Communication method, user equipment and base station

Abstract

A communication method according to a first aspect of the present invention is a method for allowing a user equipment to communicate with a primary cell group (MCG) and a secondary cell group (SCG), and comprises the steps of: transmitting, by a primary node managing the primary cell group (MCG), a radio resource control (RRC) message to the user equipment, the RRC message includes: a target MCG setting for performing conditional handover (CHO) to the target MCG, and an SCG candidate setting for each SCG candidate in a plurality of SCG candidates associated with the target MCG; receiving, by the user equipment, an RRC message; and selecting, by the user equipment, an SCG candidate from among the plurality of SCG candidates as a target SCG if an execution condition of the CHO is satisfied.

Description

Technical Field

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

[0002] The technical specifications of 3GPP (3rd Generation Partnership Project), a standardization program for mobile communication systems, have established specifications for conditional handover (CHO) and conditional PSCell change (CPC). According to 3GPP, the specifications for conditional primary and secondary cell addition (CPA: conditional PSCell addition) and inter-secondary node (inter-SN) CPC have been controversial. Note that CPC and CPA will also be collectively referred to as CPAC.

[0003] Reference List

[0004] Non-patent literature

[0005] NPL1: 3GPP Technical Specification “TS 38.300 V16.8.0” (2021-12) Summary of the invention

[0006] The present disclosure provides a communication method, a user equipment, and a base station that can simultaneously perform CHO and CPAC.

[0007] The communication method according to the first aspect is a communication method for a user equipment to communicate with a main cell group (MCG) and a secondary cell group (SCG), the communication method comprising the following steps: a master node that manages the main cell group (MCG) sends a radio resource control (RRC) message to the user equipment, the radio resource control message comprising: a target MCG configuration for performing a conditional handover (CHO) to a target MCG, and an SCG candidate configuration for each SCG candidate among a plurality of SCG candidates associated with the target MCG; the user equipment receives the RRC message; and when the execution condition of the CHO is met, the user equipment selects any SCG candidate from among the plurality of SCG candidates as the target SCG.

[0008] According to the second aspect, a user equipment is a user equipment for communicating with a main cell group (MCG) and a secondary cell group (SCG), the user equipment comprising: a receiver configured to receive a radio resource control (RRC) message from a master node managing the main cell group (MCG), the RRC message comprising: a target MCG configuration for performing a conditional handover (CHO) to a target MCG, and an SCG candidate configuration for each SCG candidate among a plurality of SCG candidates associated with the target MCG; and a controller configured to select any SCG candidate from the plurality of SCG candidates as the target SCG when an execution condition of the CHO is met.

[0009] A base station according to a third aspect is a base station for operating as a master node for managing a master cell group (MCG) used by a user equipment, the base station comprising: a transmitter configured to send a radio resource control (RRC) message to the user equipment, the radio resource control message comprising: a target MCG configuration for performing a conditional handover (CHO) to a target MCG, and an SCG candidate configuration for each SCG candidate of a plurality of SCG candidates associated with the target MCG. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a diagram showing a configuration of a mobile communication system according to an embodiment.

[0011] Figure 2 is a diagram showing a configuration of a user equipment (UE) according to an embodiment.

[0012] Figure 3 is a diagram showing the configuration of a gNB (base station) according to an embodiment.

[0013] Figure 4 is a diagram showing a configuration of a protocol stack of a radio interface of a user plane processing data.

[0014] Figure 5 : is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that processes signaling (control signals).

[0015] Figure 6 It is a diagram for explaining the outline of DC according to the embodiment.

[0016] Figure 7 is a diagram for explaining CHO according to the embodiment.

[0017] Figure 8 is a diagram for explaining CPC according to the embodiment.

[0018] Fig. 9 is a diagram for explaining CPA according to the embodiment.

[0019] Fig.10 is a diagram for explaining an operation of simultaneously performing CHO and CPC according to an embodiment.

[0020] Fig.11 is a diagram for explaining an operation of simultaneously performing CHO and CPA according to an embodiment.

[0021] Fig.12 is a diagram showing a configuration example 1 of an RRC message according to the embodiment.

[0022] Fig.13 is a diagram showing configuration example 2 of an RRC message according to the embodiment.

[0023] Fig.14 is a diagram showing an example of an operation flow of a UE according to an embodiment. DETAILED DESCRIPTION

[0024] The mobile communication system according to the embodiment is described with reference to the accompanying drawings. In the description of the drawings, the same or similar reference numerals represent the same or similar parts.

[0025] (1) Configuration of mobile communication system

[0026] First, the configuration of a mobile communication system according to the embodiment is described. Figure 1 1 is a diagram showing a configuration of a mobile communication system according to an embodiment. The mobile communication system 1 complies with the fifth generation system (5GS) of the 3GPP standard. The following description takes 5GS as an example, but a long term evolution (LTE) system or a sixth generation (6G) system may be at least partially applied to the mobile communication system.

[0027] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (next generation 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.

[0028] UE 100 is a mobile wireless communication device. UE 100 may be any device as long as UE 100 is used by a user. Examples of UE 100 include a mobile phone terminal (including a smart phone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided on a sensor, a vehicle or a device provided on a vehicle (vehicle UE), or a flying object and a device provided on the flying object (air UE).

[0029] The NG-RAN 10 includes a base station (referred to as a "gNB" in a 5G system) 200. The gNBs 200 are interconnected via an Xn interface which is an interface between base stations. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100, which has established a connection to the cell of the gNB 200. The gNB 200 has a radio resource management (RRM) function, a function of routing user data (hereinafter, referred to as "data"), a measurement control function for mobility control and scheduling, and the like. "Cell" is used as a term to represent the smallest unit of a wireless communication area. "Cell" is also used as a term to represent a function or resource used to perform wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter referred to as "frequency").

[0030] Note that the gNB can be connected to the Evolved Packet Core (EPC) corresponding to the core network of LTE. The LTE base station can also be connected to the 5GC. The LTE base station and the gNB can be connected via an inter-base station interface.

[0031] 5GC 20 includes an access and mobility management function (AMF) and a user plane function (UPF) 300. AMF performs various types of mobility control, etc. for UE 100. AMF manages the mobility of UE 100 by communicating with UE 100 using non-access stratum (NAS) signaling. UPF controls data transmission. AMF and UPF are connected to gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0032] Figure 2 1 is a diagram showing a configuration of a UE 100 (User Equipment) according to an embodiment. The UE 100 includes a receiver 110, a transmitter 120, and a controller 130. The receiver 110 and the transmitter 120 constitute a wireless communicator that performs wireless communication with the gNB 200.

[0033] The receiver 110 performs various types of reception under the control of the controller 130. The receiver 110 includes an antenna and a receiving device. The receiving device converts a radio signal received through the antenna into a baseband signal (received signal) and outputs the obtained signal to the controller 130.

[0034] The transmitter 120 performs various types of transmission under the control of the controller 130. The transmitter 120 includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller 130 into a radio signal and transmits the resultant signal through the antenna.

[0035] The controller 130 performs various types of control and processing in the UE 100. Such processing includes processing of various layers to be described later. The controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for processing by the processor. The processor may include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes the program stored in the memory, thereby performing various types of processing.

[0036] Figure 32 is a diagram showing a 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 communicator 240. The transmitter 210 and the receiver 220 constitute a wireless communicator that performs wireless communication with the UE 100. The backhaul communicator 240 constitutes a network communicator that performs communication with the CN 20.

[0037] The transmitter 210 performs various types of transmission under the control of the controller 230. The transmitter 210 includes an antenna and a transmission device. The transmission device converts a baseband signal (transmission signal) output by the controller 230 into a radio signal and transmits the resulting signal through the antenna.

[0038] The receiver 220 performs various types of reception under the control of the controller 230. The receiver 220 includes an antenna and a receiving device. The receiving device converts a radio signal received through the antenna into a baseband signal (received signal) and outputs the obtained signal to the controller 230.

[0039] The controller 230 performs various types of control and processing in the gNB 200. Such processing includes processing of various layers to be described later. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes the program stored in the memory, thereby performing various types of processing.

[0040] The backhaul communicator 240 is connected to the neighboring base station via the Xn interface which is an interface between base stations. The backhaul communicator 240 is connected to the AMF / UPF 300 via the NG interface between the base station and the core network. Note that the gNB 200 may include a central unit (CU) and a distributed unit (DU) (ie, the functions are divided), and the two units may be connected via the F1 interface which is a fronthaul interface.

[0041] Figure 4 is a diagram showing a configuration of a protocol stack of a radio interface of a user plane processing data.

[0042] The radio interface protocol of the user plane 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.

[0043] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Data and control information are transmitted between the PHY layer of UE 100 and the PHY layer of gNB 200 via a physical channel. Note that the PHY layer of UE 100 receives downlink control information (DCI) transmitted from gNB 200 through a physical downlink control channel (PDCCH). Specifically, UE 100 blindly decodes PDCCH using a radio network temporary identifier (RNTI) and obtains the successfully decoded DCI as DCI addressed to UE 100. The DCI transmitted from gNB 200 is attached with CRC parity bits scrambled by RNTI.

[0044] The MAC layer performs priority control of data, retransmission processing by hybrid ARQ (HARQ: Hybrid Automatic Repeat Request), a random access procedure, etc. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of gNB 200 via a transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) in uplink and downlink and the resource blocks to be allocated to UE 100.

[0045] The RLC layer transmits data to the RLC layer of the receiving side by using the functions of the MAC layer and the 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 a logical channel.

[0046] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0047] The SDAP layer performs mapping between IP flows (as a unit of QoS (Quality of Service) control performed by the core network) and radio bearers (as a unit of QoS control performed by the access stratum (AS)). Note that when the RAN is connected to the EPC, SDAP does not need to be provided.

[0048] Figure 5 : is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that processes signaling (control signals).

[0049] The protocol stack of the radio interface of the control plane includes the Radio Resource Control (RRC) layer and the Non-Access Stratum (NAS) layer instead of Figure 4 The SDAP layer shown in .

[0050] RRC signaling for various configurations is sent between the RRC layer of UE 100 and the RRC layer of gNB 200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, reestablishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE 100 and the RRC of gNB 200, UE 100 is in the RRC connected state. When there is no connection (RRC connection) between the RRC of UE 100 and the RRC of gNB 200, UE 100 is in the RRC idle state. When the connection between the RRC of UE 100 and the RRC of gNB 200 is suspended, UE 100 is in the RRC inactive state.

[0051] NAS located above the RRC layer performs session management, mobility management, etc. NAS signaling is sent between the NAS of the UE 100 and the NAS of the AMF 300A. Note that the UE 100 includes an application layer in addition to the protocol of the radio interface. A layer lower than the NAS is called an access stratum (AS).

[0052] (2) Dual connection

[0053] An outline of dual connectivity (DC) according to the embodiment will be described. Figure 6 It is a diagram for explaining the outline of DC according to the embodiment.

[0054] According to DC, UE 100 performs simultaneous communication with a main cell group (MCG) 201M managed by a main node (MN) 200M and a secondary cell group (SCG) 201S managed by a secondary node (SN) 200S. MN 200M may be an NR base station (gNB) or an LTE base station (eNB). MN 200M is also referred to as a main base station. SN 200S may be an NR base station (gNB) or an LTE base station (eNB). SN 200S is also referred to as a secondary base station. MN 200M and SN 200S may be 6G base stations. Hereinafter, an example in which each of MN 200M and SN 200S is an NR base station (gNB) will be mainly described.

[0055] For example, through the network interface between MN 200M and SN 200S, MN 200M sends a predetermined message (e.g., SN attachment request message) to SN 200S, and MN 200M sends an RRC reconfiguration message to UE 100 to start DC. The schedulers of MN 200M and SN 200S allocate radio resources to UE 100 in the RRC connection state to perform wireless communication using the radio resources of MN 200M and the radio resources of SN 200S. The network interface between MN 200M and SN 200 may be an Xn interface (or an X2 interface). MN 200M and SN 200 communicate with each other via the network interface.

[0056] MN 200M may have a control plane connection with a core network. MN 200M provides primary radio resources for UE 100. MN 200M manages MCG 201M. MCG 201M is a group of serving cells associated with MN 200M. MCG 201M includes a primary cell (PCell) and optionally one or more secondary cells (SCells). MN 200M controls and manages the configuration of UE 100.

[0057] The SN 200S may not have a control plane connection with the core network. The SN 200S provides additional radio resources to the UE 100. The SN 200S manages the SCG 201S. The SCG 201S includes a primary secondary cell (PSCell) and optionally one or more SCells. Note that the PCell of the MCG 201M and the PSCell of the SCG 201S are also referred to as special cells (SPCells).

[0058] (3) Overview of conditional reconfiguration

[0059] An outline of conditional reconfiguration according to the embodiment will be described.

[0060] (3.1) Conditional Switch (CHO)

[0061] According to CHO, a handover execution condition is configured to the UE 100 in advance, and handover is performed when the configured execution condition is satisfied in the UE 100 . Figure 7 is a diagram for explaining CHO according to the embodiment.

[0062] Figure 7An example is shown in which the base station managing the source cell is gNB 200, the base station managing candidate cell #1 is gNB 200C-1, and the base station managing candidate cell #2 is gNB 200C-2. However, these cells may be managed by one base station. Two candidate cells (candidate cell #1 and candidate cell #2) are shown. However, the number of candidate cells may be one, or may be three or more. UE 100 is in the RRC connected state of the source cell.

[0063] In step 1, gNB 200 sends an RRC reconfiguration message to UE 100, which includes a conditional RRC reconfiguration (conditional reconfiguration) as a CHO configuration. 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 of each of candidate cell #1 and candidate cell #2) generated by a candidate gNB 200C (i.e., gNB 200C-1 and gNB 200C-2) and condition information indicating an execution condition generated by a source gNB 200 (i.e., gNB 200). 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 for configuring the radio quality of a measurement target, a threshold to be compared with the radio quality, and the like. UE 100 starts evaluating the execution condition.

[0064] In step 2, in response to the execution condition configured in step 1 being satisfied, UE 100 initializes access to the candidate cell (here, candidate cell #1) that has satisfied the execution condition. From the point in time when UE 100 starts synchronizing with candidate cell #1, UE 100 may not monitor the source cell.

[0065] In step 3, when UE 100 successfully accesses candidate cell #1, UE 100 switches the connection from the source cell to candidate cell #1. Thus, the handover is completed. UE 100 communicates with candidate cell #1 using the candidate cell configuration (configuration information of candidate cell #1) received in step 1.

[0066] (3.2) Conditional PSCell Change (CPC)

[0067] According to CPC, an execution condition of the PSCell change is configured to the UE 100 in advance, and when the configured execution condition is satisfied in the UE 100, the PSCell change is performed. Figure 8 201S-1) is a diagram for explaining CPC according to an embodiment. It is assumed that UE 100 has connection with gNB 200M (MCG 201M) as MN and gNB 200S-1 (SCG 201S-1) as SN, and performs communication of DC scheme.

[0068] CPC includes: intra-SN CPC, which changes a PSCell from one cell to another cell in one SN 200S; and inter-SN CPC, which changes a PSCell from a cell of one SN 200S to a cell of another SN 200S. Inter-SN CPC will be mainly described below. However, the embodiment is not limited to inter-SN CPC, and may be intra-SN CPC.

[0069] In step 1, the gNB 200M as the MN sends an RRC reconfiguration message to the UE 100, which includes a conditional reconfiguration as a CPC configuration. The CPC configuration includes, for example, an SCG candidate configuration generated by the gNB 200S-2 as the SN candidate (i.e., configuration information of the PSCell of the SCG candidate 201S-2 of the gNB 200-2, for example, and may optionally include SCell configuration information) and condition information indicating an execution condition generated by the MN (i.e., gNB 200M). The SCG candidate configuration and the execution condition are associated with each other. Different execution conditions may be associated with multiple SCG candidate configurations. The execution condition is information for configuring the radio quality of the measurement target, the threshold to be compared with the radio quality, etc. The UE 100 starts to evaluate the execution condition.

[0070] In step 2, in response to the execution condition configured in step 1 being satisfied, the UE 100 initiates access to the PSCell of the SCG candidate 201S-2 that satisfies the execution condition.

[0071] In step 3, when UE 100 successfully accesses SCG candidate 201S-2 (PSCell), UE 100 switches PSCell from SCG 201S-1 (gNB 200S-1) to SCG 201S-2 (gNB 200S-2). Thus, the PSCell change is completed. UE 100 communicates with SCG 201S-2 using the SCG candidate configuration (configuration information of SCG 201S-2) received in step 1.

[0072] (3.3) Conditional PSCell Addition (CPA)

[0073] According to the CPA, the execution condition of the PSCell addition is configured to the UE 100 in advance, and when the configured execution condition is satisfied in the UE 100, the PSCell addition is performed. Fig. 9 UE 100 is in an RRC connected state in MCG 201M.

[0074] In step 1, gNB 200M as MN sends an RRC reconfiguration message to UE 100, which includes conditional reconfiguration as CPA configuration. The CPA configuration includes, for example, SCG candidate configurations (e.g., configuration information of each of SCG candidate 201S-1 and SCG candidate 201S-2) generated by SN candidates (gNB 200S-1 and gNB 200S-2) and condition information indicating execution conditions generated by MN (i.e., gNB200M). The SCG candidate configuration and the execution condition are associated with each other. Different execution conditions can be associated with multiple SCG candidate configurations. The execution condition is information for configuring the radio quality of the measurement target, the threshold to be compared with the radio quality, etc. UE 100 starts evaluating the execution condition.

[0075] In step 2, in response to the execution condition configured in step 1 being satisfied, UE 100 initiates access to the PSCell of the SCG candidate (here, SCG candidate 201S-1) that satisfies the execution condition.

[0076] In step 3, when successfully accessing the SCG candidate 201S-1 (PSCell), the UE 100 starts communication of the DC scheme. The UE 100 uses the SCG candidate configuration received in step 1 (configuration information of the SCG 201S-1) to communicate with the SCG 201S-1.

[0077] (4) Operation of mobile communication system

[0078] The operation of the mobile communication system 1 according to the embodiment will be described, more specifically, the operation for simultaneously performing CHO and CPAC (CPC and CPA). According to this operation, how the gNB 200 (MN) configures a plurality of SCG candidates to the UE 100 may become a problem. How the UE 100 determines the target SCG from the plurality of SCG candidates may become a problem.

[0079] In an embodiment, UE 100 communicates with MCG 201M and SCG 201S via DC. First, MN 200M managing MCG 201M sends an RRC message (more specifically, conditional reconfiguration) to UE 100, which includes: a target MCG configuration for performing CHO to the target MCG, and an SCG candidate configuration for each SCG candidate among the multiple SCG candidates associated with the target MCG. UE 100 receives the RRC message. Secondly, when the execution condition of CHO (also referred to as a "trigger condition") is met, UE 100 selects any SCG candidate from the multiple SCG candidates as the target SCG. Therefore, CHO and CPAC (CPC and CPA) can be performed simultaneously. When the execution condition of CHO is met, UE 100 can initialize access to the target MCG and initialize access to the selected target SCG.

[0080] (4.1) Execute CHO and CPC operations simultaneously

[0081] An operation of simultaneously performing CHO and CPC according to an embodiment will be described. Fig.10 2 is a diagram showing an operation of performing CHO and CPC simultaneously according to an embodiment. It is assumed that UE 100 has a connection with gNB 200M-1 (MCG 201M-1) as MN and gNB 200S-1 (SCG 201S-1) as SN, and performs communication of the DC scheme. Fig.10 The one SCG candidate 201S-2 is shown, but it is assumed that there are multiple SCG candidates. In the following, in order to simplify the description, it is assumed that one MCG candidate (target MCG) is configured at CHO. However, multiple MCG candidates can be configured during CHO. Multiple SCG candidates can be configured for each of the multiple MCG candidates.

[0082] In step 1, gNB 200M-1 as MN sends an RRC reconfiguration message to UE 100, which includes a conditional RRC reconfiguration (conditional reconfiguration) as CHO and CPC configuration. The conditional reconfiguration (first conditional RRC reconfiguration) includes: condition information indicating the execution condition of CHO; a target MCG configuration, which is the configuration information of the target MCG 201M-2; and a list including the SCG candidate configuration of each SCG candidate in the multiple SCG candidates. The target MCG configuration includes information necessary for communication with the target MCG 201M-2 (PCell). The SCG candidate configuration includes information necessary for communication with the corresponding SCG (PSCell). The details of the configuration of the conditional reconfiguration will be described later.

[0083] In step 2, in response to the execution condition of the CHO configured in step 1 being satisfied, the UE 100 selects a target SCG from the multiple SCG candidates configured in step 1. The details of the target SCG selection process will be described later. The UE 100 initializes access to the target MCG 201M-2 (PCell) and also initializes access to the PSCell of the selected target SCG (here, the SCG candidate 201S-2). For example, the UE 100 may initialize access to the target SCG 201S-2 (PSCell) after successfully accessing the target MCG 201M-2 (PCell).

[0084] In step 3, when successfully accessing the target MCG 201M-2 (PCell), the UE 100 switches the PCell (MN) from MCG201M-1 (gNB 200M-1) to MCG 201M-2 (gNB 200M-2). When successfully accessing the target SCG 201S-2 (PSCell), the UE 100 switches the PSCell (SN) from SCG 201S-1 (gNB 200S-1) to SCG 201S-2 (gNB200S-2). Therefore, CHO and CPC are completed. The UE 100 uses the target MCG configuration received in step 1 to communicate with MCG201M-2 (PCell). The UE 100 uses the SCG configuration of the target SCG among the multiple candidate SCG configurations received in step 1 to communicate with SCG 201S-2 (PSCell).

[0085] (4.2) Execute CHO and CPA operations simultaneously

[0086] An operation of simultaneously performing CHO and CPA according to an embodiment will be described. Fig.11 1 is a diagram for explaining an operation of simultaneously performing CHO and CPA according to an embodiment. UE 100 has a connection with gNB 200M-1 (MCG 201M-1) which is a MN.

[0087] In step 1, gNB 200M-1 as MN sends an RRC reconfiguration message to UE 100, which includes a conditional RRC reconfiguration (conditional reconfiguration) as CHO and CPA configuration. The conditional reconfiguration (first conditional RRC reconfiguration) includes: condition information indicating the execution condition of CHO; a target MCG configuration, which is the configuration information of the target MCG 201M-2; and a list including the SCG candidate configuration of each SCG candidate in the multiple SCG candidates. The target MCG configuration includes information necessary for communication with the target MCG 201M-2 (PCell). The SCG candidate configuration includes information necessary for communication with the corresponding SCG (PSCell). The details of the configuration of the conditional reconfiguration will be described later.

[0088] In step 2, in response to the execution condition of the CHO configured in step 1 being satisfied, the UE 100 selects a target SCG from the multiple SCG candidates configured in step 1. The details of the target SCG selection process will be described below. The UE 100 initializes access to the target MCG 201M-2 (PCell) and initializes access to the PSCell of the selected target SCG (here, the SCG candidate 201S-1). For example, the UE 100 may initialize access to the target SCG 201S-1 (PSCell) after successfully accessing the target MCG 201M-2 (PCell).

[0089] In step 3, when successfully accessing the target MCG 201M-2 (PCell), UE 100 switches PCell (MN) from MCG201M-1 (gNB 200M-1) to MCG 201M-2 (gNB 200M-2). When UE 100 successfully accesses the target SCG201S-2 (PSCell), PSCell (SN) is added to SCG 201S-1 (gNB 200S-1). Therefore, CHO and CPA are completed. UE 100 uses the target MCG configuration received in step 1 to communicate with MCG 201M-2 (PCell). UE 100 uses the SCG configuration of the target SCG among the multiple candidate SCG configurations received in step 1 to communicate with SCG 201S-1 (PSCell).

[0090] (4.3) Message Configuration Example

[0091] An example of configuration of an RRC message according to an embodiment, more specifically, a conditional reconfiguration (first conditional RRC reconfiguration) will be described. As described above, the conditional reconfiguration in the RRC message according to the embodiment is sent from the gNB 200 (MN) to the UE 100. The conditional reconfiguration includes: a target MCG configuration for performing CHO to the target MCG, and an SCG candidate configuration for each of a plurality of SCG candidates associated with the target MCG. That is, the conditional reconfiguration includes an MCG configuration for performing the conditional reconfiguration and the plurality of SCG candidate configurations associated with the MCG configuration.

[0092] (4.3.1) Message Configuration Example 1

[0093] Fig.12 1 is a diagram showing a configuration example 1 of an RRC message according to an embodiment. The gNB 200 (MN) transmits an RRC message (RRC reconfiguration message) for performing CHO and CPAC (CPC and CPA) simultaneously to the UE 100. The RRC reconfiguration message includes Conditional Reconfiguration-r16 as an information component. Here, "-r16" indicates an information element introduced by 3GPP Release 16.

[0094] ConditionalReconfiguration-r16 includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to be added or modified for the MCG (MN). Each entry of condReconfigToAddModList-r16 (CondReconfigToAddMod-r16) corresponds to a first conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, and encapsulates the RRC reconfiguration that needs to be applied when the execution condition is met for condRRCReconfig-r16. CondReconfigToAddMod-r16 also includes condExecutionCond-r16 (not shown) as condition information, which indicates the execution condition that needs to be met to trigger the execution of the corresponding conditional reconfiguration.

[0095] CondRRCReconfig-r16 (RRCReconfiguration) includes the masterCellGroup configured as the target MCG. In this configuration example 1, condRRCReconfig-r16 (RRCReconfiguration) also includes secondaryCellGroupCandidateList, which is a new list including information of each SCG candidate (target SCG).

[0096] Each entry in the list (secondaryCellGroupCandidateList) includes a secondaryCellGroup (or mrdc-SecondaryCellGroup), which is the configuration information of the SCG candidate (target SCG). Each entry in the list (secondaryCellGroupCandidateList) may also include at least one of an SCG identifier (SCG-ID) or a radio quality threshold. The SCG identifier (SCG-ID) is an identifier for identifying the SCG. The radio quality threshold is the reference signal received power (RSRP) and / or reference signal received quality (RSRQ) when selecting the SCG, more specifically, the minimum necessary quality threshold of the SCG for selecting the SCG.

[0097] According to this configuration example 1, the plurality of SCG candidates can be appropriately configured to the UE 100 .

[0098] (4.3.2.) Message Configuration Example 2

[0099] Fig.13 2 is a diagram showing a configuration example 2 of an RRC message according to an embodiment. The gNB 200 (MN) transmits an RRC message (RRC reconfiguration message) for simultaneously performing CHO and CPAC (CPC and CPA) to the UE 100. The RRC reconfiguration message includes conditional reconfiguration-r16 (Reconfiguration-r16) as an information component.

[0100] ConditionalReconfiguration-r16 includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to be added or modified for the MCG (MN). Each entry of condReconfigToAddModList-r16 (CondReconfigToAddMod-r16) corresponds to a first conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, and encapsulates the RRC reconfiguration that needs to be applied when the execution condition is met for condRRCReconfig-r16. CondReconfigToAddMod-r16 also includes condExecutionCond-r16 (not shown) as condition information, which indicates the execution condition that needs to be met to trigger the execution of the corresponding conditional reconfiguration.

[0101] CondRRCReconfig-r16 (RRCReconfiguration) includes a masterCellGroup configured as a target MCG. 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 of condReconfigToAddModList-r16 (CondReconfigToAddMod-r16) corresponds to a second conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates the RRC reconfiguration that needs to be applied when the execution condition is met, and the RRC reconfiguration includes an SCG candidate configuration (secondaryCellGroup or mrdcSecondaryCellGroup) as configuration information of the SCG candidate (target SCG). CondReconfigToAddMod-r16 also includes condExecutionCond-r16 (not shown) as condition information indicating an execution condition that needs to be satisfied to trigger execution of the corresponding conditional reconfiguration.

[0102] As described above, 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 of the corresponding SCG candidate and the SCG candidate configuration (secondaryCellGroup or mrdc SecondaryCellGroup) of the corresponding SCG candidate.

[0103] According to this configuration example 2, the plurality of SCG candidates can be appropriately configured to the UE 100. According to this configuration example 2, the execution condition can be configured to the UE 100 for each SCG.

[0104] (4.4) Example of operation flow

[0105] An example of an operation flow of the UE 100 according to the embodiment will be described. Fig.14 is a diagram showing an example of an operation flow of the UE 100 according to an embodiment.

[0106] In step S1, UE 100 receives an RRC message (RRC reconfiguration message) for simultaneously performing CHO and CPAC (CPC and CPA) from gNB 200. The RRC message has the configuration of message configuration example 1 or message configuration example 2 described above.

[0107] In step S2, UE 100 performs radio quality measurement and determines whether the execution condition configured for the target MCG (i.e., the CHO execution condition) has been met. The CHO execution condition may be condEventA3 or condEventA5 defined by the technical specifications of 3GPP. In the case of the above-mentioned message configuration example 1, UE 100 may determine, for each SCG, whether the corresponding radio quality threshold has been met. In the case of the above-mentioned message configuration example 2, UE 100 may determine, for each configured SCG candidate, whether the corresponding execution condition (i.e., the CPAC execution condition) has been met. The CPAC execution condition may be condEventA3, condEventA4, condEventA5, etc. defined by the technical specifications of 3GPP. Note that even when the SCG candidate meets the execution condition, UE 100 does not perform (suspend) access to the SCG candidate at this point in time.

[0108] When it is determined that the execution condition (CHO execution condition) configured for the MCG 201M has been satisfied (step S3: "Yes"), in step S4, the UE 100 selects a target SCG (PSCell) from the configured multiple SCG candidates. The details of the selection process will be described later. Note that when there is no SCG candidate that satisfies the predetermined selection criteria, the UE 100 may not be able to select a target SCG (PSCell). That is, the UE 100 does not select a target SCG.

[0109] When an SCG candidate satisfying the predetermined selection criteria is selected as the target SCG (step S5: "Yes"), in step S6, UE 100 initializes access to the target MCG (PCell). UE 100 also starts accessing the selected target SCG. Here, the following description is given assuming that such access has been successful.

[0110] In step S7, UE 100 may send an identifier associated with the SCG candidate selected as the target SCG in step S4 to the target MCG. Here, when access to the target SCG is successful, UE 100 may send the identifier to the target MCG. Regardless of whether access to the target SCG is successful, UE 100 may send the identifier to the target MCG. Therefore, the target MCG (new MN) may grasp whether UE 100 has selected the target SCG. Note that UE 100 may send an RRC reconfiguration message including the identifier to the target MCG. The identifier may be at least one selected from the group consisting of the following items in the above-mentioned message configuration example 1: the CellID 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 (SCG-ID). In response to access to the target MCG having been successful and / or access to the target SCG having been successful, UE 100 may apply the SCG configuration and discard SCG configurations other than the SCG.

[0111] On the other hand, when the SCG candidate that meets the predetermined selection criteria cannot be selected as the target SCG (step S5: "No"), in step S8, the UE 100 initializes access to the target MCG (PCell). Here, the following description is given under the assumption that such access has been successful. In step S9, the UE 100 may send information indicating that the SCG has not yet been selected to the target MCG. That is, the UE 100 may send information indicating that the target SCG cannot be selected to the target MCG without selecting the target SCG based on the absence of an SCG candidate that meets the selection criteria. Therefore, the target MCG (new MN) may grasp that the UE 100 is not yet able to select the target SCG. Note that the UE 100 may send an RRC reconfiguration completion message including the information to the target MCG. In response to the access to the target MCG having been successful and / or in response to the target SCG not being selected, the UE 100 may discard the SCG configuration. Alternatively, the UE 100 may continue the radio measurement of the SCG and the determination of the triggering condition based on the SCG configuration without discarding the SCG configuration. That is, the behavior of UE 100 (fallback to CPAC) is similar to the case where CPAC configuration has been performed. UE 100 can choose whether to discard the SCG configuration according to the configuration from gNB 200, or to continue the radio measurement of the SCG and the determination of the triggering condition according to the SCG configuration without discarding the SCG configuration.

[0112] In this operation flow, an example has been described in which an identifier related to the SCG candidate selected as the target SCG is transmitted from the UE 100 to the target MCG. However, the target SCG (SN) accessed from the UE 100 may notify the target MCG (new MN) of the access (and the identifier).

[0113] (4.5) SCG selection process

[0114] The details of the SCG selection process according to the embodiment will be described. Fig.14 UE 100 performs SCG selection processing according to at least one of the following options.

[0115] (4.5.1) Option 1

[0116] According to Option 1 of the SCG selection process, the UE 100 selects a target SCG from among the configured multiple SCG candidates according to a selection criterion for selecting the configured multiple SCG candidates in descending order of radio quality. Therefore, the UE 100 can select an appropriate target SCG.

[0117] When an execution condition (ie, a CPAC execution condition) is configured for each of the multiple SCG candidates, UE 100 may select an SCG candidate having the best radio quality as a target SCG among the SCG candidates that have satisfied the execution condition.

[0118] For example, first, the UE 100 extracts an SCG (PSCell) that meets the execution condition from the configured multiple SCG candidates (multiple PSCell candidates). Alternatively, the UE 100 may extract an SCG (PSCell) that meets the minimum required radio quality threshold from the configured multiple SCG candidates (multiple PSCell candidates). Secondly, the UE 100 selects an SCG (PSCell) with the best radio quality from the extracted SCGs (PSCells). Note that the radio quality may be RSRP and / or RSRQ measured by the UE 100. Alternatively, the UE 100 may first extract an SCG with the best radio quality from the multiple SCG candidates (the multiple PSCell candidates), and secondly, when the extracted SCG meets the execution condition, select the SCG (PSCell).

[0119] (4.5.2) Option 2

[0120] According to Option 2 of the SCG selection process, the UE 100 selects a target SCG from among the configured multiple SCG candidates according to a selection criterion for selecting the configured multiple SCG candidates in descending order of priority specified by the gNB 200 (MN). Therefore, the UE 100 can select an appropriate target SCG according to the initiative of the network.

[0121] When an execution condition (i.e., a CPAC execution condition) is configured for each of the multiple SCG candidates, UE100 can select an SCG candidate with the highest priority among the SCG candidates that have satisfied the execution condition as the target SCG 201S. Alternatively, when a minimum required radio quality threshold is configured for each of the multiple SCG candidates, UE100 can select an SCG candidate with the highest priority among the SCG candidates that have satisfied the radio quality threshold as the target SCG 201S.

[0122] According to Option 2, gNB 200 configures the multiple SCG candidates to UE 100 in the order desired by gNB 200. For example, the priority may be higher in the order of the entries in the list in which the multiple SCG candidates are configured. More specifically, the first entry in the list is the highest priority. Alternatively, the priority may be higher in the order of the IDs (SCG-IDs) of the above-mentioned SCG candidates. Alternatively, gNB 200 may assign an IE indicating priority in order to explicitly specify the priority to the SCG candidate configuration (list).

[0123] UE 100 checks whether the SCG (PSCell) with the highest priority designated by gNB 200 satisfies the execution condition (or radio quality threshold). When the execution condition is satisfied, UE 100 selects the SCG (PSCell), and when the execution condition is not satisfied, UE 100 checks whether the SCG with the second highest priority satisfies the execution condition (or radio quality threshold). Note that when there are multiple SCGs (PSCells) with the highest priority, UE 100 can select an SCG (PSCell) with better radio quality.

[0124] (4.5.3) Option 3

[0125] Option 3 of the SCG selection process is an option assuming CPC. According to this option 3, the UE 100 selects a target SCG 201S from a plurality of configured SCG candidates according to a selection criterion for preferentially selecting the SCG 201S with which the UE 100 is currently communicating. Therefore, the UE 100 can effectively select a target SCG.

[0126] When, for example, there is an SCG (PSCell) (SCG being used or configured) with which the UE 100 is currently communicating among the configured multiple SCG candidates (multiple PSCell candidates), the UE 100 temporarily selects the SCG (PSCell). When the temporarily selected SCG (PSCell) satisfies the execution condition (or radio quality threshold), the UE 100 selects the SCG (PSCell). When the temporarily selected SCG does not satisfy the execution condition (or radio quality threshold), or when the SCG with which the UE 100 is currently communicating is not a candidate, the UE 100 performs the above-mentioned option 1 or 2.

[0127] (4.5.4) Option 4

[0128] Option 4 of the SCG selection process is an exceptional operation in the case where the UE 100 cannot select an SCG. When an SCG cannot be selected as a result of applying the above options 1 to 3 (when no SCG candidate configuration satisfies the execution condition (or radio quality threshold)), the UE 100 does not select any SCG.

[0129] (4.5.5) Option 5

[0130] According to option 5 of the SCG selection process, the UE 100 selects a target SCG 201S from a plurality of configured SCG candidates according to a selection criterion for selecting an SCG whose radio quality meets a minimum quality standard. For example, in combination with option 1 above, the UE 100 may select an SCG with the best radio quality from among the SCGs that meet a minimum quality threshold. The UE 100 may include only the SCGs that meet the minimum quality threshold as selection targets.

[0131] (5) Other embodiments

[0132] The above embodiment has described DC, in which the UE 100 communicates with the MCG and the SCG. However, the embodiment may be applied to multi-connectivity (MC), in which the UE 100 communicates with the MCG and multiple SCGs. In this case, the UE 100 may select multiple SCGs in the above (4.5) SCG selection process. When two SCGs are selected, for example, an SCG with the best radio quality and an SCG with the second best radio quality may be selected. An SCG with the highest priority and an SCG with the second highest priority may be selected. The gNB 200 may configure the number of SCGs that need to be selected for the UE 100 (which may be a selectable number or a selectable number). The UE 100 may specify the number of SCGs to be selected according to the configuration of the gNB 200. This configuration may be performed only in the case of MC. That is, in the case of DC, this configuration may not be performed. The UE 100 accesses the selected SCG similarly to the above 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 that need to be selected. Even when, for example, the number of SCGs that need to be selected is configured as two and the number of selected SCGs is one, access to the selected SCG is performed.

[0133] The above operation flow can be implemented individually and independently, and can also be implemented by combining two or more of the operation flows. For example, some steps of one operation flow can be added to another operation flow, or some steps of one operation flow can be replaced by some steps of another operation flow.

[0134] The above embodiments have described an example in which the base station is an NR base station (ie, gNB). However, the base station may be an LTE base station (ie, eNB) or a 6G base station. The base station may be a relay node, such as an integrated access and backhaul (IAB) node. The base station may be a DU of an IAB node. The user equipment may be a mobile terminal (MT) of an IAB node.

[0135] A program that causes a computer to perform each process performed by UE 100 or gNB 200 may be provided. The program may be recorded in a computer-readable medium. The use of a computer-readable medium enables the program to be installed 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. A circuit for performing a process to be performed by UE 100 or gNB 200 may be integrated, and at least a portion of UE 100 or gNB 200 may be implemented as a semiconductor integrated circuit (chip set, system on chip (SoC)).

[0136] Unless otherwise expressly stated, the phrases "based on" and "depending on" used in this disclosure do not mean "based only on" and "depending only on". The phrase "based on" means both "based only on" and "based at least in part on". The phrase "depending on" means "depending only on" and "depending at least in part on". The terms "include", "comprising" and their variants do not mean "only including the items", but mean "may only include the items" or "may include not only the items but also other items". The term "or" used in this disclosure is not intended to be "exclusive or". Any reference to elements using names such as "first" and "second" in this disclosure does not generally limit the number or order of these elements. These names can be used as a convenient method to distinguish two or more elements in this article. Therefore, the reference to the first element and the second element does not mean that only two elements can be adopted there or that the first element needs to be in some way before the second element. For example, when English articles such as "one", "an" and "the" are added in this disclosure by translation, these articles include plural unless otherwise clearly indicated in the context.

[0137] The embodiments have been described in detail above with reference to the accompanying drawings, but the specific configuration is not limited to the above configuration, and various design changes may be made without departing from the gist of the present disclosure.

[0138] This application claims priority to U.S. Provisional Patent Application No. 63 / 307,248 (filed on February 7, 2022), the entire contents of which are incorporated herein by reference.

[0139] Additional Notes

[0140] Features related to the above-described embodiment are described below as supplements. (1)

[0142] A communication method for a user equipment to communicate with a primary cell group (MCG) and a secondary cell group (SCG), the communication method comprising the following steps: a master node managing the primary cell group (MCG) sends a radio resource control (RRC) message to the user equipment, the radio resource control message comprising: a target MCG configuration for performing a conditional handover (CHO) to a target MCG, and an SCG candidate configuration for each SCG candidate among a plurality of SCG candidates associated with the target MCG; the user equipment receives the RRC message; and when the execution condition of the CHO is met, the user equipment selects any SCG candidate from among the plurality of SCG candidates as the target SCG. (2)

[0144] The communication method described in (1) above also includes: when the execution condition is met, initializing access to the target MCG and initializing access to the selected target SCG. (3)

[0146] According to the communication method described in (1) or (2) above, the RRC message includes a first conditional RRC reconfiguration, and the first conditional RRC reconfiguration includes: conditional information indicating an execution condition; a target MCG configuration; and a list of SCG candidate configurations including each SCG candidate among the multiple SCG candidates. (4)

[0148] According to the communication method described in any one of (1) to (3) above, the list further includes at least one of an SCG identifier or a radio quality threshold of each SCG candidate among the multiple SCG candidates. (5)

[0150] According to the communication method described in any one of (1) to (4) above, the list includes a second conditional RRC reconfiguration of each SCG candidate among the multiple SCG candidates, and the second conditional RRC reconfiguration includes: conditional information indicating the execution condition of the corresponding SCG candidate; and the SCG candidate configuration of the corresponding SCG candidate. (6)

[0152] According to the communication method described in any one of (1) to (5) above, the selecting includes: selecting the target SCG from the plurality of SCG candidates according to a selection criterion for selecting the plurality of SCG candidates in descending order of radio quality. (7)

[0154] According to the communication method described in any one of (1) to (6) above, the selection includes: when configuring execution conditions for each of the multiple SCG candidates, selecting an SCG candidate with the best radio quality among the SCG candidates that have met the execution conditions as the target SCG. (8)

[0156] According to the communication method described in any one of (1) to (7) above, the selection includes: selecting the target SCG from the multiple SCG candidates based on a selection criterion for selecting the multiple SCG candidates in descending order of priority specified by the master node. (9)

[0158] According to the communication method described in any one of (1) to (8) above, the selection includes: when configuring execution conditions for each of the multiple SCG candidates, selecting an SCG candidate with the highest priority as the target SCG among the SCG candidates that have met the execution conditions. (10)

[0160] According to the communication method described in any one of (1) to (9) above, the selection includes: selecting a target SCG from the multiple SCG candidates based on a selection criterion for preferentially selecting an SCG with which the user equipment is currently communicating. (11)

[0162] According to the communication method described in any one of (1) to (10) above, the selection includes: selecting a target SCG from the plurality of SCG candidates according to a selection criterion for selecting an SCG whose radio quality satisfies a minimum quality standard. (12)

[0164] The communication method according to any one of (1) to (11) above further includes: the user equipment sending an identifier related to the SCG candidate selected as the target SCG to the target MCG. (13)

[0166] The communication method described in any one of (6) to (11) above also includes: based on the absence of SCG candidates that meet the selection criteria, the user equipment sends information indicating that the target SCG cannot be selected to the target MCG without selecting the target SCG. (14)

[0168] A user equipment for communicating with a master cell group (MCG) and a secondary cell group (SCG), comprising: a receiver configured to receive a radio resource control (RRC) message from a master node managing the master cell group (MCG), the RRC message comprising: a target MCG configuration for performing a conditional handover (CHO) to a target MCG, and an SCG candidate configuration for each SCG candidate among a plurality of SCG candidates associated with the target MCG; and a controller configured to select any SCG candidate from the plurality of SCG candidates as the target SCG when an execution condition of the CHO is met. (15)

[0170] A base station for operating as a master node for managing a master cell group (MCG) used by a user equipment, comprising: a transmitter configured to send a radio resource control (RRC) message to the user equipment, the radio resource control message comprising: a target MCG configuration for performing a conditional handover (CHO) to a target MCG, and an SCG candidate configuration for each SCG candidate of a plurality of SCG candidates associated with the target MCG.

[0171] Reference numerals

[0172] 1: Mobile communication system

[0173] 100: UE

[0174] 110: Receiver

[0175] 120: Transmitter

[0176] 130: Controller

[0177] 200: gNB

[0178] 200M:MN

[0179] 200S: SN

[0180] 201M: MCG

[0181] 201S: SCG

[0182] 210: Transmitter

[0183] 220: Receiver

[0184] 230: Controller

[0185] 240: Backhaul communicator.

Claims

1. A communication method for a user equipment to communicate with a primary cell group MCG and a secondary cell group SCG, the communication method comprising the following steps: A radio resource control RRC message is sent by a master node managing a master cell group MCG to a user equipment, wherein the radio resource control message includes: a target MCG configuration for performing a conditional handover CHO to a target MCG, and an SCG candidate configuration of each SCG candidate of a plurality of SCG candidates associated with the target MCG; Receiving the RRC message by the user equipment; and When the execution condition of the CHO is met, the user equipment selects any SCG candidate from among the multiple SCG candidates as the target SCG.

2. The communication method according to claim 1, further comprising: When the execution condition is met, access to the target MCG is initialized and access to the selected target SCG is initialized.

3. The communication method according to claim 1, wherein: The RRC message includes a first conditional RRC reconfiguration, and The first condition RRC reconfiguration includes: Condition information indicating the execution condition; the target MCG configuration; and A list of SCG candidate configurations including each SCG candidate in the plurality of SCG candidates.

4. The communication method according to claim 3, wherein: The list also includes at least one of an SCG identifier or a radio quality threshold for each SCG candidate of the plurality of SCG candidates.

5. The communication method according to claim 3, wherein: The list includes a second conditional RRC reconfiguration for each SCG candidate in the plurality of SCG candidates, and The second condition RRC reconfiguration includes: Condition information indicating an execution condition of the corresponding SCG candidate; and The SCG candidate configuration of the corresponding SCG candidate.

6. The communication method according to claim 1, wherein: The selecting includes selecting the target SCG from among the plurality of SCG candidates according to a selection criterion for selecting the plurality of SCG candidates in descending order of radio quality.

7. The communication method according to claim 6, wherein: The selecting includes: when an execution condition is configured for each of the multiple SCG candidates, selecting an SCG candidate with the best radio quality among the SCG candidates that have satisfied the execution condition as the target SCG.

8. The communication method according to claim 1, wherein: The selecting includes selecting the target SCG from the plurality of SCG candidates according to a selection criterion for selecting the plurality of SCG candidates in descending order of priority specified by the master node.

9. The communication method according to claim 8, wherein: The selecting includes: when configuring an execution condition for each of the multiple SCG candidates, selecting an SCG candidate with the highest priority among the SCG candidates that have satisfied the execution condition as the target SCG.

10. The communication method according to claim 1, wherein: The selecting includes: selecting the target SCG from the multiple SCG candidates according to a selection criterion for preferentially selecting the SCG with which the user equipment is currently communicating.

11. The communication method according to claim 1, wherein: The selecting includes selecting the target SCG from the plurality of SCG candidates according to a selection criterion for selecting an SCG whose radio quality satisfies a minimum quality standard.

12. The communication method according to any one of claims 1 to 11, further comprising: The user equipment sends an identifier associated with the SCG candidate selected as the target SCG to the target MCG.

13. The communication method according to any one of claims 6 to 11, further comprising: According to the absence of an SCG candidate satisfying the selection criterion, the user equipment sends information indicating that the target SCG cannot be selected to the target MCG without selecting the target SCG.

14. A user equipment for communicating with a primary cell group MCG and a secondary cell group SCG, the user equipment comprising: a receiver configured to receive a radio resource control RRC message from a master node managing a master cell group MCG, the RRC message comprising: a target MCG configuration for performing a conditional handover CHO to a target MCG, and an SCG candidate configuration for each of a plurality of SCG candidates associated with the target MCG; and The controller is configured to select any SCG candidate from the multiple SCG candidates as a target SCG when an execution condition of the CHO is met.

15. A base station for operating as a master node managing a master cell group MCG used by a user equipment, the base station comprising: The transmitter is configured to send a radio resource control RRC message to a user equipment, wherein the radio resource control message includes: a target MCG configuration for performing a conditional handover CHO to a target MCG, and an SCG candidate configuration of each SCG candidate among a plurality of secondary cell group SCG candidates associated with the target MCG.

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