Method and equipment for maintaining TA value

Abstract

Embodiments of the present application relate to a method and apparatus for maintaining a timing advance (TA) value in a 3rd generation partnership project (3GPP) 5G system or the like. According to an embodiment of the present application, a centralized unit (CU) comprises: a transceiver; and a processor coupled to the transceiver and configured to: transmit, via the transceiver, a cell handover request including identifier (ID) information of one or more candidate cells to one or more candidate distributed units (DUs) of a BS; receiving, via the transceiver, radio resource control (RRC) configuration information for the one or more candidate cells from the one or more candidate DUs; and transmitting, via the transceiver, an RRC reconfiguration message associated with the one or more candidate cells to a user equipment (UE).

Description

Technical Field

[0001] Embodiments of the present application generally relate to wireless communication technologies, and more particularly, to methods and devices for maintaining a Timing Advance (TA) value in a cell handover procedure. Background Art

[0002] Wireless communication systems have been widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcasting, and so on. A wireless communication system may employ a multiple access technology capable of supporting communication with multiple users by sharing available system resources such as time, frequency, and power. Examples of wireless communication systems may include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (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 on how to maintain a Timing Advance (TA) value in a cell handover procedure have not been addressed in 3GPP 5G technologies. Summary of the Invention

[0004] Some embodiments of the present application provide a Centralized Unit (CU). The CU includes: a transceiver; and a processor coupled to the transceiver; and the processor is configured to: transmit, via the transceiver, a cell handover request including identifier (ID) information of one or more candidate cells to one or more candidate Distributed Units (DUs) of a BS; receive, via the transceiver, radio resource control (RRC) configuration information of the one or more candidate cells from the one or more candidate DUs; and transmit, via the transceiver, an RRC reconfiguration message associated with the one or more candidate cells to a User Equipment (UE).

[0005] In some embodiments, the processor of the CU is configured to: receive, via the transceiver, a first message from the UE or from a candidate DU within the one or more candidate DUs, wherein the UE is configured to handover from a source cell to a candidate cell within the one or more candidate cells; and in response to receiving the first message, transmit, via the transceiver, a request for providing a Timing Advance (TA) list to a source DU, wherein the TA list includes at least one of the following: one or more TA values associated with the one or more candidate cells; or ID information of the one or more candidate cells.

[0006] In some embodiments, the first message includes at least one of the following: information for indicating that the UE has handover to the candidate cell; or a request for the TA list.

[0007] In some embodiments, the processor of the CU is configured to: receive the TA list from the source DU via the transceiver; and transmit the TA list to the candidate DU via the transceiver.

[0008] In some embodiments, the processor of the CU is configured to: receive, via the transceiver, one or more timing advance (TA) values associated with the one or more candidate cells from the one or more candidate DUs; and store the one or more TA values.

[0009] In some embodiments, the processor of the CU is configured to transmit, via the transceiver, the TA list of the UE to a candidate DU of the BS, where the UE is configured to switch from a source cell of the source DU of the BS to a candidate cell of the candidate DU, and where the TA list includes at least one of the following: the one or more TA values; or ID information of the one or more candidate cells.

[0010] In some embodiments, the TA list is transmitted after the processor of the CU is configured to receive one of the following: information indicating that a cell handover command has been transmitted from the source DU to the UE via the transceiver from the source DU; an RRC reconfiguration complete message from the UE via the transceiver of the candidate DU of the BS; and information indicating that the UE has switched to the candidate cell from the UE via the transceiver of the candidate DU.

[0011] In some embodiments, in response to the UE switching from a source cell to a candidate cell within the one or more candidate cells, the processor of the CU is configured to indicate the ID information of the candidate cell to other candidate DUs within the one or more candidate cells.

[0012] In some embodiments, the processor of the CU is configured to receive, via the transceiver, at least one of the following: information indicating that the UE has switched to the candidate cell from the UE via the candidate DU; information indicating that the candidate DU has received a layer 2 (L2) cell handover complete message associated with the candidate cell from the candidate DU of the BS; or the ID information of the one or more candidate cells and the ID information of the candidate cell from the source DU.

[0013] 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: receive, via the transceiver, a timing advance (TA) value associated with the source cell from the source cell; receive, via the transceiver, one or more TA values associated with the one or more candidate cells from the one or more candidate cells; receive a cell handover command for a candidate cell within the one or more candidate cells from the source cell; and access the candidate cell based on the cell handover command.

[0014] In some embodiments, after the UE switches from the source cell to the candidate cell, the processor of the UE is configured to perform at least one of the following: continue to maintain the TA value associated with the source cell; or maintain a time alignment timer (TAT) associated with the source cell.

[0015] In some embodiments, after the UE switches from the source cell to the candidate cell, the source cell serves as one of the candidate cells.

[0016] In some embodiments, the processor of the UE is configured to receive first information from the source cell via the transceiver, and wherein the first information indicates at least one of the following: whether to maintain the TA value associated with the source cell; or whether to maintain the TAT associated with the source cell.

[0017] In some embodiments, after the UE switches from the source cell to the candidate cell, the processor of the UE is configured to: release the one or more TA values associated with the one or more candidate cells; or continue to maintain all or a subset of the one or more TA values associated with the one or more candidate cells.

[0018] In some embodiments, in response to continuing to maintain all or the subset of the one or more TA values, the processor of the UE is configured to transmit, via the transceiver, a list of identifiers (IDs) of a set of candidate cells within the one or more candidate cells to the candidate cell, wherein the TA value associated with each candidate cell within the set of candidate cells is maintained by the UE.

[0019] In some embodiments, the processor of the UE is configured to receive second information from the source cell via the transceiver, and wherein the second information indicates which candidate cell's TA value the UE maintains after the UE switches from the source cell to the candidate cell.

[0020] Some embodiments of the present application provide a source distributed unit (DU). The source DU includes: a transceiver; and a processor coupled to the transceiver; and the processor is configured to: receive a timing advance (TA) list from a centralized unit (CU) of the BS via the transceiver, where the TA list includes at least one of the following: one or more TA values associated with one or more candidate cells of one or more candidate DUs of the BS; or identifier (ID) information of the one or more candidate cells; and transmit a cell handover command to a candidate cell within the one or more candidate cells to a user equipment (UE) via the transceiver.

[0021] In some embodiments, the processor of the source DU is configured to: receive a request for providing the TA list from the CU via the transceiver; transmit the TA list to the CU via the transceiver.

[0022] In some embodiments, after transmitting the cell handover command, the processor of the source DU is configured to: transmit the ID information of the one or more candidate cells to the CU via the transceiver; and transmit the ID information of the candidate cell to the CU via the transceiver.

[0023] Some embodiments of the present application provide a candidate distributed unit (DU). The candidate DU includes: a transceiver; and a processor coupled to the transceiver; and the processor is configured to transmit a first message to the CU via the transceiver, where the first message includes at least one of the following: information indicating that a user equipment (UE) has switched from a source cell of a source DU of the BS to a candidate cell within a set of candidate cells of the candidate DU; or a request for a timing advance (TA) list.

[0024] In some embodiments, the TA list includes at least one of the following: one or more TA values associated with one or more candidate cells of one or more candidate DUs of the BS; or the ID information of the one or more candidate cells.

[0025] In some embodiments, the processor of the candidate DU is configured to receive the TA list from the CU via the transceiver.

[0026] In some embodiments, the TA list is received by the candidate DU after the CU is configured to receive one of the following: information from the source DU indicating that a cell handover command has been transmitted from the source DU to the UE; a radio resource control (RRC) reconfiguration complete message from the UE via the candidate DU; and information from the UE via the candidate DU indicating that the UE has switched to the candidate cell.

[0027] In some embodiments, the processor of the candidate DU is configured to: receive, via the transceiver, from the UE the information indicating that the UE has switched from the source cell to the candidate cell.

[0028] In some embodiments, the processor of the candidate DU is configured to: receive, via the transceiver, from the UE a layer 2 (L2) cell handover completion message associated with the candidate cell; and transmit, via the transceiver, to the CU information indicating that the L2 cell handover completion message has been received.

[0029] Some embodiments of the present application provide a method performed by a centralized unit (CU). The method includes: transmitting a cell handover request including identifier (ID) information of one or more candidate cells to one or more candidate distributed units (DUs) of the BS; receiving radio resource control (RRC) configuration information of the one or more candidate cells from the one or more candidate DUs; and transmitting an RRC reconfiguration message associated with the one or more candidate cells to a user equipment (UE).

[0030] Some embodiments of the present application provide a method performed by a UE. The method includes: receiving a timing advance (TA) value associated with a source cell from the source cell; receiving one or more TA values associated with one or more candidate cells from the one or more candidate cells; receiving a cell handover command for a candidate cell within the one or more candidate cells from the source cell; and accessing the candidate cell based on the cell handover command.

[0031] Some embodiments of the present application provide a method performed by a source distributed unit (DU). The method includes: receiving a timing advance (TA) list from a centralized unit (CU) of the BS, where the TA list includes at least one of the following: one or more TA values associated with one or more candidate cells of one or more candidate DUs of the BS; or identifier (ID) information of the one or more candidate cells; and transmitting a cell handover command for a candidate cell within the one or more candidate cells to a user equipment (UE).

[0032] Some embodiments of the present application provide a method performed by a candidate distributed unit (DU). The method includes: transmitting a first message to the CU, where the first message includes at least one of the following: information indicating that a user equipment (UE) has switched from a source cell of a source DU of the BS to a candidate cell within the set of candidate cells; or a request for a timing advance (TA) list.

[0033] 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; receiving circuitry; transmitting circuitry; and a processor coupled to the non-transitory computer-readable medium, the receiving circuitry, and the transmitting circuitry, wherein the computer-executable instructions cause the processor to implement the above-described method performed by a UE or a network node (such as a base station (BS), CU, or DU).

[0034] 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

[0035] To describe the manner in which the advantages and features of the present application can be obtained, a description of the present application is presented by reference to specific embodiments of the present application illustrated in the accompanying drawings. These drawings only depict example embodiments of the present application and are thus not to be considered as limiting its scope.

[0036] Figure 1 Schematic diagram illustrating a wireless communication system according to some embodiments of the present application.

[0037] Figure 2 Schematic diagram illustrating layer 1 / layer 2 (L1 / L2)-triggered mobility (LTM) between cells according to some embodiments of the present application.

[0038] Figure 3 Exemplary flowchart illustrating transmitting a cell handover request according to some embodiments of the present application.

[0039] Figure 4 Exemplary flowchart illustrating receiving a cell handover command according to some embodiments of the present application.

[0040] Figure 5 Exemplary flowchart illustrating transmitting a cell handover command according to some embodiments of the present application.

[0041] Figures 6 to 9 Exemplary flowchart illustrating maintaining a TA value according to some embodiments of the present application.

[0042] Figure 10 Block diagram illustrating an exemplary device according to some embodiments of the present application. DETAILED DESCRIPTION

[0043] The detailed description of the 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 is to be understood that the same or equivalent functions can be accomplished by different embodiments that are intended to be covered within the spirit and scope of the present application.

[0044] Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. For the sake of promoting understanding, the embodiments are provided in a specific network architecture and new service scenarios (such as 3GPP 5G, 3GPP LTE Release 8, etc.). It is considered that with the development of the network architecture and new service scenarios, all embodiments in the present application are also suitable for similar technical problems; and in addition, the terms cited in the present application may change, which should not affect the principles of the present application.

[0045] Figure 1 Schematic diagram of a wireless communication system according to some embodiments of the present application. As Figure 1 shown, the wireless communication system 100 includes at least one base station (BS) 101 and at least one user equipment (UE) 102. Specifically, for illustrative purposes, the wireless communication system 100 includes one BS 101 and two UEs 102 (such as UE 102a and UE 102b). Although a specific number of BSs and UEs are illustrated for simplicity, it is considered that in some other embodiments of the present application, the wireless communication system 100 may include more or fewer BSs and UEs. Figure 1 In the present application, although a specific number of BSs and UEs are illustrated for simplicity, it is considered that in some other embodiments of the present application, the wireless communication system 100 may include more or fewer BSs and UEs.

[0046] 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 phone network, a time division multiple access (TDMA)-based network, a code division multiple access (CDMA)-based network, an orthogonal frequency division multiple access (OFDMA)-based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0047] The BS 101 can communicate with a core network (CN) node (not shown) via an interface, such as a mobility management entity (MME) or a serving gateway (S-GW), an access and mobility management function (AMF) or a user plane function (UPF), etc. The BS can also be referred to as an access point, an access terminal, a base, a macro cell, a Node B, an evolved Node B (eNB), a gNB, a home Node B, a relay node or device, or described using other terms used in the art. In 5G NR, the BS can also be referred to as a RAN node or a network device. Each BS can serve several UEs within a service area via a wireless communication link, such as a cell or a cell sector. Adjacent BSs can communicate with each other when necessary, for example, during the handover procedure of a UE.

[0048] The UE 102 (such as 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 gaming console, a security system (including security cameras), an in-vehicle computer, a network device (such as a router, a switch, and a modem), or the like. According to an embodiment of the present application, the 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 transmitting and receiving communication signals over a wireless network. In some embodiments, the 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, the 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 other terms used in the art to describe. The UE 102 may communicate directly with the BS101 via an uplink (UL) communication signal.

[0049] In Release 18 of 3GPP, support for inter-cell mobility based on layer 1 / layer 2 (L1 / L2) signaling has been discussed. Specifically, the UE may be pre-provided with configurations from multiple cells, and the BS (such as a gNB) may use L1 / L2 signaling to switch the UE to a new cell considering the received physical layer measurement results. According to the 3GPP standard document, the BS may consist of a BS central unit (CU) and one or more BS distributed units (DUs). The BS-CU and the BS-DU are connected via an F1 interface as a logical interface. One BS-DU is only connected to one BS-CU.

[0050] Figure 2 A schematic diagram illustrating layer 1 / layer 2 (L1 / L2)-triggered mobility (LTM) between cells according to some embodiments of the present application. As Figure 2 shown, the CU may communicate with two DUs (i.e., DU1 or DU2) via the F1 interface. Figure 2 The CU in may implement traditional mobility decisions based on layer 3 (L3) measurement results. Figure 2 DU1 or DU2 in may implement L1 / L2-triggered mobility decisions based on physical layer measurement results.

[0051] Compared with traditional L3-based mobility, L1 / L2-triggered mobility is considered faster, with less processing delay and signaling delay. In traditional L3-based mobility, the CU (e.g., Figure 2The CU shown in makes mobility decisions based on the received radio resource management (RRM) measurement reports. The RRC configuration information will be used to trigger L3-based mobility. Different from traditional L3-based mobility, in L1 / L2-triggered mobility, the DU (e.g., Figure 2 the DU1 or DU2 shown in ) makes mobility decisions based on physical layer measurement results carried, for example, in the channel state information (CSI) report. The medium access control (MAC) control element (CE) can be used to trigger LTM. In addition, in traditional L3 mobility, the handover command is sent from the CU to the UE via the RRC message, while in L1 / L2 mobility, the "handover" command is sent from the DU to the UE via L1 / L2 signaling (e.g., downlink control information (DCI) or MAC CE). The "handover" command in L1 / L2 mobility can be about cell activation or deactivation, for example, activating the new serving PCell while deactivating the old serving PCell.

[0052] Currently, several issues regarding maintaining the TA value during L1 / L2 mobility need to be solved. Embodiments of this application aim to solve such problems. Some embodiments of this application can be applicable to the case of "lower layer-triggered mobility" or "L1 / L2-triggered mobility", and the abbreviation of at least one of them can be "LTM". In the LTM case, the UE can access the serving BS (e.g., serving gNB). The UE can report 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 hand over the UE to a candidate cell based on the measurement results, the serving gNB can request the target DU to prepare the configuration for one or more candidate cells. After receiving the candidate cell configuration from the target DU of the serving gNB, the serving gNB can transmit an RRC reconfiguration message containing the ID information of one or more candidate cells to the UE. For example, the CU can transmit the RRC reconfiguration message to the UE via the source DU of the serving gNB. The UE can transmit an RRC reconfiguration complete message to the serving gNB (e.g., CU) via the source DU. The UE can ensure UL synchronization or DL synchronization before receiving the cell handover command. For example, the UE can obtain or acquire the TA value via random access (RA) or preamble transmission. The UE can report layer 1 (L1) measurement results for dynamic handover purposes. The serving gNB (e.g., source DU) can transmit a cell handover command, such as MAC CE or DCI. The UE can apply the RRC reconfiguration message and start a timer after receiving the lower layer command.

[0053] More specifically, some embodiments of the present application study the behavior of a UE regarding whether the UE continues to maintain the TA value of the source cell after the UE accesses a candidate cell when the UE performs a lower layer-triggered mobility. Some embodiments of the present application study a mechanism for a target cell to know which TA values of candidate cells the UE already has when TA acquisition based on a Random Access Response (RAR) response is not used and other candidate cell TA values can be used after a lower layer-triggered mobility is performed on a candidate cell. Some embodiments of the present application study a mechanism for the UE to release the TA values of other candidate cells after a lower layer-triggered mobility is performed on a candidate cell. Some embodiments of the present application study a mechanism for a target cell to know which TA values of candidate cells the UE already has when the UE maintains the TA values of other candidate cells after a lower layer-triggered mobility is performed on a candidate cell. Some embodiments of the present application study a mechanism for other candidate cells to know the cell handover state in the UE side after the cell is handed over to a candidate cell.

[0054] Some embodiments of the present application study a use case where, before the UE performs a lower layer-triggered mobility on a candidate cell, one of the UE, the source DU, and the CU can maintain a list of TA values of some candidate cells. Some embodiments of the present application study whether the UE continues to maintain the TA value of the source cell or other candidate cells after the UE performs a lower layer-triggered mobility on a candidate cell (assuming the UE stores the TA values of the candidate cells). Some embodiments of the present application study how to notify the target cell which TA values have been obtained if the source DU or CU maintains a list of TA values of conditional cells. In some embodiments of the present application, after the UE switches from the source cell to a candidate cell, the cell handover state in the UE side is indicated to other candidate cells that the UE has not accessed.

[0055] Specifically, in the Figures 3 to 10 embodiments of the present application, both inter-DU mobility scenarios and intra-DU mobility scenarios are considered, such as LTM between gNB-DUs or LTM within a gNB-DU. Inter-DU mobility means that when 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, the connection to the CU remains the same, and both the source DU and the target DU are managed by the CU. Intra-DU mobility means that when the UE may change from a source cell to a target cell associated with the same DU due to mobility, the connection to the CU remains the same. More details will be described below with reference to the drawings.

[0056] Figure 3 Illustrate an exemplary flowchart of transmitting a cell handover request according to some embodiments of the present application. Figure 3 In the embodiments of, the exemplary method 300 can be performed by the CU of the BS (such asFigure 2 and 6 is performed by the CU, CU604, CU 704, CU 804, or CU 904 shown and described in any of 1 to 9. Although described with respect to the CU, it should be understood that other devices may be configured to perform methods similar to those of Figure 3 The details described in all other embodiments of this application apply to Figure 3 the embodiments of Figure 3 In addition, the details described in the embodiments of Figure 1 apply to 2 and all embodiments from 4 to 10.

[0057] In Figure 3 In the exemplary method 300 shown in, in operation 301, the CU of the BS (e.g., Figure 7 or Figure 8 the CU 704 or CU 804 shown and described in) transmits a cell handover request (e.g., a UE CONTEXT SETUP REQUEST message) to one or more candidate DUs of the BS (e.g., Figure 7 or Figure 8 the candidate DU703, candidate DU 706, candidate DU 803, or candidate DU 806 shown and described in). The cell handover request includes ID information of one or more candidate cells.

[0058] In operation 302, the CU receives RRC configuration information of one or more candidate cells from one or more candidate DUs. In operation 303, the CU transmits an RRC reconfiguration message associated with one or more candidate cells to the UE (e.g., Figure 7 or Figure 8 the UE 701 or UE 801 shown and described in).

[0059] In some embodiments, the CU may receive a message (simply denoted as message #1) from the UE or from a candidate DU within one or more candidate DUs. The UE may be configured to switch from a source cell to a candidate cell within one or more candidate cells (e.g., a target serving cell). In response to receiving message #1, the CU may transmit a request for providing a TA list to the source DU (e.g., Figure 7 or Figure 8 the source DU 702 or source DU802 shown and described in).

[0060] In the embodiments of this application, the TA list may include TA values, information of associated candidate cells, and / or information of associated candidate DUs. For example, the TA list may include at least one of the following: (1) one or more TA values associated with one or more candidate cells or (2) ID information of one or more candidate cells.

[0061] For example, Message #1 may be received in a scenario without an RAR message for TA acquisition (i.e., without an RAR response for TA acquisition), such as in the case where a candidate DU calculates the TA and transmits it to the source DU of the UE. Then, the source DU maintains the TA list.

[0062] In some embodiments, Message #1 includes at least one of the following: (1) information indicating that the UE has switched to a candidate cell (e.g., a cell handover success indication) or (2) a request for the TA list.

[0063] In some embodiments, the CU may receive the TA list from the source DU and transmit the TA list to the candidate DU, such as in a scenario without an RAR message for TA acquisition (i.e., without an RAR response for TA acquisition).

[0064] In some embodiments, the CU may receive one or more TA values associated with one or more candidate cells from one or more candidate DUs and store the one or more TA values, such as in a scenario without an RAR message for TA acquisition (i.e., without an RAR response for TA acquisition), such as when the CU maintains the TA list.

[0065] In some embodiments, the CU may transmit the TA list of the UE to a candidate DU of the BS (i.e., the target DU). The UE may be configured to switch from the source cell of the source DU of the BS to the candidate cell of the candidate DU (i.e., the target serving cell). The TA list may include at least one of the following: (1) one or more TA values associated with one or more candidate cells or (2) ID information of one or more candidate cells. For example, the TA list may be transmitted before or after the UE switches from the source cell to the candidate cell.

[0066] In an embodiment, the CU may transmit the TA list after the CU receives information from the source DU indicating that a cell handover command has been transmitted from the source DU to the UE. In another embodiment, the CU may transmit the TA list after the CU receives an RRC reconfiguration complete message from the UE via a candidate DU of the BS. In an additional embodiment, the CU may transmit the TA list after the CU receives information from the UE via a candidate DU indicating that the UE has switched to a candidate cell (e.g., after a successful cell handover).

[0067] In some embodiments, if the UE switches from the source cell to a candidate cell within one or more candidate cells, the CU may indicate the ID information of the candidate cell to other candidate DUs within the one or more candidate cells.

[0068] In some embodiments, the CU may receive at least one of the following:

[0069] (1) Information from the UE via a candidate DU indicating that the UE has switched to a candidate cell;

[0070] (2) The indicator candidate DU has received layer 2 associated with the candidate cell from the candidate DU of the BS (e.g., the target DU).

[0071] (L2) Information of the cell handover completion message (e.g., MAC CE); or

[0072] (3) ID information of one or more candidate cells and ID information of the candidate cells from the source DU. Specific examples are described below in the embodiments of Figure 7 or Figure 8 as follows.

[0073] Figure 4 Exemplary flowchart showing the reception of a cell handover command according to some embodiments of the present application. Figure 4 In the embodiment of Figure 1 and 6 the exemplary method 400 shown and described in any one of 1 to 9 can be executed by a UE (e.g., Figure 4 the UE 102, UE601, UE 701, UE 801 or UE 901 shown and described in Figure 4 ). Although described with respect to a UE, it should be understood that other devices can be configured to execute methods similar to the Figure 4 methods. The details described in all other embodiments of the present application apply to the Figures 1 to 3 embodiments. In addition,

[0074] In Figure 4 the exemplary method 400 shown in Figure 6 or Figure 9 the UE 601 or 901 shown and described in Figure 6 or Figure 9 the cell associated with the source cell (e.g., the cell of the source DU 602 or the cell of the source DU 902 shown and described in Figure 6 or Figure 9 ). For example, the TA value associated with the source cell and / or the TA value associated with the candidate cell can be an absolute TA value or an offset TA value.

[0075] In operation 403, the UE can receive a cell handover command for the candidate cell within one or more candidate cells from the source cell. In operation 404, the UE can access the candidate cell based on the cell handover command.

[0076] In some embodiments, after the UE switches from a source cell to a candidate cell (e.g., a target cell), the UE may continue to maintain the TA value associated with the source cell and / or maintain the Time Alignment Timer (TAT) associated with the source cell. In an embodiment, after the UE switches from a source cell to a candidate cell (e.g., a target cell), the source cell serves as a candidate cell.

[0077] In an embodiment, the UE may receive information from the source cell indicating at least one of the following: (1) whether to maintain the TA value associated with the source cell; or (2) whether to maintain the TAT associated with the source cell. The information may be included in the RRC configuration information.

[0078] In some embodiments, after the UE switches from a source cell to a candidate cell, for example, in a scenario with a RAR message when the UE maintains a TA list, the UE may release one or more TA values associated with one or more candidate cells, or the UE may continue to maintain all or a subset of the one or more TA values associated with one or more candidate cells. In an embodiment, if the UE continues to maintain all or a subset of the one or more TA values, the UE may transmit a list of IDs of a set of candidate cells within one or more candidate cells (e.g., a target cell). The TA value associated with each candidate cell within the set of candidate cells may be maintained by the UE. That is, the UE notifies the target cell of the list of IDs of the candidate cells whose TA values are maintained by the UE.

[0079] In some embodiments, the UE may receive information from the source cell indicating which candidate cell's TA value the UE is to maintain after the UE switches from the source cell to the candidate cell. For example, the information indicates a list of IDs of candidate cells whose TA values need to be maintained by the UE. The information may be included in the RRC configuration information. Specific examples are described in Figure 6 or Figure 9 the embodiments below.

[0080] Figure 5 Exemplary flowchart illustrating the transmission of a cell handover command according to some embodiments of the present application. Figure 5 The exemplary method 500 in the embodiments of Figure 2 and 6 any one of DU1, DU2, source DU 602, source DU 702, source DU 802, or source DU 902 shown and described in Figure 5 to 9 may be performed by the source DU of the BS (e.g., Figure 5 ). Although described with respect to the source DU, it should be understood that other devices may be configured to perform methods similar to the Figure 5 method. The details described in all other embodiments of the present application apply to theFigures 1 to 4 and all embodiments from 6 to 10.

[0081] In Figure 5 exemplary method 500 shown in, at operation 501, a source DU (e.g., Figure 7 source DU 702 shown and described in) may receive a TA list from a CU of the BS (e.g., Figure 7 CU 704 shown and described in). The TA list may include at least one of the following: (1) one or more TA values associated with one or more candidate cells of one or more candidate DUs of the BS; or (2) ID information of one or more candidate cells. In some embodiments, the source DU may receive a request for providing the TA list from the CU and transmit the TA list to the CU.

[0082] At operation 502, the source DU may transmit a cell handover command to a candidate cell (e.g., a target cell) within one or more candidate cells to the UE (e.g., Figure 7 UE 701 shown and described in). In some embodiments, after transmitting the cell handover command, the source DU may transmit the ID information of one or more candidate cells to the CU and transmit the ID information of the candidate cell (e.g., the target cell) to the CU. Based on the ID information received from the source DU, the CU may know which candidate cell is the target cell among the one or more candidate cells. A specific example is described as follows in the embodiments of Figure 7 .

[0083] Those skilled in the art should understand that the sequence of operations in any of the exemplary procedures 300, 400, and 500 may be changed and some operations in any of the exemplary procedures 300, 400, and 500 may be omitted or modified without departing from the spirit and scope of the present disclosure.

[0084] Some other embodiments of the present application refer to an exemplary flowchart performed by a candidate DU of the BS (e.g., Figure 2 and 6 any one of DU1, DU2, candidate DU 603, candidate DU 703, candidate DU 706, candidate DU 803, candidate DU 806, or candidate DU 903 shown and described in from to 9). Although described with respect to a candidate DU, it should be understood that other devices may be configured to perform a method similar to this exemplary flowchart. The details described in all other embodiments of the present application apply to this exemplary flowchart. In addition, the details described in the embodiments of this exemplary flowchart apply to Figures 1 to 10 all embodiments of. Those skilled in the art should understand that the sequence of operations in this exemplary flowchart may be changed and some operations may be omitted or modified without departing from the spirit and scope of the present disclosure.

[0085] Specifically, in this exemplary flowchart, a candidate DU (simply denoted as candidate DU#1) may transmit a message to the CU. The message may include at least one of the following:

[0086] (1) Information indicating that the UE has switched from the source cell of the source DU of the BS to a candidate cell (e.g., the target cell) within a set of candidate cells of candidate DU#1 (e.g., a cell handover success indication).

[0087] (2) A request for a TA list.

[0088] In some embodiments, the TA list includes at least one of the following: (1) a TA value associated with a candidate cell of a candidate DU of the BS; or (2) ID information of one or more candidate cells. The candidate DU may include candidate DU#1 and / or other candidate DUs. If the candidate DU only includes candidate DU#1, then the candidate cells of the candidate DU are the set of candidate cells of candidate DU#1. If the candidate DU includes candidate DU#1 and other candidate DUs, then the candidate cells of the candidate DU include both the set of candidate cells of candidate DU#1 and the candidate cells of the other candidate DUs.

[0089] In some embodiments, candidate DU#1 may receive a TA list from the CU, for example, when the source DU maintains the TA list or when the CU maintains the TA list. For example, the CU may receive the TA list from the source DU. The TA list may be received by candidate DU#1 from the CU before or after the UE switches from the source cell to the target cell.

[0090] In some embodiments, candidate DU#1 may receive a TA list from the CU after the CU receives one of the following:

[0091] (1) Information from the source DU indicating that a cell handover command has been transmitted from the source DU to the UE;

[0092] (2) An RRC reconfiguration complete message from the UE via the candidate DU; and

[0093] (3) Information from the UE via the candidate DU indicating that the UE has switched to a candidate cell (e.g., the target cell).

[0094] In some embodiments, candidate DU#1 may receive information from the UE indicating that the UE has switched from the source cell to a candidate cell (e.g., the target cell).

[0095] In some embodiments, candidate DU#1 may receive a layer 2 (L2) cell handover complete message (e.g., MAC CE) associated with a candidate cell (e.g., the target cell) from the UE, and transmit information indicating that the L2 cell handover complete message has been received to the CU.

[0096] Described belowFigures 3 to 5 The specific embodiments of the flowcharts shown and described in any of or the exemplary flowcharts performed by the candidate DU described above. Those skilled in the art should understand that Figures 6 to 9 the sequence of operations in any of the exemplary flowcharts 600, 700, 800, and 900 in can be changed and Figures 6 to 9 some operations in any of the exemplary flowcharts 600, 700, 800, and 900 in can be omitted or modified without departing from the spirit and scope of the present disclosure.

[0097] Figure 6 An exemplary flowchart for maintaining the TA value according to some embodiments of the present application. The details described in all other embodiments of the present application are applicable to Figure 6 the embodiments shown in.

[0098] As Figure 6 shown in, the BS 605 has a CU-DU architecture and includes a CU 604, a source DU 602, and a candidate DU 603. In Figure 6 the embodiments shown in, the cell handover or change of the UE 601 can refer to the in-DU scenario where the source cell and the target cell are in the same DU or the inter-DU scenario where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 6 the flowchart 600 shown in only shows the cell change in the inter-DU scenario.

[0099] In Figure 6 the exemplary flowchart 600 shown in, in operation 611, the UE 601 can access the serving BS (e.g., gNB) and send a measurement report to the serving BS (e.g., BS 605). The serving BS can include a CU (e.g., gNB-CU) and one or more DUs (e.g., 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, as Figure 6 shown in, the BS 605 includes a CU 604, a source DU 602, and a candidate DU 603. The BS 605 can include one or more other candidate DUs ( Figure 6 not shown in).

[0100] In operation 612, the CU 604 can determine the start of cell-interference-based L1 / L2-triggered mobility (LTM) configuration and transmit a request message, such as a UE CONTEXT SETUPREQUEST message, to the candidate DU (e.g., candidate DU 603) associated with the candidate cell. For example, the request message can be named "cell handover request" or "LTM configuration request" or the like, and can include the ID information of the candidate cell.

[0101] In the exemplary flowchart 600, subsequent LTM procedures after the LTM procedure can be supported. For example, after a cell handover procedure, the UE 601 can continue to maintain the candidate cell configurations associated with some candidate cells for subsequent LTM purposes. In some embodiments, for example, in operation 612, the CU 604 can transmit a candidate cell list to the UE 601, and the UE 601 can store the candidate cell configurations associated with each candidate cell in the candidate cell list after the UE 601 switches from the source serving cell to the target cell (e.g., the candidate cell of the candidate DU 603). The UE 601 can switch from the target cell to another target cell (i.e., perform a subsequent LTM procedure) by using the stored candidate cell configurations associated with the candidate cell list. The candidate cell list in which the UE 601 stores its candidate cell configurations after a cell handover can indicate to the target DU (e.g., the candidate DU 603) to which the UE 601 is connected. The candidate list can be included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message.

[0102] In operation 613, if the candidate DU 603 decides to accept the LTM configuration request, then the candidate DU 603 can generate a lower layer RRC configuration for the accepted one or more candidate cells and send a response message containing the generated lower layer RRC configuration to the CU 604. The response message can be a UE CONTEXT SETUP RESPONSE message.

[0103] In operation 614, the CU 604 can generate an RRC reconfiguration message based on the configurations of the accepted candidate cells received from the candidate DU 603, and transmit the RRC reconfiguration message associated with the candidate cells of the LTM configuration to the UE 601 via the source DU 602.

[0104] In operation 615, the UE 601 can receive information for triggering TA acquisition for the candidate cells within the candidate cells (e.g., the candidate cells of the candidate DU 603) from the source DU 602. In some embodiments, the information can be DCI, MAC CE, or RRC signaling. If the information is DCI, then it can be a PDCCH command.

[0105] In operation 616, the UE 601 can transmit a signal (e.g., a sequence, e.g., a dedicated preamble or SRS) for TA acquisition to the candidate DU 603, for example.

[0106] In operation 617, the UE 601 may receive a TA value from the serving cell. The TA value may be an absolute TA value or an offset of the TA value. For example, the TA value is included in the MAC CE of the timing advance command or the absolute timing advance command, such as the timing advance command MAC CE or the absolute timing advance command MAC CE. The MAC CE may include the ID of the timing advance group (TAG).

[0107] In operation 618, after the UE 601 receives the MAC CE of the timing advance command or the absolute timing advance command together with the indicated TAG ID, and if the TA value is maintained together with the indicated TAG ID, then the UE 601 may apply the timing advance command to the indicated TAG ID. The UE 601 may start or restart the time alignment timer (TAT) associated with the indicated TAG ID.

[0108] In operation 619, the candidate DU 603 may determine to perform LTM based on the received L1 measurement results.

[0109] In operation 620, the source DU 602 transmits a cell handover command (e.g., an LTM command) to the candidate cell (i.e., the target serving cell) of the candidate DU 603 to the UE 601.

[0110] In operation 621, after the UE 601 receives the cell handover command, the UE 601 may access the candidate cell of the candidate DU 603.

[0111] In operation 622, if the original source cell (i.e., the original serving cell of the source DU 602) is still used as a candidate cell after the cell handover to the candidate cell of the candidate DU 603 (i.e., the target serving cell) or if the UE 601 has received an indication from the network (e.g., the CU 604) regarding whether to maintain the TA value of the source cell, then the UE 601 may continue to maintain the TA value associated with the source cell and / or maintain the corresponding TAT associated with the source cell. For example, the CU 604 may transmit an indication in operation 614 to indicate that the UE 601 maintains the TA value of the source cell after switching from the source cell to the target cell.

[0112] Figure 7 An exemplary flowchart for maintaining the TA value according to some embodiments of the present application. The details described in all other embodiments of the present application apply to Figure 7 the embodiments shown in

[0113] As Figure 7 shown, the BS 705 has a CU-DU architecture and includes the CU 704, the source DU 702, and the candidate DUs 703 and 706. In Figure 7In the embodiments shown, the cell handover or change of the UE 701 may refer to the in-DU scenario where the source cell and the target cell are in the same DU or the inter-DU scenario where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 7 The flowchart 700 shown only shows cell change in the inter-DU scenario.

[0114] In Figure 7 In the exemplary flowchart 700 shown, in operation 711, the UE 701 may access the serving BS (e.g., gNB) and send a measurement report to the serving BS (e.g., BS 705). The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., 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, as Figure 7 shown, the BS 705 includes a CU 704, a source DU 702, and a candidate DU 703. The BS 705 may include one or more other candidate DUs (e.g., candidate DU 706).

[0115] In operation 712, the CU 704 may determine the start of the cell-to-cell L1 / L2-triggered mobility (LTM) configuration and transmit a request message, such as a UE CONTEXT SETUP REQUEST message, to one or more candidate DUs (e.g., candidate DU 703) associated with one or more candidate cells. For example, the request message may be named "cell handover request" or "LTM configuration request" or the like, and may include the ID information of the candidate cells.

[0116] In operation 713, if the candidate DU 703 decides to accept the LTM configuration request, then the candidate DU 703 may generate the lower-layer RRC configuration for the accepted one or more candidate cells and send a response message containing the generated lower-layer RRC configuration to the CU 704. The response message may be a UE CONTEXT SETUP RESPONSE message.

[0117] In operation 714, the CU 704 may generate an RRCReconfiguration message based on the configuration of the accepted candidate cells received from the candidate DU 703, and transmit the RRCReconfiguration message associated with the candidate cells of the LTM configuration to the UE 701 via the source DU 702.

[0118] In operation 715, the UE 701 may receive information for candidate cell-triggered TA acquisition within the candidate cell from the source DU 702. In some embodiments, the information may be DCI, MAC CE, or RRC signaling. If the information is DCI, then it may be a PDCCH command.

[0119] In operation 716, the UE 701 may transmit, for example, a signal (such as a sequence, such as a dedicated preamble or SRS) for TA acquisition to the candidate DU 703 and / or the candidate DU 706.

[0120] In operation 717, after the candidate DU 703 successfully receives a signal (such as a dedicated preamble) in the candidate cell, the candidate DU 703 may calculate or generate a TA value associated with the candidate cell.

[0121] In operation 718, the candidate DU 703 may transmit a message containing the calculated TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 701 to the CU 704 via the F1 interface. The F1 message may be a UL RRC MESSAGE TRANSFER message or a UE context modification request message. In some embodiments, if one or more candidate cells are associated with the candidate DU 703, the candidate DU 703 may calculate one or more TA values and transmit the TA values, the ID information of one or more candidate cells, and / or the ID information of the UE 701 to the CU 704 via the F1 interface.

[0122] In operation 719, after the CU 704 receives the TA value from the candidate DU 703, the CU 704 may transmit the TA value to the source DU 702. In some embodiments, the CU 704 will transmit the TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 701 to the source DU 702 via the F1 interface. In operation 719, the source DU 702 may receive one or more TA values associated with one or more candidate cells of one or more candidate DUs (such as including the candidate DU 703 and / or the candidate DU 706 and / or other candidate DUs).

[0123] In operation 720, the source DU 702 may transmit a cell handover command containing the ID information of the candidate cell (such as the candidate cell of the candidate DU 703) to the UE 701. After the UE 701 receives the cell handover command, the UE 701 may access the candidate cell (i.e., the target cell) of the candidate DU 703 based on the cell handover command.

[0124] After step 720, in different embodiments, there may be the following two options, namely, option X and option Y.

[0125] (1) Option X: In operation 721B (optional), the source DU 702 may transmit the TA list and ID information of the candidate cell to the candidate cell (i.e., the target cell) of the candidate DU 703 to which the UE 701 switches from the source cell.

[0126] a) In some embodiments, in operation 721A (optional), if CU 704 receives an indication from a candidate cell (i.e., the target cell) of a candidate DU 703 accessed by UE 701, then CU 704 may transmit a request for providing a TA list to source DU

[0127] 702. The indication may be a "cell handover success indication" or a "TA value transfer request". In response to receiving the request from CU 704 in operation 721A, source DU 702 may transmit the TA list and ID information of the corresponding candidate cell (i.e., the target cell) to the candidate cell.

[0128] (2) Option Y: In operation 722A (optional), after source DU 702 transmits a cell handover command to UE 701, source DU 702 may indicate the ID information of the candidate cell (i.e., the target cell) to CU 704. For example, source DU 702 indicates to CU 704 that UE 701 is handed over to the candidate cell of candidate DU 703. In operation 722B

[0129] (optional), CU 704 may notify other candidate DUs (such as candidate DU 706) of the ID information of the candidate cell (i.e., the target cell) accessed by UE 701.

[0130] Figure 8 Another exemplary flowchart for maintaining a TA value according to some embodiments of the present application. The details described in all other embodiments of the present application are applicable to the Figure 8 embodiments shown.

[0131] As Figure 8 shown, BS 805 has a CU-DU architecture and includes CU 804, source DU 802, and candidate DUs 803 and 806. In the Figure 8 embodiments shown, the cell handover or change of UE 801 may refer to the intra-DU situation where the source cell and the target cell are in the same DU or the inter-DU situation where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 8 the flowchart 800 shown only shows the cell change in the inter-DU situation.

[0132] In Figure 8 the exemplary flowchart 800 shown, in operation 811, UE 801 may access a serving BS (such as a gNB) and send a measurement report to the serving BS (such as BS 805). The serving BS may include a CU (such as a gNB-CU) and one or more DUs (such as gNB-DUs). The serving cell is associated with the CU and the DUs. There is an F1 interface between the DU and the CU. For example, as Figure 8As shown, BS 805 includes CU 804, source DU 802, and candidate DU 803. BS 805 may include one or more other candidate DUs (such as candidate DU 806).

[0133] In operation 812, CU 804 may determine an initial cell - based L1 / L2 triggered mobility (LTM) configuration and transmit a request message, such as a UE CONTEXT SETUP REQUEST message, to a candidate DU (such as candidate DU 803) associated with a candidate cell. For example, the request message may be named "cell handover request" or "LTM configuration request" or the like, and may include the ID information of the candidate cell.

[0134] In exemplary flowchart 800, subsequent LTM procedures after the LTM procedure may be supported. For example, after a cell handover procedure, UE 801 may continue to maintain the candidate cell configurations associated with some candidate cells for subsequent LTM purposes. In some embodiments, such as in operation 812, CU 804 may transmit a candidate cell list to UE 801, and UE 801 may store the candidate cell configurations associated with each candidate cell in the candidate cell list after UE 801 switches from the source serving cell to a target cell (such as the candidate cell of candidate DU 803). UE 801 may perform a subsequent LTM procedure by switching from the target cell to another target cell by using the stored candidate cell configurations associated with the candidate cell list. The candidate cell list in which UE 801 will store its candidate cell configurations after a cell handover may be indicated to the target DU (such as candidate DU 803) to which UE 601 is connected. The candidate list may be included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message.

[0135] In operation 813, if candidate DU 803 decides to accept the LTM configuration request, then candidate DU 803 may generate a lower - layer RRC configuration for one or more accepted candidate cells and send a response message containing the generated lower - layer RRC configuration to CU 804. The response message may be a UE CONTEXT SETUP RESPONSE message.

[0136] In operation 814, CU 804 may generate an RRC reconfiguration message based on the configuration of the accepted candidate cells received from candidate DU 803, and transmit the RRC reconfiguration message associated with the candidate cells of the LTM configuration to UE 801 via source DU 802.

[0137] In operation 815, the UE 801 may receive information triggering TA acquisition for a candidate cell within a candidate cell (e.g., the candidate cell of candidate DU 803) from the source DU 802. In some embodiments, the information may be DCI, MAC CE, or RRC signaling. If the information is DCI, it may be a PDCCH command.

[0138] In operation 816, the UE 801 may transmit a signal (e.g., a sequence, such as a dedicated preamble or SRS) for TA acquisition to, for example, the candidate DU 803 and / or the candidate DU 806.

[0139] In operation 817, after successfully receiving a signal (e.g., a dedicated preamble) in the candidate cell of the candidate DU 803, the candidate DU 803 may calculate or generate a TA value associated with the candidate cell.

[0140] In operation 818, the candidate DU 803 may transmit a message containing the calculated TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 801 to the CU 804 via the F1 interface. The F1 message may be a UL RRC MESSAGE TRANSFER message or a UE context modification request message. In some embodiments, if one or more candidate cells are associated with the candidate DU 803, the candidate DU 803 may calculate one or more TA values and transmit the TA values, the ID information of one or more candidate cells, and / or the ID information of the UE 801 to the CU 804 via the F1 interface.

[0141] In operation 819, after the CU 804 receives the TA value from the candidate DU 803, the CU 804 may store the received TA value and ID information of the corresponding candidate cell.

[0142] In operation 820, the CU 804 may transmit the received TA value to the source DU 802. In some embodiments, the CU 804 will transmit the TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 801 to the source DU 802 via the F1 interface. In some embodiments, in operation 820, the source DU 802 may receive one or more TA values associated with one or more candidate cells of one or more candidate DUs (including the candidate DU 803 and / or the candidate DU 806 and / or other candidate DUs).

[0143] In operation 821, the source DU 802 may transmit a cell handover command containing the ID information of the candidate cell (e.g., the candidate cell of the candidate DU 803) to the UE 801.

[0144] In operation 822, after the UE 801 receives a cell handover command, the UE 801 may access the candidate cell (i.e., the target cell) of the candidate DU 803 based on the cell handover command.

[0145] In operation 823, the UE 801 may transmit a completion message to the CU 804 or the candidate DU 803 (i.e., the target DU).

[0146] In operation 824, the CU 804 may transmit a TA list to the candidate DU 803 (i.e., the target DU). The TA list may include TA values associated with the corresponding candidate cell and / or ID information of the corresponding candidate cell. In some embodiments, the CU 804 may maintain the TA list. In some embodiments, the CU 804 may transmit the TA list to the candidate DU 803 (i.e., the target DU) before or after the UE 801 switches from the source serving cell to the candidate cell of the candidate DU 803 (i.e., the target cell).

[0147] In some embodiments, the CU 804 may transmit the TA list based on one of the following situations:

[0148] (1) Receiving an indication from the source DU 802 indicating that the cell handover command has been transmitted to the UE 801.

[0149] (2) Receiving an RRC reconfiguration complete message from the UE 801 via the candidate DU 803 (i.e., the target DU).

[0150] (3) Receiving an indication of successful LTM from the candidate DU 803 (i.e., the target DU) in the case where the UE 801 transmits a successful handover indication to the candidate DU 803 (i.e., the target DU) (e.g., information indicating that the UE has switched to the candidate cell).

[0151] 803 (i.e., the target DU) (e.g., information indicating that the UE has switched to the candidate cell).

[0152] In operation 825, the CU 804 may indicate to other candidate DUs (e.g., candidate DU 806) to which the UE 801 is not connected that the cell handover to the candidate cell of the candidate DU 803 (i.e., the target cell) has been completed.

[0153] In some embodiments, after a successful cell handover to the target cell, the CU 804 should indicate the ID information of the target cell accessed by the UE 801 to other candidate DUs. For example, in different embodiments, there may be the following options, namely, option A, option B, and option C.

[0154] (1) Option A: After the UE 801 cell switches to the target cell, the CU 804 can receive a completion message from the UE 801 via the candidate DU 803 (i.e., the target DU). Subsequently, the CU 804 can indicate to the candidate DU 806 that the cell switch to the target cell has been completed.

[0155] (2) Option B: After the UE 801 cell switch to the target cell, the candidate DU 803 (i.e., the target DU) will receive an L2 completion message, such as a MAC CE. Subsequently, the candidate DU 803 can trigger the CU 804 to notify the candidate DU 806.

[0156] (3) Option C: After the source DU 802 transmits a cell switch command to the UE 801 in operation 821, the source DU

[0157] 802 can indicate to the CU 804 the ID information of the candidate cell (i.e., the target cell) of the candidate DU 803. For example, the source DU 802 can indicate to the CU 804 that the UE 801 switches to the target cell. Subsequently, the CU 804 can transmit the ID information of the target cell to which the UE801 accesses to the candidate DU 806.

[0158] Figure 9 Another exemplary flowchart for maintaining the TA value according to some embodiments of the present application. The details described in all other embodiments of the present application apply to the Figure 9 embodiments shown in

[0159] As Figure 9 shown, the BS 905 has a CU-DU architecture and includes a CU 904, a source DU 902, and a candidate DU 903. In the Figure 9 embodiments shown, the cell switch or change of the UE 901 can refer to the intra-DU situation where the source cell and the target cell are in the same DU or the inter-DU situation where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 9 the flowchart 900 shown only shows the cell change in the inter-DU situation.

[0160] In Figure 9 the exemplary flowchart 900 shown, in operation 911, the UE 901 can access the serving BS (e.g., gNB) and send a measurement report to the serving BS (e.g., BS 905). The serving BS can include a CU (e.g., gNB-CU) and one or more DUs (e.g., 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, as Figure 9As shown, BS 905 includes CU 904, source DU 902, and candidate DU 903. BS 905 may include one or more other candidate DUs ( Figure 9 not shown in).

[0161] In operation 912, CU 904 may determine the initial cell - based L1 / L2 - triggered mobility (LTM) configuration and transmit a request message, such as a UE CONTEXT SETUP REQUEST message, to a candidate DU (e.g., candidate DU 903) associated with a candidate cell. For example, the request message may be named "cell handover request" or "LTM configuration request" or the like, and may include the ID information of the candidate cell.

[0162] In operation 913, if candidate DU 903 decides to accept the LTM configuration request, then candidate DU 903 may generate the lower - layer RRC configuration for one or more accepted candidate cells and send a response message containing the generated lower - layer RRC configuration to CU 904. The response message may be a UE CONTEXT SETUP RESPONSE message.

[0163] In operation 914, CU 904 may generate an RRC re - configuration message based on the configuration of the accepted candidate cells received from candidate DU 903, and transmit the RRC re - configuration message associated with the candidate cells of the LTM configuration to UE 901 via source DU 902.

[0164] In operation 915, UE 901 may receive information for candidate cell - triggered TA acquisition within the candidate cell from source DU 902. In some embodiments, the information may be DCI, MAC CE, or RRC signaling. If the information is DCI, then it may be a PDCCH command.

[0165] In operation 916, UE 901 may perform a RA procedure for TA acquisition on candidate DU 903, for example.

[0166] In operation 917, UE 901 may receive a random access response (RAR) message containing the TA value of a specific candidate cell from candidate DU 903, for example. In some embodiments, UE 901 may receive one or more TA values associated with one or more candidate cells from a candidate DU (e.g., including candidate DU 903).

[0167] In operation 918, UE 901 may maintain or store the TA list corresponding to the candidate cell. The TA list may include the TA values associated with the candidate cell and / or the ID information of the candidate cell from one or more candidate DUs.

[0168] In operation 919, the UE 901 may receive a cell handover command for a candidate cell (i.e., a target cell, e.g., a candidate cell of the candidate DU 903) from the source DU 902. In operation 920, the UE 901 accesses the target cell based on the cell handover command.

[0169] After operation 920, in different embodiments, there may be the following options, as follows, i.e., option 1 and option 2.

[0170] (1) Option 1: In operation 921, after the cell handover to the target cell, the UE 901 may release all TA values of the corresponding candidate cell.

[0171] (2) Option 2: After the cell handover to the target cell, it may be desirable for the UE 901 to maintain or store the TA values of the corresponding candidate cell. In operation 922A (optional), the network may transmit an indication of a candidate cell for which the UE 901 needs to maintain the TA value associated therewith after the cell handover. The indication may be included in the RRC configuration information. In operation 922B (optional), if the TA values of the corresponding candidate cell are maintained or stored by the UE 901, then the UE 901 may transmit information indicating a list of candidate cells to the serving cell, and the UE 901 stores the TA values of each candidate cell within the list of candidate cells.

[0172] Figure 10 A block diagram of an exemplary device 1000 according to some embodiments of the present application is illustrated. As Figure 10 shown, the device 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 processor 1006 are described in singular form in this figure, plural forms are contemplated unless explicitly stated to be limited to the singular form. 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 device 1000 may further include an input device, a memory, and / or other components.

[0173] In some embodiments of the present application, the device 1000 may be a UE or a network node (e.g., a BS, a CU, or a DU). The transceiver 1002 and the processor 1006 may interact with each other to perform operations regarding the UE or the network node as described above, for example, in any of Figures 1 to 9 the above.

[0174] In some embodiments of the present application, the apparatus 1000 may further include at least one non-transitory computer-readable medium. For example, in some embodiments of the present disclosure, computer-executable instructions may be stored on the non-transitory computer-readable medium to cause the processor 1006 to implement methods regarding a UE or a network node (e.g., a BS, a CU, or a DU), as described above. For example, when executed, the computer-executable instructions cause the processor 1006 to interact with the transceiver 1002 to perform operations regarding the UE or the network node described in Figures 1 to 9 The operations regarding the UE or the network node described in

[0175] Those of ordinary skill in the art will understand that the operations or steps of the methods described in connection with the aspects disclosed herein may be embodied directly in hardware, in software modules executed by a processor, or in a combination of both. The software modules 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. Additionally, in some aspects, the operations or steps of the methods may reside on a non-transitory computer-readable medium as one or any combination or collection of code and / or instructions that may be incorporated into a computer program product.

[0176] In this document, the term "includes / including" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element that begins with "a / an" or the like does not, without further limitation, preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element. Moreover, the term "another" is defined as at least a second or more. As used herein, the terms "has" and the like are defined as "includes". For example, an expression such as "A and / or B" or "at least one of A and B" may include any one and all combinations of the words enumerated with that 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 terms "first", "second", or the like are used only to clearly illustrate embodiments of the present application and do not limit the substance of the present application.

Claims

1. A centralized unit CU of a base station BS, comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Transmit, via the transceiver, a cell handover request including identifier ID information of one or more candidate cells to one or more candidate distributed units DUs of the BS; Receive, via the transceiver, radio resource control RRC configuration information of the one or more candidate cells from the one or more candidate DUs; And Transmit, via the transceiver, an RRC reconfiguration message associated with the one or more candidate cells to a user equipment UE.

2. The CU according to claim 1, wherein the processor of the CU is configured to: Receive, via the transceiver, a first message from the UE or from a candidate DU within the one or more candidate DUs, wherein the UE is configured to handover from a source cell to a candidate cell within the one or more candidate cells; and In response to receiving the first message, transmit, via the transceiver, a request for providing a timing advance TA list to a source DU, wherein the TA list includes at least one of the following: One or more TA values associated with the one or more candidate cells; or ID information of the one or more candidate cells.

3. The CU according to claim 2, wherein the first message includes at least one of the following: Information for indicating that the UE has handed over to the candidate cell; or A request for the TA list.

4. The CU according to claim 2, wherein the processor of the CU is configured to: Receive, via the transceiver, the TA list from the source DU; and Transmit, via the transceiver, the TA list to the candidate DU.

5. The CU according to claim 1, wherein the processor of the CU is configured to: Receive, via the transceiver, one or more timing advance TA values associated with the one or more candidate cells from the one or more candidate DUs; and Store the one or more TA values.

6. The CU according to claim 5, wherein the processor of the CU is configured to transmit, via the transceiver, the TA list of the UE to a candidate DU of the BS, wherein the UE is configured to handover from a source cell of a source DU of the BS to a candidate cell of the candidate DU, and wherein the TA list includes at least one of the following: The one or more TA values; or ID information of the one or more candidate cells.

7. The CU according to claim 6, wherein the TA list is transmitted after the processor of the CU is configured to receive one of the following: Information indicating that a cell handover command has been transmitted from the source DU to the UE from the source DU via the transceiver; An RRC reconfiguration complete message from the UE via the transceiver via the candidate DU of the BS; and Information indicating that the UE has handed over to the candidate cell from the UE via the transceiver via the candidate DU.

8. The CU according to claim 1, in response to the UE switching from a source cell to a candidate cell within the one or more candidate cells, the processor of the CU is configured to indicate the ID information of the candidate cell to other candidate DUs within the one or more candidate cells.

9. The CU according to claim 8, wherein the processor of the CU is configured to receive, via the transceiver, at least one of the following: Information indicating that the UE has switched to the candidate cell from the UE via the candidate DU; Information from the candidate DU of the BS indicating that the candidate DU has received a layer 2 (L2) cell handover completion message associated with the candidate cell; or The ID information of the one or more candidate cells and the ID information of the candidate cell from the source DU.

10. A user equipment (UE) comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Receive, via the transceiver, a timing advance (TA) value associated with the source cell from the source cell; Receive, via the transceiver, one or more TA values associated with the one or more candidate cells from the one or more candidate cells; Receive a cell handover command for a candidate cell within the one or more candidate cells from the source cell; And Access the candidate cell based on the cell handover command.

11. The UE according to claim 10, after the UE switches from the source cell to the candidate cell, the processor of the UE is configured to perform at least one of the following: Continue to maintain the TA value associated with the source cell; or Maintain a time alignment timer (TAT) associated with the source cell.

12. The UE according to claim 11, wherein after the UE switches from the source cell to the candidate cell, the source cell serves as one of the candidate cells.

13. The UE according to claim 11, wherein the processor of the UE is configured to receive first information from the source cell via the transceiver, and wherein the first information indicates at least one of the following: Whether to maintain the TA value associated with the source cell; or Whether to maintain the TAT associated with the source cell.

14. The UE according to claim 10, after the UE switches from the source cell to the candidate cell, the processor of the UE is configured to: Release the one or more TA values associated with the one or more candidate cells; or Continue to maintain all or a subset of the one or more TA values associated with the one or more candidate cells.

15. A candidate distributed unit (DU) of a base station (BS) comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Transmit a first message to the CU via the transceiver, wherein the first message includes at least one of the following: Information indicating that a user equipment (UE) has switched from a source cell of a source DU of the BS to a candidate cell within a set of candidate cells of the candidate DU; or A request for a timing advance (TA) list.

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