Wireless access network node and method for same

Abstract

According to the present invention, a candidate target node of a conditional handover receives a first control message from a source node and sends a second control message to the source node in response to the first control message. The first control message includes an indication of a subsequent conditional handover. The second control message indicates at least one candidate target cell prepared by the candidate target node. In addition, the second control message includes information indicating execution conditions for the subsequent conditional handover from each of the at least one prepared candidate target cell to another cell. This may, for example, contribute to solving problems related to the realization of subsequent CHO.

Description

Radio access network node and method thereof

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

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

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

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

[0005] Patent Documents 1, 2, and 3 disclose various techniques related to selective activation of cell groups. Patent Document 1 discloses, for example, in paragraphs 0083 to 0085, 0125 to 0128, and Figures 5 and 16, that a source node or MN of conditional mobility (i.e., CHO, CPA, or CPC) includes an indication regarding selective cell activation in a conditional mobility request message. The indication regarding selective cell activation indicates to a candidate target node or SN of the conditional mobility that selective cell group (CG) / cell activation is requested or recommended for subsequent conditional mobility that may be performed after the initial conditional mobility.

[0006] For example, in paragraphs 0127 and 0134, Patent Document 1 discloses that a source node transmits a CHO request message to a candidate target node for CHO and subsequent CHO (selective cell activation). The CHO request message includes a list of one or more candidate target cells proposed by the source node.

[0007] For example, in paragraphs 0103 to 0105 and Figure 14, Patent Document 2 discloses an operation when a candidate target node or SN of conditional mobility (i.e., CHO, CPA, or CPC) does not support selective CG / cell activation. Specifically, the candidate target node or SN receives a request message for conditional mobility and selective CG / cell activation from the source node or MN. Then, if the candidate target node or SN does not support selective CG / cell activation, the candidate target node or SN replies to the source node or MN with a response message indicating rejection of the conditional mobility.

[0008] International Publication No. WO 2023 / 127271 International Publication No. WO 2023 / 127272 International Publication No. WO 2023 / 127273

[0009] MediaTek Inc., Apple, "Revised WID on Further NR mobility enhancements", RP-231475, 3GPP TSG RAN Meeting #100, Taipei, June 12-14, 2023MediaTek Inc., vivo, "38.300 running CR for introduction of NR further mobility enhancements", R2-2306957, 3GPP TSG-RAN WG2 Meeting #122, Incheon, Korea, May 22-26, 2023ZTE Corporation, Sanechips, "37.340 running CR for introduction of NR further mobility enhancements", R2-2306952, 3GPP TSG-RAN WG2 Meeting #122, Incheon, Korea, May 22-26, 2023Huawei, "(SCG Selective Activation BL CR to TS 38.423) Introduction of SCG Selective Activation", R3-232559, 3GPP TSG-RAN WG3 Meeting #120, Incheon, Korea, May 22-26, 2023ZTE, "(TP to TS 38.423): Support of SCG selective activation", R3-233524, Incheon, Korea, May 22-26, 2023

[0010] As mentioned above, 3GPP is working on standardizing subsequent CPAC (or SCG selective activation). However, at present, discussions on subsequent CHO or MCG selective activation have not progressed sufficiently. The details of the procedure for implementing subsequent CHO have not yet been fully clarified, and various issues remain. For example, the details of signaling between the source node and the candidate target node regarding the generation of execution conditions for subsequent CHO are not fully clear.

[0011] One of the objectives of the embodiments disclosed herein is to provide an apparatus, a method, and a program that contribute to solving at least one of the problems related to the realization of subsequent CHO, including the problems described above. It should be noted that this objective is only one of the objectives of the embodiments disclosed herein. Other objectives or objectives and novel features will become apparent from the description of this specification or the accompanying drawings.

[0012] A first aspect is directed to a Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover (CHO) of a UE. The RAN node is configured to receive a first control message from a source node and to transmit a second control message to the source node in response to the first control message. The first control message requests the candidate target node to prepare one or more candidate target cells for an initial CHO of the UE. Additionally, the first control message includes an indication of a subsequent conditional handover. Meanwhile, the second control message indicates at least one candidate target cell prepared by the candidate target node. Additionally, the second control message includes information indicating a condition for executing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell.

[0013] A second aspect is directed to a method performed by a RAN node configured to operate as a candidate target node for a CHO of a UE. The method includes receiving a first control message from a source node and transmitting a second control message to the source node in response to the first control message. The first control message requests the candidate target node to prepare one or more candidate target cells for an initial CHO of the UE. Additionally, the first control message includes an indication of a subsequent conditional handover. Meanwhile, the second control message indicates at least one candidate target cell prepared by the candidate target node. Additionally, the second control message includes information indicating a condition for executing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell.

[0014] A third aspect is directed to a RAN node configured to act as a source node for a CHO of a UE. The RAN node is configured to transmit a first control message to a candidate target node and to receive a second control message transmitted from the candidate target node in response to the first control message. The first control message requests the candidate target node to prepare one or more candidate target cells for an initial CHO of the UE. In addition, the first control message includes an indication of a subsequent conditional handover. Meanwhile, the second control message indicates at least one candidate target cell prepared by the candidate target node. In addition, the second control message includes information indicating a condition for executing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell.

[0015] A fourth aspect is directed to a method performed by a RAN node configured to act as a source node for a CHO of a UE. The method includes transmitting a first control message to a candidate target node and receiving a second control message transmitted from the candidate target node in response to the first control message. The first control message requests the candidate target node to prepare one or more candidate target cells for an initial CHO of the UE. Additionally, the first control message includes an indication of a subsequent conditional handover. Meanwhile, the second control message indicates at least one candidate target cell prepared by the candidate target node. Additionally, the second control message includes information indicating a condition for executing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell.

[0016] A fifth aspect is directed to a RAN node configured to act as a source node for a CHO of a UE, the RAN node being configured to send a first control message to a first candidate target node requesting the first candidate target node to prepare one or more candidate target cells for an initial conditional handover for the UE and for subsequent conditional handovers, the first control message including information indicating whether the first candidate target node is permitted or required to prepare cells other than the one or more candidate target cells as candidate target cells for the subsequent conditional handover.

[0017] A sixth aspect is directed to a method performed by a RAN node configured to act as a source node for a CHO of a UE, the method comprising: sending a first control message to a first candidate target node requesting the first candidate target node to prepare one or more candidate target cells for an initial conditional handover for the UE and for subsequent conditional handovers, the first control message including information indicating whether the first candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover.

[0018] A seventh aspect is directed to a RAN node configured to operate as a candidate target node for a CHO of a UE, the RAN node being configured to receive a first control message from a source node requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover and for subsequent conditional handovers for the UE, the first control message including information indicating whether the candidate target node is permitted or required to prepare cells other than the one or more candidate target cells as candidate target cells for the subsequent conditional handover.

[0019] An eighth aspect is directed to a method performed by a RAN node configured to operate as a candidate target node for a CHO of a UE, the method including receiving a first control message from a source node requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover and for subsequent conditional handovers for the UE, the first control message including information indicating whether the candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover.

[0020] A ninth aspect is directed to a RAN node configured to act as a source node for a CHO of a UE, the RAN node being configured to send first information to each of one or more candidate target nodes indicating whether one or more cells managed by the source node are candidate target cells for a subsequent conditional handover that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the one or more candidate target nodes.

[0021] A tenth aspect is directed to a method performed by a RAN node configured to act as a source node for a CHO of a UE, the method comprising sending first information to each of one or more candidate target nodes indicating whether one or more cells managed by the source node are candidate target cells for a subsequent conditional handover that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the one or more candidate target nodes.

[0022] An eleventh aspect is directed to a RAN node configured to operate as a candidate target node for a CHO of a UE, the RAN node being configured to receive, from the source node, first information indicating whether one or more cells managed by the source node are candidate target cells for subsequent conditional handovers that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the candidate target node.

[0023] A twelfth aspect is directed to a method performed by a RAN node configured to operate as a candidate target node for a CHO of a UE, the method comprising receiving first information from the source node indicating whether one or more cells managed by the source node are candidate target cells for subsequent conditional handovers that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the candidate target node.

[0024] A thirteenth aspect is directed to a program, which includes a group of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to any of the above aspects.

[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 the realization of subsequent CHO.

[0026] FIG. 1 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 2 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 3 illustrates an example format of a Handover Request message according to one or more embodiments. FIG. 4 illustrates a sequence diagram of example signaling for a subsequent CHO according to one or more embodiments. FIG. 5 illustrates a sequence diagram of example signaling for a subsequent CHO according to one or more embodiments. FIG. 6 illustrates an example format of a Handover Request Acknowledge message according to one or more embodiments. FIG. 7 illustrates a sequence diagram of example signaling for a subsequent CHO according to one or more embodiments. FIG. 8 illustrates a sequence diagram of example signaling for a subsequent CHO according to one or more embodiments. FIG. 9 illustrates a flowchart of example operation of a source node in a subsequent CHO according to one or more embodiments. FIG. 10 illustrates a sequence diagram of example signaling for a subsequent CHO according to one or more embodiments. FIG. 11 illustrates a flowchart of example operation of a source node in a subsequent CHO according to one or more embodiments. 1A and 1B are block diagrams illustrating example configurations of a RAN node and a UE, respectively, in accordance with one or more embodiments.

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

[0029] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0030] The following embodiments are described primarily for the 3GPP 5th generation mobile communication system (5G system), but may also be applied to other wireless communication systems that support techniques similar to 3GPP conditional mobility (e.g., CHO, CPA, or CPC).

[0031] As used herein, depending on the context, "if" may be interpreted to mean "when," "while," "at or around the time," "after," "upon," "in response to determining," "in accordance with a determination," or "in response to detecting." These expressions may be interpreted to have the same meaning, depending on the context.

[0032] First, the configurations and operations of several network elements common to several embodiments will be described. Figure 1 shows an example configuration of a wireless communication system related to several embodiments. In the example of Figure 1, the wireless communication system includes a RAN node 1, a RAN node 2, and a UE 3. Each element (network function) shown in Figure 1 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on the dedicated hardware, or as a virtualized function instantiated on an application platform.

[0033] The RAN node 1 may be a Central Unit (e.g., gNB-CU) in a cloud RAN (C-RAN) deployment, or may be a combination of a CU and one or more Distributed Units (e.g., gNB-DUs). C-RAN is also referred to as a CU / DU split. Furthermore, a CU may include a Control Plane (CP) Unit (e.g., gNB-CU-CP) and one or more User Plane (UP) Units (e.g., gNB-CU-UP). Thus, the RAN node 1 may be a CU-CP or a combination of a CU-CP and a CU-UP. Similarly, the RAN node 2 may be a CU or a combination of a CU and one or more DUs. The RAN node 2 may be a CU-CP or a combination of a CU-CP and a CU-UP.

[0034] Each of RAN nodes 1 and 2 may be an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN) node or a Next Generation Radio Access Network (NG-RAN) node. The EUTRAN node may be an eNB or an en-gNB. The NG-RAN node may be a gNB. The Radio Access Technology (RAT) of RAN node 1 may be different from that of RAN node 2. RAN node 1 and RAN node 2 communicate with each other via a node-to-node interface (e.g., X2 interface or Xn interface).

[0035] RAN node 1 provides at least one cell 11. RAN node 2 provides one or more cells (e.g., four cells 21-24). In the example of FIG. 1, cell 11 provided by RAN node 1 is the current serving cell of UE 3, and UE 3 is handed over from cell 11 to one of the cells provided by RAN node 2. Therefore, hereinafter, RAN node 1 may be referred to as a source node or source RAN node, and RAN node 2 may be referred to as a target node or target RAN node. Cell 11 is referred to as a source cell. In addition, source node 1, target node 2, and UE 3 support conditional handover (CHO). CHO is a handover procedure that is executed only when CHO execution conditions are met. Therefore, RAN node 2 may be referred to as a candidate target node or candidate target RAN node. Handover may be referred to as reconfiguration with sync (or reconfiguration with synchronization) from the perspective of Radio Resource Control (RRC) signaling (e.g., IE name, parameter name). Similarly, CHO may be called Conditional Reconfiguration with sync (or Conditional Reconfiguration with synchronization).

[0036] A handover or CHO from the source node 1 to the (candidate) target node 2 may be an inter-master node (inter-MN) handover or CHO of the MR-DC. An inter-MN CHO may be called a conditional Primary Cell (PCell) change. An inter-MN handover or CHO may or may not involve a secondary node change. In an inter-MN handover or CHO, the target MN (i.e., target node 2) can decide whether to keep, change, or release the SN. If the SN is released, this handover or CHO may be called a Master Node to eNB / gNB Change.

[0037] Although not shown in FIG. 1 , multiple candidate target cells provided by multiple candidate target nodes 2 may be prepared for CHO. In the CHO procedure, the source node 1 requests the candidate target node 2 to prepare one or more candidate targets. If the source node 1's request can be accepted, the candidate target node 2 (or a radio resource management entity of the candidate target node 2) allocates radio resources and transport network resources for each of the one or more candidate target cells. The candidate target node 2 provides the source node 1 with the configurations of the prepared candidate target cells. In other words, the preparation of one or more candidate target cells by the candidate target node 2 can be said to include the allocation of radio resources for each of the one or more candidate target cells and the allocation of transport network resources. Additionally or alternatively, the preparation of one or more candidate target cells by the candidate target node 2 can be said to include the creation of the configurations of one or more candidate target cells.

[0038] In the CHO procedure, the UE 3 receives a CHO configuration from the source node 1 via a Radio Resource Control (RRC) message, specifically an RRCReconfiguration message from the source node. The CHO configuration includes the configuration of one or more candidate target cells and associated CHO execution conditions. The configuration of each candidate target cell is generated by the candidate target node 2 and is included in an RRCReconfiguration* message generated by each candidate target node 2. Meanwhile, the CHO execution conditions are generated by the source node 1. The UE 3 applies the RRCReconfiguration message received from the source node 1, stores the CHO configuration, and responds to the source node 1 with an RRCReconfigurationComplete message. Then, in response to receiving the CHO configuration, the UE 3 starts evaluating the CHO execution conditions of one or more candidate target cells. If at least one candidate target cell satisfies the corresponding execution condition, the UE 3 detaches from the source node 1 and applies the stored configuration (i.e., the RRCReconfiguration* message generated by the candidate target node 2) corresponding to the selected (i.e., fulfilling the execution condition) candidate target cell. If the execution condition for more than one candidate target cell is fulfilled, the UE 3 may select one of the candidate target cells and perform the operations described above.

[0039] In the current 3GPP specification, up to two CHO execution conditions can be set for one candidate target cell. The conditions or criteria for triggering a CHO 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."

[0040] The condition or criterion that triggers a CHO event may be that for a measurement reporting event related to a Non-Terrestrial Network (NTN), such as CondEvent D1 or CondEvent T1. NTN is a technology in which a ground station (e.g., a base station) communicates with a UE via a satellite or an Unmanned Aircraft System (UNS). The UNS may be a High Altitude Platform Station (HAPS). CondEvent D1 is "The distance between the UE and a reference location, referenceLocation1, becomes larger than the configured threshold distanceThreshFromReference1, and the distance between the UE and a reference location, referenceLocation2, of the conditional reconfiguration candidate becomes shorter than the configured threshold distanceThreshFromReference2." CondEvent T1 is "The time measured at the UE becomes more than the configured threshold t1-Threshold but is less than t1-Threshold + duration."

[0041] One or both of the RAN nodes 1 and 2 may have the configuration shown in Figure 2. Each element (network function) shown in Figure 2 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 both of the RAN nodes 1 and 2 may include, but are not limited to, a CU 201 and one or more DUs 202 as shown in Figure 2. The CU 201 and each DU 202 are connected by an interface 221. A UE 3 is connected to at least one DU 202 via at least one air interface 222.

[0042] The CU201 may be a logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols (or the RRC and PDCP protocols) of the gNB. The DU202 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 CU201 is a gNB-CU and the DUs202 are gNB-DUs, the interface 221 may be an F1 interface. The CU201 may include a CU-CP and a CU-UP.

[0043] The embodiments described below provide an improvement to CHO. Specifically, the following embodiments provide an improvement to CHO to support subsequent CHO. Subsequent CHO may be called, for example, selective cell activation or selective cell group (CG) activation. Furthermore, when focusing on inter-MN handover and CHO of MR-DC, subsequent CHO may be called selective MCG activation, MCG selective activation, adaptive MCG switch, MCG adaptive switch, subsequent MCG selection, or MCG subsequent selection.

[0044] As defined herein, a subsequent CHO may be a conditional handover change procedure performed after an initial handover based on a pre-configured configuration of candidate target cells for the CHO without re-initiation of the CHO. A subsequent CHO may be a conditional handover change procedure performed after an initial handover based on a pre-configured configuration of candidate target cells for the CHO without re-configuration and restart of the CHO. In other words, as defined herein, a subsequent CHO may enable the UE 3 to reuse or maintain at least some (or all) of the configuration of candidate target cells received from the network for the initial CHO for the subsequent CHO. At least some of the execution conditions for the initial CHO may be re-configured, updated, or modified for the subsequent CHO. At least a portion of the information regarding security key configuration (e.g., sk-Counter, Next Hop (NH), NH Chaining Count (NCC)) for the initial CHO or the security key information (e.g., SN Security Key) may be reset, updated, or modified for a subsequent CHO.

[0045] In the case of a subsequent CHO, the CHO configuration included in the first RRCReconfiguration message sent from the source node 1 to the UE 3 (which may also be called the subsequent CHO configuration) may include the configuration of each of one or more candidate target cells, the CHO execution conditions associated with each candidate target cell for the first CHO, and the CHO execution conditions for subsequent CHOs from each candidate target cell.

[0046] In the case of a subsequent CHO, the source node 1 may generate the execution conditions for the first CPAC, and each candidate target node may generate the execution conditions for the subsequent CHO. Alternatively, the source node 1 may generate some or all of the execution conditions for the subsequent CHO in addition to generating the execution conditions for the first CPAC.

[0047] FIG. 3 shows an example of a format of a Handover Request message extended to support subsequent CHO. The Handover Request message is transmitted by the source node 1 to request the (candidate) target node 2 to prepare resources for the initial CHO and subsequent CHOs. The Handover Request message of FIG. 3 may include a Selective Activation Information Request information element (IE) 301. IE 301 may have other names. For example, the name of IE 301 may be "Subsequent CHO Information Request" or "Selective CHO Information Request." If the Handover Request message includes IE 301, the target node 2 may recognize that the handover request is for subsequent CHO. The format of the Handover Request message shown in FIG. 3 helps to clarify the signaling details related to the preparation of subsequent CHO.

[0048] FIG. 4 shows an example of signaling for a subsequent CHO. The source node 401 and the candidate target node 402 may be RAN node 1 and RAN node 2, respectively, shown in FIG. 1. In step 421, the source node 401 sends a first control message to the candidate target node 402. The first control message requests the candidate target node 402 to prepare multiple candidate target cells for the initial CHO and for subsequent CHOs. The first control message may include a list of multiple candidate target cells. The first control message may be a Handover Request message extended to request the preparation of multiple candidate target cells. Alternatively, the first control message may be a newly defined inter-RAN node message (e.g., an Xn message) to enable the request for the preparation of multiple candidate target cells.

[0049] The first control message may include an indication of CHO, an indication of subsequent CHO, and a list of multiple candidate target cells. The indication of CHO may be an information element regarding CHO. The indication of CHO (or the information element regarding CHO) may indicate to the candidate target node 402 that CHO is required. The indication of CHO may be a Conditional Handover Information Request IE included in the Handover Request message.

[0050] The indication of subsequent CHO may be an information element regarding subsequent CHO. The indication of subsequent CHO (or the information element regarding subsequent CHO) may indicate to the candidate target node 402 that a subsequent CHO is required. The indication of subsequent CHO may be a Selective Activation Information Request IE, a Subsequent CHO Information Request IE, or a Selective CHO Information Request IE included in the Handover Request message.

[0051] The list of candidate target cells may be a newly defined IE that can be included in the Handover Request message, for example, the Target Cell Global ID IE may be extended to indicate a list of cell identities (i.e., Cell Global Identities (CGIs)) of candidate target cells.

[0052] Alternatively, the list of multiple candidate target cells may be a sub-IE included in the Conditional Handover Information Request IE, or may be a sub-IE included in the Selective Activation Information Request IE, the Subsequent CHO Information Request IE, or the Selective CHO Information Request IE.

[0053] Alternatively, the list of multiple candidate target cells may be included in a HandoverPreparationInformation message carried in an RRC Context IE in a UE Context Information IE in the Handover Request message. The HandoverPreparationInformation message is an inter-node RRC message. Typically, an inter-node RRC message is an RRC message transmitted between RAN nodes over an inter-node interface such as an Xn interface or an X2 interface. The HandoverPreparationInformation message is used to transfer RRC information used by the target node 402 during handover preparation.

[0054] In step 422, the target node 402 sends a second control message to the source node 401 in response to the first control message. The second control message indicates that one or more of the multiple candidate target cells proposed by the source node 401 have been prepared. In other words, the second control message includes the configuration of one or more candidate target cells prepared for the initial CHO and the subsequent CHO. The second control message may be a Handover Request Acknowledge message extended to include the configuration of multiple candidate target cells for the initial CHO and the subsequent CHO. Alternatively, the second control message may be a newly defined inter-RAN node message (e.g., an Xn message) to include the configuration of multiple candidate target cells for the initial CHO and the subsequent CHO.

[0055] According to the operation shown in Fig. 4, the source node 401 can request the candidate target node 402 to prepare multiple candidate target cells for the initial CHO and subsequent CHO via a single control message (e.g., an extended Handover Request message). This can reduce signaling overhead compared to a procedure in which a Handover Request message is transmitted multiple times for each candidate target cell. Furthermore, the candidate target node 402 can provide the source node 401 with the configuration of multiple candidate target cells prepared for the initial CHO and subsequent CHO via a single control message (e.g., an extended Handover Request Acknowledge message). This can reduce signaling overhead compared to a procedure in which a Handover Request Acknowledge message is transmitted multiple times for each candidate target cell.

[0056] First Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1. This embodiment relates to subsequent CHO.

[0057] 5 shows an example of signaling for a subsequent CHO. The source node 501 and the candidate target node 502 may be the RAN node 1 and the RAN node 2 shown in FIG. 1, respectively. In step 521, the source node 501 sends a first control message to the candidate target node 502. The first control message requests the candidate target node 502 to prepare one or more candidate target cells for the initial CHO of the UE 3. In addition, the first control message includes an indication of the subsequent CHO. In other words, the first control message requests the candidate target node 502 to prepare one or more candidate target cells for both the initial CHO and the subsequent CHO.

[0058] The first control message may be a Handover Request message, or may be a newly defined inter-RAN node message (e.g., Xn message) to enable requesting the preparation of multiple candidate target cells.

[0059] The first control message may include an indication of CHO, an indication of subsequent CHO, and a list of one or more candidate target cells. The indication of CHO may be an information element about CHO. The indication of CHO (or the information element about CHO) may indicate to the candidate target node 502 that a CHO is required. The indication of CHO may be a Conditional Handover Information Request IE included in the Handover Request message.

[0060] The indication of subsequent CHO may be an information element regarding subsequent CHO. The indication of subsequent CHO (or the information element regarding subsequent CHO) may indicate to the candidate target node 402 that a subsequent CHO is required. The indication of subsequent CHO may be a Selective Activation Information Request IE, a Subsequent CHO Information Request IE, or a Selective CHO Information Request IE included in the Handover Request message.

[0061] If preparation of only one candidate target cell is requested, the one candidate target cell may be indicated by the Target Cell Global ID IE included in the Handover Request message. If preparation of multiple candidate target cells is requested, the messages and information elements described above with reference to FIG. 4 may be used. That is, the list of multiple candidate target cells may be a newly defined IE that may be included in the Handover Request message. For example, the Target Cell Global ID IE may be extended to indicate a list of cell identifiers (i.e., CGIs) of multiple candidate target cells.

[0062] The list of multiple candidate target cells may be a sub-IE included in the Conditional Handover Information Request IE, or may be a sub-IE included in the Selective Activation Information Request IE, the Subsequent CHO Information Request IE, or the Selective CHO Information Request IE.

[0063] Alternatively, the list of multiple candidate target cells may be included in a Handover Preparation Information message carried in an RRC Context IE within a UE Context Information IE in a Handover Request message.

[0064] In step 522, the candidate target node 502 sends a second control message to the source node 501 in response to the first control message. The second control message indicates at least one candidate target cell prepared by the candidate target node. In addition, the second control message includes information indicating the execution conditions for subsequent CHO from each of the at least one prepared candidate target cell to another cell.

[0065] The second control message may be a Handover Request Acknowledge message, or may be a Handover Request Acknowledge message extended to include configuration of multiple candidate target cells for the initial CHO and the subsequent CHO, or may be a newly defined inter-RAN node message (e.g., Xn message) to include configuration of multiple candidate target cells for the initial CHO and the subsequent CHO.

[0066] The information indicating the execution condition may be included in a HandoverCommand message carried in a Target NG-RAN node To Source NG-RAN node Transparent Container IE in the Handover Request Acknowledge message. The HandoverCommand message is one of inter-node RRC messages. The HandoverCommand message includes an RRCReconfiguration message generated by the candidate target node 502. In this case, the name of the IE indicating the execution condition that can be included in the HandoverCommand message may be, for example, "condExecutionCondSubsequentCHO", "executionCondSubsequentCHO", or "condSubsequentCHO".

[0067] As described above, an extended Handover Request Acknowledge message may be used so that it can include the configuration of multiple candidate target cells. In this case, the Target NG-RAN node To Source NG-RAN node Transparent Container IE in the extended Handover Request Acknowledge message may carry multiple HandoverCommand messages, each corresponding to a respective candidate target cell. Alternatively, the Target NG-RAN node To Source NG-RAN node Transparent Container IE may include a new inter-node RRC message (e.g., a HandoverCommandList message) that includes a list of HandoverCommand messages.

[0068] Alternatively, the information indicating the execution condition may be a sub-IE 601 included in the Conditional Handover Information Acknowledge IE in the Handover Request Acknowledge message, as shown in Fig. 6. The name of the sub-IE 601 may be, for example, Execution Condition IE. Alternatively, the information indicating the execution condition may be a sub-IE of an IE newly defined in the Handover Request Acknowledge message. The newly defined IE may be a Selective Activation Information Acknowledge IE, a Subsequent CHO Information Acknowledge IE, or a Selective CHO Information Acknowledge IE.

[0069] The Conditional Handover Information Acknowledge IE includes, apart from the sub-IE 601, a Requested Target Cell ID IE. The Requested Target Cell ID IE indicates the candidate target cell indicated in the corresponding Handover Request message. Furthermore, the Conditional Handover Information Acknowledge IE may include a Maximum Number of CHO Preparations IE. The Maximum Number of CHO Preparations IE indicates the maximum number of CHO candidate cells that are prepared in parallel for the UE 3 at the candidate target node 502. If the Conditional Handover Information Acknowledge IE included in the Handover Request Acknowledge message includes the Maximum Number of CHO Preparations IE, the source node 501 will not request the target node 502 to prepare more candidate target cells for CHO of the same UE than the number indicated in the IE.

[0070] According to the operation shown in Fig. 5, the candidate target node 502 can send execution conditions for subsequent CHOs from each of the at least one prepared candidate target cell to other cells to the source node 501 in response to a request for preparation of the initial CHO and subsequent CHOs from the source node 501. This contributes to clarifying the signaling details regarding the generation of the execution conditions for the subsequent CHO. The candidate target node 502 may generate the execution conditions for the subsequent CHO in response to receiving the request for preparation of the subsequent CHO.

[0071] 7 shows an example of signaling for a subsequent CHO. A source node 701 and a candidate target node 702 may be RAN node 1 and RAN node 2 shown in FIG. 1, respectively.

[0072] Step 721 is similar to step 521 of Figure 5. Specifically, in step 721, source node 701 sends a first control message to candidate target node 702. The first control message requests candidate target node 702 to prepare one or more candidate target cells for the initial CHO of UE3. In addition, the first control message includes an indication of a subsequent CHO. In other words, the first control message requests candidate target node 702 to prepare one or more candidate target cells for both the initial CHO and the subsequent CHO. Specific examples of the first control message of step 721 and the information elements included therein are similar to those described with respect to the first control message of step 521.

[0073] Furthermore, in step 721, the first control message includes information indicating whether the candidate target node 702 is permitted or requested to generate an execution condition for a subsequent CHO. This information may be a sub-IE included in the Conditional Handover Information Request IE in the Handover Request message. In this case, the name of the IE (or sub-IE) corresponding to this information may be, for example, "Condition (generation) request" or "Requested condition (generation)".

[0074] Alternatively, the information indicating permission, request, or instruction for generation of an execution condition may be included in a HandoverPreparationInformation message carried in an RRC Context IE in a UE Context Information IE in a Handover Request message. As already described, the HandoverPreparationInformation message is one of the inter-node RRC messages. The HandoverPreparationInformation message is used to transfer RRC information used by the target node 402 during handover preparation. In this case, the IE corresponding to the information indicating permission, request, or instruction for generation of an execution condition may be, for example, an allowExecutionConditionGeneration IE, which may be of enumerated type and indicate "true". Alternatively, the IE corresponding to the information may be, for example, an executionConditionGeneration IE, which may be of enumerated type and indicate "source" or "candidate".

[0075] In step 722, the candidate target node 702 sends a second control message to the source node 701 in response to the first control message. In other words, the source node 701 receives the second control message sent from the candidate target node 702 in response to the first control message. The second control message includes configuration for at least one candidate target cell prepared by the candidate target node 702. In addition, if the first control message of step 721 indicates that the candidate target node 702 is permitted or requested to generate execution conditions for a subsequent CHO, the second control message includes information indicating whether these execution conditions have been generated. If the candidate target node 702 has generated execution conditions for a subsequent CHO, the second control message may include information indicating the generated execution conditions for the subsequent CHO.

[0076] The second control message of step 722 may be a Handover Request Acknowledge message. The information indicating whether the execution condition has been generated may be a sub-IE included in a Conditional Handover Information Acknowledge IE in the Handover Request Acknowledge message. In this case, the sub-IE may be, for example, a Condition prepared IE, which is an enumerated type and may indicate "true."

[0077] Alternatively, the information indicating whether the execution condition has been generated may be included in a HandoverCommand message carried in a Target NG-RAN node To Source NG-RAN node Transparent Container IE in a Handover Request Acknowledge message. In this case, the IE corresponding to the information indicating whether the execution condition has been generated may be, for example, a condExecutionCond IE, which may be an enumeration type and indicate "true".

[0078] As described above, an extended Handover Request Acknowledge message may be used so that it can include the configuration of multiple candidate target cells. In this case, the Target NG-RAN node To Source NG-RAN node Transparent Container IE in the extended Handover Request Acknowledge message may carry multiple HandoverCommand messages, each corresponding to a respective candidate target cell. Alternatively, the Target NG-RAN node To Source NG-RAN node Transparent Container IE may include a new inter-node RRC message (e.g., a HandoverCommandList message) that includes a list of HandoverCommand messages.

[0079] In one example, the first control message of step 721 may indicate to the candidate target node 702 permission to generate an execution condition for the subsequent CHO. In this case, the candidate target node 702 may either generate or not generate an execution condition for the subsequent CHO. If the candidate target node 702 generates an execution condition for the subsequent CHO, the second control message may include information indicating the generated execution condition for the subsequent CHO and may also include information explicitly or implicitly indicating to the source node 701 that an execution condition for the subsequent CHO has been generated (or included). On the other hand, if the candidate target node 702 did not generate an execution condition for the subsequent CHO, the second control message may include information explicitly or implicitly indicating to the source node 701 that an execution condition for the subsequent CHO has not been generated (or included). Alternatively, the second control message may not include any explicit information, thereby indicating to the source node 701 that an execution condition for the subsequent CHO has not been generated.

[0080] In another example, the first control message of step 721 may indicate to the candidate target node 702 an instruction or request to generate execution conditions for the subsequent CHO. In this case, the candidate target node 702 is essentially required to generate the execution conditions for the subsequent CHO. If the candidate target node 702 has generated execution conditions for the subsequent CHO, the second control message may include information indicating the generated execution conditions for the subsequent CHO and information indicating, explicitly or implicitly, to the source node 701 that the execution conditions for the subsequent CHO have been generated (or included). Alternatively, the second control message may include information indicating the generated execution conditions for the subsequent CPC but not include any explicit information, thereby indicating to the source node 701 that the execution conditions for the subsequent CHO have been generated. On the other hand, if the candidate target node 702 has not generated execution conditions for the subsequent CHO, the second control message may include information indicating, explicitly or implicitly, to the source node 701 that the execution conditions for the subsequent CHO have not been generated (or are not included).

[0081] According to the operation shown in Fig. 7, when requesting the candidate target node 702 to prepare the first CHO, the source node 701 can explicitly inform the candidate target node 702 of permission, instruction, or request to generate execution conditions for the subsequent CHO. In addition, if the source node 701 has permitted or requested generation of execution conditions for the subsequent CHO, the candidate target node 702 can inform the source node 701 whether execution conditions for the subsequent CHO have been generated. This contributes to clarifying the signaling details regarding generation of execution conditions for the subsequent CHO.

[0082] The candidate target node 702 may operate not to generate an execution condition for the subsequent CHO if the generation of the execution condition for the subsequent CHO is not permitted or required by the source node 701. Alternatively, the candidate target node 702 may operate not to include the execution condition for the subsequent CHO in a response message (e.g., Handover Request Acknowledge message) to the first control message (e.g., Handover Request message).

[0083] If the source node 701 neither allows nor requests the candidate target node 702 to generate execution conditions for the subsequent CHO, the source node 701 may generate execution conditions for the subsequent CPC in addition to the execution conditions for the initial CHO. The source node 701 may transmit to the UE 3 a subsequent CHO configuration including the configuration for at least one candidate target cell received from the candidate target node 702, the execution conditions for the initial CHO generated by the source node 701, and the execution conditions for the subsequent CHO generated by the source node 701. The source node 702 may transmit to the UE 3 an RRCReconfiguration message including the subsequent CHO configuration.

[0084] 8 shows an example of signaling for subsequent CHO. A source node 801 and a candidate target node 802 may be RAN node 1 and RAN node 2 shown in FIG. 1, respectively.

[0085] Step 821 is similar to step 721 in Figure 7. Specifically, the source node 801 sends a first control message to the candidate target node 802. The first control message in step 821 requests the candidate target node 802 to prepare one or more candidate target cells for the initial CHO for UE3. In addition, the first control message includes information indicating whether the candidate target node 802 is permitted or required to generate execution conditions for subsequent CHOs that may be performed after the initial CHO. In the example of Figure 8, the information indicates that the candidate target node 802 is required to generate execution conditions for the subsequent CHOs. In other words, the information instructs the candidate target node 802 to generate execution conditions for the subsequent CHOs.

[0086] If the first control message of step 821 indicates or requests the generation of execution conditions for the subsequent CHO but the candidate target node 802 does not or cannot generate the execution conditions, the candidate target node 802 responds to the source node 801 with a rejection message in step 822. The rejection message of step 822 indicates that preparation for all of the one or more candidate target cells proposed in the first control message of step 821 has been rejected or failed. The rejection message may be a Handover Request Reject message. The rejection message may indicate that the rejection is due to the fact that the execution conditions for the subsequent CHO are not or cannot be generated.

[0087] 8, when requesting the candidate target node 802 to prepare for the first CHO, the source node 801 can explicitly inform the candidate target node 802 of an instruction or request to generate execution conditions for the subsequent CHO. In addition, if the candidate target node 802 does not or cannot generate the execution conditions for the subsequent CHO, the candidate target node 802 rejects the preparation for all of the one or more proposed candidate target cells. This contributes to clarifying the signaling details regarding the generation of execution conditions for the subsequent CHO.

[0088] Second Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1. This embodiment relates to subsequent CHO.

[0089] 9 shows an example of signaling for a subsequent CHO. A source node 901 and a candidate target node 902 may be RAN node 1 and RAN node 2 shown in FIG. 1, respectively.

[0090] In step 921, the source node 901 sends a first control message to the candidate target node 902. The first control message requests the candidate target node 902 to prepare one or more candidate target cells for the initial CHO and for any subsequent CHOs for the UE 3. In addition, the first control message includes information indicating whether the candidate target node 902 is permitted or required to prepare a cell other than these proposed one or more candidate target cells as a candidate target cell for the subsequent CHO.

[0091] The first control message may be a Handover Request message. The first control message may include an indication of CHO, an indication of subsequent CHO, and the above-mentioned information. The indication of CHO may be an information element regarding CHO. The indication of CHO (or the information element regarding CHO) may indicate a list of one or more candidate target nodes proposed by the source node 901. The indication of CHO may be a Conditional Handover Information Request IE in the Handover Request message. The indication of subsequent CHO may be an information element regarding subsequent CHO. The indication of subsequent CHO (or the information element regarding subsequent CHO) may indicate to the candidate target node 902 that a subsequent CHO is requested. The indication of subsequent CHO may be a Selective Activation Information Request IE, a Subsequent CHO Information Request IE, or a Selective CHO Information Request IE included in the Handover Request message.

[0092] In one example, the above information, i.e., information indicating whether a cell other than the proposed candidate target cell(s) may be prepared for the subsequent CHO, may be a sub-IE included in the Conditional Handover Information Request IE in the Handover Request message. Alternatively, the information may be a sub-IE included in the Selective Activation Information Request IE, Subsequent CHO Information Request IE, or Selective CHO Information Request IE in the Handover Request message.

[0093] In another example, information indicating whether a cell other than the proposed candidate target cell(s) may be prepared for the subsequent CHO may be included in a HandoverPreparationInformation message carried in an RRC Context IE within a UE Context Information IE in a Handover Request message. In this case, the IE corresponding to the information may be, for example, an allowCellSelection IE, which may be an enumeration type and indicate "true". Alternatively, the IE corresponding to the information may be, for example, a cellSelection IE, which may be an enumeration type and indicate "suggestedCell (or requestedCell, listedCell)" or "anyCell".

[0094] According to the operation shown in FIG. 9 , the source node 901 can indicate to the candidate target node 902 whether or not it may prepare a cell other than the proposed candidate target cell(s) for the subsequent CHO. This contributes to clarifying the signaling details regarding the preparation of a candidate target cell for the subsequent HO. In the CHO, the candidate target node decides whether or not to prepare the candidate target cell proposed by the source node. However, it may be preferable to be able to prepare another cell managed by the candidate target node for the subsequent CHO. In such a case, the source node 901 may allow the candidate target node 902 to prepare a cell other than the proposed candidate target cell(s) for the subsequent CHO. For example, the candidate target node 902 may prepare a cell for the subsequent CHO that is adjacent to one of the candidate target cells proposed by the source node 901 but is not included in the list of candidate target cells proposed by the source node 901.

[0095] Figure 10 shows an example of the operation of a source node (e.g., source node 1 in Figure 1) for a subsequent CHO. In step 1001, the source node transmits a first control message to a first candidate target node. The first control message requests the preparation of one or more candidate target cells for the initial CHO and for the subsequent CHO. In addition, the first control message indicates permission, request, or instruction to the first candidate target node to prepare cells other than these proposed candidate target cells for the subsequent CHO. The first control message may be a Handover Request message.

[0096] In step 1002, the source node receives a second control message transmitted from the first candidate target node in response to the first control message. The second control message may be a Handover Request Acknowledge message.

[0097] In step 1003, if a first cell that is not included in the one or more candidate target cells indicated in the first control message is prepared by the first candidate target node for the subsequent CHO, the source node indicates the first cell to the second candidate target node for the initial CHO via a third control message. The third control message may be a Handover Request message. This notification may be performed using a Conditional Handover Information Request IE in the Handover Request message. Alternatively, this notification may be performed using a newly defined IE in the Handover Request message, such as a Conditional Handover Information Update IE or a Subsequent CHO Information Update IE.

[0098] According to the operation shown in Figure 10, the source node informs the second candidate target node of one or more candidate target cells additionally prepared by the first candidate target node. This enables the second candidate target node to update the execution conditions for the subsequent CHO. Specifically, the second candidate target node can generate execution conditions for the subsequent CHO from the candidate target cell prepared by the second candidate target node to each of the one or more candidate target cells additionally prepared by the first candidate target node.

[0099] 11 shows an example of signaling for a subsequent CHO. In step 1121, the source node 1101 requests a first candidate target node 1102A to prepare for the subsequent CHO. The source node 1101 provides the first candidate target node 1102A with a list of one or more candidate target cells proposed by the source node 1101. The first candidate target node 1102A prepares a first cell for the subsequent CHO that is different from the candidate target cell(s) proposed by the source node 1101.

[0100] In step 1122, the source node 1101 informs the second candidate target node 1102B of the first cell prepared by the first candidate target node 1102A. This notification may be done using a Handover Request message.

[0101] In step 1123, the source node 1101 receives a response message transmitted from the second candidate target node 1102B, which may be a Handover Request Acknowledge message, containing information indicating the conditions for executing a subsequent CHO from each of one or more candidate target cells prepared by the second candidate target node 1102B to the first cell prepared by the first candidate target node 1102A.

[0102] The procedure shown in Figure 11 allows the second candidate target node 1102B to update the execution conditions for the subsequent CHO. Specifically, the second candidate target node 1102B can add the execution conditions for the subsequent CHO to the first cell that has been additionally prepared by the first candidate target node 1102A.

[0103] Third Embodiment A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1. This embodiment relates to subsequent CHO.

[0104] 12 shows an example of the operation of a source node (e.g., source node 1 in FIG. 1) for a subsequent CHO. In step 1201, the source node acts as a source node for an initial CHO. The initial CHO is a CHO from a source cell managed by the source node to any one or more candidate target cells managed by one or more candidate target nodes. In step 1202, the source node sends information to each of the one or more candidate target nodes indicating whether one or more cells managed by the source node will be candidate target cells for a subsequent CHO that may occur after the initial CHO.

[0105] The information in step 1202 may indicate or be a list of one or more cells managed by the source node and designated as candidate target cells for the subsequent CHO. The one or more cells managed by the source node and designated as candidate target cells for the subsequent CHO may include the source cell of the initial CHO. Additionally or alternatively, these cells may include cells other than the source cell.

[0106] The source node sends the information of step 1202 to each candidate target node via a first control message, which requests each candidate target node to prepare one or more candidate target cells managed by each candidate target node for the initial CHO and for subsequent CHOs. The first control message may be a Handover Request message.

[0107] The information in step 1202 may be a Selective Activation Information Request IE, a Subsequent CHO Information Request IE, or a sub-IE included in the Selective CHO Information Request IE in the Handover Request message. Alternatively, the information in step 1202 may be included in a Handover Preparation Information message carried by an RRC Context IE in a UE Context Information IE in the Handover Request message. In this case, the IE corresponding to the information may be, for example, a pCellAsCandidate (or sourceCellAsCandidate) IE, which may be an enumeration type and indicate "true". Alternatively, the IE corresponding to the information may be, for example, a sourcePCell (or sourceCells) IE, which may be an enumeration type and indicate "release" or "store".

[0108] After step 1202, the source node may operate as follows: The source node receives a second control message transmitted from each candidate target node in response to the first control message. The second control message indicates at least one candidate target cell prepared by each candidate target node. In addition, the second control message includes information indicating the execution conditions for a conditional handover from each candidate target cell prepared by each candidate target node to each of the one or more cells managed by the source node (i.e., cells indicated by the source node to be candidate target cells for the subsequent CHO). The second control message may be a Handover Request Acknowledge message.

[0109] According to the operation described with reference to Figure 12, the source node can inform the candidate target node whether one or more cells managed by the source node are candidate target cells for the subsequent CHO, which contributes to clarifying the signaling details regarding the determination of candidate target cells for the subsequent CHO.

[0110] <Fourth embodiment> A configuration example of a wireless communication system according to this embodiment is the same as the configuration example described with reference to Fig. 1. This embodiment relates to subsequent CHO.

[0111] 3GPP Release 18 will specify CHO with candidate SCG(s). CHO with candidate SCG(s) is also referred to as CHO in NR-NR Dual Connectivity (NR-DC) or CHO with NR-DC. CHO with candidate SCG(s) is defined as a PCell change accompanied by a PSCell addition / change, which is performed by the UE when the execution conditions for both the PCell and associated PSCell are met. When the UE receives a CHO configuration accompanied by candidate SCG(s) configuration, it begins evaluating both the execution conditions for the candidate PCell(s) and the execution conditions for the candidate PSCell(s). The UE stops evaluating the execution conditions when a PCell change is triggered. The UE does not perform CHO with candidate SCG(s) until the execution conditions for both the PCell and associated PSCell are met.

[0112] The source node 1 and the candidate target node 2 support subsequent CHOs performed after the initial CHO with candidate SCG(s). The source node 1 and the candidate target node 2 also support subsequent CHOs with candidate SCG(s) performed after the initial CHO. In this case, the candidate target node 2 can be called a candidate (target) MN. The candidate MN 2 may determine in advance whether to keep NR-DC (or configure NR-DC) when performing subsequent CHOs, when preparing the configuration of the initial CHO and subsequent CHOs. In other words, the candidate MN 2 may determine in advance whether the subsequent CHO is a "CHO ​​with candidate SCG(s)" when preparing the configuration of the initial CHO and subsequent CHOs. Based on this determination, the candidate MN 2 may include configuration information required for the configuration of the subsequent CHO. If the subsequent CHO is a "CHO ​​with candidate SCG(s)," the candidate MN 2 may perform the procedure for (preparing for) the configuration of NR-DC with the candidate SN of the subsequent CHO with candidate SCG(s). This procedure may be performed in preparation of the first CHO and subsequent CHOs.

[0113] Next, exemplary configurations of RAN nodes and UEs related to the above-described embodiments will be described below. FIG. 13 is a block diagram illustrating an exemplary configuration of a RAN node 1 according to the above-described embodiments. The configurations of other RAN nodes 2, 401, and 402 may be similar to the configuration illustrated in FIG. 13. Referring to FIG. 13, the RAN node 1 includes a Radio Frequency (RF) transceiver 1301, a network interface 1303, a processor 1304, and a memory 1305. The RF transceiver 1301 performs analog RF signal processing for communication with UEs, including UE 3. The RF transceiver 1301 may include multiple transceivers. The RF transceiver 1301 is coupled to an antenna array 1302 and a processor 1304. The RF transceiver 1301 receives modulation symbol data from the processor 1304, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1302. The RF transceiver 1301 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1302 and supplies the baseband receive signal to the processor 1304. The RF transceiver 1301 may include an analog beamformer circuit for beamforming. The analog beamformer circuit may include, for example, multiple phase shifters and multiple power amplifiers.

[0114] The network interface 1303 is used to communicate with network nodes (e.g., RAN nodes 2 and control and forwarding nodes of the core network), and may include, for example, a network interface card (NIC) conforming to the IEEE 802.3 series.

[0115] The processor 1304 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. The processor 1304 may include multiple processors. For example, the processor 1304 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.

[0116] For example, digital baseband signal processing by the processor 1304 may include signal processing for the Service Data Adaptation Protocol (SDAP) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, Medium Access Control (MAC) layer, and Physical (PHY) layer. Also, control plane processing by the processor 1304 may include processing of Non-Access Stratum (NAS) messages, RRC messages, MAC Control Elements (CEs), and Downlink Control Information (DCI).

[0117] The processor 1304 may include a digital beamformer module for beamforming, which may include a Multiple Input Multiple Output (MIMO) encoder and precoder.

[0118] The memory 1305 is configured by a combination of volatile memory and non-volatile memory. The volatile memory is, for example, Static Random Access Memory (SRAM), Dynamic RAM (DRAM), or a combination thereof. The non-volatile memory is, for example, Mask Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. The memory 1305 may include storage located remotely from the processor 1304. In this case, the processor 1304 may access the memory 1305 via the network interface 1303 or an I / O interface (not shown).

[0119] The memory 1305 may store one or more software modules (computer programs) 1306 including instructions and data for performing the processes of the RAN node 1 described in the above embodiments. In some implementations, the processor 1304 may be configured to read and execute the software modules 1306 from the memory 1305 to perform the processes of the RAN node 1 described in the above embodiments.

[0120] Note that if the RAN node 1 is a CU (e.g., eNB-CU or gNB-CU) or a CU-CP, the RAN node 1 may not include the RF transceiver 1301 (and the antenna array 1302).

[0121] FIG. 14 is a block diagram showing an example configuration of a UE 3. A radio frequency (RF) transceiver 1401 performs analog RF signal processing for communication with a RAN node. The RF transceiver 1401 may include multiple transceivers. The analog RF signal processing performed by the RF transceiver 1401 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1401 is coupled to an antenna array 1402 and a baseband processor 1403. The RF transceiver 1401 receives modulation symbol data (or orthogonal frequency-division multiplexing (OFDM) symbol data) from the baseband processor 1403, generates a transmit RF signal, and provides the transmit RF signal to the antenna array 1402. The RF transceiver 1401 also generates a baseband receive signal based on the receive RF signal received by the antenna array 1402 and provides the baseband receive signal to the baseband processor 1403. The RF transceiver 1401 may include an analog beamformer circuit for beamforming. The analog beamformer circuitry includes, for example, multiple phase shifters and multiple power amplifiers.

[0122] The baseband processor 1403 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communications. Digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) transmission format (transmission frame) generation / decomposition, (d) transmission path coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using Inverse Fast Fourier Transform (IFFT). Meanwhile, control plane processing includes communication management for Layer 1 (e.g., transmit power control), Layer 2 (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and Layer 3 (e.g., signaling related to attachment, mobility, and call management).

[0123] For example, the digital baseband signal processing by the baseband processor 1403 may include signal processing of the SDAP layer, PDCP layer, RLC layer, MAC layer, and PHY layer. Also, the control plane processing by the baseband processor 1403 may include processing of the Non-Access Stratum (NAS) protocol, the RRC protocol, MAC CEs, and DCIs.

[0124] The baseband processor 1403 may perform MIMO encoding and precoding for beamforming.

[0125] The baseband processor 1403 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 1404, which will be described later.

[0126] The application processor 1404 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1404 may include multiple processors (multiple processor cores). The application processor 1404 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 1406 or a memory not shown, thereby realizing various functions of the UE 3.

[0127] In some implementations, the baseband processor 1403 and the application processor 1404 may be integrated on a single chip, as shown by the dashed line (1405) in Figure 14. In other words, the baseband processor 1403 and the application processor 1404 may be implemented as a single System on Chip (SoC) device 1405. An SoC device may also be called a system Large Scale Integration (LSI) or chipset.

[0128] The memory 1406 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1406 may include multiple physically independent memory devices. The volatile memory is, for example, SRAM, DRAM, or a combination thereof. The nonvolatile memory is, for example, MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1406 may include an external memory device accessible from the baseband processor 1403, the application processor 1404, and the SoC 1405. The memory 1406 may also include an internal memory device integrated within the baseband processor 1403, the application processor 1404, or the SoC 1405. Furthermore, the memory 1406 may include memory within a Universal Integrated Circuit Card (UICC).

[0129] The memory 1406 may store one or more software modules (computer programs) 1407 including instructions and data for performing the processing by the UE 3 described in the above-described embodiments. In some implementations, the baseband processor 1403 or the application processor 1404 may be configured to read and execute the software modules 1407 from the memory 1406, thereby performing the processing by the UE 3 described in the above-described embodiments using the drawings.

[0130] In addition, the control plane processing and operations performed by UE3 described in the above embodiment can be realized by elements other than the RF transceiver 1401 and the antenna array 1402, i.e., at least one of the baseband processor 1403 and the application processor 1404, and the memory 1406 storing the software module 1407.

[0131] As described with reference to Figures 13 and 14, each of the processors included in the RAN node and the UE according to the above-described embodiments may execute one or more programs including instructions for causing a computer to perform the algorithms described with reference to the drawings. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0132] 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.

[0133] For example, some or all of the above embodiments may also be described as, but are not limited to, the following appendices. Some or all of the elements (e.g., configurations and functions) described in appendices directed to devices (e.g., RAN nodes) may naturally also be described as appendices directed to methods and programs. For example, some or all of the elements described in appendices 2-8 dependent on appendices 1 may also be described as appendices dependent on appendices 16 and 18, due to the same dependency relationship as appendices 2-8. Some or all of the elements described in any appendice may be applied to various hardware, software, recording means for recording software, systems, and methods.

[0134] (Supplementary Note 1) A Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of a User Equipment (UE), comprising: means for receiving a first control message from a source node; and means for transmitting a second control message to the source node in response to the first control message, wherein the first control message requests the candidate target node to prepare one or more candidate target cells for an initial conditional handover of the UE, the first control message including an indication of a subsequent conditional handover, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for executing a subsequent conditional handover from each of the prepared at least one candidate target cell to another cell. (Supplementary Note 2) The RAN node of Supplementary Note 1, wherein the first control message is a HANDOVER REQUEST message, and the second control message is a HANDOVER REQUEST ACKNOWLEDGE message. (Supplementary Note 3) The RAN node according to Supplementary Note 2, wherein the transmitting means is adapted to include the information indicating the execution condition in a HandoverCommand message or an RRCReconfiguration message carried in a Target NG-RAN node To Source NG-RAN node Transparent Container information element (IE) in the HANDOVER REQUEST ACKNOWLEDGE message. (Supplementary Note 4) The RAN node according to Supplementary Note 2, wherein the transmitting means is adapted to include the information indicating the execution condition in a Conditional Handover Information Acknowledge IE in the HANDOVER REQUEST ACKNOWLEDGE message.(Supplementary Note 5) The RAN node of any one of Supplements 1 to 4, wherein the first control message indicates whether the candidate target node is allowed or requested to generate an execution condition for the subsequent conditional handover. (Supplementary Note 6) The RAN node of Supplementary Note 5, wherein the transmitting means is adapted to include the information indicating the execution condition in the second control message in response to the first control message indicating that the candidate target node is allowed or requested to generate an execution condition. (Supplementary Note 7) The RAN node of any one of Supplements 1 to 6, wherein the subsequent conditional handover is a conditional handover procedure that is performed after the initial conditional handover without restarting a conditional handover based on a configuration of conditional handover candidate target cells pre-configured for the initial conditional handover. (Supplementary Note 8) The RAN node according to any one of Supplementary Notes 1 to 7, wherein each of the initial conditional handover and the subsequent conditional handover is a conditional handover from a source Master Node (MN) to a target MN of dual connectivity for the UE. (Supplementary Note 9) A Radio Access Network (RAN) node configured to operate as a source node for a conditional handover of a User Equipment (UE), comprising: means for transmitting a first control message to a candidate target node; and means for receiving a second control message transmitted from the candidate target node in response to the first control message, wherein the first control message requests the candidate target node to prepare one or more candidate target cells for an initial conditional handover of the UE, the first control message including an indication of a subsequent conditional handover, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for executing a subsequent conditional handover from each of the prepared at least one candidate target cell to another cell.(Supplementary note 10) The RAN node of Supplementary note 9, wherein the first control message is a HANDOVER REQUEST message, and the second control message is a HANDOVER REQUEST ACKNOWLEDGE message. (Supplementary note 11) The RAN node of Supplementary note 10, wherein the information indicating the execution condition is encapsulated in a Handover Command message or an RRC Reconfiguration message carried in a Target NG-RAN node To Source NG-RAN node Transparent Container information element (IE) in the HANDOVER REQUEST ACKNOWLEDGE message. (Supplementary note 12) The RAN node of Supplementary note 10, wherein the information indicating the execution condition is encapsulated in a Conditional Handover Information Acknowledge IE in the HANDOVER REQUEST ACKNOWLEDGE message. (Supplementary note 13) The RAN node of any one of Supplements 10 to 12, wherein the first control message indicates whether the candidate target node is allowed or required to create an execution condition for the subsequent conditional handover. (Supplementary Note 14) The RAN node according to any one of Supplementary Notes 9 to 13, wherein the subsequent conditional handover is a conditional handover procedure that is performed after the initial conditional handover without restarting the conditional handover based on a configuration of candidate target cells for the conditional handover that is pre-configured for the initial conditional handover. (Supplementary Note 15) The RAN node according to any one of Supplementary Notes 9 to 14, wherein each of the initial conditional handover and the subsequent conditional handover is a conditional handover from a source Master Node (MN) to a target MN of dual connectivity for the UE.(Supplementary Note 16) A method performed by a Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of a User Equipment (UE), comprising: receiving a first control message from a source node; and transmitting a second control message to the source node in response to the first control message, wherein the first control message requests the candidate target node to prepare one or more candidate target cells for an initial conditional handover of the UE, the first control message including an indication of a subsequent conditional handover, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for executing a subsequent conditional handover from each of the prepared at least one candidate target cell to another cell. (Supplementary Note 17) A method performed by a Radio Access Network (RAN) node configured to operate as a source node for conditional handover of User Equipment (UE), comprising: transmitting a first control message to a candidate target node; and receiving a second control message transmitted from the candidate target node in response to the first control message, wherein the first control message requests the candidate target node to prepare one or more candidate target cells for an initial conditional handover of the UE, the first control message including an indication of a subsequent conditional handover, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for execution of a subsequent conditional handover from each of the prepared at least one candidate target cell to another cell.(Supplementary Note 18) A program causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of User Equipment (UE), the method comprising: receiving a first control message from a source node; and transmitting a second control message to the source node in response to the first control message, the first control message requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover of the UE, the first control message including an indication of a subsequent conditional handover, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for executing a subsequent conditional handover from each of the prepared at least one candidate target cell to another cell. (Supplementary Note 19) A program causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a source node for a conditional handover of User Equipment (UE), the method comprising: transmitting a first control message to a candidate target node; and receiving a second control message transmitted from the candidate target node in response to the first control message, the first control message requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover of the UE, the first control message including an indication of a subsequent conditional handover, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for executing a subsequent conditional handover from each of the prepared at least one candidate target cell to another cell.(Supplementary Note 20) A Radio Access Network (RAN) node configured to operate as a source node for conditional handover of User Equipment (UE), comprising: means for transmitting to a first candidate target node a first control message requesting the first candidate target node to prepare one or more candidate target cells for an initial conditional handover for the UE and for subsequent conditional handovers, the first control message including information indicating whether the first candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover. (Supplementary Note 21) The RAN node according to Supplementary Note 20, further comprising: means for receiving a second control message transmitted from the first candidate target node in response to the first control message; and means for indicating, via a third control message, a first cell to a second candidate target node for the initial conditional handover, if a first cell not included in the one or more candidate target cells indicated in the first control message has been prepared by the first candidate target node for the subsequent conditional handover. (Supplementary Note 22) The RAN node according to Supplementary Note 21, further comprising: means for receiving a fourth control message transmitted from the second candidate target node in response to the third control message, the fourth control message including information indicating a condition for executing a subsequent conditional handover from the candidate target cell prepared by the second candidate target node to the first cell. (Supplementary Note 23) The RAN node according to Supplementary Note 21 or 22, wherein the first control message is a HANDOVER REQUEST message, the second control message is a HANDOVER REQUEST ACKNOWLEDGE message, and the third control message is a HANDOVER REQUEST message.(Supplementary Note 24) The RAN node according to any one of Supplementary Notes 20 to 23, wherein the subsequent conditional handover is a conditional handover procedure performed after the initial conditional handover without restarting the conditional handover based on a configuration of candidate target cells for the conditional handover that is pre-configured for the initial conditional handover. (Supplementary Note 25) The RAN node according to any one of Supplementary Notes 20 to 24, wherein each of the initial conditional handover and the subsequent conditional handover is a conditional handover from a source Master Node (MN) to a target MN of dual connectivity for the UE. (Supplementary Note 26) A Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of a User Equipment (UE), comprising: means for receiving from a source node a first control message requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover for the UE and for subsequent conditional handovers, the first control message including information indicating whether the candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover. (Supplementary Note 27) The RAN node of Supplementary Note 26 further comprising means for transmitting to the source node a second control message in response to the first control message, the second control message indicating that a first cell not included in the one or more candidate target cells indicated in the first control message has been prepared by the candidate target node for the subsequent conditional handover. (Supplementary Note 28) The RAN node according to Supplementary Note 27, wherein the first control message is a HANDOVER REQUEST message, and the second control message is a HANDOVER REQUEST ACKNOWLEDGE message.(Supplementary Note 29) A method performed by a Radio Access Network (RAN) node configured to operate as a source node for conditional handover of a User Equipment (UE), comprising: sending a first control message to a first candidate target node requesting the first candidate target node to prepare one or more candidate target cells for an initial conditional handover for the UE and for subsequent conditional handovers, the first control message including information indicating whether the first candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover. (Supplementary Note 30) A method performed by a Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of a User Equipment (UE), comprising receiving a first control message from a source node requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover and for subsequent conditional handovers for the UE, the first control message including information indicating whether the candidate target node is permitted or requested to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover.(Supplementary Note 31) A program causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a source node for conditional handover of User Equipment (UE), the method comprising: sending a first control message to a first candidate target node requesting the first candidate target node to prepare one or more candidate target cells for an initial conditional handover for the UE and for subsequent conditional handovers, the first control message including information indicating whether the first candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover. (Supplementary Note 32) A program causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of User Equipment (UE), the method comprising receiving a first control message from a source node requesting the candidate target node to prepare one or more candidate target cells for an initial conditional handover and for subsequent conditional handovers for the UE, the first control message including information indicating whether the candidate target node is permitted or required to prepare a cell other than the one or more candidate target cells as a candidate target cell for the subsequent conditional handover.(Supplementary Note 33) A Radio Access Network (RAN) node configured to operate as a source node for conditional handover of User Equipment (UE), comprising: means for sending first information to each of the one or more candidate target nodes indicating whether one or more cells managed by the source node will be candidate target cells for a subsequent conditional handover that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by one or more candidate target nodes. (Supplementary Note 34) The RAN node of Supplementary Note 33, wherein the sending means is adapted to send the first information to each candidate target node via a first control message, the first control message requesting each candidate target node to prepare one or more candidate target cells managed by each candidate target node for the initial conditional handover and for subsequent conditional handovers. (Supplementary Note 35) The RAN node of Supplementary Note 34, wherein the first control message is a HANDOVER REQUEST message. (Supplementary Note 36) The RAN node according to Supplementary Note 34 or 35, further comprising means for receiving a second control message transmitted from each candidate target node in response to the first control message, the second control message indicating at least one candidate target cell prepared by each candidate target node, and the second control message including information indicating a condition for executing a conditional handover from each of the prepared at least one candidate target cell to each of the one or more cells managed by the source node. (Supplementary Note 37) The RAN node according to any one of Supplements 33 to 36, wherein the one or more cells managed by the source node include a source cell of the initial conditional handover. (Supplementary Note 38) The RAN node according to any one of Supplements 33 to 37, wherein the one or more cells managed by the source node include a cell other than the source cell of the initial conditional handover.(Supplementary Note 39) The RAN node according to any one of Supplements 33 to 38, wherein the subsequent conditional handover is a conditional handover procedure performed after the initial conditional handover without restarting the conditional handover based on a configuration of candidate target cells for the conditional handover that is pre-configured for the initial conditional handover. (Supplementary Note 40) The RAN node according to any one of Supplements 33 to 39, wherein each of the initial conditional handover and the subsequent conditional handover is a conditional handover from a source Master Node (MN) to a target MN of dual connectivity for the UE. (Supplementary Note 41) A Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of a User Equipment (UE), comprising: means for receiving from the source node first information indicating whether one or more cells managed by the source node will be candidate target cells for a subsequent conditional handover that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the candidate target node. (Supplementary Note 42) The RAN node of Supplementary Note 41, wherein the receiving means is adapted to receive the first information via a first control message, the first control message requesting the candidate target node to prepare one or more candidate target cells managed by the candidate target node for the initial conditional handover and for subsequent conditional handovers. (Supplementary Note 43) The RAN node of Supplementary Note 42, wherein the first control message is a HANDOVER REQUEST message.(Supplementary Note 44) The RAN node according to Supplementary Note 42 or 43, further comprising means for transmitting a second control message to the source node in response to the first control message, the second control message indicating at least one candidate target cell prepared by the candidate target node, and the second control message including information indicating a condition for executing a conditional handover from each of the prepared at least one candidate target cell to each of the one or more cells managed by the source node. (Supplementary Note 45) The RAN node according to any one of Supplements 41 to 44, wherein the one or more cells managed by the source node include a source cell of the initial conditional handover. (Supplementary Note 46) The RAN node according to any one of Supplements 41 to 45, wherein the one or more cells managed by the source node include a cell other than the source cell of the initial conditional handover. (Supplementary Note 47) The RAN node according to any one of Supplements 41 to 46, wherein the subsequent conditional handover is a conditional handover procedure that is performed after the initial conditional handover without restarting the conditional handover based on a configuration of candidate target cells for the conditional handover that is pre-configured for the initial conditional handover. (Supplementary Note 48) The RAN node according to any one of Supplements 41 to 47, wherein each of the initial conditional handover and the subsequent conditional handover is a conditional handover from a source Master Node (MN) to a target MN of dual connectivity for the UE.(Supplementary Note 49) A method performed by a Radio Access Network (RAN) node configured to operate as a source node for conditional handover of User Equipment (UE), comprising sending first information to each of the one or more candidate target nodes indicating whether one or more cells managed by the source node will be candidate target cells for subsequent conditional handovers that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the candidate target nodes. (Supplementary Note 50) A method performed by a Radio Access Network (RAN) node configured to operate as a candidate target node for conditional handover of User Equipment (UE), comprising receiving from the source node first information indicating whether one or more cells managed by the source node will be candidate target cells for subsequent conditional handovers that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the candidate target nodes. (Supplementary Note 51) A program causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a source node for a conditional handover of User Equipment (UE), the method comprising sending first information to each of the one or more candidate target nodes indicating whether one or more cells managed by the source node will be candidate target cells for a subsequent conditional handover that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the one or more candidate target nodes.(Supplementary Note 52) A program causing a computer to perform a method for a Radio Access Network (RAN) node configured to operate as a candidate target node for a conditional handover of User Equipment (UE), the method comprising receiving, from the source node, first information indicating whether one or more cells managed by the source node will be candidate target cells for a subsequent conditional handover that may occur after an initial conditional handover from a source cell managed by the source node to any of one or more candidate target cells managed by the candidate target node.

[0135] This application claims priority based on Japanese Patent Application No. 2023-125264, filed August 1, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0136] 1 Source node 2 Target node 3 User Equipment (UE) 1304 Processor 1305 Memory 1306 Modules 1403 Baseband processor 1404 Application processor 1406 Memory 1407 Modules

Claims

1. A radio access network (RAN) node configured to act as a candidate target node for conditional handover of User Equipment (UE), Means for receiving a first control message from the source node, The system includes means for transmitting a second control message to the source node in response to the first control message, The first control message requests the candidate target node to prepare one or more candidate target cells for the first conditional handover of the UE, The first control message includes the subsequent indication of a conditional handover. The second control message indicates at least one candidate target cell prepared by the candidate target node, The second control message includes information indicating the conditions for performing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell. RAN node.

2. The first control message is a HANDOVER REQUEST message, The second control message is a HANDOVER REQUEST ACKNOWLEDGE message. The RAN node according to claim 1.

3. The means for transmitting is adapted to include the information indicating the execution conditions in the HandoverCommand message or RRCReconfiguration message carried in the Target NG-RAN node To Source NG-RAN node Transparent Container information element (IE) within the HANDOVER REQUEST ACKNOWLEDGE message. The RAN node according to claim 2.

4. The means for transmitting is adapted to include the information indicating the execution conditions in the Conditional Handover Information Acknowledge IE within the HANDOVER REQUEST ACKNOWLEDGE message. The RAN node according to claim 2.

5. The first control message indicates whether the candidate target node is permitted or required to generate the execution conditions for the subsequent conditional handover. A RAN node according to any one of claims 1 to 4.

6. The transmitting means is adapted to include the information indicating the execution conditions in a second control message in response to a first control message indicating that the candidate target node permits or requests the generation of execution conditions. The RAN node according to claim 5.

7. The subsequent conditional handover is a conditional handover procedure performed after the initial conditional handover, without restarting the conditional handover, based on the pre-configured setting of candidate target cells for the conditional handover with respect to the initial conditional handover. A RAN node according to any one of claims 1 to 4.

8. A radio access network (RAN) node configured to act as a source node for conditional handover of User Equipment (UE), Means for sending a first control message to a candidate target node, The system includes means for receiving a second control message transmitted from the candidate target node in response to the first control message, The first control message requests the candidate target node to prepare one or more candidate target cells for the first conditional handover of the UE, The first control message includes the subsequent indication of a conditional handover. The second control message indicates at least one candidate target cell prepared by the candidate target node, The second control message includes information indicating the conditions for performing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell. RAN node.

9. A method performed by a radio access network (RAN) node configured to act as a candidate target node for conditional handover of User Equipment (UE), Receiving the first control message from the source node, and The system includes transmitting a second control message to the source node in response to the first control message, The first control message requests the candidate target node to prepare one or more candidate target cells for the first conditional handover of the UE, The first control message includes the subsequent indication of a conditional handover. The second control message indicates at least one candidate target cell prepared by the candidate target node, The second control message includes information indicating the conditions for performing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell. method.

10. A program that causes a computer to perform a method for a radio access network (RAN) node configured to act as a candidate target node for conditional handover of User Equipment (UE), The aforementioned method, Receiving the first control message from the source node, and The system includes transmitting a second control message to the source node in response to the first control message, The first control message requests the candidate target node to prepare one or more candidate target cells for the first conditional handover of the UE, The first control message includes the subsequent indication of a conditional handover. The second control message indicates at least one candidate target cell prepared by the candidate target node, The second control message includes information indicating the conditions for performing a subsequent conditional handover from each of the at least one prepared candidate target cell to another cell. program.