Wireless access network node and method therefor

Abstract

A master node according to the present invention transmits a first control message to a candidate secondary node. The first control message requires that the candidate secondary node prepare one or more candidate PSCells for initial conditional PSCell addition or change for user equipment. In addition, the first control message includes first information indicating whether or not the candidate SN is allowed or required to generate execution conditions for a subsequent conditional PSCell change that may be performed after the initial conditional PSCell addition or change. This can contribute to, for example, solving a problem related to achieving a subsequent CPAC.

Description

Radio access network node and method thereof

[0001] The present disclosure relates to wireless communication systems.

[0002] The 3rd Generation Partnership Project (3GPP®) Release 17 supports conditional mobility, which includes conditional handover (CHO), conditional primary secondary cell group (SCG) cell (PSCell) addition (CPA), and conditional PSCell change (CPC). CPC includes intra-Secondary Node (SN) CPC and inter-SN CPC.

[0003] Furthermore, for 3GPP Release 18, 3GPP is considering further mobility enhancements, including "Multi-Radio Dual Connectivity (MR-DC) with selective activation of cell groups" (see, for example, Non-Patent Documents 1-5). Focusing on CPA and CPC, selective activation of cell groups can be referred to as SCG selective activation. In Release 17 CPA and CPC, a user equipment (UE) must select one of the candidate target PSCells and perform random access to the selected target PSCell, thereby releasing unused (unselected) CPA or CPC configurations. Therefore, the UE does not have an opportunity to perform subsequent CPC without reconfiguration and reinitialization of the CPC from the network. Selective activation of cell groups aims to address this issue. Specifically, according to Non-Patent Document 1, the purpose of selective activation of cell groups is to enable subsequent CPC to be performed after an initial CPA or CPC without reconfiguration and reinitialization for CPC preparation from the network. This can reduce the signaling overhead and interruption time of subsequent CPCs.

[0004] Annex to Non-Patent Document 2 describes the agreements on selective activation of cell groups in the 3GPP Technical Specification Group (TSG) Radio Access Network (RAN) Working Group #2 (WG2) (RAN2). Similarly, Annex A to Non-Patent Document 3 describes the agreements on selective activation of cell groups in RAN2. Furthermore, Annex B to Non-Patent Document 3 describes an open issue list on selective activation of cell groups. According to these, the term "subsequent Conditional PSCell Addition or Change (CPAC)" is used in the 3GPP specifications to represent SCG selective activation. Subsequent CPAC is defined as a conditional PSCell change procedure that is executed after a PSCell addition or PSCell change based on pre-configured CPA or CPC configuration of candidate PSCells without reconfiguration and re-initiation of CPC / CPA. Even after the first PSCell addition or PSCell change is triggered, the UE keeps the configured candidate PSCell configuration and evaluates the execution conditions of the candidate PSCells.SN initiated intra-SN subsequent CPAC, Master Node (MN) initiated inter-SN subsequent CPAC, and SN initiated inter-SN subsequent CPAC are supported.

[0005] In the case of an MN initiated inter-SN subsequent CPAC, the MN generates the execution conditions for the first CPAC. It is still under discussion whether the MN generates the execution conditions for all subsequent CPCs or whether the candidate SN may generate the execution conditions for the subsequent CPCs. On the other hand, in the case of an SN initiated inter-SN subsequent CPAC, the source SN generates the execution conditions for the first CPC, and the candidate SN generates the execution conditions for the subsequent CPCs. It is still under discussion when and how the candidate SN generates the execution conditions for the subsequent CPCs. For example, it is conceivable that the candidate SN may generate the execution conditions for the subsequent CPC when determining the candidate PSCells for the first CPC, or after the candidate SN has learned all the candidate PSCells prepared by other candidate SNs.

[0006] Patent Documents 1, 2, and 3 disclose various techniques related to selective activation of cell groups. Patent Document 1 discloses, for example, in paragraphs 0083 to 0085, 0125 to 0128, and Figures 5 and 16, that a source node or MN of conditional mobility (i.e., CHO, CPA, or CPC) includes an indication regarding selective cell activation in a conditional mobility request message. The indication regarding selective cell activation indicates to a candidate target node or SN of the conditional mobility that selective cell group (CG) / cell activation is requested or recommended for subsequent conditional mobility that may be performed after the initial conditional mobility.

[0007] For example, in paragraphs 0127 and 0134, Patent Document 1 discloses that a source node transmits a CHO request message to a candidate target node for CHO and subsequent CHO (selective cell activation). The CHO request message includes a list of one or more candidate target cells proposed by the source node.

[0008] For example, in paragraphs 0103 to 0105 and Figure 14, Patent Document 2 discloses an operation when a candidate target node or SN of conditional mobility (i.e., CHO, CPA, or CPC) does not support selective CG / cell activation. Specifically, the candidate target node or SN receives a request message for conditional mobility and selective CG / cell activation from the source node or MN. Then, if the candidate target node or SN does not support selective CG / cell activation, the candidate target node or SN replies to the source node or MN with a response message indicating rejection of the conditional mobility.

[0009] International Publication No. WO 2023 / 127271 International Publication No. WO 2023 / 127272 International Publication No. WO 2023 / 127273

[0010] MediaTek Inc., Apple, "Revised WID on Further NR mobility enhancements", RP-231475, 3GPP TSG RAN Meeting #100, Taipei, June 12-14, 2023MediaTek Inc., vivo, "38.300 running CR for introduction of NR further mobility enhancements", R2-2306957, 3GPP TSG-RAN WG2 Meeting #122, Incheon, Korea, May 22-26, 2023ZTE Corporation, Sanechips, "37.340 running CR for introduction of NR further mobility enhancements", R2-2306952, 3GPP TSG-RAN WG2 Meeting #122, Incheon, Korea, May 22-26, 2023Huawei, "(SCG Selective Activation BL CR to TS 38.423) Introduction of SCG Selective Activation", R3-232559, 3GPP TSG-RAN WG3 Meeting #120, Incheon, Korea, May 22-26, 2023ZTE, "(TP to TS 38.423): Support of SCG selective activation", R3-233524, Incheon, Korea, May 22-26, 2023

[0011] As mentioned above, 3GPP is working on standardizing subsequent CPAC (or SCG selective activation). However, the details of the procedure for realizing subsequent CPAC have not yet been fully clarified, and various issues remain. For example, the details of signaling between the MN and candidate SNs regarding the generation of execution conditions for subsequent CPC in inter-SN subsequent CPAC are not fully clear.

[0012] One of the objectives that the embodiments disclosed in this specification aim to achieve is to provide an apparatus, a method, and a program that contribute to solving at least one of the multiple objectives related to realizing subsequent CPAC, including the above-mentioned problem. It should be noted that this objective is only one of the multiple objectives that the multiple embodiments disclosed in this specification aim to achieve. Other objectives or objectives and novel features will become apparent from the description of this specification or the accompanying drawings.

[0013] A first aspect is directed to 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 UE. The RAN node is configured to transmit a first control message to a candidate Secondary Node (SN). The first control message requests the candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC for the UE. Additionally, the first control message includes first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent CPCs that may occur after the initial CPA or CPC.

[0014] A second aspect is directed to a method performed by a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE, the method including transmitting a first control message to a candidate SN, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC for the UE, and the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent CPCs that may occur after the initial CPA or CPC.

[0015] A third 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 configured to receive a first control message from a dual connectivity MN, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC for the UE, and the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent CPCs that may occur after the initial CPA or CPC.

[0016] A fourth 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 receiving a first control message from a dual connectivity MN, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC for the UE. Additionally, the first control message includes first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent CPCs that may occur after the initial CPA or CPC.

[0017] A fifth aspect is directed to a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE, the RAN node being configured to send a first control message to a first candidate SN requesting the first candidate SN to prepare multiple candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE, and to receive a second control message sent from the first candidate SN in response to the first control message, the second control message indicating that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.

[0018] A sixth aspect is directed to a method performed by a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE, the method including: (a) sending a first control message to a first candidate SN, requesting the first candidate SN to prepare multiple candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE, and (b) receiving a second control message sent from the first candidate SN in response to the first control message, the second control message indicating that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.

[0019] A seventh 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 is configured to receive a first control message from a MN for the dual connectivity requesting the candidate SN to prepare multiple candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE. Additionally, the RAN node is configured to send a second control message to the MN in response to the first control message if only some of the candidate PSCells can be prepared. The second control message indicates that preparation of all of the candidate PSCells has been rejected or failed because only some of the candidate PSCells can be prepared.

[0020] An 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 including: (a) receiving a first control message from a dual connectivity MN requesting the candidate SN to prepare multiple candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE; and (b) if only some of the multiple candidate PSCells can be prepared, transmitting a second control message to the MN in response to the first control message, the second control message indicating that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.

[0021] A ninth aspect is directed to a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE. The RAN node is configured to transmit a first control message to a first candidate SN, requesting the first candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE. Additionally, the RAN node is configured to receive a second control message transmitted from the first candidate SN in response to the first control message. Furthermore, the RAN node is configured to, if not all of the one or more candidate PSCells have been prepared by the first candidate SN, indicate at least one candidate PSCell that has or has not been prepared by the first candidate SN to a second candidate SN for the initial CPA or CPC via a third control message.

[0022] A tenth aspect is directed to a method performed by a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE, the method including the steps of: (a) sending a first control message to a first candidate SN, requesting the first candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE, (b) receiving a second control message sent from the first candidate SN in response to the first control message, and (c) if not all of the one or more candidate PSCells have been prepared by the first candidate SN, indicating at least one candidate PSCell that has or has not been prepared by the first candidate SN to a second candidate SN for the initial CPA or CPC via a third control message.

[0023] An eleventh aspect is directed to a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE, the RAN node being configured to send a first control message to a first candidate SN, the first control message requesting the first candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE, and the first control message including information indicating whether the first candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0024] A twelfth aspect is directed to a method performed by a RAN node configured to operate as an MN associated with an MCG in dual connectivity for a UE. The method includes transmitting a first control message to a first candidate SN, the first control message requesting the first candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC and for subsequent CPCs for the UE. Additionally, the first control message includes information indicating whether the first candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0025] A thirteenth 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 being configured to receive a first control message from a dual connectivity MN, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC and for a subsequent CPC for the UE, and the first control message including information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0026] A fourteenth 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 receiving a first control message from the dual connectivity MN. The first control message requests the candidate SN to prepare one or more candidate PSCells for an initial CPA or CPC and for a subsequent CPC for the UE. Additionally, the first control message includes information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0027] A fifteenth aspect is directed to a RAN node configured to act as a source SN associated with an SCG in dual connectivity for a UE, the RAN node being configured to send a control message to the dual connectivity MN, the control message triggering an initial CPC for the UE, including a list of one or more candidate PSCells managed by a candidate SN, and including an indication of a subsequent CPC. Additionally, the control message further includes information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0028] A sixteenth aspect is directed to a method performed by a RAN node configured to act as a source SN associated with an SCG in dual connectivity for a UE. The method includes transmitting a control message to the dual connectivity MN. The control message triggers an initial CPC for the UE, includes a list of one or more candidate PSCells managed by a candidate SN, and includes an indication of a subsequent CPC. In addition, the control message further includes information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0029] A seventeenth aspect is directed to a RAN node configured to operate as a source SN associated with an SCG in dual connectivity for a UE, the RAN node being configured to send first information to an MN in the dual connectivity, or to the candidate SN via the MN, indicating whether one or more cells managed by the source SN will be candidate PSCells for a subsequent CPC that may occur after an initial CPC from a source PSCell managed by the source SN to any of one or more candidate PSCells managed by one or more candidate SNs.

[0030] An eighteenth aspect is directed to a method performed by a RAN node configured to operate as a source SN associated with an SCG in dual connectivity for a UE, the method including sending first information to a MN in the dual connectivity or to the candidate SN via the MN indicating whether one or more cells managed by the source SN will be candidate PSCells for a subsequent CPC that may occur after an initial CPC from a source PSCell managed by the source SN to any of one or more candidate PSCells managed by one or more candidate SNs.

[0031] A nineteenth aspect is directed to a program, the program including a set of instructions (software code) for causing a computer to perform a method according to any of the above aspects when the program is loaded into the computer.

[0032] According to the above-described aspects, 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 subsequent CPAC.

[0033] FIG. 1 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 2 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 3 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 4 illustrates an example sequence diagram of example signaling related to inter-SN subsequent CPAC according to one or more embodiments. FIG. 5 illustrates an example sequence diagram of example signaling related to inter-SN subsequent CPAC according to one or more embodiments. FIG. 6 illustrates an example sequence diagram of example signaling related to inter-SN subsequent CPAC according to one or more embodiments. FIG. 7 illustrates an example sequence diagram of example signaling related to SN initiated inter-SN subsequent CPC according to one or more embodiments. FIG. 8 illustrates a flowchart of example operation of a candidate SN in inter-SN subsequent CPAC according to one or more embodiments. FIG. 9 illustrates an example flowchart of example operation of a MN in inter-SN subsequent CPAC according to one or more embodiments. FIG. 10 illustrates an example sequence diagram of example signaling related to inter-SN subsequent CPAC according to one or more embodiments. 1 is a flowchart illustrating an example of MN operation in inter-SN subsequent CPAC, according to one or more embodiments; 2 is a sequence diagram illustrating an example of signaling related to inter-SN subsequent CPAC, according to one or more embodiments; 3 is a sequence diagram illustrating an example of signaling related to SN initiated inter-SN subsequent CPC, according to one or more embodiments;1 is a flowchart illustrating an example of a source SN's operation in an SN initiated inter-SN subsequent CPC, in accordance with one or more embodiments; 2 is a block diagram illustrating an example RAN node configuration, in accordance with one or more embodiments; 3 is a block diagram illustrating an example UE configuration, in accordance with one or more embodiments;

[0034] Hereinafter, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0035] The multiple embodiments described below may be used independently, or two or more embodiments may be combined as appropriate. These multiple embodiments may have different novel features. Therefore, these multiple embodiments may contribute to achieving different objectives or solving different problems, and may contribute to achieving different effects.

[0036] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0037] The following embodiments are described primarily for the 3GPP 5th generation mobile communication system (5G system), but may also be applied to other wireless communication systems that support techniques similar to 3GPP conditional mobility (e.g., CHO, CPA, or CPC).

[0038] As used herein, depending on the context, "if" may be interpreted to mean "when," "while," "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.

[0039] First, the configurations and operations of several network elements common to several embodiments will be described. Figure 1 shows an example configuration of a wireless communication system related to several embodiments. In the example of Figure 1, the wireless communication system includes RAN node 1, RAN node 2, RAN node 4, and UE 3. Each element (network function) shown in Figure 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.

[0040] The RAN node 1 may be a Central Unit (e.g., 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., gNB-DUs). C-RAN is also referred to as a CU / DU split. Furthermore, a 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, the RAN node 1 may be a CU-CP or a combination of a CU-CP and a CU-UP. Similarly, each of the RAN nodes 2 and 4 may be a CU or a combination of a CU and one or more Distributed Units (DUs). Each of the RAN nodes 2 and 4 may be a CU-CP or a combination of a CU-CP and a CU-UP.

[0041] 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 provides NR user plane and control plane protocol terminations to UEs and operates as a secondary node (SN) for Evolved Universal Terrestrial Radio Access (E-UTRA)-NR Dual Connectivity (EN-DC). The ng-eNB provides E-UTRA user plane and control plane protocol terminations to UEs and is connected to the 5GC via the NG interface. The Radio Access Technology (RAT) of RAN node 1 may be different from that of RAN nodes 2 and 4.

[0042] RAN node 1 and RAN node 2 communicate with each other via a node-to-node interface (e.g., X2 interface or Xn interface) 103. RAN node 1 and RAN node 2 operate as a master node (MN) and a secondary node (SN), respectively, in dual connectivity. Furthermore, RAN node 1 and RAN node 4 communicate with each other via a node-to-node interface (e.g., X2 interface or Xn interface) 105. RAN node 1 and RAN node 4 can operate as a MN and SN, respectively, in dual connectivity. UE 3 communicates with RAN nodes 1 and 2 via air interfaces 101 and 102, achieving dual connectivity for the MCG provided by RAN node 1 and the SCG provided by RAN node 2. Alternatively, UE 3 communicates with RAN nodes 1 and 4 via air interfaces 101 and 104, achieving dual connectivity for the MCG provided by RAN node 1 and the SCG provided by RAN node 4.

[0043] 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, the MN1 may be a master eNB (in EN-DC), a master ng-eNB (in NGEN-DC), or a master gNB (in NR-DC and NE-DC). Similarly, the S-SN2 and T-SN4 may be an en-gNB (in EN-DC), a secondary ng-eNB (in NE-DC), or a secondary gNB (in NR-DC and NGEN-DC). In EN-DC, the UE3 is connected to an eNB operating as the MN1 and an en-gNB operating as the S-SN2 or T-SN4. In NGEN-DC, UE3 is connected to an ng-eNB operating as MN1 and 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 also connected to an 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 also connected to another gNB (or gNB-DU) operating as S-SN2 or T-SN4.

[0044] The MCG is a group of serving cells associated with (or provided to) the MN1, and includes an SpCell (i.e., a Primary Cell (PCell)) and optionally one or more Secondary Cells (SCells). On the other hand, the SCG is a group of serving cells associated with (or provided to) the S-SN2 or T-SN4, and includes a Primary SCG Cell (PSCell) and optionally one or more Secondary Cells (SCells). The PSCell is a Special Cell (SpCell) of the SCG, and supports Physical Uplink Control Channel (PUCCH) transmission and contention-based Random Access.

[0045] As used herein, the term "primary SCG cell" and its abbreviation "PSCell" refer to a cell included in a cell group provided by a dual connectivity SN, having an uplink component carrier, and configured with uplink control channel (e.g., PUCCH) resources. Specifically, the term "primary SCG cell" and its abbreviation "PSCell" may refer to the Primary SCG Cell of a cell group provided by an SN supporting 5G NR, or the Primary SC Cell of a cell group provided by an SN supporting E-UTRA.

[0046] 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 MN 1, 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 SN 4. Inter-SN CPC may also be referred to as conditional SN change. Inter-SN CPC is an inter-SN PSCell change procedure (or SN change procedure) that is executed by UE 3 only when a CPC execution condition is met. Although not shown in FIG. 1, multiple candidate cells (i.e., candidate PSCells) provided by multiple candidate SNs 4 may be prepared for inter-SN CPC.

[0047] The UE 3 communicates with the MN 1 and the S-SN 2 via the air interfaces 101 and 102, and performs dual connectivity between the MCG provided by the MN 1 and the SCG provided by the S-SN 2. Furthermore, by performing inter-SN CPC, the UE 3 communicates with the MN 1 and the T-SN 4 via the air interfaces 101 and 104, and performs dual connectivity between the MCG provided by the MN 1 and the SCG provided by the T-SN 4.

[0048] In the Inter-SN CPC procedure, the MN1 requests the candidate SN4 to prepare one or more candidate PSCells. If the MN1 request can be accepted, the candidate SN4 (or its radio resource management entity) allocates radio resources for each of the one or more candidate PSCells and, depending on the bearer options, transport network resources. That is, the preparation of one or more candidate PSCells by the candidate SN4 includes the allocation of radio resources for each of the one or more candidate PSCells and the allocation of transport network resources depending on the bearer options. Specifically, from the list of cells indicated in the measurement results provided by the MN1, the candidate SN4 determines a list of PSCell(s) to prepare (taking into account the maximum number indicated by the MN1), and for each prepared PSCell, the candidate SN4 determines other SCG SCell(s) and provides the corresponding SCG configuration (SCG radio resource configuration) to the MN1.

[0049] In the Inter-SN CPC procedure, the UE 3 receives CPC configuration from the MN 1 via an MN Radio Resource Control (RRC) message, specifically an MN RRCReconfiguration message. The CPC configuration includes configurations of one or more candidate PSCells and associated CPC execution conditions to be applied when CPC execution is triggered, and may include MCG configuration for inter-SN CPC. The configuration of each candidate PSCell is included in an MN RRCReconfiguration* message generated by the MN 1. Each MN RRCReconfiguration* message includes an SN RRCReconfiguration** message containing the SCG configuration received from the candidate SN 4, and possibly the MCG configuration. The UE 3 applies the MN RRCReconfiguration message received from the MN 1, stores the CPC configuration, and responds to the MN 1 with an MN RRCReconfigurationComplete message. The UE 3 then begins evaluating the CPC execution conditions of one or more candidate PSCells in response to receiving the CPC configuration. If the execution conditions for one candidate PSCell are met, the UE 3 applies the MN RRCReconfiguration* message corresponding to that candidate PSCell, i.e., the SCG configuration (SN RRCReconfiguration** message) and possibly the MCG configuration. If the execution conditions for two or more candidate PSCells are met, the UE 3 may select one of the candidate PSCells and perform the operations described above.

[0050] In the current 3GPP specification, up to two CPC execution conditions can be configured for one candidate PSCell. The CPC execution condition is generated by the 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 condition may consist 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, and may be, 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”.

[0051] Figure 2 illustrates another exemplary configuration of a wireless communication system according to several embodiments. In the example of Figure 2, the wireless communication system includes a RAN node 1, a RAN node 2, and a UE 3. Each element (network function) illustrated in Figure 2 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on the dedicated hardware, or as a virtualized function instantiated on an application platform.

[0052] RAN node 1, RAN node 2, and UE 3 in the example of FIG. 2 may have the same configurations and functions as those in the example of FIG. 1. Specifically, RAN node 1 and RAN node 2 communicate with each other via a node-to-node interface (e.g., X2 interface or Xn interface) 103. RAN node 1 and RAN node 2 can operate as a MN and SN, respectively, for dual connectivity. Therefore, hereinafter, RAN node 1 may be referred to as MN 1, and RAN node 2 may be referred to as candidate SN 2. Once candidate SN 2 is added through the SN addition procedure, UE 3 communicates with MN 1 and SN 2 via air interfaces 101 and 102 to provide dual connectivity for MCG and SCG. This dual connectivity may be MR-DC.

[0053] RAN nodes 1 and 2 and UE 3 support conditional PSCell addition (CPA), which adds an SCG provided by RAN node 2 for UE 3. CPA may also 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 CPA execution conditions are met. Although not shown in Figure 2, multiple candidate PSCells provided by multiple candidate SNs 2 may be prepared for CPA.

[0054] In the CPA procedure, MN1 requests the candidate SN2 to prepare one or more candidate PSCells. If the candidate SN2 can accept MN1's request, it (or its radio resource management entity) allocates radio resources for each of the one or more candidate PSCells and transport network resources depending on the bearer options. Specifically, from the list of cells indicated in the measurement results provided by MN1, the candidate SN2 determines a list of PSCells to prepare (considering the maximum number indicated by MN1). For each prepared PSCell, the candidate SN2 determines other SCG SCells and provides the corresponding SCG configuration (SCG radio resource configuration) to MN1. In other words, it can be said that the preparation of one or more candidate PSCells by the candidate SN2 includes the allocation of radio resources for each of the one or more candidate PSCells and the allocation of transport network resources depending on the bearer options. Additionally or alternatively, it can be said that the preparation of one or more candidate PSCells by the candidate SN2 includes the creation of a configuration (or SCG configuration) for one or more candidate PSCells.

[0055] In the CPA procedure, the UE 3 receives a CPA configuration from the MN 1 via an MN RRC message, specifically an MN RRCReconfiguration message. The CPA configuration includes configurations of one or more candidate PSCells and associated CPA execution conditions to be applied when CPA execution is triggered, and may include an MCG configuration for CPA. The configuration of each candidate PSCell is included in an MN RRCReconfiguration* message generated by the MN 1. Each MN RRCReconfiguration* message includes an SN RRCReconfiguration** message containing the SCG configuration received from the candidate SN 4, and possibly the MCG configuration. The UE 3 applies the MN RRCReconfiguration message received from the MN 1, stores the CPC configuration, and responds to the MN 1 with an MN RRCReconfigurationComplete message. In response to receiving the CPA configuration, the UE 3 then begins evaluating the CPA execution conditions of one or more candidate PSCells. If the execution conditions for one candidate PSCell are met, the UE 3 applies the MN RRCReconfiguration* message corresponding to that candidate PSCell, i.e., the SCG configuration (SN RRCReconfiguration** message) and possibly the MCG configuration. If the execution conditions for two or more candidate PSCells are met, the UE 3 may select one of the candidate PSCells and perform the operations described above.

[0056] In the current 3GPP specification, up to two CPA execution conditions can be configured for one candidate PSCell. The CPA execution condition is generated by the MN1. The CPA execution condition may consist of one or more trigger conditions. The condition or criterion for triggering a CPA event may be similar to that for a measurement report event, and may be, for example, CondEvent A3, CondEvent A4, or CondEvent A5.

[0057] In addition, the RAN node 2 and the UE 3 support intra-SN CPC, which may also be called SN-initiated Conditional SN Modification without MN involvement. Intra-SN CPC is an intra-SN PSCell change procedure that is executed only when the CPC execution conditions are met.

[0058] In the Intra-SN CPC procedure, the UE 3 receives CPC configuration from the SN 2 via an SN RRC message, specifically an SN RRCReconfiguration message. The SN 2 may send the CPC configuration to the UE 3 via the MN 1 or via a direct signaling radio bearer (i.e., Signaling Radio Bearer 3 (SRB3)) between the SN 2 and the UE 3. The CPC configuration includes the configuration of one or more candidate PSCells and associated CPC execution conditions that are applied when CPC execution is triggered. The configuration of each candidate PSCell is included in an SN RRCReconfiguration** message generated by the SN 2. The UE 3 applies the SN RRCReconfiguration message received from the SN 2, stores the CPC configuration, and responds to the SN 2 with an SN RRCReconfigurationComplete message. The SN RRCReconfigurationComplete message may be forwarded to the SN 2 via the MN 1. Then, in response to receiving the CPC configuration, the UE 3 starts evaluating the CPC execution conditions of one or more candidate PSCells. If the execution conditions of one candidate PSCell are met, the UE 3 applies the SN RRCReconfiguration** message, i.e., the SCG configuration, corresponding to that candidate PSCell. If the execution conditions of two or more candidate PSCells are met, the UE 3 may select one of the candidate PSCells and perform the operations described above.

[0059] One or more of the RAN nodes 1, 2, and 4 may have the configuration shown in Figure 3. Each element (network function) shown in Figure 3 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. One or more of the RAN nodes 1, 2, and 4 may include, but are not limited to, a CU 301 and one or more DUs 302 as shown in Figure 3. The CU 301 and each DU 302 are connected by an interface 321. A UE 3 is connected to at least one DU 302 via at least one air interface 322.

[0060] The CU 301 may be a logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols (or the RRC and PDCP protocols) of the gNB. The DU 302 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 301 is a gNB-CU and the DUs 302 are gNB-DUs, the interface 321 may be an F1 interface. The CU 301 may include a CU-CP and a CU-UP.

[0061] In this specification, the term conditional mobility is used, which 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 modification).

[0062] The embodiments described below provide improvements to conditional mobility. Specifically, the following embodiments provide improvements to CPA and CPC to support subsequent CPAC. Subsequent CPAC includes SN-initiated intra-SN subsequent CPAC, MN-initiated inter-SN subsequent CPAC, and SN-initiated inter-SN subsequent CPAC. Subsequent CPAC may also be referred to as subsequent CPC, selective SCG activation, SCG selective activation, adaptive SCG switch, SCG adaptive switch, subsequent SCG selection, or SCG subsequent selection, for example.

[0063] As defined herein, a subsequent CPAC may be a conditional PSCell change procedure performed after an initial PSCell addition or PSCell change based on the configuration of a previously configured CPA or candidate PSCells for a CPA, without re-initiation of the CPC or CPA. A subsequent CPAC may be a conditional PSCell change procedure performed after an initial PSCell addition or PSCell change based on the configuration of a previously configured CPA or candidate PSCells for a CPA, without re-configuration and restart of the CPC or CPA. In other words, as defined herein, a subsequent CPAC may enable the UE 3 to reuse or maintain, for a subsequent CPC, at least some (or all) of the configuration of candidate PSCells received from the network for the initial CPA or CPC. At least some of the execution conditions for the initial CPA or CPC may be re-configured, updated, or modified for the subsequent CPC. Similarly, at least a portion of the information regarding security key configuration (e.g., sk-Counter, Next Hop (NH), NH Chaining Count (NCC)) for an initial CPA or CPC, or security key information (e.g., SN Security Key), may be reset, updated, or modified for a subsequent CPC.

[0064] In the case of Inter-SN subsequent CPAC, the CPA, CPC, or CPAC configuration (which may also be called subsequent CPAC configuration) included in the initial MN RRCReconfiguration message sent from the MN to the UE may include the configuration of each of one or more candidate PSCells (SCG configuration), the CPA or CPC execution conditions associated with each candidate PSCell for the initial CPA or CPC, and the CPC execution conditions for subsequent CPCs from each candidate PSCell.

[0065] In the case of MN initiated inter-SN subsequent CPAC, the MN may generate the execution conditions for the first CPAC and then generate the execution conditions for all subsequent CPCs. Alternatively, some of the execution conditions for subsequent CPCs, for example, the execution conditions for subsequent CPCs from some candidate PSCell(s), may be generated by the candidate SN(s) managing these candidate PSCell(s). On the other hand, in the case of SN initiated inter-SN subsequent CPAC, the source SN may generate the execution conditions for the first CPC and the candidate SN may generate the execution conditions for subsequent CPCs.

[0066] The subsequent CPC in the Inter-SN subsequent CPAC may be an intra-SN CPC, not necessarily an inter-SN CPC. Specifically, even if the first CPC is an inter-SN CPC, the subsequent CPC may be an intra-SN CPC from one candidate PSCell prepared by one candidate SN (i.e., the candidate PSCell selected by the UE 3 in the first CPC) to another candidate PSCell prepared by the candidate SN.

[0067] As already used, the terms MN RRC message, MN RRC Reconfiguration message, SN RRC message, and SN RRC Reconfiguration message are used in this specification. 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 be simply referred to as the RRC message and the RRC Reconfiguration message. Similarly, the SN RRC message and the SN RRC Reconfiguration message may be simply referred to as the RRC message and the RRC Reconfiguration message.

[0068] First Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to inter-SN subsequent CPAC.

[0069] 4 shows an example of signaling related to inter-SN subsequent CPAC. If the initial conditional mobility is CPC, the MN 401 and candidate SN 402 may be RAN node 1 and RAN node 4, respectively, shown in FIG. 1. On the other hand, if the initial conditional mobility is CPA, the MN 401 and candidate SN 402 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 2.

[0070] In step 421, the MN 401 sends a first control message to the candidate SN 402. The first control message of step 421 requests the candidate SN 402 to prepare one or more candidate PSCells for the first CPA or CPC for the UE 3. In addition, the first control message includes first information indicating whether the candidate SN 402 is permitted or required to generate execution conditions for subsequent CPCs that may occur after the first CPA or CPC.

[0071] The first control message may be an SN Addition Request message. The first control message may include an indication of a CPA or CPC, an indication of a subsequent CPC, and the above-mentioned first information. The indication of a CPA or CPC may be an information element regarding a CPA, CPC, or CPAC. The indication of a CPA or CPC (or an information element regarding a CPA, CPC, or CPAC) may indicate a list of one or more candidate PSCells proposed by the MN 401 or the source SN. The indication of a CPA or CPC may be a Conditional PSCell Addition Information Request information element (IE) in the SN Addition Request message. The indication of a subsequent CPC may be an information element regarding a subsequent CPC. The indication of a subsequent CPC (or an information element regarding a subsequent CPC) may indicate to the candidate SN 402 that a subsequent CPC is requested. The indication of a subsequent CPC may be a Selective Activation Information Request IE or a subsequent CPAC Information Request IE in the SN Addition Request message.

[0072] In one example, the first information may be a sub-IE included in a Selective Activation Information Request IE or a subsequent CPAC Information Request IE in the SN Addition Request message, in which case the name of the IE (or sub-IE) corresponding to the first information may be, for example, "Condition (generation) request" or "Requested condition (generation)."

[0073] Alternatively, the first information may be included in a CG-ConfigInfo message carried in an M-NG-RAN node to S-NG-RAN node Container IE in an SN Addition Request message. The CG-ConfigInfo message is one of inter-node RRC messages. Generally, an inter-node RRC message is an RRC message transmitted between RAN nodes via an inter-node interface such as an Xn interface or an X2 interface. The CG-ConfigInfo message is used by an MN to request an SN to establish, modify, or release an SCG. In this case, the IE corresponding to the first information may be, for example, an allowExecutionConditionGeneration IE, which may be of an enumerated type and indicate "true." Alternatively, the IE corresponding to the first information may be, for example, an executionConditionGeneration IE, which may be of an enumerated type and indicate "MN" or "candidateSN."

[0074] According to the operation shown in FIG. 4, when requesting the candidate SN 402 to prepare the first CPA or CPC, the MN 401 can explicitly inform the candidate SN 402 of permission, instruction, or request to generate execution conditions for the subsequent CPC. This contributes to clarifying the signaling details related to the generation of execution conditions for the subsequent CPC in inter-SN subsequent CPAC. If the candidate SN 402 is not permitted or requested by the MN 401 to generate execution conditions for the subsequent CPC, the candidate SN 402 may operate not to generate execution conditions for the subsequent CPC. Alternatively, the candidate SN 402 may operate not to include execution conditions for the subsequent CPC in a response message (e.g., an SN Addition Request Acknowledge message) to the first control message (e.g., an SN Addition Request message).

[0075] According to Non-Patent Documents 2 and 3, in the case of an MN initiated inter-SN subsequent CPAC, it is still being debated whether the MN generates execution conditions for all subsequent CPCs or whether the candidate SNs may generate execution conditions for the subsequent CPCs. There are advantages and disadvantages to both the MN and the candidate SNs generating execution conditions for the subsequent CPCs. Therefore, in some implementations, the MN 401 may decide whether the MN 401 or the candidate SN 402 should generate execution conditions for the subsequent CPCs. In other words, the MN 401 may decide whether to permit or request the candidate SN 402 to generate execution conditions for the subsequent CPCs. Based on the result of this decision, the MN 401 may indicate to the candidate SN 402 whether the candidate SN 402 is permitted (or requested) to generate execution conditions for the subsequent CPCs.

[0076] According to the current 3GPP agreement described in Non-Patent Documents 2 and 3, in the case of an SN initiated inter-SN subsequent CPC, the candidate SN generates the execution conditions for the subsequent CPC. Therefore, in one implementation, the MN 402 may operate to permit or request the candidate SN 402 to generate execution conditions for the subsequent CPC in the case of an SN initiated inter-SN subsequent CPC, and not permit or request the candidate SN 402 to generate these conditions in the case of an MN initiated inter-SN subsequent CPC. However, the current agreement may be changed. For example, in the case of an SN initiated inter-SN subsequent CPC, the source SN may decide whether the candidate SN should generate execution conditions for the subsequent CPC. In this case, the MN 401 may receive from the source SN a control message (e.g., an SN Change Required message) containing information indicating whether the candidate SN 402 is permitted (or requested) to generate execution conditions for the subsequent CPC. The MN 401 may then forward the information received from the source SN to the candidate SN 402.

[0077] 5 shows an example of signaling related to inter-SN subsequent CPAC. If the initial conditional mobility is CPC, the MN 501 and candidate SN 502 may be RAN node 1 and RAN node 4, respectively, shown in FIG. 1. On the other hand, if the initial conditional mobility is CPA, the MN 501 and candidate SN 502 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 2.

[0078] Step 521 is similar to step 421 in Fig. 4. Specifically, MN 501 sends a first control message to candidate SN 502. The first control message requests candidate SN 502 to prepare one or more candidate PSCells for an initial CPA or CPC for UE 3. In addition, the first control message includes first information indicating whether candidate SN 502 is permitted or requested to generate execution conditions for subsequent CPCs that may occur after the initial CPA or CPC. In the example of Fig. 5, the first information indicates that candidate SN 502 is permitted or requested to generate execution conditions for subsequent CPCs.

[0079] In step 522, the candidate SN 502 sends a second control message to the MN 501 in response to the first control message. In other words, the MN 501 receives the second control message sent from the candidate SN 502 in response to the first control message. The second control message includes configuration for at least one candidate PSCell prepared by the candidate SN 502. The configuration for each candidate PSCell included in the second control message, i.e., the SCG configuration, is used for the first CPA or CPC and may also be used in subsequent CPCs. In addition, if the first control message of step 521 (or the first information in the message) indicates that the candidate SN 502 is permitted or required to generate execution conditions for subsequent CPCs, the second control message includes second information indicating whether these execution conditions have been generated (or whether they are included). If the candidate SN 502 has generated execution conditions for the subsequent CPC, the second control message may include information indicating the generated execution conditions for the subsequent CPC.

[0080] The first control message of step 521 may be an SN Addition Request message. Examples of the first control message and the first information of step 521 are similar to those described above with respect to the first control message and the first information of step 421 of FIG.

[0081] The second control message of step 522 may be an SN Addition Request Acknowledge message. The second information may be a sub-IE included in a Conditional PSCell Addition Information Acknowledge IE in the SN Addition Request Acknowledge message. In this case, the IE (or sub-IE) corresponding to the second information may be, for example, a Condition prepared IE, which may be an enumeration type and indicate "true".

[0082] Alternatively, the second information may be included in a CG-CandidateList message carried in an S-NG-RAN node to M-NG-RAN node Container IE in the SN Addition Request Acknowledge message. The CG-CandidateList message is one of the inter-node RRC messages. The CG-CandidateList message is used to transfer the SCG radio configuration of the CPC or one or more candidate cells for the CPC. The CG-CandidateList message includes a list of one or more CG-Config messages, each corresponding to a respective one of the one or more candidate cells. In this case, the IE corresponding to the second information may be, for example, a condExecutionCond IE, which may be of enumerated type and indicate "true".

[0083] In one example, the first control message (or the first information in the message) of step 521 may indicate to the candidate SN 502 permission to generate an execution condition for the subsequent CPC. In this case, the candidate SN 502 may either generate an execution condition for the subsequent CPC or not. If the candidate SN 502 has generated an execution condition for the subsequent CPC, the second control message may include information indicating the generated execution condition for the subsequent CPC and may include second information that explicitly or implicitly indicates to the MN 501 that an execution condition for the subsequent CPC has been generated (or included). On the other hand, if the candidate SN 502 has not generated an execution condition for the subsequent CPC, the second control message may include second information that explicitly or implicitly indicates to the MN 501 that an execution condition for the subsequent CPC has not been generated (or not included). Alternatively, the second control message may indicate to the MN 501 that an execution condition for the subsequent CPC has not been generated by omitting the second information.

[0084] In another example, the first control message of step 521 (or the first information in the message) may indicate to the candidate SN 502 an instruction or request to generate execution conditions for the subsequent CPC. In this case, the candidate SN 502 is essentially required to generate execution conditions for the subsequent CPC. If the candidate SN 502 has generated execution conditions for the subsequent CPC, the second control message may include information indicating the generated execution conditions for the subsequent CPC and second information that explicitly or implicitly indicates to the MN 501 that execution conditions for the subsequent CPC have been generated (or included). Alternatively, the second control message may include information indicating the generated execution conditions for the subsequent CPC but not the second information, thereby indicating to the MN 501 that execution conditions for the subsequent CPC have been generated. On the other hand, if the candidate SN 502 has not generated execution conditions for the subsequent CPC, the second control message may include second information that explicitly or implicitly indicates to the MN 501 that execution conditions for the subsequent CPC have not been generated (or are not included).

[0085] 5, when requesting the candidate SN 502 to prepare the first CPA or CPC, the MN 501 can explicitly notify the candidate SN 502 of permission, instruction, or request to generate an execution condition for the subsequent CPC. In addition, if the candidate SN 502 is permitted or requested by the MN 501 to generate an execution condition for the subsequent CPC, the candidate SN 502 can notify the MN 501 whether or not the execution condition for the subsequent CPC has been generated. This contributes to clarifying the signaling details regarding the generation of an execution condition for the subsequent CPC in an inter-SN subsequent CPAC.

[0086] The candidate SN 502 may operate not to generate an execution condition for the subsequent CPC if the generation of the execution condition for the subsequent CPC is not permitted or requested by the MN 501. Alternatively, the candidate SN 502 may operate not to include an execution condition for the subsequent CPC in a response message (e.g., an SN Addition Request Acknowledge message) to the first control message (e.g., an SN Addition Request message).

[0087] 6 shows an example of signaling related to inter-SN subsequent CPAC. If the initial conditional mobility is CPC, the MN 601 and candidate SN 602 may be RAN node 1 and RAN node 4, respectively, shown in FIG. 1. On the other hand, if the initial conditional mobility is CPA, the MN 601 and candidate SN 602 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 2.

[0088] Step 621 is similar to step 421 in Figure 4 and step 521 in Figure 5. Specifically, the MN 601 sends a first control message to the candidate SN 602. The first control message in step 621 requests the candidate SN 602 to prepare one or more candidate PSCells for the first CPA or CPC for the UE 3. In addition, the first control message includes first information indicating whether the candidate SN 602 is permitted or required to generate execution conditions for subsequent CPCs that may be performed after the first CPA or CPC. In the example of Figure 6, the first information indicates that the candidate SN 602 is required to generate execution conditions for the subsequent CPCs. In other words, the first information instructs the candidate SN 602 to generate execution conditions for the subsequent CPCs.

[0089] If the first control message of step 621 instructs or requests the generation of execution conditions for the subsequent CPC but the candidate SN 602 does not or cannot generate the execution conditions, the candidate SN 602 responds to the MN 601 with a rejection message in step 622. The rejection message of step 622 indicates that the preparation of all of the one or more candidate PSCells proposed in the first control message of step 621 has been rejected or failed. The rejection message may be an SN Addition Request Reject message. The rejection message may indicate that the rejection is due to the fact that the execution conditions for the subsequent CPC have not or cannot be generated.

[0090] 6, when requesting the candidate SN 602 to prepare the first CPA or CPC, the MN 601 can explicitly inform the candidate SN 602 of an instruction or request to generate execution conditions for the subsequent CPC. In addition, if the candidate SN 602 does not or cannot generate execution conditions for the subsequent CPC, the candidate SN 602 rejects the preparation of all of the proposed one or more candidate PSCells. This contributes to clarifying the signaling details regarding the generation of execution conditions for the subsequent CPC in inter-SN subsequent CPACs.

[0091] FIG. 7 shows an example of signaling related to an SN initiated inter-SN subsequent CPC. MN 701 and source SN 702 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 1. In an SN initiated inter-SN subsequent CPC, source SN 702 determines whether a candidate SN (e.g., candidate SN 4 in FIG. 1) should generate execution conditions for the subsequent CPC. In step 721, source SN 702 sends a third control message to MN 701, the third control message including third information indicating whether the candidate SN is permitted or required to generate execution conditions for the subsequent CPC. The third control message may include an indication of the CPC and an indication of the subsequent CPC and may trigger an SN change. Specifically, the third control message may be an SN Change Required message.

[0092] The MN 701 may include the first information in the first control message (steps 421, 521, and 621 in FIGS. 4, 5, and 6) to be transmitted to the candidate SN based on the third information received from the source SN 702. In other words, the MN 701 may determine the content of the first information included in the first control message (steps 421, 521, and 621 in FIGS. 4, 5, and 6) based on the third information received from the source SN 702. Alternatively, the MN 701 may forward the third information received from the source SN 702 to the candidate SN. In other words, the MN 701 may include the third information received from the source SN 702 (as the first information) in the first control message (steps 421, 521, and 621 in FIGS. 4, 5, and 6).

[0093] According to the operation shown in Fig. 7, when triggering the first CPC, the source SN 702 can inform the MN 701, or the candidate SN via the MN 701, whether the candidate SN is permitted or required to generate an execution condition for the subsequent CPC. This contributes to clarifying the signaling details regarding the generation of an execution condition for the subsequent CPC in the inter-SN subsequent CPAC.

[0094] Second Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to inter-SN subsequent CPAC.

[0095] Figure 8 shows an example of the operation of a candidate SN in inter-SN subsequent CPAC. If the initial conditional mobility is CPC, the candidate SN may be RAN node 4 shown in Figure 1. On the other hand, if the initial conditional mobility is CPA, the candidate SN may be RAN node 2 shown in Figure 2.

[0096] In step 801, a candidate SN receives a first control message from an MN requesting the preparation of multiple candidate PSCells for an initial CPA or CPC and for a subsequent CPC. The first control message may be an SN Addition Request message. The first control message may include an indication of a CPA or CPC and an indication of a subsequent CPC. The multiple candidate PSCells are proposed by the MN in the case of an MN-initiated subsequent CPC and by the source SN in the case of an SN-initiated subsequent CPC.

[0097] In step 802, if the candidate SN can prepare some but not the rest of the plurality of candidate PSCells proposed by the MN (or source SN), the candidate SN transmits a second control message to the MN indicating that preparation of all of the plurality of candidate PSCells has been rejected or failed. The second control message indicates that preparation of all of the plurality of candidate PSCells has been rejected or failed because only some of the proposed plurality of candidate PSCells can be prepared. For example, the rejection message may include a Cause IE indicating "partially accepted," "partially preparable," or "not all acceptable." The second control message may be an SN Addition Request Reject message.

[0098] The first control message of step 801 may include information indicating whether the request should be rejected if only some of the proposed candidate PSCells can be prepared. The name of the IE corresponding to this information may be, for example, "partial (preparation) allow" or "partial (preparation) not-allow".

[0099] If the first control message includes the partial (preparation) not-allow IE, the candidate SN may perform the operation of step 802. Alternatively, if the first control message does not include the partial (preparation) allow IE, the candidate SN may perform the operation of step 802. That is, if the candidate SN can prepare some but not the rest of the multiple candidate PSCells proposed by the MN (or source SN), it may send a second control message to the MN indicating that preparation for all of the multiple candidate PSCells has been rejected or failed.

[0100] On the other hand, if the first control message does not include the partial (preparation) not-allow IE, the candidate SN may or may not perform the operation of step 802. Alternatively, if the first control message includes the partial (preparation) allow IE, the candidate SN may or may not perform the operation of step 802. For example, the candidate SN may prepare some candidate PSCell(s) among multiple candidate PSCells proposed for the first CPA or CPC and subsequent CPCs, and may transmit a response message (e.g., SN Addition Request Acknowledge message) including the configuration of these some candidate PSCell(s) to the MN.

[0101] 9 shows an example of an MN's operation in inter-SN subsequent CPAC. In step 901, the MN sends a first control message to a candidate SN requesting the preparation of multiple candidate PSCells for an initial CPA or CPC and for a subsequent CPC. The first control message may be an SN Addition Request message. The first control message may include an indication of the CPA or CPC and an indication of the subsequent CPC. The multiple candidate PSCells are proposed by the MN in the case of MN-initiated subsequent CPAC and by the source SN in the case of SN-initiated subsequent CPC.

[0102] In step 902, the MN receives a second control message from the candidate SN indicating that the preparation of all of the plurality of candidate PSCells has been rejected or failed because only some of the plurality of candidate PSCells can be prepared. The second control message may be an SN Addition Request Reject message.

[0103] 8 and 9, in an inter-SN subsequent CPAC, if a candidate SN can prepare only some of the proposed candidate PSCells, it rejects the provision of all of these candidate PSCells. This contributes to clarifying the procedure and process when a candidate SN can prepare some of the proposed candidate PSCells for an inter-SN subsequent CPAC but cannot prepare the rest.

[0104] <Third Embodiment> A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to inter-SN subsequent CPAC.

[0105] 10 shows an example of an MN's operation in inter-SN subsequent CPAC. In step 1001, the MN sends a first control message to a first candidate SN requesting the preparation of one or more candidate PSCells for an initial CPA or CPC and for a subsequent CPC. The first control message may be an SN Addition Request message. The first control message may include an indication of the CPA or CPC and an indication of the subsequent CPC. The candidate PSCells are proposed by the MN in the case of MN-initiated subsequent CPAC and by the source SN in the case of SN-initiated subsequent CPC.

[0106] In step 1002, the MN receives a second control message transmitted from the first candidate SN in response to the first control message. If the first candidate SN has prepared some or all of the proposed one or more candidate PSCells, the second control message may be an SN Addition Request Acknowledge message. On the other hand, if the first candidate SN has rejected the preparation of all of the proposed one or more candidate PSCells, the second control message may be an SN Addition Request Reject message.

[0107] In step 1003, if all of the one or more candidate PSCells proposed by the MN or source SN have not been prepared by the first candidate SN, the MN indicates to the second candidate SN via a third control message the candidate PSCell(s) that have or have not been prepared by the first candidate SN.

[0108] The second candidate SN may be a candidate SN that has completed preparation of one or more candidate PSCells for subsequent CPAC before the MN sends the first control message to the first candidate SN. The second candidate SN may be a candidate SN that has completed preparation of one or more candidate PSCells for subsequent CPAC before the MN receives the second control message from the first candidate SN. The second candidate SN may be a candidate SN to which the MN has requested preparation of subsequent CPAC (e.g., sent an SN Addition Request message) before the MN receives the second control message from the first candidate SN. In these cases, the third control message may be an SN Modification Request message.

[0109] Alternatively, the second candidate SN may be a candidate SN for which the MN has not yet requested the preparation of a subsequent CPAC when the MN receives the second control message from the first candidate SN, in which case the third control message may be an SN Addition Request message.

[0110] According to the operation shown in FIG. 10, in an inter-SN subsequent CPAC, the MN informs the second candidate SN of the candidate PSCell(s) that have or have not been prepared by the first candidate SN. This enables the second candidate SN to update or generate execution conditions for the subsequent CPC. Specifically, the second candidate SN can generate execution conditions for the subsequent CPC from the candidate PSCell prepared by the second candidate SN to each of one or more candidate PSCells prepared by the first candidate SN. Alternatively, if the second candidate SN has already completed preparation of the subsequent CPAC, the second candidate SN can delete the execution conditions for the subsequent CPC to each of one or more candidate PSCells that have not been prepared by the first candidate SN.

[0111] In the case of SN-initiated subsequent CPC, similar to the case of SN-initiated CPC, the MN may also inform the source SN of the candidate PSCell(s) that have been or have not been prepared by the first candidate SN. This notification may be performed using an SN Modification Request message, more specifically, using a Conditional PSCell Change Information Update IE in the SN Modification Request message. In response to receiving the notification, the source SN may update the previous CPC preparation. Specifically, the source SN may reply to the MN with an SN Modification Request Acknowledge message containing information indicating the CPC execution conditions of one or more candidate PSCells prepared by the first candidate SN. The information indicating the CPC execution conditions may be included in a CG-Config message carried in the S-NG-RAN node to M-NG-RAN node Container IE in the SN Modification Request Acknowledge message. The CG-Config message is one of the inter-node RRC messages.

[0112] 11 shows an example of signaling regarding an inter-SN subsequent CPAC. In step 1121, the MN 1101 requests the first candidate SN 1102A to prepare a subsequent CPAC. The MN 1101 provides the first candidate SN 1102A with a list of one or more candidate PSCells proposed by the MN 1101 or the source SN. The first candidate SN 1102A rejects the preparation of some or all of the candidate PSCell(s) proposed by the MN 1101 or the source SN.

[0113] In step 1122, the MN 1101 informs the second candidate SN 1102B of the candidate PSCell(s) that have or have not been prepared by the first candidate SN 1102A. The second candidate SN 1102B may be a candidate SN that has completed preparation of one or more candidate PSCells for the subsequent CPAC before the MN 1101 requests preparation of the subsequent CPAC from the first candidate SN 1102A. The second candidate SN 1102B may be a candidate SN that has completed preparation of one or more candidate PSCells for the subsequent CPAC before the MN 1101 receives a response message regarding the preparation of the subsequent CPAC from the first candidate SN 1102A. The second candidate SN may be a candidate SN for which the MN 1101 has requested the preparation of a subsequent CPAC (e.g., sent an SN Addition Request message) before the MN 1101 receives a response message regarding the preparation of a subsequent CPAC from the first candidate SN 1102A. In these cases, the notification in step 1122 may be performed using an SN Modification Request message, as shown in Fig. 11. Alternatively, the second candidate SN 1102B may be a candidate SN for which the MN 1101 has not yet requested the preparation of a subsequent CPAC at the end of step 1121. In this case, the notification in step 1122 may be performed using an SN Addition Request message.

[0114] In step 1123, the MN 1101 receives a response message transmitted from the second candidate SN 1102B. The response message may be an SN Modification Request Acknowledge message or an SN Addition Request Acknowledge message. The response message includes information indicating the execution conditions of a subsequent CPC from the candidate PSCell prepared by the second candidate SN 1102B to each of one or more candidate PSCells prepared by the first candidate SN 1102A.

[0115] The procedure shown in Figure 11 enables the second candidate SN 1102B to update or generate execution conditions for a subsequent CPC. Specifically, the second candidate SN 1102B can generate execution conditions for a subsequent CPC from a candidate PSCell prepared by the second candidate SN 1102B to each of one or more candidate PSCells prepared by the first candidate SN 1102A. Alternatively, if the second candidate SN 1102B has already completed preparation of a subsequent CPC, the second candidate SN 1102B can delete the execution conditions for a subsequent CPC to each of one or more candidate PSCells that were not prepared by the first candidate SN 1102A.

[0116] <Fourth embodiment> A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to inter-SN subsequent CPAC.

[0117] 12 shows an example of signaling related to inter-SN subsequent CPAC. If the initial conditional mobility is CPC, the MN 1201 and candidate SN 1202 may be RAN node 1 and RAN node 4, respectively, shown in FIG. 1. On the other hand, if the initial conditional mobility is CPA, the MN 1201 and candidate SN 1202 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 2.

[0118] In step 1221, the MN 1201 sends a first control message to the candidate SN 1202. The first control message requests the candidate SN 1202 to prepare one or more candidate PSCells for the first CPA or CPC and for subsequent CPCs for the UE 3. In addition, the first control message includes information indicating whether the candidate SN 1202 is permitted or required to prepare a cell other than these proposed one or more candidate PSCells as a candidate PSCell for the subsequent CPC.

[0119] The first control message may be an SN Addition Request message. The first control message may include an indication of a CPA or CPC, an indication of a subsequent CPC, and the above-mentioned information. The indication of a CPA or CPC may be an information element regarding a CPA, CPC, or CPAC. The indication of a CPA or CPC (or an information element regarding a CPA, CPC, or CPAC) may indicate a list of one or more candidate PSCells proposed by the MN 1201 or the source SN. The indication of a CPA or CPC may be a Conditional PSCell Addition Information Request IE in the SN Addition Request message. The indication of a subsequent CPC may be an information element regarding a subsequent CPC. The indication of a subsequent CPC (or an information element regarding a subsequent CPC) may indicate to the candidate SN 1202 that a subsequent CPC is requested. The indication of a subsequent CPC may be a Selective Activation Information Request IE or a subsequent CPAC Information Request IE in the SN Addition Request message.

[0120] In one example, the above information, i.e., the information indicating whether a cell other than the proposed candidate PSCell(s) may be prepared for subsequent CPC, may be a sub-IE included in a Conditional PSCell Addition Information Request IE in the SN Addition Request message, or alternatively, the information may be a sub-IE included in a Selective Activation Information Request IE or a subsequent CPAC Information Request IE in the SN Addition Request message.

[0121] The MN 1201 may inform the candidate SN 1202 of the maximum number of candidate PSCell(s) that may be prepared apart from the proposed candidate PSCell(s). Specifically, the first control message may include information indicating the maximum number of candidate PSCell(s) that may be prepared apart from the proposed candidate PSCell(s). The first control message may include information indicating a first maximum number of candidate PSCell(s) that may be prepared and information indicating a second maximum number of candidate PSCell(s) that may be prepared apart from the proposed candidate PSCell(s). The second maximum number is equal to or smaller than the first maximum number. In this case, the candidate SN 1202 may prepare cells apart from the proposed candidate PSCell(s) for the subsequent CPC within the indicated maximum number (or the second maximum number).

[0122] Alternatively, the MN 1201 may not explicitly inform the candidate SN 1202 of the maximum number of candidate PSCell(s) that may be prepared apart from the proposed candidate PSCell(s). Specifically, the MN 1201 may indicate to the candidate SN 1202 the maximum number of candidate PSCell(s) that may be prepared. The first control message may include information indicating the maximum number of candidate PSCell(s) that may be prepared. In this case, the candidate SN 1202 may prepare the proposed candidate PSCell(s) and the other candidate PSCell(s) within the indicated maximum number.

[0123] According to the operation shown in FIG. 12 , the MN 1201 can indicate to the candidate SN 1202 whether or not it is permitted to prepare a cell other than the proposed candidate PSCell(s) for the subsequent CPC. This contributes to clarifying the signaling details regarding the preparation of candidate PSCells for the subsequent CPC in an inter-SN subsequent CPC. In an inter-SN CPC, the candidate SN selects candidate PSCell(s) to prepare from among the candidate PSCell(s) proposed by the MN or source SN. However, it may be preferable to be able to prepare other cells managed by the candidate SN for the subsequent CPC. In such a case, the MN 1201 may permit the candidate SN 1202 to prepare a cell other than the proposed candidate PSCell(s) for the subsequent CPC. For example, the candidate SN 1202 may prepare a cell for the subsequent CPC that is adjacent to one of the candidate PSCell(s) proposed by the MN 1201 or source SN but is not included in the list of candidate PSCell(s) proposed by the MN 1201 or source SN.

[0124] 13 shows an example of an MN's operation in an inter-SN subsequent CPAC. In step 1301, the MN transmits a first control message to a first candidate SN. The first control message requests the preparation of one or more candidate PSCells for the initial CPA or CPC and for the subsequent CPC. In addition, the first control message indicates permission, request, or instruction to the first candidate SN to prepare cells other than these proposed candidate PSCells for the subsequent CPC. The first control message may be an SN Addition Request message.

[0125] In step 1302, the MN receives a second control message sent from the first candidate SN in response to the first control message. The second control message may be an SN Addition Request Acknowledge message.

[0126] In step 1303, if a first cell that is not included in one or more candidate PSCells indicated in the first control message is prepared by the first candidate SN for the subsequent CPC, the MN indicates the first cell to the second candidate SN for the initial CPA or CPC via a third control message.

[0127] The second candidate SN may be a candidate SN that has completed preparation of one or more candidate PSCells for subsequent CPAC before the MN sends the first control message to the first candidate SN. The second candidate SN may be a candidate SN that has completed preparation of one or more candidate PSCells for subsequent CPAC before the MN receives the second control message from the first candidate SN. The second candidate SN may be a candidate SN to which the MN has requested preparation of subsequent CPAC (e.g., sent an SN Addition Request message) before the MN receives the second control message from the first candidate SN. In these cases, the third control message may be an SN Modification Request message. This notification may be made using a Conditional PSCell Change Information Update IE in the SN Modification Request message. Alternatively, this notification may be made using a newly defined IE, such as a subsequent CPAC Information Update IE, in the SN Modification Request message.

[0128] Alternatively, the second candidate SN may be a candidate SN for which the MN has not yet requested the preparation of a subsequent CPAC when the MN receives the second control message from the first candidate SN, in which case the third control message may be an SN Addition Request message.

[0129] According to the operation shown in Figure 13, in an inter-SN subsequent CPAC, the MN informs the second candidate SN of one or more candidate PSCells additionally prepared by the first candidate SN. This enables the second candidate SN to update or generate execution conditions for the subsequent CPC. Specifically, the second candidate SN can generate execution conditions for the subsequent CPC from the candidate PSCell prepared by the second candidate SN to each of the one or more candidate PSCells additionally prepared by the first candidate SN.

[0130] 14 shows an example of signaling related to an inter-SN subsequent CPAC. In step 1421, the MN 1401 requests the first candidate SN 1402A to prepare a subsequent CPAC. The MN 1401 provides the first candidate SN 1402A with a list of one or more candidate PSCells proposed by the MN 1401 or the source SN. The first candidate SN 1402A prepares a first cell, other than the candidate PSCell(s) proposed by the MN 1401 or the source SN, for the subsequent CPC.

[0131] In step 1422, the MN 1401 notifies the second candidate SN 1402B of the first cell prepared by the first candidate SN 1402A. The second candidate SN 1402B may be a candidate SN that has completed preparation of one or more candidate PSCells for the subsequent CPAC before the MN 1401 requests preparation of the subsequent CPAC from the first candidate SN 1402A. The second candidate SN 1402B may be a candidate SN that has completed preparation of one or more candidate PSCells for the subsequent CPAC before the MN 1401 receives a response message regarding the preparation of the subsequent CPAC from the first candidate SN 1402A. The second candidate SN may be a candidate SN for which the MN 1401 has requested the preparation of a subsequent CPAC (e.g., sent an SN Addition Request message) before the MN 1401 receives a response message regarding the preparation of a subsequent CPAC from the first candidate SN 1402A. In these cases, the notification in step 1422 may be performed using an SN Modification Request message, as shown in Fig. 14. Alternatively, the second candidate SN 1402B may be a candidate SN for which the MN 1401 has not yet requested the preparation of a subsequent CPAC at the end of step 1421. In this case, the notification in step 1422 may be performed using an SN Addition Request message.

[0132] In step 1423, the MN 1401 receives a response message transmitted from the second candidate SN 1402B. The response message may be an SN Modification Request Acknowledge message or an SN Addition Request Acknowledge message. The response message includes information indicating the execution conditions of subsequent CPC from each of one or more candidate PSCells prepared by the second candidate SN 1402B to the first cell prepared by the first candidate SN 1402A.

[0133] The procedure shown in Figure 14 enables the second candidate SN 1402B to update or create execution conditions for a subsequent CPC. Specifically, the second candidate SN 1402B can add execution conditions for a subsequent CPC to a first cell that has been additionally prepared by the first candidate SN 1402A.

[0134] FIG. 15 shows an example of signaling for an SN-initiated inter-SN subsequent CPC. MN 1501 and source SN 1502 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 1. In step 1521, source SN 1502 sends a control message to MN 1501 containing information indicating whether a candidate SN (e.g., candidate SN 4 in FIG. 1) is permitted or required to prepare cells other than the proposed candidate PSCells for the subsequent CPC. The control message may contain an indication of the CPC and an indication of the subsequent CPC and may trigger an SN change. Specifically, the third control message may be an SN Change Required message.

[0135] The MN 1501 may include permission, a request, or an instruction to prepare a cell other than the proposed candidate PSCell for a subsequent CPC in a first control message (step 1221 in FIG. 12 , step 1301 in FIG. 13 , and step 1401 in FIG. 14 ) to be transmitted to the candidate SN based on the information received in step 1521 from the source SN 1502. In other words, the MN 1501 may determine the content of the first control message (step 1221 in FIG. 12 , step 1301 in FIG. 13 , and step 1401 in FIG. 14 ) based on the information received in step 1521 from the source SN 1502. Alternatively, the MN 1501 may forward the information received in step 1521 from the source SN 1502 to the candidate SN. In other words, the MN 1501 may include the information received in step 1521 from the source SN 1502 in the first control message (step 1221 in FIG. 12, step 1301 in FIG. 13, and step 1401 in FIG. 14).

[0136] 15, when triggering the first CPC, the source SN 1502 can inform the MN 1501, or the candidate SNs via the MN 1501, whether it is permitted or required to prepare cells other than the proposed candidate PSCell(s) for the subsequent CPC. This contributes to clarifying the signaling details regarding the preparation of candidate PSCells for the subsequent CPC in an SN-initiated inter-SN subsequent CPC.

[0137] Fifth Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to inter-SN subsequent CPAC.

[0138] FIG. 16 shows an example of the operation of a source SN (e.g., source SN 2 in FIG. 1) in an MN or SN-initiated inter-SN subsequent CPC. In step 1601, the source SN operates as a source SN for an initial CPC. In step 1602, the source SN sends information to the MN, or to the candidate SN via the MN, indicating whether one or more cells managed by the source SN (e.g., the source PSCell or the current serving cell of UE 3) will be candidate PSCells for a subsequent CPC that may occur after the initial CPC. The information may be forwarded to the candidate SN via the MN. Alternatively, the information may cause the MN to inform the candidate SN whether one or more cells managed by the source SN will be candidate PSCells for the subsequent CPC.

[0139] The information in step 1602 may indicate one or more cells managed by the source SN and designated as candidate PSCells of the subsequent CPC, or may be a list of these cells. The one or more cells managed by the source SN and designated as candidate PSCells of the subsequent CPC may include the source PSCell of the initial CPC. Additionally or alternatively, these cells may include cells other than the source PSCell.

[0140] The source SN sends the information of step 1602 to the MN via a control message. The control message may trigger the initial CPC and include a list of one or more candidate PSCells managed by each candidate SN. In addition, the control message may include a list of one or more cells managed by the source SN that are candidate PSCells for the subsequent CPC. The control message may be an SN Change Required message. The information of step 1602 may be a sub-IE included in the Selective Activation Information Required IE or the subsequent CPAC Information Required IE in the SN Change Required message.

[0141] In the case of an MN-initiated inter-SN subsequent CPC, the source SN may receive a notification from the MN indicating that a cell managed by the source SN is permitted to be a candidate PSCell for the subsequent CPC. Conditional on receiving this notification from the MN, the source SN may transmit the information in step 1602.

[0142] According to the operation shown in Figure 16, the source SN can inform the MN, or the candidate SN via the MN, whether one or more cells managed by the source SN will be candidate PSCells of the subsequent CPC. This contributes to clarifying the signaling details regarding the determination of candidate PSCells of the subsequent CPC in the inter-SN subsequent CPAC.

[0143] Sixth Embodiment A configuration example of a wireless communication system according to this embodiment is similar to the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to subsequent CPAC.

[0144] When a handover or CHO is performed after a subsequent CPAC is prepared, the network (e.g., MN1, source SN2 or candidate SN2, and candidate SN4) and UE3 release the subsequent CPAC configuration. Here, the subsequent CPAC includes the SN initiated intra-SN subsequent CP(A)C, the Master Node (MN) initiated inter-SN subsequent CPAC, and the SN initiated inter-SN subsequent CP(A)C. The handover or CHO includes the inter-MN handover or CHO.

[0145] For the release of the subsequent CPAC configuration in the network, the MN may instruct the candidate SN, and in the case of SN-initiated subsequent CPC, the source SN, to release or cancel the subsequent CPAC configuration. On the other hand, for the release of the subsequent CPAC configuration in the UE 3, the MN (or the source SN) may explicitly instruct the UE 3 to release or cancel the subsequent CPAC configuration. Alternatively, the UE 3 may autonomously release the subsequent CPAC configuration in response to the execution of handover or CHO.

[0146] The operations described in this embodiment contribute to clarifying the details of the operations of the network and the UE 3 when handover or CHO is executed after preparation of subsequent CPAC.

[0147] Seventh Embodiment A configuration example of a wireless communication system according to this embodiment is similar to the configuration example described with reference to Fig. 1 or Fig. 2. This embodiment relates to subsequent CPAC.

[0148] When an inter-MN handover or CHO without a secondary node change is performed after a subsequent CPAC is prepared, the network (e.g., MN1, source SN2 or candidate SN2, and candidate SN4) and UE3 keep some or all of the subsequent CPAC configurations without releasing them. Here, the subsequent CPAC includes the SN initiated intra-SN subsequent CP(A)C, the Master Node (MN) initiated inter-SN subsequent CPAC, and the SN initiated inter-SN subsequent CP(A)C. The network and UE3 may reuse the kept subsequent CPAC configurations for the subsequent CPAC performed after the handover or CHO.

[0149] An inter-MN handover or CHO without a secondary node change does not change the candidate SN (and the source SN if the initial CPAC is a CPC). Therefore, it may be wasteful to release a prepared subsequent CPAC configuration and then prepare a subsequent CPAC again. The operation described in this embodiment reduces the signaling overhead for re-preparing and re-initializing a subsequent CPAC, and contributes to quickly preparing a subsequent CPAC after an inter-MN handover or CHO without a secondary node change.

[0150] Next, exemplary configurations of RAN nodes and UEs related to the above-described embodiments will be described below. FIG. 17 is a block diagram illustrating an exemplary configuration of a RAN node 1 according to the above-described embodiments. The configurations of other RAN nodes 2, 4, 401, and 402, etc., may be similar to the configuration illustrated in FIG. 17. Referring to FIG. 17, the RAN node 1 includes a Radio Frequency (RF) transceiver 1701, a network interface 1703, a processor 1704, and a memory 1705. The RF transceiver 1701 performs analog RF signal processing for communication with UEs, including UE 3. The RF transceiver 1701 may include multiple transceivers. The RF transceiver 1701 is coupled to an antenna array 1702 and a processor 1704. The RF transceiver 1701 receives modulation symbol data from the processor 1704, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1702. The RF transceiver 1701 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1702 and supplies the baseband receive signal to the processor 1704. The RF transceiver 1701 may include an analog beamformer circuit for beamforming. The analog beamformer circuit may include, for example, multiple phase shifters and multiple power amplifiers.

[0151] The network interface 1703 is used to communicate with network nodes (e.g., RAN nodes 2 and 4, and control and forwarding nodes of the core network), and may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series.

[0152] The processor 1704 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. The processor 1704 may include multiple processors. For example, the processor 1704 may include a modem processor (e.g., a Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit (CPU) or a Micro Processing Unit (MPU)) that performs control plane processing.

[0153] For example, digital baseband signal processing by processor 1704 may include signal processing for 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, control plane processing by processor 1704 may include processing of Non-Access Stratum (NAS) messages, RRC messages, MAC Control Elements (CEs), and Downlink Control Information (DCI).

[0154] The processor 1704 may include a digital beamformer module for beamforming, which may include a Multiple Input Multiple Output (MIMO) encoder and precoder.

[0155] The memory 1705 is configured by a combination of volatile memory and non-volatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The non-volatile memory is, for example, Mask Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. The memory 1705 may include storage located remotely from the processor 1704. In this case, the processor 1704 may access the memory 1705 via the network interface 1703 or an I / O interface (not shown).

[0156] The memory 1705 may store one or more software modules (computer programs) 1706 including instructions and data for performing the processes of the RAN node 1 described in the above embodiments. In some implementations, the processor 1704 may be configured to read and execute the software modules 1706 from the memory 1705 to perform the processes of the RAN node 1 described in the above embodiments.

[0157] Note that if the RAN node 1 is a CU (e.g., eNB-CU or gNB-CU) or a CU-CP, the RAN node 1 may not include the RF transceiver 1701 (and the antenna array 1702).

[0158] FIG. 18 is a block diagram showing an example configuration of a UE 3. A radio frequency (RF) transceiver 1801 performs analog RF signal processing for communication with a RAN node. The RF transceiver 1801 may include multiple transceivers. The analog RF signal processing performed by the RF transceiver 1801 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1801 is coupled to an antenna array 1802 and a baseband processor 1803. The RF transceiver 1801 receives modulation symbol data (or orthogonal frequency-division multiplexing (OFDM) symbol data) from the baseband processor 1803, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1802. The RF transceiver 1801 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1802 and provides the baseband receive signal to the baseband processor 1803. The RF transceiver 1801 may include an analog beamformer circuit for beamforming. The analog beamformer circuitry includes, for example, multiple phase shifters and multiple power amplifiers.

[0159] The baseband processor 1803 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communications. Digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) transmission format (transmission frame) generation / decomposition, (d) transmission path coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using Inverse Fast Fourier Transform (IFFT). Meanwhile, control plane processing includes communication management for Layer 1 (e.g., transmit 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).

[0160] For example, digital baseband signal processing by the baseband processor 1803 may include signal processing of an SDAP layer, a PDCP layer, an RLC layer, a MAC layer, and a PHY layer, and control plane processing by the baseband processor 1803 may include processing of a Non-Access Stratum (NAS) protocol, an RRC protocol, MAC CEs, and DCIs.

[0161] The baseband processor 1803 may perform MIMO encoding and precoding for beamforming.

[0162] The baseband processor 1803 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 1804, which will be described later.

[0163] The application processor 1804 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1804 may include multiple processors (multiple processor cores). The application processor 1804 executes a system software program (operating system (OS)) and various application programs (e.g., a calling application, a web browser, a mailer, a camera operation application, and a music playback application) read from the memory 1806 or a memory not shown, thereby realizing various functions of the UE 3.

[0164] In some implementations, the baseband processor 1803 and the application processor 1804 may be integrated on a single chip, as shown by the dashed line (1805) in Figure 18. In other words, the baseband processor 1803 and the application processor 1804 may be implemented as a single System on Chip (SoC) device 1805. An SoC device may also be called a system Large Scale Integration (LSI) or chipset.

[0165] The memory 1806 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1806 may include multiple physically independent memory devices. The volatile memory is, for example, SRAM, DRAM, or a combination thereof. The nonvolatile memory is, for example, MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1806 may include an external memory device accessible from the baseband processor 1803, the application processor 1804, and the SoC 1805. The memory 1806 may also include an internal memory device integrated within the baseband processor 1803, the application processor 1804, or the SoC 1805. Furthermore, the memory 1806 may include memory within a Universal Integrated Circuit Card (UICC).

[0166] The memory 1806 may store one or more software modules (computer programs) 1807 including instructions and data for performing the processing by the UE 3 described in the above-described embodiments. In some implementations, the baseband processor 1803 or the application processor 1804 may be configured to read and execute the software modules 1807 from the memory 1806, thereby performing the processing by the UE 3 described in the above-described embodiments using the drawings.

[0167] In addition, the control plane processing and operations performed by UE3 described in the above embodiment can be realized by elements other than the RF transceiver 1801 and the antenna array 1802, i.e., at least one of the baseband processor 1803 and the application processor 1804, and the memory 1806 storing the software module 1807.

[0168] As described with reference to Figures 17 and 18, each of the processors included in the RAN node and the UE according to the above-described embodiments may execute one or more programs including instructions for causing a computer to perform the algorithms described with reference to the drawings. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0169] The above-described embodiments are merely examples of application of the technical ideas obtained by the inventors of the present invention. In other words, the technical ideas are not limited to the above-described embodiments, and various modifications are possible.

[0170] For example, some or all of the above embodiments may also be described as, but are not limited to, the following appendices. Some or all of the elements (e.g., configurations and functions) described in appendices directed to devices (e.g., RAN nodes) may naturally also be described as appendices directed to methods and programs. For example, some or all of the elements described in appendices 2-10, which are dependent on appendices 1-10, may also be described as appendices dependent on appendices 16 and 18, due to the same dependency relationship as appendices 2-10. Some or all of the elements described in any appendice may be applied to various hardware, software, recording means for recording software, systems, and methods.

[0171] (Supplementary Note 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 User Equipment (UE), comprising: means for transmitting a first control message to a candidate Secondary Node (SN), the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or modification for the UE, the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell modifications that may occur after the initial conditional PSCell addition or modification. (Supplementary Note 2) The RAN node of Supplementary Note 1, further comprising means for receiving a second control message transmitted from the candidate SN in response to the first control message, the second control message including configuration for at least one candidate cell prepared by the candidate SN, and if the first information indicates that the candidate SN is permitted or requested to generate the execution condition, the second control message including second information indicating whether the execution condition has been generated. (Supplementary Note 3) The RAN node of Supplementary Note 2, further comprising means for receiving a second control message transmitted from the candidate SN in response to the first control message, the second control message including configuration for at least one candidate cell prepared by the candidate SN, and if the first information indicates that the candidate SN is permitted or requested to generate the execution condition, the second control message including second information indicating whether the execution condition has been generated. (Supplementary Note 4) The RAN node according to Supplementary Note 1, further comprising means for receiving a second control message transmitted from the candidate SN in response to the first control message, wherein if the first information indicates that the candidate SN is requested to generate the execution condition for the subsequent conditional PSCell change but the candidate SN does not generate the execution condition, the second control message indicates that preparation of the one or more candidate PSCells has been rejected or failed.(Supplementary Note 5) The RAN node of Supplementary Note 4, wherein the first control message is an SN ADDITION REQUEST message, and the second control message is an SN ADDITION REQUEST REJECT message. (Supplementary Note 6) The RAN node of any one of Supplements 1 to 5, comprising: means for deciding whether to allow or request the candidate SN to create the execution conditions for the subsequent conditional PSCell change. (Supplementary Note 7) The RAN node of any one of Supplements 1 to 5, wherein the first conditional PSCell addition or change is a conditional PSCell change initiated by a source SN, and further comprising: means for receiving from the source SN a third control message containing third information indicating whether the candidate SN is allowed or requested to create the execution conditions for the subsequent conditional PSCell change; and means for including the first information in the first control message based on the third information. (Supplementary Note 8) The RAN node of Supplementary Note 7, wherein the third control message is an SN CHANGE REQUIRED message. (Supplementary Note 9) The RAN node according to any one of Supplements 1 to 5, wherein the initial conditional PSCell addition or modification is a conditional PSCell modification initiated by a source SN, and further comprising: means for receiving from the source SN a third control message containing an indication of the conditional PSCell modification and the first information and triggering a change of SN; and means for including the first information that was included in the third control message in the first control message. (Supplementary Note 10) The RAN node according to Supplementary Note 9, wherein the third control message is an SN CHANGE REQUIRED message.(Supplementary Note 11) 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 User Equipment (UE), comprising: means for receiving a first control message from a Master Node (MN) of the dual connectivity, the first control message requesting the candidate SN to prepare one or more candidate Primary Secondary Cell Group (SCG) Cell (PSCell)s for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE, and the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell changes that may occur after the initial conditional PSCell addition or change. (Supplementary Note 12) The RAN node according to Supplementary Note 11, further comprising means for transmitting a second control message to the MN in response to the first control message, the second control message including configuration for at least one candidate cell prepared by the candidate SN, and if the first information indicates that the candidate SN is allowed or requested to generate the execution condition, the second control message including second information indicating whether the execution condition has been generated. (Supplementary Note 13) The RAN node according to Supplementary Note 12, further comprising means for transmitting a second control message to the MN in response to the first control message, the second control message including configuration for at least one candidate cell prepared by the candidate SN, and if the first information indicates that the candidate SN is allowed or requested to generate the execution condition, the second control message including second information indicating whether the execution condition has been generated. (Supplementary Note 14) The RAN node according to Supplementary Note 11, further comprising means for sending a second control message to the MN in response to the first control message, wherein if the first information indicates that the candidate SN is requested to generate the execution condition for the subsequent conditional PSCell change but the candidate SN does not generate the execution condition, the second control message indicates that the preparation of the one or more candidate PSCells has been rejected or failed.(Supplementary Note 15) The RAN node according to Supplementary Note 14, wherein the first control message is an SN ADDITION REQUEST message, and the second control message is an SN ADDITION REQUEST REJECT message. (Supplementary Note 16) 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: sending a first control message to a candidate Secondary Node (SN), the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or modification for the UE, the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell modifications that may occur after the initial conditional PSCell addition or modification.(Supplementary Note 17) 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 User Equipment (UE), comprising: receiving a first control message from a Master Node (MN) of the dual connectivity, the first control message requesting the candidate SN to prepare one or more candidate Primary Secondary Cell Group (SCG) Cell (PSCell)s for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE, the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell changes that may occur after the initial conditional PSCell addition or change. (Supplementary Note 18) A program 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 User Equipment (UE), the method comprising: transmitting a first control message to a candidate Secondary Node (SN), the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE, the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell changes that may occur after the initial conditional PSCell addition or change.(Supplementary Note 19) A program causing a computer to perform a method for 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 User Equipment (UE), the method comprising: receiving a first control message from a Master Node (MN) of the dual connectivity, the first control message requesting the candidate SN to prepare one or more candidate Primary Secondary Cell Group (SCG) Cell (PSCell)s for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE, the first control message including first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell changes that may occur after the initial conditional PSCell addition or change. (Supplementary Note 20) 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 User Equipment (UE), comprising: means for transmitting a first control message to a first candidate Secondary Node (SN) requesting the first candidate SN to prepare multiple candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for subsequent conditional PSCell changes; and means for receiving a second control message transmitted from the first candidate SN in response to the first control message, wherein the second control message indicates that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.(Supplementary Note 21) The RAN node according to Supplementary Note 20, wherein the first control message is an SN ADDITION REQUEST message, and the second control message is an SN ADDITION REQUEST REJECT message. (Supplementary Note 22) The RAN node according to Supplementary Note 20 or 21, further comprising means for indicating, if not all of the plurality of candidate PSCells have been prepared by the first candidate SN, at least one candidate PSCell that has been prepared or not prepared by the first candidate SN to a second candidate SN for the initial conditional PSCell addition or modification via a third control message. (Supplementary Note 23) The RAN node according to Supplementary Note 22, further comprising means for receiving a fourth control message transmitted from the second candidate SN in response to the third control message, the fourth control message including information indicating a condition for executing a subsequent conditional PSCell change from a candidate PSCell prepared by the second candidate SN to each of one or more candidate PSCells prepared by the first candidate SN. (Supplementary Note 24) The RAN node according to Supplementary Note 22 or 23, wherein the third control message is a SN MODIFICATION REQUEST message.(Supplementary Note 25) 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 User Equipment (UE), comprising: means for receiving from a Master Node (MN) of the dual connectivity a first control message requesting the candidate SN to prepare multiple candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for subsequent conditional PSCell changes; and means for transmitting a second control message to the MN in response to the first control message when only some of the multiple candidate PSCells can be prepared, the second control message indicating that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared. (Supplementary Note 26) The RAN node according to Supplementary Note 25, wherein the first control message is an SN ADDITION REQUEST message, and the second control message is an SN ADDITION REQUEST REJECT message.(Supplementary Note 27) 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 User Equipment (UE), comprising: sending a first control message to a first candidate Secondary Node (SN), requesting the first candidate SN to prepare multiple candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for subsequent conditional PSCell changes; and receiving a second control message sent from the first candidate SN in response to the first control message, wherein the second control message indicates that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared. (Supplementary Note 28) 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 User Equipment (UE), comprising: receiving a first control message from a Master Node (MN) of the dual connectivity requesting the candidate SN to prepare multiple candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for subsequent conditional PSCell changes; and, if only some of the multiple candidate PSCells can be prepared, sending a second control message to the MN in response to the first control message, wherein the second control message indicates that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.(Supplementary Note 29) A program 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 User Equipment (UE), the method comprising: transmitting a first control message to a first candidate Secondary Node (SN), requesting the first candidate SN to prepare multiple candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for subsequent conditional PSCell changes; and receiving a second control message transmitted from the first candidate SN in response to the first control message, the second control message indicating that preparation of all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.(Supplementary Note 30) A program causing a computer to perform a method for 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 User Equipment (UE), the method comprising: receiving a first control message from a Master Node (MN) of the dual connectivity requesting the candidate SN to prepare multiple candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for subsequent conditional PSCell changes; and, if only some of the multiple candidate PSCells can be prepared, sending a second control message to the MN in response to the first control message, the second control message indicating that preparation for all of the multiple candidate PSCells has been rejected or failed because only some of the multiple candidate PSCells can be prepared.(Supplementary Note 31) 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 User Equipment (UE), comprising: means for transmitting a first control message to a first candidate Secondary Node (SN) requesting the first candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change; means for receiving a second control message transmitted from the first candidate SN in response to the first control message; and means for indicating, via a third control message, to a second candidate SN for the initial conditional PSCell addition or change, at least one candidate PSCell that has been prepared or not prepared by the first candidate SN, if not all of the one or more candidate PSCells have been prepared by the first candidate SN. (Supplementary Note 32) The RAN node according to Supplementary Note 31, further comprising means for receiving a fourth control message transmitted from the second candidate SN in response to the third control message, the fourth control message containing information indicating a condition for executing a subsequent conditional PSCell change from a candidate PSCell prepared by the second candidate SN to each of one or more candidate PSCells prepared by the first candidate SN. (Supplementary Note 33) The RAN node according to Supplementary Note 31 or 32, wherein the first control message is an SN ADDITION REQUEST message, the second control message is an SN ADDITION REQUEST ACKNOWLEDGE message or an SN ADDITION REQUEST REJECT message, and the third control message is an SN MODIFICATION REQUEST message.(Supplementary Note 34) 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 User Equipment (UE), comprising: transmitting a first control message to a first candidate Secondary Node (SN) requesting the first candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change; receiving a second control message transmitted from the first candidate SN in response to the first control message; and, if not all of the one or more candidate PSCells have been prepared by the first candidate SN, indicating at least one candidate PSCell that has or has not been prepared by the first candidate SN via a third control message to a second candidate SN for the initial conditional PSCell addition or change.(Supplementary Note 35) A program 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 User Equipment (UE), the method comprising: transmitting a first control message to a first candidate Secondary Node (SN) requesting the first candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change; receiving a second control message transmitted from the first candidate SN in response to the first control message; and, if not all of the one or more candidate PSCells have been prepared by the first candidate SN, indicating at least one candidate PSCell that has or has not been prepared by the first candidate SN via a third control message to a second candidate SN for the initial conditional PSCell addition or change.(Supplementary Note 36) 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 User Equipment (UE), comprising: means for transmitting a first control message to a first candidate Secondary Node (SN), the first control message requesting the first candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change, the first control message including information indicating whether the first candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change. (Supplementary Note 37) The RAN node according to Supplementary Note 36, further comprising: means for receiving a second control message transmitted from the first candidate SN in response to the first control message; and means for indicating, via a third control message, a first cell that is not included in the one or more candidate PSCells indicated in the first control message to a second candidate SN for the initial conditional PSCell addition or change, if the first cell is prepared by the first candidate SN for the subsequent conditional PSCell change. (Supplementary Note 38) The RAN node according to Supplementary Note 37, further comprising: means for receiving a fourth control message transmitted from the second candidate SN in response to the third control message, the fourth control message including information indicating a condition for executing a subsequent conditional PSCell change from the candidate PSCell prepared by the second candidate SN to the first cell.(Supplementary Note 39) The RAN node according to Supplementary Note 37 or 38, wherein the first control message is an SN ADDITION REQUEST message, the second control message is an SN ADDITION REQUEST ACKNOWLEDGE message, and the third control message is an SN MODIFICATION REQUEST message. (Supplementary Note 40) The RAN node according to any one of Supplements 36 to 39, wherein the first control message includes information indicating a maximum number of cells that may be prepared in addition to the one or more candidate PSCells proposed in the first control message. (Supplementary Note 41) The RAN node according to any one of Supplements 36 to 40, wherein the subsequent conditional PSCell change is a conditional PSCell change procedure that is performed after the initial conditional PSCell addition or change based on configuration of candidate PSCells for conditional PSCell addition or change that are pre-configured for the initial conditional PSCell addition or change, without restarting the conditional PSCell addition or change. (Supplementary Note 42) 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 User Equipment (UE), comprising: means for receiving a first control message from a Master Node (MN) of the dual connectivity, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change, the first control message including information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change.(Supplementary Note 43) The RAN node according to Supplementary Note 42, further comprising means for transmitting a second control message to the MN in response to the first control message, the second control message indicating that a first cell not included in the one or more candidate PSCells indicated in the first control message has been prepared by the candidate SN for the subsequent conditional PSCell change. (Supplementary Note 44) The RAN node according to Supplementary Note 43, wherein the first control message is an SN ADDITION REQUEST message, and the second control message is an SN ADDITION REQUEST ACKNOWLEDGE message. (Supplementary Note 45) The RAN node according to any one of Supplements 42 to 44, wherein the first control message includes information indicating a maximum number of cells that may be prepared in addition to the one or more candidate PSCells proposed in the first control message. (Supplementary Note 46) The RAN node according to any one of Supplementary Notes 42 to 45, wherein the subsequent conditional PSCell change is a conditional PSCell change procedure that is performed after the initial conditional PSCell addition or change, without restarting the conditional PSCell addition or change, based on configuration of candidate PSCells for the conditional PSCell addition or change that are pre-configured for the initial conditional PSCell addition or change.(Supplementary Note 47) 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 User Equipment (UE), comprising: means for sending a control message to a Master Node (MN) of the dual connectivity, the control message triggering an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change for the UE and containing a list of one or more candidate PSCells managed by a candidate SN, and containing an indication of a subsequent conditional PSCell change, the control message further containing information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change. (Supplementary Note 48) The RAN node according to Supplementary Note 47, wherein the control message is an SN CHANGE REQUIRED message. (Supplementary Note 49) The RAN node according to Supplementary Note 47 or 48, wherein the subsequent conditional PSCell change is a conditional PSCell change procedure that is performed after the initial conditional PSCell addition or change without restarting the conditional PSCell addition or change, based on configuration of candidate PSCells for the conditional PSCell addition or change that are pre-configured for the initial conditional PSCell addition or change.(Supplementary Note 50) 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 User Equipment (UE), comprising: sending a first control message to a first candidate Secondary Node (SN), the first control message requesting the first candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change, the first control message including information indicating whether the first candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change. (Supplementary Note 51) 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 User Equipment (UE), comprising: receiving a first control message from a Master Node (MN) of the dual connectivity, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change, the first control message including information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change.(Supplementary Note 52) 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 User Equipment (UE), comprising: sending a control message to a Master Node (MN) of the dual connectivity, the control message triggering an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change for the UE and including a list of one or more candidate PSCells managed by a candidate SN, and including an indication of a subsequent conditional PSCell change, the control message further including information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change. (Supplementary Note 53) A program 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 User Equipment (UE), the method comprising: sending a first control message to a first candidate Secondary Node (SN), the first control message requesting the first candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change, the first control message including information indicating whether the first candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change.(Supplementary Note 54) A program causing a computer to perform a method for 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 User Equipment (UE), the method comprising: receiving a first control message from a Master Node (MN) of the dual connectivity, the first control message requesting the candidate SN to prepare one or more candidate PSCells for an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or change for the UE and for a subsequent conditional PSCell change, the first control message including information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change. (Supplementary Note 55) A program causing a computer to perform a method for 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 User Equipment (UE), the method comprising: sending a control message to a Master Node (MN) of the dual connectivity, the control message triggering an initial conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change for the UE, containing a list of one or more candidate PSCells managed by a candidate SN, and containing an indication of a subsequent conditional PSCell change, the control message further containing information indicating whether the candidate SN is permitted or required to prepare a cell other than the one or more candidate PSCells as a candidate PSCell for the subsequent conditional PSCell change.(Supplementary Note 56) 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 User Equipment (UE), comprising: means for sending, to a Master Node (MN) of the dual connectivity or to the candidate SN via the MN, first information indicating whether one or more cells managed by the source SN will be candidate PSCells for a subsequent conditional PSCell change that may occur after an initial conditional PSCell change from a source Primary Secondary Cell Group (SCG) Cell (PSCell) managed by the source SN to any of one or more candidate PSCells managed by one or more candidate SNs. (Supplementary Note 57) The RAN node according to Supplementary Note 56, wherein the first information is forwarded to the candidate SN via the MN. (Supplementary Note 58) The RAN node of Supplementary Note 56, wherein the first information causes the MN to inform the candidate SNs whether one or more cells managed by the source SN will be candidate PSCells for the subsequent conditional PSCell change. (Supplementary Note 59) The RAN node of any one of Supplements 56 to 58, wherein the means for sending the first information is adapted to send the first information to the MN via a control message, the control message triggering the initial conditional PSCell change and including a list of one or more candidate PSCells managed by each candidate SN. (Supplementary Note 60) The RAN node of Supplementary Note 59, wherein the control message is an SN CHANGE REQUIRED message. (Supplementary Note 61) The RAN node according to any one of Supplementary Notes 56 to 58, further comprising means for receiving second information from the MN indicating that a cell managed by the source SN is permitted to be a candidate PSCell for the subsequent conditional PSCell change, wherein the means for sending the first information is adapted to send the first information in response to receiving the second information.(Supplementary Note 62) The RAN node according to any one of Supplements 56 to 58, wherein the one or more cells managed by the source SN include a source PSCell of the initial conditional PSCell change. (Supplementary Note 63) 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, to a Master Node (MN) of the dual connectivity or to the candidate SN via the MN, first information indicating whether one or more cells managed by the source SN will be candidate PSCells for subsequent conditional PSCell changes that may occur after an initial conditional PSCell change from a source Primary Secondary Cell Group (SCG) Cell (PSCell) managed by the source SN to any of one or more candidate PSCells managed by one or more candidate SNs. (Supplementary Note 64) A program causing a computer to perform a method for 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 User Equipment (UE), the method comprising sending, to a Master Node (MN) of the dual connectivity or to the candidate SN via the MN, first information indicating whether one or more cells managed by the source SN will be candidate PSCells for a subsequent conditional PSCell change that may occur after an initial conditional PSCell change from a source Primary Secondary Cell Group (SCG) Cell (PSCell) managed by the source SN to any of one or more candidate PSCells managed by one or more candidate SNs.

[0172] This application claims priority based on Japanese Patent Application No. 2023-125263, filed August 1, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0173] 1 Master Node (MN) 2 Source Secondary Node (S-SN) 3 User Equipment (UE) 4 Target Secondary Node (T-SN) 1704 Processor 1705 Memory 1706 Modules 1803 Baseband Processor 1804 Application Processor 1806 Memory 1807 Modules

Claims

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 User Equipment (UE), The system includes means for sending a first control message to a candidate Secondary Node (SN), The first control message requests the candidate SN to prepare one or more candidate PSCells for the first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or modification for the UE, The first control message includes first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell modifications that may occur after the initial conditional PSCell addition or modification. RAN node.

2. The system further includes means for receiving a second control message transmitted from the candidate SN in response to the first control message, The second control message includes settings for at least one candidate cell prepared by the candidate SN, If the first information indicates that the candidate SN is permitted or requested to generate the execution condition, the second control message includes second information indicating whether or not the execution condition has been generated. The RAN node according to claim 1.

3. The first control message is an SN ADDITION REQUEST message, The second control message is the SN ADDITION REQUEST ACKNOWLEDGE message. The RAN node according to claim 2.

4. The system further includes means for receiving a second control message transmitted from the candidate SN in response to the first control message, If the first information indicates that the candidate SN is required to generate the execution conditions for the subsequent conditional PSCell modification, but the candidate SN does not generate the execution conditions, the second control message indicates that the preparation of the one or more candidate PSCells has been refused or failed. The RAN node according to claim 1.

5. The first control message is an SN ADDITION REQUEST message, The second control message is the SN ADDITION REQUEST REJECT message. The RAN node according to claim 4.

6. The system includes means for determining whether to allow or require the candidate SN to generate the execution conditions for the subsequent conditional PSCell modification. A RAN node according to any one of claims 1 to 5.

7. The aforementioned first conditional PSCell addition or modification is a conditional PSCell modification initiated by source SN, Means for receiving a third control message from the source SN, which includes third information indicating whether the candidate SN is permitted or required to generate the execution conditions for the subsequent conditional PSCell modification, Means for including the first information in the first control message based on the third information, Furthermore, A RAN node according to any one of claims 1 to 5.

8. The aforementioned first conditional PSCell addition or modification is a conditional PSCell modification initiated by source SN, Means for displaying a conditional PSCell change and receiving a third control message from the source SN that includes the first information and triggers a change in SN, Means for including the first information contained in the third control message in the first control message, Furthermore, A RAN node according to any one of claims 1 to 5.

9. 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 User Equipment (UE), The system includes means for receiving a first control message from the Master Node (MN) of the dual connectivity, The first control message requests the candidate SN to prepare one or more candidate PSCells for the first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or modification for the UE, The first control message includes first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell modifications that may occur after the initial conditional PSCell addition or modification. RAN node.

10. A method performed by a radio access network (RAN) node configured to act as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), The system includes sending a first control message to a candidate Secondary Node (SN), The first control message requests the candidate SN to prepare one or more candidate PSCells for the first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or modification for the UE, The first control message includes first information indicating whether the candidate SN is permitted or required to generate execution conditions for subsequent conditional PSCell modifications that may occur after the initial conditional PSCell addition or modification. method.