Candidate secondary node, master node, and methods thereof

Abstract

To provide an improved procedure for adding a prepared PSCell in response to a request from a candidate secondary node (SN) regarding SN-initiated inter-SN CPC.SOLUTION: A candidate SN sends an S-Node Modification Required message to a master node (MN). This message is sent to add or delete prepared PSCells and contains a list of newly prepared PSCells by the candidate SN. The candidate SN receives an S-Node Modification Confirm message from the MN.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure relates to wireless communication systems, and more particularly to mobility of wireless terminals in multi-connectivity (eg, dual connectivity). [Background technology]

[0002] The 3rd Generation Partnership Project (3GPP (registered trademark)) Release 17 brings enhancements to conditional mobility. The newly introduced conditional mobility in 3GPP Release 17 includes conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition (Conditional PSCell Addition (CPA)) and inter-Secondary Node (SN) conditional PSCell change (Conditional PSCell Change (CPC)) (see, for example, Non-Patent Documents 1-3). CPA is also called conditional SN addition, and inter-SN CPC is also called conditional SN change.

[0003] CPA (or conditional SN addition) is a PSCell addition procedure (or SN addition procedure) that is executed only when one or more execution conditions are met or satisfied. After receiving a PSCell addition instruction from a master node (MN), a wireless terminal (i.e., User Equipment (UE)) starts evaluating the execution condition(s) of one or more candidate PSCells configured by the instruction. Then, in response to the execution condition(s) of any candidate PSCell being met, the UE starts synchronization to the PSCell. That is, CPA differs from normal PSCell addition in that the UE starts synchronization or access to the PSCell not in response to the PSCell addition instruction but in response to the satisfaction of the execution condition(s) configured by the instruction. In CPA, the MN generates the CPA execution conditions. The candidate SN generates an SCG configuration and sends it to the MN. The MN transmits a CPA configuration (eg, a Conditional Reconfiguration Information Element (IE)) including both the CPA execution condition and the SCG configuration to the UE via a Radio Resource Control (RRC) (Connection) Reconfiguration message.

[0004] Inter-SN CPC is an SN change procedure that is executed only when one or more execution conditions are met or satisfied. The target SN of Inter-SN CPC is also called a candidate SN or a target candidate SN. After receiving an SN change instruction from the MN, the UE maintains a connection with the source SN and source SCG and starts evaluating the execution conditions (configured execution condition(s)) configured by the instruction. Then, the UE starts accessing the target candidate SN and the selected candidate PSCell in response to the execution conditions being met. That is, CPC differs from a normal SN change in that the UE starts accessing the target candidate SN in response to the execution conditions being met, not in response to the SN change instruction.

[0005] An inter-SN CPC can be initiated by the MN or the source SN. An inter-SN CPC initiated by the MN is called an MN-initiated inter-SN CPC. On the other hand, an inter-SN CPC initiated by the source SN is called an SN-initiated inter-SN CPC. In an MN-initiated inter-SN CPC, the MN generates a CPC execution condition. In contrast, in an SN-initiated inter-SN CPC, the source SN generates a CPC execution condition and sends it to the MN. In both the MN-initiated inter-SN CPC and the SN-initiated inter-SN CPC, the target candidate SN generates an SCG configuration and sends it to the MN. Then, the MN transmits the CPC configuration (e.g., ConditionalReconfiguration IE), which includes both the CPC execution condition and the SCG configuration, to the UE via an RRC (Connection) Reconfiguration message.

[0006] The 3GPP Technical Specification Group (TSG) Radio Access Network (RAN) has agreed that a candidate SN can add a new prepared PSCell after a CPA or inter-SN CPC is prepared or configured (see, for example, Non-Patent Documents 2 and 4-8). Specifically, a (target) candidate SN can add one or more prepared PSCells from a list suggested by the MN or source SN, within a limit given by the MN or source SN, using an SN-initiated SN modification procedure. This operation or procedure may be referred to, for example, but not limited to, candidate SN triggered prepared cell addition. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] 3GPP TS 37.340 V17.0.0 (2022-03), "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-connectivity; Stage 2 (Release 17)", April 2022 [Non-patent document 2] 3GPP TS 38.423 V17.1.0 (2022-06), "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NG-RAN; Xn application protocol (XnAP) (Release 17)", June 2022 [Non-patent document 3] 3GPP TS 38.331 V17.0.0 (2022-03), "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Radio Resource Control (RRC) protocol specification (Release 17)", April 2022

Non-licensed Document 4

Non-licensed Document 5

Non-licensed Document 6

Non-licensed Document 7

[0008] The inventors have studied CPA and inter-SN CPC and found various issues. One of these issues relates to candidate SN triggered prepared cell addition in inter-SN CPC. According to Non-Patent Document 2 and Non-Patent Document 7, the Xn Application Protocol message, i.e., the S-NODE MODIFICATION REQUIRED message, sent from a candidate SN to an MN to propose or request the addition of prepared PSCell(s), can include a Candidate PSCell List IE in its CPAC Information Required IE. The Candidate PSCell List IE indicates the full list of candidate PSCells prepared in the (target) candidate SN. However, this S-NODE MODIFICATION REQUIRED message does not include information indicating whether it is for an MN-initiated inter-SN CPC or an S-SN initiated inter-SN CPC.

[0009] It should be noted that a single candidate SN can configure or prepare an MN-initiated inter-SN CPC and an S-SN-initiated inter-SN CPC in parallel. Therefore, it is possible that the same cell is prepared as a PSCell for both CPCs. In particular, there may be a case where all prepared PSCells included in the Candidate PSCell List provided to the MN by the candidate SN are commonly or overlappingly included in the suggested list for the MN-initiated inter-SN CPC and the suggested list for the SN-initiated inter-SN CPC. In this case, the MN may not be able to distinguish whether one or more newly prepared PSCells added to the Candidate PSCell List are for the MN-initiated inter-SN CPC or the SN-initiated inter-SN CPC. In such a case, it is unclear how the MN should behave.

[0010] The inventors have found various other issues in realizing candidate SN triggered prepared cell addition. One issue is that it is unclear which node processes a request or proposal for adding one or more prepared PSCells from a candidate SN in a CPA or inter-SN CPC. Another issue is that it is unclear whether an MN or a source SN is allowed to partially or entirely reject one or more prepared PSCells requested or proposed for addition by a candidate SN. Yet another issue is that it is unclear how and which node determines the execution conditions for added prepared PSCell(s) from an RRC perspective.

[0011] 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 problems, including the problems described above. It should be noted that this objective is only one of the objectives that the 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. [Means for solving the problem]

[0012] A first aspect is directed to a Radio Access Network (RAN) node configured to operate as a MN associated with a Master Cell Group (MCG) in dual connectivity for a UE. The RAN node includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive a first message from a common candidate SN for both a first conditional PSCell change initiated by the MN and a second conditional PSCell change initiated by a source SN. The at least one processor is configured to determine whether an updated list of one or more prepared PSCells indicated by the first message relates to the first conditional PSCell change or the second conditional PSCell change.

[0013] A second aspect is directed to a method performed by a RAN node configured to act as a MN associated with an MCG in dual connectivity for a UE, the method comprising the steps of: (a) receiving a first message from a common candidate SN for both the MN-initiated first conditional PSCell change and the source SN-initiated second conditional PSCell change; and (b) determining whether the updated list of one or more prepared PSCells indicated by the first message relates to the first conditional PSCell change or the second conditional PSCell change;

[0014] 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 includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to prepare SN resources for the UE for both a first conditional PSCell change initiated by an MN and a second conditional PSCell change initiated by a source SN. The at least one processor is configured to send a first message to the MN. The first message includes an information element or field indicating whether the modification of conditional PSCell addition or modification information requested by the first message relates to the first conditional PSCell change or the second conditional PSCell change.

[0015] A fourth aspect is directed to a method performed by a RAN node configured to act as a candidate SN associated with an SCG in dual connectivity for a UE, the method comprising the steps of: (a) preparing SN resources for the UE for both a first conditional PSCell change initiated by an MN and a second conditional PSCell change initiated by a source SN; and (b) sending a first message to the MN, wherein the first message includes an information element or field indicating whether the modification of conditional PSCell addition or modification information requested by the first message relates to the first conditional PSCell modification or the second conditional PSCell modification;

[0016] 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 including at least one memory and at least one processor coupled to the at least one memory, the at least one processor configured to receive a first message from a candidate SN for a conditional PSCell change initiated by a source SN, and the at least one processor configured to determine whether to accept the addition of one or more prepared PSCells requested or proposed in the first message for the conditional PSCell change initiated by the source SN.

[0017] A sixth aspect is directed to a method performed by a RAN node configured to act as a MN associated with an MCG in dual connectivity for a UE, the method comprising the steps of: (a) receiving a first message from a candidate SN for a conditional PSCell change initiated by a source SN; and (b) determining whether to accept the addition of one or more prepared PSCells requested or proposed in the first message with respect to the conditional PSCell change initiated by the source SN;

[0018] A seventh 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 including at least one memory and at least one processor coupled to the at least one memory, the at least one processor configured to receive a first message from a candidate SN for a conditional PSCell addition or conditional PSCell modification, and the at least one processor configured to determine whether to reject some or all of one or more prepared PSCells requested or proposed for addition in the first message.

[0019] An eighth aspect is directed to a method performed by a RAN node configured to act as a MN associated with an MCG in dual connectivity for a UE, the method comprising the steps of: (a) receiving a first message from a candidate SN for a conditional PSCell addition or a conditional PSCell modification; and (b) determining whether to reject some or all of one or more prepared PSCells requested or proposed to be added by the first message;

[0020] A ninth 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 includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to receive a first message from an MN regarding a modification of a conditional PSCell change initiated by the source SN that has already been prepared. The first message indicates one or more prepared PSCells requested or proposed for addition by a candidate SN. The at least one processor is configured to determine whether to reject some or all of the one or more prepared PSCells requested or proposed for addition by the candidate SN.

[0021] A tenth 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 comprising the steps of: (a) receiving a first message from an MN regarding a modification of a conditional PSCell change initiated by the source SN that has already been prepared, wherein the first message indicates one or more prepared PSCells that are requested or proposed to be added by a candidate SN; and (b) determining whether to reject some or all of one or more prepared PSCells requested or proposed for addition by the candidate SN;

[0022] 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 includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to retain execution condition information received from a source SN when a conditional PSCell change initiated by the source SN is prepared. The at least one processor is configured to receive a first message from a candidate SN for the conditional PSCell change that has already been prepared. The at least one processor is configured to select, from the retained execution condition information, one or more execution conditions for each of one or more prepared PSCells requested or proposed for addition in the first message. The at least one processor is further configured to transmit to the UE an RRC message including an SCG configuration for each of the one or more prepared PSCells provided from the candidate SN in the first message and including the selected one or more execution conditions for each of the one or more prepared PSCells.

[0023] A twelfth aspect is directed to a method performed by a RAN node configured to act as a MN associated with an MCG in dual connectivity for a UE, the method comprising the steps of: (a) retaining execution condition information received from a source SN when a conditional PSCell change initiated by the source SN is prepared; (b) receiving a first message from a candidate SN for the conditional PSCell change that has already been prepared; (c) selecting from the retained execution condition information one or more execution conditions for each of the one or more prepared PSCells requested or proposed to be added by the first message; and (d) sending an RRC message to the UE containing an SCG configuration for each of the one or more prepared PSCells provided by the candidate SN in the first message and containing the selected one or more execution conditions for each of the one or more prepared PSCells.

[0024] A thirteenth aspect is directed to a program, which includes a set of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to the second, fourth, sixth, eighth, tenth, or twelfth aspect. [Effects of the Invention]

[0025] 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 conditional mobility, including the above-described problems. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. [Figure 2] 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. [Figure 3] FIG. 1 is a diagram illustrating a configuration example of a RAN node according to an embodiment. [Figure 4] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 5] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 6] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 7] FIG. 10 is a sequence diagram showing an example of signaling related to inter-SN CPC (or conditional SN change) according to an embodiment. [Figure 8]FIG. 10 is a diagram illustrating an example of the format of an S-NODE MODIFICATION REQUIRED message according to the embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of the format of a CG-CandidateList message according to the embodiment. [Figure 10] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 11] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 12] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 13] FIG. 10 is a sequence diagram illustrating an example of signaling related to SN-initiated inter-SN CPC (or conditional SN change) according to an embodiment. [Figure 14] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 15] 10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 16] FIG. 10 is a diagram illustrating an example of the format of an S-NODE MODIFICATION CONFIRM message according to the embodiment. [Figure 17] FIG. 10 is a diagram illustrating an example of the format of an S-NODE MODIFICATION CONFIRM message according to the embodiment. [Figure 18] 10 is a flowchart illustrating an example of the operation of a RAN node (ie, source SN) according to an embodiment. [Figure 19] 10 is a flowchart illustrating an example of the operation of a RAN node (ie, source SN) according to an embodiment. [Figure 20] FIG. 10 is a diagram illustrating an example of the format of an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message according to the embodiment. [Figure 21]10 is a flowchart showing an example of the operation of a RAN node (ie, MN) according to an embodiment. [Figure 22] FIG. 2 is a block diagram illustrating a configuration example of a RAN node according to the embodiment. [Figure 23] FIG. 2 is a block diagram illustrating an example of the configuration of a UE according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] 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.

[0028] The multiple embodiments described below can be implemented independently or in appropriate combination. These multiple embodiments have different novel features. Therefore, these multiple embodiments contribute to solving different purposes or problems and to achieving different effects.

[0029] The following embodiments will be described primarily with respect to the 3GPP Long Term Evolution (LTE) system and the fifth generation mobile communication system (5G system). However, these embodiments may be applied to other wireless communication systems that support technologies similar to 3GPP multi-connectivity (e.g., dual connectivity). The term LTE used in this specification includes improvements and developments of LTE and LTE-Advanced that enable interworking with the 5G system, unless otherwise specified.

[0030] As used herein, depending on the context, "if" may be construed to mean "when," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be construed to have the same meaning, depending on the context.

[0031] First, the configurations and operations of multiple network elements common to multiple embodiments will be described. Figure 1 illustrates an example configuration of a wireless communication system according to multiple 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) illustrated 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.

[0032] RAN node 1 may be a Central Unit (e.g., eNB-CU or gNB-CU) in a cloud RAN (C-RAN) deployment, or may be a combination of a CU and one or more Distributed Units (e.g., eNB-DUs or gNB-DUs). C-RAN is also referred to as 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, RAN node 1 may be a CU-CP or a combination of a CU-CP and a CU-UP. Similarly, each of RAN nodes 2 and 4 may be a CU or a combination of a CU and one or more DUs. Each of RAN nodes 2 and 4 may be a CU-CP or a combination of a CU-CP and a CU-UP.

[0033] Each of RAN nodes 1, 2, and 4 may be an Evolved Universal 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 the UE and acts as an SN for E-UTRA-NR Dual Connectivity (EN-DC). The ng-eNB provides E-UTRA user plane and control plane protocol terminations to the UE and is connected to the 5GC via the NG interface. The Radio Access Technology (RAT) of RAN node 1 may be different from that of RAN nodes 2 and 4.

[0034] RAN node 1 and RAN node 2 communicate with each other via a node-to-node interface (i.e., X2 interface or Xn interface) 103. RAN node 1 and RAN node 2 act as MN and SN of dual connectivity, respectively. Furthermore, RAN node 1 and RAN node 4 communicate with each other via a node-to-node interface (i.e., X2 interface or Xn interface) 105. RAN node 1 and RAN node 4 can act as MN and SN of DC, respectively. A node-to-node interface (i.e., X2 interface or Xn interface) 106 may be established between RAN node 2 and RAN node 4.

[0035] 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, candidate SN 4, or target candidate SN 4. Inter-SN CPC may also be referred to as conditional SN change.

[0036] Inter-SN CPC (or conditional SN change) is an inter-SN PSCell change procedure (or SN change procedure) that is executed only when one or more CPC execution conditions are met or satisfied. After receiving an SN change instruction from MN1, UE3 maintains its connection with source SN2 and source SCG and starts evaluating the execution conditions set by the instruction. Then, UE2 starts accessing target candidate SN4 and the selected candidate PSCell in response to the execution conditions being met.

[0037] An inter-SN CPC can be initiated by the MN1 or the source SN2. An inter-SN CPC initiated by the MN1 is called an MN-initiated inter-SN CPC. On the other hand, an inter-SN CPC initiated by the source SN2 is called an SN-initiated inter-SN CPC. In an MN-initiated inter-SN CPC, the MN1 generates a CPC execution condition. In contrast, in an SN-initiated inter-SN CPC, the source SN2 generates a CPC execution condition and sends it to the MN1. In both the MN-initiated inter-SN CPC and the SN-initiated inter-SN CPC, the target candidate SN4 generates an SCG configuration and sends it to the MN. Then, the MN1 transmits the CPC configuration (e.g., ConditionalReconfiguration IE) including the CPC execution condition and the SCG configuration to the UE3 via an RRC (Connection) Reconfiguration message. The SCG configuration may also be called an SCG radio resource configuration.

[0038] 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. In the inter-SN CPC procedure, the UE 3 receives from the MN 1 the configurations of one or more candidate PSCells (i.e., one or more SCG configurations) prepared by one or more candidate SNs and one or more CPC execution conditions associated therewith. More specifically, the configuration of each candidate PSCell is included in an information element (e.g., condRRCReconfig) of the RRC message from the MN 1, and the configurations of one or more candidate PSCells and the associated CPC execution conditions are included in conditional mobility configuration information (e.g., conditionalReconfiguration IE) generated by the MN 1.

[0039] The configuration (i.e., SCG configuration) of each candidate PSCell is generated by the candidate SN (e.g., candidate SN4) that provides (or prepares) this candidate PSCell. The configuration of each candidate PSCell includes at least configuration information for the candidate PSCell. The configuration of each candidate PSCell may further include configuration information for one or more SCells associated with the candidate PSCell (i.e., configured together with or in association with the candidate PSCell). The configuration or SCG configuration of each candidate PSCell may be a radio bearer (RB) configuration, a cell group (CG) configuration, an SCG radio resource configuration, or any combination thereof. More specifically, the configuration or SCG configuration of each candidate PSCell may be an SN RRC Reconfiguration message generated by the candidate SN (e.g., candidate SN4) that provides (or prepares) this candidate PSCell. Some or all of the configurations of one or more candidate PSCells are included in the CPC configuration sent from MN1 to UE3. The CPC configuration of an Inter-SN CPC includes a list of one or more MN RRC Reconfiguration messages and associated execution conditions. Each MN RRC Reconfiguration message contains the candidate PSCell configuration or SCG configuration (e.g., one or any combination of RB configuration, CG configuration, SCG radio resource configuration, and SN RRC Reconfiguration messages) received from a candidate SN.

[0040] On the other hand, the CPC execution condition is generated by the MN1 in the case of MN-initiated inter-SN CPC, and is generated 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". The UE3 evaluates the CPC execution conditions. If the execution condition of one candidate PSCell is satisfied, the UE 3 applies the PSCell configuration or SCG configuration (e.g., one or any combination of RB configuration, CG configuration, SCG radio resource configuration, and SN RRC Reconfiguration message) corresponding to the selected candidate PSCell (i.e., the candidate PSCell whose execution condition is satisfied). If a bearer requiring SCG radio resources is configured, the UE 3 synchronizes to the selected 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 above-mentioned operations.

[0041] UE3 communicates with MN1 and S-SN2 via air interfaces 101 and 102, and provides dual connectivity between the MCG provided by MN1 and the SCG provided by S-SN2. Also, by performing inter-SN CPC, UE3 communicates with MN1 and T-SN4 via air interfaces 101 and 104, and provides dual connectivity between the MCG provided by MN1 and the SCG provided by T-SN4.

[0042] 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 a gNB operating as S-SN2 or T-SN4. In NE-DC, UE3 is connected to a gNB operating as MN1 and a ng-eNB operating as S-SN2 or T-SN4. In NR-DC, UE3 is connected to one gNB (or gNB-DU) operating as MN1 and another gNB (or gNB-DU) operating as S-SN2 or T-SN4.

[0043] The MCG is a group of serving cells associated with (or provided by) 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 by) 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. Note that in LTE (e.g., LTE-DC and NE-DC), PSCell may be an abbreviation for Primary SCell.

[0044] 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 (e.g., en-gNB in ​​EN-DC, gNB in ​​NGEN-DC, or gNB in ​​NR-DC), or the Primary SC Cell of a cell group provided by an SN supporting E-UTRA (e.g., eNB in ​​LTE DC, or ng-eNB in ​​NE-DC).

[0045] Figure 2 illustrates another exemplary configuration of a wireless communication system according to various embodiments. In the example of Figure 2, the wireless communication system includes RAN node 1, RAN node 4, and 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.

[0046] 2 may have the same configurations and functions as those in the example of FIG. 1. Specifically, RAN node 1 and RAN node 4 communicate with each other via an inter-node interface (i.e., X2 interface or Xn interface) 105. RAN node 1 and RAN node 4 operate as MN and SN, respectively, for dual connectivity. UE 3 communicates with MN 1 and SN 4 via air interfaces 101 and 104, and performs dual connectivity for MCG and SCG. This dual connectivity may be Multi-Radio Dual Connectivity (MR-DC).

[0047] RAN nodes 1 and 4 and UE 3 support conditional PSCell addition (CPA), which adds an SCG provided by RAN node 4 for UE 3. Therefore, hereinafter, RAN node 1 may be referred to as MN 1, and RAN node 4 may be referred to as candidate SN 4. 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 a CPA execution condition is met.

[0048] CPA (or conditional SN addition) is a PSCell addition procedure (or SN addition procedure) that is executed only when one or more CPA execution conditions are met or satisfied. After receiving a PSCell addition instruction from the MN1, the UE3 starts evaluating the execution conditions of one or more candidate PSCells configured by the instruction. Then, in response to the execution condition of any candidate PSCell being met, the UE3 starts synchronization with the PSCell. In CPA, the MN1 generates the CPA execution condition. The candidate SN4 generates an SCG configuration and sends it to the MN1. The MN1 sends the CPA configuration (e.g., ConditionalReconfiguration IE), which includes both the CPA execution condition and the SCG configuration, to the UE3 via an RRC (Connection) Reconfiguration message.

[0049] Although not shown in Fig. 2, multiple candidate PSCells provided by multiple candidate SNs 4 may be prepared for CPA. In the CPA procedure, the UE 3 receives from the MN 1 configurations of one or more candidate PSCells (i.e., one or more SCG configurations) prepared by one or more candidate SNs and one or more CPA execution conditions associated therewith. More specifically, the configuration of each candidate PSCell is included in an information element (e.g., condRRCReconfig) of the RRC message from the MN 1, and the configurations of one or more candidate PSCells and the associated CPA execution conditions are included in conditional mobility configuration information (e.g., conditionalReconfiguration IE) generated by the MN 1.

[0050] The configuration of each candidate PSCell is generated by a candidate SN (e.g., candidate SN4) that provides (or prepares) this candidate PSCell. The configuration of each candidate PSCell includes at least configuration information for the candidate PSCell. The configuration of each candidate PSCell may further include configuration information for one or more SCells associated with the candidate PSCell (i.e., configured together with or in association with the candidate PSCell). The configuration or SCG configuration of each candidate PSCell may be one or any combination of RB configuration, CG configuration, and SCG radio resource configuration. More specifically, the configuration or SCG configuration of each candidate PSCell may be an SN RRC Reconfiguration message generated by a candidate SN (e.g., candidate SN4) that provides (or prepares) this candidate PSCell. Some or all of the configurations of one or more candidate PSCells are included in a CPA configuration sent from MN1 to UE3. The CPA configuration includes a list of one or more MN RRC Reconfiguration messages and associated execution conditions. Each MN RRC Reconfiguration message includes the candidate PSCell configuration or SCG configuration (eg, one or any combination of RB configuration, CG configuration, SCG radio resource configuration, and SN RRC Reconfiguration message) received from the candidate SN.

[0051] Meanwhile, the CPA execution condition is generated by the MN 1. The CPA execution condition may consist of one or more trigger conditions. The conditions or criteria for triggering a CPA event may be similar to those for a measurement report event, such as CondEvent A3, CondEvent A4, or CondEvent A5. The UE 3 evaluates the CPA execution conditions. If the execution condition for one candidate PSCell is met, the UE 3 applies the PSCell configuration (i.e., CG configuration, SCG configuration, SCG radio resource configuration, or SN RRC Reconfiguration message) corresponding to the selected candidate PSCell (i.e., the candidate PSCell whose execution condition is met). If a bearer requiring SCG radio resources is configured, the UE 3 synchronizes to the selected PSCell. 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 above-mentioned operations.

[0052] 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 31 and one or more DUs 32 as shown in Figure 3. The CU 31 and each DU 32 are connected by an interface 3301. A UE 3 is connected to at least one DU 32 via at least one air interface 302.

[0053] The CU31 may be a logical node that hosts the RRC, Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols (or the RRC and PDCP protocols) of the gNB. The DU32 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 CU31 is a gNB-CU and the DUs32 are gNB-DUs, the interface 301 may be an F1 interface. The CU31 may include a CU-CP and a CU-UP.

[0054] In this specification, the term conditional mobility is used, which is a general term that refers to one or more of Conditional Handover (CHO), CPA, intra-SN CPC (or conditional SN modification), and inter-SN CPC (or conditional SN modification).

[0055] In this specification, the terms MN RRC message, MN RRC (Connection) Reconfiguration message, SN RRC message, and SN RRC Reconfiguration message are used. These terms are used for convenience to distinguish RRC messages generated by an MN from RRC messages generated by an SN. Therefore, the MN RRC message and the MN RRC (Connection) Reconfiguration message may be simply referred to as an RRC message and an RRC Reconfiguration message (or an RRC Connection Reconfiguration message). Similarly, the SN RRC message and the SN RRC Reconfiguration message may be simply referred to as an RRC message and an RRC Reconfiguration message.

[0056] The embodiments described below provide improvements to conditional mobility. Some embodiments provide improvements to a procedure in which a candidate SN 4 adds one or more new prepared PSCs in a prepared CPA or Inter-SN CPC. This operation or procedure may be referred to, for example and without limitation, as candidate SN triggered prepared cell addition.

[0057] First Embodiment This embodiment provides an improvement of inter-SN CPC for candidate SN triggered prepared cell addition. Specifically, this embodiment relates to clarifying various procedures related to candidate SN triggered prepared cell addition when multiple inter-SN CPCs are prepared in parallel. An example configuration of a wireless communication system according to this embodiment may be the same as the example shown in FIG. 1.

[0058] FIG. 4 illustrates an example of the operation of MN1. FIG. 4 is directed to a case in which a first inter-SN CPC initiated by MN1 and a second inter-SN CPC initiated by source SN2 are configured or prepared in parallel in one target candidate SN4. In step 401, MN1 receives a first message from candidate SN4. The candidate SN4 is a candidate SN for the first inter-SN CPC (i.e., MN-initiated inter-SN CPC) and also a candidate SN for the second inter-SN CPC (i.e., SN-initiated inter-SN CPC). The first message may be a message sent by candidate SN4 to request or propose modification of SN resources for UE3. The first message may be a message requesting or proposing modification or update of prepared CPA or CPC information. The first message may be an S-NODE MODIFICATION REQUIRED message. The first message may include information elements (e.g., Conditional PSCell Addition or Change (CPAC) Information Required IE, Prepared Cell Addition IE, Prepared CPC Update IE) indicating a request or proposal to update the prepared CPA or CPC information. Here, the prepared CPA or CPC information is information that was acknowledged by the candidate SN4 in a previous SN addition procedure and provided to the MN1 via an S-NODE ADDITION REQUEST ACKNOWLEDGE message (e.g., a Conditional PSCell Addition Information Acknowledge IE in the message). The CPA or CPC information includes a list of one or more prepared PSCells prepared by the candidate SN4. The list of prepared PSCells may be referred to as a prepared PSCell list or a prepared candidate PSCell list.

[0059] The first message indicates or includes an updated list of one or more prepared PSCells. The updated list may be referred to as an updated prepared PSCell list or an updated prepared candidate PSCell list. The updated list may indicate the addition of at least one new prepared PSCell, or the cancellation (or release) of at least one existing prepared PSCell, or both. In other words, the updated list may be a list of prepared PSCells updated by the addition of at least one new prepared PSCell, or the cancellation of at least one existing prepared PSCell, or both. The updated list may indicate an updated full list of prepared PSCells. In other words, the updated list may include not only newly added prepared PSCell(s) but also existing prepared PSCell(s) that have not been canceled.

[0060] In step 402, MN1 determines whether the updated list of one or more prepared PSCells indicated by the first message pertains to the first inter-SN CPC or the second inter-SN CPC. In other words, MN1 determines whether the modification or update of CPA or CPC information indicated in the first message pertains to the first inter-SN CPC or the second inter-SN CPC.

[0061] In some implementations, MN1 may operate as shown in Figure 5. Step 501 is similar to step 401 in Figure 4. In step 502, MN1 determines whether the updated list pertains to the first or second inter-SN CPC based on (a) the updated list itself, or (b) the inter-node RRC message included in the first message, or (c) both.

[0062] Specifically, MN1 may check whether one or more prepared PSCells included in the updated list received from candidate SN4 are included in either a first suggested PSCell list for the first inter-SN CPC or a second suggested PSCell list for the second inter-SN CPC. Here, the first suggested PSCell list is a list of candidate PSCells proposed by MN1 for the MN-initiated inter-SN CPC. Conversely, the second suggested PSCell list is a list of candidate PSCells proposed by source SN2 for the SN-initiated inter-SN CPC. If the updated list includes a PSCell included in the first suggested PSCell list but not included in the second suggested PSCell list, MN1 may determine (or conclude) that the updated list received from candidate SN4 relates to the first inter-SN CPC initiated by MN1. Conversely, if the updated list includes a PSCell that is included in the second proposed PSCell list but not included in the first proposed PSCell list, MN1 may determine (or conclude) that the updated list received from candidate SN4 relates to a second inter-SN CPC initiated by source SN2.

[0063] Additionally or alternatively, the MN1 may check the inter-node RRC message included in the first message received from the candidate SN4. If the MN1 cannot determine from the updated list itself whether the updated list relates to the first or second inter-SN CPC, the MN1 may consider the inter-node RRC message in the first message. Generally, an inter-node RRC message is an RRC message transmitted between RAN nodes via an inter-node interface such as the X2 interface or the Xn interface. The inter-node RRC message in the first message is sent from the candidate SN4 to the MN1. The inter-node RRC message in the first message may be a CG-CandidateList message specified in Chapter 11.2.2 of Non-Patent Document 3.

[0064] MN1 may check the list of prepared PSCells to be released indicated by the inter-node RRC message in the first message (e.g., cg-CandidateToReleaseList included in the CG-CandidateList message). MN1 may then determine whether the updated list relates to the first or second inter-SN CPC based on whether one or more cell identifiers included in the list of prepared PSCells to be released relate to the first or second inter-SN CPC. Specifically, if one or more cell identifiers included in the list of prepared PSCells to be released relate to the first inter-SN CPC, MN1 may determine (or conclude) that the updated prepared PSCell list also relates to the first inter-SN CPC. Conversely, if one or more cell identifiers included in the list of prepared PSCells to be released relate to a second inter-SN CPC, MN1 may determine (or conclude) that the updated prepared PSCell list also relates to the second inter-SN CPC.

[0065] It may be impossible to determine whether the updated list relates to the first or second inter-SN CPC using the updated list itself, the inter-node RRC message, or both. For example, there may be a case where all PSCells included in the updated prepared PSCell list are commonly included in both the first proposed PSCell list and the second proposed PSCell list. Furthermore, there may be a case where all cell identifiers included in the list of prepared PSCells to be released indicated by the inter-node RRC message in the first message are PSCells commonly prepared for both the first and second inter-SN CPCs. In such a case, the MN1 may autonomously determine (or conclude) whether the updated list relates to the first or second inter-SN CPC. In one example, the MN1 may determine that the updated list relates to the first or second inter-SN CPC, whichever has the larger maximum number of PSCells that the candidate SN4 can prepare. Conversely, the MN1 may determine that the updated list relates to whichever of the first and second inter-SN CPCs has the smaller maximum number of PSCells that the candidate SN4 can prepare. Alternatively, the MN1 may finally determine that the updated list relates to whichever of the first and second inter-SN CPCs has the larger headroom for the maximum number of PSCells that the candidate SN4 can prepare. Conversely, the MN1 may finally determine that the updated list relates to whichever of the first and second inter-SN CPCs has the smaller headroom for the maximum number of PSCells that the candidate SN4 can prepare. The maximum number of PSCells that the candidate SN4 can prepare is determined by the node that initiates the inter-SN CPC, i.e., by the MN1 in the case of an MN-initiated inter-SN CPC, or by the source SN2 in the case of an SN-initiated inter-SN CPC. The maximum number of PSCells that the candidate SN4 can prepare can be sent from the MN1 to the target candidate SN4 via an S-NODE ADDITION REQUEST message when preparing the inter-SN CPC.In the case of an SN-initiated inter-SN CPC, the maximum number of PSCells that the candidate SN 4 can prepare can be sent from the source SN 2 to the MN 1 via an S-NODE CHANGE REQUIRED message. The maximum number of PSCells that the candidate SN 4 can prepare may be included in the "Maximum Number of PSCells To Prepare" IE of the S-NODE ADDITION REQUEST message (and the S-NODE CHANGE REQUIRED message).

[0066] In another implementation, MN1 may operate as shown in FIG. 6 instead of the operation in FIG. 5. Step 601 is similar to step 401 in FIG. 4. In step 602, MN1 considers an information element or field in the first message that explicitly or implicitly indicates whether the modification of CPA or CPC information requested by the first message relates to the first or second inter-SN CPC. MN1 determines whether the updated prepared PSCell list relates to the first inter-SN CPC or the second inter-SN CPC according to the content of the information element or field. In other words, in this implementation, the first message (e.g., S-NODE MODIFICATION REQUIRED message) is enhanced to include an information element or field that indicates whether the modification of CPA or CPC information requested by the first message relates to the first or second inter-SN CPC.

[0067] 7 shows an example of the operation of MN1 and target candidate SN4. In step 701, MN1 and candidate SN4 prepare a first and second inter-SN CPC, i.e., both an MN-initiated inter-SN CPC and an SN-initiated inter-SN CPC. In step 702, candidate SN4 sends an S-NODE MODIFICATION REQUIRED message to MN1 to update the CPA or CPC information of either the first or second inter-SN CPC. The S-NODE MODIFICATION REQUIRED message includes (or indicates) an updated list of prepared PSCell(s). Furthermore, the S-NODE MODIFICATION REQUIRED message includes an information element or field that explicitly or implicitly indicates which of the two inter-SN CPCs the update of the CPA or CPC information (or update of the prepared PSCell list) relates to. The information element or field may specify whether the node initiating the inter-SN CPC is the MN (e.g., MN1) or the source SN (e.g., source SN2). The name of the information element or field may be, but is not limited to, "CPC Initiating Node." Alternatively, the name of the information element or field may be "CPC Source Node," meaning the node initiating the inter-SN CPC procedure. The information element or field may be an X2AP or XnAP information element in the first message. Alternatively, the information element or field may be a field in an inter-node RRC message (e.g., CG-CandidateList message) included in the first message.

[0068] Figure 8 shows an example of the format of an S-NODE MODIFICATION REQUIRED message. In the example of Figure 8, a new information element "CPC Initiating Node" is included in the Candidate PSCell List IE. This information element may be an enumerated type and may indicate an MN or SN. The format of Figure 8 can be modified as appropriate. For example, the CPC Initiating Node IE may be included in the CPAC Information Required IE in parallel with the Candidate PSCell List IE.

[0069] FIG. 9 shows an example of the format of a CG-CandidateList message, which is one of the inter-node RRC messages. The CG-CandidateList message can be included in an S-NG-RAN node to M-NG-RAN node Container IE in an S-NODE MODIFICATION REQUIRED message sent from the target candidate SN 4 to the MN 1. In the example of FIG. 9, the CG-CandidateList message includes a CPC initiatingNode information element or field 902 within a CG-CandidateInfo information element or field 901. The information element or field 902 may be an enumerated type and may indicate an MN or an SN. The format of FIG. 9 can be modified as appropriate. For example, the CPC initiatingNode information element or field 902 may be included in a CG-CandidateInfoId information element or field 903. Alternatively, the CPCinitiatingNode information element or field 902 may be included within a CG-CandidateList information element or field 904 in parallel with either the cg-CandidateToAddModList or the cg-CandidateToReleaseList or both.

[0070] The operations of MN1 and target candidate SN4 described in this embodiment can bring about the following advantages: when both the MN-initiated inter-SN CPC and the SN-initiated inter-SN CPC are prepared, MN1 can determine (or conclude) which of the two inter-SN CPCs the updated list of prepared PSCell lists proposed or requested by candidate SN4 relates to.

[0071] <Second embodiment> This embodiment provides an improvement of inter-SN CPC for candidate SN triggered prepared cell addition. Specifically, this embodiment relates to clarifying various procedures related to candidate SN triggered prepared cell addition when SN-initiated inter-SN CPC is prepared. Here, when inter-SN CPC is prepared means, for example, a state in which MN1 has already completed transmission of an RRC message for inter-SN CPC (e.g., RRC (Connection) Reconfiguration) to UE3, or a state in which UE3 has received an RRC message for inter-SN CPC and started an operation required for inter-SN CPC (e.g., evaluation of candidate PSCells). An example configuration of a wireless communication system according to this embodiment may be the same as the example shown in FIG. 1.

[0072] 10 shows an example of the operation of MN1. In step 1001, MN1 receives a first message from a candidate SN4 for an already prepared SN-initiated inter-SN CPC. As described in the first embodiment, the first message may be a message sent by the candidate SN4 to request or propose modification of SN resources for UE3. The first message may be a message requesting or proposing update of prepared CPA or CPC information. The first message may be an S-NODE MODIFICATION REQUIRED message.

[0073] The first message may indicate (or may include) an updated list of one or more prepared PSCells. The updated list may be referred to as an updated prepared PSCell list. The updated list may indicate the addition of at least one new prepared PSCell, or the cancellation (or release) of at least one existing prepared PSCell, or both. In other words, the updated list may be a list of prepared PSCells updated by the addition of at least one new prepared PSCell, or the cancellation of at least one existing prepared PSCell, or both. The updated list may indicate an updated full list of prepared PSCells. In other words, the updated list may include not only newly added prepared PSCell(s) but also existing prepared PSCell(s) that have not been canceled.

[0074] In step 1002, the MN1 determines whether to accept the addition of one or more prepared PSCells requested or proposed in the first message for an already prepared SN-initiated inter-SN CPC.

[0075] 10, the MN 1 does not need to inquire of the source SN 2 that initiated the SN-initiated inter-SN CPC whether to accept one or more prepared PSCells requested or proposed to be added by the candidate SN 4. This can contribute to quickly sending the configuration (SCG configuration) of the added prepared PSCell and related execution conditions to the UE 3.

[0076] In some implementations, MN1 determines whether to accept or reject the entire update of the prepared PSCell list. In other words, MN1 may not support accepting (or rejecting) only a portion of the addition of new prepared PSCells that resulted in an updated prepared PSCell list. Similarly, MN1 may not support accepting (or rejecting) only a portion of the cancellation of one or more existing prepared PSCells that resulted in an updated prepared PSCell list.

[0077] In another implementation, the MN1 determines whether to reject some or all of the prepared PSCells requested or proposed to be added in the first message. The MN1 may also determine whether to reject some or all of the cancellation of existing prepared PSCells requested or proposed in the first message. The MN1 may also reject only one of the addition of new prepared PSCell(s) and the cancellation of existing prepared PSCell(s) requested or proposed in the first message.

[0078] Figure 11 shows an example of the operation of MN1. Steps 1101 and 1102 are similar to steps 1001 and 1002 in Figure 10. In step 1103, if some or all of one or more prepared PSCells requested or proposed to be added in the first message are accepted, the MN1 notifies the source SN2 of the accepted at least one additional prepared PSCell via a second message. The second message may be an S-NODE MODIFICATION REQUEST message.

[0079] Figure 12 shows an example of the operation of MN1. The operation of Figure 12 may be performed by MN1 together with the operation of Figure 11. Steps 1201 and 1202 are similar to steps 1001 and 1002 of Figure 10. In step 1203, MN1 sends a third message to the candidate SN4 indicating at least one PSCell that has been accepted or rejected among one or more prepared PSCells requested or proposed for addition in the first message. The third message may indicate a complete list of one or more accepted prepared PSCells. The third message may be an S-NODE MODIFICATION CONFIRM message or an S-NODE MODIFICATION REFUSE message.

[0080] If the third message is an S-NODE MODIFICATION REFUSE message, the S-NODE MODIFICATION REFUSE message may indicate a new Cause value. The new Cause value may be, for example, but not limited to, "CPA-CPC resources partially (NOT) accepted." The S-NODE MODIFICATION REFUSE message may include an M-NG-RAN node to S-NG-RAN node Container IE. The M-NG-RAN node to S-NG-RAN node Container IE includes a CG-ConfigInfo message. The CG-ConfigInfo message is an inter-node RRC message sent from MN1 to candidate SN4 and may indicate a full list of one or more prepared PSCells accepted by MN1.

[0081] If MN1 rejects all of the one or more prepared PSCells requested or proposed to be added in the first message, MN1 may send a fourth message to candidate SN4 indicating that the modification of CPA or CPC information requested in the first message is rejected. The fourth message may be an S-NODE MODIFICATION REFUSE message. The S-NODE MODIFICATION REFUSE message may indicate a new Cause value. The new Cause value may be, for example, but not limited to, "CPA-CPC resources NOT accepted" or "CPA-CPC resources NOT updated."

[0082] The MN1 may retain the execution condition information received from the source SN2 when the SN-initiated inter-SN CPC was prepared. Then, the MN1 may select (or read or retrieve) one or more execution conditions for each of one or more prepared PSCells requested or proposed to be added in the first message from the retained execution condition information. Note that if the MN1 accepts only a portion of one or more prepared PSCells requested or proposed to be added, the MN1 may retrieve the execution conditions for the accepted prepared PSCell(s). Then, the MN1 may transmit an RRC message to the UE3, which includes the SCG configuration for each of the prepared PSCell(s) provided by the candidate SN4 in the first message and includes the selected one or more execution conditions for each of these prepared PSCell(s). The RRC message may be an MN RRC (Connection) Reconfiguration message. According to this operation, when prepared PSCell(s) for an SN-initiated inter-SN CPC are added based on a request from a candidate SN 4, the MN 1 does not need to inquire about the execution conditions associated with the added prepared PSCell(s) from the source SN 2. Therefore, the MN 1 can quickly provide the configuration (SCG configuration) and execution conditions of the added prepared PSCell(s) to the UE 3.

[0083] Figure 13 shows an example of signaling related to an SN-initiated inter-SN CPC. In step 1301, an inter-SN CPC initiated by the source SN2 is prepared. Step 1302 corresponds to step 1001 in Figure 10, step 1101 in Figure 11, and step 1201 in Figure 12. That is, the target candidate SN4 sends a first message (here, an S-NODE MODIFICATION REQUIRED message) to the MN1. The S-NODE MODIFICATION REQUIRED message includes a CPAC Information Required IE. The CPAC Information Required IE indicates an updated prepared PSCell list for the SN-initiated inter-SN CPC prepared in step 1301. The MN1 determines whether to accept the updated prepared PSCell list for the SN-initiated inter-SN CPC. In the example of Figure 13, MN1 accepts some or all of the one or more prepared PSCells proposed or requested in the updated prepared PSCell list. Step 1303 corresponds to step 1203 in Figure 12. Specifically, MN1 sends an S-NODE MODIFICATION CONFIRM message to candidate SN4. The S-NODE MODIFICATION CONFIRM message indicates at least one PSCell that has been accepted from the one or more prepared PSCells requested or proposed for addition in the S-NODE MODIFICATION REQUIRED message of step 1302.

[0084] In step 1304, the MN 1 sends an MN RRC (Connection) Reconfiguration message to the UE 3. This RRC message includes the configuration (or SCG configuration) of each prepared PSCell(s) provided by the candidate SN 4 in the S-NODE MODIFICATION REQUIRED message of step 1302. As already explained, the configuration or SCG configuration of each prepared PSCell may be referred to as an SCG radio resource configuration. The configuration or SCG configuration of each prepared PSCell may be included in a CG-CandidateList message included in an S-NG-RAN node to M-NG-RAN node Container IE in the S-NODE MODIFICATION REQUIRED message of step 1302. More specifically, the configuration or SCG configuration of each prepared PSCell may be included in a corresponding scg-CellGroupConfig field of one or more CG-Config IEs included in the CG-CandidateList message. The configuration of each prepared PSCell or the SCG configuration may be an SN RRC Reconfiguration message, or one or more IEs (e.g., CellGroupConfig IE) included in the SN RRC Reconfiguration message. The CellGroupConfig IE is used to configure the SCG. Furthermore, the RRC message includes one or more selected execution conditions for each of these prepared PSCell(s). Note that the bearer configuration associated with each prepared PSCell may also be included in the CG-CandidateList message. More specifically, the bearer configuration associated with each prepared PSCell may be included in a corresponding scg-RB-Config field of one or more CG-Config IEs included in the CG-CandidateList message. The MN RRC message may include the bearer configuration associated with each prepared PSCell.

[0085] Step 1305 corresponds to step 1103 in Fig. 11. That is, MN1 informs source SN2 of the accepted at least one additional prepared PSCell, for example, via an S-NODE MODIFICATION REQUEST message. The message may indicate an updated complete list of prepared PSCells. The complete list may be indicated by a Conditional PSCell Change Information Update IE included in the S-NODE MODIFICATION REQUEST message.

[0086] In step 1306, the source SN2 may respond to the MN1 with an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message. Step 1306 may be omitted. In step 1306, the source SN2 may provide the MN1 with one or more CPC execution conditions for each of the additional prepared PSCell(s). These execution conditions may be indicated by a CG-Config message carried by an S-NG-RAN node to M-NG-RAN node Container IE included in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message. The CG-Config message is an inter-node RRC message sent from the source SN2 to the MN1.

[0087] In step 1307, the MN 1 may send an MN RRC Reconfiguration message to the UE 3. The MN RRC Reconfiguration message may indicate modification or updating of one or more execution conditions of the prepared PSCell(s). If step 1306 is omitted, or if the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message in step 1306 does not indicate updated CPC execution conditions, step 1307 may be omitted.

[0088] The order of the steps shown in Figure 13 may be changed as appropriate. For example, step 1304 may be performed after step 1305 or after step 1306. Step 1303 may be performed after step 1304, step 1305, step 1306, or step 1307. Alternatively, step 1304 may be integrated into or replaced by step 1307.

[0089] The procedure shown in Fig. 13 can provide the following advantages: As shown in Fig. 13, the transmission of an MN RRC (Connection) Reconfiguration message from MN1 to UE3 (step 1304) is performed before or without querying the source SN2 (step 1305), which can contribute to quickly sending the configuration of the added prepared PSCell (SCG configuration) and related execution conditions to UE3.

[0090] <Third embodiment> This embodiment provides an improvement of inter-SN CPC or CPA for candidate SN triggered prepared cell addition. A configuration example of a wireless communication system according to this embodiment may be the same as the example shown in FIG. 1 or FIG. 2.

[0091] 14 shows an example of the operation of MN1. In step 1401, MN1 receives a first message from candidate SN4 for an already prepared CPA or inter-SN CPC. The inter-SN CPC may be an MN-initiated inter-SN CPC initiated by MN1 or an SN-initiated inter-SN CPC initiated by source SN2. As described in the first embodiment, the first message may be a message sent by candidate SN4 to request or propose modification of SN resources for UE3. The first message may be a message requesting or proposing update of prepared CPA or CPC information. The first message may be an S-NODE MODIFICATION REQUIRED message.

[0092] The first message may indicate (or may include) an updated list of one or more prepared PSCells. The updated list may be referred to as an updated prepared PSCell list. The updated list may indicate the addition of at least one new prepared PSCell, or the cancellation (or release) of at least one existing prepared PSCell, or both. In other words, the updated list may be a list of prepared PSCells updated by the addition of at least one new prepared PSCell, or the cancellation of at least one existing prepared PSCell, or both. The updated list may indicate an updated full list of prepared PSCells. In other words, the updated list may include not only newly added prepared PSCell(s) but also existing prepared PSCell(s) that have not been canceled.

[0093] In step 1402, MN1 determines whether to reject some or all of one or more prepared PSCells requested or proposed to be added in the first message. In other words, MN1 supports rejecting the addition of new prepared PSCells that have resulted in an updated prepared PSCell list. In yet other words, MN1 supports accepting (or rejecting) only some of the addition of new prepared PSCells that have resulted in an updated prepared PSCell list.

[0094] According to the operation shown in Figure 14, MN1 is allowed to partially or completely reject one or more prepared PSCells that are requested or proposed for addition by candidate SN4. Candidate PSCell(s) that were proposed to candidate SN4 but not prepared when CPA or inter-SN CPC was prepared may no longer be suitable candidates for MN1 or UE3 due to subsequent changes in circumstances. According to the operation shown in Figure 14, MN1 can reject prepared PSCell(s) that are no longer suitable. In other words, MN1 can reject the addition of candidate PSCell(s) that are no longer suitable.

[0095] Figure 15 shows an example of the operation of MN1. Steps 1501 and 1502 are similar to steps 1401 and 1402 in Figure 14. In step 1503, MN1 sends a second message to the candidate SN4 indicating at least one PSCell that has been accepted or rejected among one or more prepared PSCells requested or proposed for addition in the first message. The second message may indicate a complete list of one or more prepared PSCells that have been accepted by MN1. The second message may be an S-NODE MODIFICATION CONFIRM message or an S-NODE MODIFICATION REFUSE message.

[0096] If the second message in step 1503 is an S-NODE MODIFICATION REFUSE message, the S-NODE MODIFICATION REFUSE message may indicate a new Cause value. The new Cause value may be, for example, but not limited to, “CPA-CPC resources partially (NOT) accepted.” The S-NODE MODIFICATION REFUSE message may include an M-NG-RAN node to S-NG-RAN node Container IE. The M-NG-RAN node to S-NG-RAN node Container IE includes a CG-ConfigInfo message. The CG-ConfigInfo message is an inter-node RRC message sent from MN1 to candidate SN4 and may indicate a full list of one or more prepared PSCells accepted by MN1.

[0097] If the second message in step 1503 is an S-NODE MODIFICATION CONFIRM message, the format of the S-NODE MODIFICATION CONFIRM message may be extended as shown in FIG. 16 or FIG.

[0098] 16, the S-NODE MODIFICATION CONFIRM message includes a newly defined XnAP IE to indicate a complete list of one or more prepared PSCells accepted by MN1 or a list of one or more newly added prepared PSCell(s) accepted by MN1. The name of the XnAP IE may be, for example, but not limited to, CPAC Information Modification Acknowledge IE.

[0099] In the example of Figure 17, the S-NODE MODIFICATION CONFIRM message includes a new XnAP IE that can include a CG-ConfigInfo message. The name of the XnAP IE may be, for example, but not limited to, "Additional M-NG-RAN node to S-NG-RAN node Container IE." This CG-ConfigInfo message is an inter-node RRC message sent from MN1 to candidate SN4, and may indicate a full list of one or more prepared PSCells accepted by MN1, or may indicate a list of one or more newly added prepared PSCell(s) accepted by MN1.

[0100] If MN1 rejects all of the one or more prepared PSCells requested or proposed to be added in the first message, MN1 may send a third message to the candidate SN4 indicating that the modification of CPA or CPC information requested in the first message is rejected. The third message may be an S-NODE MODIFICATION REFUSE message. The S-NODE MODIFICATION REFUSE message may indicate a new Cause value. The new Cause value may be, for example, but not limited to, "CPA-CPC resources NOT accepted" or "CPA-CPC resources NOT updated."

[0101] <Fourth embodiment> This embodiment provides an improvement of SN-initiated inter-SN CPC for candidate SN triggered prepared cell addition. A configuration example of a wireless communication system according to this embodiment may be the same as the example shown in FIG.

[0102] Figure 18 shows an example of the operation of source SN2. In step 1801, source SN2 receives a first message from MN1 regarding modification of an already prepared SN-initiated inter-SN CPC. The first message indicates one or more prepared PSCells requested or proposed for addition by candidate SN4. The first message may be a message sent by MN1 to request or propose modification of SN resources for UE3. The first message may be a message requesting or proposing modification or update of CPA or CPC information. The first message may be an S-NODE MODIFICATION REQUEST message.

[0103] The first message may indicate (or may include) an updated list of one or more prepared PSCells. The updated list may be referred to as an updated prepared PSCell list. The updated list may indicate the addition of at least one new prepared PSCell, or the cancellation (or release) of at least one existing prepared PSCell, or both. In other words, the updated list may be a list of prepared PSCells updated by the addition of at least one new prepared PSCell, or the cancellation of at least one existing prepared PSCell, or both. The updated list may indicate an updated full list of prepared PSCells. In other words, the updated list may include not only newly added prepared PSCell(s) but also existing prepared PSCell(s) that have not been canceled.

[0104] In step 1802, the source SN2 determines whether to reject some or all of one or more prepared PSCells requested or proposed for addition by the candidate SN4. In other words, the source SN2 supports the rejection of the addition of new prepared PSCells that result in an updated list of prepared PSCells. In yet other words, the source SN2 supports the acceptance (or rejection) of only some of the addition of new prepared PSCells that result in an updated list of prepared PSCells.

[0105] According to the operation shown in Figure 18, the source SN2 is allowed to partially or entirely reject one or more prepared PSCells that are requested or proposed for addition by the candidate SN4. Candidate PSCell(s) that were proposed to the candidate SN4 but not prepared when the SN-initiated inter-SN CPC was prepared may no longer be suitable candidates for the source SN2 or the UE3 due to subsequent changes in circumstances. According to the operation shown in Figure 18, the source SN2 can reject the prepared PSCell(s) that are no longer suitable.

[0106] Figure 19 shows an example of the operation of source SN2. Steps 1901 and 1902 are similar to steps 1801 and 1802 in Figure 18. In step 1903, source SN2 sends a second message to MN1 indicating at least one PSCell that has been accepted or rejected among one or more prepared PSCells requested or proposed for addition. The second message may indicate a full list of one or more prepared PSCells accepted by source SN2, or may indicate a list of one or more newly added prepared PSCells accepted by source SN2. The second message may be an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

[0107] If the second message in step 1903 is an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message, the format of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message may be extended as shown in Figure 20. In the example of Figure 20, the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message includes a newly defined XnAP IE to indicate a full list of one or more prepared PSCells accepted by source SN2 or a list of one or more newly added prepared PSCells accepted by source SN2. The name of the XnAP IE may be, for example, but is not limited to, a Conditional PSCell Change Information Update Acknowledge IE.

[0108] If the source SN2 rejects all of the one or more prepared PSCells requested or proposed to be added in the first message, the source SN2 may send a third message to the MN1 indicating that the modification of the CPA or CPC information requested in the first message is rejected. The third message may be an S-NODE MODIFICATION REQUEST REJECT message. The S-NODE MODIFICATION REQUEST REJECT message may indicate a new Cause value. The new Cause value may be, for example, but not limited to, "CPC resources NOT accepted" or "CPA-CPC resources NOT updated."

[0109] <Fifth embodiment> This embodiment provides an improvement of SN-initiated inter-SN CPC for candidate SN triggered prepared cell addition. A configuration example of a wireless communication system according to this embodiment may be the same as the example shown in FIG.

[0110] 21 shows an example of the operation of MN1. In step 2101, MN1 stores execution condition information received from source SN2 when an SN-initiated inter-SN CPC is prepared. The execution condition information indicates one or more CPC execution conditions for each PSCell included in the candidate PSCell list proposed by source SN2.

[0111] In step 2102, the MN1 receives a first message from a candidate SN4 for an already prepared SN-initiated inter-SN CPC. As described in the first embodiment, the first message may be a message sent by the candidate SN4 to request or propose modification of SN resources for the UE3. The first message may be a message requesting or proposing modification or update of prepared CPA or CPC information. The first message may be an S-NODE MODIFICATION REQUIRED message.

[0112] The first message may indicate (or may include) an updated list of one or more prepared PSCells. The updated list may be referred to as an updated prepared PSCell list. The updated list may indicate the addition of at least one new prepared PSCell, or the cancellation (or release) of at least one existing prepared PSCell, or both. In other words, the updated list may be a list of prepared PSCells updated by the addition of at least one new prepared PSCell, or the cancellation of at least one existing prepared PSCell, or both. The updated list may indicate an updated full list of prepared PSCells. In other words, the updated list may include not only newly added prepared PSCell(s) but also existing prepared PSCell(s) that have not been canceled.

[0113] In step 2103, MN1 selects (or reads or retrieves) from the stored execution condition information one or more execution conditions for each of one or more prepared PSCells requested or proposed to be added in the first message. MN1 may or may not decide whether to accept one or more prepared PSCells requested or proposed to be added in the first message. In other words, MN1 may accept all proposed PSCell(s) requested to be added by candidate SN4. More specifically, MN1 may accept all proposed PSCell(s) requested to be added by candidate SN4 as long as they are included in the candidate PSCell list proposed by source SN2.

[0114] In step 2104, the MN 1 sends an RRC message to the UE 3, the RRC message including the SCG configuration of each of the prepared PSCell(s) provided by the candidate SN 4 in the first message and including one or more selected execution conditions for each of these prepared PSCell(s). The RRC message may be an MN RRC (Connection) Reconfiguration message.

[0115] 21, when prepared PSCell(s) for an SN-initiated inter-SN CPC are added based on a request from a candidate SN 4, the MN 1 does not need to inquire about the execution conditions associated with the added prepared PSCell(s) from the source SN 2. Therefore, the MN 1 can quickly provide the configuration (SCG configuration) and execution conditions of the added prepared PSCell(s) to the UE 3.

[0116] <Another embodiment 1> The MN1 or source SN2 may send information indicating whether a proposal to add a new prepared PSCell is permitted to the candidate SN4 in advance. This information may be sent to the candidate SN4 when an inter-SN CPC is prepared. In the case of an MN-initiated inter-SN CPC, the MN1 may send this information to the candidate SN4. The MN1 may send this information to the candidate SN4, for example, in an S-NODE ADDITION REQUEST message or an S-NODE MODIFICATION REQUEST message. In the case of an SN-initiated inter-SN CPC, the source SN2 may send this information to the candidate SN4 via the MN1. The SN2 may send this information to the MN1, for example, in an S-NODE CHANGE REQUIRED message or an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message. Alternatively, in the case of an SN-initiated inter-SN CPC, the MN1 may send this information to the candidate SN4 based on its own judgment. Candidate SN4 may initiate the procedure described in the above embodiment only if the proposal to add a new prepared PSCell is permitted.

[0117] <Other embodiment 2> As already described in the above embodiments, in some implementations, MN1 or source SN2 may not necessarily support partial acceptance of requests or proposals for adding prepared PSCells (or updating the prepared PSCell list). For example, if any one of the multiple prepared PSCells requested or proposed for addition by candidate SN4 is not accepted, MN1 or source SN2 may reject the addition of all multiple prepared PSCells.

[0118] <Other embodiment 3> If the candidate SN4 requests or proposes adding prepared PSCell(s) and canceling prepared PSCell(s) simultaneously in a single message (e.g., an S-NODE MODIFICATION REQUIRED message), the total number of prepared PSCells may temporarily exceed the maximum number of PSCells that the candidate SN4 is permitted to prepare. The maximum number of PSCells is determined by the node initiating the inter-SN CPC, i.e., by the MN1 in the case of an MN-initiated inter-SN CPC, or by the source SN2 in the case of an SN-initiated inter-SN CPC. In some implementations, such a temporary exceedance of the maximum number may be tolerated as long as the number of prepared PSCells after the additions and deletions requested in a single message does not exceed the maximum number. If the size of the updated entire list of prepared PSCells received from the candidate SN4 does not exceed the maximum number, the MN1 or source SN2 may accept the proposed or requested updates to that list (i.e., adding prepared PSCell(s) and canceling prepared PSCell(s)).

[0119] Next, exemplary configurations of RAN nodes 1, 2, and 4 and UE 3 according to the above-described embodiments will be described below. FIG. 22 is a block diagram illustrating an exemplary configuration of RAN node 1 according to the above-described embodiments. The configurations of the other RAN nodes 2 and 4 may be similar to the configuration illustrated in FIG. 22. Referring to FIG. 22, RAN node 1 includes a Radio Frequency (RF) transceiver 2201, a network interface 2203, a processor 2204, and a memory 2205. The RF transceiver 2201 performs analog RF signal processing for communication with UEs, including UE 3. The RF transceiver 2201 may include multiple transceivers. The RF transceiver 2201 is coupled to an antenna array 2202 and a processor 2204. The RF transceiver 2201 receives modulation symbol data from the processor 2204, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 2202. The RF transceiver 2201 also generates a baseband receive signal based on the receive RF signal received by the antenna array 2202 and supplies the baseband receive signal to the processor 2204. The RF transceiver 2201 may include an analog beamformer circuit for beamforming. The analog beamformer circuit includes, for example, multiple phase shifters and multiple power amplifiers.

[0120] The network interface 2203 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.

[0121] The processor 2204 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. The processor 2204 may include multiple processors. For example, the processor 2204 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.

[0122] For example, digital baseband signal processing by processor 2204 may include signal processing of a Service Data Adaptation Protocol (SDAP) layer, a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer, a Medium Access Control (MAC) layer, and a Physical (PHY) layer. Also, control plane processing by processor 2204 may include processing of Non-Access Stratum (NAS) messages, RRC messages, MAC Control Elements (CE), and Downlink Control Information (DCI).

[0123] The processor 2204 may include a digital beamformer module for beamforming, which may include a Multiple Input Multiple Output (MIMO) encoder and precoder.

[0124] The memory 2205 is configured by a combination of volatile memory and nonvolatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The nonvolatile 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 2205 may include storage located remotely from the processor 2204. In this case, the processor 2204 may access the memory 2205 via the network interface 2203 or an I / O interface (not shown).

[0125] The memory 2205 may store one or more software modules (computer programs) 2206 including instructions and data for performing the processing by the RAN node 1 described in the above embodiments. In some implementations, the processor 2204 may be configured to read and execute the software modules 2206 from the memory 2205 to perform the processing by the RAN node 1 described in the above embodiments.

[0126] Note that if the RAN node 1 is a CU (eg, eNB-CU or gNB-CU) or a CU-CP, the RAN node 1 may not include the RF transceiver 2201 (and the antenna array 2202).

[0127] 23 is a block diagram showing an example configuration of UE3. A radio frequency (RF) transceiver 2301 performs analog RF signal processing for communication with RAN nodes 1, 2, and 4. The RF transceiver 2301 may include multiple transceivers. The analog RF signal processing performed by the RF transceiver 2301 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 2301 is coupled to an antenna array 2302 and a baseband processor 2303. The RF transceiver 2301 receives modulation symbol data (or OFDM symbol data) from the baseband processor 2303, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 2302. The RF transceiver 2301 also generates a baseband receive signal based on the receive RF signal received by the antenna array 2302 and provides the baseband receive signal to the baseband processor 2303. The RF transceiver 2301 may include an analog beamformer circuit for beamforming. The analog beamformer circuitry includes, for example, multiple phase shifters and multiple power amplifiers.

[0128] The baseband processor 2303 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. 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).

[0129] For example, digital baseband signal processing by the baseband processor 2303 may include signal processing of an SDAP layer, a PDCP layer, an RLC layer, a MAC layer, and a PHY layer. Also, control plane processing by the baseband processor 2303 may include processing of a Non-Access Stratum (NAS) protocol, an RRC protocol, MAC CEs, and DCIs.

[0130] The baseband processor 2303 may perform MIMO encoding and precoding for beamforming.

[0131] The baseband processor 2303 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 2304, which will be described later.

[0132] The application processor 2304 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 2304 may include multiple processors (multiple processor cores). The application processor 2304 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 2306 or a memory not shown, thereby realizing various functions of the UE3.

[0133] In some implementations, the baseband processor 2303 and the application processor 2304 may be integrated on a single chip, as indicated by the dashed line (2305) in Figure 23. In other words, the baseband processor 2303 and the application processor 2304 may be implemented as a single System on Chip (SoC) device 2305. An SoC device is sometimes called a system Large Scale Integration (LSI) or a chipset.

[0134] The memory 2306 is volatile memory, nonvolatile memory, or a combination thereof. The memory 2306 may include multiple physically independent memory devices. The volatile memory is, for example, SRAM, DRAM, or a combination thereof. The nonvolatile memory is MROM, EEPROM, flash memory, a hard disk drive, or any combination thereof. For example, the memory 2306 may include an external memory device accessible from the baseband processor 2303, the application processor 2304, and the SoC 2305. The memory 2306 may also include an internal memory device integrated within the baseband processor 2303, the application processor 2304, or the SoC 2305. Furthermore, the memory 2306 may include memory within a Universal Integrated Circuit Card (UICC).

[0135] The memory 2306 may store one or more software modules (computer programs) 2307 including instructions and data for performing the processing by the UE 3 described in the above-described embodiments. In some implementations, the baseband processor 2303 or the application processor 2304 may be configured to read and execute the software modules 2307 from the memory 2306, thereby performing the processing by the UE 3 described using the drawings in the above-described embodiments.

[0136] It should be noted that the control plane processing and operations performed by UE3 described in the above embodiment can be realized by elements other than the RF transceiver 2301 and the antenna array 2302, namely, at least one of the baseband processor 2303 and the application processor 2304, and the memory 2306 storing the software module 2307.

[0137] As described with reference to Figures 22 and 23, each of the processors included in the RAN nodes 1, 2, and 4 and the UE 3 according to the above-described embodiments can 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® disk 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.

[0138] 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.

[0139] For example, some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0140] (Appendix 1) 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: at least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: receiving a first message from a common candidate SN for both a first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by the MN and a second conditional PSCell change initiated by a source Secondary Node (SN); determining whether the updated list of one or more prepared PSCells indicated by the first message relates to the first conditional PSCell change or the second conditional PSCell change; It is configured as follows: RAN node. (Appendix 2) the at least one processor is configured to determine whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change based on the updated list itself, or based on an inter-node Radio Resource Control (RRC) message included in the first message, or based on both. RAN node as described in Appendix 1. (Appendix 3) the at least one processor is configured to determine whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change based on whether one or more prepared PSCells included in the updated list are included in a first proposed PSCell list for the first conditional PSCell change or a second proposed PSCell list for the second conditional PSCell change. RAN node as described in Appendix 2. (Appendix 4) The at least one processor: Checking the list of prepared PSCells to be released indicated by the inter-node RRC message; and determining whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change based on whether one or more cell identifiers included in the list of prepared PSCells to be released relate to the first conditional PSCell change or the second conditional PSCell change. RAN node as defined in Supplementary Note 2 or 3. (Appendix 5) the at least one processor is configured to autonomously determine whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change, if it is not possible to determine whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change using the updated list itself, the inter-node RRC message, or both. 5. The RAN node according to any one of Supplementary Note 2 to 4. (Appendix 6) the at least one processor is configured to determine that the updated list relates to the first conditional PSCell change or the second conditional PSCell change, whichever has a larger maximum number of PSCells that the candidate SN can prepare. RAN node as described in Appendix 5. (Appendix 7) the at least one processor is configured to determine that the updated list relates to the first conditional PSCell change or the second conditional PSCell change, whichever has a smaller maximum number of PSCells that the candidate SN can prepare. RAN node as described in Appendix 5. (Appendix 8) the at least one processor is configured to autonomously determine whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change if all PSCells included in the updated list are commonly included in both the first proposed PSCell list and the second proposed PSCell list. RAN node as described in Appendix 3. (Appendix 9) the first message includes an information element or field indicating whether the modification of conditional PSCell addition or modification information requested by the first message relates to the first conditional PSCell modification or the second conditional PSCell modification; the at least one processor is configured to determine whether the updated list relates to the first conditional PSCell change or the second conditional PSCell change based on the information element or field. RAN node as described in Appendix 1. (Appendix 10) The information element or field specifies whether the node that initiated the conditional PSCell change is the MN or the source SN. RAN node as described in Appendix 9. (Appendix 11) the information element or field is a field in an inter-node Radio Resource Control (RRC) message included in the first message; 11. A RAN node as defined in Supplementary Note 9 or 10. (Appendix 12) the at least one processor is configured to accept the updated list if the number of prepared PSCells included in the updated list does not exceed a predetermined maximum number for the MN or the source SN. 12. The RAN node according to any one of Supplementary Notes 1 to 11. (Appendix 13) the updated list indicates the addition of at least one new prepared PSCell, or the cancellation of at least one existing prepared PSCell, or both; 13. The RAN node according to any one of Supplementary Notes 1 to 12. (Appendix 14) the first message is an S-NODE MODIFICATION REQUIRED message; 14. The RAN node according to any one of Supplementary Notes 1 to 13. (Appendix 15) the at least one processor is configured to, if the updated list relates to the second conditional PSCell change, determine whether to accept the addition of one or more prepared PSCells requested or proposed by the first message for the second conditional PSCell change. 15. The RAN node according to any one of Supplementary Notes 1 to 14. (Appendix 16) the at least one processor is configured to determine whether to reject some or all of the one or more prepared PSCells requested or proposed to be added by the first message; 16. The RAN node according to any one of Supplementary Notes 1 to 15. (Appendix 17) The at least one processor is configured to, if the updated list relates to the second conditional PSCell change and if the addition of some or all of the one or more prepared PSCells is accepted, notify the source SN of the accepted at least one additional prepared PSCell in a second message. 17. The RAN node of claim 15 or 16. (Appendix 18) the second message is an S-NODE MODIFICATION REQUEST message; RAN node as described in Supplementary Note 17. (Appendix 19) The at least one processor is configured to send a third message to the candidate SN indicating at least one PSCell that has been accepted or rejected among the one or more prepared PSCells whose addition has been requested or proposed by the first message. 19. The RAN node according to any one of Supplementary Notes 15 to 18. (Appendix 20) the first message indicates an updated complete list of prepared PSCells prepared by the candidate SN, including the one or more prepared PSCells requested or proposed for addition by the first message; the third message indicating a complete list of one or more accepted prepared PSCells; RAN node as described in Supplementary Note 19. (Appendix 21) the third message is an S-NODE MODIFICATION CONFIRM message or an S-NODE MODIFICATION REFUSE message; 21. The RAN node of claim 19 or 20. (Appendix 22) the at least one processor is configured to send a fourth message to the candidate SN indicating that the modification of the conditional PSCell addition or modification information requested by the first message is rejected if all of the one or more prepared PSCells requested or proposed to be added by the first message are rejected. 22. The RAN node according to any one of Supplementary Notes 15 to 21. (Appendix 23) The fourth message is an S-NODE MODIFICATION REFUSE message. RAN node as described in Supplementary Note 22. (Appendix 24) The at least one processor: Storing execution condition information received from the source SN when the second conditional PSCell change is prepared; selecting one or more execution conditions for each of the one or more prepared PSCells requested or proposed to be added by the first message from the retained execution condition information; sending a Radio Resource Control (RRC) message to the UE, the RRC message including an SCG configuration for each of the one or more prepared PSCells provided by the candidate SN in the first message and including the selected one or more execution conditions for each of the one or more prepared PSCells; It is configured as follows: 22. The RAN node according to any one of Supplementary Notes 15 to 21. (Appendix 25) 1. A method performed by a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), comprising: receiving a first message from a common candidate SN for both a first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by the MN and a second conditional PSCell change initiated by a source Secondary Node (SN); and determining whether the updated list of one or more prepared PSCells indicated by the first message relates to the first conditional PSCell change or the second conditional PSCell change; A method for providing the above. (Appendix 26) 1. A program for causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), the method comprising: The method comprises: receiving a first message from a common candidate SN for both a first conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by the MN and a second conditional PSCell change initiated by a source Secondary Node (SN); and determining whether the updated list of one or more prepared PSCells indicated by the first message relates to the first conditional PSCell change or the second conditional PSCell change; A program that includes: (Appendix 27) 1. 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: at least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: preparing SN resources for the UE for both a first conditional Primary SCG Cell (PSCell) change initiated by a Master Node (MN) and a second conditional PSCell change initiated by a source SN; Sending a first message to the MN; It is configured as the first message includes an information element or field indicating whether the modification of conditional PSCell addition or modification information requested by the first message relates to the first conditional PSCell modification or the second conditional PSCell modification; RAN node. (Appendix 28) The information element or field specifies whether the source node of the conditional PSCell change is the MN or the source SN; RAN node as described in Supplementary Note 27. (Appendix 29) the information element or field is a field in an inter-node Radio Resource Control (RRC) message included in the first message; 29. The RAN node of claim 27 or 28. (Appendix 30) 1. 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: Preparing SN resources for the UE for both a first conditional Primary SCG Cell (PSCell) change initiated by a Master Node (MN) and a second conditional PSCell change initiated by a source SN; and sending a first message to the MN; Equipped with the first message includes an information element or field indicating whether the modification of conditional PSCell addition or modification information requested by the first message relates to the first conditional PSCell modification or the second conditional PSCell modification; method. (Appendix 31) 1. A program for 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: The method comprises: Preparing SN resources for the UE for both a first conditional Primary SCG Cell (PSCell) change initiated by a Master Node (MN) and a second conditional PSCell change initiated by a source SN; and sending a first message to the MN; Equipped with the first message includes an information element or field indicating whether the modification of conditional PSCell addition or modification information requested by the first message relates to the first conditional PSCell modification or the second conditional PSCell modification; program. (Appendix 32) 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: at least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: receiving a first message from a candidate SN for a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by a source Secondary Node (SN); determining whether to accept the addition of one or more prepared PSCells requested or proposed by the first message with respect to the conditional PSCell modification initiated by the source SN; It is configured as follows: RAN node. (Appendix 33) the at least one processor is configured to determine whether to reject some or all of the one or more prepared PSCells requested or proposed to be added by the first message; RAN node as described in Supplementary Note 32. (Appendix 34) the first message is an S-NODE MODIFICATION REQUIRED message; 34. The RAN node of claim 32 or 33. (Appendix 35) The at least one processor is configured to, if accepting some or all of the addition of the one or more prepared PSCells, notify the source SN of the accepted at least one additional prepared PSCell in a second message. 35. The RAN node according to any one of Supplementary Notes 32 to 34. (Appendix 36) the second message is an S-NODE MODIFICATION REQUEST message; RAN node as described in Supplementary Note 35. (Appendix 37) The at least one processor is configured to send a third message to the candidate SN indicating at least one PSCell that has been accepted or rejected among the one or more prepared PSCells whose addition has been requested or proposed by the first message. 37. The RAN node according to any one of Supplementary Notes 32 to 36. (Appendix 38) the first message indicates an updated complete list of prepared PSCells prepared by the candidate SN, including the one or more prepared PSCells requested or proposed for addition by the first message; the third message indicating a complete list of one or more accepted prepared PSCells; RAN node as described in Appendix 37. (Appendix 39) the third message is an S-NODE MODIFICATION CONFIRM message or an S-NODE MODIFICATION REFUSE message; 39. The RAN node of claim 37 or 38. (Appendix 40) the at least one processor is configured to send a fourth message to the candidate SN indicating that the modification of the conditional PSCell addition or modification information requested by the first message is rejected if all of the one or more prepared PSCells requested or proposed to be added by the first message are rejected. 39. The RAN node according to any one of Supplementary Notes 32 to 39. (Appendix 41) The fourth message is an S-NODE MODIFICATION REFUSE message. RAN node as described in Supplementary Note 40. (Appendix 42) The at least one processor: Storing execution condition information received from the source SN when the conditional PSCell change is prepared; selecting one or more execution conditions for each of the one or more prepared PSCells requested or proposed to be added by the first message from the retained execution condition information; sending a Radio Resource Control (RRC) message to the UE, the RRC message including an SCG configuration for each of the one or more prepared PSCells provided by the candidate SN in the first message and including the selected one or more execution conditions for each of the one or more prepared PSCells; It is configured as follows: 39. The RAN node according to any one of Supplementary Notes 32 to 39. (Appendix 43) 1. A method performed by a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), comprising: receiving a first message from a candidate SN for a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by a source Secondary Node (SN); and determining whether to accept the addition of one or more prepared PSCells requested or proposed in the first message with respect to the conditional PSCell modification initiated by the source SN; A method for providing the above. (Appendix 44) 1. A program for causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), the method comprising: The method comprises: receiving a first message from a candidate SN for a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by a source Secondary Node (SN); and determining whether to accept the addition of one or more prepared PSCells requested or proposed in the first message with respect to the conditional PSCell modification initiated by the source SN; A program that includes: (Appendix 45) 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: at least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: receiving a first message from a candidate SN for a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or conditional PSCell change; determining whether to reject some or all of one or more prepared PSCells requested or proposed to be added by the first message; It is configured as follows: RAN node. (Appendix 46) The at least one processor is configured to send a second message to the candidate SN indicating at least one PSCell that has been accepted or rejected among the one or more prepared PSCells requested or proposed for addition by the first message. RAN node as described in Appendix 45. (Appendix 47) the first message indicates an updated complete list of prepared PSCells prepared by the candidate SN, including the one or more prepared PSCells requested or proposed for addition by the first message; The second message indicates a complete list of one or more accepted prepared PSCells. RAN node as described in Appendix 46. (Appendix 48) the first message is an S-NODE MODIFICATION REQUIRED message; the second message is an S-NODE MODIFICATION CONFIRM message or an S-NODE MODIFICATION REFUSE message; 48. A RAN node as defined in claim 46 or 47. (Appendix 49) the at least one processor is configured to send a third message to the candidate SN indicating that the modification of the conditional PSCell addition or modification information requested by the first message is rejected if all of the one or more prepared PSCells requested or proposed to be added by the first message are rejected. 49. The RAN node according to any one of Supplementary Notes 45 to 48. (Appendix 50) the third message is an S-NODE MODIFICATION REFUSE message; RAN node as described in Supplementary Note 49. (Appendix 51) The conditional PSCell change is a conditional PSCell change initiated by the MN. 51. The RAN node according to any one of Supplementary Notes 45 to 50. (Appendix 52) 1. A method performed by a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), comprising: receiving a first message from a candidate SN for a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or conditional PSCell change; and determining whether to reject some or all of one or more prepared PSCells requested or proposed to be added in the first message; A method for providing the above. (Appendix 53) 1. A program for causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), the method comprising: The method comprises: receiving a first message from a candidate SN for a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition or conditional PSCell change; and determining whether to reject some or all of one or more prepared PSCells requested or proposed to be added in the first message; A program that includes: (Appendix 54) 1. 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: at least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: Receive a first message from a Master Node (MN) regarding a modification of a conditional Primary SCG Cell (PSCell) change initiated by the source SN that has already been prepared, wherein the first message indicates one or more prepared PSCells that are requested or proposed to be added by a candidate SN; Determine whether to reject some or all of one or more prepared PSCells requested or proposed for addition by the candidate SN; It is configured as follows: RAN node. (Appendix 55) the at least one processor is configured to send a second message to the MN indicating at least one PSCell that has been accepted or rejected among the one or more prepared PSCells. RAN node as described in Appendix 54. (Appendix 56) the first message indicates an updated full list of prepared PSCells prepared by the candidate SN, including the one or more prepared PSCells; The second message indicates a complete list of one or more accepted prepared PSCells. RAN node as described in Appendix 55. (Appendix 57) the first message is an S-NODE MODIFICATION REQUEST message; the second message is an S-NODE MODIFICATION REQUEST ACKNOWLEDGE message; 57. The RAN node of claim 55 or 56. (Appendix 58) the at least one processor is configured to, if rejecting all of the one or more prepared PSCells, send a third message to the MN indicating that the modification requested by the first message is rejected. 58. The RAN node according to any one of Supplementary Notes 54 to 57. (Appendix 59) the third message is an S-NODE MODIFICATION REQUEST REJECT message; RAN node as described in Supplementary Note 58. (Appendix 60) 1. 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: receiving a first message from a Master Node (MN) regarding a modification of a conditional Primary SCG Cell (PSCell) change initiated by the source SN that has already been prepared, wherein the first message indicates one or more prepared PSCells that are requested or proposed to be added by a candidate SN; determining whether to reject some or all of one or more prepared PSCells requested or proposed for addition by the candidate SN; A method for providing the above. (Appendix 61) 1. A program for 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: The method comprises: receiving a first message from a Master Node (MN) regarding a modification of a conditional Primary SCG Cell (PSCell) change initiated by the source SN that has already been prepared, wherein the first message indicates one or more prepared PSCells that are requested or proposed to be added by a candidate SN; determining whether to reject some or all of one or more prepared PSCells requested or proposed for addition by the candidate SN; A program that includes: (Appendix 62) 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: at least one memory; at least one processor coupled to the at least one memory; Equipped with The at least one processor: Storing execution condition information received from a source Secondary Node (SN) when a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by the source Secondary Node (SN) is prepared; receiving a first message from a candidate SN for the conditional PSCell change that has already been prepared; selecting one or more execution conditions for each of the one or more prepared PSCells requested or proposed to be added by the first message from the retained execution condition information; sending a Radio Resource Control (RRC) message to the UE, the RRC message including an SCG configuration for each of the one or more prepared PSCells provided by the candidate SN in the first message and including the selected one or more execution conditions for each of the one or more prepared PSCells; It is configured as follows: RAN node. (Appendix 63) 1. A method performed by a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), comprising: Maintaining execution condition information received from a source Secondary Node (SN) when a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by the source SN is prepared; receiving a first message from a candidate SN for the conditional PSCell change that has already been prepared; selecting from the retained execution condition information one or more execution conditions for each of the one or more prepared PSCells requested or proposed to be added by the first message; and sending a Radio Resource Control (RRC) message to the UE, the RRC message including an SCG configuration for each of the one or more prepared PSCells provided by the candidate SN in the first message and including the selected one or more execution conditions for each of the one or more prepared PSCells; A method for providing the above. (Appendix 64) 1. A program for causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a Master Node (MN) associated with a Master Cell Group (MCG) in dual connectivity for User Equipment (UE), the method comprising: The method comprises: Maintaining execution condition information received from a source Secondary Node (SN) when a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) change initiated by the source SN is prepared; receiving a first message from a candidate SN for the conditional PSCell change that has already been prepared; selecting from the retained execution condition information one or more execution conditions for each of the one or more prepared PSCells requested or proposed to be added by the first message; and sending a Radio Resource Control (RRC) message to the UE, the RRC message including an SCG configuration for each of the one or more prepared PSCells provided by the candidate SN in the first message and including the selected one or more execution conditions for each of the one or more prepared PSCells; A program that includes:

[0141] This application claims priority based on Japanese Patent Application No. 2022-112409, filed on July 13, 2022, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0142] 1 Master Node (MN) 2. Source Secondary Node (S-SN) 3. User Equipment (UE) 4. Target Secondary Node (T-SN) 2204 processor 2205 memory 2206 Modules 2303 Baseband Processor 2304 Application Processor 2306 memory 2307 Modules

Claims

1. A method for a candidate SN in a Secondary Node (SN)-initiated inter-SN Conditional Primary Secondary Cell Group (SCG) Cell (PSCell) Change (CPC), comprising: Send an S-Node Modification Required message to the Master Node (MN), The S-Node Modification Required message is sent to add or remove a prepared PSCell; The S-Node Modification Required message includes a list of PSCells newly prepared by the candidate SN for the SN-initiated inter-SN CPC; receiving an S-Node Modification Confirm message from the MN; method.

2. The list of PSCells is a list newly prepared by the candidate SN. The method of claim 1.

3. A method for a Master Node (MN) in a Secondary Node (SN)-initiated inter-SN Conditional Primary Secondary Cell Group (SCG) Cell (PSCell) Change (CPC), comprising: receiving an S-Node Modification Required message from the candidate SN; The S-Node Modification Required message is sent to add or remove a prepared PSCell; The S-Node Modification Required message includes a list of PSCells newly prepared by the candidate SN for the SN-initiated inter-SN CPC; sending an S-Node Modification Confirm message to the candidate SN; method.

4. The list of PSCells is a list newly prepared by the candidate SN. The method of claim 3.

5. Sending an RRC Reconfiguration message to a User Equipment (UE), the RRC Reconfiguration message including the list of PSCells; The method of claim 3.

6. A candidate SN in a Secondary Node (SN)-initiated inter-SN Conditional Primary Secondary Cell Group (SCG) Cell (PSCell) Change (CPC), a means for transmitting an S-Node Modification Required message to a Master Node (MN); The S-Node Modification Required message is sent to add or remove a prepared PSCell; The S-Node Modification Required message includes a list of PSCells newly prepared by the candidate SN for the SN-initiated inter-SN CPC; means for receiving an S-Node Modification Confirm message from the MN; A candidate SN comprising:

7. The list of PSCells is a list newly prepared by the candidate SN. The candidate SN according to claim 6.

8. A Master Node (MN) in a Secondary Node (SN)-initiated inter-SN Conditional Primary Secondary Cell Group (SCG) Cell (PSCell) Change (CPC), means for receiving an S-Node Modification Required message from a candidate SN; The S-Node Modification Required message is sent to add or remove a prepared PSCell; The S-Node Modification Required message includes a list of PSCells newly prepared by the candidate SN for the SN-initiated inter-SN CPC; means for sending an S-Node Modification Confirm message to the candidate SN; MN equipped with.

9. The list of PSCells is a list newly prepared by the candidate SN. The MN according to claim 8.

10. means for transmitting an RRC Reconfiguration message to a User Equipment (UE), the RRC Reconfiguration message including the list of PSCells; The MN according to claim 8.

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