Method and device for supporting subsequent LTM

Abstract

The invention relates to a method and apparatus for supporting subsequent L1 / L2 triggered mobility (LTM). An embodiment of the present disclosure provides a central unit (CU) comprising: a transceiver; and a processor coupled with the transceiver and configured to: determine, for each candidate cell of one or more candidate cells, a candidate cell configuration and an index of the candidate cell configuration, where the index of the candidate cell configuration for each candidate cell is generated by the CU or received from a source distributed unit (DU) or from a candidate DU; transmitting, to a user equipment (UE) via the source DU, a first message indicating the candidate cell configuration for each candidate cell and the index of the candidate cell configuration; transmitting, to the source DU, a second message indicating the index of the candidate cell configuration for each candidate cell; and transmitting a third message indicating the index of the candidate cell configuration for each candidate cell to the candidate DUs.

Description

Technical Field

[0001] The present disclosure relates to wireless communications, and in particular, to methods and apparatus for supporting subsequent L1 / L2 triggered mobility (LTM). Background Art

[0002] User equipment (UE) may move from one cell to another and therefore at some point, a serving cell change needs to be performed.

[0003] Currently, serving cell change is performed through explicit radio resource control (RRC) reconfiguration signaling to trigger synchronization of the target cell based on layer 3 (L3) measurement reports. This results in longer latency, more overhead, and longer outage times compared to beam-level mobility.

[0004] In the 3rd Generation Partnership Project (3GPP) Release 18, a new work item on further New Radio (NR) mobility enhancements was approved to enable serving cell change via lower layer signaling (e.g., Layer 1 (L1) or Layer 2 (L2) signaling) to reduce latency, overhead, and interruption time.

[0005] Therefore, how to support subsequent LTM will be studied and addressed. Summary of the invention

[0006] One purpose of this disclosure is to propose some solutions to support subsequent LTM.

[0007] An embodiment of the present disclosure provides a central unit (CU), comprising: a transceiver; and a processor, which is coupled to the transceiver and configured to: determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells, wherein the index of the candidate cell configuration of each candidate cell is generated by the CU, or received from a source distributed unit (DU) or from a candidate DU; transmit a first message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a UE via the source DU; transmit a second message indicating the index of the candidate cell configuration of each candidate cell to the source DU; and transmit a third message indicating the index of the candidate cell configuration of each candidate cell to the candidate DU.

[0008] In some embodiments, the one or more candidate cells include candidate cells in the candidate DU.

[0009] In some embodiments, the one or more candidate cells further include candidate cells in the source DU.

[0010] In some embodiments, the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not the serving cell of the UE.

[0011] In some embodiments, the first message further includes an indicator instructing the UE to maintain the candidate cell configuration and the index of the candidate cell configuration for each candidate cell after LTM cell switching.

[0012] In some embodiments, the second message further includes a candidate cell configuration in the candidate DU.

[0013] In some embodiments, the third message further includes at least one of: a serving cell configuration of a serving cell in the source DU; or a source cell configuration of a source cell in the source DU.

[0014] Another embodiment of the present disclosure provides a source DU, comprising: a transceiver; and a processor, which is coupled to the transceiver and configured to: determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells; transmit a first message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a UE; transmit a second message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a CU; and provide the index of the candidate cell configuration of each candidate cell to the candidate DU.

[0015] In some embodiments, the one or more candidate cells include candidate cells in the candidate DU.

[0016] In some embodiments, the one or more candidate cells further include candidate cells in the source DU.

[0017] In some embodiments, the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not the serving cell of the UE.

[0018] In some embodiments, the first message further includes an indicator instructing the UE to maintain the candidate cell configuration and the index of the candidate cell configuration for each candidate cell after LTM cell switching.

[0019] In some embodiments, the processor is further configured to provide the candidate DU with at least one of: a serving cell configuration of a serving cell in the source DU; or a source cell configuration of a source cell in the source DU.

[0020] In some embodiments, the index of the candidate cell configuration of the candidate cell is provided to the candidate DU directly or via the CU.

[0021] Another embodiment of the present disclosure provides a candidate DU, comprising: a transceiver; and a processor, which is coupled to the transceiver and configured to: determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells; transmit a message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a CU; and provide the index of the candidate cell configuration of each candidate cell to a source DU.

[0022] In some embodiments, the one or more candidate cells include candidate cells in the candidate DU.

[0023] In some embodiments, the one or more candidate cells further include candidate cells in the source DU.

[0024] In some embodiments, the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not the serving cell of the UE.

[0025] In some embodiments, the processor is further configured to provide the source DU with a candidate cell configuration of a candidate cell in the candidate DU.

[0026] In some embodiments, the index of the candidate cell configuration for each candidate cell is provided to the source DU directly or via the CU.

[0027] Another embodiment of the present disclosure provides a UE, comprising: a transceiver; and a processor, which is coupled to the transceiver and configured to: receive a message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration; perform LTM cell switching based on the message; and maintain the candidate cell configuration of each candidate cell and the index of the candidate cell configuration after the LTM cell switching.

[0028] In some embodiments, the one or more candidate cells include candidate cells in the candidate DU.

[0029] In some embodiments, the one or more candidate cells further include candidate cells in the source DU.

[0030] In some embodiments, the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not the serving cell of the UE.

[0031] In some embodiments, the message includes an indicator instructing the UE to maintain the candidate cell configuration and the index of the candidate cell configuration for each candidate cell after the LTM cell switch.

[0032] Another embodiment of the present disclosure provides a method performed by a CU, comprising: determining a candidate cell configuration and an index of the candidate cell configuration for each candidate cell among one or more candidate cells, wherein the index of the candidate cell configuration of each candidate cell is generated by the CU, or received from a source DU or from a candidate DU; transmitting a first message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a UE via the source DU; transmitting a second message indicating the index of the candidate cell configuration of each candidate cell to the source DU; and transmitting a third message indicating the index of the candidate cell configuration of each candidate cell to the candidate DU.

[0033] Another embodiment of the present disclosure provides a method performed by a source DU, comprising: determining a candidate cell configuration and an index of the candidate cell configuration for each candidate cell among one or more candidate cells; transmitting a first message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a UE; transmitting a second message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a CU; and providing the index of the candidate cell configuration of each candidate cell to the candidate DU.

[0034] Another embodiment of the present disclosure provides a method performed by a candidate DU, comprising: determining a candidate cell configuration and an index of the candidate cell configuration for each candidate cell among one or more candidate cells; transmitting a message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a CU; and providing the index of the candidate cell configuration of each candidate cell to a source DU.

[0035] Another embodiment of the present disclosure provides a method performed by a UE, comprising: receiving a message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration; performing LTM cell switching based on the message; and maintaining the candidate cell configuration of each candidate cell and the index of the candidate cell configuration after the LTM cell switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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 to limit its scope.

[0037] Figure 1A A schematic diagram illustrating intra-CU and intra-DU mobility scenarios according to some embodiments of the present disclosure.

[0038] Figure 1B A schematic diagram illustrating intra-CU inter-DU mobility scenarios according to some embodiments of the present disclosure.

[0039] Figure 2 A method for supporting subsequent LTM performed by a CU according to some embodiments of the present disclosure is described.

[0040] Figure 3 A method for supporting subsequent LTM performed by a source DU according to some embodiments of the present disclosure is described.

[0041] Figure 4 A method performed by a candidate DU to support a subsequent LTM according to some embodiments of the present disclosure is described.

[0042] Figure 5 A method for supporting subsequent LTM performed by a UE according to some embodiments of the present disclosure is described.

[0043] Figure 6 A flow chart illustrating support for subsequent LTM according to some embodiments of the present disclosure.

[0044] Figure 7 A flow chart illustrating support for subsequent LTM according to some embodiments of the present disclosure.

[0045] Figure 8 A flow chart illustrating support for subsequent LTM according to some embodiments of the present disclosure.

[0046] Fig. 9 A simplified block diagram illustrating an apparatus according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0047] The detailed description of the drawings is intended as a description of the currently preferred embodiments of the present invention, and is not intended to represent the only form in which the present invention can be practiced. It should be understood that the same or equivalent functions can be achieved by different embodiments that are intended to be included in the spirit and scope of the present invention.

[0048] Although the operations are depicted in a particular order in the drawings, those skilled in the art will readily recognize that such operations need not be performed in the particular order shown or in sequential order, or that all of the illustrated operations need not be performed to achieve a desired result; one or more operations may sometimes be skipped. In addition, the drawings may schematically depict one or more example processes in the form of a flow chart. However, other operations not depicted may be incorporated into the schematically illustrated example processes. For example, one or more additional operations may be performed before, after, simultaneously with, or between any of the illustrated operations. In some cases, multitasking and parallel processing may be advantageous.

[0049] Reference will now be made in detail to some embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided in specific network architectures and new service scenarios, such as cellular telephone networks, networks based on time division multiple access (TDMA), networks based on code division multiple access (CDMA), networks based on orthogonal frequency division multiple access (OFDMA), LTE networks, 3GPP-based networks, LTE, LTE-Advanced (LTE-A), 3GPP 4G, 3GPP 5G NR, 3GPP Release 16 and higher, satellite communication networks, high-altitude platform networks, etc. It is conceivable that with the development of network architectures and new service scenarios, all embodiments in the present disclosure are also applicable to similar technical problems; and in addition, the terms listed in the present disclosure may be changed, which should not affect the principles of the present disclosure.

[0050] The main objectives for further mobility enhancements may include:

[0051] -Configure and maintain multiple candidate cells to allow for rapid application of candidate cell configuration.

[0052] -Dynamic switching mechanism among candidate serving cells for potential applicable scenarios.

[0053] Potential applicable scenarios of lower layer mobility may include intra-CU intra-DU mobility and intra-CU inter-DU mobility. In the present disclosure, lower layer mobility is compared with legacy L3 mobility based on RRC signaling, such as L1 or L2 mobility based on L1 or L2 signaling.

[0054] Figure 1A A schematic diagram illustrating intra-CU and intra-DU mobility scenarios according to some embodiments of the present disclosure.

[0055] Figure 1A The wireless communication system in FIG. 1 includes a DU (e.g., DU 102A), a UE (e.g., UE 101A), and some access nodes (e.g., access node 103A1 and access node 103A2). Access node 103A1 and access node 103A2 are controlled by DU 102A and provide services to UEs in cell #1A and cell #2A, respectively. Figure 1A There is only one UE and two access nodes in the system, but those skilled in the art will recognize that any number of UEs and access nodes may be included in the wireless communication system.

[0056] UE 101A 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 vehicle onboard computer, a network device (e.g., a router, a switch, a modem), or the like. According to an embodiment of the present disclosure, UE 101A 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 101A includes a wearable device, such as a smart watch, a fitness bracelet, an optical head-mounted display, or the like. In addition, UE 101A may be referred to as a subscriber unit, a mobile phone, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, a device, or other terms used in the art.

[0057] Access nodes 103A1 and 103A2 may be distributed over a geographic area. In some embodiments, access nodes may also be referred to as access points, access terminals, base stations, base stations, macro cells, Node Bs, enhanced Node Bs (eNBs), gNBs, home Node Bs, relay nodes, devices, or by any other terminology used in the art. Access nodes 103A1 and 103A2 may generally be part of a radio access network, which may include one or more controllers communicatively coupled to one or more corresponding base stations.

[0058] The wireless communication system complies with any type of network capable of sending and receiving wireless communication signals. For example, the wireless communication system complies with a wireless communication network, a cellular telephone network, a TDMA-based network, a CDMA-based network, an OFDMA-based network, a Long Term Evolution (LTE) network, a 3GPP-based network, a 3GPP 5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0059] In one embodiment, the wireless communication system complies with the NR of the 3GPP protocol, where transmission may be performed using an OFDM modulation scheme. More generally, the wireless communication system may implement some other open or proprietary communication protocol, such as WiMAX, among other protocols.

[0060] In other embodiments, the transmission may be performed using other communication protocols, such as the IEEE 802.11 family of wireless communication protocols. Furthermore, in some embodiments, the transmission may be performed on a licensed spectrum, while in other embodiments, the transmission may be performed on an unlicensed spectrum. The present disclosure is not intended to be limited to implementations of any particular wireless communication system architecture or protocol. In another embodiment, the transmission may be performed using a 3GPP 5G protocol.

[0061] exist Figure 1A In the example, UE 101A is moving from cell #1A to cell #2A, and a handover procedure starting from cell #1A to access cell #2A may be performed, which is a handover procedure performed between different cells within a DU. This scenario may be referred to as intra-CU intra-DU mobility. In short, this scenario may be referred to as intra-DU mobility.

[0062] Figure 1B A schematic diagram illustrating intra-CU inter-DU mobility scenarios according to some embodiments of the present disclosure.

[0063] Figure 1B The wireless communication system in FIG. 1 includes a CU (e.g., CU 104B), a UE (e.g., UE 101B), and some DUs (e.g., DU 102B1 and DU 102B2). DU 102B1 and DU 102B2 are controlled by CU 104B and provide services to UEs in cell #1B and cell #2B, respectively. Figure 1B There is only one UE and two DUs in the system, but those skilled in the art will recognize that any number of UEs and DUs may be included in the wireless communication system.

[0064] exist Figure 1B In the example, UE#101B is moving from cell#1B to cell#2B, and a handover procedure starting from cell#1B for accessing cell#2B may be performed, which is a handover procedure performed between different cells belonging to different DUs but within the same CU. This scenario may be referred to as intra-CU inter-DU mobility. In short, this scenario may be referred to as inter-DU mobility.

[0065] With LTM, the UE can obtain multiple candidate cell configurations via RRC reconfiguration messages before cell switching. Based on the L1 measurement report from the UE, the source DU can select one of the candidate cells as the target cell and send the index of the candidate cell configuration to the UE via the medium access control-control element (MAC CE) to trigger the LTM cell switching. Each index can be used to identify the candidate cell configuration of the UE. From the perspective of the UE, the index indicates which candidate cell configuration should be applied (or used, activated, etc.) by the UE when the UE receives the LTM cell switching command (e.g., MAC CE).

[0066] Currently, the UE may maintain the target cell configuration and release other candidate cell configurations after triggering a cell handover. Considering the complexity of candidate cell configuration preparation and handover latency, it is agreed to support subsequent LTM between candidate cells. Therefore, after triggering an LTM cell handover, the UE may not release other candidate cell configurations, and thus support LTM cell handover without RRC reconfiguration for handover preparation.

[0067] For subsequent LTM, the following issues need to be addressed:

[0068] Question 1:

[0069] LTM cell switching can be triggered by the source DU via a MAC CE containing the index of the candidate cell configuration. For subsequent LTM, the candidate DU may not know the index of the candidate cell configuration stored by the UE. In addition, the candidate DU and the UE may not have a common understanding of the index of the candidate cell configuration.

[0070] Question 2:

[0071] For subsequent LTM, the candidate cells may include the serving cell and the source cell in the source DU, and the candidate cells in the candidate DU. Therefore, it is not clear which node can generate the index of the candidate cell configuration. It is also unclear how the candidate DU knows the index of the serving cell configuration.

[0072] Question 3:

[0073] For subsequent LTM, the UE may not know whether to maintain or release the index and the corresponding cell configuration.

[0074] The present disclosure proposes at least some solutions to address the above-mentioned problems.

[0075] Figure 2 A method for supporting subsequent LTM performed by a CU according to some embodiments of the present disclosure is described.

[0076] In operation 201, the CU may determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells, wherein the index of the candidate cell configuration of each candidate cell is generated by the CU, or received from a source DU or from a candidate DU. The source DU may also be referred to as a serving DU. The candidate DU may also be referred to as a target DU. In operation 202, the CU may transmit a first message (e.g., an RRC RECONFIGURATION message) indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to the UE via the source DU. In operation 203, the CU may transmit a second message (e.g., a DL RRC MESSAGE TRANSFER message) indicating the index of the candidate cell configuration of each candidate cell to the source DU; and in operation 204, the CU may transmit a third message (e.g., a DL RRC MESSAGE TRANSFER message) indicating the index of the candidate cell configuration of each candidate cell to the candidate DU.

[0077] In some embodiments, the one or more candidate cells include a candidate cell in a candidate DU. In some embodiments, the one or more candidate cells further include a candidate cell in a source DU. In some embodiments, the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not a serving cell of the UE.

[0078] In some embodiments, the first message further includes an indicator instructing the UE to maintain the candidate cell configuration and the index of the candidate cell configuration for each candidate cell after the LTM cell switching.

[0079] In some embodiments, the second message (eg, DL RRC MESSAGE TRANSFER message) further includes the candidate cell configuration in the candidate DU. That is, the candidate cell configuration in the candidate DU may be transmitted to the source DU, so the source DU knows the candidate cell configuration in the candidate DU.

[0080] In some embodiments, the third message (e.g., DL RRC MESSAGE TRANSFER message) further includes at least one of the following: a serving cell configuration of a serving cell in the source DU; or a source cell configuration of a source cell in the source DU. That is, the serving cell configuration and / or the source cell configuration in the source DU may be transmitted to the candidate DU, so that the candidate DU knows the candidate cell configuration in the source DU.

[0081] Figure 3 A method for supporting subsequent LTM performed by a source DU according to some embodiments of the present disclosure is described.

[0082] In operation 301, the source DU may determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell in one or more candidate cells. In operation 302, the source DU may transmit a first message (e.g., an RRC RECONFIGURATION message) indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to the UE. In operation 303, the source DU may transmit a second message (e.g., a UE CONTEXT MODIFICATION RESPONSE message) indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to the CU. In operation 304, the source DU may provide the index of the candidate cell configuration of each candidate cell to the candidate DU.

[0083] In some embodiments, the index of the candidate cell configuration of the candidate cell is provided to the candidate DU directly or via the CU.

[0084] Figure 4 A method performed by a candidate DU to support a subsequent LTM according to some embodiments of the present disclosure is described.

[0085] In operation 401, the candidate DU may determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells. In operation 402, the candidate DU may transmit a message (e.g., a UE CONTEXT MODIFICATION RESPONSE message) indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to the CU. In operation 403, the candidate DU may provide the index of the candidate cell configuration of each candidate cell to the source DU.

[0086] In some embodiments, the index of the candidate cell configuration of the candidate cell is provided to the candidate DU directly or via the CU.

[0087] Figure 5 A method for supporting subsequent LTM performed by a UE according to some embodiments of the present disclosure is described.

[0088] In operation 501, the UE may receive a message (e.g., an RRC RECONFIGURATION message) indicating a candidate cell configuration of each candidate cell and an index of the candidate cell configuration. In operation 502, the UE may perform LTM cell switching based on the message. In operation 503, the UE may maintain the candidate cell configuration of each candidate cell and the index of the candidate cell configuration after the LTM cell switching.

[0089] Figure 6 A flow chart illustrating support for subsequent LTM according to some embodiments of the present disclosure.

[0090] exist Figure 6There are: UE, source DU, one or more candidate DUs (which are in Figure 6 The source DU and one or more candidate DUs are within the CU, and the UE is moving from the source DU to one of the one or more candidate DUs. The source DU may manage (or control) the serving cell and one or more source cells of the UE. The serving cell and one or more source cells are considered to be in the source DU. In the following of the present disclosure, the source cell may refer to a cell in the source DU (or managed or controlled by the source DU), but not the serving cell of the UE. Each candidate DU in the candidate DU may manage one or more candidate cells, and one or more candidate cells are considered to be in each candidate DU. One of the one or more candidate DUs manages the candidate cell to which the UE switches. In some embodiments, the candidate cell to which the UE switches may be referred to as a "candidate target cell".

[0091] In this solution, the index of the candidate cell configuration can be generated by the CU, and this solution can be applied to the inter-DU scenario or the intra-DU scenario. The source DU can provide the serving cell configuration and the source cell configuration to the CU, and the candidate DU (one or more candidate DUs) can provide the candidate cell configuration of each candidate cell controlled by the candidate DU to the CU. In response to the reception of the cell configuration of the candidate cell (simply speaking, the candidate cell configuration), the cell configuration of the source cell (simply speaking, the source cell configuration), and the cell configuration of the serving cell (simply speaking, the serving cell configuration), the CU can determine (or generate, assign) the index of each candidate cell configuration (including the candidate cell configuration, the source cell configuration, and the serving cell configuration). The CU can send the index and the corresponding cell configuration to the UE, and can transmit the index of the corresponding cell configuration to the source DU and the candidate DU. The detailed process is presented as follows.

[0092] In operation 601, when the K candidate cells are controlled by the same candidate DU, the CU may transmit a message indicating the number of candidate cell IDs (expressed as K candidate cell IDs for simplicity) to the candidate DU, such as a UE CONTEXT SETUP REQUEST message; or when the K candidate cells are controlled by multiple candidate DUs, the message may be transmitted to multiple candidate DUs. The message may request preparation of the K candidate cells controlled by the candidate DU to create a UE context and set up one or more data bearers.

[0093] In some embodiments, a UE CONTEXT SETUP REQUEST message may be sent for each candidate cell. That is, the CU may transmit K UE CONTEXT SETUP REQUEST messages, where each UE CONTEXT SETUP REQUEST message may indicate a candidate cell ID.

[0094] In some other embodiments, the UE CONTEXT SETUP REQUEST message may include multiple candidate cell IDs (eg, a list of K candidate cell IDs) and be transmitted to the candidate DUs controlling the multiple candidate cells.

[0095] In operation 602, at the candidate DU side, among the K requested candidate cells, some may be accepted, while others may not be accepted. For simplicity, it is assumed that the total number of accepted candidate cells is represented as L, where L may be an integer equal to or greater than 1, and L≤K. In some cases, all K requested candidate cells are accepted. The candidate DU may transmit a response message or multiple response messages to the CU, such as one or more UE CONTEXT SETUP RESPONSE messages. The UE CONTEXT SETUP RESPONSE message may indicate the candidate cell IDs of the L candidate cells requested from the CU, and the candidate cell configuration corresponding to the candidate cell IDs.

[0096] Each candidate cell configuration may include a cell configuration for LTM. For example, the candidate cell configuration may include at least one of the following:

[0097] - A cell group configuration, which may be denoted as: CellGroupConfig and may include a MAC entity, a set of logical channels with an associated radio link control (RLC) entity, a primary cell and one or more secondary cells.

[0098] - Radio bearer configuration, which may be denoted: RadioBearerConfig and may contain parameters for the Packet Data Convergence Protocol (PDCP) and, if applicable, the Service Data Adaptation Protocol (SDAP) entity of the radio bearer.

[0099] - Measurement configuration, which may be denoted as: MeasConfig and may contain the configuration of measurements to be performed by the UE.

[0100] -Multi-RAT Dual Connectivity (MRDC) secondary cell group configuration, which can be expressed as:

[0101] MRDC-SecondaryCellGroupConfig and may contain configuration for secondary cell group (SCG) configuration in dual connectivity (DC).

[0102] - SCell ID, which can be expressed as: SCell ID, which is used to globally identify the cell.

[0103] - Index of the SCell, which may be represented as: SCellIndex, which may be a short identity used to identify the SCell. The value range is shared across cell groups.

[0104] Hereinafter in the present disclosure, a cell configuration, such as a candidate cell configuration, a source cell configuration, or a serving cell configuration, may include at least one of the above information.

[0105] In some embodiments, a UE CONTEXT SETUP RESPONSE message may be sent for each requested candidate cell, i.e., each UE CONTEXT SETUP RESPONSE message may be sent for one candidate cell, and the candidate DU may send L UE CONTEXT SETUP RESPONSE messages to the CU. In some other embodiments, when there is only one candidate DU, the one candidate DU may transmit one UE CONTEXT SETUP RESPONSE message indicating the configurations of the L candidate cells. In some other embodiments, each candidate DU in the plurality of DUs may transmit one UE CONTEXT SETUP RESPONSE message indicating all of its own requested candidate cell configurations to the CU.

[0106] In operation 603, the CU may transmit a message to the source DU, such as a UE CONTEXT MODIFICATION REQUEST message, which may indicate the number of candidate cell IDs (expressed as X candidate cell IDs for simplicity, where X may be an integer equal to or greater than 1). The message may modify the UE context. The candidate cell in the source DU may refer to the source cell in the source DU, or the serving cell in the source DU.

[0107] In some embodiments, a UE CONTEXT MODIFICATION REQUEST message may be sent for each candidate cell. That is, the CU may transmit X UE CONTEXT MODIFICATION REQUEST messages to the source DU, where each UE CONTEXT MODIFICATION REQUEST message may indicate a candidate cell ID.

[0108] In some other embodiments, the CU may transmit one UE CONTEXT MODIFICATION REQUEST message to the source DU, which may include multiple candidate cell IDs (eg, a list of X candidate cell IDs).

[0109] In operation 604, among the X requested candidate cells, some may be accepted, while others may not be accepted. For simplicity, assume that the total number of accepted candidate cells is represented as Y, where Y may be an integer equal to or greater than 1, and Y≤X. In some cases, all of the X requested candidate cells are accepted. In some cases, the X requested candidate cells may include the serving cell of the UE, and in other cases, the X requested candidate cells may not include the serving cell of the UE.

[0110] The source DU may transmit a response message, such as a UE CONTEXT MODIFICATION RESPONSE message, to the CU. The UE CONTEXT MODIFICATION RESPONSE message may indicate the candidate cell ID requested from the CU (e.g., the IDs of Y accepted candidate cells), and the candidate cell configuration corresponding to the candidate cell ID. Since the candidate cells in the source DU may include a serving cell and one or more source cells, the UE CONTEXT MODIFICATION RESPONSE message may indicate the IDs of one or more source cells in the source DU, and the one or more source cell configurations corresponding to the IDs. The UE CONTEXT MODIFICATION RESPONSE message may also indicate the ID of the serving cell in the source DU and the serving cell configuration.

[0111] In operation 605, after receiving L candidate cell configurations from the candidate DU and Y candidate cell configurations from the source DU, the CU may determine (or assign, generate, etc.) an index for each candidate cell configuration in a total number (denoted as M for simplicity) of candidate cell configurations, wherein the index is used to identify the candidate cell configuration. When the Y candidate cell configurations include the serving cell configuration, M=L+Y; when the Y candidate cell configurations do not include the serving cell configuration, M=L+Y+1. There are a total of M determined indexes.

[0112] The index may be a numerical value, such as 0, 1, 2, 3, etc. The maximum value of the index may be preconfigured, such as 8, 16, 32, 64, 128, etc. Alternatively, the index may be a candidate cell configuration ID, which is used to identify the candidate cell configuration.

[0113] In operation 606a, the CU may transmit a message to the source DU, which may include the M indices and the generated RRCRECONFIGURATION message. The message may be a UE CONTEXT MODIFICATION REQUEST message, a DL RRCMESSAGE TRANSFER message, or other message.

[0114] The M indexes may include at least one of the following:

[0115] -Index of candidate cell configuration;

[0116] - the index of the source cell configuration; or

[0117] - Index of serving cell configuration.

[0118] The RRC RECONFIGURATION message transmitted to the UE may include M indices and cell configurations corresponding to the M indices.

[0119] In some embodiments, the RRC RECONFIGURATION message may also include an indicator indicating that the cell configuration and index should be maintained by the UE after the LTM cell handover.

[0120] For example, the RRC RECONFIGURATION message includes a field named "Subsequent LTM". If the field is set to true or has a value of "1", the UE can maintain the cell configuration and index after the LTM cell switch. The field may be called other names.

[0121] In some other cases, the UE may be configured to maintain the cell configuration and index after LTM cell switching according to predefined rules, specifications, etc. That is, there is no indicator instructing the UE to maintain the cell configuration and index after LTM cell switching, and the UE may still maintain the cell configuration and index after LTM cell switching.

[0122] In some embodiments, a message, such as a UE CONTEXT MODIFICATION REQUEST message or a DL RRCMESSAGE TRANSFER message, may further include a candidate cell configuration.

[0123] In operation 606b, the CU may transmit a message including M indexes to the candidate DU. The message may be a UE CONTEXT MODIFICATION REQUEST message or a DL RRC MESSAGE TRANSFER message or other message. In some embodiments, the message may further include a serving cell configuration, a source cell configuration, or both. In some cases, in operation 606b, the CU may not provide the candidate DU with M indexes, serving cell configuration, and / or source cell configuration, but in operation 613, the CU may provide the candidate DU with M indexes, serving cell configuration, and / or source cell configuration.

[0124] In operation 607, the source DU may store the M indexes for cell configuration and may forward the RRC RECONFIGURATION message to the UE.

[0125] In operation 608, the UE may transmit a message, such as an RRC RECONFIGURATION COMPLETE message, as a response to the source DU.

[0126] In operation 609, the source DU may forward the RRC RECONFIGURATION COMPLETE message to the CU via a UL RRC MESSAGE TRANSFER message, a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0127] In operation 610, the UE may start reporting L1 measurements of a serving cell, a source cell, and / or a candidate cell.

[0128] In operation 611, the source DU may determine that an LTM cell handover to a candidate cell is required.

[0129] In operation 612a, the source DU may send an LTM cell switching command (eg, MAC CE) to the UE to trigger the UE to change from the current serving cell to a candidate cell, hereinafter referred to as candidate cell 1 for clarity.

[0130] In operation 612b, the source DU may send a LTM cell handover command report to the CU, which may include the identity of the candidate cell towards which the LTM cell handover is to be initiated, such as the identity of candidate cell 1.

[0131] In operation 613, the CU may send a message to the candidate DU, and the message may include M indexes of the candidate cell configuration, the serving cell configuration and / or the source cell configuration. The message may be a DL RRC MESSAGE TRANSFER message, a UECONTEXT MODIFICATION REQUEST message, or other messages. In some cases, in operation 613, the CU may not provide M indexes to the candidate DU.

[0132] In operation 614 , an access procedure may be performed between the UE and the candidate DU controlling the candidate cell 1 .

[0133] Figure 7 A flow chart illustrating support for subsequent LTM according to some embodiments of the present disclosure.

[0134] Figure 7 Contains Figure 6 The same components as described in and the details are omitted here.

[0135] In this solution, the index of the candidate cell configuration can be generated by the source DU, and this solution can be applied to the inter-DU scenario or the intra-DU scenario. The candidate DU can provide the candidate cell configuration to the source DU directly or via the CU. The source DU can determine (or generate, assign) an index for each candidate cell configuration, determine an index for each source cell configuration, and determine an index for the serving cell configuration. Then, the source DU can send the index and the corresponding cell configuration (including the candidate cell configuration, the source cell configuration, and the serving cell configuration) to the CU. The CU can send the index and the corresponding cell configuration to the UE, and can send the index of the corresponding cell configuration to the candidate DU. Alternatively, the source DU can send the index of the corresponding cell configuration directly to the candidate DU. The detailed process is presented as follows.

[0136] Operations 701 and 702 are similar to operations 601 and 602, respectively, and the details are omitted here.

[0137] In operation 703, the CU may transmit a message to the source DU, such as a UE CONTEXT MODIFICATION REQUEST message, which may indicate X candidate cell IDs in the source DU and L candidate cell configurations in the candidate DUs.

[0138] In some embodiments, a UE CONTEXT MODIFICATION REQUEST message may be sent for each candidate cell. That is, the CU may transmit X UE CONTEXT MODIFICATION REQUEST messages to the source DU, where each UE CONTEXT MODIFICATION REQUEST message may indicate a candidate cell ID.

[0139] In some other embodiments, the CU may transmit one UE CONTEXT MODIFICATION REQUEST message to the source DU, which may include multiple candidate cell IDs (eg, a list of X candidate cell IDs).

[0140] The X candidate cells may include candidate cells in the source DU that are not the serving cells of the UE, that is, the X candidate cells may include only the source cell; alternatively, the X candidate cells may include the serving cell of the UE in the source DU. That is, the X candidate cells may include the serving cell and X-1 source cells.

[0141] Among the X requested candidate cells, some may be accepted, while others may not be accepted. For simplicity, assume that the total number of accepted candidate cells is represented as Y, where Y may be an integer equal to or greater than 1, and Y≤X. In some cases, all of the X requested candidate cells are accepted. In some cases, the X requested candidate cells may include the serving cell, and in other cases, the X requested candidate cells may not include the serving cell.

[0142] In some cases, the candidate DU may transmit the L candidate cell configurations in the candidate DU directly to the source DU.

[0143] In operation 704, the source DU may determine (or assign, generate, etc.) an index for each candidate cell configuration in a total number (denoted as M for simplicity) of candidate cell configurations, wherein the index is used to identify the candidate cell configuration. The M cell configurations may include candidate cell configurations, source cell configurations, serving cell configurations, or any combination thereof.

[0144] In operation 705a, the source DU may transmit one or more messages, such as one or more UE CONTEXT MODIFICATION RESPONSE messages, as a response to the CU, which may include M cell configurations (including candidate cell configurations, source cell configurations and / or serving cell configurations) and corresponding M indices.

[0145] The M indexes may include at least one of the following:

[0146] -Index of candidate cell configuration;

[0147] - the index of the source cell configuration; or

[0148] - Index of serving cell configuration.

[0149] A UE CONTEXT MODIFICATION RESPONSE message may be sent for each of the M candidate cells, so there are M UE CONTEXT MODIFICATION RESPONSE messages, each indicating one index and a corresponding cell configuration. Alternatively, one UE CONTEXT MODIFICATION RESPONSE message may include a list of M cell configurations and corresponding indices.

[0150] In some embodiments, in operation 705b, the source DU may transmit a message to the candidate DU, which may indicate M indexes to the candidate DU. In some cases, the message may further include a serving cell configuration, a source cell configuration, or both. In some embodiments, the source DU may not be able to transmit a message to the candidate DU, and therefore may not be able to perform operation 705b.

[0151] In operation 706a, the CU may send a DL RRC MESSAGE TRANSFER message to the source DU, which includes the generated RRC RECONFIGURATION message. The generated RRC RECONFIGURATION message may include M indexes and corresponding cell configurations.

[0152] In some embodiments, the RRC RECONFIGURATION message may also include an indicator indicating the cell configuration and index that should be maintained by the UE. That is, after the LTM cell handover, the index and the corresponding cell configuration should be maintained by the UE.

[0153] For example, the RRC RECONFIGURATION message contains a field named "Subsequent LTM." If the field is set to true or has a value of "1," the UE may maintain the cell configuration and index after LTM cell switching.

[0154] In some other cases, the UE may be configured to maintain the cell configuration and index after LTM cell switching according to predefined rules, specifications, etc.

[0155] In some cases, a message, such as a DL RRC MESSAGE TRANSFER message, may further include a candidate cell configuration.

[0156] In operation 706b, the CU may transmit a message including M indices to the candidate DUs. The message may be a UE CONTEXT MODIFICATION REQUEST message or a DL RRC MESSAGE TRANSFER message or other message. In some cases, the message may further include a serving cell configuration, a source cell configuration, or both.

[0157] Operations 707 to 714 are similar to operations 607 to 614, respectively, and the details are omitted here.

[0158] Figure 8 A flow chart illustrating support for subsequent LTM according to some embodiments of the present disclosure.

[0159] Figure 8 Contains Figure 6 The same components as described in and the details are omitted here.

[0160] In this solution, the index of the candidate cell configuration can be generated by the candidate DU, and this solution can be applied to the inter-DU scenario or the intra-DU scenario. The source DU can provide the source cell configuration and the optional serving cell configuration to the candidate DU directly or via the CU. The candidate DU can determine (or generate, assign) an index for each candidate cell configuration, each source cell configuration and the serving cell configuration. Then, the candidate DU can send the index and the corresponding cell configuration (including the candidate cell configuration, the source cell configuration and the serving cell configuration) to the CU. The CU can send the index and the corresponding cell configuration to the UE, and can send the index of the corresponding cell configuration to the source DU. Alternatively, the candidate DU can send the index of the corresponding cell configuration directly to the source DU. The detailed process is presented as follows.

[0161] Operations 801 and 802 are similar to operations 603 and 604, respectively, and the details are omitted here.

[0162] In operation 803, when the K candidate cells are controlled by the same candidate DU, the CU may transmit a message indicating the number of candidate cell IDs (expressed as K candidate cell IDs for simplicity) to the candidate DU, such as a UE CONTEXT SETUP REQUEST message; or when the K candidate cells are controlled by multiple candidate DUs, the message may be transmitted to multiple candidate DUs. The message may request preparation of the K candidate cells controlled by the candidate DU to create a UE context and set up one or more data bearers.

[0163] In some embodiments, a UE CONTEXT SETUP REQUEST message may be sent for each candidate cell. That is, the CU may transmit K UE CONTEXT SETUP REQUEST messages, where each UE CONTEXT SETUP REQUEST message may indicate a candidate cell ID.

[0164] In some other embodiments, the UE CONTEXT SETUP REQUEST message may include multiple candidate cell IDs (eg, a list of K candidate cell IDs) and be transmitted to the candidate DUs controlling the multiple candidate cells.

[0165] The UE CONTEXT SETUP REQUEST message may also include Y candidate cell configurations in the source DU, which may include the source cell configuration, the serving cell configuration, or both.

[0166] In some cases, the source DU may transmit the Y candidate cell configurations directly to the candidate DUs.

[0167] In operation 804, a preparation request may be accepted, and among the K requested candidate cells, L requested candidate cells may be accepted, where L may be an integer equal to or greater than 1, and L ≤ K. The CU may determine (or assign, generate, etc.) an index for each candidate cell configuration in a total number (denoted as M for simplicity) of candidate cell configurations, where the index is used to identify the candidate cell configuration.

[0168] In operation 805a, the candidate DU may transmit a message, such as a UE CONTEXT SETUP RESPONSE message, as a response to the CU, which may include M cell configurations and corresponding M indices.

[0169] The M indexes may include at least one of the following:

[0170] -Index of candidate cell configuration;

[0171] - the index of the source cell configuration; or

[0172] - Index of serving cell configuration.

[0173] In some embodiments, in operation 805b, the candidate DU may transmit a message to the source DU, which may indicate M indexes to the source DU. In some cases, the message may further include a candidate cell configuration. In some embodiments, the candidate DU may not be able to transmit a message to the source DU, and therefore operation 805b may not be performed.

[0174] Operations 806 to 813 are similar to operations 606a, 607 to 612, and 614, respectively, and the details are omitted here.

[0175] Fig. 9 A simplified block diagram illustrating an apparatus according to some embodiments of the present disclosure.

[0176] As in Fig. 9 , an example of apparatus 900 may include at least one processor 904 and at least one transceiver 902 coupled to the processor 904. Apparatus 900 may be a UE, a BS, a CU, a candidate DU, a source DU, a target DU, or any other device having similar functionality.

[0177] Although in this figure, elements such as at least one transceiver 902 and processor 904 are described in the singular, the plural may be contemplated unless limitation to the singular is explicitly stated. In some embodiments of the present disclosure, the transceiver 902 may be divided into two devices, such as a receiving circuit system and a transmitting circuit system. In some embodiments of the present disclosure, the device 900 may further include an input device, a memory, and / or other components.

[0178] In some embodiments of the present disclosure, the device 900 may be a UE. The transceiver 902 and the processor 904 may interact with each other to perform the operations of the UE described in any of Figures 1 to 8. In some embodiments of the present disclosure, the device 900 may be a CU, a candidate DU, a source DU, a target DU, or the like. The transceiver 902 and the processor 904 may interact with each other to perform the operations of the CU or DU described in any of Figures 1 to 8.

[0179] In some embodiments of the present disclosure, the apparatus 900 may further include at least one non-transitory computer-readable medium.

[0180] For example, in some embodiments of the present disclosure, a non-transitory computer-readable medium may store computer-executable instructions thereon to cause the processor 904 to implement the method for the UE as described above. For example, when the computer-executable instructions are executed, the processor 904 interacts with the transceiver 902 to perform the operations of the UE described in any of Figures 1 to 8.

[0181] In some embodiments of the present disclosure, a non-transitory computer-readable medium may store computer-executable instructions thereon to cause the processor 904 to implement the method for the CU, candidate DU, source DU, target DU, or candidate DU as described above. For example, when the computer-executable instructions are executed, the processor 904 interacts with the transceiver 902 to perform the operations of the CU or DU described in any of Figures 1 to 8.

[0182] The methods of the present disclosure may be implemented on a programmed processor. However, the controller, flow charts, and modules may also be implemented on a general or special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit components, an integrated circuit, a hardware electronic or logic circuit (e.g., a discrete component circuit), a programmable logic device, or the like. In general, any device having a finite state machine capable of implementing the flow charts shown in the figures may be used to implement the processing functions of the present disclosure.

[0183] Although the present disclosure has been described with specific embodiments of the present disclosure, it is apparent that many alternatives, modifications and variations will be apparent to those skilled in the art. For example, in other embodiments, the various components of the embodiments may be interchangeable, added or replaced. In addition, all elements of each figure are not necessary for the operation of the disclosed embodiments. For example, a person skilled in the art of the disclosed embodiments will be able to make and use the teachings of the present disclosure by simply adopting the elements of the independent claims. Therefore, the embodiments of the present disclosure set forth herein are intended to be illustrative, rather than restrictive. Various changes may be made without departing from the spirit and scope of the present disclosure.

[0184] In the present disclosure, for example, the relational terms of "first", "second" can only be used to distinguish an entity or action from another entity or action, without requiring or implying any actual relationship or order between this entity or action. The term "includes / including" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements not only comprises the elements, but also may comprise other elements that are not clearly listed or inherent to the process, method, article or equipment. In the absence of more constraints, the elements beginning with "one" or the like do not exclude the presence of additional equivalent elements in the process, method, article or equipment comprising the elements. In addition, the term "another" is defined as at least the second or more. The terms "include", "have" and the like used herein are defined as "comprising".

Claims

1. A central unit CU, comprising: Transceiver; and a processor coupled to the transceiver and configured to: determining a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells, wherein the index of the candidate cell configuration for each candidate cell is generated by the CU or received from a source distributed unit DU or from a candidate DU; transmitting, via the source DU, to a user equipment UE, a first message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration; transmitting a second message indicating the index of the candidate cell configuration of each candidate cell to the source DU; as well as A third message indicating the index of the candidate cell configuration for each candidate cell is transmitted to the candidate DUs.

2. The CU of claim 1, wherein the one or more candidate cells include candidate cells in the candidate DU.

3. The CU of claim 2, wherein the one or more candidate cells further include candidate cells in the source DU.

4. The CU according to claim 3, wherein the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not the serving cell of the UE. 5 . The CU of claim 1 , wherein the first message further comprises an indicator instructing the UE to maintain the candidate cell configuration and the index of the candidate cell configuration for each candidate cell after L1 / L2 triggered mobility (LTM) cell switching. The CU according to claim 1 , wherein the second message further includes candidate cell configuration in the candidate DU.

7. The CU of claim 1, wherein the third message further includes at least one of the following: The serving cell configuration of the serving cell in the source DU; or The source cell configuration of the source cell in the source DU.

8. A source distributed unit DU, comprising: Transceiver; and a processor coupled to the transceiver and configured to: determining, for each candidate cell of the one or more candidate cells, a candidate cell configuration and an index of the candidate cell configuration; transmitting a first message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a user equipment UE; transmitting a second message indicating the candidate cell configuration of each candidate cell and the index of the candidate cell configuration to a central unit CU; as well as The index of the candidate cell configuration for each candidate cell is provided to the candidate DU.

9. The source DU of claim 8, wherein the one or more candidate cells include candidate cells in the candidate DU.

10. The source DU of claim 9, wherein the one or more candidate cells further include a candidate cell in the source DU.

11. The source DU according to claim 10, wherein the candidate cell in the source DU is a serving cell or a source cell, wherein the source cell is a cell in the source DU that is not the serving cell of the UE.

12. The source DU of claim 8, wherein the first message further comprises an indicator instructing the UE to maintain the candidate cell configuration and the index of the candidate cell configuration for each candidate cell after L1 / L2 triggered mobility (LTM) cell switching.

13. The source DU of claim 8, wherein the processor is further configured to provide the candidate DU with at least one of: The serving cell configuration of the serving cell in the source DU; or The source cell configuration of the source cell in the source DU.

14. The source DU of claim 8, wherein the index of the candidate cell configuration of the candidate cell is provided to the candidate DU directly or via the CU.

15. A user equipment UE, comprising: Transceiver; and a processor coupled to the transceiver and configured to: receiving a message indicating the candidate cell configuration and the index of the candidate cell configuration for each candidate cell; performing L1 / L2 triggered mobility LTM cell switching based on the message; as well as After the LTM cell switching, the candidate cell configuration and the index of the candidate cell configuration for each candidate cell are maintained.

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