system. In some embodiments of the present application, the apparatus 1000 may further include an input device, a memory, and / or other components.

[0322] In some embodiments of the present application, the device 1000 may be a UE or a network node (eg, a BS, a CU, or a DU). The transceiver 1002 and the processor 1006 may interact with each other to execute the above, for example, Figures 1 to 9 The operations of the UE or the network node described in any one of the foregoing.

[0323] In some embodiments of the present application, the device 1000 may further include at least one non-transitory computer-readable medium. For example, in some embodiments of the present disclosure, the non-transitory computer-readable medium may store thereon computer-executable instructions that cause the processor 1006 to implement the method described above for the UE or network node (e.g., BS, CU, or DU). For example, when the computer-executable instructions are executed, the processor 1006 interacts with the transceiver 1002 to perform Figures 1 to 9 The operations of the UE or network node described in.

[0324] It should be understood by those of ordinary skill in the art that the operations or steps of the methods described in conjunction with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In addition, in some aspects, the operations or steps of the methods may reside as one or any combination or set of codes and / or instructions on a non-transitory computer-readable medium that can be incorporated into a computer program product.

[0325] In this document, the term "includes / including" or any other changes thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment containing the element list not only includes those elements but also may include other elements that are not explicitly listed or inherent to this process, method, article or equipment. The element starting with "a / an" or the like (without more constraints) does not exclude the existence of additional identical elements in the process, method, article or equipment containing the element. Moreover, the term "another" is defined as at least one second or more. As used herein, the term "having" and the like are defined as "including". For example, the expression of "A and / or B" or "at least one of A and B" may include any and all combinations of words listed together with the expression. For example, the expression "A and / or B" or "at least one of A and B" may include A, B or both A and B. The words of "first", "second" or the like are only used to clearly illustrate the embodiments of the present application, and are not used to limit the essence of the present application.

Claims

1. A candidate distributed unit DU of a base station BS, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to cause the candidate DU to: receiving a first request from a centralized unit CU of the BS, wherein the first request includes identifier ID information of one or more candidate cells; and A response message is transmitted to the CU based on the first request, wherein the response message is associated with a cell switching procedure.

2. The candidate DU according to claim 1, wherein the response message includes at least one of the following: lower layer radio resource control (RRC) configuration information associated with at least one candidate cell among the one or more candidate cells; Random access channel RACH configuration information, which is used for a timing advance TA acquisition process performed by a user equipment UE; a first indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; or The second indication is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching procedure for the at least one candidate cell.

3. The candidate DU according to claim 2, wherein the RACH configuration information comprises at least one of the following: Random access RA preamble index; Synchronization signal / physical broadcast channel SS / PBCH index; or RACH timing RO.

4. The candidate DU according to claim 2, wherein: The RACH configuration information is included in a dedicated information element IE in the response message; or The lower layer RRC configuration information is included in one or more IEs in the response message, and the The RACH configuration information is incorporated into the one or more IEs.

5. The candidate DU according to claim 4, wherein the RACH configuration information is included in a DU to CU RRC information IE included in the response message.

6. The candidate DU of claim 1, wherein the first request further comprises at least one of the following: a third indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for a candidate cell within the one or more candidate cells; or A fourth indication is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching process for the candidate cell.

7. A centralized unit CU of a base station BS, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to cause the CU to: transmitting a first request to a candidate distributed unit DU of the BS, wherein the first request includes identifier ID information of one or more candidate cells; and A response message is received from the candidate DU, wherein the response message is associated with a cell handover procedure.

8. The CU according to claim 7, wherein the response message includes at least one of the following: lower layer radio resource control (RRC) configuration information associated with at least one candidate cell among the one or more candidate cells; Random access channel RACH configuration information, which is used for a timing advance TA acquisition process performed by a user equipment UE; a first indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; or The second indication is used to indicate whether the UE performs a downlink (DL) synchronization operation before the cell switching procedure for the at least one candidate cell.

9. The CU of claim 7, wherein the processor is configured to cause the CU to transmit a first message to a source DU of the BS, the first message including the RRC configuration information associated with the at least one candidate cell, and the RRC configuration information including the lower layer RRC configuration information.

10. The CU of claim 9, wherein the first message further includes first information, and the first information includes at least one of the following: a third indication, which is used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; or a fourth indication, used to indicate whether the UE performs a DL synchronization operation before the cell switching procedure for the at least one candidate cell; or The RACH configuration information.

11. A user equipment UE, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to cause the UE to: receiving a first message from a source distributed unit DU of a base station BS, wherein the first message comprises radio resource control RRC configuration information associated with at least one candidate cell related to a cell handover procedure; as well as A first indication is received from the source DU to trigger a timing advance TA acquisition procedure or a downlink DL synchronization operation.

12. The UE according to claim 11, wherein the first message is an RRC reconfiguration message.

13. The UE according to claim 11, wherein the first message further comprises at least one of the following: a second indication, used to indicate whether the UE performs the TA acquisition process before the cell switching process for the at least one candidate cell; a third indication, used to indicate whether the UE performs a downlink DL synchronization operation before the cell switching process for the at least one candidate cell; or Random access channel RACH configuration information used for the TA acquisition process.

14. The UE according to claim 11, wherein the first message further comprises at least one of the following: a fourth indication for indicating whether a first TA value associated with the at least one candidate cell is the same as a second TA value associated with a first candidate cell associated with the LTM; or ID information of the first candidate cell. 15 . The UE of claim 11 , wherein the processor is configured to cause the UE to start performing the DL synchronization operation to the at least one candidate cell after receiving the first message.

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