Method and apparatus for UL synchronization before performing cell change

Abstract

Embodiments of the present application relate to a method and apparatus for uplink (UL) synchronization prior to performing a cell change in a 3rd Generation Partnership Project (3GPP) 5G system or the like. In accordance with an embodiment of the present application, a user equipment (UE) includes a transceiver and a processor coupled to the transceiver, and the processor is configured to: receive, via the transceiver, a radio resource control (RRC) reconfiguration message associated with one or more candidate cells; in response to receiving the RRC reconfiguration message, performing one or more random access (RA) procedures for the one or more candidate cells to obtain a timing advance (TA); and in response to receiving, via the transceiver, an indication associated with one of the one or more candidate cells from a source cell, handover from the source cell to the one candidate cell.

Description

Technical Field

[0001] Embodiments of the present application relate generally to wireless communication techniques, and more particularly to methods and apparatus for uplink (UL) synchronization prior to performing a cell change. Background Art

[0002] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcast, etc. Wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of wireless communication systems may include fourth generation (4G) systems 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 regarding UL synchronization before performing a cell change have not been discussed in 3GPP 5G technology. Summary of the invention

[0004] 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 a radio resource control (RRC) reconfiguration message associated with one or more candidate cells via the transceiver; in response to receiving the RRC reconfiguration message, perform one or more random access (RA) procedures for the one or more candidate cells to obtain a timing advance (TA); and in response to receiving a first indication associated with one of the one or more candidate cells from a source cell via the transceiver, switch from the source cell to the one candidate cell.

[0005] In some embodiments, the first indication is included in downlink control information (DCI) or a medium access control (MAC) control element (CE).

[0006] In some embodiments, the processor of the UE is configured to initiate the one or more RA procedures for the one or more candidate cells in response to one of the following: receiving the RRC reconfiguration message including an updated configuration of a first candidate cell, wherein the UE has received the configuration of the first candidate cell before receiving the RRC reconfiguration message, and the UE does not have an available TA for the first candidate cell; receiving the RRC reconfiguration message including the configuration of a second candidate cell and the UE does not have an available TA for the second candidate cell; and receiving the RRC reconfiguration message including a configuration for adding a third candidate cell.

[0007] In some embodiments, in response to the RRC reconfiguration message including a set of configurations of multiple candidate cells, the processor of the UE is configured to: simultaneously execute multiple RA procedures for the multiple candidate cells to obtain the TA; or select one candidate cell from the multiple candidate cells and simultaneously execute an RA procedure for the selected one candidate cell to obtain the TA.

[0008] In some embodiments, in order to select the one candidate cell, the processor of the UE is configured to select the one candidate cell from the one or more candidate cells based on at least one of the following: channel quality of the one or more candidate cells, or channel quality of beams of the one or more candidate cells.

[0009] In some embodiments, the processor of the UE is configured to initiate the one or more RA procedures for the one or more candidate cells in response to satisfaction of a configuration condition.

[0010] In some embodiments, the configuration condition is a threshold value of channel quality.

[0011] In some embodiments, the processor of the UE is configured to receive an indication instructing the UE to perform a RA procedure for obtaining the TA, or wherein the RRC reconfiguration message includes a set of parameters for obtaining the TA for implicitly instructing the UE to perform the RA procedure for obtaining the TA.

[0012] In some embodiments, the set of parameters includes at least one of: a dedicated preamble, or a dedicated random access channel opportunity (RO).

[0013] In some embodiments, the indication or the RRC reconfiguration message comprising the set of parameters for obtaining the TA is generated by the source cell, the one candidate cell or a centralized unit (CU).

[0014] In some embodiments, the RRC reconfiguration message includes at least one of: a dedicated preamble for obtaining an RA procedure within the one or more RA procedures of the TA; or dedicated time-frequency domain resources for obtaining the RA procedure within the one or more RA procedures of the TA.

[0015] In some embodiments, the RA procedure within the one or more RA procedures for obtaining the TA is associated with a timer for obtaining the RA of the TA, and the processor of the UE is configured to start the timer for obtaining the RA of the TA in response to initiating the RA procedure within the one or more RA procedures for obtaining the TA.

[0016] In some embodiments, the processor of the UE is configured to transmit, via the transceiver, to a target distributed unit (DU), a second indication indicating that the one or more RA procedures are for obtaining the TA.

[0017] In some embodiments, the second indication is transmitted in Msg 3 or Msg A during the one or more RA procedures.

[0018] In some embodiments, in response to the reception of the first indication associated with the one candidate cell, the processor of the UE is configured to perform one of the following: continue to perform the RA procedure for the one candidate cell to obtain the TA; stop at least one RA procedure for other candidate cells within the one or more candidate cells except the one candidate cell indicated in the first indication; and stop the RA procedure for obtaining the TA for the one candidate cell.

[0019] In some embodiments, in response to stopping the RA procedure for the one candidate cell, the processor of the UE is configured to stop a timer for obtaining a RA for the TA, wherein the timer is associated with the RA procedure for the one candidate cell.

[0020] In some embodiments, in response to successfully completing the one or more RA procedures for obtaining the TA for the one or more candidate cells, the processor of the UE is configured to: determine whether the TA of each candidate cell is invalid; and in response to determining that the TA is invalid, initiate an RA procedure for the candidate cell to obtain an updated TA.

[0021] In some embodiments, in order to determine whether the TA is invalid, the processor of the UE is configured to: store the RSRP value of the UE when obtaining the TA; monitor the updated RSRP value of the UE; and in response to the difference between the updated RSRP value and the RSRP value being equal to or greater than a configured threshold, determine that the TA is invalid.

[0022] In some embodiments, in order to determine whether the TA is invalid, the processor of the UE is configured to: determine whether the duration since the time point when the TA was obtained is equal to or greater than a configured time period; and in response to the duration being equal to or greater than the configured time period, determine that the TA is invalid.

[0023] In some embodiments, the RRC reconfiguration message includes at least one of the configured threshold or the configured time period.

[0024] In some embodiments, the at least one of the configured threshold or the configured time period is generated by the CU or a target distributed unit (DU) managed by the CU.

[0025] Some embodiments of the present application provide a target distributed unit (DU). The target DU includes a transceiver and a processor coupled to the transceiver; and the processor is configured to: receive a cell change of a user equipment (UE) from a centralized unit (CU) managing the target DU via the transceiver; and transmit a response to the CU via the transceiver, wherein the response includes a set of configurations about the target cell, and wherein the UE applies the set of configurations when receiving a first indication associated with a candidate cell.

[0026] In some embodiments, the first indication is included in downlink control information (DCI) or a medium access control (MAC) control element (CE).

[0027] In some embodiments, the processor of the target DU is configured to generate at least one of: an indication instructing the UE to perform a random access (RA) procedure for obtaining a timing advance (TA); or a set of parameters for obtaining the TA for implicitly instructing the UE to perform the RA procedure for obtaining the TA, wherein the response includes at least one of the indication or the set of parameters for obtaining the TA.

[0028] In some embodiments, the set of parameters includes at least one of: a dedicated preamble, or a dedicated random access channel opportunity (RO).

[0029] In some embodiments, the processor of the target DU is configured to receive, from the CU via the transceiver, information for requesting the target DU to provide the at least one of the indication or the set of parameters for obtaining the TA.

[0030] In some embodiments, the processor of the target DU is configured to transmit, via the transceiver, to the UE at least one of: a dedicated preamble for obtaining a RA procedure for the TA; or dedicated time-frequency domain resources for obtaining the RA procedure for the TA.

[0031] In some embodiments, the RA procedure for obtaining the TA is associated with a timer for obtaining a RA for the TA.

[0032] In some embodiments, the processor of the target DU is configured to receive, via the transceiver, from the UE a second indication indicating that one or more RA procedures performed by the UE for one or more candidate cells are for obtaining the TA.

[0033] In some embodiments, the second indication is received in Msg 3 or Msg A during the one or more RA procedures.

[0034] In some embodiments, the processor of the target DU is configured to: generate at least one of a configured threshold or a configured time period of channel quality; and transmit the configured threshold or the at least one of the configured time period to the UE via the transceiver, wherein the UE determines whether the TA is invalid based on the configured threshold or the at least one of the configured time period.

[0035] 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 a cell change request of a user equipment (UE) to a target distributed unit (DU) managed by the CU via the transceiver; receive a response from the target DU via the transceiver, wherein the response includes a set of configurations about the target cell, and wherein the UE applies the set of configurations when receiving a first indication associated with a candidate cell; and transmit a radio resource control (RRC) reconfiguration message associated with one or more candidate cells to the UE via the transceiver.

[0036] In some embodiments, the first indication is included in downlink control information (DCI) or a medium access control (MAC) control element (CE).

[0037] In some embodiments, the RRC reconfiguration message includes a set of parameters for obtaining the TA for implicitly instructing the UE to perform the RA procedure for obtaining the TA, or wherein the processor of the CU is configured to transmit an indication to the UE via the transceiver instructing the UE to perform the RA procedure for obtaining the TA.

[0038] In some embodiments, the set of parameters includes at least one of: a dedicated preamble, or a dedicated random access channel opportunity (RO).

[0039] In some embodiments, the processor of the CU is configured to: generate the indication or at least one of the set of parameters for obtaining the TA; or receive the indication or at least one of the set of parameters for obtaining the TA from the target DU via the transceiver.

[0040] In some embodiments, before receiving the indication for obtaining the TA or at least one of the set of parameters from the target DU, the processor of the CU is configured to transmit to the target DU via the transceiver information for requesting the target DU to provide the indication for obtaining the TA or at least one of the set of parameters.

[0041] In some embodiments, the processor of the CU is configured to transmit at least one of a configured threshold value or a configured time period of channel quality to the UE via the transceiver, and wherein the UE determines whether the TA is invalid based on the at least one of the configured threshold value or the configured time period.

[0042] In some embodiments, the processor of the CU is configured to: generate the at least one of the configured threshold value or the configured time period; or receive the at least one of the configured threshold value or the configured time period from the target DU via the transceiver.

[0043] Some embodiments of the present application provide a method performed by a UE. The method includes: receiving a radio resource control (RRC) reconfiguration message associated with one or more candidate cells; in response to receiving the RRC reconfiguration message, performing one or more random access (RA) procedures on the one or more candidate cells to obtain a timing advance (TA); and in response to receiving a first indication associated with a candidate cell in the one or more candidate cells from a source cell, switching from the source cell to the candidate cell.

[0044] Some embodiments of the present application provide a method performed by a target distributed unit (DU). The method includes: receiving a cell change request of a user equipment (UE) from a centralized unit (CU) managing the target DU; and transmitting a response to the CU, wherein the response includes a set of configurations about the target cell, and wherein the UE applies the set of configurations when receiving a first indication associated with a candidate cell.

[0045] Some embodiments of the present application provide a method performed by a centralized unit (CU). The method includes: transmitting a cell change request of a user equipment (UE) to a target distributed unit (DU) managed by the CU; receiving a response from the target DU, wherein the response includes a set of configurations about the target cell, and wherein the UE applies the set of configurations when receiving a first indication associated with a candidate cell; and transmitting a radio resource control (RRC) reconfiguration message associated with one or more candidate cells to the UE.

[0046] Some embodiments of the present application provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement the above-mentioned method performed by a UE or a network node (e.g., a base station (BS), a CU, or a DU).

[0047] The details of one or more examples are set forth in the accompanying drawings and the description below.Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] 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 are therefore not to be considered as limiting the scope of the present application.

[0049] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present application.

[0050] Figure 2 Schematic diagram illustrating inter-cell layer 1 / layer 2 (L1 / L2) mobility according to some embodiments of the present application.

[0051] Figure 3 An exemplary flow chart illustrating execution of a RA procedure for obtaining a TA according to some embodiments of the present application.

[0052] Figure 4 An exemplary flow chart illustrating receiving a cell change request according to some embodiments of the present application.

[0053] Figure 5 An exemplary flow diagram illustrating transmitting a cell change request according to some embodiments of the present application.

[0054] Figures 6 to 8 An exemplary flow chart illustrating performing a cell change procedure according to some embodiments of the present application.

[0055] Fig. 9 A block diagram illustrating an exemplary apparatus according to some embodiments of the present application. DETAILED DESCRIPTION

[0056] The detailed description of the accompanying drawings is intended as a description of the preferred embodiments of the present application, and is not intended to represent the only form in which the present application can be practiced. It should be understood that the same or equivalent functions can be implemented by different embodiments that are intended to be included in the spirit and scope of the present application.

[0057] Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided under specific network architectures and new service scenarios, such as 3GPP 5G, 3GPP LTE version 8, etc. It is considered that, with the development of network architectures and new service scenarios, all embodiments in the present application are also applicable to similar technical problems; and in addition, the terms cited in the present application may change, which should not affect the principles of the present application.

[0058] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present application. Figure 1 , the wireless communication system 100 includes at least one base station (BS) 101 and at least one user equipment (UE) 102. Specifically, for illustrative purposes, the wireless communication system 100 includes one BS 101 and two UEs 102 (e.g., UE 102a and UE 102b). Although for simplicity, Figure 1 A specific number of BSs and UEs are illustrated in FIG. 1 , but it is considered that in some other embodiments of the present application, the wireless communication system 100 may include more or fewer BSs and UEs.

[0059] 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 wireless communication networks, cellular telephone networks, time division multiple access (TDMA)-based networks, code division multiple access (CDMA)-based networks, orthogonal frequency division multiple access (OFDMA)-based networks, LTE networks, 3GPP-based networks, 3GPP 5G networks, satellite communication networks, high altitude platform networks, and / or other communication networks.

[0060] BS101 may communicate with a core network (CN) node (not shown) (e.g., a mobility management entity (MME) or a serving gateway (S-GW), a mobility management function (AMF), or a user plane function (UPF), etc.) via an interface. BSs are also referred to as access points, access terminals, base stations, macro cells, Node Bs, enhanced Node Bs (eNBs), gNBs, home Node Bs, relay nodes, or devices, or are described using other terms used in the art. In 5G NR, BSs may also be referred to as RAN nodes or network equipment. Each BS may serve several UEs within a service area (e.g., a cell or a cell sector) via wireless communication links. Neighboring BSs may communicate with each other as needed (e.g., during a handover procedure of a UE).

[0061] UE 102 (e.g., UE 102a and UE 102b) should be understood as any type of terminal device, which may include a computing device, such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (e.g., a TV connected to the Internet), a set-top box, a game console, a security system (including a security camera), a car computer, a network device (e.g., a router, a switch and a modem), or the like. According to an embodiment of the present application, UE 102 may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identification module, a personal computer, a selective call receiver, or any other device capable of sending and receiving communication signals on a wireless network. In some embodiments, UE 102 may include a wearable device, such as a smart watch, a fitness bracelet, an optical head-mounted display, or the like. In addition, UE 102 may be referred to as a subscriber unit, a mobile device, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal or a device, or described using other terms used in the art. UE 102 may communicate directly with BS 101 via uplink (UL) communication signals.

[0062] In 3GPP Release 18, support for inter-cell mobility based on layer 1 / layer 2 (L1 / L2) signaling has been discussed. In particular, the UE may be provided with configurations from multiple cells in advance, and the BS (e.g., gNB) may switch the UE to a new cell using L1 / L2 signaling in consideration of received physical layer measurement results. According to 3GPP standard documents, a BS may be composed of a BS centralized unit (CU) and one or more BS distributed units (DUs). The BS-CU and the BS-DU are connected via the F1 interface as a logical interface. One BS-DU is connected to only one BS-CU.

[0063] Figure 2 Schematic diagram illustrating inter-cell layer 1 / layer 2 (L1 / L2) mobility according to some embodiments of the present application. Figure 2 As shown in , the CU can communicate with two DUs (ie, 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 the L1 / L2 mobility decision can be implemented based on the physical layer measurement results.

[0064] Compared with traditional L3 mobility, L1 / L2 mobility is considered to be faster and has less processing delay and signaling delay. In traditional L3 mobility, CU (e.g. Figure 2) makes mobility decisions based on received radio resource management (RRM) measurement reports. Unlike traditional L3 mobility, in L1 / L2 mobility, the DU (e.g., Figure 2 DU1 or DU2 shown in the figure makes mobility decisions based on physical layer measurements carried, for example, in channel state information (CSI) reports. In addition, in traditional l3 mobility, the handover command is sent from the SN CU to the UE via an 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 medium access control (MAC) control element (CE)). The "handover" command in L1 / L2 mobility can be about cell activation or deactivation, for example, activating a new serving PCell while deactivating the old serving PCell.

[0065] Currently, the issue of when to perform RA to obtain TA (or early TA) after receiving an L1 / L2 command (e.g., a DCI or MAC CE command) has been resolved. Some embodiments of the present application study a use case in which a UE receives a configuration of a candidate cell, and before performing a SpCell change or a Scell ​​change, the UE may obtain the TA via a RA procedure. Some embodiments of the present application study the behavior of the UE when the UE receives a DCI or MAC CE indication for switching toward the candidate cell while the UE is performing a RA procedure for a candidate cell to obtain the TA. Some embodiments of the present application study a mechanism to distinguish a RA procedure for obtaining a TA from a normal RA procedure for switching. Some embodiments of the present application study a mechanism to determine whether a TA is invalid after successfully obtaining the TA via a RA procedure.

[0066] Specifically, in the present application Figures 3 to 9 In the embodiments of the present invention, inter-DU mobility scenarios and intra-DU mobility scenarios are considered. Inter-DU mobility means that the connection with the CU remains unchanged, and the UE may change from a source cell associated with a source DU to a target cell associated with a target DU due to mobility, and both the source DU and the target DU are managed by the CU. Intra-DU mobility means that the connection with the CU remains unchanged, and the UE may change from a source cell to a target cell associated with the same DU due to mobility. More details will be explained below in conjunction with the accompanying drawings.

[0067] Figure 3 An exemplary flow chart illustrating execution of a RA procedure for obtaining a TA according to some embodiments of the present application. Figure 3 The exemplary method 400 in the embodiment of the present invention may be performed by a UE (e.g., Figure 1Although described with respect to a UE, it should be understood that other devices may be configured to perform similar Figure 3 The details described in all other embodiments of this application apply to Figure 3 In addition, Figure 3 The details described in the embodiments apply to Figure 1 , 2 And all embodiments from 4 to 9.

[0068] In such Figure 3 In the exemplary method 300 shown in , in operation 301, the UE receives an RRC reconfiguration message associated with one or more candidate cells. In operation 302, in response to receiving the RRC reconfiguration message, the UE performs one or more RA procedures for the one or more candidate cells to obtain a TA.

[0069] In operation 303, in response to a request from a source cell (eg, from a source DU, such as Figure 2 In some embodiments, the UE may receive a DCI or MAC CE command or indication associated with a candidate cell, and the UE may switch from the source cell to a candidate cell among the one or more candidate cells. In some embodiments, the indication #1 is included in the DCI or MAC CE. That is, the UE may receive a DCI or MAC CE command or indication associated with a candidate cell.

[0070] In some embodiments, in response to receiving indication #1 associated with a candidate cell, the UE may perform one of the following:

[0071] (1) Continue to perform the RA procedure for a candidate cell to obtain a TA;

[0072] (2) stopping at least one RA procedure for other candidate cells among the one or more candidate cells except the candidate cell indicated in indication #1; and

[0073] (3) Stopping the RA procedure for obtaining the TA for a candidate cell. In some embodiments, in response to stopping the RA procedure for a candidate cell, the UE may stop a timer for RA for obtaining the TA, wherein the timer is associated with the RA procedure for the candidate cell. For example, the time may be similar to a timer for handover (e.g., T304 as defined in the 3GPP standard document), which is associated with a normal RA procedure for handover.

[0074] In some embodiments, the UE may initiate one or more RA procedures for one or more candidate cells in response to one of the following:

[0075] (1) receiving an RRC reconfiguration message including an updated configuration of a candidate cell, wherein the UE has received the configuration of the candidate cell before receiving the RRC reconfiguration message, and the UE does not have an available TA for the candidate cell;

[0076] (2) receiving an RRC reconfiguration message including the configuration of a candidate cell and the UE does not have an available TA for this candidate cell; and

[0077] (3) Receive an RRC reconfiguration message including a configuration for adding a candidate cell.

[0078] In some embodiments, in response to an RRC reconfiguration message including a set of configurations of multiple candidate cells, the UE may simultaneously perform multiple RA procedures for the multiple candidate cells to obtain a TA.

[0079] In some other embodiments, in response to an RRC reconfiguration message including a set of configurations of a plurality of candidate cells, the UE may select one candidate cell from the plurality of candidate cells and simultaneously perform an RA procedure for the selected one candidate cell to obtain a TA. In an embodiment, the UE may select a candidate cell from the one or more candidate cells based on: channel quality of the one or more candidate cells, and / or channel quality of beams of the one or more candidate cells.

[0080] In some embodiments, the UE may initiate one or more RA procedures for one or more candidate cells in response to the satisfaction of a configured condition. In an embodiment, the configured condition is a threshold of channel quality, such as a "RSRP threshold" or a "threshold of RSRP change". Figure 8 Specific examples are described below in the Examples.

[0081] In some embodiments, the UE may receive an indication (e.g., an explicit indication) instructing the UE to perform a RA procedure for obtaining a TA (represented as indication #2 for simplicity). In an embodiment, the source cell, a candidate cell, or a CU (e.g., Figure 2 CU shown and described in ) generates indication #2.

[0082] In some other embodiments, the RRC reconfiguration message received in operation 301 includes a set of parameters for obtaining a TA for implicitly instructing the UE to perform a RA procedure for obtaining a TA. In an embodiment, the set of parameters includes a dedicated preamble and / or a dedicated random access channel opportunity (RO). In an embodiment, the source cell, a candidate cell, or a CU (e.g., Figure 2 CU) generates an RRC reconfiguration message including the set of parameters for obtaining the TA. Figure 6 Specific examples are described below in the Examples.

[0083] In some embodiments, the RRC reconfiguration message received in operation 301 includes at least one of the following:

[0084] (1) Dedicated preamble for RA procedure within one or more RA procedures for obtaining TA In an embodiment, the RA procedure for obtaining TA and the normal RA procedure for handover may be configured to have different preambles.

[0085] (2) Dedicated time-frequency domain resources for an RA procedure within one or more RA procedures for obtaining a TA In an embodiment, the RA procedure for obtaining a TA and the normal RA procedure for handover may be configured to have different time-frequency domain resources.

[0086] In some embodiments, an RA procedure within one or more RA procedures for obtaining a TA is associated with a "timer for obtaining RA for the TA". The time may be similar to the timer for handover (e.g., T304). In response to initiating an RA procedure within one or more RA procedures for obtaining a TA, the UE may start a timer for obtaining RA for the TA.

[0087] In some embodiments, the UE may send a signal to a target DU (e.g., Figure 2 DU2) is used to transmit an indication that one or more RA procedures are for obtaining a TA. For example, such an indication may be transmitted in Msg 3 or Msg A during one or more RA procedures.

[0088] In some embodiments, in response to successfully completing one or more RA procedures for obtaining a TA for one or more candidate cells, the UE may determine whether the TA of each candidate cell is invalid, and in response to determining that the TA is invalid, initiate an RA procedure for the candidate cell to obtain an updated TA.

[0089] In an embodiment, the UE may store the RSRP value of the UE when obtaining the TA, monitor the updated RSRP value of the UE, and determine that the TA is invalid in response to the difference between the updated RSRP value and the RSRP value being equal to or greater than a "configuration threshold" (e.g., a threshold for RSRP change).

[0090] In another embodiment, the UE may determine whether the duration since the time point of obtaining the TA is equal to or greater than the "configured time period", and determine that the TA is invalid in response to the duration being equal to or greater than the "configured time period".

[0091] For example, the RRC reconfiguration message received in operation 301 includes at least one of a "configured threshold" or a "configured time period". In some embodiments, at least one of the "configured threshold" or the "configured time period" is generated by the CU or the target DU managed by the CU. Figure 8 Specific examples are described below in the Examples.

[0092] Figure 4 An exemplary flow chart illustrating receiving a cell change request according to some embodiments of the present application. Figure 4 The exemplary method 400 in the embodiment of the present invention may be performed by a target DU (e.g., Figure 2 Although described with respect to a target DU, it should be understood that other devices may be configured to perform similar Figure 4 The details described in all other embodiments of this application apply to Figure 4 In addition, Figure 4 The details described in the embodiments apply to Figures 1 to 3 And all embodiments of 5 to 9.

[0093] In such Figure 4 In the exemplary method 400 shown in FIG. 4 , in operation 401, a target DU (e.g., Figure 2 DU2) from the CU managing the target DU (e.g., Figure 2 CU shown and described in ) receiving UE (e.g., as Figure 1 A cell change request of UE 102) shown and described in FIG.

[0094] In operation 402, the target DU transmits a response to the CU. The response includes a set of configurations about the target cell. The UE may apply the set of configurations upon receiving an indication associated with a candidate cell (denoted as indication #1 for simplicity). For example, indication #1 may be included in a DCI or a MAC CE.

[0095] In some embodiments, the target DU may generate an "indication instructing the UE to perform a RA procedure for obtaining a TA" (represented as indication #2 for simplicity) and / or a "set of parameters for obtaining a TA for implicitly instructing the UE to perform a RA procedure for obtaining a TA". The response transmitted in operation 402 may include indication #2 and / or the set of parameters for obtaining a TA. In an embodiment, the set of parameters includes at least one of the following: a dedicated preamble, or a dedicated random access channel opportunity (RO). In an embodiment, the target DU may receive information from the CU for requesting the target DU to provide indication #2 and / or the set of parameters for obtaining a TA.

[0096] In some embodiments, the target DU may transmit to the UE at least one of: a dedicated preamble for obtaining the TA's RA procedure; or dedicated time-frequency domain resources for obtaining the TA's RA procedure.

[0097] In some embodiments, the RA procedure for obtaining the TA is associated with a timer for obtaining the RA for the TA.

[0098] In some embodiments, the target DU may receive an indication (denoted as indication #3 for simplicity) from the UE indicating that one or more RA procedures performed by the UE for one or more candidate cells are for obtaining a TA. In an embodiment, indication #3 is received in Msg 3 or Msg A during one or more RA procedures.

[0099] In some embodiments, the target DU may generate at least one of a configured threshold or a configured time period of channel quality; and the target DU transmits at least one of the configured threshold or the configured time period to the UE. The UE may determine whether the TA is invalid based on at least one of the configured threshold or the configured time period.

[0100] Figure 5 An exemplary flow diagram illustrating transmitting a cell change request according to some embodiments of the present application. Figure 5 The exemplary method 500 in the embodiment of the present invention may be performed by a CU (e.g., Figure 2 Although described with respect to a CU, it should be understood that other devices may be configured to perform similar Figure 5 The details described in all other embodiments of this application apply to Figure 5 In addition, Figure 5 The details described in the embodiments apply to Figures 1 to 4 and all embodiments of 6 to 9.

[0101] In such Figure 5 In the exemplary method 500 shown in FIG. 5 , in operation 501, a CU sends a request to a target DU (e.g., Figure 2 DU2) transmitting UE (e.g., as shown and described in Figure 1 A cell change request of UE 102) shown and described in FIG.

[0102] In operation 502, the CU receives a response from the target DU. The response includes a set of configurations about the target cell. The UE applies the set of configurations upon receiving an indication associated with a candidate cell (denoted as indication #1 for simplicity). In some embodiments, indication #1 is included in a DCI or MAC CE.

[0103] In operation 503, the CU transmits an RRC reconfiguration message associated with one or more candidate cells to the UE. In some embodiments, the RRC reconfiguration message includes a set of parameters for obtaining a TA for implicitly instructing the UE to perform a RA procedure for obtaining the TA. In an embodiment, the set of parameters includes at least one of the following: a dedicated preamble, or a dedicated random access channel opportunity (RO). In some other embodiments, the CU may transmit an indication to the UE instructing the UE to perform a RA procedure for obtaining the TA (denoted as indication #2 for simplicity).

[0104] In some embodiments, the CU may generate the indication #2 and / or the set of parameters for obtaining the TA. In some other embodiments, the CU may receive the indication #2 and / or the set of parameters for obtaining the TA from the target DU.

[0105] In some embodiments, before receiving indication #2 and / or the set of parameters for obtaining the TA from the target DU, the CU may transmit to the target DU information for requesting the target DU to provide indication #2 and / or the set of parameters for obtaining the TA.

[0106] In some embodiments, the CU may transmit at least one of a "configured threshold of channel quality" or a "configured time period" to the UE. The UE may determine whether the TA is invalid based on at least one of the configured threshold or the configured time period. In an embodiment, the CU may generate at least one of the configured threshold or the configured time period. In another embodiment, the CU may receive at least one of the configured threshold or the configured time period from the target DU.

[0107] Figure 6 Another exemplary flow chart illustrating the execution of a cell change procedure according to some embodiments of the present application. The details described in all other embodiments of the present application apply to Figure 6 The embodiments shown in . Those skilled in the art should understand that Figure 6 The order of operations in the exemplary process 600 may be changed and Figure 6 Some operations in the exemplary process 600 in FIG. 6 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0108] like Figure 6 As shown in FIG. 6 , BS 605 is in a CU-DU architecture and includes CU 604, source DU 602, and target DU 603. Figure 6 In the embodiment shown in , the cell change of UE 601 may refer to an intra-DU situation where the source cell and the target cell are located in the same DU or to an inter-DU situation where the source cell and the target cell are located in different DUs. For example, for exemplary purposes, Figure 6The flowchart 600 shown in FIG. 6 shows only the cell change in the inter-DU case.

[0109] In such Figure 6 In the exemplary flow chart 600 shown in FIG. 6 , in operation 611, the UE 601 reports to the serving cell (eg, the CU 604) an indication of the capability of the UE 601 to support the cell change based on the DCI or the MAC CE.

[0110] In operation 612, the UE 601 reports the measurement result to the serving cell (eg, the CU 604) via an RRC message. For example, the UE 601 may report the measurement result based on the RRC reconfiguration including the measurement configuration.

[0111] In operation 613A (optional), CU 604 transmits a cell change request related to DCI or MAC CE based mobility to a target cell related to target DU 603, for example. In some embodiments, a CU (e.g., CU 604) requests a target DU (e.g., target DU 603) to provide a configuration to obtain a TA.

[0112] In an embodiment, the source cell and the target cell may be located at the same DU, i.e., in the intra-DU case where the serving cell and the candidate cell have the same DU. In another embodiment, the source cell and the target cell may be located at different DUs, i.e., in the inter-DU case, for example, the serving cell is in DU#1 (e.g., source DU 602) and the candidate cell is in DU#2 (e.g., target DU 603). With respect to the intra-DU case and the inter-DU case, the source cell and the target cell share the same CU. In this case, CU 604 will transmit a "cell change request related to mobility based on DCI or MAC CE" to the target DU (e.g., target DU 603).

[0113] In operation 613B (optional), the target cell, for example, associated with the target DU 603, transmits a response to the CU 604. The CU 604 will then transmit a configuration to the source DU 602.

[0114] In some embodiments, the network node may indicate to the UE 601 whether to obtain a TA. Obtaining a TA means that the UE 601 needs to ensure UL synchronization before performing a cell change. In some cases, the "RA procedure for obtaining a TA" may also be named "RA procedure for obtaining an early TA" or similar.

[0115] In an embodiment, an explicit indication is required to instruct UE 601 to perform a RA procedure for obtaining a TA. In another embodiment, it may be indicated implicitly. For example, the RRC reconfiguration message includes a set of parameters for obtaining a TA for implicitly instructing UE 601 to perform a RA procedure for obtaining a TA. For example, when UE 601 receives the set of parameters for obtaining a TA (e.g., a dedicated preamble and / or a dedicated RO), UE 601 considers that the TA is expected.

[0116] In some embodiments, whether to obtain a TA is configured by a target cell (eg, associated with the target DU 603) or a serving cell (eg, the CU 604).

[0117] In operation 614, the serving cell (eg, CU 604) transmits the configuration of the candidate cell to the UE 601 after receiving a response from the target cell (eg, in operation 613B). That is, the UE 601 receives the configuration of the candidate cell from the serving cell.

[0118] In operation 615, after the UE 601 receives the configuration of the candidate cell from the serving cell, the UE 601 performs a RA procedure for obtaining a TA. In operation 616, the UE 601 performs measurement for the serving cell and the candidate cell and reports the measurement result to the serving cell.

[0119] exist Figure 6 In some embodiments, there is a period of time between, for example, receiving the configuration of the candidate cell from the source DU 602 and receiving the "DCI or MAC CE command" (which may also be named "DCI or MAC CE indication" or "indication based on DCI or MAC CE" or the like). The UE 601 does not know the time point of receiving the DCI or MAC CE command. Therefore, the problem of when to perform the RA procedure for obtaining the TA needs to be solved. There may be the following three options in the following different embodiments, namely, option 1, option 2 and option 3.

[0120] (1) Option 1: When at least one of the following conditions is met, UE 601 performs the RA procedure for the candidate cell:

[0121] a) UE 601 receives the configuration of a candidate cell that has already been configured and UE 601 does not have an available

[0122] TA.

[0123] b) UE 601 receives configuration of a candidate cell and UE 601 does not have an available TA for this candidate cell.

[0124] c) UE 601 receives configuration for adding candidate cells.

[0125] In option 1, when UE 601 receives the configuration of candidate cells and UE 601 has an available TA, UE 601 does not perform the RA procedure for obtaining the TA. In some cases, if multiple candidate cells are received in a single message, there may be the following two options in different embodiments, namely, option a and option b.

[0126] Option a: UE 601 may perform multiple RAs simultaneously. That is, UE 601 may maintain multiple ongoing random access procedures simultaneously.

[0127] Option b: Only one RA program is allowed to run at a time, as in the past.

[0128] (2) Option 2: When to perform the RA procedure for a candidate cell is based on a configuration condition, for example, the condition is a threshold (eg, RSRP value). Once the condition of the candidate cell is met, the UE 601 performs the RA procedure for the candidate cell.

[0129] (3) Option 3: An explicit indication via DCI or MAC CE for triggering the RA procedure for obtaining the TA is transmitted to the UE 601 .

[0130] exist Figure 6 In some embodiments, one of the following two options can be used to distinguish the "RA procedure for obtaining TA" from the "normal RA procedure for switching", namely, Option A and Option B.

[0131] (1) Option A: separate preambles or separate time-frequency domain resources are configured for the “RA procedure for obtaining a TA” and the “normal RA procedure for handover”.

[0132] (2) Option B: Add an indication in Msg 3 or Msg A to indicate “RA procedure for obtaining TA”

[0133] Aims to obtain TA.

[0134] In operation 617 , based on the above measurement result reported by UE 601 , the serving cell transmits a DCI or MAC CE indication to UE 601 to activate the cell change.

[0135] In operation 618, the UE 601 changes the serving cell and starts receiving or transmitting using the preconfigured UE-dedicated channel.

[0136] Figure 7 Another exemplary flow chart illustrating the execution of a cell change procedure 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 . Those skilled in the art should understand that Figure 7 The order of operations in the exemplary process 700 may be changed and Figure 7 Some operations in the exemplary process 700 in may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0137] like Figure 7 As shown in FIG. 7 , BS 705 is in a CU-DU architecture and includes CU 704, source DU 702, and target DU 703. Figure 7 In the embodiment shown in , the cell change of UE 701 may refer to an intra-DU situation where the source cell and the target cell are located in the same DU or to an inter-DU situation where the source cell and the target cell are located in different DUs. For example, for exemplary purposes, Figure 7 The flowchart 700 shown in FIG. 7 only shows the cell change in the inter-DU case.

[0138] In such Figure 7 In the exemplary flow chart 700 shown in FIG. 7 , in operation 711, the UE 701 reports to the serving cell (eg, the CU 704) an indication of the capability of the UE 701 to support the cell change based on the DCI or the MAC CE.

[0139] In operation 712, the UE 701 reports the measurement result to the serving cell (eg, the CU 704) via an RRC message. For example, the UE 701 may report the measurement result based on the RRC reconfiguration including the measurement configuration.

[0140] In operation 713, the serving cell transmits the configuration of the candidate cell to the UE 701. The configuration of the candidate cell may be generated by the target cell (eg, by the target DU 703).

[0141] In operation 714, after UE 701 receives the configuration of the candidate cell from the serving cell, UE 701 performs a RA procedure for obtaining a TA. In operation 715, UE 601 performs measurement for the serving cell and the candidate cell and reports the measurement result to the serving cell.

[0142] exist Figure 7 In some embodiments, there is a period of time between receiving the configuration of the candidate cell and receiving the DCI or MAC CE command. UE 701 does not know the time point of receiving the DCI or MAC CE command. Therefore, after receiving the configuration of the candidate cell, UE 701 can perform a RA procedure for obtaining a TA.

[0143] exist Figure 7In some embodiments, UE 701 wants to obtain TA before receiving DCI or MAC CE command. When receiving DCI or MAC CE command, UE 701 may be performing RA procedure.

[0144] In operation 716, when UE 701 is performing the RA procedure for candidate cell #1 or candidate cell #2 to obtain a TA, UE 701 may receive an indication of switching to candidate cell #1, for example, from source DU 702 via DCI or MAC CE. There may be the following two options, namely, option X and option Y, in different embodiments.

[0145] (1) Option X: UE 701 continues to perform the RA procedure for candidate cell #1. UE 701 may stop the RA procedure for other candidate cells (eg, candidate cell #2) after receiving the indication of candidate cell #1.

[0146] (2) Option Y: UE 701 stops the ongoing RA procedure for obtaining the TA for candidate cell #1 and stops the corresponding timer for RA for obtaining the TA. UE 701 starts a timer for handover (e.g., T304 as defined in the 3GPP standard document) and performs a new normal RA procedure for candidate cell #1 for handover purposes.

[0147] In operation 717, the UE 701 transmits an RRC reconfiguration complete message to the target cell after completing the RA procedure.

[0148] Figure 8 Another exemplary flow chart illustrating the execution of a cell change procedure according to some embodiments of the present application. The details described in all other embodiments of the present application apply to Figure 8 The embodiments shown in . Those skilled in the art should understand that Figure 8 The order of operations in the exemplary process 800 may be changed and Figure 8 Some operations in the exemplary process 800 in FIG. 8 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0149] like Figure 8 As shown in FIG. 8 , BS 805 is in a CU-DU architecture and includes CU 804, source DU 802, and target DU 803. Figure 8 In the embodiment shown in , the cell change of UE 801 may refer to an intra-DU situation where the source cell and the target cell are located in the same DU or to an inter-DU situation where the source cell and the target cell are located in different DUs. For example, for exemplary purposes, Figure 8 The flowchart 800 shown in FIG. 8 shows only the cell change in the inter-DU case.

[0150] In such Figure 8 In the exemplary flow chart 800 shown in FIG. 8 , in operation 811, the UE 801 reports to the serving cell (eg, the CU 804) an indication of the capability of the UE 801 to support the cell change based on the DCI or the MAC CE.

[0151] In operation 812, UE 801 reports the measurement result to the serving cell (eg, CU 804) via an RRC message. For example, UE 801 may report the measurement result based on an RRC reconfiguration including a measurement configuration.

[0152] In operation 813 , the serving cell (eg, CU 804 ) transmits the configuration of the candidate cells to the UE 801 .

[0153] In some embodiments, in operation 813A (optional), the CU 804 may transmit a cell change request via the F1 interface to, for example, a target cell associated with the target DU 803. In operation 813B (optional), the target cell may transmit a response to the CU 804.

[0154] In operation 814, after the UE 801 receives the configuration of the candidate cell from the serving cell, the UE 801 performs a RA procedure for obtaining a TA.

[0155] In some embodiments, there is a period of time between receiving the configuration of the candidate cell and receiving the DCI or MAC CE command. UE 801 may not know the time point of receiving the DCI or MAC CE command. Therefore, after receiving the configuration of the candidate cell, UE 801 may perform a RA procedure for obtaining a TA.

[0156] After successfully obtaining the TA via the RA procedure, the TA may be invalid after a period of time before receiving the DCI or MAC CE command. Therefore, the network node needs to control when to reacquire the TA. In some embodiments, the target cell or the source cell may configure a threshold of channel quality (e.g., an RSRP threshold or a threshold of RSRP change) or a period threshold. The UE 801 may use the threshold to determine whether the TA is valid. For example, there may be the following options in the following different embodiments, namely, option M, option N, and option O.

[0157] (1) Option M: Configure RSRP threshold. For example, when UE 801 obtains the TA of the candidate cell, UE 801 stores RSRP#1. UE 801 will continue to monitor RSRP. In an embodiment, if RSRP#1 changes to RSRP#2, for example, RSRP#2 is equal to or greater than the configured RSRP threshold, UE 801 may trigger the RA procedure again to obtain the TA.

[0158] (2) Option N: Configure a threshold for RSRP change. For example, when UE 801 obtains the TA of the candidate cell, UE 801 stores RSRP#1. UE 801 will continue to monitor RSRP. In an embodiment, if RSRP#1 changes to RSRP#2, for example, the difference between RSRP#2 and RSRP#1 is equal to or greater than the configured threshold for RSRP change, then UE 801 may trigger the RA procedure again to obtain the TA.

[0159] (3) Option O: Configure for a period. After a configured period since obtaining the TA, UE 801 may determine that the TA is invalid. Then, UE 801 may trigger the RA procedure again to obtain the TA.

[0160] In operation 815, if the UE 801 determines that the TA is invalid, the UE 801 may perform a RA procedure to obtain a new TA.

[0161] In operation 816, the source cell, for example, associated with the source DU 802, transmits a DCI or MAC CE indication to the UE 801 to activate the cell change.

[0162] In operation 817, UE 801 changes the serving cell and starts receiving or transmitting using the preconfigured UE-dedicated channel.

[0163] Fig. 9 900 is a block diagram illustrating an exemplary apparatus 900 according to some embodiments of the present application. Fig. 9 , the apparatus 900 may include at least one processor 906 and at least one transceiver 902 coupled to the processor 906. Although elements such as at least one transceiver 902 and processor 906 are described in singular form in this figure, plural forms are contemplated unless limitation to the singular form is explicitly stated. In some embodiments of the present application, the transceiver 902 may be divided into two devices, such as a receive circuit system and a transmit circuit system. In some embodiments of the present application, the apparatus 900 may further include an input device, a memory, and / or other components.

[0164] In some embodiments of the present application, the apparatus 900 may be a UE or a network node (eg, a BS, a CU, or a DU). The transceiver 902 and the processor 906 may interact with each other to execute the above (eg, Figures 1 to 8 The operations of the UE or network node described in any of the foregoing.

[0165] In some embodiments of the present application, the device 900 may further include at least one non-transitory computer-readable medium. For example, in some embodiments of the present disclosure, the non-transitory computer-readable medium may store thereon computer-executable instructions to enable the processor 906 to implement the method described above with respect to the UE or network node (e.g., BS, CU, or DU). For example, when the computer-executable instructions are executed, the processor 906 interacts with the transceiver 902 to perform Figures 1 to 8 The operations of the UE or network node described in.

[0166] It will be appreciated by those skilled in the art that the operations or steps of the methods described in conjunction with the aspects disclosed herein may be directly embodied in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the operations or steps of the methods may reside as one or any combination or set of codes and / or instructions on a non-transitory computer-readable medium that may be incorporated into a computer program product.

[0167] In this document, the term "includes / including" or any other variation thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment containing a series of elements not only contains those elements, but also may contain other elements that are not explicitly listed or inherent to this process, method, article or equipment. Elements starting with "one", "one" or the like do not exclude the presence of additional identical elements in the process, method, article or equipment containing the elements without more constraints. Moreover, the term "another" is defined as at least the second or more. The term "having" and the like as used herein are defined as "including". For example, the expression of "A and / or B" or "at least one of A and B" may include any and all combinations of the words enumerated together with the expression. For example, the expression "A and / or B" or "at least one of A and B" may include A, B, or both A and B. The wording "first", "second" or the like is only used to clearly illustrate the embodiments of the present application, and is not used to limit the essence of the present application.

Claims

1. A user equipment UE, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to: receiving, via the transceiver, a radio resource control (RRC) reconfiguration message associated with one or more candidate cells; In response to receiving the RRC reconfiguration message, performing one or more random access RA procedures on the one or more candidate cells to obtain a timing advance TA; and In response to receiving, via the transceiver, a first indication associated with a candidate cell within the one or more candidate cells from a source cell, switching from the source cell to the one candidate cell.

2. The UE according to claim 1, wherein the first indication is contained in downlink control information (DCI) or medium access control (MAC) control element (CE).

3. The UE of claim 1 , wherein the processor of the UE is configured to initiate the one or more RA procedures for the one or more candidate cells in response to one of: receiving the RRC reconfiguration message including an updated configuration of a first candidate cell, wherein the UE has received the configuration of the first candidate cell before receiving the RRC reconfiguration message, and the UE does not have an available TA for the first candidate cell; receiving the RRC reconfiguration message including configuration of a second candidate cell and the UE does not have an available TA for the second candidate cell; and The RRC reconfiguration message including a configuration for adding a third candidate cell is received.

4. The UE of claim 1 , wherein in response to the RRC reconfiguration message comprising a set of configurations of a plurality of candidate cells, the processor of the UE is configured to: performing a plurality of RA procedures for the plurality of candidate cells simultaneously to obtain the TA; or A candidate cell is selected from the plurality of candidate cells and a RA procedure is simultaneously performed on the selected one candidate cell to obtain the TA.

5. The UE according to claim 4, wherein in order to select the one candidate cell, the processor of the UE is configured to select the one candidate cell from the one or more candidate cells based on at least one of the following: channel quality of the one or more candidate cells, or channel quality of beams of the one or more candidate cells. 6 . The UE of claim 1 , wherein the processor of the UE is configured to initiate the one or more RA procedures for the one or more candidate cells in response to satisfaction of a configured condition. The UE according to claim 6 , wherein the configuration condition is a threshold value of channel quality.

8. The UE according to claim 1, wherein the processor of the UE is configured to receive an indication instructing the UE to perform a RA procedure for obtaining the TA, or wherein the RRC reconfiguration message includes a set of parameters for obtaining the TA for implicitly instructing the UE to perform the RA procedure for obtaining the TA.

9. The UE of claim 8, wherein the set of parameters comprises at least one of: a dedicated preamble, or a dedicated random access channel opportunity (RO).

10. The UE according to claim 8, wherein the indication or the RRC reconfiguration message including the set of parameters for obtaining the TA is generated by the source cell, the one candidate cell or a centralized unit (CU).

11. The UE of claim 1 , wherein the RRC reconfiguration message comprises at least one of: a dedicated preamble for obtaining an RA procedure within the one or more RA procedures of the TA; or Dedicated time-frequency domain resources for obtaining the RA procedure within the one or more RA procedures of the TA.

12. The UE according to claim 11, wherein the RA procedure within the one or more RA procedures for obtaining the TA is associated with a timer for obtaining the RA of the TA, and the processor of the UE is configured to start the timer for obtaining the RA of the TA in response to starting the RA procedure within the one or more RA procedures for obtaining the TA. 13 . The UE according to claim 1 , wherein the processor of the UE is configured to transmit, via the transceiver, to a target distributed unit DU, a second indication for indicating that the one or more RA procedures are for obtaining the TA.

14. A target distributed unit DU, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to: receiving, via the transceiver, a cell change request of a user equipment UE from a centralized unit CU managing the target DU; and A response is transmitted to the CU via the transceiver, wherein the response includes a set of configurations regarding a target cell, and wherein the UE applies the set of configurations upon receiving a first indication associated with a candidate cell.

15. A centralized unit CU, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to: transmitting, via the transceiver, a cell change request of a user equipment UE to a target distributed unit DU managed by the CU; receiving, via the transceiver, a response from the target DU, wherein the response includes a set of configurations for a target cell, and wherein the UE applies the set of configurations upon receiving a first indication associated with a candidate cell; and A radio resource control (RRC) reconfiguration message associated with one or more candidate cells is transmitted to the UE via the transceiver.

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