Method and device for supporting lower mobility

Abstract

The invention relates to a method and equipment for supporting lower mobility. An embodiment of the present disclosure provides a distributed unit (DU) comprising: a transceiver; and a processor coupled with the transceiver and configured to: determine, for each candidate cell of one or more candidate cells, a candidate cell configuration and an index of the candidate cell configuration, where the index of the candidate cell configuration is generated by the DU or received from other network nodes; and transmitting, to a user equipment (UE), an indication indicating that the UE switches from a serving cell to a candidate cell of the one or more candidate cells.

Description

Technical Field

[0001] The present disclosure relates to wireless communications, and in particular to methods and apparatuses for supporting underlay mobility. Background Art

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

[0003] Currently, serving cell change is performed by triggering synchronization of the target cell based on Layer 3 (L3) measurement reports through explicit Radio Resource Control (RRC) reconfiguration signaling, which results in longer latency, greater overhead, and longer outage time than beam-level mobility.

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

[0005] Therefore, how to support lower layer mobility will be studied and solved. Summary of the invention

[0006] One object of the present disclosure is to propose some solutions to support underlying mobility.

[0007] An embodiment of the present disclosure provides a distributed unit (DU), comprising: a transceiver; and a processor, which is coupled to the transceiver and configured to: determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell in one or more candidate cells, wherein the index of the candidate cell configuration is generated by the DU or received from other network nodes; and transmit an indication to a user equipment (UE) indicating that the UE switches from a serving cell to a candidate cell in the one or more candidate cells.

[0008] In some embodiments, the indication is transmitted via a Medium Access Control (MAC)-Control Element (CE) or Downlink Control Information (DCI).

[0009] In some embodiments, the indication indicates at least one of: an index of a candidate cell configuration corresponding to the candidate cell; or an indicator indicating whether the candidate cell configuration is to be maintained.

[0010] In some embodiments, the processor is further configured to: receive a first message indicating a candidate cell configuration of each candidate cell in a set of candidate cells and an index of the candidate cell configuration from a central unit (CU), wherein the set of candidate cells includes the one or more candidate cells; and transmit a second message indicating the candidate cell configuration of each candidate cell in the one or more candidate cells and the index of the candidate cell configuration to the CU.

[0011] In some embodiments, the processor is further configured to: receive a first message indicating a candidate cell configuration of each candidate cell in a set of candidate cells from the CU; determine the one or more candidate cells from the set of candidate cells; generate an index of each candidate cell configuration for each candidate cell in the one or more candidate cells; and transmit a second message indicating the candidate cell configuration of each candidate cell in the one or more candidate cells and the index of the candidate cell configuration to the CU.

[0012] In some embodiments, the processor is further configured to: receive a first message indicating a group of candidate cells from the CU; determine the one or more candidate cells from the group of candidate cells; generate a candidate cell configuration and an index of each candidate cell configuration for each candidate cell in the one or more candidate cells; and transmit a second message indicating the candidate cell configuration and the index of the candidate cell configuration for each candidate cell in the one or more candidate cells to the CU.

[0013] In some embodiments, the processor is further configured to: receive a first message indicating a set of candidate cells from the CU; determine the one or more candidate cells from the set of candidate cells; generate a candidate cell configuration for each candidate cell in the one or more candidate cells; and transmit a second message indicating the candidate cell configuration for each candidate cell in the one or more candidate cells to the CU.

[0014] In some embodiments, the candidate cell configuration includes at least one of: a channel state information (CSI) resource configuration; or a state of a transmission configuration indicator.

[0015] Another embodiment of the present disclosure provides a CU, which includes: a transceiver; and a processor, which is coupled to the transceiver and configured to: transmit a first message indicating at least a group of candidate cells; and receive a second message indicating a candidate cell configuration of each candidate cell in one or more candidate cells in the group of candidate cells and an index of the candidate cell configuration.

[0016] In some embodiments, the first message further indicates a candidate cell configuration of each candidate cell in the set of candidate cells, and the processor is further configured to: transmit a request message indicating at least one candidate cell to the candidate DU; and receive a response message indicating the candidate cell configuration of each candidate cell of at least a portion of the at least one candidate cell.

[0017] In some embodiments, the first message further indicates an index of each candidate cell configuration of each candidate cell in a set of candidate cells.

[0018] In some embodiments, the processor is further configured to: determine, for each candidate cell of at least a portion of the at least one candidate cell, an index of each candidate cell configuration.

[0019] In some embodiments, the processor is further configured to: transmit a request message indicating at least one candidate cell and an index range to the candidate DU; and receive a response message indicating a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of at least a portion of the at least one candidate cell.

[0020] In some embodiments, the processor is further configured to: transmit a message to a UE indicating the candidate cell configuration and the index of the candidate cell configuration for each candidate cell of one or more candidate cells.

[0021] In some embodiments, the candidate cell configuration includes at least one of: a CSI resource configuration; or a state of a transmission configuration indicator.

[0022] Another embodiment of the present disclosure provides a UE, comprising: a transceiver; and a processor, which is coupled to the transceiver and configured to: receive a message indicating a candidate cell configuration of each candidate cell in one or more candidate cells and an index of the candidate cell configuration; and in response to receiving an indication indicating that the UE switches from a serving cell to a candidate cell in the one or more candidate cells, perform a random access procedure toward the candidate cell.

[0023] In some embodiments, the indication is received via a MAC CE or a DCI.

[0024] In some embodiments, the indication indicates at least one of: an index of a candidate cell configuration corresponding to the candidate cell; or an indicator indicating that the candidate cell configuration is to be maintained.

[0025] In some embodiments, the candidate cell configuration includes at least one of: a CSI resource configuration; or a state of a transmission configuration indicator.

[0026] Another embodiment of the present disclosure provides a method for supporting lower layer mobility, which includes: determining a candidate cell configuration and an index of the candidate cell configuration for each candidate cell in one or more candidate cells, wherein the index of the candidate cell configuration is generated by a DU or received from other network nodes; and transmitting an indication to a UE indicating that the UE switches from a serving cell to a candidate cell in the one or more candidate cells.

[0027] Another embodiment of the present disclosure provides a method for supporting lower layer mobility, comprising: transmitting a first message indicating at least a group of candidate cells; and receiving a second message indicating a candidate cell configuration and an index of the candidate cell configuration for each candidate cell in one or more candidate cells in the group of candidate cells.

[0028] Another embodiment of the present disclosure provides a method for supporting lower layer mobility, comprising: receiving a message indicating a candidate cell configuration of each candidate cell in one or more candidate cells and an index of the candidate cell configuration; and in response to receiving an indication indicating that a UE switches from a serving cell to a candidate cell in the one or more candidate cells, performing a random access procedure toward the candidate cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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 proceeds with reference to specific embodiments thereof which are illustrated in the accompanying drawings. These drawings depict only example embodiments of the present application and therefore should not be considered limiting of its scope.

[0030] Figure 1A A schematic diagram illustrating intra-CU and intra-DU mobility scenarios according to some embodiments of the present disclosure.

[0031] Figure 1B A schematic diagram illustrating intra-CU inter-DU mobility scenarios according to some embodiments of the present disclosure.

[0032] Figure 2 A method performed by a source DU according to some embodiments of the present disclosure is described.

[0033] Figure 3 A method performed by a CU according to some embodiments of the present disclosure is described.

[0034] Figure 4 A method performed by a UE according to some embodiments of the present disclosure is described.

[0035] Figure 5 A flow chart illustrating supporting lower layer mobility in an inter-DU mobility scenario according to some embodiments of the present disclosure.

[0036] Figure 6 The structure of an indication according to some embodiments of the present disclosure is described.

[0037] Figure 7 A flow chart illustrating supporting lower layer mobility in an inter-DU mobility scenario according to some embodiments of the present disclosure.

[0038] Figure 8 A flow chart illustrating supporting lower layer mobility in an inter-DU mobility scenario according to some embodiments of the present disclosure.

[0039] Fig. 9 A flow chart illustrating supporting lower layer mobility in an intra-DU mobility scenario according to some embodiments of the present disclosure.

[0040] Fig.10 A flow chart illustrating supporting lower layer mobility in an intra-DU mobility scenario according to some embodiments of the present disclosure.

[0041] Fig.11 A simplified block diagram illustrating an apparatus according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0042] The detailed description of the drawings is intended as a description of the currently preferred embodiments of the present invention and is not intended to represent the only form in which the present invention can be practiced. It should be understood that the same or equivalent functions can be achieved by different embodiments intended to be included in the spirit and scope of the present invention.

[0043] Although the operations are depicted in a particular order in the figures, those skilled in the art will readily recognize that such operations need not be performed in the particular order shown or in a sequential order, or that all of the illustrated operations need not be performed to achieve a desired result; one or more operations may sometimes be skipped. In addition, the accompanying drawings may schematically depict one or more example processes in the form of a flow chart. However, other operations not depicted may be incorporated into the schematically illustrated example processes. For example, one or more additional operations may be performed before, after, simultaneously with, or between any of the illustrated operations. In some cases, multitasking and parallel processing may be advantageous.

[0044] Reference will now be made in detail to some embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. For ease of understanding, embodiments are provided under specific network architectures and new service scenarios (e.g., cellular telephone networks, networks based on time division multiple access (TDMA), networks based on code division multiple access (CDMA), networks based on orthogonal frequency division multiple access (OFDMA), LTE networks, 3GPP-based networks, LTE, LTE-Advanced (LTE-A), 3GPP 4G, 3GPP 5G NR, 3GPP Release 16 and higher, satellite communication networks, high altitude platform networks, etc.). It is considered that with the development of network architectures and new business scenarios, all embodiments in the present disclosure are also applicable to similar technical problems; and in addition, the terms cited in the present disclosure may change, which should not affect the principles of the present disclosure.

[0045] Key objectives for further enhancing liquidity could include:

[0046] - Configuration and maintenance of multiple candidate cells to allow rapid application of configuration of candidate cells.

[0047] -Dynamic switching mechanism among candidate serving cells for potential applicable scenarios.

[0048] Potential applicable scenarios of lower layer mobility may include intra-CU intra-DU mobility and intra-CU inter-DU mobility. In the present disclosure, lower layer mobility is compared with traditional L3 mobility based on RRC signaling, such as L1 or L2 mobility based on L1 or L2 signaling.

[0049] Figure 1A A schematic diagram illustrating intra-CU and intra-DU mobility scenarios according to some embodiments of the present disclosure.

[0050] Figure 1A The wireless communication system in FIG. 1 includes a DU (e.g., DU 102A), a UE (e.g., UE 101A), and some access nodes (e.g., access node 103A1 and access node 103A2). Access node 103A1 and access node 103A2 are controlled by DU 102A and provide services to UEs in cell #1A and cell #2A, respectively. Figure 1A There is only one UE and two access nodes in the UE, but those skilled in the art will recognize that any number of UEs and access nodes may be included in the wireless communication system.

[0051] UE 101A may include a computing device, such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (e.g., a TV connected to the Internet), a set-top box, a game console, a security system (including a security camera), a car computer, a network device (e.g., a router, a switch, a modem), or the like. According to an embodiment of the present disclosure, UE 101A may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identity module, a personal computer, a selective call receiver, or any other device capable of sending and receiving communication signals on a wireless network. In some embodiments, UE 101A includes a wearable device, such as a smart watch, a fitness bracelet, an optical head-mounted display, or the like. In addition, UE 101A may be referred to as a subscriber unit, a mobile device, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, a device, or other terms used in the art.

[0052] Access nodes 103A1 and 103A2 may be distributed throughout a geographic area. In some embodiments, access nodes may also be referred to as access points, access terminals, base stations, base stations, macro cells, Node Bs, enhanced Node Bs (eNBs), gNBs, home Node Bs, relay nodes, devices, or any other terminology used in the art. Access nodes 103A1 and 103A2 may generally be part of a radio access network, which may include one or more controllers communicatively coupled to one or more corresponding base stations.

[0053] The wireless communication system is compatible with any type of network capable of sending and receiving wireless communication signals. For example, the wireless communication system is compatible with wireless communication networks, cellular telephone networks, TDMA-based networks, CDMA-based networks, OFDMA-based networks, Long Term Evolution (LTE) networks, 3GPP-based networks, 3GPP 5G networks, satellite communication networks, high altitude platform networks, and / or other communication networks.

[0054] In one embodiment, the wireless communication system is compatible with NR of the 3GPP protocol, where transmission may be performed using an OFDM modulation scheme. More generally, the wireless communication system may implement some other open or proprietary communication protocols, such as WiMAX, among others.

[0055] In other embodiments, the transmission may be performed using other communication protocols, such as the IEEE 802.11 family of wireless communication protocols. Furthermore, in some embodiments, the transmission may be performed over a licensed spectrum, while in other embodiments, the transmission may be performed over an unlicensed spectrum. The present disclosure is not intended to be limited to implementations of any particular wireless communication system architecture or protocol. In another embodiment, the transmission may be performed using the 3GPP 5G protocol.

[0056] exist Figure 1A In the example, UE 101A is moving from cell #1A to cell #2A and may perform a handover procedure from cell #1A to access cell #2A, which is a handover procedure performed between different cells within a DU. This scenario may be referred to as intra-CU intra-DU mobility. In short, this scenario may be referred to as intra-DU mobility.

[0057] Figure 1B A schematic diagram illustrating intra-CU inter-DU mobility scenarios according to some embodiments of the present disclosure.

[0058] Figure 1B The wireless communication system in FIG. 1 includes a CU (e.g., CU 104B), a UE (e.g., UE 101B), and some DUs (e.g., DU 102B1 and DU 102B2). DU 102B1 and DU 102B2 are controlled by CU 104B and provide services to UEs in cell #1B and cell #2B, respectively. Figure 1B There is only one UE and two DUs in the UE, but those skilled in the art will recognize that any number of UEs and DUs may be included in a wireless communication system.

[0059] exist Figure 1B In the example, UE#101B is moving from cell#1B to cell#2B and can perform a handover procedure from cell#1B to access cell#2B, which is a handover procedure performed between different cells belonging to different DUs but within the same CU. This scenario can be referred to as intra-CU intra-DU mobility. In short, this scenario can be referred to as inter-DU mobility.

[0060] For lower layer mobility, the following issues will be addressed:

[0061] Question 1:

[0062] If the UE requires mobility to a different cell, the network may trigger the UE to change from the current source cell to a target candidate cell. In conventional L3 signaling, a cell ID with 32 bits and a physical cell identity (PCI) with 10 bits are used, which results in overhead in L1 or L2 signaling.

[0063] Therefore, the present disclosure proposes a more efficient solution to reduce the signaling overhead in L1 or L2 signaling. Specifically, the present disclosure proposes to introduce an index indicating a candidate cell configuration.

[0064] Question 2:

[0065] In inter-DU mobility scenarios, e.g. Figure 1B In the scenario shown in , the candidate cell configuration is generated by the candidate DU and sent to the CU via an information element (IE), such as CellGroupConfig (which is transparent to the CU).

[0066] If the index-based approach proposed in Problem 1 is used, there must be no conflict or confusion among the generated indices of the candidate cell configurations of different candidate DUs. In addition, the source DU and the UE need to have a common understanding of the indices.

[0067] Question 3:

[0068] In the intra-DU mobility scenario, it is also necessary to determine which node generates the index of the candidate cell configuration.

[0069] The present disclosure at least proposes some solutions to solve the above problems.

[0070] Figure 2 A method performed by a DU (eg, a source DU) according to some embodiments of the present disclosure is described.

[0071] In operation 201, the source DU may determine a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells (e.g., N candidate cells, where N is an integer), where the index of the candidate cell configuration is generated by the DU or received from other network nodes; and in operation 202, the source DU may transmit an indication to the UE instructing the UE to switch from the serving cell to a candidate cell among the one or more candidate cells.

[0072] In some embodiments, the indication is transmitted via a MAC CE or a DCI.

[0073] In some embodiments, the indication may indicate at least one of the following:

[0074] - an index of a candidate cell configuration corresponding to the candidate cell; or

[0075] - An indicator indicating whether the candidate cell configuration is to be maintained.

[0076] In some embodiments, the DU may receive a first message (e.g., a UE context modification request message) from the CU indicating the candidate cell configuration and the index of the candidate cell configuration of each candidate cell in a set of candidate cells (e.g., M candidate cells, where M is an integer and is equal to or greater than N), wherein the set of candidate cells includes the one or more candidate cells (e.g., M candidate cells); and transmit a second message (e.g., a UE context modification response message) to the CU indicating the candidate cell configuration and the index of the candidate cell configuration of each candidate cell in the one or more candidate cells.

[0077] In some embodiments, the DU may receive a first message (e.g., a UE context modification request message) from the CU indicating a candidate cell configuration of each candidate cell in a set of candidate cells (e.g., M candidate cells); determine one or more candidate cells (e.g., N candidate cells) from the set of candidate cells (e.g., M candidate cells); generate an index of each candidate cell configuration for each candidate cell in the one or more candidate cells; and transmit a second message (e.g., a UE context modification response message) to the CU indicating the candidate cell configuration of each candidate cell in the one or more candidate cells and the index of the candidate cell configuration.

[0078] In some embodiments, the DU may receive a first message (e.g., a UE context modification request message) from the CU indicating a group of candidate cells (e.g., M candidate cells); determine one or more candidate cells (e.g., N candidate cells) from the group of candidate cells; generate a candidate cell configuration and an index of each candidate cell configuration for each candidate cell in the one or more candidate cells; and transmit a second message to the CU indicating the candidate cell configuration and the index of the candidate cell configuration for each candidate cell in the one or more candidate cells.

[0079] In some embodiments, the DU may receive a first message (e.g., a UE context modification request message) indicating a group of candidate cells from the CU; determine one or more candidate cells (e.g., N candidate cells) from the group of candidate cells (e.g., M candidate cells); generate a candidate cell configuration for each of the one or more candidate cells; and transmit a second message (e.g., a UE context modification response message) indicating the candidate cell configuration of each of the one or more candidate cells to the CU.

[0080] In some embodiments, the candidate cell configuration includes at least one of the following:

[0081] -CSI resource allocation; or

[0082] - The status of the transport configuration indicator.

[0083] Figure 3A method performed by a CU according to some embodiments of the present disclosure is described.

[0084] In operation 301, the CU may transmit a first message (e.g., a UE context modification request message) indicating at least a group of candidate cells (e.g., M candidate cells); and receive a second message (e.g., a UE context modification response message) indicating a candidate cell configuration of each candidate cell in one or more candidate cells (e.g., N candidate cells) in the group of candidate cells and an index of the candidate cell configuration.

[0085] In some embodiments, the first message (e.g., a UE context modification request message) further indicates a candidate cell configuration of each candidate cell in the set of candidate cells, and the CU is further configured to: transmit a request message indicating at least one candidate cell (e.g., K candidate cells, where K is an integer) to the DU; and receive a response message indicating the candidate cell configuration of each candidate cell of at least a portion of at least one candidate cell (e.g., L candidate cells, where L is an integer and L≤K).

[0086] In some embodiments, the first message further indicates an index of each candidate cell configuration of each candidate cell in a set of candidate cells.

[0087] In some embodiments, the CU may determine an index of each candidate cell configuration for each candidate cell of at least a portion of the at least one candidate cell.

[0088] In some embodiments, the CU may transmit a request message (e.g., a UE context setup request message) indicating at least one candidate cell and an index range to the candidate DU; and receive a response message (e.g., a UE context setup response message) indicating the candidate cell configuration of each candidate cell of at least a part of the at least one candidate cell and the index of the candidate cell configuration.

[0089] In some embodiments, the CU may transmit a message (eg, an RRCReconfiguration message) to the UE indicating a candidate cell configuration and an index of the candidate cell configuration for each of the one or more candidate cells.

[0090] Figure 4 A method performed by a UE according to some embodiments of the present disclosure is described.

[0091] In operation 401, the UE may receive a message (e.g., an RRCReconfiguration message) indicating a candidate cell configuration of each candidate cell in one or more candidate cells and an index of the candidate cell configuration; and in operation 402, in response to receiving an indication indicating that the UE switches from a serving cell to a candidate cell in the one or more candidate cells, the UE may perform a random access procedure toward the candidate cell.

[0092] Figure 5 A flow chart illustrating supporting lower layer mobility in an inter-DU mobility scenario according to some embodiments of the present disclosure.

[0093] exist Figure 5 It includes four components, namely, UE, source DU, one or more candidate DUs (which are Figure 5 The source DU and one or more candidate DUs are within the CU, and the UE is moving from the source DU to one of the one or more candidate DUs. The source DU manages the serving cell of the UE, and one of the one or more candidate DUs manages the candidate cell to which the UE is switched. In some embodiments, the candidate cell to which the UE is switched may be referred to as a “candidate target cell”.

[0094] In this solution, the index of the candidate cell configuration is generated by the CU. The candidate DU (one or more candidate DUs) may provide the cell configuration of each candidate cell to the CU. In response to receiving the cell configuration of the candidate cell (in short, the candidate cell configuration), the CU may generate (or allocate) an index for each candidate cell configuration. The CU may send the candidate cell configuration and the generated index to the source DU. The CU may also send the candidate cell configuration and the generated index to the UE. The detailed process is presented as follows.

[0095] In operation 501, the CU may transmit a message indicating the number of candidate cell IDs (expressed as K candidate cell IDs for simplicity) to the candidate DU (or to multiple candidate DUs), for example, a UE context setup request message. It should be noted that the K candidate cells may be controlled by the same candidate DU or by different candidate DUs. The message may request to prepare the K candidate cells controlled by the candidate DU to create a UE context and set up one or more data bearers.

[0096] In some embodiments, a UE context setup request message may be sent for each candidate cell. That is, the CU may transmit K UE context setup request messages, where each UE context setup request message may indicate a candidate cell ID.

[0097] In other embodiments, the UE context setup request message may include multiple candidate cell IDs (eg, a list of K candidate cell IDs) and be transmitted to the candidate DU controlling the multiple candidate cells.

[0098] In operation 502, if the preparation request is accepted, the candidate DU may transmit a response message, for example, a UE context setup response message, to the CU. The UE context setup response message may indicate the candidate cell ID requested from the CU and the candidate cell configuration.

[0099] The candidate cell configuration may include a cell configuration for lower layer mobility. For example, the candidate cell configuration may include at least one of the following:

[0100] - CSI resource configuration, which may be referred to as: CSI-resourceConfig; or

[0101] - The state of TCI, which associates one or two downlink reference signals with the corresponding quasi co-location type.

[0102] The CSI resource configuration may define at least one of the following in the candidate cell: 1) a set of one or more non-zero power (NZP) CSI reference signal (RS) resource sets, which may be referred to as: NZP-CSI-RS-ResourceSet, 2) a CSI interference management (IM) resource set, which may be referred to as: CSI-IM-ResourceSet, or 3) a CSI synchronization signal / physical broadcast channel (SSB) resource set, which may be referred to as: CSI-SSB-ResourceSet.

[0103] NZP-CSI-RS-ResourceSet is a set of NZP CSI-RS resources and set-specific parameters, where each NZP CSI-RS resource is used to configure an NZP CSI-RS transmitted in a cell in which a UE can be configured to measure. CSI-IM-ResourceSet is used to configure a set of one or more CSI IM resources and set-specific parameters. CSI-SSB-ResourceSet is used to configure one SS / PBCH block resource set.

[0104] Among the K requested candidate cells, some may be accepted, while others may not be accepted. Assume that the total number of accepted candidate cells is represented as L for simplicity, where L may be an integer equal to or greater than 1, and L≤K. The candidate DU may transmit, for example, a UE context setup response message indicating the configurations of L candidate cells. In some embodiments, a UE context setup response message may be sent for each requested candidate cell, that is, one UE context setup response message for each candidate cell, and the candidate DU may send L UE context setup response messages to the CU. In other embodiments, in the presence of one candidate DU, one candidate DU may transmit one UE context setup response message indicating the configurations of L candidate cells. In some other embodiments, each candidate DU of multiple DUs may transmit to the CU one UE context setup response message indicating all of its own candidate cell configurations.

[0105] In operation 503 , after receiving the L candidate cell configurations, the CU may generate an index for each of the L candidate cell configurations, wherein the index is used to identify the candidate cell configuration.

[0106] For example, the index may be a numerical value, such as 0, 1, 2, 3, etc. The maximum value of the index may be preconfigured, such as 8, 16, 32, 64, 128, etc. As another example, the index may be a candidate cell configuration ID, which is used to identify the candidate cell configuration.

[0107] At operation 504, the CU may transmit a message, such as a UE context modification request message or a DL RRC message transmission message, to the source DU, which may indicate a certain number of candidate cell configurations (for simplicity, represented as M candidate cell configurations, where M may be an integer equal to or greater than 1) and corresponding indexes. The M candidate cell configurations may come from one candidate DU, or from multiple candidate DUs. For simplicity, the UE context modification request message is used to describe the solution.

[0108] In some embodiments, a UE context modification request message may be sent for each candidate cell. That is, the CU may send M UE context modification request messages, where each UE context modification request message may indicate a candidate cell configuration and a corresponding index.

[0109] In some other embodiments, the UE context modification request message may indicate multiple candidate cell configurations and corresponding indexes (eg, a list of M candidate cell configurations and corresponding indexes), and be transmitted to the source DU.

[0110] In some cases, for example, based on reported L3 measurements, the CU may identify a potential set of candidate cells from the L candidate cells to which the UE may be switched. In this case, M is less than the total number of candidate cells from one or more candidate DUs, i.e., M≤L.

[0111] At operation 505 , if the modification request is accepted, the source DU may transmit a response message to the CU, such as a UE context modification response message or a UL RRC message transfer message, and the response message may indicate that N candidate cell configurations and corresponding indexes are accepted, where N≤M.

[0112] In some embodiments, a UE context modification response message may be sent for each accepted candidate cell. That is, the source DU may transmit M UE context modification response messages, where each UE context modification response message may indicate an accepted candidate cell configuration and a corresponding index.

[0113] In some other embodiments, the UE context modification response message may include a list of N accepted candidate cell IDs, which may indicate that the candidate cell configurations and indexes are accepted, where N≤M. Alternatively, the UE context modification response message may indicate N candidate cell configurations and corresponding indexes, where N≤M.

[0114] At operation 506, having received N candidate cell configurations and corresponding indices from the source DU, the CU may generate the required RRC reconfiguration and send an RRC reconfiguration message to the UE. The RRC reconfiguration message may indicate the N candidate cell configurations and corresponding indices.

[0115] In some embodiments, the CU may send a certain number of candidate cell configurations (the number may be equal to or less than N) and corresponding indexes to the UE. For example, the CU may exclude some candidate cells to which the UE may not switch (for simplicity, the number of these candidate cells is represented as A, where A may be an integer equal to or greater than 1), and then send information of NA candidate cells to the UE, including NA candidate cell configurations and corresponding NA indexes.

[0116] At operation 507, the UE may respond to the CU with an RRC reconfiguration complete message, which may be represented as: RRCReconfigurationComplete.

[0117] At operation 508, the UE may start reporting L1 measurement values ​​of the serving cell and the candidate cells to the source DU.

[0118] In operation 509, the source DU may determine that lower layer mobility to a candidate cell is required.

[0119] At operation 510, the source DU may send an indication to the UE, such as a lower layer mobility command, to trigger the UE to switch from the current serving cell to the candidate cell. The candidate cell may also be referred to as a candidate target cell. The indication may be transmitted via MAC CE or DCI or other messages or signaling.

[0120] The indication may indicate an index which may indicate a candidate cell configuration to be applied (or used or activated) by the UE when the UE receives the indication. The indication may further include an indicator which may indicate whether the candidate cell configuration is to be maintained by the UE when the UE is connected to the candidate cell.

[0121] At operation 511, the UE may perform a random access procedure toward a target cell indicated by the source DU.

[0122] Figure 6 The structure of an indication according to some embodiments of the present disclosure is described.

[0123] exist Figure 6 In the embodiment, the indication may be a MAC CE command, which has a fixed size of one octet. Specifically, the octet may include at least one of the following:

[0124] - Lower Layer Handover (HO) Command: This field may indicate an index value for the candidate cell configuration that the UE must apply. The size of the field may be 6 bits.

[0125] -M: This field may indicate whether the candidate cell configuration will be maintained by the UE when the UE is connected to the candidate cell. The length of the field may be 1 bit. If the M field is set to 1, the candidate cell configuration will be maintained by the UE.

[0126] -R: Reserved bit, which can be set to 0.

[0127] The MAC CE used for indication may have a logical channel ID (LCID) value in the MAC subheader. For example, code point 35 is used for indication. Other code points may also be used for indication.

[0128] Figure 6 The MAC CE depicted in is an example of the structure of the MAC CE, and other formats of the MAC CE may also be used. For example, the MAC CE may consist of two octets, three octets, the size of the lower layer HO command field may be 3 bits, etc.

[0129] In some other embodiments, the indication may be a DCI command. For example, DCI format 2_8 may be used to indicate the candidate cell configuration that the UE must apply, and optionally, whether the candidate cell configuration will be maintained by the UE when the UE is connected to the candidate cell. At least one of the following information is transmitted via DCI format 2_8:

[0130] - Lower Layer Handover (HO) Command: This field may indicate an index value for the candidate cell configuration that the UE must apply. The size of the field may be 6 bits.

[0131] -M: This field may indicate whether the candidate cell configuration will be maintained by the UE when the UE is connected to the candidate cell. The length of the field may be 1 bit. If the M field is set to 1, the candidate cell configuration will be maintained by the UE.

[0132] DCI format 2_8 is an example of the structure of DCI, and other formats of DCI may also be used. For example, the size of the lower layer HO command field may be 3 bits, etc.

[0133] As can be seen, compared with conventional L3 signaling, one octet may be sufficient to indicate the candidate cell configuration, where a cell ID with 32 bits and a physical cell identity (PCI) with 10 bits are used, and the solution of the present application significantly reduces the signaling overhead.

[0134] Figure 7 A flow chart illustrating supporting lower layer mobility in an inter-DU mobility scenario according to some embodiments of the present disclosure. Figure 7 The components contained in Figure 5 The details are omitted here.

[0135] In this solution, the index of the candidate cell configuration of each candidate cell is generated by the source DU. The candidate DU may provide the candidate cell configuration to the CU. The CU may send the candidate cell configuration from the candidate DU to the source DU. In response to receiving the candidate cell configuration, the source DU may generate (or allocate) an index for each candidate cell configuration. The source DU may send the candidate cell configuration and the generated index to the CU. The CU may send the candidate cell configuration and the generated index to the UE. The detailed process is presented as follows.

[0136] Operations 701, 702, and 706 to 711 are similar to Figure 5 Operations 501, 502, and 506 to 511 described in FIG. 5 are described in detail, and the details are omitted here.

[0137] At operation 703, the CU may transmit a message, such as a UE context modification request message or a DL RRC message transfer message, to the source DU, which may indicate the M candidate cell configurations. The M candidate cell configurations may be from one candidate DU or from multiple candidate DUs.

[0138] In some embodiments, a UE context modification request message may be sent for each candidate cell. That is, the CU may send M UE context modification request messages, where each UE context modification request message may indicate one candidate cell configuration.

[0139] In some other embodiments, the UE context modification request message may include multiple candidate cell configurations (eg, a list of M candidate cell configurations) and be transmitted to the source DU.

[0140] In another example, the CU may identify potential region one candidate cells to which the UE may be handed over, for example, based on reported L3 measurements. In this case, M is less than the total number of candidate cells (ie, L) from one or more candidate DUs, ie, M≤L.

[0141] At operation 704, after receiving the M candidate cell configurations, the source DU may generate an index for each of the M candidate cell configurations, wherein the index is used to identify the candidate cell configuration.

[0142] For example, the index may be a numerical value, such as 0, 1, 2, 3, etc. The maximum value of the index may be preconfigured, such as 8, 16, 32, 64, 128, etc. As another example, the index may be a candidate cell configuration ID, which is used to identify the candidate cell configuration.

[0143] At operation 705, the modification request may be accepted, and the source DU may transmit a response message to the CU, such as a UE context modification response message or a UL RRC messaging message, which may indicate that N candidate cell configurations and corresponding indices are accepted, where N≤M.

[0144] In some embodiments, a UE context modification response message may be sent for each accepted candidate cell. That is, the source DU may transmit N UE context modification response messages, wherein each UE context modification response message may indicate an accepted candidate cell configuration and a corresponding generated index.

[0145] In other embodiments, the UE context modification response message may include a list of N accepted candidate cell IDs and corresponding generated indices, which may indicate that the candidate cell configurations and indices are accepted, where N ≤ M. Alternatively, the UE context modification response message may include N candidate cell configurations and corresponding generated indices, where N ≤ M.

[0146] Figure 8 A flow chart illustrating supporting lower layer mobility in an inter-DU mobility scenario according to some embodiments of the present disclosure. Figure 8 The components contained in Figure 5 The details are omitted here.

[0147] In this solution, the index of the candidate cell configuration is generated by the candidate DU (or each of multiple candidate DUs). The CU may allocate an index range for the candidate cell configuration of each candidate DU. The candidate DU (or each of multiple candidate DUs) may select an index from the index range of each candidate cell configuration and send the selected index and the corresponding candidate cell configuration to the CU. The CU may send the index and the corresponding candidate cell configuration received from the candidate DU (or multiple candidate DUs) to the source DU. The CU may also send the index and the corresponding candidate cell configuration to the UE. The detailed process is presented as follows.

[0148] At operation 801, the CU may transmit a message, such as a UE context setup request message, to the candidate DU, including the number of candidate cell IDs (for simplicity, represented as K candidate cell IDs, where K may be an integer equal to or greater than 1). It should be noted that the K candidate cells may be controlled by the same candidate DU or by different candidate DUs. The message may also indicate an index range allocated by the CU, where an index within the index range may be used by the candidate DU.

[0149] In some embodiments, a UE context setup request message may be sent for each candidate cell. That is, the CU may transmit K UE context setup request messages, where each UE context setup request message may indicate a candidate cell ID and an index range.

[0150] In other embodiments, the UE context setup request message may indicate multiple candidate cell IDs (eg, a list of K candidate cell IDs) and index ranges, and be transmitted to a candidate DU that may control multiple candidate cells.

[0151] A preparation request may be accepted at operation 802. The candidate DU may prepare candidate cell configurations and select an index for each candidate cell configuration from an index range.

[0152] For example, an index range may be from 0 to 5, and the selected index may be a numeric value, such as 0, 1, 2, 3, etc. The maximum value of the index range may be preconfigured, such as 8, 16, 32, 64, 128, etc. As another example, the index range may be a set of candidate cell configuration IDs, and the selected index may be an ID from the set, which is used to identify the candidate cell configuration.

[0153] At operation 803, the candidate DU may transmit a response message, such as a UE context setup response message, to the CU. The UE context setup response message may indicate the candidate cell ID requested from the CU for each candidate cell, the candidate cell configuration, and the corresponding selected index of the candidate cell configuration.

[0154] Among the K requested candidate cells, some may be accepted, while others may not be accepted. Assume that the number of accepted candidate cells is represented as L, and L≤K. The candidate DU may transmit a UE context setup response message indicating L candidate cell configurations and corresponding L selected indexes. In some embodiments, a UE context setup response message may be sent for each requested candidate cell, that is, one UE context setup response message for each candidate cell, and the candidate DU may send L UE context setup response messages to the CU. In other embodiments, in the presence of one candidate DU, one candidate DU may transmit a UE context setup response message indicating L candidate cell configurations and corresponding selected indexes. In some other embodiments, each candidate DU among multiple DUs may transmit a UE context setup response message indicating all of its own candidate cell configurations and corresponding selected indexes to the CU.

[0155] Operations 804 to 811 are similar to Figure 5 Operations 504 to 511 described in , and the details are omitted here.

[0156] Fig. 9 A flow chart illustrating supporting lower layer mobility in an intra-DU mobility scenario according to some embodiments of the present disclosure. Fig. 9 In the example, there are three components, namely, UE, DU and CU. DU can also be called source DU, and UE is performing a handover procedure from a source cell to a target cell, and the two cells are managed by DU.

[0157] In this solution, the index is generated by the DU. The DU can provide the candidate cell configuration and the index of each candidate cell configuration to the CU. The CU can send the index and the corresponding candidate cell configuration to the UE. The detailed process is presented as follows.

[0158] In operation 901, the CU may transmit a message, such as a UE context modification request message, to the DU, which may include M candidate cell IDs. The CU may request to prepare M candidate cells to modify the UE context by sending a message to the DU.

[0159] In some embodiments, a UE context modification request message may be sent for each candidate cell. That is, the CU may send M UE context modification request messages, where each UE context modification request message may include a candidate cell ID.

[0160] In other embodiments, the UE context modification request message may include multiple candidate cell IDs (eg, a list of M candidate cell configurations) and be transmitted to the DU.

[0161] At operation 902, a modification request may be accepted, for example, N candidate cells among M candidate cells are accepted, where N≤M, and the DU may prepare N candidate cell configurations and generate an index for each of the N candidate cell configurations, where the index is used to identify the candidate cell configuration. In some embodiments, the index may be a numerical value, such as 0, 1, 2, 3, etc. The maximum value of the index may be preconfigured, such as 8, 16, 32, 64, 128, etc. In other embodiments, the index may be a candidate cell configuration ID, which is used to identify the candidate cell configuration.

[0162] In operation 903, the DU may transmit a response message to the CU, for example, a UE context modification response message, where the response message may indicate N candidate cell configurations and corresponding indexes.

[0163] In some embodiments, a UE context modification response message may be sent for each accepted candidate cell. That is, the DU may transmit N UE context modification response messages, where each UE context modification response message may indicate an accepted candidate cell configuration and a corresponding index.

[0164] In some other embodiments, the UE context modification response message may indicate N candidate cell configurations and corresponding indexes, where N≤M.

[0165] Operations 904 to 909 are similar to Figure 5 Operations 506 to 511 described in , and the details are omitted here.

[0166] Fig.10 A flow chart illustrating supporting lower layer mobility in an intra-DU mobility scenario according to some embodiments of the present disclosure. Fig.10 The components contained in Fig. 9 The details are omitted here.

[0167] In this solution, the index is generated by the CU. The DU may provide the cell configuration of each candidate cell to the CU. In response to receiving the candidate cell configuration, the CU may generate (or allocate) an index for each candidate cell configuration. The CU may send the candidate cell configuration and the generated index to the DU. The CU may also send the candidate cell configuration and the generated index to the UE. The detailed process is presented as follows.

[0168] In operation 1001, the CU may transmit a message including K candidate cell IDs, for example, a UE context modification request message, to the DU. The CU may request to prepare K candidate cells to modify the UE context by sending a message to the DU.

[0169] In some embodiments, a UE context modification request message may be sent for each candidate cell. That is, the CU may send K UE context modification request messages, where each UE context modification request message may indicate a candidate cell ID.

[0170] In other embodiments, the UE context modification request message may include multiple candidate cell IDs (eg, a list of M candidate cell configurations) to the DU.

[0171] At operation 1002, if the modification request is accepted, for example, L candidate cells among the K candidate cells are accepted candidate cells, where L≤K, then the DU may transmit a response message, for example, a UE context modification response message, to the CU. The UE context modification response message may include a candidate cell configuration for each of the L candidate cells.

[0172] In operation 1003 , after receiving the L candidate cell configurations, the CU may generate an index for each of the L candidate cell configurations, wherein the index is used to identify the candidate cell configuration.

[0173] At operation 1004, the CU may transmit a message, such as a UE context modification request message, to the DU, which may indicate M candidate cell configurations and corresponding indexes.

[0174] In some embodiments, a UE context modification request message may be sent for each candidate cell. That is, the CU may send M UE context modification request messages, where each UE context modification request message includes a candidate cell configuration and a corresponding index.

[0175] In some other embodiments, the UE context modification request message may include multiple candidate cell configurations and corresponding indexes to the source DU (eg, a list of M candidate cell configurations and corresponding indexes).

[0176] At operation 1005 , if the modification request is accepted, the source DU may transmit a response message to the CU, for example, a UE context modification response message, where the response message may indicate that the N candidate cell configurations and corresponding indexes are accepted.

[0177] In some embodiments, a UE context modification response message may be sent for each accepted candidate cell. That is, the DU may transmit N UE context modification response messages, where each UE context modification response message may indicate an accepted candidate cell configuration and a corresponding index.

[0178] In other embodiments, the UE context modification response message may indicate a list of N accepted candidate cell IDs, which may indicate that the candidate cell configurations and indexes are accepted, where N≤M. Alternatively, the UE context modification response message may indicate N candidate cell configurations and corresponding indexes, where N≤M.

[0179] Operations 1006 to 1011 are similar to Figure 5 Operations 506 to 511 described in , and the details are omitted here.

[0180] Fig.11 A simplified block diagram illustrating an apparatus according to some embodiments of the present disclosure.

[0181] like Fig.11 , an example of apparatus 1100 may include at least one processor 1104 and at least one transceiver 1102 coupled to the processor 1104. Apparatus 1100 may be a UE, a BS, a CU, a candidate DU, a source DU, a target DU, a candidate DU, or any other device having similar functionality.

[0182] Although elements such as at least one transceiver 1102 and a processor 1104 are described in the singular in this figure, the plural form is contemplated unless limitation to the singular form is explicitly stated. In some embodiments of the present disclosure, the transceiver 1102 may be divided into two devices, such as a receiving circuit system and a transmitting circuit system. In some embodiments of the present disclosure, the device 1100 may further include an input device, a memory, and / or other components.

[0183] In some embodiments of the present disclosure, the device 1100 may be a UE. The transceiver 1102 and the processor 1104 may interact with each other to perform the operation of the UE described in any one of Figures 1 to 10. In some embodiments of the present disclosure, the device 1100 may be a CU, a candidate DU, a source DU, a target DU, a candidate target DU, or the like. The transceiver 1102 and the processor 1104 may interact with each other to perform the operation of the node described in any one of Figures 1 to 10.

[0184] In some embodiments of the present disclosure, the device 1100 may further include at least one non-transitory computer-readable medium.

[0185] For example, in some embodiments of the present disclosure, a non-transitory computer-readable medium may store computer-executable instructions to enable the processor 1104 to implement the method described above with respect to the UE. For example, when the computer-executable instructions are executed, the processor 1104 interacts with the transceiver 1102 to perform the operation of the UE described in any one of Figures 1 to 10.

[0186] In some embodiments of the present disclosure, a non-transitory computer-readable medium may store computer-executable instructions to enable the processor 1104 to implement the method described above with respect to a CU, a candidate DU, a source DU, a target DU, or a candidate target DU. For example, when the computer-executable instructions are executed, the processor 1104 interacts with the transceiver 1102 to perform the operation of the node described in any one of Figures 1 to 10.

[0187] The methods of the present disclosure may be implemented on a programmed processor. However, the controller, flow charts, and modules may also be implemented on a general or special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit components, an integrated circuit, a hardware electronic or logic circuit (e.g., a discrete component circuit), a programmable logic device, or the like. In general, any device having a finite state machine capable of implementing the flow charts shown in the figures may be used to implement the processing functions of the present disclosure.

[0188] Although the present disclosure has been described using specific embodiments of the present disclosure, it is apparent that many substitutions, modifications, and variations will be apparent to those skilled in the art. For example, the various components of the embodiments may be interchangeable, added, or substituted in other embodiments. Moreover, the operation of the disclosed embodiments may not necessarily require all of the elements shown in each figure. For example, a person skilled in the art of the disclosed embodiments will be able to make and use the teachings of the present disclosure by simply adopting the elements of the independent claims. Therefore, the embodiments of the present disclosure set forth herein are intended to be illustrative and not restrictive. Various changes may be made without departing from the spirit and scope of the present disclosure.

[0189] In the present disclosure, for example, the relational terms of "first", "second" and the like can be used only to distinguish an entity or action from another entity or action without necessarily requiring or implying any actual this relationship or order between such entities or actions. The term "includes (includes, including)" or any other variation thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements not only comprises those elements, but also may comprise other elements that are not clearly listed or inherent to this process, method, article or equipment. The element beginning with "a (a, an)" or the like does not exclude the existence of additional identical elements in the process, method, article or equipment comprising the element without more constraints. Moreover, the term "another" is defined as at least the second or more. As used herein, the terms "includes", "having" and the like are defined as "comprising".

Claims

1. A distributed unit DU, comprising: Transceiver; and a processor coupled to the transceiver and configured to: determining, for each candidate cell of one or more candidate cells, a candidate cell configuration and an index of the candidate cell configuration, wherein the index of the candidate cell configuration is generated by the DU or received from another network node; and An indication is transmitted to a user equipment (UE) instructing the UE to handover from a serving cell to a candidate cell of the one or more candidate cells.

2. The DU according to claim 1, wherein the indication is transmitted via a medium access control MAC-control element CE or a downlink control information DCI.

3. The DU of claim 1, wherein the indication indicates at least one of: an index of a candidate cell configuration corresponding to the candidate cell; or An indicator indicating whether the candidate cell configuration is to be maintained.

4. The DU of claim 1, wherein the processor is further configured to: receiving from a central unit CU a first message indicating a candidate cell configuration and an index of the candidate cell configuration for each candidate cell in a set of candidate cells, wherein the set of candidate cells includes the one or more candidate cells; and A second message indicating the candidate cell configuration of each candidate cell of the one or more candidate cells and the index of the candidate cell configuration is transmitted to the CU.

5. The DU of claim 1, wherein the processor is further configured to: receiving from the central unit CU a first message indicating a candidate cell configuration for each candidate cell in a set of candidate cells; determining the one or more candidate cells from the set of candidate cells; generating an index of each candidate cell configuration for each candidate cell of the one or more candidate cells; and A second message indicating the candidate cell configuration of each candidate cell of the one or more candidate cells and the index of the candidate cell configuration is transmitted to the CU.

6. The DU of claim 1, wherein the processor is further configured to: receiving a first message from a central unit CU indicating a set of candidate cells; determining the one or more candidate cells from the set of candidate cells; generating a candidate cell configuration and an index of each candidate cell configuration for each candidate cell of the one or more candidate cells; and A second message indicating the candidate cell configuration of each candidate cell of the one or more candidate cells and the index of the candidate cell configuration is transmitted to the CU.

7. The DU of claim 4, wherein the processor is further configured to: receiving a first message from a central unit CU indicating a set of candidate cells; determining the one or more candidate cells from the set of candidate cells; generating a candidate cell configuration for each candidate cell of the one or more candidate cells; and A second message indicating the candidate cell configuration of each candidate cell of the one or more candidate cells is transmitted to the CU.

8. The DU of claim 1, wherein the candidate cell configuration comprises at least one of: Channel state information CSI resource configuration; or The status of the transport configuration indicator.

9. A central unit CU, comprising: Transceiver; and a processor coupled to the transceiver and configured to: transmitting a first message indicating at least a set of candidate cells; and A second message is received indicating a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of one or more candidate cells in the set of candidate cells.

10. The CU of claim 9, wherein the first message further indicates a candidate cell configuration of each candidate cell in the set of candidate cells, the processor being further configured to: transmitting a request message indicating at least one candidate cell to a candidate distributed unit DU; and A response message indicating a candidate cell configuration of each candidate cell of at least a portion of the at least one candidate cell is received. The CU of claim 10 , wherein the first message further indicates an index of each candidate cell configuration of each candidate cell in a set of candidate cells.

12. The CU of claim 11, wherein the processor is further configured to: An index of each candidate cell configuration is determined for each candidate cell of at least a portion of the at least one candidate cell.

13. The CU of claim 11, wherein the processor is further configured to: transmitting a request message indicating at least one candidate cell and an index range to the candidate DU; and A response message indicating a candidate cell configuration of each candidate cell of at least a portion of the at least one candidate cell and an index of the candidate cell configuration is received.

14. The CU of claim 9, wherein the processor is further configured to: A message indicating the candidate cell configuration and the index of the candidate cell configuration for each candidate cell of one or more candidate cells is transmitted to the UE.

15. A user equipment UE, comprising: Transceiver; and a processor coupled to the transceiver and configured to: receiving a message indicating a candidate cell configuration and an index of the candidate cell configuration for each candidate cell of the one or more candidate cells; and In response to receiving an indication instructing the UE to switch from a serving cell to a candidate cell among the one or more candidate cells, a random access procedure toward the candidate cell is performed.

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