Communication method, user device, processor, program, and system

Abstract

To provide a communication method, user equipment, and a base station that enable conditional handover (CHO) and conditional primary / secondary cell change, conditional primary / secondary cell addition (CPAC) to be performed simultaneously.SOLUTION: A communication method in which user equipment communicates with a master cell group (MCG) and a secondary cell group (SCG) includes the steps of managing the MCG transmitting to the user equipment a radio resource control (RRC) message including a target MCG setting for performing CHO to the target MCG and each SCG candidate setting for a plurality of SCG candidates associated with the target MCG by a master node, receiving the RRC message by the user equipment, and selecting one of the SCG candidates from the plurality of SCG candidates as the target SCG by the user equipment when an execution condition for CHO is satisfied.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present disclosure relates to a communication method, a user equipment, and a base station for use in a mobile communication system. [Background technology]

[0002] The technical specifications of the Third Generation Partnership Project (3GPP), a standardization project for mobile communication systems, have been formulated for conditional handover (CHO) and conditional primary-secondary cell change (CPC). 3GPP is also currently discussing the formulation of specifications for conditional primary-secondary cell addition (CPA) and inter-secondary node (Inter-SN) CPC. Note that CPC and CPA are sometimes collectively referred to as CPAC. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP Technical Specification: TS38.300 V16.8.0 (2021-12) Summary of the Invention

[0004] The present disclosure provides a communication method, a user equipment, and a base station that enable CHO and CPAC to be performed simultaneously.

[0005] A communication method according to a first aspect is a communication method in which a user equipment communicates with a master cell group (MCG) and a secondary cell group (SCG), and includes the steps of: a master node managing the master cell group (MCG) transmitting to the user equipment a radio resource control (RRC) message including a target MCG setting for performing a conditional handover (CHO) to a target MCG and SCG candidate settings for each of a plurality of SCG candidates associated with the target MCG; the user equipment receiving the RRC message; and the user equipment selecting, when an execution condition for the CHO is satisfied, one of the SCG candidates from the plurality of SCG candidates as a target SCG.

[0006] A user equipment according to a second aspect is a user equipment that communicates with a master cell group (MCG) and a secondary cell group (SCG), and includes a receiver that receives a radio resource control (RRC) message from a master node that manages the master cell group (MCG) including a target MCG setting for performing a conditional handover (CHO) to a target MCG and SCG candidate settings for each of a plurality of SCG candidates associated with the target MCG, and a controller that selects one of the SCG candidates as a target SCG when an execution condition for the CHO is satisfied.

[0007] A base station according to a third aspect is a base station that operates as a master node that manages a master cell group (MCG) used by a user equipment, and includes a transmitter that transmits to the user equipment a radio resource control (RRC) message that includes a target MCG setting for performing a conditional handover (CHO) to a target MCG, and each SCG candidate setting for a plurality of secondary cell group (SCG) candidates associated with the target MCG. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] 1 is a diagram illustrating a configuration of a UE (user equipment) according to an embodiment. [Figure 3] A diagram showing the configuration of a gNB (base station) according to an embodiment. [Figure 4] FIG. 10 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. [Figure 5] FIG. 1 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). [Figure 6] FIG. 1 is a diagram for explaining an overview of a DC according to an embodiment. [Figure 7] FIG. 1 is a diagram for explaining a CHO according to an embodiment. [Figure 8] FIG. 2 is a diagram for explaining a CPC according to the embodiment. [Figure 9] FIG. 1 is a diagram for explaining a CPA according to an embodiment. [Figure 10] FIG. 10 is a diagram for explaining operations related to simultaneous execution of CHO and CPC according to an embodiment. [Figure 11] FIG. 10 is a diagram for explaining operations related to simultaneous execution of CHO and CPA according to an embodiment. [Figure 12] FIG. 2 is a diagram illustrating a first example of a configuration of an RRC message according to the embodiment. [Figure 13] FIG. 10 is a diagram illustrating a second example of a configuration of an RRC message according to the embodiment. [Figure 14] FIG. 10 is a diagram illustrating an example of an operation flow of a UE according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0010] (1) Configuration of mobile communication system First, the configuration of a mobile communication system according to an embodiment will be described. Fig. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. A mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following description, 5GS will be taken as an example, but the mobile communication system may also be at least partially applied with an LTE (Long Term Evolution) system or at least partially applied with a 6th Generation (6G) system.

[0011] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. The 5GC 20 may be simply referred to as the core network (CN) 20.

[0012] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone), a tablet terminal, a laptop PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0013] The NG-RAN 10 includes a base station (called "gNB" in the 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with a UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-base station interface.

[0015] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0016] 2 is a diagram showing the configuration of a UE 100 (user equipment) according to the embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB 200.

[0017] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0018] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0019] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer, which will be described later. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0020] 3 is a diagram showing the configuration of a gNB 200 (base station) according to an embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that performs communication with the CN 20.

[0021] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0022] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0023] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer, which will be described later. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processes by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0024] The backhaul communication unit 240 is connected to neighboring base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 may be configured (i.e., functionally divided) with a CU (Central Unit) and a DU (Distributed Unit), and both units may be connected via an F1 interface, which is a fronthaul interface.

[0025] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0026] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0027] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has CRC parity bits scrambled by the RNTI added.

[0028] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via transport channels. The MAC layer of gNB200 includes a scheduler, which determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0029] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via logical channels.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0031] The SDAP layer maps IP flows, which are the units for Quality of Service (QoS) control by the core network, to radio bearers, which are the units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP is not necessary.

[0032] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0033] The protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) instead of the SDAP layer shown in FIG.

[0034] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0035] The NAS, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS of the UE 100 and the NAS of the AMF 300A. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. The layer below the NAS is called an AS (Access Stratum).

[0036] (2) Overview of Dual Connectivity Next, an overview of dual connectivity (DC) according to an embodiment will be described. Fig. 6 is a diagram for explaining the overview of DC according to an embodiment.

[0037] In DC, the UE 100 simultaneously communicates with a master cell group (MCG) 201M managed by a master node (MN) 200M and a secondary cell group (SCG) 201S managed by a secondary node (SN) 200S. The MN 200M may be an NR base station (gNB) or an LTE base station (eNB). The MN 200M is also referred to as a master base station. The SN 200S may be an NR base station (gNB) or an LTE base station (eNB). The SN 200S is also referred to as a secondary base station. The MN 200M and the SN 200S may be 6G base stations. In the following, an example in which each of the MN 200M and the SN 200S is an NR base station (gNB) will be mainly described.

[0038] For example, the MN 200M transmits a predetermined message (e.g., an SN Addition Request message) to the SN 200S via the network interface between the MN 200M and the SN 200S, and the MN 200M transmits an RRC Reconfiguration message to the UE 100, thereby starting the DC. The UE 100 in the RRC connected state is allocated radio resources by the respective schedulers of the MN 200M and the SN 200S, and performs radio communication using the radio resources of the MN 200M and the SN 200S. The network interface between the MN 200M and the SN 200S may be an Xn interface (or an X2 interface). The MN 200M and the SN 200 communicate with each other via this network interface.

[0039] The MN 200M may have a control plane connection with the core network. The MN 200M provides primary radio resources for the UE 100. The MN 200M manages the MCG 201M. The MCG 201M is a group of serving cells associated with the MN 200M. The MCG 201M has a primary cell (PCell) and optionally has one or more secondary cells (SCells). The MN 200M controls and manages settings for the UE 100.

[0040] The SN200S may not have a control plane connection with the core network. The SN200S provides additional radio resources to the UE100. The SN200S manages the SCG201S. The SCG201S has a primary and secondary cell (PSCell) and optionally has one or more SCells. The PCell of the MCG201M and the PSCell of the SCG201S are also called special cells (SpCells).

[0041] (3) Overview of conditional reset Next, an overview of conditional reconfiguration according to the embodiment will be described.

[0042] (3.1) Conditional Handover (CHO) In the CHO, a condition for executing handover is set in advance in the UE 100, and the handover is executed when the set execution condition is satisfied in the UE 100. Fig. 7 is a diagram for explaining the CHO according to the embodiment.

[0043] 7 shows an example in which the base station managing the source cell is gNB200, the base station managing candidate cell #1 is gNB200C-1, and the base station managing candidate cell #2 is gNB200C-2, but these cells may be managed by a single base station. Also, while two candidate cells (candidate cell #1 and candidate cell #2) are shown as an example, the number of candidate cells may be one, or three or more. UE100 is in an RRC connected state in the source cell.

[0044] In STEP 1, the gNB200 transmits an RRC Reconfiguration message including a conditional RRC reconfiguration, which is a CHO configuration, to the UE100. The RRC Reconfiguration message is an example of an RRC message. The CHO configuration includes, for example, a candidate cell configuration (i.e., configuration information for each of candidate cell #1 and candidate cell #2) generated by the candidate gNB200C (i.e., gNB200C-1 and gNB200C-2) and condition information indicating an execution condition generated by the source gNB200 (i.e., gNB200). The candidate cell configuration and the execution condition are associated with each other. Different execution conditions may be associated with multiple candidate cells. The execution condition is information that sets the radio quality to be measured, a threshold to be compared with the radio quality, etc. The UE100 starts evaluating the execution condition.

[0045] In STEP 2, UE 100 starts accessing the candidate cell (here, candidate cell #1) for which the execution condition is satisfied in response to the satisfaction of the execution condition set in STEP 1. Note that UE 100 does not need to monitor the source cell from the time when synchronization with candidate cell #1 is started.

[0046] In STEP 3, when UE 100 has successfully accessed candidate cell #1, it switches the connection from the source cell to candidate cell #1. This completes the handover. UE 100 communicates with candidate cell #1 using the candidate cell configuration (configuration information of candidate cell #1) received in STEP 1.

[0047] (3.2) Conditional PSCell Change (CPC) In the CPC, an execution condition for a PSCell change is set in advance in the UE 100, and a PSCell change is performed when the set execution condition is satisfied in the UE 100. Fig. 8 is a diagram for explaining the CPC according to the embodiment. It is assumed that the UE 100 has a connection with a gNB 200M (MCG 201M) which is an MN and a gNB 200S-1 (SCG 201S-1) which is an SN, and is performing communication in the DC method.

[0048] CPCs include intra-SN (Intra-SN) CPCs that change a PSCell from one cell to another cell within one SN 200S, and inter-SN (Inter-SN) CPCs that change a PSCell from a cell of one SN 200S to a cell of another SN 200S. While Inter-SN CPCs will be mainly described below, embodiments are not limited to Inter-SN CPCs and may be Intra-SN CPCs.

[0049] In STEP 1, the gNB200M, which is an MN, transmits an RRC Reconfiguration message including Conditional Reconfiguration, which is a CPC setting, to the UE100. The CPC setting includes, for example, an SCG candidate setting (e.g., PSCell setting information for the SCG candidate 201S-2 of the gNB200-2. Optionally, SCell setting information may be included) generated by the gNB200S-2, which is an SN candidate, and condition information indicating an execution condition generated by the MN (i.e., the gNB200M). The SCG candidate setting and the execution condition are associated with each other. Different execution conditions may be associated with multiple SCG candidate settings. The execution condition is information that sets the radio quality to be measured, a threshold to be compared with the radio quality, etc. The UE100 starts evaluating the execution condition.

[0050] In STEP 2, in response to the execution condition set in STEP 1 being satisfied, the UE 100 starts accessing the PSCell of the SCG candidate 201S-2 for which the execution condition is satisfied.

[0051] In STEP 3, if UE 100 successfully accesses the SCG candidate 201S-2 (PSCell), it switches the PSCell from SCG 201S-1 (gNB 200S-1) to SCG 201S-2 (gNB 200S-2). This completes the PSCell change. UE 100 communicates with SCG 201S-2 using the SCG candidate configuration (configuration information of SCG 201S-2) received in STEP 1.

[0052] (3.3) Conditional PSCell Addition (CPA) In CPA, an execution condition for PSCell addition is set in advance in the UE 100, and the PSCell addition is executed when the set execution condition is satisfied in the UE 100. Fig. 9 is a diagram for explaining CPA according to the embodiment. The UE 100 is in an RRC connected state in the MCG 201M.

[0053] In STEP 1, the gNB200M, which is an MN, transmits an RRC Reconfiguration message including a Conditional Reconfiguration, which is a CPA setting, to the UE100. The CPA setting includes, for example, an SCG candidate setting (e.g., setting information for each of the SCG candidates 201S-1 and 201S-2) generated by the SN candidates (gNB200S-1, gNB200S-2) and condition information indicating an execution condition generated by the MN (i.e., the gNB200M). The SCG candidate setting and the execution condition are associated with each other. Different execution conditions may be associated with multiple SCG candidate settings. The execution condition is information that sets the radio quality to be measured, a threshold to be compared with the radio quality, etc. The UE100 starts evaluating the execution condition.

[0054] In STEP 2, in response to the execution condition set in STEP 1 being satisfied, UE 100 starts accessing the PSCell of the SCG candidate for which the execution condition is satisfied (here, SCG candidate 201S-1).

[0055] In STEP 3, when the UE 100 has successfully accessed the SCG candidate 201S-1 (PSCell), the UE 100 starts communication in the DC scheme. The UE 100 communicates with the SCG 201S-1 using the SCG candidate configuration (configuration information of the SCG 201S-1) received in STEP 1.

[0056] (4) Operation of the mobile communication system Next, an operation of the mobile communication system 1 according to the embodiment, specifically, an operation for simultaneously performing CHO and CPAC (CPC, CPA), will be described. Note that in such an operation, a problem may arise as to how the gNB 200 (MN) sets multiple SCG candidates to the UE 100. Another problem may arise as to how the UE 100 determines a target SCG from multiple SCG candidates.

[0057] In an embodiment, the UE 100 communicates with the MCG 201M and the SCG 201S via DC. First, the MN 200M managing the MCG 201M transmits to the UE 100 an RRC message (specifically, Conditional Reconfiguration) including a target MCG configuration for performing CHO to a target MCG and an SCG candidate configuration for each of a plurality of SCG candidates associated with the target MCG. The UE 100 receives the RRC message. Second, when an execution condition (also referred to as a "trigger condition") in the CHO is satisfied, the UE 100 selects one of the plurality of SCG candidates as a target SCG. This makes it possible to simultaneously perform CHO and CPAC (CPC, CPA). When the execution condition in the CHO is satisfied, the UE 100 may start accessing the target MCG and also start accessing the selected target SCG.

[0058] (4.1) Operations related to simultaneous implementation of CHO and CPC An operation related to simultaneous implementation of CHO and CPC according to an embodiment will be described. Fig. 10 is a diagram for describing an operation related to simultaneous implementation of CHO and CPC according to an embodiment. It is assumed that UE 100 has a connection with gNB 200M-1 (MCG 201M-1) which is an MN and gNB 200S-1 (SCG 201S-1) which is an SN, and is performing communication using the DC method. Although one SCG candidate 201S-2 is illustrated in Fig. 10, it is assumed that there are multiple SCG candidates. In the following, for the sake of simplicity of explanation, it is assumed that there is one MCG candidate (target MCG) set in the CHO, but there may be multiple MCG candidates set in the CHO. Multiple SCG candidates may be set for each of such multiple MCG candidates.

[0059] In STEP 1, the gNB 200M-1, which is an MN, transmits an RRC Reconfiguration message including a conditional RRC reconfiguration, which is a CHO and CPC configuration, to the UE 100. The Conditional Reconfiguration (first conditional RRC reconfiguration) includes condition information indicating an execution condition for CHO, a target MCG configuration, which is configuration information for the target MCG 201M-2, and a list including SCG candidate configurations for each of a plurality of SCG candidates. The target MCG configuration includes information required for communication with the target MCG 201M-2 (PCell). The SCG candidate configuration includes information required for communication with the corresponding SCG (PSCell). Details of the configuration of the Conditional Reconfiguration will be described later.

[0060] In STEP 2, in response to the execution condition of CHO set in STEP 1 being satisfied, UE 100 selects a target SCG from the multiple SCG candidates set in STEP 1. Details of the target SCG selection process will be described later. Then, UE 100 starts accessing the target MCG 201M-2 (PCell) and starts accessing the PSCell of the selected target SCG (here, SCG candidate 201S-2). For example, UE 100 may start accessing the target SCG 201S-2 (PSCell) after successfully accessing the target MCG 201M-2 (PCell).

[0061] In STEP 3, when UE 100 has successfully accessed the target MCG 201M-2 (PCell), it switches the PCell (MN) from MCG 201M-1 (gNB 200M-1) to MCG 201M-2 (gNB 200M-2). Furthermore, when UE 100 has successfully accessed the target SCG 201S-2 (PSCell), it switches the PSCell (SN) from SCG 201S-1 (gNB 200S-1) to SCG 201S-2 (gNB 200S-2). This completes CHO and CPC. UE 100 communicates with MCG 201M-2 (PCell) using the target MCG configuration received in STEP 1. Furthermore, UE 100 communicates with SCG 201S-2 (PSCell) using the SCG configuration of the target SCG from among the multiple candidate SCG configurations received in STEP 1.

[0062] (4.2) Operations related to simultaneous implementation of CHO and CPA An operation related to simultaneous execution of CHO and CPA according to the embodiment will be described. Fig. 11 is a diagram for explaining an operation related to simultaneous execution of CHO and CPA according to the embodiment. The UE 100 has a connection with a gNB 200M-1 (MCG 201M-1) which is an MN.

[0063] In STEP 1, the gNB 200M-1, which is an MN, transmits an RRC Reconfiguration message including a conditional RRC reconfiguration, which is a CHO and CPA configuration, to the UE 100. The Conditional Reconfiguration (first conditional RRC reconfiguration) includes condition information indicating an execution condition for CHO, a target MCG configuration, which is configuration information for the target MCG 201M-2, and a list including SCG candidate configurations for each of a plurality of SCG candidates. The target MCG configuration includes information required for communication with the target MCG 201M-2 (PCell). The SCG candidate configuration includes information required for communication with the corresponding SCG (PSCell). Details of the configuration of the Conditional Reconfiguration will be described later.

[0064] In STEP 2, the UE 100 selects a target SCG from the multiple SCG candidates set in STEP 1 in response to the execution condition of CHO set in STEP 1 being satisfied. Details of the target SCG selection process will be described later. Then, the UE 100 starts accessing the target MCG 201M-2 (PCell) and starts accessing the PSCell of the selected target SCG (here, the SCG candidate 201S-1). For example, the UE 100 may start accessing the target SCG 201S-1 (PSCell) after successfully accessing the target MCG 201M-2 (PCell).

[0065] In STEP 3, when UE 100 successfully accesses target MCG 201M-2 (PCell), it switches PCell (MN) from MCG 201M-1 (gNB 200M-1) to MCG 201M-2 (gNB 200M-2). Also, when UE 100 successfully accesses target SCG 201S-2 (PSCell), PSCell (SN) is added to SCG 201S-1 (gNB 200S-1). This completes CHO and CPA. UE 100 communicates with MCG 201M-2 (PCell) using the target MCG configuration received in STEP 1. Also, UE 100 communicates with SCG 201S-1 (PSCell) using the SCG configuration of the target SCG from among the multiple candidate SCG configurations received in STEP 1.

[0066] (4.3) Message structure example A configuration example of an RRC message according to the embodiment, specifically, Conditional Reconfiguration (first conditional RRC reconfiguration) will be described. As described above, the Conditional Reconfiguration in the RRC message according to the embodiment is transmitted from the gNB 200 (MN) to the UE 100. The Conditional Reconfiguration includes a target MCG configuration for performing CHO to a target MCG, and SCG candidate configurations of each of a plurality of SCG candidates associated with the target MCG. That is, the Conditional Reconfiguration includes an MCG configuration for performing conditional reconfiguration, and a plurality of SCG candidate configurations associated with the MCG configuration.

[0067] (4.3.1) Message configuration example 1 12 is a diagram showing a first configuration example of an RRC message according to the embodiment. The gNB 200 (MN) transmits an RRC message (RRC Reconfiguration message) for simultaneously performing CHO and CPAC (CPC, CPA) to the UE 100. The RRC Reconfiguration message includes Conditional Reconfiguration-r16 as an information element. Here, "-r16" means that the information element is introduced in 3GPP Release 16.

[0068] Conditional Reconfiguration-r16 includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to be added or modified for the MCG (MN). Each entry (CondReconfigToAddMod-r16) in condReconfigToAddModList-r16 corresponds to a first conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates an RRC Reconfiguration to be applied when an execution condition is satisfied. CondReconfigToAddMod-r16 also includes condExecutionCond-r16 (not shown), which is condition information indicating an execution condition that must be satisfied to trigger the execution of the corresponding conditional reconfiguration.

[0069] condRRCReconfig-r16(RRCReconfiguration) includes masterCellGroup, which is a target MCG configuration. In this configuration example 1, condRRCReconfig-r16(RRCReconfiguration) further includes secondaryCellGroupCandidateList, which is a new list including information for each SCG candidate (target SCG).

[0070] Each entry in the list (secondaryCellGroupCandidateList) includes secondaryCellGroup (or mrdc-SecondaryCellGroup), which is configuration information for an SCG candidate (target SCG). Each entry in the list (secondaryCellGroupCandidateList) may further include at least one of an SCG identifier (SCG-ID) and a wireless quality threshold. The SCG identifier (SCG-ID) is an identifier that identifies an SCG. The wireless quality threshold is the reference signal received power (RSRP) and / or reference signal received quality (RSRQ) when selecting the SCG, specifically, a threshold of the minimum quality required for the SCG when selecting the SCG.

[0071] According to the present configuration example 1, it is possible to appropriately set a plurality of SCG candidates in the UE 100.

[0072] (4.3.2) Message configuration example 2 13 is a diagram showing a second configuration example of an RRC message according to the embodiment. The gNB 200 (MN) transmits an RRC message (RRC Reconfiguration message) for simultaneously performing CHO and CPAC (CPC, CPA) to the UE 100. The RRC Reconfiguration message includes Conditional Reconfiguration-r16 as an information element.

[0073] Conditional Reconfiguration-r16 includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to be added or modified for the MCG (MN). Each entry (CondReconfigToAddMod-r16) in condReconfigToAddModList-r16 corresponds to a first conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates an RRC Reconfiguration to be applied when an execution condition is satisfied. CondReconfigToAddMod-r16 also includes condExecutionCond-r16 (not shown), which is condition information indicating an execution condition that must be satisfied to trigger the execution of the corresponding conditional reconfiguration.

[0074] condRRCReconfig-r16 (RRCReconfiguration) includes masterCellGroup, which is the target MCG configuration. In this configuration example 2, condRRCReconfig-r16 (RRCReconfiguration) includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to be added or modified for the SCG (SN). Each entry (CondReconfigToAddMod-r16) of the condReconfigToAddModList-r16 corresponds to a second conditional RRC reconfiguration. The CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates RRCReconfiguration to be applied when the execution condition is satisfied, and the RRCReconfiguration includes an SCG candidate configuration (secondaryCellGroup or mrdc-SecondaryCellGroup), which is configuration information of an SCG candidate (target SCG). The CondReconfigToAddMod-r16 also includes a condExecutionCond-r16 (not shown) that is condition information indicating an execution condition that must be met to trigger execution of the corresponding conditional reconfiguration.

[0075] Thus, in this configuration example 2, the second conditional RRC reconfiguration provided for each of the multiple SCG candidates includes condition information (condExecutionCond-r16) indicating the execution condition for the corresponding SCG candidate and an SCG candidate configuration (secondaryCellGroup or mrdc-SecondaryCellGroup) for the corresponding SCG candidate.

[0076] According to this configuration example 2, it is possible to appropriately set a plurality of SCG candidates in the UE 100. Furthermore, according to this configuration example 2, it is possible to set an execution condition in the UE 100 for each SCG candidate.

[0077] (4.4) Example of operation flow An example of an operation flow of the UE 100 according to the embodiment will be described below. Fig. 14 is a diagram showing an example of an operation flow of the UE 100 according to the embodiment.

[0078] In step S1, the UE 100 receives an RRC message (RRC Reconfiguration message) for simultaneously performing CHO and CPAC (CPC, CPA) from the gNB 200 (MN). The RRC message has the configuration of the above-described Message Configuration Example 1 or Message Configuration Example 2.

[0079] In step S2, UE 100 measures radio quality and determines whether or not an execution condition set for the target MCG (i.e., an execution condition for CHO) is satisfied. Such an execution condition for CHO may be condEventA3, condEventA5, or the like, specified in the 3GPP technical specifications. In addition, in the case of the above-mentioned message configuration example 1, UE 100 may determine whether or not a corresponding radio quality threshold is satisfied for each SCG candidate. In the case of the above-mentioned message configuration example 2, UE 100 may determine whether or not a corresponding execution condition (i.e., an execution condition for CPAC) is satisfied for each set SCG candidate. Such an execution condition for CPAC may be condEventA3, condEventA4, condEventA5, or the like, specified in the 3GPP technical specifications. Note that even if an SCG candidate satisfies the execution condition, UE 100 does not access (suspends) the SCG candidate at this point.

[0080] If it is determined that the execution condition (CHO execution condition) set for the MCG201M is satisfied (step S3: YES), in step S4, the UE100 selects a target SCG (PSCell) from among the multiple set SCG candidates. Details of such selection processing will be described later. Note that if there is no SCG candidate that satisfies a predetermined selection criterion, the UE100 may fail to select a target SCG (PSCell). In other words, the UE100 does not select a target SCG.

[0081] When an SCG candidate that satisfies a predetermined selection criterion is selected as a target SCG (step S5: YES), in step S6, UE 100 starts accessing the target MCG (PCell). UE 100 also starts accessing the selected target SCG. Here, the description will proceed assuming that such access is successful.

[0082] In step S7, UE 100 may transmit, to the target MCG, an identifier related to the SCG candidate selected as the target SCG in step S4. Here, UE 100 may transmit the identifier to the target MCG when access to the target SCG is successful. UE 100 may also transmit the identifier to the target MCG regardless of whether access to the target SCG is successful. This enables the target MCG (new MN) to know whether UE 100 has selected the target SCG. UE 100 may also transmit an RRC Reconfiguration Complete message including the identifier to the target MCG. The identifier may be at least one of the Cell ID of the PSCell of the selected target SCG, the identifier of the SCG candidate configuration of the selected target SCG (condReconfigId-r16), and the ID of the SCG candidate in the above-described message configuration example 1 (SCG-ID). In addition, UE100 may apply the SCG settings and discard SCG settings other than the target SCG in response to successful access to the target MCG and / or in response to successful access to the target SCG.

[0083] On the other hand, if an SCG candidate satisfying the predetermined selection criteria cannot be selected as the target SCG (step S5: NO), in step S8, UE 100 starts access to the target MCG (PCell). Here, the description will proceed assuming that such access is successful. Then, in step S9, UE 100 may transmit, to the target MCG, information indicating that an SCG has not been selected. That is, UE 100 may transmit, to the target MCG, information indicating that a target SCG cannot be selected, without selecting a target SCG, in response to the absence of an SCG candidate satisfying the selection criteria. This enables the target MCG (new MN) to understand that UE 100 has not been able to select a target SCG. Note that UE 100 may transmit an RRC Reconfiguration Complete message including the information to the target MCG. Furthermore, UE 100 may discard the SCG configuration in response to successful access to the target MCG and / or in response to not selecting a target SCG. Alternatively, UE 100 may not discard the SCG configuration, and may continue radio measurement of the SCG and determination of trigger conditions in accordance with the SCG configuration. That is, the UE 100 behaves in the same manner as when the CPAC configuration is performed (falls back to the CPAC). The UE 100 may select, according to the configuration from the gNB 200, whether to discard the SCG configuration or to continue radio measurement of the SCG and determination of the trigger condition according to the SCG configuration without discarding the SCG configuration.

[0084] This operation flow describes an example in which UE100 transmits an identifier for an SCG candidate selected as the target SCG to the target MCG, but the target SCG (SN) accessed by UE100 may also notify the target MCG (new MN) of the access (and the identifier).

[0085] (4.5) SCG selection process The SCG selection process according to the embodiment, that is, step S4 in Fig. 14, will be described in detail. The UE 100 performs the SCG selection process using at least one of the following options.

[0086] (4.5.1) Option 1 In option 1 of the SCG selection process, the UE 100 selects a target SCG from among a plurality of set SCG candidates in accordance with a selection criterion that selects in descending order of radio quality, thereby enabling the UE 100 to select an appropriate target SCG.

[0087] When execution conditions (i.e., execution conditions in CPAC) are set for each of the multiple SCG candidates, UE100 may select the SCG candidate with the best wireless quality among the SCG candidates for which the execution conditions are satisfied as the target SCG.

[0088] For example, UE 100 may first extract an SCG (PSCell) for which an execution condition is satisfied from among a plurality of configured SCG candidates (a plurality of PSCell candidates). Alternatively, UE 100 may extract an SCG (PSCell) for which a minimum required radio quality threshold is satisfied from among a plurality of configured SCG candidates (a plurality of PSCell candidates). Second, UE 100 selects an SCG (PSCell) having the best radio quality from among the extracted SCGs (PSCells). Note that the radio quality may be RSRP and / or RSRQ measured by UE 100. Alternatively, UE 100 may first extract an SCG having the best radio quality from among a plurality of SCG candidates (a plurality of PSCell candidates), and second, if the extracted SCG satisfies the execution condition, select the SCG (PSCell).

[0089] (4.5.2) Option 2 In option 2 of the SCG selection process, the UE 100 selects a target SCG from among a plurality of set SCG candidates in accordance with a selection criterion for selecting in descending order of priority specified by the gNB 200 (MN). This enables the UE 100 to select an appropriate target SCG under network initiative.

[0090] When an execution condition (i.e., an execution condition in CPAC) is set for each of a plurality of SCG candidates, the UE 100 may select the SCG candidate with the highest priority among the SCG candidates for which the execution condition is satisfied as the target SCG 201S. Alternatively, when a minimum required wireless quality threshold is set for each of a plurality of SCG candidates, the UE 100 may select the SCG candidate with the highest priority among the SCG candidates for which the wireless quality threshold is satisfied as the target SCG 201S.

[0091] In this option 2, the gNB 200 configures the UE 100 with multiple SCG candidates in the order of its preference. For example, the priority may be determined in the order of entries in a list in which multiple SCG candidates are configured. Specifically, the first entry in the list has the highest priority. Alternatively, the priority may be determined in the order of the IDs (SCG-IDs) of the SCG candidates described above. Alternatively, the gNB 200 may assign an IE indicating priority to the SCG candidate configuration (list) so as to explicitly specify the priority.

[0092] The UE 100 checks whether the execution condition (or radio quality threshold) is satisfied for the SCG (PSCell) with the highest priority specified by the gNB 200. If the execution condition is satisfied, the UE 100 selects the SCG (PSCell), and if the execution condition is not satisfied, the UE 100 checks whether the execution condition (or radio quality threshold) is satisfied for the SCG with the next highest priority. Note that if there are multiple SCGs (PSCells) with the highest priority, the UE 100 may select the SCG (PSCell) with the better radio quality.

[0093] (4.5.3) Option 3 Option 3 of the SCG selection process is an option that assumes CPC. In this option 3, the UE 100 selects a target SCG 201S from multiple set SCG candidates according to a selection criterion that preferentially selects the SCG 201S with which the UE 100 is currently communicating. This allows the UE 100 to perform efficient target SCG selection.

[0094] For example, if there is an SCG (PSCell) with which UE 100 is currently communicating (used or configured) among multiple configured SCG candidates (multiple PSCell candidates), UE 100 provisionally selects the SCG (PSCell). If the provisionally selected SCG (PSCell) satisfies an execution condition (or a wireless quality threshold), UE 100 selects the SCG (PSCell), and if the execution condition (or wireless quality threshold) is not satisfied or if the currently communicating SCG is not present in the candidates, UE 100 executes option 1 or 2 above.

[0095] (4.5.4) Option 4 Option 4 of the SCG selection process is an exceptional operation when an SCG cannot be selected by the UE 100. If an SCG cannot be selected as a result of applying the above options 1 to 3 (if none of the SCG candidate settings satisfy the execution condition (or the wireless quality threshold)), the UE 100 does not select any SCG.

[0096] (4.5.5) Option 5 In option 5 of the SCG selection process, the UE 100 selects a target SCG 201S from among the multiple configured SCG candidates according to a selection criterion for selecting an SCG whose wireless quality satisfies a minimum quality standard. For example, the UE 100 may use this in combination with option 1 described above to select an SCG whose wireless quality is the best from among the SCGs that satisfy a minimum quality threshold. The UE 100 may also include only SCGs that satisfy the minimum quality threshold in the selection candidates.

[0097] (5) Other embodiments In the above-described embodiment, the DC in which the UE 100 communicates with an MCG and an SCG has been described. However, the present invention may also be applied to multi-connectivity (MC) in which the UE 100 communicates with an MCG and multiple SCGs. In this case, the UE 100 may select multiple SCGs in the above-described (4.5) SCG selection process. For example, when selecting two SCGs, the UE 100 may select an SCG with the best wireless quality and an SCG with the second best wireless quality. Alternatively, the UE 100 may select an SCG with the highest priority and an SCG with the second highest priority. The gNB 200 may configure the number of SCGs to be selected (which may be a selectable number or a permitted number of selections) for the UE 100. The UE 100 may specify the number of SCGs to be selected according to the configuration by the gNB 200. This configuration may be performed only in the case of an MC. In other words, this configuration may not be performed in the case of a DC. The UE 100 accesses the selected SCG in the same manner as in the above-described embodiment. Note that the UE 100 may access the selected SCG even if the number of selected SCGs does not reach the number of SCGs to be selected. For example, even if the number of SCGs to be selected is set to 2 and the number of selected SCGs is 1, access to the selected SCG is executed.

[0098] The above-mentioned operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow.

[0099] In the above embodiment, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The user equipment may also be an MT (Mobile Termination) of the IAB node.

[0100] A program may be provided that causes a computer to execute each process performed by UE100 or gNB200. The program may be recorded on a computer-readable medium. The computer-readable medium can be used to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0101] As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." Furthermore, the terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Furthermore, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0102] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0103] This application claims priority to U.S. Provisional Application No. 63 / 307,248 (filed February 7, 2022), the entire contents of which are incorporated herein by reference.

[0104] (Addendum) The following additional notes are about the features of the above-described embodiment.

[0105] (1) A communication method in which a user equipment communicates with a master cell group (MCG) and a secondary cell group (SCG), comprising: A master node managing the master cell group (MCG) transmits to the user equipment a radio resource control (RRC) message including a target MCG configuration for performing a conditional handover (CHO) to a target MCG and each SCG candidate configuration of a plurality of SCG candidates associated with the target MCG; receiving the RRC message by the user equipment; and when an execution condition in the CHO is satisfied, the user device selects one of the plurality of SCG candidates as a target SCG. Communication method.

[0106] (2) If the execution condition is satisfied, the method further includes the step of initiating access to the target MCG and initiating access to the selected target SCG. The communication method described in (1) above.

[0107] (3) the RRC message includes a first conditional RRC reconfiguration; The first conditional RRC reconfiguration comprises: condition information indicating the execution condition; the target MCG setting; a list including the SCG candidate configuration for each of the plurality of SCG candidates; The communication method according to (1) or (2) above.

[0108] (4) The list further includes, for each of the plurality of SCG candidates, at least one of an SCG identifier and a wireless quality threshold. A communication method according to any one of (1) to (3) above.

[0109] (5) the list includes a second conditional RRC reconfiguration for each of the plurality of SCG candidates; The second conditional RRC reconfiguration includes: condition information indicating execution conditions for the corresponding SCG candidate; the SCG candidate configuration for the corresponding SCG candidate; A communication method according to any one of (1) to (4) above.

[0110] (6) The selecting step includes selecting the target SCG from the plurality of SCG candidates according to a selection criterion for selecting in descending order of wireless quality. A communication method according to any one of (1) to (5) above.

[0111] (7) When execution conditions are set for each of the plurality of SCG candidates, The selecting step includes a step of selecting, as the target SCG, an SCG candidate having the best wireless quality from among the SCG candidates for which the execution condition is satisfied. A communication method according to any one of (1) to (6) above.

[0112] (8) The selecting step includes a step of selecting the target SCG from among the plurality of SCG candidates in accordance with a selection criterion for selecting in descending order of priority specified by the master node. A communication method according to any one of (1) to (7) above.

[0113] (9) When execution conditions are set for each of the plurality of SCG candidates, The selecting step includes a step of selecting, as the target SCG, an SCG candidate with the highest priority among the SCG candidates for which the execution condition is satisfied. A communication method according to any one of (1) to (8) above.

[0114] (10) The selecting step includes selecting the target SCG from the plurality of SCG candidates according to a selection criterion that preferentially selects an SCG with which the user device is currently communicating. A communication method according to any one of (1) to (9) above.

[0115] (11) The selecting step includes selecting the target SCG from the plurality of SCG candidates according to a selection criterion for selecting an SCG whose wireless quality satisfies a minimum quality standard. A communication method according to any one of (1) to (10) above.

[0116] (12) The method further comprises the step of the user device transmitting to the target MCG an identifier for the SCG candidate selected as the target SCG. A communication method according to any one of (1) to (11) above.

[0117] (13) The method further comprises the step of: in response to the absence of an SCG candidate that satisfies the selection criteria, the user device not selecting the target SCG and transmitting information indicating that the target SCG cannot be selected to the target MCG. A communication method according to any one of (6) to (11) above.

[0118] (14) A user equipment (UE) communicating with a master cell group (MCG) and a secondary cell group (SCG), comprising: A receiver that receives, from a master node that manages the master cell group (MCG), a radio resource control (RRC) message including a target MCG configuration for performing a conditional handover (CHO) to a target MCG and each SCG candidate configuration of a plurality of SCG candidates associated with the target MCG; a control unit that selects one of the plurality of SCG candidates as a target SCG when an execution condition in the CHO is satisfied. User equipment.

[0119] (15) A base station operating as a master node managing a master cell group (MCG) used by a user equipment, A transmitter is provided to transmit to the user equipment a radio resource control (RRC) message including a target MCG configuration for performing a conditional handover (CHO) to a target MCG and a secondary cell group (SCG) candidate configuration for each of a plurality of SCG candidates associated with the target MCG. Base station. [Explanation of symbols]

[0120] 1: Mobile communication system 100:UE 110: Receiving unit 120: Transmitter 130: Control unit 200 :gNB 200M :MN 200S :SN 201M:MCG 201S:SCG 210: Transmission unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication method in which a user equipment communicates with a master cell group (MCG) and a secondary cell group (SCG), comprising: A master node managing the master cell group (MCG) transmits to the user equipment a radio resource control (RRC) message including a target MCG configuration for performing a conditional handover (CHO) to a target MCG, an SCG configuration of a candidate SCG associated with the target MCG, condition information indicating an execution condition for a primary cell (PCell) in the target MCG, and condition information indicating an execution condition for a primary cell (PSCell) in the candidate SCG; the user equipment receiving the RRC message; The user equipment performs a PCell change involving a PSCell addition / change based on the RRC message. Communication method.

2. A user equipment communicating with a master cell group (MCG) and a secondary cell group (SCG), comprising: a receiver that receives, from a master node that manages the master cell group (MCG), a radio resource control (RRC) message including a target MCG setting for performing a conditional handover (CHO) to a target MCG, an SCG setting of a candidate SCG associated with the target MCG, condition information indicating an execution condition for a primary cell (PCell) in the target MCG, and condition information indicating an execution condition for a primary cell (PSCell) in the candidate SCG; and a control unit that executes a PCell change involving a PSCell addition / change based on the RRC message. User equipment.

3. A processor for controlling user equipment communicating with a master cell group (MCG) and a secondary cell group (SCG), comprising: A process of receiving a radio resource control (RRC) message from a master node managing the master cell group (MCG), the message including: a target MCG configuration for performing a conditional handover (CHO) to a target MCG; an SCG configuration of a candidate SCG associated with the target MCG; condition information indicating an execution condition for a primary cell (PCell) in the target MCG; and condition information indicating an execution condition for a primary cell (PSCell) in the candidate SCG; A process of performing a PCell change involving a PSCell addition / change based on the RRC message. Processor.

4. A program for controlling a user equipment that communicates with a master cell group (MCG) and a secondary cell group (SCG), A process of receiving a radio resource control (RRC) message from a master node managing the master cell group (MCG), the message including: a target MCG configuration for performing a conditional handover (CHO) to a target MCG; an SCG configuration of a candidate SCG associated with the target MCG; condition information indicating an execution condition for a primary cell (PCell) in the target MCG; and condition information indicating an execution condition for a primary cell (PSCell) in the candidate SCG; and causing the user equipment to perform a process of performing a PCell change involving a PSCell addition / change based on the RRC message. program.

5. A system including the user device and master node of claim 2.

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