Method performed by a radio access network node and method performed by a User Equipment

Abstract

In the present invention, a master node (MN) (1) transmits a control message to a candidate secondary node (SN) (4). The control message indicates that it is necessary for one or more candidate PSCells to be prepared by the candidate SN (4) for a first conditional mobility accompanying an addition of or a change to a PSCell for a UE (3). In addition, the control message indicates the recommendation of an operation mode in which one or more candidate PSCell settings provided to the UE (3) for the first conditional mobility are reused by the UE (3) for a subsequent conditional PSCell change after the first conditional mobility. This invention can contribute to, for example, the realization of a function or an operation mode which enables a subsequent second conditional mobility without a reconfiguration or a re-initialization from a network after a first conditional mobility.

Description

Technical Field

[0001] The present disclosure relates to a wireless communication system, and more particularly to conditional mobility of a wireless terminal.

Background Art

[0002] The 3rd Generation Partnership Project (3GPP (registered trademark)) Release 16 supports Conditional Handover (CHO) and Conditional Primary Secondary Cell Group (SCG) Cell (PSCell) Change (CPC) (see, for example, Non-Patent Documents 1 and 2). Note that the CPC in 3GPP Release 16 is an inter-Secondary Node (SN) CPC without Master Node (MN) involvement, and supports conditional PSCell change from a source PSCell to one or more candidate cells (i.e., candidate PSCs) within one SN. This CPC is also referred to as SN-initiated Conditional SN Modification without MN involvement, which is initiated by the SN without MN involvement.

[0003] The 3GPP Radio Access Network (RAN) Working Group is currently considering enhancements to conditional mobility, which will be introduced in 3GPP Release 17 (see, for example, Non-Patent Document 3). The conditional mobility newly planned to be introduced in 3GPP Release 17 includes Conditional PSCell Addition (CPA) and inter-SN CPC. CPA is also called conditional SN addition, and inter-SN CPC is also called conditional SN change. Inter-SN CPC or conditional SN change is initiated by the MN or the source SN.

[0004] Furthermore, for 3GPP Release 18, discussions have been initiated on further enhancing mobility functions, including "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups" (see, for example, Non-Patent Documents 4 and 5). In the CPA and CPC of Release 17, when the UE selects any candidate target PSCell and performs random access to the selected target PSCell, it is necessary to release the unused (unselected) CPC / CPA settings. Therefore, the UE has no opportunity to execute subsequent CPC without reconfiguring and re-initializing the CPC from the network. "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups" aims to address this issue. Specifically, according to Non-Patent Document 5, MR-DC with selective activation of cell groups aims to enable subsequent CPC / CPA without reconfiguring and re-initializing the CPC / CPA preparation from the network after changing the SCG, thereby reducing the signaling overhead and interruption time of CPC / CPA.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] The inventors have studied mechanisms and procedures for realizing a function or operation mode called "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups" and have found various problems.

[0007] One of these problems relates to the clarification of various procedures regarding a function or operation mode called "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups". At present, the procedures for enabling this function or operation mode are not clear. For example, it is not clear which node (e.g., MN, source SN, or candidate SN) makes the decision on whether to utilize the function or operation mode, and when this decision is made.

[0008] Another one of these problems relates to reusing the setting of multiple candidate PSCs for CPA or Inter-SN CPC (or conditional SN change) for subsequent CPC. The setting of the candidate PSC may be a cell group (CG) setting, an SCG setting, or an SCG radio resource setting. For example, it is not clear which of the settings of multiple candidate PSCs for CPA or Inter-SN CPC (or conditional SN change) the UE reuses for subsequent CPC.

[0009] Yet another one of these problems relates to implementing a function or operation mode similar to "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups" in CHO. For example, after the UE performs a first CHO from a source cell to one of the candidate target cells, enabling a subsequent second CHO by the UE without the network reconfiguring or re-initializing for CHO preparation may contribute to enhancing the mobility function. However, at present, the mechanisms and procedures for implementing the function or operation mode for CHO are not clear.

[0010] One of the objectives to be achieved by the embodiments disclosed in this specification is to contribute to providing an apparatus, a method, and a program that solve at least one of a plurality of problems related to the realization of a function or an operation mode that enables a subsequent second conditional mobility without reconfiguration or re-initialization from the network after the first conditional mobility, including the problems described above. It should be noted that this objective is only one of the plurality of objectives to be achieved by the plurality of embodiments disclosed in this specification. Other objectives or problems and novel features will be clarified from the description of this specification or the accompanying drawings.

Means for Solving the Problems

[0011] The first aspect is directed to a RAN node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for a User Equipment (UE). The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to transmit a control message to a candidate Secondary Node (SN). The control message indicates that one or more candidate Primary Secondary Cell Group (SCG) Cells (PSCells) need to be prepared by the candidate SN for a first conditional mobility involving addition or change of a Primary Secondary Cell (PSCell) for the UE. In addition, the control message indicates that an operation mode in which the setting of the one or more candidate PSCs supplied to the UE for the first conditional mobility is reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended.

[0012] The second aspect is directed to a method performed by a RAN node configured to operate as a MN associated with the MCG in dual connectivity for a UE. The method includes transmitting a control message to a candidate SN. The control message indicates that one or more candidate PSCs need to be prepared by the candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE. Additionally, the control message indicates that an operation mode in which settings of the one or more candidate PSCs provided to the UE for the first conditional mobility are reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended.

[0013] The third aspect is directed to a RAN node configured to operate as a source SN associated with the SCG in dual connectivity for a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to transmit a control message to the MN of the dual connectivity. The control message indicates one or more candidate PSCs recommended by the source SN for a first conditional PSCell change for the UE. Additionally, the control message indicates that an operation mode in which settings of the one or more candidate PSCs provided to the UE for the first conditional PSCell change are reused by the UE for subsequent conditional PSCell changes after the first conditional PCell change is recommended.

[0014] The fourth aspect is directed to a method performed by a RAN node configured to operate as a source SN associated with the SCG in dual connectivity for a UE. The method includes transmitting a control message to the MN of the dual connectivity. The control message indicates one or more candidate PSCs recommended by the source SN for a first conditional PSCell change for the UE. In addition, the control message indicates that an operation mode in which settings of the one or more candidate PSCs provided to the UE for the first conditional PSCell change are reused by the UE for subsequent conditional PSCell changes after the first conditional PCell change is recommended.

[0015] The fifth aspect is directed to a RAN node configured to operate as a candidate SN associated with the SCG in dual connectivity for a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive a first control message from the MN of the dual connectivity and transmit a second control message to the MN in response to the first control message. The first control message indicates that one or more candidate PSCs need to be prepared for a first conditional mobility involving addition or change of a PSCell for the UE. On the other hand, the second control message indicates at least one candidate PSC prepared by the candidate SN among the one or more candidate PSCs. In addition, the second control message indicates that an operation mode in which settings of the at least one candidate PSC provided to the UE for the first conditional mobility are reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended.

[0016] The sixth aspect is directed to a method performed by a RAN node configured to operate as a candidate SN associated with a SCG in dual connectivity for a UE. The method includes receiving, from a MN of the dual connectivity, a first control message and transmitting, in response to the first control message, a second control message to the MN. The first control message indicates that one or more candidate PSCs need to be prepared for a first conditional mobility involving addition or change of a PSCell for the UE. On the other hand, the second control message indicates at least one candidate PSCell prepared by the candidate SN among the one or more candidate PSCs. In addition, the second control message indicates that an operation mode in which settings of the at least one candidate PSCell provided to the UE for the first conditional mobility are reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended.

[0017] The seventh aspect is directed to a RAN node configured to operate as a candidate SN associated with a SCG in dual connectivity for a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to prepare one or more candidate PSCs in a first conditional mobility involving addition or change of a PSCell for the UE. In addition, the at least one processor is configured to transmit, to the UE, an SN Radio Resource Control (RRC) message if one of the one or more candidate PSCs is selected by the UE. The SN RRC message indicates that an operation mode in which settings of one or more candidate PSCs other than the selected candidate PSC prepared for the first conditional mobility are reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended.

[0018] The eighth aspect is directed to a method performed by a RAN node configured to operate as a candidate SN associated with an SCG in dual connectivity for a UE. The method includes: (a) preparing one or more candidate PSCs in a first conditional mobility involving addition or change of a PSC for the UE; and (b) if one of the one or more candidate PSCs is selected by the UE, sending an SN Radio Resource Control (RRC) message to the UE. The SN RRC message indicates that an operation mode is recommended in which settings of one or more candidate PSCs other than the selected candidate PSC prepared for the first conditional mobility are reused by the UE for subsequent conditional PSC changes after the first conditional mobility.

[0019] The ninth aspect is directed to a RAN node configured to operate as a source node for conditional handover of a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to send a control message to a candidate target node. The control message indicates that one or more candidate target cells need to be prepared by the candidate target node for a first conditional handover of the UE. In addition, the control message indicates that an operation mode is recommended in which settings of the one or more candidate target cells provided to the UE for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover.

[0020] The tenth aspect is directed to a method performed by a RAN node configured to operate as a source node for a conditional handover of a UE. The method includes transmitting a control message to a candidate target node. The control message indicates that one or more candidate target cells need to be prepared by the candidate target node for a first conditional handover of the UE. In addition, the control message indicates that an operation mode in which settings of the one or more candidate target cells provided to the UE for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended.

[0021] The eleventh aspect is directed to a RAN node configured to operate as a candidate target node for a conditional handover of a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive a first control message from a source node and transmit a second control message to the source node in response to the first control message. The first control message indicates that one or more candidate target cells need to be prepared for a first conditional handover of the UE. On the other hand, the second control message indicates at least one candidate target cell prepared by the source node among the one or more candidate target cells. In addition, the second control message indicates that an operation mode in which settings of the at least one candidate target cell provided to the UE for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended.

[0022] The 12th aspect is directed to a method performed by a RAN node configured to operate as a candidate target node for conditional handover of a UE. The method includes receiving a first control message from a source node and transmitting a second control message to the source node in response to the first control message. The first control message indicates that one or more candidate target cells need to be prepared for a first conditional handover of the UE. On the other hand, the second control message indicates at least one candidate target cell prepared by the source node among the one or more candidate target cells. In addition, the second control message indicates that an operation mode in which the setting of the at least one candidate target cell provided to the UE for the first conditional handover is reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended.

[0023] The 13th aspect is directed to a RAN node configured to operate as a candidate target node for conditional handover of a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to prepare one or more candidate target cells in a first conditional handover of the UE. In addition, the at least one processor is configured to transmit an RRC message to the UE if one of the one or more candidate target cells is selected by the UE. The RRC message indicates that an operation mode in which the setting of one or more candidate target cells other than the selected candidate target cell prepared for the first conditional handover is reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended.

[0024] The 14th aspect is directed to a method performed by a RAN node configured to operate as a candidate target node for conditional handover of a UE. The method includes: (a) preparing one or more candidate target cells in a first conditional handover of the UE; and (b) if one of the one or more candidate target cells is selected by the UE, sending an RRC message to the UE. The RRC message indicates that an operation mode in which settings of one or more candidate target cells other than the selected candidate target cell prepared for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended.

[0025] The 15th aspect is directed to a UE. The UE includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive, from a MN, settings of a plurality of candidate PSCs provided by a plurality of candidate SNs for a first conditional mobility involving addition or change of a PSC for the UE. The at least one processor is configured to apply settings corresponding to the one candidate PSC if an execution condition of the one candidate PSC among the plurality of candidate PSCs is satisfied. Further, the at least one processor is configured to selectively maintain only settings of one or more other candidate PSCs provided by a selected candidate SN that provides the one candidate PSC for a subsequent conditional PSC change after the first conditional mobility.

[0026] The 16th aspect is directed to a method performed by a UE. The method includes the following steps: (a) receiving, from a MN, settings of a plurality of candidate PSCs provided by a plurality of candidate SNs for a first conditional mobility involving addition or change of a PSC for the UE; (b) If an execution condition of one of the plurality of candidate PSCs is satisfied, apply the setting corresponding to the one candidate PSC; and (c) Selectively maintain only the settings of one or more other candidate PSCs provided by a selected candidate SN that provides the one candidate PSC for subsequent conditional PSC changes after the first conditional mobility.

[0027] The seventeenth aspect is directed to a UE. The UE includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive, from an MN, settings of a plurality of candidate PSCs provided by a plurality of candidate SNs for a first conditional mobility involving addition or change of a PSC for the UE. The at least one processor is configured to apply the setting corresponding to one of the plurality of candidate PSCs if an execution condition of the one candidate PSC is satisfied. Further, the at least one processor is configured to selectively maintain the settings of one or more candidate PSCs specified by the MN or one or more candidate SNs among the plurality of candidate PSCs other than the one candidate PSC for subsequent conditional PSC changes after the first conditional mobility.

[0028] The eighteenth aspect is directed to a method performed by a UE. The method includes the following steps: (a) Receiving, from an MN, settings of a plurality of candidate PSCs provided by a plurality of candidate SNs for a first conditional mobility involving addition or change of a PSC for the UE; (b) If an execution condition of one of the plurality of candidate PSCs is satisfied, applying the setting corresponding to the one candidate PSC; and (c) Among the plurality of candidate PSCs other than the one candidate PSC, selectively maintaining the configuration of one or more candidate PSCs designated by the MN or one or more candidate SNs for subsequent conditional PSCell changes after the first conditional mobility.

[0029] The nineteenth aspect is directed to a RAN node configured to operate as a candidate SN associated with an SCG in dual connectivity for a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to indicate to the MN one or more candidate PSCs prepared by the candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE. Additionally, the at least one processor is configured to indicate to the MN at least one candidate PSC among the one or more candidate PSCs whose configuration needs to be maintained for subsequent conditional PSCell changes after the first conditional mobility.

[0030] The twentieth aspect is directed to a method performed by a RAN node configured to operate as a candidate SN associated with an SCG in dual connectivity for a UE. The method includes the following steps: (a) Indicating to the MN one or more candidate PSCs prepared by the candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE; and (b) Indicating to the MN at least one candidate PSC among the one or more candidate PSCs whose configuration needs to be maintained for subsequent conditional PSCell changes after the first conditional mobility.

[0031] The 21st aspect is directed to a RAN node configured to operate as a MN associated with the MCG in dual connectivity for a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive a control message from a first candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE. The control message indicates one or more candidate PSCs prepared by the first candidate SN for the first conditional mobility. Additionally, the control message indicates at least one candidate PSC among the one or more candidate PSCs, for which its setting needs to be maintained for subsequent conditional PSCell changes after the first conditional mobility.

[0032] The 22nd aspect is directed to a method performed by a RAN node configured to operate as a MN associated with the MCG in dual connectivity for a UE. The method includes receiving a control message from a first candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE. The control message indicates one or more candidate PSCs prepared by the first candidate SN for the first conditional mobility. Additionally, the control message indicates at least one candidate PSC among the one or more candidate PSCs, for which its setting needs to be maintained for subsequent conditional PSCell changes after the first conditional mobility.

[0033] The 23rd aspect is directed to a UE. The UE includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive, from a source node, a configuration of a plurality of candidate target cells provided by a plurality of candidate target nodes for a first conditional handover of the UE. The at least one processor is configured to apply the configuration corresponding to one of the plurality of candidate target cells if an execution condition of the one candidate target cell is satisfied. Further, the at least one processor is configured to selectively maintain only the configurations of one or more other candidate target cells provided by the selected candidate target node that provides the one candidate target cell, for a subsequent second conditional handover after the first conditional handover.

[0034] The 24th aspect is directed to a method performed by a UE. The method includes the following steps: (a) Receiving, from a source node, a configuration of a plurality of candidate target cells provided by a plurality of candidate target nodes for a first conditional handover of the UE; (b) Applying the configuration corresponding to one of the plurality of candidate target cells if an execution condition of the one candidate target cell is satisfied; and (c) Selectively maintaining only the configurations of one or more other candidate target cells provided by the selected candidate target node that provides the one candidate target cell, for a subsequent second conditional handover after the first conditional handover.

[0035] The 25th aspect is directed to a UE. The UE includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive from a source node a configuration of a plurality of candidate target cells provided by a plurality of candidate target nodes for a first conditional handover of the UE. The at least one processor is configured to apply the configuration corresponding to one of the plurality of candidate target cells if an execution condition of the one candidate target cell is satisfied. Further, the at least one processor is configured to selectively maintain, for a subsequent second conditional handover of the first conditional handover, the configuration of one or more candidate target cells designated by the source node or one or more candidate target nodes among the plurality of candidate target cells excluding the one candidate target cell.

[0036] The 26th aspect is directed to a method performed by a UE. The method includes the following steps: (a) Receiving from a source node a configuration of a plurality of candidate target cells provided by a plurality of candidate target nodes for a first conditional handover of the UE; (b) Applying the configuration corresponding to one of the plurality of candidate target cells if an execution condition of the one candidate target cell is satisfied; and (c) Selectively maintaining, for a subsequent second conditional handover of the first conditional handover, the configuration of one or more candidate target cells designated by the source node or one or more candidate target nodes among the plurality of candidate target cells excluding the one candidate target cell.

[0037] The 27th aspect is directed to a RAN node configured to operate as a candidate target node for a conditional handover of a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to indicate to a source node one or more candidate target cells prepared by the target node for a first conditional handover of the UE. In addition, the at least one processor is configured to indicate to the source node at least one candidate target cell among the one or more candidate target cells, the setting of which needs to be maintained for a subsequent second conditional handover after the first conditional handover.

[0038] The 28th aspect is directed to a method performed by a RAN node configured to operate as a candidate target node for a conditional handover of a UE. The method includes the following steps: (a) indicating to a source node one or more candidate target cells prepared by the target node for a first conditional handover of the UE; and (b) indicating to the source node at least one candidate target cell among the one or more candidate target cells, the setting of which needs to be maintained for a subsequent second conditional handover after the first conditional handover.

[0039] The 29th aspect is directed to a RAN node configured to operate as a source node for conditional handover of a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive a control message from a first candidate target node for a first conditional handover of the UE. The control message indicates one or more candidate target cells prepared by the first candidate target node for the first conditional handover. In addition, the control message indicates at least one candidate target cell among the one or more candidate target cells for which its settings need to be maintained for a subsequent second conditional handover after the first conditional handover.

[0040] The 30th aspect is directed to a method performed by a RAN node configured to operate as a source node for conditional handover of a UE. The method includes receiving a control message from a first candidate target node for a first conditional handover of the UE. The control message indicates one or more candidate target cells prepared by the first candidate target node for the first conditional handover. In addition, the control message indicates at least one candidate target cell among the one or more candidate target cells for which its settings need to be maintained for a subsequent second conditional handover after the first conditional handover.

[0041] The 31st aspect is directed to a program. The program includes a set of instructions (software code) for causing a computer to perform the method according to any of the above aspects when loaded into the computer.

Advantages of the Invention

[0042] According to the above aspect, it is possible to provide an apparatus, a method, and a program that contribute to solving at least one of a plurality of problems related to the realization of a function or an operation mode that enables a subsequent second conditional mobility without reconfiguration or re-initialization from the network after the first conditional mobility.

Brief Description of the Drawings

[0043]

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Modes for Carrying Out the Invention

[0044] Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions may be omitted as necessary for clarity of explanation.

[0045] The plurality of embodiments described below can be implemented independently or in appropriate combination. These plurality of embodiments have different novel features from each other. Therefore, these plurality of embodiments contribute to solving different purposes or problems from each other and contribute to achieving different effects from each other.

[0046] The plurality of embodiments shown below are mainly described with respect to the 3GPP Long Term Evolution (LTE) system and the 5th generation mobile communication system (5G system). However, these embodiments may be applied to other wireless communication systems that support technologies similar to 3GPP's multi-connectivity (e.g., Dual Connectivity). Note that the term LTE as used in this specification includes improvements and developments of LTE and LTE-Advanced for enabling interworking with the 5G System unless otherwise specified.

[0047] As used in this specification, depending on the context, "(if) ~ then" may be interpreted to mean "when", "at or around the time", "after", "upon", "in response to determining", "in accordance with a determination", or "in response to detecting". These expressions may be interpreted to have the same meaning depending on the context.

[0048] First, the configuration and operation of a plurality of network elements common to multiple embodiments are described. FIG. 1 shows a configuration example of a wireless communication system according to multiple embodiments. In the example of FIG. 1, the wireless communication system includes RAN Node 1, RAN Node 2, RAN Node 4, and UE 3. Each element (network function) shown in FIG. 1 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0049] RAN Node 1 may be a Central Unit (e.g., eNB-CU or gNB-CU) in a cloud RAN (C-RAN) deployment, or may be a combination of a CU and one or more Distributed Units (e.g., eNB-DUs or gNB-DUs). C-RAN is also referred to as CU / DU split. Further, the CU may include a Control Plane (CP) Unit (e.g., gNB-CU-CP) and one or more User Plane (UP) Units (e.g., gNB-CU-UP). Thus, RAN Node 1 may be a CU-CP, or may be a combination of a CU-CP and a CU-UP. Similarly, each of RAN Nodes 2 and 4 may be a CU, or may be a combination of a CU and one or more DUs. Each of RAN Nodes 2 and 4 may be a CU-CP, or may be a combination of a CU-CP and a CU-UP.

[0050] Each of RAN nodes 1, 2, and 4 may be an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN) node or a Next generation Radio Access Network (NG-RAN) node. The EUTRAN node may be an eNB or an en-gNB. The NG-RAN node may be a gNB or an ng-eNB. The en-gNB is a node that provides NR user plane and control plane protocol termination to the UE and operates as a secondary node (SN) for E-UTRA-NR Dual Connectivity (EN-DC). The ng-eNB is a node that provides E-UTRA user plane and control plane protocol termination to the UE and is connected to the 5GC via the NG interface. The Radio Access Technology (RAT) of RAN node 1 may be different from those of RAN nodes 2 and 4.

[0051] RAN node 1 and RAN node 2 communicate with each other via an inter-node interface (i.e., X2 interface or Xn interface) 103. RAN node 1 and RAN node 2 operate as the master node (MN) and secondary node (SN) of dual connectivity, respectively. Further, RAN node 1 and RAN node 4 communicate with each other via an inter-node interface (i.e., X2 interface or Xn interface) 105. RAN node 1 and RAN node 4 can each operate as the MN and SN of DC.

[0052] RAN nodes 1, 2, and 4, and UE 3 support inter-SN CPC from the SCG provided by RAN node 2 to the SCG provided by RAN node 4. Therefore, hereinafter, RAN node 1 may be referred to as MN1, RAN node 2 may be referred to as source SN (S-SN) 2, and RAN node 4 may be referred to as target SN (T-SN) 4 or candidate SN4. Inter-SN CPC may be referred to as conditional SN change. Inter-SN CPC (or conditional SN change) is an inter-SN PSCell change procedure (or SN change procedure) that is executed only when the CPC execution conditions are met.

[0053] Although not shown in FIG. 1, a plurality of candidate cells (i.e., candidate PSCs) provided by a plurality of candidate SN4s may be prepared for inter-SN CPC. In the inter-SN CPC procedure, UE 3 receives from MN1 the configuration of one or more candidate PSCs prepared by one or more candidate SNs and one or more CPC execution conditions associated therewith. More specifically, the configuration of each candidate PSC is an information element (IE) (e.g., condRRCReconfig) of the RRC message of MN1, and the configuration of one or more candidate PSCs and the associated CPC execution conditions are included in the conditional mobility configuration information (e.g., conditionalReconfiguration IE) generated by MN1.

[0054] The configuration of each candidate PSCell is generated by a candidate SN (e.g., candidate SN4) that provides (or prepares) this candidate PSCell. The configuration of each candidate PSCell includes at least configuration information for the candidate PSCell. The configuration of each candidate PSCell may further include configuration information for one or more SCells that are associated with (i.e., configured together with or associated with) the candidate PSCell. The configuration of each candidate PSCell may be a radio bearer (RB) configuration, a cell group (CG) configuration, an SCG configuration, or an SCG radio resource configuration, or any combination thereof. More specifically, the configuration of each candidate PSCell may be an SN RRC Reconfiguration message generated by a candidate SN (e.g., candidate SN4) that provides (or prepares) this candidate PSCell. Some or all of the configurations of one or more candidate PSCells are included in the CPC configuration sent from MN1 to UE3. The CPC configuration of Inter-SN CPC is a list of one or more MN RRC Reconfiguration messages. Each MN RRC Reconfiguration message includes the configuration of a candidate PSCell received from a candidate SN (e.g., RB configuration, CG configuration, SCG configuration, SCG radio resource configuration, and one or any combination of SN RRC Reconfiguration messages).

[0055] On the one hand, the CPC execution conditions are generated by MN1 in the case of MN-initiated inter-SN CPC and by the source SN2 in the case of SN-initiated inter-SN CPC. The CPC execution conditions may be composed of one or more trigger conditions. The conditions or criteria for triggering a CPC event may be similar to those for a measurement report event, for example, CondEvent B1, CondEvent A3, CondEvent A4, or CondEvent A5. CondEvent B1 is "Conditional reconfiguration candidate becomes better than absolute threshold". CondEvent A3 is "Conditional reconfiguration candidate becomes amount of offset better than PCell / PSCell". CondEvent A4 is "Conditional reconfiguration candidate becomes better than absolute threshold". CondEvent A5 is "PCell / PSCell becomes worse than absolute threshold1 AND Conditional reconfiguration candidate becomes better than another absolute threshold2". UE3 evaluates the CPC execution conditions. If the execution conditions for one candidate PSCell are satisfied, UE3 applies the settings of the PSCell corresponding to the selected candidate PSCell (i.e., the candidate PSCell whose execution conditions are satisfied), such as RB settings, CG settings, SCG settings, SCG radio resource settings, and one or any combination of SN RRC Reconfiguration messages. If a bearer that requires SCG radio resources is configured, UE3 synchronizes to the selected PSCell.If the execution conditions of two or more candidate PSCs are satisfied, UE3 may select one from these candidate PSCs and perform the operations described above.

[0056] UE3 communicates with MN1 and S-SN2 via air interfaces 101 and 102, and performs dual connectivity of MCG provided by MN1 and SCG provided by S-SN2. Also, by performing inter-SN CPC, UE3 communicates with MN1 and T-SN4 via air interfaces 101 and 104, and performs dual connectivity of MCG provided by MN1 and SCG provided by T-SN4.

[0057] This dual connectivity may be Multi-Radio Dual Connectivity (MR-DC). MR-DC includes E-UTRA-NR Dual Connectivity (EN-DC), NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC), NR-E-UTRA Dual Connectivity (NE-DC), and NR-NR Dual Connectivity (NR-DC). Accordingly, MN1 may be any of a master eNB (in EN-DC), a master ng-eNB (in NGEN-DC), and a master gNB (in NR-DC and NE-DC). Similarly, each of S-SN2 and T-SN4 may be any of an en-gNB (in EN-DC), a secondary ng-eNB (in NE-DC), and a secondary gNB (in NR-DC and NGEN-DC). In EN-DC, UE3 is connected to an eNB operating as MN1 and is also connected to an en-gNB operating as S-SN2 or T-SN4. In NGEN-DC, UE3 is connected to a ng-eNB operating as MN1 and is also connected to a gNB operating as S-SN2 or T-SN4. In NE-DC, UE3 is connected to a gNB operating as MN1 and is also connected to a ng-eNB operating as S-SN2 or T-SN4. In NR-DC, UE3 is connected to one gNB (or gNB-DU) operating as MN1 and is also connected to another gNB (or gNB-DU) operating as S-SN2 or T-SN4.

[0058] MCG is a group of serving cells associated with (or provided to) MN1, including a SpCell (i.e., Primary Cell (PCell)) and optionally one or more Secondary Cells (SCells). On the other hand, SCG is a group of serving cells associated with (or provided to) S-SN2 or T-SN4, including a Primary SCG Cell (PSCell) and optionally one or more Secondary Cells (SCells). The PSCell is the Special Cell (SpCell) of the SCG and supports Physical Uplink Control Channel (PUCCH) transmission and contention-based Random Access. Note that in LTE (e.g., LTE-DC and NE-DC), the PSCell may be an abbreviation of Primary SCell.

[0059] As used herein, the terms "Primary SCG Cell" and its abbreviation "PSCell" mean a cell that is included in a cell group provided by an SN for dual connectivity, has an uplink component carrier, and has an uplink control channel (e.g., PUCCH) resource configured. Specifically, the terms "Primary SCG Cell" and its abbreviation "PSCell" may mean the Primary SCG Cell of a cell group provided by an SN that supports 5G NR (e.g., en-gNB in EN-DC, gNB in NGEN-DC, or gNB in NR-DC), or may mean the Primary SCell of a cell group provided by an SN that supports E-UTRA (e.g., eNB in LTE DC, or ng-eNB in NE-DC).

[0060] Figure 2 shows another configuration example of a wireless communication system according to multiple embodiments. In the example of Figure 2, the wireless communication system includes RAN Node 1, RAN Node 2, and UE 3. Each element (network function) shown in Figure 2 can be implemented, for example, as a network element on dedicated hardware, as a software instance operating on dedicated hardware, or as a virtualized function instantiated on an application platform.

[0061] RAN Node 1, RAN Node 2, and UE 3 in the example of Figure 2 may have the same configuration and functions as those in the example of Figure 1. Specifically, RAN Node 1 and RAN Node 2 communicate with each other via an inter-node interface (i.e., X2 interface or Xn interface) 103. RAN Node 1 and RAN Node 2 each operate as the MN and SN of dual connectivity. UE 3 communicates with MN 1 and SN 2 via air interfaces 101 and 102 and performs dual connectivity of MCG and SCG. This dual connectivity may be Multi-Radio Dual Connectivity (MR-DC).

[0062] RAN Nodes 1 and 2 and UE 3 support conditional PSCell addition (CPA) that adds the SCG provided by RAN Node 2 for UE 3. Therefore, hereinafter, RAN Node 1 may be referred to as MN 1, and RAN Node 2 may be referred to as candidate SN 2. CPA may be referred to as conditional SN addition. CPA (or conditional SN addition) is a PSCell addition procedure (or SN addition procedure) that is executed only when the CPA execution condition is satisfied.

[0063] Although not shown in FIG. 2, a plurality of candidate PSCs provided by a plurality of candidate SNs 2 may be prepared for CPA. In the CPA procedure, the UE 3 receives from the MN 1 the setting of one or more candidate PSCs prepared by one or more candidate SNs and one or more CPA execution conditions associated therewith. More specifically, the setting of each candidate PSC is an information element (IE) (e.g., condRRCReconfig) of the RRC message of the MN 1, and the setting of one or more candidate PSCs and the associated CPA execution conditions are included in the conditional mobility setting information (e.g., conditionalReconfiguration IE) generated by the MN 1.

[0064] The setting of each candidate PSC is generated by the candidate SN (e.g., candidate SN 2) that provides (or prepares) this candidate PSC. The setting of each candidate PSC includes at least setting information for the candidate PSC. The setting of each candidate PSC may further include setting information for one or more SCells associated with (i.e., set together with or associated with) the candidate PSC. The setting of each candidate PSC may be one or any combination of RB setting, CG setting, SCG setting, and SCG radio resource setting. More specifically, the setting of each candidate PSC may be an SN RRC Reconfiguration message generated by the candidate SN (e.g., candidate SN 2) that provides (or prepares) this candidate PSC. Some or all of the settings of one or more candidate PSCs are included in the CPA setting sent from the MN 1 to the UE 3. The CPA setting is a list of one or more MN RRC Reconfiguration messages. Each MN RRC Reconfiguration message includes the setting of the candidate PSC received from the candidate SN (e.g., one or any combination of RB setting, CG setting, SCG setting, SCG radio resource setting, and SN RRC Reconfiguration message).

[0065] On one hand, the CPA execution conditions are generated by MN1. The CPA execution conditions may be composed of one or more trigger conditions. The conditions or criteria for triggering a CPA event may be similar to those for a measurement report event, for example, CondEvent A3, CondEvent A4, or CondEvent A5. UE3 evaluates the CPA execution conditions. If the execution conditions of one candidate PSCell are met, UE3 applies the configuration of the PSCell corresponding to the selected candidate PSCell (i.e., the candidate PSCell whose execution conditions are met), such as CG configuration, SCG configuration, SCG radio resource configuration, or SN RRC Reconfiguration message. If there is a bearer configured that requires SCG radio resources, UE3 synchronizes to the selected PSCell. If the execution conditions of two or more candidate PSCs are met, UE3 may select one from those candidate PSCs and perform the above operations.

[0066] In addition, RAN node 2 and UE3 support intra-SN CPC. Intra-SN CPC may be called conditional SN modification initiated by the SN without MN involvement. Intra-SN CPC is an intra-SN PSCell change procedure that is executed only when the CPC execution conditions are met.

[0067] In the intra-SN CPC procedure, the UE3 receives from the SN2 the configuration of one or more candidate PSCs prepared by the SN2 and one or more CPC execution conditions associated therewith. The configuration of each candidate PSC and the associated CPC execution conditions are included in the CPC configuration for intra-SN CPC. The SN2 may send these to the UE3 via the MN1, or may send them to the UE3 via a direct signaling radio bearer (i.e., Signaling Radio Bearer 3 (SRB3)) between the SN2 and the UE3. More specifically, the configuration of each candidate PSC is an information element (IE) (e.g., condRRCReconfig) of the RRC message of the SN2, and the configuration of one or more candidate PSCs and the associated CPC execution conditions are included in the conditional mobility configuration information (e.g., conditionalReconfiguration IE) generated by the SN2.

[0068] The configuration of each candidate PSC includes at least the configuration information for the candidate PSC. The configuration of each candidate PSC may further include the configuration information for one or more SCells associated with (i.e., configured together with or associated with) the candidate PSC. The configuration of each candidate PSC may be a radio bearer (RB) configuration, a cell group (CG) configuration, an SCG configuration, or an SCG radio resource configuration, or any combination thereof. Specifically, the configuration of each candidate PSC may be an SN RRC Reconfiguration message generated by the SN2.

[0069] The CPC execution conditions of the Intra-SN CPC may be constituted by one or more trigger conditions. The conditions or criteria for triggering a CPC event may be similar to those for a measurement report event, and may be, for example, CondEvent A3, CondEvent A4, or CondEvent A5. UE3 evaluates the CPC execution conditions. If the execution conditions of one candidate PSCell are satisfied, UE3 detaches from the source PSCell, applies the settings corresponding to the selected candidate PSCell (i.e., the candidate PSCell whose execution conditions are satisfied), and synchronizes with the selected candidate PSCell. If the execution conditions of two or more candidate PSCs are satisfied, UE3 may select one from those candidate PSCs and perform the above-described operations.

[0070] FIG. 3 shows still another configuration example of a wireless communication system according to a plurality of embodiments. In the example of FIG. 3, the wireless communication system includes RAN node 6, RAN node 7, and UE3. Each element (network function) shown in FIG. 3 can be implemented, for example, as a network element on dedicated hardware, as a software instance operating on dedicated hardware, or as a virtualized function instantiated on an application platform. Each of RAN nodes 6 and 7 may be an EUTRAN node or an NG-RAN node. The EUTRAN node may be an eNB or an en-gNB. The NG-RAN node may be a gNB or an ng-eNB. The RAT of RAN node 6 may be different from that of RAN node 7.

[0071] RAN node 6 provides at least one cell 61. RAN node 7 provides one or more cells (e.g., four cells 71 - 74). In the example of FIG. 3, the cell 61 provided by RAN node 6 is the current serving cell of UE3, and UE3 is handed over from cell 61 to any of the cells provided by RAN node 7. Thus, hereinafter, RAN node 6 may be referred to as the source node or source RAN node, and RAN node 7 may be referred to as the target node or target RAN node. Cell 61 is referred to as the source cell. Source node 6, target node 7, and UE3 support conditional handover (CHO). CHO is a handover procedure that is executed only when the CHO execution conditions are met.

[0072] Although not shown in FIG. 3, a plurality of candidate target cells provided by a plurality of candidate target nodes 7 may be prepared for CHO. In the CHO procedure, UE3 receives the configuration of one or more candidate target cells prepared by one or more candidate target nodes and one or more CHO execution conditions (e.g., condExecutionCond) associated therewith from source node 6. The configuration of one or more candidate target cells and the associated CHO execution conditions are included in the CHO configuration. More specifically, the configuration of each candidate target cell is an information element (IE) (e.g., condRRCReconfig) of the RRC message of source node 6, and the configuration of one or more candidate target cells and the associated CHO execution conditions are included in the conditional mobility configuration information (e.g., conditionalReconfiguration IE) generated by source node 6.

[0073] The setting of each candidate target cell is generated by a candidate target node (e.g., target node 7) that provides (or prepares) this candidate target cell. The setting of each candidate target cell may be a radio bearer (RB) setting, a radio resource setting, or an RRC Reconfiguration message, or any combination thereof, generated by a candidate target node (e.g., target node 7) that provides (or prepares) this candidate target cell.

[0074] On the other hand, the CHO execution conditions are generated by the source node 6. The CHO execution conditions may be composed of one or more trigger conditions. The conditions or criteria for triggering a CHO event may be similar to those for a measurement report event, for example, CondEvent A3, CondEvent A4, or CondEvent A5. UE3 evaluates the CHO execution conditions. If the execution conditions of one candidate target cell are met, UE3 detaches from the source node 6, applies the settings corresponding to the selected candidate target cell (i.e., the candidate target cell whose execution conditions are met), and synchronizes with the selected candidate target cell. If the execution conditions of two or more candidate target cells are met, UE3 may select one from these candidate target cells and perform the above operations.

[0075] One or more of RAN nodes 1, 2, 4, 6, and 7 may have the configuration shown in FIG. 4. Each element (network function) shown in FIG. 4 can be implemented, for example, as a network element on dedicated hardware, as a software instance operating on dedicated hardware, or as a virtualized function instantiated on an application platform. One or more of RAN nodes 1, 2, 4, 6, and 7 may include, but are not limited to, a CU 41 and one or more DUs 42 as shown in FIG. 4. The CU 41 and each DU 42 are connected by an interface 401. The UE 3 is connected to at least one DU 42 via at least one air interface 402.

[0076] The CU 41 may be a logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols of the gNB (or the RRC and PDCP protocols of the gNB). The DU 42 may be a logical node that hosts the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers of the gNB. If the CU 41 is a gNB-CU and the DUs 42 are gNB-DUs, the interface 401 may be an F1 interface. The CU 41 may include a CU-CP and a CU-UP.

[0077] In this specification, the term conditional mobility is used. Conditional mobility is a general term that refers to one or more of CHO, CPA, intra-SN CPC (or conditional SN modification), and inter-SN CPC (or conditional SN change).

[0078] The embodiments described below provide an improvement in conditional mobility. Specifically, the following embodiments provide an improvement in conditional mobility for supporting a function or operation mode called "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups". Note that in this specification, the function or operation mode may be applied to conditional mobility that does not necessarily involve MR-DC, i.e., CHO. Further, the function or operation mode may be applied to an improved CHO in which an SCG (at least the PSCell) is added along with the execution of CHO. In the definition in this specification, the function or operation mode, for example, enables subsequent second conditional mobility without at least re-initialization of conditional mobility preparation after changing or adding a serving cell, serving cell group, PSCell, or SCG in the first conditional mobility. In other words, in the definition in this specification, the function or operation mode, for example, enables UE3 to reuse or maintain at least a part of the candidate target cell setting or candidate PSCell setting (e.g., one or any combination of RB setting, CG setting, SCG setting, radio resource setting, and SCG radio resource setting) received from the network in the first conditional mobility for subsequent second conditional mobility. At least a part of the execution conditions for the first conditional mobility may be reset, updated, or modified for the second conditional mobility. Similarly, at least a part of the information regarding the setting of the security key for the first conditional mobility (e.g., sk-Counter, Next Hop (NH), NH Chaining Count (NCC)), or the security key information (e.g., SN Security Key) may be reset, updated, or modified for the second conditional mobility. The type of the second conditional mobility may be different from the type of the first conditional mobility.For example, while the first conditional mobility is CPA, the second conditional mobility may be Inter-SN CPC or Intra-SN CPC. Alternatively, while the first conditional mobility is Inter-SN CPC, the second conditional mobility may be Intra-SN CPC.

[0079] The function or operation mode may be called, but not limited to, for example, selective cell activation, selective cell group (CG) activation, selective SCG activation, adaptive cell switch, adaptive CG switch, adaptive SCG switch, subsequent cell change, subsequent CG change, subsequent CG selection, CPC kept, or CHO kept. For the sake of convenience of explanation, in the following embodiments, the function or operation mode is called selective CG activation or selective cell activation. The term selective CG activation may be used for conditional mobility (e.g., CPA, inter-SN CPC, intra-SN CPC) involving MR-DC. On the other hand, the term selective cell activation may be used for conditional mobility (e.g., CHO) not necessarily involving MR-DC.

[0080] In this specification, a combination of a candidate Special Cell (SpCell) and SCell(s) may be referred to as a candidate Cell Group (CG) set for conditional mobility or selective CG activation. Selective CG activation can also be regarded as a change or switch of the serving SCG among a plurality of candidate CG sets. One candidate CG set includes at least a candidate SpCell and optionally one or more SCells. A candidate cell (candidate SpCell) may be the current SCell (i.e., the SCell included in the current SCG) or a non-serving cell not provided to the UE3. The UE3 may be configured with a plurality of candidate CG sets in which those candidate SpCells are different from each other. If it is conditional mobility (e.g., CHO) regarding the MCG, the candidate SpCells are candidate PCells and the plurality of candidate CG sets are a plurality of candidate MCG sets. On the other hand, if it is conditional mobility (e.g., CPA, intra-SN CPC, inter-SN CPC) regarding the SCG, the candidate SpCells are candidate PSCs and the plurality of candidate CG sets are a plurality of candidate SCG sets.

[0081] In this specification, the terms MN RRC message, MN RRC Reconfiguration message, SN RRC message, and SN RRC Reconfiguration message are used. These terms are used for convenience to distinguish RRC messages generated by the MN from RRC messages generated by the SN. Therefore, the MN RRC message and the MN RRC Reconfiguration message may simply be referred to as the RRC message and the RRC Reconfiguration message. Similarly, the SN RRC message and the SN RRC Reconfiguration message may simply be referred to as the RRC message and the RRC Reconfiguration message.

[0082] <The first embodiment> This embodiment provides improvements to CPA and inter-SN CPC for selective CG activation. Specifically, this embodiment relates to clarifying various procedures regarding selective CG / cell activation. A configuration example of the wireless communication system according to this embodiment may be the same as the example shown in FIG. 1 or FIG. 2.

[0083] In a first implementation, MN1 determines whether to perform, utilize, prepare for, or recommend selective CG activation before sending a CPA request to candidate SN2 or before sending a CPC request to candidate (target) SN4. The CPC request may be sent by MN1 in response to MN1 determining to initiate inter-SN CPC (i.e., MN-initiated inter-SN CPC). Alternatively, the CPC request may be sent by MN1 in response to source SN2 determining to initiate inter-SN CPC (i.e., SN-initiated inter-SN CPC). In other words, in SN-initiated inter-SN CPC, the CPC request may be sent by MN1 in response to source SN2 determining to initiate inter-SN CPC and requesting MN1 to execute it. If it is determined to perform, utilize, prepare for, or recommend selective CG activation, MN4 operates as shown in FIG. 5.

[0084] In step 501, MN1 includes an indication regarding selective CG activation in the CPA request or CPC request message. In step 502, MN1 sends the CPA request message or CPC request message to candidate SN2 or 4. The CPA request message indicates that one or more candidate PSCs need to be prepared by candidate SN2 for CPA. The CPC request message indicates that one or more candidate PSCs need to be prepared by candidate SN4 for inter-SN CPC.

[0085] The CPA request messages in steps 501 and 502 may be SN Addition Request messages for conditional SN addition. At this time, the CPA request may be indicated by a Conditional PSCell Addition Information Request IE. The CPC request message may be an SN Addition Request message for conditional SN change. At this time, the CPC request may be indicated by a Conditional PSCell Addition Information Request IE, or a Conditional PSCell Change Information Request IE. The indication regarding selective CG activation indicates to candidate SN2 or 4 that selective CG activation is required or recommended for a subsequent CPC after the CPA or inter-SN CPC. The subsequent CPC may be an inter-SN CPC or an intra-SN CPC. The indication regarding selective CG activation may be called, but is not limited to, for example, "Selective CG activation request", "CPC kept request", or "Store CPC request".

[0086] In the second implementation, when initiating an SN-initiated inter-SN CPC, the source SN2 determines whether to perform, utilize, prepare for, or recommend selective CG activation. If it is determined to perform, utilize, prepare for, or recommend selective CG activation, the source SN2 operates as shown in FIG. 6. In step 601, the source SN2 includes an indication regarding selective CG activation in an SN Change Required message for conditional SN change. In step 602, the source SN2 sends the SN Change Required message to MN1.

[0087] The SN Change Required messages in steps 601 and 602 indicate one or more candidate PSCs recommended by source SN2 for inter-SN CPC. At this time, that it is a message for inter-SN CPC may be indicated by the message including the Conditional PSCell Change Information Required IE. The indication regarding selective CG activation indicates to MN1 that selective CG activation is required or recommended for subsequent CPC after the inter-SN CPC. The subsequent CPC may be an inter-SN CPC or an intra-SN CPC. The indication regarding selective CG activation may be called, but not limited to, for example, "Selective CG activation required", "CPC kept required", or "Store CPC required".

[0088] In the third implementation, candidate SN2 or 4 determines whether to perform, utilize, prepare, or recommend selective CG activation in response to receiving a CPA request or a CPC request from MN1. Candidate SN2 or 4 operates as shown in FIG. 7. In step 701, candidate SN2 or 4 receives a CPA request or a CPC request message from MN1. The CPA request message indicates that one or more candidate PSCs need to be prepared by candidate SN2 for CPA. The CPC request message indicates that one or more candidate PSCs need to be prepared by candidate SN4 for inter-SN CPC. The CPA request message may be an SN Addition Request message for conditional SN addition. The CPC request message may be an SN Addition Request message for conditional SN change.

[0089] In step 702, candidate SN2 or 4 accepts to prepare at least one of the one or more candidate PSCs required by MN1. Additionally, candidate SN2 or 4 determines whether to perform, utilize, prepare, or recommend selective CG activation. If it is determined to perform, utilize, prepare, or recommend selective CG activation, candidate SN2 or 4 includes an indication regarding selective CG activation in the CPA request acknowledge or CPC request acknowledge message. In step 703, candidate SN2 or 4 sends the CPA request acknowledge or CPC request acknowledge message to MN1.

[0090] The CPA request acknowledge or CPC request acknowledge message in steps 702 and 703 indicates at least one candidate PSC prepared by candidate SN2 or 4. The CPA request acknowledge message may be an SN Addition Request Acknowledge message for conditional SN addition. The CPC request acknowledge message may be an SN Addition Request Acknowledge message for conditional SN change. The indication regarding selective CG activation indicates to MN1 that selective CG activation is required or recommended for a subsequent CPC after the said CPA or inter-SN CPC. The subsequent CPC may be an inter-SN CPC or an intra-SN CPC. The indication regarding selective CG activation may be called, but is not limited to, for example, "Selective CG activation request", "Selective CG activation indication", "CPC kept request", "CPC kept indication", "Store CPC request", or "Store CPC indication".

[0091] In the fourth implementation, the selected candidate SN2 or 4 that provides the candidate PSCell selected by UE3 in response to the CPA or CPC execution condition being satisfied determines whether to perform, utilize, prepare for, or recommend selective CG activation. The selected candidate SN2 or 4 operates as shown in FIG. 8. In step 801, the candidate SN2 or 4 prepares one or more candidate PSCells for UE3 for CPA or inter-SN CPC. In other words, the candidate SN2 or 4 prepares one or more candidate PSCells for conditional SN addition or change for UE3. In step 801, the candidate SN2 or 4 may exchange signaling with MN1 in the same manner as the existing CPA or inter-SN CPC. Specifically, the candidate SN2 or 4 may receive a CPA request or CPC request message from MN1 and send a CPA request acknowledgment or CPC request acknowledgment message to MN1. The CPA request or CPC request message may be an SN Addition Request message for conditional SN addition or change. The CPA request acknowledgment or CPC request acknowledgment message may be an SN Addition Request Acknowledge message for conditional SN addition or change.

[0092] In step 802, if one of the candidate SN2 or 4 and one or more candidate PSCs are selected by UE3, the SN RRC message including the indication regarding selective CG activation is sent to UE3. The SN RRC message may be an SN RRC Reconfiguration message. The indication indicates to UE3 that selective CG activation is required or recommended for the subsequent CPC after the CPA or inter-SN CPC. The subsequent CPC may also be an intra-SN CPC. In other words, the subsequent CPC may be an intra-SN CPC to one or more other candidate PSCs not selected by UE3 among the plurality of candidate PSCs prepared for the CPA or inter-SN CPC by the selected candidate SN2 or 4. The indication regarding selective CG activation may be called, but not limited to, for example, "Selective CG activation indication", "CPC kept indication", "Store CPC indication", or "Keep unused CPC configuration indication".

[0093] Figure 9 shows an example of the signaling in the CPC preparation phase in the inter-SN CPC (or conditional SN change) procedure. In step 901, when the source SN2 starts the inter-SN CPC, the source SN2 sends an SN Change Required message to MN1. The SN Change Required message includes a list of proposed PSCell candidates recommended by the source SN2 and the associated CPC execution conditions. Step 901 is omitted in the case of MN-initiated inter-SN CPC.

[0094] In step 902, MN1 sends a SN Addition Request message to each of one or more candidate target SNs 4 (e.g., SN4A and 4B). The SN Addition Request message includes a list of PSCell candidates. The list indicates one or more candidate PSCs proposed by MN1 in the case of MN-initiated inter-SN CPC, or one or more candidate PSCs proposed by the source SN2 in the case of SN-initiated inter-SN CPC.

[0095] In step 903, each candidate target SN4 sends a SN Addition Request Acknowledge message to MN1. The SN Addition Request Acknowledge message includes the configuration of each of one or more candidate PSCs prepared by the candidate target SN4. As already explained, the configuration of each candidate PSC may be one or any combination of RB configuration, CG configuration, SCG configuration, SCG radio resource configuration, and SN RRC Reconfiguration message.

[0096] In the case of SN-initiated inter-SN CPC, step 904 or steps 904 and 905 may be performed. In step 904, MN1 may, if necessary, indicate to the source SN2 one or more candidate PSCs accepted by the candidate target SN4, for example, if the candidate target SN4 has not accepted all candidate PSCs proposed by the source SN2. In step 905, the source SN2 may provide MN1 with settings (e.g., measurement settings, or CPC execution conditions) for the updated or modified CPC.

[0097] In step 906, MN1 transmits an MN RRC Reconfiguration message (RRC Reconfiguration*) to UE3, which includes the CPC configuration (e.g., condRRCReconfig) and the associated CPC execution conditions. The CPC configuration of the Inter-SN CPC is a list of one or more MN RRC Reconfiguration messages (RRC Reconfiguration**). Each MN RRC Reconfiguration message (RRC Reconfiguration**) includes the configuration of the candidate PSCell received from the candidate SN (i.e., the SN RRC Reconfiguration message (RRC Reconfiguration***)). The CPC configuration (i.e., the list of MN RRC Reconfiguration messages (RRC Reconfiguration**)) and the associated CPC execution conditions are included in the conditional mobility configuration information (e.g., conditionalReconfiguration IE) within the MN RRC Reconfiguration message (RRC Reconfiguration*).

[0098] In the first implementation described above, as shown in FIG. 9 as option 1, MN1 includes an indication regarding selective CG activation in the SN Addition Request message (step 902). The candidate target SN4 may include an indication in the SN Addition Request Acknowledge message (step 903) indicating whether selective CG activation is accepted or not.

[0099] In the above-described second implementation, as shown in FIG. 9 as Option 2, the source SN2 includes a display regarding selective CG activation in the SN Change Required message (step 901). MN1 may include a display regarding selective CG activation in the SN Addition Request message (step 902). The candidate target SN4 may include a display indicating whether the selective CG activation is accepted in the SN Addition Request Acknowledge message (step 903). MN1 may indicate to the source SN2, for example, in step 904, whether the selective CG activation requested, recommended, or proposed by the source SN2 has been accepted.

[0100] In the above-described third implementation, as shown in FIG. 9 as Option 3, the candidate target SN4 includes a display regarding selective CG activation in the SN Addition Request Acknowledge message (step 903). In this case, MN1 may indicate to the candidate target SN4 whether the selective CG activation is accepted. For example, as shown in step 1003 of FIG. 10, MN1 may send a control message (e.g., Xn or X2 message) indicating acceptance or rejection of the selective CG activation to the candidate target SN4. The control message may be sent only when MN1 accepts the selective CG activation requested, recommended, or proposed by the candidate target SN4, or alternatively, may be sent only when MN1 rejects it. Steps 1001 and 1002 in FIG. 10 are the same as steps 902 and 903 in FIG. 9.

[0101] In any of the first to third implementations, the MN RRC Reconfiguration message in step 906 may include an indication regarding selective CG activation. In other words, MN1 may inform UE3 via the MN RRC Reconfiguration message in step 906 that selective CG activation is required, recommended, or available. In the first implementation described above, this indication may be generated by MN1 and be one of the information elements (IEs) within the MN RRC Reconfiguration message. In the second implementation described above, this indication may be generated by source SN2, sent from source SN2 to MN1 via the SN RRC information element (Information Element (IE)) or SN RRC Reconfiguration, and may be embedded in the MN RRC Reconfiguration message. In the third and fourth implementations described above, this indication may be generated by candidate SN4, sent from source SN2 to MN1 via the SN RRC IE or SN RRC Reconfiguration, and may be embedded in the MN RRC Reconfiguration message.

[0102] Figure 11 shows an example of the signaling of the inter-SN CPC (or conditional SN change) procedure for the above-described fourth implementation. In step 1101, MN1, source SN2, and one or more candidate target SN4s (e.g., candidate target SN4A and 4B) prepare for the inter-SN CPC. In step 1102, MN1 sends a MN RRC Reconfiguration message (RRC Reconfiguration*) including the CPC setting and associated CPC execution conditions to UE3. The MN RRC Reconfiguration message in step 1102 indicates the inter-SN CPC. Additionally, the MN RRC Reconfiguration message may indicate to UE3 that selective CG activation is planned, predicted, or possible for subsequent intra-SN or inter-SN CPCs after the inter-SN CPC.

[0103] In step 1103, if the execution condition of one of the prepared candidate PSCs is met, UE3 executes the CPC (i.e., SN change or PSCell change) by applying the setting of the selected candidate PSCell (i.e., the candidate PSCell whose execution condition is met). In the example of Figure 11, UE3 selects one of the one or more candidate PSCs prepared by candidate target SN4A. Note that UE3 maintains or holds the CPC execution conditions associated with the settings of one or more other candidate PSCs without releasing them after the establishment of the CPC execution condition. UE3 may selectively maintain or hold only the settings of one or more other candidate PSCs prepared by the selected candidate SN4A. UE3 may operate in this way when the MN RRC Reconfiguration message in step 1102 indicates the plan, prediction, or possibility of selective CG activation.

[0104] In step 1104, the selected candidate SN4A sends an SN RRC message including an indication regarding selective CG activation to UE3. The SN RRC message may be an SN RRC Reconfiguration message. The indication indicates to UE3 that selective CG activation is required or recommended for subsequent CPCs after the inter-SN CPC. The subsequent CPC may also be an intra-SN CPC. In response to receiving the indication in step 1104, UE3 maintains or holds the CPC settings that were not used (i.e., the settings of the candidate PSCell) for subsequent CPCs (step 1105). UE3 may selectively maintain or hold only the settings of one or more other candidate PSCs prepared by the selected candidate SN4A. In addition to the CPC settings that were not used, UE3 may also maintain or hold the associated CPC execution conditions. If the indication in step 1104 is not received, UE3 may release the CPC settings (and CPC execution conditions) that were tentatively maintained or held.

[0105] In addition, when the UE3 selects a candidate PSCell provided by the candidate SN4A (or 4B), the candidate SN4A (or 4B) may notify the UE3 in advance that there is a possibility (or the setting information therefor) of performing selective CG activation for other candidate PSCs provided by the candidate SN4A (or 4B). For example, when transmitting the setting information for inter-SN CPC to the UE3 via the MN1, the candidate SN4A (or 4B) may give such notification. When receiving the notification, the UE3 may (temporarily) hold the setting information for inter-SN CPC of the unselected candidate PSCell in consideration of the possibility of performing selective CG activation even when inter-SN CPC is executed. Further or alternatively, when supporting selective CG activation, the UE3 may (temporarily) hold the setting information for inter-SN CPC of the unselected candidate PSCell autonomously until receiving the above-mentioned SN RRC message (step 1104) from the candidate SN4A.

[0106] FIG. 12 shows an example of the signaling of the inter-SN CPC (or conditional SN change) procedure according to this embodiment. The MN1 may notify the candidate SN4 (selected candidate SN4) (e.g., 4A) that provides the candidate PSCell selected by the UE3 of the candidate PSCell(s) prepared by another candidate SN4 (e.g., 4B) to which selective CG activation is applied. Based on this information, the selected candidate SN4 (e.g., 4A) may update the measurement setting and / or the CPC execution condition or both. The selected candidate SN4 (e.g., 4A) may transmit the updated measurement setting and / or execution condition to the UE3 via the MN1.

[0107] Additionally or alternatively, MN1 may inform a non-selected candidate target SN4 (e.g., 4B) of candidate PSCell(s) prepared by another candidate SN4 (e.g., 4A) to which selective CG activation is applied (or imposed). Based on this information, the non-selected candidate SN4 (e.g., 4B) may update the measurement configuration or the CPC execution conditions or both. The non-selected candidate SN4 (e.g., 4B) may transmit the updated measurement configuration and / or execution conditions to UE3 via MN1.

[0108] Additionally or alternatively, MN1 may inform source SN2 of candidate PSCell(s) prepared by other candidate SN4s (e.g., 4A and 4B) to which selective CG activation is applied (or imposed). This may be done when selective CG activation is applied or imposed on the immediately preceding serving PSCell provided by source SN2. Based on this information, source SN2 may update the measurement configuration and may generate CPC execution conditions. Source SN2 may transmit the updated measurement configuration and / or the generated execution conditions to UE3 via MN1.

[0109] In step 1201 of FIG. 12, an inter-SN CPC is prepared. In step 1202, UE3 evaluates the CPC execution conditions. If the execution condition of one candidate PSCell is satisfied, UE3 sends a corresponding MN RRC Reconfiguration Complete message to MN1 (step 1203). This MN RRC Reconfiguration Complete message includes an SN RRC Reconfiguration Complete message for the candidate PSCell whose execution condition is satisfied (i.e., the selected candidate PSCell), and further includes information on the selected candidate PSCell. The information on the selected candidate PSCell may be implicitly (or indirectly) indicated by an identifier (e.g., CondReconfigId) associated with the configuration of the candidate PSCell and the CPC execution condition (e.g., condExecutionCond or condExecutionCondSN).

[0110] In step 1204, MN1 may notify the selected candidate SN4 (e.g., 4A) of the candidate PSCell(s) prepared by other candidate SN4s (e.g., 4B) to which selective CG activation is applied. For the transmission in step 1204, an existing SN Reconfiguration Complete message including an SN RRC Reconfiguration Complete message for the selected candidate PSCell may be reused or extended. Alternatively, a new Xn / X2 message may be defined for the transmission in step 1204.

[0111] In step 1205, MN1 may inform a candidate SN4 (e.g., 4B) that was not selected of the candidate PSCell(s) prepared by another candidate SN4 (e.g., 4A) to which selective CG activation is applied. An existing Xn / X2 message for CPC Cancel (e.g., CPC Cancel, SN Release Request, or UE Context Release) may be reused or extended for the transmission in step 1205. Alternatively, a new Xn / X2 message may be defined for the transmission in step 1205.

[0112] In step 1206, MN1 may inform source SN2 of the candidate PSCell(s) prepared by other candidate SN4s (e.g., 4A and 4B) to which selective CG activation is applied. An existing Xn / X2 message for UE context release (e.g., UE Context Release) may be reused or extended for the transmission in step 1206. Alternatively, a new Xn / X2 message may be defined for the transmission in step 1206. Note that the order from step 1204 to 1206 is not limited.

[0113] The operations of the above-described MN1, source SN2, candidate SN4, and UE3 may be modified as follows. In some implementations, selective CG activation may be applied or imposed on the immediately preceding serving PSCell provided by the source SN2. In this case, after the inter-SN CPC is completed, UE3 maintains the settings of the immediately preceding serving PSCell for reuse in subsequent CPCs. In the case of MN-initiated inter-SN CPC, MN1 may notify the source SN2 that selective CG activation is applied to or required for the source PSCell. In the case of SN-initiated inter-SN CPC, the source SN2 may notify MN1 that selective CG activation is applied to or possible for the source PSCell. For example, the source SN2 may include an indication indicating the application of selective CG activation to the source PSCell in the SN Change Required message at step 901 of FIG. 9. The indication may be, but is not limited to, for example, "S-SN kept" or "Source PSCell kept". MN1 may notify the candidate SN4 that selective CG activation is applied to or required for the source PSCell. For example, MN1 may include an indication indicating the application of selective CG activation to the source PSCell in the SN Addition Request message at step 902 of FIG. 9. The indication may be, but is not limited to, for example, "S-SN kept".

[0114] MN1 may reset, update, or modify the security key information (e.g., SN Security Key) for selective CG activation and send it to the candidate SN4 (e.g., 4A) selected by UE3 in the inter-SN CPC. For example, MN1 may send the security key information to the selected candidate SN4 (e.g., 4A) in a message that is the same as or different from the message in step 1204. Further, MN1 may reset, update, or modify at least a part of the information related to the security key setting (e.g., sk-Counter, Next Hop (NH), NH Chaining Count (NCC)) for selective CG activation and send it to UE3.

[0115] MN1 may reset, update, or modify the security key information (e.g., SN Security Key) for selective CG activation and send it to the candidate SN4 (e.g., 4B) not selected by UE3 in the inter-SN CPC. For example, MN1 may send the security key information to the unselected candidate SN4 (e.g., 4B) in a message that is the same as or different from the message in step 1205. Further, MN1 may reset, update, or modify at least a part of the information related to the security key setting (e.g., sk-Counter, Next Hop (NH), NH Chaining Count (NCC)) for selective CG activation and send it to UE3.

[0116] The operations of MN1, source SN2 (or candidate SN2 at the CPA), candidate SN4, and UE3, and the procedures described in this embodiment can contribute to clarifying the procedures for enabling selective CG activation for CPA and inter-SN CPC. Specifically, these can clarify which node (e.g., MN, source SN, or candidate SN) makes the decision on whether to utilize selective CG activation for CPA and inter-SN CPC, and when this decision is made.

[0117] <Second Embodiment> This embodiment provides improvements to CPA and inter-SN CPC for selective CG activation. This embodiment relates to reusing the settings of multiple candidate PSCs for CPA or Inter-SN CPC (or conditional SN change) for subsequent CPC. The configuration example of the wireless communication system according to this embodiment may be the same as the example shown in FIG. 1 or FIG. 2.

[0118] In the first implementation, UE3 maintains or holds all the configurations of one or more candidate PSCs other than the selected one among the configurations of multiple candidate PSCs for CPA or inter-SN CPC for subsequent CPC. As already explained, the configuration of each candidate PSC may be one or any combination of RB configuration, CG configuration, SCG configuration, SCG radio resource configuration, and SN RRC Reconfiguration message. UE3 may further maintain or hold the associated CPA or CPC execution conditions as the CPC execution conditions for subsequent CPC. UE3 may update or modify one or more CPC execution conditions in response to an instruction from MN1 or candidate SN2 or 4, or autonomously. For example, UE3 may switch the reference cell in one or more CPC execution conditions (e.g., CondEvent A3 or CondEvent A5) from the serving PSC provided by the source cell of the first CPC (i.e., the serving PSC provided by source SN2) to the selected PSC provided by the selected candidate SN2 or 4.

[0119] In the second implementation, UE3 selectively maintains or holds only the configurations of one or more other candidate PSCs provided by the selected candidate SN2 or 4 that provides the candidate PSC selected in the first CPA or CPC for subsequent CPC after the first CPA or CPC. Thus, in the second implementation, the subsequent CPC is an intra-SN CPC within the selected candidate SN2 or 4. The configuration of each candidate PSC may be one or any combination of RB configuration, CG configuration, SCG configuration, SCG radio resource configuration, and SN RRC Reconfiguration message. Similar to the first implementation, UE3 may maintain or hold the associated CPC execution conditions for subsequent CPC. UE3 may update or modify one or more CPC execution conditions in response to an instruction from MN1 or candidate SN2 or 4, or autonomously.

[0120] In the third implementation, UE3 selectively maintains or holds the configuration of one or more candidate PSCs designated by MN1 or one or more candidate SN2s or 4s among the candidate PSCs other than the candidate PSC selected in the first CPA or CPC for the subsequent CPC. The configuration of each candidate PSC may be one or any combination of RB configuration, CG configuration, SCG configuration, SCG radio resource configuration, and SN RRC Reconfiguration message. Similar to the first implementation, UE3 may maintain or hold the associated CPC execution conditions for the subsequent CPC. UE3 may update or modify one or more CPC execution conditions in response to an instruction from MN1 or candidate SN2 or 4, or autonomously.

[0121] Figure 13 shows an example of the operation of UE3 in the second implementation. In step 1301, UE3 receives from MN1 the configurations of a plurality of candidate PSCs provided by a plurality of candidate SN2s or 4s for conditional SN addition (i.e., CPA) or SN change (i.e., inter-SN CPC). UE3 also receives from MN1 a plurality of CPC execution conditions associated with the plurality of candidate PSCs. In step 1302, UE3 evaluates the plurality of CPC execution conditions. If the execution condition of one of the plurality of candidate PSCs is satisfied, UE3 applies the configuration corresponding to the selected candidate PSC (i.e., the candidate PSC whose execution condition is satisfied). In step 1303, UE3 selectively maintains only the configurations of one or more other candidate PSCs provided by the selected candidate SN2 or 4 that provides the selected candidate PSC for subsequent conditional PSC change (i.e., intra-SN CPC).

[0122] FIG. 14 shows an example of the operation of UE3 in the third implementation. Steps 1401 and 1402 are the same as steps 1301 and 1302 in FIG. 13. In step 1403, UE3 selectively maintains the configuration of one or more candidate PSCs specified by MN1 or one or more candidate SN2s or 4s among a plurality of candidate PSCs other than the selected candidate PSC for subsequent conditional PSCell change (i.e., inter-SN CPC).

[0123] FIG. 15 shows an example of the signaling in the CPC preparation phase in the inter-SN CPC (or conditional SN change) procedure for the above-described third implementation. The basic roles and configurations of the messages from steps 1501 to 1504 are the same as those of the messages from steps 901 to 903 and 906 in FIG. 9. In step 1503, each candidate SN4 includes an indication of selective CG activation for each candidate PSC in the SN Addition Request Acknowledge message. In other words, each candidate SN4 indicates to MN1 whether selective CG activation is required, recommended, or proposed for each candidate PSC. In step 1504, MN1 may include an indication of selective CG activation for each candidate PSC in the MN RRC Reconfiguration message. In other words, MN1 may indicate to UE3 whether selective CG activation is recommended, proposed, or available for each candidate PSC. Although not shown in FIG. 15, MN1 may inform at least one candidate PSC of a candidate SN4 (e.g., 4A) for which selective CG activation is applied to other candidate SN4s (e.g., 4B).

[0124] According to the operations and procedures of MN1, candidate SN2 or 4, and UE3 described in this embodiment, it can contribute to clarifying the procedures for enabling selective CG activation. Specifically, these can clarify which of the settings of multiple candidate PSCs for CPA or Inter-SN CPC (or conditional SN change) UE3 will reuse for subsequent CPC.

[0125] <Third Embodiment> This embodiment provides an improvement to CHO for selective CG activation. Specifically, this embodiment relates to clarifying various procedures regarding selective CG / cell activation. The configuration example of the wireless communication system according to this embodiment may be the same as the example shown in FIG. 3.

[0126] In the first implementation, before the source node 6 sends a CHO request to the candidate target node 7, it determines whether to perform, utilize, prepare for, or recommend selective cell activation. If it is determined to perform, utilize, prepare for, or recommend selective cell activation, the source node 6 operates as shown in FIG. 16.

[0127] In step 1601, the source node 6 includes an indication regarding selective cell activation in the CHO request message. In step 1602, the source node 6 sends the CHO request message to the candidate target node 7. The CHO request message indicates that one or more candidate target cells need to be prepared by the candidate target node 7 for CHO.

[0128] The indication regarding selective cell activation indicates to candidate target node 7 that selective cell activation is required or recommended for subsequent CHOs after the said CHO. The indication regarding selective cell activation may be called, for example, but not limited to, "Selective cell activation request", "CHO kept request", or "Store CHO request".

[0129] In a second implementation, candidate target node 7 determines whether to perform, utilize, prepare for, or recommend selective cell activation in response to receiving a CHO request from source node 6. Candidate target node 7 operates as shown in FIG. 17. In step 1701, candidate target node 7 receives a CHO request message from source node 6. The CHO request message indicates that one or more candidate cells (i.e., candidate target cells) need to be prepared by candidate target node 7 for the CHO.

[0130] In step 1702, candidate target node 7 accepts to prepare at least one of the one or more candidate target cells requested by source node 6. Additionally, candidate target node 7 determines whether to perform, utilize, prepare for, or recommend selective cell activation. If it is determined to perform, utilize, prepare for, or recommend selective cell activation, candidate target node 7 includes an indication regarding selective cell activation in the CHO request acknowledge message. In step 1703, candidate target node 7 sends the CHO request acknowledge message to source node 6.

[0131] The CHO request acknowledgment messages of steps 1702 and 1703 indicate at least one candidate target cell prepared by candidate target node 7. The indication regarding selective cell activation indicates to source node 6 that selective cell activation is required or recommended for subsequent CHOs after the said CHO. The indication regarding selective cell activation may be referred to as, but is not limited to, for example, "Selective cell activation request", "Selective cell activation indication", "CHO kept request", "CHO kept indication", "Store CHO request", or "Store CHO indication".

[0132] In a third implementation, the selected candidate target node 7 that provides the candidate target cell selected by UE3 in response to the CHO execution condition being met determines whether to perform, utilize, prepare, or recommend selective cell activation. The selected candidate target node 7 operates as shown in FIG. 18. In step 1801, the candidate target node 7 prepares one or more candidate target cells for UE3 for the CHO. In step 1801, the candidate target node 7 may exchange signaling with source node 6 in the same manner as in the existing CHO. Specifically, the candidate target node 7 may receive a CHO request message from source node 6 and send a CHO request acknowledgment message to source node 6.

[0133] In step 1802, if one of the one or more candidate target nodes 7 has been selected by UE3 among the one or more candidate target cells, the candidate target node 7 transmits an RRC message including an indication regarding selective cell activation to UE3. The RRC message may be an RRC Reconfiguration message. The indication indicates to UE3 that selective cell activation is required or recommended for subsequent CHOs after the current CHO. The subsequent CHO may be a CHO to one or more other candidate target cells that were not selected by UE3 among the plurality of candidate target cells prepared for the CHO by the selected candidate target node 7. The indication regarding selective cell activation may be called, but is not limited to, for example, "Selective cell activation indication", "CHO kept indication", "Store CHO indication", or "Keep unused CHO configuration indication".

[0134] Figure 19 shows an example of signaling in the CHO preparation phase in the CHO procedure. In step 1901, the source node 6 sends a CHO Request message to each of the one or more candidate target nodes 7 (e.g., 7A and 7B). The CHO Request message includes a list of target cell candidates. The list indicates one or more candidate target cells proposed by the source node 6. The CHO Request message may be a Handover Request message including a Conditional Handover Information Request IE.

[0135] In step 1902, each candidate target node 7 sends a CHO Request Acknowledge message to the source node 6. The CHO Request Acknowledge message includes the settings of each of the one or more candidate target cells prepared by the candidate target node 7. As already explained, the setting of each candidate target cell may be a radio resource setting or an RRC Reconfiguration message. The CHO Request Acknowledge message may also be a Handover Request Acknowledge message including Conditional Handover Information Acknowledge.

[0136] In step 1903, the source node 6 sends an RRC Reconfiguration message including CHO settings to the UE 3. The CHO settings include the settings of the candidate target cells generated by the candidate target node 7 and the CHO execution conditions generated by the source node 6.

[0137] In the above-described first implementation, as shown in FIG. 19 as option 1, the source node 6 includes an indication regarding selective cell activation in the CHO Request message (step 1901). The candidate target node 7 may include an indication indicating whether the selective cell activation is accepted in the CHO Request Acknowledge message (step 1902).

[0138] In the above-described second implementation, as shown in FIG. 19 as option 2, the candidate target node 7 includes an indication regarding selective cell activation in the CHO Request Acknowledge message (step 1902).

[0139] In both the first and second implementations, the RRC Reconfiguration message in step 1903 may include an indication regarding selective cell activation. In other words, the source node 6 may inform the UE3 via the RRC Reconfiguration message in step 1903 that selective cell activation is required, recommended, or available.

[0140] Figure 20 shows an example of the signaling of the CHO procedure for the above-described third implementation. In step 2001, the source node 6 and one or more target nodes 7 prepare for the CHO. In step 2002, the source node 6 sends an RRC Reconfiguration message including the CHO configuration to the UE3. The RRC Reconfiguration message in step 2002 indicates the CHO. Additionally, the RRC Reconfiguration message may indicate to the UE3 that selective cell activation is planned, predicted, or possible for subsequent CHOs after the current CHO.

[0141] In step 2003, if the execution condition for one of the prepared candidate target cells is not met, the UE3 executes the CHO by applying the configuration of the selected candidate target cell. In the example of Figure 20, the UE3 selects one of the one or more candidate target cells prepared by the candidate target node 7A. Note that the UE3 maintains or holds the CHO execution conditions associated with the configurations of the other one or more candidate target cells without releasing them after the establishment of the CHO execution condition. The UE3 may selectively maintain or hold only the configurations of the other one or more candidate target cells prepared by the selected candidate target node 7A. The UE3 may operate in this manner when the RRC Reconfiguration message in step 2002 indicates the plan, prediction, or possibility of selective cell activation.

[0142] In step 2004, the selected candidate target node 7A transmits to the UE3 an RRC message including an indication regarding selective cell activation. The indication indicates to the UE3 that selective cell activation is required or recommended for subsequent CHOs after the current CHO. In response to receiving the indication in step 2004, the UE3 maintains or holds the unused CHO settings (i.e., the settings of the candidate target cells) for subsequent CHOs (step 2005). The UE3 may selectively maintain or hold only the settings of one or more other candidate target cells prepared by the selected candidate target node 7A. In addition to the settings of the unused candidate target cells, the UE3 may also maintain or hold the associated CHO execution conditions. If the indication in step 2004 is not received, the UE3 may release the temporarily maintained or held CHO settings.

[0143] The operations of the source node 6, target node 7, and UE3 described above may be modified as follows. The source node 6 may inform the candidate target node 7 (e.g., 7A) selected by the UE3 of candidate target cells prepared by other candidate target nodes 7 (e.g., 7B) to which selective cell activation is applied. Based on this information, the selected candidate target node 7 (e.g., 7A) may update the measurement settings and / or the CHO execution conditions or both. The selected candidate target node 7 (e.g., 7A) may transmit the updated measurement settings and / or execution conditions to the UE3.

[0144] The operations of the source node 6, target node 7, and UE 3 described above may be modified as follows. In some implementations, selective cell activation may be applied or imposed on the previous serving cell provided by the source node 6. In this case, after the CHO is completed, UE 3 maintains the settings of the previous serving cell for reuse in subsequent CHOs. The source node 6 may inform the candidate target node 7 that selective cell activation is applied to or required for the source cell. For example, the source node 6 may include an indication indicating the application of selective cell activation to the source cell in the CHO Request message of step 1902 in FIG. 19. The indication may be, for example, but not limited to, "Source cell kept".

[0145] According to the operations and procedures of the source node 6, target node 7, and UE 3 described in this embodiment, it is possible to contribute to the clarification of the procedures for enabling selective cell activation for CHO. Specifically, these can clarify which node (e.g., source node or target node) makes the decision on whether to use selective cell activation for CHO and when this decision is made.

[0146] <Fourth Embodiment> This embodiment provides an improvement to CHO for selective cell activation. This embodiment relates to reusing the settings of a plurality of candidate target cells for CHO for subsequent CHOs. A configuration example of the wireless communication system according to this embodiment may be the same as the example shown in FIG. 3.

[0147] In the first implementation, UE3 maintains or holds all the settings of one or more candidate target cells other than the selected one among the settings of multiple candidate target cells for CHO for subsequent CHO. As already explained, the setting of each candidate target cell may be a radio resource setting or an RRC Reconfiguration message. UE3 may further maintain or hold the associated CHO execution conditions for subsequent CHO. UE3 may update or modify one or more CHO execution conditions in response to an instruction from the selected candidate target node 7 or autonomously. For example, UE3 may switch the reference cell in one or more CHO execution conditions (e.g., CondEvent A3 or CondEvent A5) from the serving cell 61 provided by the source node 6, which is the source cell of the first CHO, to the selected target cell (e.g., cell 71) provided by the selected candidate target node 7, that is, the new serving cell.

[0148] In the second implementation, UE3 selectively maintains or holds only the settings of one or more other candidate target cells provided by the selected candidate target node 7 that provides the candidate target cell selected in the first CHO for subsequent CHO after the first CHO. Therefore, in the second implementation, the subsequent CHO is a CHO within the selected candidate target node 7. The setting of each candidate target cell may be a radio resource setting or an RRC Reconfiguration message. Similar to the first implementation, UE3 may maintain or hold the associated CHO execution conditions for subsequent CHO. UE3 may update or modify one or more CHO execution conditions in response to an instruction from the selected candidate target node 7 or autonomously.

[0149] In the third implementation, UE3 selectively maintains or holds the settings of one or more candidate target cells specified by source node 6 or 1 or one or more candidate target nodes 7 among the candidate target cells other than the candidate target cell selected in the first CHO for subsequent CHOs. The setting of each candidate target cell may be a radio resource setting or an RRC Reconfiguration message. Similar to the first implementation, UE3 may maintain or hold the associated CHO execution conditions for subsequent CHOs. UE3 may update or modify one or more CPC execution conditions in response to an instruction from the selected candidate target node 7 or autonomously.

[0150] Figure 21 shows an example of the operation of UE3 in the second implementation. In step 2101, UE3 receives the settings of a plurality of candidate target cells provided by a plurality of candidate target nodes 7 for the CGO from source node 6. UE3 also receives a plurality of CHO execution conditions associated with the plurality of candidate target cells from source node 6. In step 2102, UE3 evaluates the plurality of CHO execution conditions. If the execution condition of one of the plurality of candidate target cells is satisfied, UE3 applies the setting corresponding to the selected candidate target cell (i.e., the candidate target cell whose execution condition is satisfied). In step 2103, UE3 selectively maintains only the settings of one or more other candidate PSCs provided by the selected candidate target node 7 that provides the selected candidate target cell for subsequent CHOs.

[0151] Figure 22 shows an example of the operation of UE3 in the third implementation. Steps 2201 and 2202 are the same as steps 2101 and 2102 in Figure 21. In step 2103, UE3 selectively maintains the settings of one or more candidate target cells specified by source node 6 or 1 or one or more candidate target nodes 7 among the plurality of candidate target cells other than the selected candidate target cell for subsequent CHOs.

[0152] Figure 23 shows an example of signaling in the CHO preparation phase in the CHO procedure for the above-described third implementation. The basic roles and configurations of the messages in steps 2301 to 2303 are the same as those of the messages in steps 1901 to 1903 in Figure 19. In step 2302, each candidate target node 7 includes an indication of selective cell activation for each candidate target cell in the CHO Request Acknowledge message. In other words, each candidate target node 7 indicates to the source node 6 for each candidate target cell whether selective cell activation is requested, recommended, or proposed. In step 2303, the source node 6 may include an indication of selective cell activation for each candidate target cell in the RRC Reconfiguration message. In other words, the source node 6 may indicate to the UE 3 for each candidate target cell whether selective cell activation is recommended, proposed, or available. Although not shown in Figure 23, the source node 6 may notify at least one candidate target cell of the candidate target node 7 (e.g., 7A) to which selective cell activation is applied to other candidate target nodes 7 (e.g., 7B).

[0153] According to the operations and procedures of the source node 6, target node 7, and UE 3 described in this embodiment, it is possible to contribute to the clarification of the procedure for enabling selective cell activation. Specifically, these can clarify which of the settings of a plurality of candidate target cells for CHO the UE 3 will reuse for subsequent CHO.

[0154] Next, the configuration examples of the RAN nodes 1, 2, 4, 6, and 7, and the UE 3 according to the above-described multiple embodiments will be described. FIG. 24 is a block diagram showing a configuration example of the RAN node 1 according to the above-described embodiment. The configurations of the other RAN nodes 2, 4, 6, and 7 may also be the same as the configuration shown in FIG. 24. Referring to FIG. 24, the RAN node 1 includes a Radio Frequency transceiver 2401, a network interface 2403, a processor 2404, and a memory 2405. The RF transceiver 2401 performs analog RF signal processing to communicate with UEs including the UE 3. The RF transceiver 2401 may include a plurality of transceivers. The RF transceiver 2401 is coupled to the antenna array 2402 and the processor 2404. The RF transceiver 2401 receives modulation symbol data from the processor 2404, generates a transmission RF signal, and supplies the transmission RF signal to the antenna array 2402. Also, the RF transceiver 2401 generates a baseband reception signal based on the reception RF signal received by the antenna array 2402 and supplies this to the processor 2404. The RF transceiver 2401 may include an analog beamformer circuit for beamforming. The analog beamformer circuit includes, for example, a plurality of phase shifters and a plurality of power amplifiers.

[0155] The network interface 2403 is used to communicate with network nodes (e.g., RAN nodes 2 and 4, and control nodes and transfer nodes of the core network). The network interface 2403 may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series.

[0156] Processor 2404 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. Processor 2404 may include a plurality of processors. For example, processor 2404 may include a modem processor (e.g., Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., Central Processing Unit (CPU) or Micro Processing Unit (MPU)) that performs control plane processing.

[0157] For example, the digital baseband signal processing by processor 2404 may include signal processing of the Service Data Adaptation Protocol (SDAP) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, Medium Access Control (MAC) layer, and Physical (PHY) layer. Also, the control plane processing by processor 2404 may include processing of Non-Access Stratum (NAS) messages, RRC messages, MAC Control Elements (CE), and Downlink Control Information (DCI).

[0158] Processor 2404 may include a digital beamformer module for beamforming. The digital beamformer module may include a Multiple Input Multiple Output (MIMO) encoder and a precoder.

[0159] Memory 2405 is composed of a combination of volatile memory and non-volatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM) or Dynamic RAM (DRAM) or a combination thereof. The non-volatile memory is Mask Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. Memory 2405 may include storage located away from processor 2404. In this case, processor 2404 may access memory 2405 via network interface 2403 or an I / O interface (not shown).

[0160] Memory 2405 may store one or more software modules (computer programs) 2406 containing instruction groups and data for performing the processing by RAN node 1 described in the above-described multiple embodiments. In some implementations, processor 2404 may be configured to perform the processing of RAN node 1 described in the above embodiments by reading and executing the software module 2406 from memory 2405.

[0161] Note that when RAN node 1 is a CU (e.g., eNB-CU or gNB-CU) or CU-CP, RAN node 1 may not include RF transceiver 2401 (and antenna array 2402).

[0162] FIG. 25 is a block diagram showing a configuration example of UE3. A Radio Frequency (RF) transceiver 2501 performs analog RF signal processing to communicate with RAN nodes 1, 2, 4, 6, and 7. The RF transceiver 2501 may include a plurality of transceivers. The analog RF signal processing performed by the RF transceiver 2501 includes frequency upconversion, frequency downconversion, and amplification. The RF transceiver 2501 is coupled to an antenna array 2502 and a baseband processor 2503. The RF transceiver 2501 receives modulation symbol data (or OFDM symbol data) from the baseband processor 2503, generates a transmission RF signal, and supplies the transmission RF signal to the antenna array 2502. Also, the RF transceiver 2501 generates a baseband reception signal based on the received RF signal received by the antenna array 2502 and supplies this to the baseband processor 2503. The RF transceiver 2501 may include an analog beamformer circuit for beamforming. The analog beamformer circuit includes, for example, a plurality of phase shifters and a plurality of power amplifiers.

[0163] The baseband processor 2503 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. The digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) generation / decomposition of a transmission format (transmission frame), (d) channel coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) by Inverse Fast Fourier Transform (IFFT), etc. On the other hand, the control plane processing includes communication management of layer 1 (e.g., transmission power control), layer 2 (e.g., radio resource management, and hybrid automatic repeat request (HARQ) processing), and layer 3 (e.g., signaling related to attachment, mobility, and call management).

[0164] For example, the digital baseband signal processing by the baseband processor 2503 may include signal processing of the SDAP layer, PDCP layer, RLC layer, MAC layer, and PHY layer. Also, the control plane processing by the baseband processor 2503 may include processing of the Non-Access Stratum (NAS) protocol, RRC protocol, MAC CEs, and DCIs.

[0165] The baseband processor 2503 may perform MIMO encoding and precoding for beamforming.

[0166] The baseband processor 2503 may include a modem processor (e.g., DSP) that performs digital baseband signal processing and a protocol stack processor (e.g., CPU or MPU) that performs control plane processing. In this case, the protocol stack processor that performs control plane processing may be shared with the application processor 2504 described later.

[0167] The application processor 2504 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 2504 may include a plurality of processors (a plurality of processor cores). The application processor 2504 realizes various functions of the UE3 by executing a system software program (Operating System (OS)) and various application programs (e.g., call application, WEB browser, mailer, camera operation application, music playback application) read from the memory 2506 or a memory not shown.

[0168] In some implementations, as shown by the dashed line (2505) in FIG. 25, the baseband processor 2503 and the application processor 2504 may be integrated on one chip. In other words, the baseband processor 2503 and the application processor 2504 may be implemented as one System on Chip (SoC) device 2505. The SoC device may also be referred to as a system Large Scale Integration (LSI) or a chipset.

[0169] The memory 2506 is a volatile memory, a non-volatile memory, or a combination thereof. The memory 2506 may physically include multiple independent memory devices. The volatile memory is, for example, SRAM, DRAM, or a combination thereof. The non-volatile memory is MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, the memory 2506 may include an external memory device accessible from the baseband processor 2503, the application processor 2504, and the SoC 2505. The memory 2506 may include an embedded memory device integrated within the baseband processor 2503, the application processor 2504, or the SoC 2505. Further, the memory 2506 may include the memory within a Universal Integrated Circuit Card (UICC).

[0170] The memory 2506 may store one or more software modules (computer programs) 2507 including instructions and data for performing the processing by the UE3 described in the above-described embodiments. In some implementations, the baseband processor 2503 or the application processor 2504 may be configured to perform the processing of the UE3 described with reference to the drawings in the above-described embodiments by reading and executing the software module 2507 from the memory 2506.

[0171] Note that the control plane processing and operations performed by the UE3 described in the above embodiments can be realized by other elements excluding the RF transceiver 2501 and the antenna array 2502, that is, at least one of the baseband processor 2503 and the application processor 2504 and the memory 2506 storing the software module 2507.

[0172] As described with reference to FIGS. 24 and 25, each of the processors of the RAN nodes 1, 2, 4, 6, and 7 and the UE3 according to the above embodiments can execute one or more programs including a set of instructions for causing a computer to perform the algorithms described with reference to the drawings. The program, when loaded into a computer, includes a set of instructions (or software code) for causing the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disk (DVD), Blu-ray (registered trademark) disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted on a transient computer-readable medium or a communication medium. By way of example and not limitation, the transient computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0173] The above-described embodiments are merely examples regarding the application of the technical idea obtained by the present inventor. That is, the technical idea is not limited to the above-described embodiments only, and it goes without saying that various modifications are possible.

[0174] For example, some or all of the above embodiments may be described as follows in the appended claims, but are not limited thereto.

[0175] (Appendix 1) A radio access network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for a User Equipment (UE), at least one memory, at least one processor coupled to the at least one memory, comprising, the at least one processor is configured to transmit a control message to a candidate Secondary Node (SN), the control message indicates that one or more candidate Primary Secondary Cell Group (SCG) Cells (PSCells) need to be prepared by the candidate SN for first conditional mobility involving addition or change of a PSCell for the UE, the control message indicates that an operation mode in which settings of the one or more candidate PSCs supplied to the UE for the first conditional mobility are reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended, RAN node. (Appendix 2) the at least one processor is configured to determine whether settings of the one or more candidate PSCs need to be maintained by the UE for the subsequent conditional PSCell change, The RAN node according to Appendix 1. (Appendix 3) the control message is an SN Addition Request message, The RAN node according to Appendix 1 or 2. (Appendix 4) The first conditional mobility is a conditional Secondary Node (SN) change or a PSCell change between SNs, The at least one processor is configured to indicate to the candidate SN, via the control message or another control message, that a source PSCell of the first conditional mobility is to be one of candidate PSCs in the subsequent conditional PSCell change, The RAN node according to any one of Appendices 1 to 3. (Appendix 5) The first conditional mobility is a conditional Secondary Node (SN) change or a PSCell change between SNs, The at least one processor is configured to indicate to a source SN that provides the source PSCell that the source PSCell of the first conditional mobility is to be one of candidate PSCs in the subsequent conditional PSCell change, The RAN node according to any one of Appendices 1 to 4. (Appendix 6) A method performed by a radio access network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for a User Equipment (UE), Comprising transmitting a control message to a candidate Secondary Node (SN), The control message indicates that one or more candidate PSCs need to be prepared by the candidate SN for a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE, The control message indicates that an operation mode in which settings of the one or more candidate PSCs supplied to the UE for the first conditional mobility are reused by the UE for a subsequent conditional PSCell change after the first conditional mobility is recommended, Method. (Appendix 7) A program for causing a computer to perform a method for a radio access network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for a User Equipment (UE), The method comprises transmitting a control message to a candidate Secondary Node (SN), The control message indicates that one or more candidate PSCs need to be prepared by the candidate SN for first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE, The control message indicates that an operation mode in which the setting of the one or more candidate PSCs supplied to the UE for the first conditional mobility is reused by the UE for subsequent conditional PSCell changes after the first conditional mobility is recommended, Program. (Appendix 8) A radio access network (RAN) node configured to operate as a source Secondary Node (SN) associated with a Secondary Cell Group (SCG) in dual connectivity for a User Equipment (UE), At least one memory, At least one processor coupled to the at least one memory, Comprising, The at least one processor is configured to transmit a control message to the Master Node (MN) of the dual connectivity, The control message indicates one or more candidate PSCs recommended by the source SN for a first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change for the UE, The control message indicates that the setting of the one or more candidate PSCs supplied to the UE for the first conditional PSCell change is recommended to be reused by the UE for subsequent conditional PSCell changes after the first conditional PCell change. RAN node. (Appendix 9) The at least one processor is configured to determine whether the setting of the one or more candidate PSCs needs to be maintained by the UE for the subsequent conditional PSCell change. The RAN node according to Appendix 8. (Appendix 10) The control message is a SN Change Required message. The RAN node according to Appendix 8 or 9. (Appendix 11) A method performed by a radio access network (RAN) node configured to operate as a source secondary node (SN) associated with a secondary cell group (SCG) in dual connectivity for a user equipment (UE), comprising transmitting a control message to a master node (MN) of the dual connectivity, the control message indicating one or more candidate PSCs recommended by the source SN for a first conditional primary secondary cell group (SCG) cell (PSCell) change for the UE, The control message indicates that the setting of the one or more candidate PSCs supplied to the UE for the first conditional PSCell change is recommended to be reused by the UE for subsequent conditional PSCell changes after the first conditional PCell change. Method. (Appendix 12) A radio access network (RAN) node configured to operate as a candidate secondary node (SN) associated with a secondary cell group (SCG) in dual connectivity for a user equipment (UE), comprising at least one memory, at least one processor coupled to the at least one memory, wherein the at least one processor is configured to receive a first control message from a master node (MN) of the dual connectivity and transmit a second control message to the MN in response to the first control message, the first control message indicating that one or more candidate primary secondary cell group (SCG) cells (PSCells) need to be prepared for a first conditional mobility involving addition or change of a PSCell for the UE, the second control message indicating at least one candidate PSCell prepared by the candidate SN among the one or more candidate PSCs, the second control message indicating that an operation mode in which a setting of the at least one candidate PSCell provided to the UE for the first conditional mobility is reused by the UE for a subsequent conditional PSCell change after the first conditional mobility is recommended, RAN node. (Appendix 13) (Appendix 14) the at least one processor is configured to determine whether a setting of the at least one candidate PSCell needs to be maintained by the UE for the subsequent conditional PSCell change, The RAN node according to Appendix 12. (Appendix 14) The first control message is an SN Addition Request message, and the second control message is an SN Addition Request Acknowledge message. The RAN node according to Appendix 12 or 13. (Appendix 15) A method performed by a radio access network (RAN) node configured to operate as a candidate Secondary Node (SN) associated with a Secondary Cell Group (SCG) in dual connectivity for a User Equipment (UE), Receiving a first control message from a Master Node (MN) of the dual connectivity, and Transmitting a second control message to the MN in response to the first control message, Comprising: The first control message indicates that one or more candidate PSCs need to be prepared for a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE, The second control message indicates at least one candidate PSC prepared by the candidate SN among the one or more candidate PSCs, The second control message indicates that an operation mode in which the setting of the at least one candidate PSC supplied to the UE for the first conditional mobility is reused by the UE for subsequent conditional PSC changes after the first conditional mobility is recommended. Method. (Appendix 16) A radio access network (RAN) node configured to operate as a candidate Secondary Node (SN) associated with a Secondary Cell Group (SCG) in dual connectivity for a User Equipment (UE), At least one memory, and At least one processor coupled to the at least one memory, comprising, wherein the at least one processor is configured to: prepare one or more candidate PSCs in a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE; if one of the one or more candidate PSCs is selected by the UE, send an SN Radio Resource Control (RRC) message to the UE; configured to be, wherein the SN RRC message indicates that an operation mode in which settings of one or more candidate PSCs other than the selected candidate PSC prepared for the first conditional mobility are reused by the UE for subsequent conditional PSC changes after the first conditional mobility is recommended; RAN node. (Appendix 17) wherein the at least one processor is configured to determine whether settings of the one or more other candidate PSCs need to be maintained by the UE for the subsequent conditional PSC change; The RAN node according to Appendix 16. (Appendix 18) A method performed by a radio access network (RAN) node configured to operate as a candidate Secondary Node (SN) associated with a Secondary Cell Group (SCG) in dual connectivity for a User Equipment (UE), the method comprising: preparing one or more candidate PSCs in a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE; and If one of the one or more candidate PSCs is selected by the UE, sending an SN Radio Resource Control (RRC) message to the UE, comprising, The SN RRC message indicates that the settings of one or more candidate PSCs other than the selected candidate PSC prepared for the first conditional mobility are recommended to be reused by the UE for subsequent conditional PSC changes after the first conditional mobility. Method. (Appendix 19) A radio access network (RAN) node configured to operate as a source node for conditional handover of a User Equipment (UE), at least one memory, at least one processor coupled to the at least one memory, comprising, The at least one processor is configured to send a control message to a candidate target node, The control message indicates that one or more candidate target cells need to be prepared by the candidate target node for the first conditional handover of the UE, The control message indicates that the settings of the one or more candidate target cells provided to the UE for the first conditional handover are recommended to be reused by the UE for a subsequent second conditional handover after the first conditional handover. RAN node. (Appendix 20) The at least one processor is configured to determine whether the settings of the one or more candidate target cells need to be maintained by the UE for the second conditional handover. The RAN node according to Appendix 19. (Appendix 21) A method performed by a radio access network (RAN) node configured to operate as a source node for conditional handover of a User Equipment (UE), comprising: Sending a control message to a candidate target node; wherein the control message indicates that one or more candidate target cells need to be prepared by the candidate target node for a first conditional handover of the UE; wherein the control message indicates that an operation mode in which settings of the one or more candidate target cells provided to the UE for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended. A method. (Appendix 22) A radio access network (RAN) node configured to operate as a candidate target node for conditional handover of a User Equipment (UE), comprising: at least one memory; at least one processor coupled to the at least one memory; wherein the at least one processor is configured to receive a first control message from a source node and send a second control message to the source node in response to the first control message; wherein the first control message indicates that one or more candidate target cells need to be prepared for a first conditional handover of the UE; wherein the second control message indicates at least one candidate target cell prepared by the source node among the one or more candidate target cells; wherein the second control message indicates that an operation mode in which settings of the at least one candidate target cell provided to the UE for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended. ​ RAN node. (Appendix 23) The at least one processor is configured to determine whether the UE needs to maintain the setting of the one or more candidate target cells for the second conditional handover. The RAN node according to Appendix 22. (Appendix 24) A method performed by a radio access network (RAN) node configured to operate as a candidate target node for conditional handover of a User Equipment (UE), Receiving a first control message from a source node, and Sending a second control message to the source node in response to the first control message, comprising: The first control message indicates that one or more candidate target cells need to be prepared for the first conditional handover of the UE, The second control message indicates at least one candidate target cell prepared by the source node among the one or more candidate target cells, The second control message indicates that an operation mode in which the setting of the at least one candidate target cell supplied to the UE for the first conditional handover is reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended. Method. (Appendix 25) A radio access network (RAN) node configured to operate as a candidate target node for conditional handover of a User Equipment (UE), At least one memory, and At least one processor coupled to the at least one memory, comprising: The at least one processor is Prepare one or more candidate target cells for the first conditional handover of the UE, If one of the one or more candidate target cells is selected by the UE, send a Radio Resource Control (RRC) message to the UE, configured as The RRC message indicates that an operation mode in which settings of one or more candidate target cells other than the selected candidate target cell prepared for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended. RAN node. (Appendix 26) The at least one processor is configured to determine whether settings of the one or more other candidate target cells need to be maintained by the UE for the second conditional handover. The RAN node according to Appendix 25. (Appendix 27) A method performed by a radio access network (RAN) node configured to operate as a candidate target node for conditional handover of a User Equipment (UE), preparing one or more candidate target cells for the first conditional handover of the UE, and if one of the one or more candidate target cells is selected by the UE, sending a Radio Resource Control (RRC) message to the UE, comprising The RRC message indicates that an operation mode in which settings of one or more candidate target cells other than the selected candidate target cell prepared for the first conditional handover are reused by the UE for a subsequent second conditional handover after the first conditional handover is recommended. Method. (Appendix 28) A User Equipment (UE), comprising at least one memory, at least one processor coupled to the at least one memory, and wherein the at least one processor is configured to: receive, from a Master Node (MN), settings of a plurality of candidate Primary Secondary Cell Group (SCG) Cells (PSCells) provided by a plurality of candidate Secondary Nodes (SNs) for a first conditional mobility involving addition or change of a PSCell for the UE; if an execution condition of one of the plurality of candidate PSCs is satisfied, apply settings corresponding to the one candidate PSC; and selectively maintain only settings of one or more other candidate PSCs provided by a selected candidate SN that provides the one candidate PSC for subsequent conditional PSCell changes after the first conditional mobility. configured UE. (Appendix 29) A method performed by a User Equipment (UE), the method comprising: receiving, from a Master Node (MN), settings of a plurality of candidate Primary Secondary Cell Group (SCG) Cells (PSCells) provided by a plurality of candidate Secondary Nodes (SNs) for a first conditional mobility involving addition or change of a PSCell for the UE; if an execution condition of one of the plurality of candidate PSCs is satisfied, applying settings corresponding to the one candidate PSC; and selectively maintaining only settings of one or more other candidate PSCs provided by a selected candidate SN that provides the one candidate PSC for subsequent conditional PSCell changes after the first conditional mobility. The method as claimed. (Appendix 30) ​A User Equipment (UE), comprising at least one memory, and at least one processor coupled to the at least one memory, wherein the at least one processor is configured to receive, from a Master Node (MN), settings of a plurality of candidate Primary Secondary Cell Group (SCG) Cells (PSCells) for a first conditional mobility involving addition or change of a PSCell for the UE, apply, if an execution condition of one of the plurality of candidate PSCs is satisfied, settings corresponding to the one candidate PSCell, and selectively maintain, for one or more candidate PSCs among the plurality of candidate PSCs other than the one candidate PSC, settings of the one or more candidate PSCs designated by the MN or one or more candidate Secondary Nodes (SNs) for subsequent conditional PSCell changes after the first conditional mobility. configured UE. (Appendix 31) A method performed by a User Equipment (UE), comprising at least one memory, receiving, from a Master Node (MN), settings of a plurality of candidate Primary Secondary Cell Group (SCG) Cells (PSCells) for a first conditional mobility involving addition or change of a PSCell for the UE, applying, if an execution condition of one of the plurality of candidate PSCs is satisfied, settings corresponding to the one candidate PSCell, and selectively maintaining, for one or more candidate PSCs among the plurality of candidate PSCs other than the one candidate PSC, settings of the one or more candidate PSCs designated by the MN or one or more candidate Secondary Nodes (SNs) for subsequent conditional PSCell changes after the first conditional mobility. ​A method comprising (Appendix 32) A radio access network (RAN) node configured to operate as a candidate secondary node (SN) associated with a secondary cell group (SCG) in dual connectivity for a user equipment (UE), comprising at least one memory, at least one processor coupled to the at least one memory, and comprising wherein the at least one processor indicates to a master node (MN) one or more candidate primary secondary cell group (SCG) cells (PSCells) prepared by the candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE, and indicates to the MN at least one candidate PSCell among the one or more candidate PSCells, the setting of which needs to be maintained for subsequent conditional PSCell change after the first conditional mobility, and is configured to RAN node. (Appendix 33) A method performed by a radio access network (RAN) node configured to operate as a candidate secondary node (SN) associated with a secondary cell group (SCG) in dual connectivity for a user equipment (UE), indicating to a master node (MN) one or more candidate primary secondary cell group (SCG) cells (PSCells) prepared by the candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE, and indicating to the MN at least one of the one or more candidate PSCs among the one or more candidate PSCs for which the setting needs to be maintained for subsequent conditional PSCell changes after the first conditional mobility, A method comprising. (Appendix 34) A radio access network (RAN) node configured to operate as a master node (MN) associated with a master cell group (MCG) in dual connectivity for a user equipment (UE), at least one memory, at least one processor coupled to the at least one memory, comprising, the at least one processor is configured to receive a control message from a first candidate secondary node (SN) for a first conditional mobility involving addition or change of a primary secondary cell group (SCG) cell (PSCell) for the UE, the control message indicates one or more candidate PSCs prepared by the first candidate SN for the first conditional mobility, the control message indicates at least one of the one or more candidate PSCs for which the setting needs to be maintained for subsequent conditional PSCell changes after the first conditional mobility, RAN node. (Appendix 35) the at least one processor is configured to inform the UE of the at least one candidate PSC, The RAN node according to Appendix 34. (Appendix 36) the at least one processor is configured to inform a second candidate SN for the first conditional mobility different from the first candidate SN of the at least one candidate PSC, The RAN node according to Appendix 34 or 35. (Appendix 37) A method performed by a radio access network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for a User Equipment (UE), comprising: Receiving a control message from a first candidate Secondary Node (SN) of a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE; The control message indicates one or more candidate PSCs prepared by the first candidate SN for the first conditional mobility; The control message indicates at least one candidate PSC among the one or more candidate PSCs, the settings of which need to be maintained for subsequent conditional PSC changes after the first conditional mobility; Method. (Appendix 38) A User Equipment (UE) comprising: At least one memory; At least one processor coupled to the at least one memory; Comprising: The at least one processor is configured to: Receive, from a source node, settings of a plurality of candidate target cells provided by a plurality of candidate target nodes for a first conditional handover of the UE; If an execution condition of one of the plurality of candidate target cells is satisfied, apply the settings corresponding to the one candidate target cell; Selectively maintain only the settings of one or more other candidate target cells provided by the selected candidate target node providing the one candidate target cell for a subsequent second conditional handover after the first conditional handover; Configured to: UE. (Appendix 39) A method performed by a User Equipment (UE), receiving, from a source node, settings of a plurality of candidate target cells provided by a plurality of candidate target nodes for a first conditional handover of the UE; if an execution condition of one of the plurality of candidate target cells is satisfied, applying the settings corresponding to the one candidate target cell; and selectively maintaining, for a subsequent second conditional handover of the first conditional handover, only the settings of one or more other candidate target cells provided by a selected candidate target node that provides the one candidate target cell. A method comprising the above steps. (Appendix 40) A User Equipment (UE), comprising at least one memory, at least one processor coupled to the at least one memory, wherein the at least one processor is configured to: receive, from a source node, settings of a plurality of candidate target cells for a first conditional handover of the UE; if an execution condition of one of the plurality of candidate target cells is satisfied, apply the settings corresponding to the one candidate target cell; and selectively maintain, for a subsequent second conditional handover of the first conditional handover, the settings of one or more candidate target cells specified by the source node or one or more candidate target nodes among the plurality of candidate target cells excluding the one candidate target cell. The UE is configured as above. UE. (Appendix 41) A method performed by a User Equipment (UE), ​Receiving, from a source node, a setting of a plurality of candidate target cells for a first conditional handover of the UE; If an execution condition of one of the plurality of candidate target cells is satisfied, applying the setting corresponding to the one candidate target cell, and Among the plurality of candidate target cells excluding the one candidate target cell, selectively maintaining the setting of one or more candidate target cells designated by the source node or one or more candidate target nodes for a subsequent second conditional handover of the first conditional handover, A method comprising. (Appendix 42) A radio access network (RAN) node configured to operate as a candidate target node for conditional handover of a User Equipment (UE), At least one memory, and At least one processor coupled to the at least one memory, Comprising, The at least one processor is Indicating to a source node one or more candidate target cells prepared by the candidate target node for a first conditional handover of the UE, Indicating to the source node at least one candidate target cell among the one or more candidate target cells whose setting needs to be maintained for a subsequent second conditional handover of the first conditional handover, Configured to be, RAN node. (Appendix 43) A method performed by a radio access network (RAN) node configured to operate as a candidate target node for conditional handover of a User Equipment (UE), Indicating to a source node one or more candidate target cells prepared by the candidate target node for a first conditional handover of the UE, and indicating to the source node at least one candidate target cell among the one or more candidate target cells, the setting of which needs to be maintained for a subsequent second conditional handover after the first conditional handover; A method comprising. (Appendix 44) A radio access network (RAN) node configured to operate as a source node for conditional handover of a User Equipment (UE), comprising at least one memory, at least one processor coupled to the at least one memory, and comprising, the at least one processor is configured to receive a control message from a first candidate target node of a first conditional handover of the UE, the control message indicates one or more candidate target cells prepared by the first candidate target node for the first conditional handover, the control message indicates at least one candidate target cell among the one or more candidate target cells, the setting of which needs to be maintained for a subsequent second conditional handover after the first conditional handover, RAN node. (Appendix 45) A method performed by a radio access network (RAN) node configured to operate as a source node for conditional handover of a User Equipment (UE), comprising receiving a control message from a first candidate target node of a first conditional handover of the UE, the control message indicates one or more candidate target cells prepared by the first candidate target node for the first conditional handover, The control message indicates at least one candidate target cell among the one or more candidate target cells, for which the setting needs to be maintained for a subsequent second conditional handover after the first conditional handover. Method.

[0176] This application claims priority based on Japanese Patent Application No. 2021-215149 filed on December 28, 2021, and incorporates the entire disclosure thereof herein.

Explanation of Signs

[0177] 1 Master Node (MN) 2 Source Secondary Node (S-SN) 3 User Equipment (UE) 4 Target Secondary Node (T-SN) 6 Source Node 7 Target Node 2404 Processor 2405 Memory 2406 Modules 2503 Baseband Processor 2504 Application Processor 2506 Memory 2507 Modules

Claims

1. A method performed by a radio access network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for a User Equipment (UE), the method comprising: sending a control message to a candidate Secondary Node (SN); wherein the control message indicates that one or more candidate Primary Secondary Cell Group (SCG) Cells (PSCells) need to be prepared by the candidate SN for a first conditional mobility involving addition or change of a PSCell for the UE; wherein the control message indicates that an operation mode is recommended in which settings of the one or more candidate PSCs supplied to the UE for the first conditional mobility are reused by the UE for subsequent conditional PSCell changes after the first conditional mobility; a method.

2. The method according to claim 1, further comprising determining whether settings of the one or more candidate PSCs need to be maintained by the UE for the subsequent conditional PSCell change. The method according to claim 1.

3. The control message is an SN Addition Request message. The method according to claim 1 or 2.

4. The first conditional mobility is a conditional Secondary Node (SN) change or an inter-SN PSCell change, and the method further comprises indicating to the candidate SN, via the control message or another control message, that a source PSCell of the first conditional mobility is to be one of the candidate PSCs in the subsequent conditional PSCell change. The method according to claim 1 or 2.

5. The first conditional mobility is a conditional Secondary Node (SN) change or an inter-SN PSCell change, and the method further comprises indicating to a source SN providing the source PSCell that the source PSCell of the first conditional mobility is to be one of the candidate PSCs in the subsequent conditional PSCell change. The method according to claim 1 or 2.

6. ​ ​ A method performed by a radio access network (RAN) node configured to operate as a source Secondary Node (SN) associated with a Secondary Cell Group (SCG) in dual connectivity for a User Equipment (UE), comprising: sending a control message to a Master Node (MN) of the dual connectivity; wherein the control message indicates one or more candidate Primary Secondary Cell Group (SCG) Cells (PSCells) recommended by the source SN for a first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change for the UE; wherein the control message indicates that an operation mode is recommended in which settings of the one or more candidate PSCs supplied to the UE for the first conditional PSCell change are reused by the UE for subsequent conditional PSCell changes after the first conditional PCell change; A method. **Claim 7**: The method further comprising determining whether settings of the one or more candidate PSCs need to be maintained by the UE for the subsequent conditional PSCell change. The method according to claim 6. **Claim 8**: The control message is a SN Change Required message. The method according to claim 6 or 7. **Claim 9** A method performed by a radio access network (RAN) node configured to operate as a candidate Secondary Node (SN) associated with a Secondary Cell Group (SCG) in dual connectivity for a User Equipment (UE), comprising: receiving a first control message from a Master Node (MN) of the dual connectivity; and sending a second control message to the MN in response to the first control message. The method comprising: wherein the first control message indicates that one or more candidate PSCs need to be prepared for a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE; The second control message indicates at least one candidate PSCell prepared by the candidate SN among the one or more candidate PSCs, The second control message indicates that an operation mode in which the setting of the at least one candidate PSCell provided to the UE for the first conditional mobility is reused by the UE for a subsequent conditional PSCell change after the first conditional mobility is recommended, Method.

10. The method further comprises determining whether the setting of the at least one candidate PSCell needs to be maintained by the UE for the subsequent conditional PSCell change, The method according to claim 9.

11. The first control message is an SN Addition Request message, and the second control message is an SN Addition Request Acknowledge message, The method according to claim 9 or 10.

12. A method performed by a User Equipment (UE), At least one memory, and Receiving, from a Master Node (MN), settings of a plurality of candidate PSCs for a first conditional mobility involving addition or change of a Primary Secondary Cell Group (SCG) Cell (PSCell) for the UE, If an execution condition of one of the plurality of candidate PSCs is satisfied, applying the setting corresponding to the one candidate PSC, and Among the plurality of candidate PSCs other than the one candidate PSC, selectively maintaining the settings of one or more candidate PSCs designated by the MN or one or more candidate Secondary Nodes (SNs) for a subsequent conditional PSCell change after the first conditional mobility, A method comprising.

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