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

Abstract

A communication method according to a first aspect of this invention is a method for allowing a user device to communicate with a master cell group (MCG) and a secondary cell group (SCG), and comprises: a step of transmitting, to the user device by a master node managing the master cell group (MCG), a radio resource control (RRC) message including a target MCG setting for performing conditional handover (CHO) to a target MCG and an SCG candidate setting of each of a plurality of SCG candidates associated with the target MCG; a step of receiving the RRC message by the user device; and a step of selecting, by the user device, 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 device, and a base station used in a mobile communication system.

Background Art

[0002] In the technical specifications of 3GPP (Third Generation Partnership Project), which is a standardization project for mobile communication systems, the specifications of conditional handover (CHO) and conditional primary-secondary cell change (CPC) have been established. Also, in 3GPP, discussions are underway regarding the specification establishment of 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 Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] The present disclosure provides a communication method, a user device, and a base station that enable the simultaneous implementation of CHO and CPAC.

[0005] The communication method according to the first aspect is a communication method in which a user equipment communicates with a master cell group (MCG) and a secondary cell group (SCG). A master node that manages 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 an SCG candidate configuration for each of a plurality of SCG candidates associated with the target MCG. The user equipment receives the RRC message. When the execution condition in the CHO is satisfied, the user equipment selects any one of the plurality of SCG candidates as a target SCG.

[0006] The user equipment according to the second aspect is a user equipment that communicates with a master cell group (MCG) and a secondary cell group (SCG). The user equipment includes a receiving unit 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 an SCG candidate configuration for each of a plurality of SCG candidates associated with the target MCG, and a control unit that selects any one of the plurality of SCG candidates as a target SCG when the execution condition in the CHO is satisfied.

[0007] The base station according to the 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 transmitting unit that 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 an SCG candidate configuration for each of a plurality of secondary cell group (SCG) candidates associated with the target MCG.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out 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 the mobile communication system according to the embodiment will be described. FIG. 1 is a diagram showing the configuration of the mobile communication system according to the embodiment. The mobile communication system 1 complies with the 5th generation system (5GS) of the 3GPP standard. In the following, the 5GS will be described as an example, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system, or the 6th generation (6G) system may be at least partially applied.

[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. In the following, the NG-RAN 10 may be simply referred to as the RAN 10. Also, the 5GC 20 may be simply referred to as the core network (CN) 20.

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

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

[0014] Note that the gNB can also be connected to the EPC (Evolved Packet Core), which is the core network of LTE. The base station of LTE can also be connected to the 5GC. The base station of LTE and the gNB can also be connected via an interface between base stations.

[0015] The 5GC 20 includes the AMF (Access and Mobility Management Function) and the UPF (User Plane Function) 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 performs transfer control of data. The AMF and the UPF are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network.

[0016] Figure 2 is a diagram showing the configuration of the 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 receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it 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 the 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 the processes of each layer 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 for 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 the baseband signal, etc. The CPU executes the programs stored in the memory to perform various processes.

[0020] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to the embodiment. The gNB 200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and a backhaul communication unit 240. The transmitting unit 210 and the receiving unit 220 constitute a radio communication unit that performs radio communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0021] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the 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 receptions under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 230.

[0023] The control unit 230 performs various controls and processes in the gNB 200. Such processes include the processes of each layer 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 for the processor's processing. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of the baseband signal, etc. The CPU executes the programs stored in the memory to perform various processes.

[0024] The backhaul communication unit 240 is connected to an adjacent base station via the Xn interface, which is a base station - to - base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via the NG interface, which is a base station - to - core network interface. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally split), and the two units may be connected by the F1 interface, which is a fronthaul interface.

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

[0026] The radio interface protocol of the user plane has a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

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

[0028] The MAC layer performs priority control of data, retransmission processing by hybrid automatic repeat request (HARQ), and random access procedures, etc. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via transport channels. The MAC layer of gNB200 includes a scheduler. The scheduler determines the uplink and downlink transport formats (transport block size, modulation and coding scheme (MCS)) and the resource blocks allocated to UE100.

[0029] The RLC layer transmits data to the RLC layer on the receiving side by utilizing the functions of the MAC layer and the PHY layer. Between the RLC layer of UE100 and the RLC layer of gNB200, data and control information are transmitted via logical channels.

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

[0031] The SDAP layer performs the mapping between the IP flow, which is the unit for the core network to perform QoS (Quality of Service) control, and the radio bearer, which is the unit for the AS (Access Stratum) to perform QoS control. Note that when the RAN is connected to the EPC, the SDAP may not be required.

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

[0033] The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) instead of the SDAP layer shown in Figure 4.

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

[0035] The NAS located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS of UE100 and the NAS of AMF300A. Note that UE100 has an application layer, etc. in addition to the protocol of the radio interface. Also, the layer below the NAS is called the 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 the embodiment.

[0037] In DC, the UE 100 performs simultaneous communication 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. Hereinafter, 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, DC is started by the MN 200M transmitting a predetermined message (e.g., SN Addition Request message) to the SN 200S via the network interface between the MN 200M and the SN 200S, and the MN 200M transmitting an RRC reconfiguration (RRC Reconfiguration) message to the UE 100. The UE 100 in the RRC connected state has radio resources allocated from the schedulers of the MN 200M and the SN 200S respectively, and performs radio communication using the radio resources of the MN 200M and the radio resources of the SN 200 S The network interface between the MN 200M and the SN 200 may be an Xn interface (or an X2 interface). The MN 200M and the SN 200 communicate with each other via the network interface.

[0039] The MN200M may have a control plane connection with the core network. The MN200M provides the main radio resources of the UE100. The MN200M manages the MCG201M. The MCG201M is a group of serving cells associated with the MN200M. The MCG201M has a primary cell (PCell) and optionally one or more secondary cells (SCells). The MN200M controls and manages the settings for the UE100.

[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-secondary cell (PSCell) and optionally one or more SCells. Note that the PCell of the MCG201M and the PSCell of the SCG201S are also referred to as special cells (SpCells).

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

[0042] (3.1) Conditional Handover (CHO) In CHO, the execution conditions for the handover are preset for the UE100, and the handover is executed when the set execution conditions are satisfied in the UE100. FIG. 7 is a diagram for explaining the CHO according to the embodiment.

[0043] In FIG. 7, an example is shown where 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, although two candidate cells (candidate cell #1 and candidate cell #2) are illustrated, the number of candidate cells may be one or three or more. The UE100 is in the RRC connected state in the source cell.

[0044] In STEP1, gNB200 sends an RRC Reconfiguration message including a Conditional Reconfiguration which is a CHO configuration to UE100. The RRC Reconfiguration message is an example of an RRC message. The CHO configuration includes, for example, candidate cell configurations (i.e., the respective configuration information of candidate cell #1 and candidate cell #2) generated by candidate gNB200C (i.e., gNB200C-1 and gNB200C-2), and condition information indicating execution conditions generated by 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 a plurality of candidate cells. The execution condition is information for setting the radio quality to be measured and a threshold value to be compared with the radio quality. UE100 starts evaluating the execution condition.

[0045] In STEP2, in response to the execution condition set in STEP1 being satisfied, UE100 starts accessing the candidate cell (here, candidate cell #1) for which the execution condition is satisfied. Note that UE100 does not have to monitor the source cell from the time when synchronization with candidate cell #1 is started.

[0046] In STEP3, when UE100 successfully accesses candidate cell #1, it switches the connection from the source cell to candidate cell #1. Thereby, the handover is completed. UE100 communicates with candidate cell #1 using the candidate cell configuration (configuration information of candidate cell #1) received in STEP1.

[0047] (3.2) Conditional PSCell Change (CPC) In the CPC, the execution conditions for PSCell change are preset for the UE100, and when the set execution conditions are satisfied in the UE100, the PSCell change is executed. FIG. 8 is a diagram for explaining the CPC according to the embodiment. Assume that the UE100 has connections with the gNB200M (MCG201M) which is the MN and the gNB200S-1 (SCG201S-1) which is the SN, and is performing DC mode communication.

[0048] The CPC includes an Intra-SN CPC for changing the PSCell from one cell to another within one SN200S, and an Inter-SN CPC for changing the PSCell from a cell of one SN200S to a cell of another SN200S. In the following, the Inter-SN CPC will be mainly described, but the embodiment is not limited to the Inter-SN CPC and may be the Intra-SN CPC.

[0049] In STEP1, the gNB200M which is the MN transmits an RRC Reconfiguration message including Conditional Reconfiguration which is the CPC setting to the UE100. The CPC setting includes, for example, an SCG candidate setting (for example, the PSCell setting information in the SCG candidate 201S-2 of the gNB200-2. Optionally, it may include SCell setting information.) generated by the gNB200S-2 which is the SN candidate, and condition information indicating the execution conditions generated by the MN (that is, the gNB200M). The SCG candidate setting and the execution conditions are associated with each other. Different execution conditions may be associated with a plurality of SCG candidate settings. The execution conditions are information for setting the radio quality to be measured and the threshold value to be compared with the radio quality. The UE100 starts evaluating the execution conditions.

[0050] In STEP2, in response to the execution conditions set in STEP1 being satisfied, the UE100 starts accessing the PSCell of the SCG candidate 201S-2 for which the execution conditions are satisfied.

[0051] In STEP3, when the UE100 successfully accesses the SCG candidate 201S-2 (PSCell), it switches the PSCell from the SCG201S-1 (gNB200S-1) to the SCG201S-2 (gNB200S-2). As a result, the PSCell change is completed. The UE100 communicates with the SCG201S-2 using the SCG candidate configuration (configuration information of the SCG201S-2) received in STEP1.

[0052] (3.3) Conditional PSCell Addition (CPA) In CPA, the execution conditions for PSCell addition are set in advance for the UE100, and the PSCell addition is executed when the set execution conditions are satisfied in the UE100. FIG. 9 is a diagram for explaining the CPA according to the embodiment. The UE100 is in the RRC connected state in the MCG201M.

[0053] In STEP1, the gNB200M, which is the MN, transmits an RRC Reconfiguration message including a Conditional Reconfiguration, which is a CPA configuration, to the UE100. The CPA configuration includes, for example, SCG candidate configurations (for example, respective configuration information of the SCG candidate 201S-1 and the SCG candidate 201S-2) generated by SN candidates (gNB200S-1, gNB200S-2) and condition information indicating the execution conditions generated by the MN (that is, the gNB200M). The SCG candidate configurations and the execution conditions are associated with each other. Different execution conditions may be associated with a plurality of SCG candidate configurations. The execution conditions are information for setting the radio quality of the measurement target and a threshold value to be compared with the radio quality. The UE100 starts evaluating the execution conditions.

[0054] In STEP2, in response to the execution conditions set in STEP1 being satisfied, the UE100 starts accessing the PSCell of the SCG candidate (here, the SCG candidate 201S-1) for which the execution conditions are satisfied.

[0055] In STEP3, when the UE100 successfully accesses the SCG candidate 201S-1 (PSCell), it starts communication in DC mode. The UE100 communicates with the SCG201S-1 using the SCG candidate setting (the setting information of the SCG201S-1) received in STEP1.

[0056] (4) Operation of the mobile communication system Next, the operation of the mobile communication system 1 according to the embodiment, specifically, the operation for simultaneously performing CHO and CPAC (CPC, CPA) will be described. In such an operation, it may be a problem how the gNB200 (MN) sets a plurality of SCG candidates for the UE100. Also, it may be a problem how the UE100 determines the target SCG from among the plurality of SCG candidates.

[0057] In the embodiment, the UE100 communicates with the MCG201M and the SCG201S by DC. First, the MN200M that manages the MCG201M transmits an RRC message (specifically, Conditional Reconfiguration) including a target MCG setting for performing CHO to the target MCG and SCG candidate settings of a plurality of SCG candidates associated with the target MCG to the UE100. The UE100 receives the RRC message. Second, when the execution condition (also referred to as the "trigger condition") in the CHO is satisfied, the UE100 selects any one of the plurality of SCG candidates as the target SCG. Thereby, it becomes possible to simultaneously perform CHO and CPAC (CPC, CPA). When the execution condition in the CHO is satisfied, the UE100 may start access to the target MCG and start access to the selected target SCG.

[0058] (4.1) Operations related to simultaneous execution of CHO and CPC The operations related to the simultaneous execution of CHO and CPC according to the embodiment will be described. FIG. 10 is a diagram for explaining the operations related to the simultaneous execution of CHO and CPC according to the embodiment. Assume that the UE 100 has connections with the gNB 200M-1 (MCG 201M-1) which is the MN and the gNB 200S-1 (SCG 201S-1) which is the SN, and is performing DC mode communication. In FIG. 10, one SCG candidate 201S-2 is illustrated, but assume that there are multiple SCG candidates. In the following, for simplicity of explanation, assume that there is one MCG candidate (target MCG) set by CHO, but there may be multiple MCG candidates set by CHO. Multiple SCG candidates may be set for each of such multiple MCG candidates.

[0059] In STEP1, the gNB 200M-1 which is the MN transmits an RRC Reconfiguration message including a conditional RRC reconfiguration (Conditional Reconfiguration) which is a CHO and CPC setting to the UE 100. The Conditional Reconfiguration (the first conditional RRC reconfiguration) includes condition information indicating the execution conditions in CHO, a target MCG setting which is the setting information of the target MCG 201M-2, and a list including the SCG candidate settings of each of the multiple SCG candidates. The target MCG setting includes information necessary for communication with the target MCG 201M-2 (PCell). The SCG candidate setting includes information necessary for communication with the corresponding SCG (PSCell). Details of the configuration of the Conditional Reconfiguration will be described later.

[0060] In STEP2, in response to the execution conditions of the CHO set in STEP1 being satisfied, UE100 selects a target SCG from among the multiple SCG candidates set in STEP1. Details of the target SCG selection process will be described later. Then, UE100 starts accessing the target MCG201M-2 (PCell) and also starts accessing the PSCell of the selected target SCG (here, SCG candidate 201S-2). For example, UE100 may start accessing the target SCG201S-2 (PSCell) after the access to the target MCG201M-2 (PCell) is successful.

[0061] In STEP3, when UE100 successfully accesses the target MCG201M-2 (PCell), it switches the PCell (MN) from MCG201M-1 (gNB200M-1) to MCG201M-2 (gNB200M-2). Also, when UE100 successfully accesses the target SCG201S-2 (PSCell), it switches the PSCell (SN) from SCG201S-1 (gNB200S-1) to SCG201S-2 (gNB200S-2). Thereby, the CHO and CPC are completed. UE100 communicates with MCG201M-2 (PCell) using the target MCG settings received in STEP1. Also, UE100 communicates with SCG201S-2 (PSCell) using the SCG settings of the target SCG among the multiple candidate SCG settings received in STEP1.

[0062] (4.2) Operations related to simultaneous execution of CHO and CPA The operations related to the simultaneous execution of CHO and CPA according to the embodiment will be described. FIG. 11 is a diagram for explaining the operations related to the simultaneous execution of CHO and CPA according to the embodiment. UE100 has a connection with gNB200M-1 (MCG201M-1) which is the MN.

[0063] In STEP1, gNB200M-1 which is MN sends an RRC Reconfiguration message including a Conditional Reconfiguration (conditional RRC reconfiguration) which is a CHO and CPA setting to UE100. The Conditional Reconfiguration (the first conditional RRC reconfiguration) includes condition information indicating the execution conditions in CHO, target MCG settings which are the setting information of target MCG201M-2, and a list including the respective SCG candidate settings of a plurality of SCG candidates. The target MCG settings include information necessary for communication with target MCG201M-2 (PCell). The SCG candidate settings include information necessary for communication with the corresponding SCG (PSCell). Details of the configuration of the Conditional Reconfiguration will be described later.

[0064] In STEP2, in response to the execution conditions of the CHO set in STEP1 being satisfied, UE100 selects a target SCG from among the plurality of SCG candidates set in STEP1. Details of the selection process of the target SCG will be described later. Then, UE100 starts access to target MCG201M-2 (PCell) and also starts access to the PSCell of the selected target SCG (here, SCG candidate 201S-1). For example, UE100 may start access to target SCG201S-1 (PSCell) after access to target MCG201M-2 (PCell) is successful.

[0065] In STEP3, when the UE100 successfully accesses the target MCG201M-2 (PCell), it switches the PCell (MN) from MCG201M-1 (gNB200M-1) to MCG201M-2 (gNB200M-2). Also, when the UE100 successfully accesses the target SCG201S-2 (PSCell), the PSCell (SN) is added to SCG201S-1 (gNB200S-1). Thereby, the CHO and CPA are completed. The UE100 communicates with the MCG201M-2 (PCell) using the target MCG configuration received in STEP1. Also, the UE100 communicates with the SCG201S-1 (PSCell) using the SCG configuration of the target SCG among the multiple candidate SCG configurations received in STEP1.

[0066] (4.3) Message Configuration Example The RRC message according to the embodiment, specifically, the configuration example of Conditional Reconfiguration (the 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 gNB200 (MN) to the UE100. The Conditional Reconfiguration includes the target MCG configuration for performing CHO to the target MCG and the SCG candidate settings of each of the multiple SCG candidates associated with the target MCG. That is, the Conditional Reconfiguration includes the MCG configuration for performing conditional reconfiguration and the multiple SCG candidate settings associated with the MCG configuration.

[0067] (4.3.1) Message Configuration Example 1 FIG. 12 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 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 an information element introduced in 3GPP Release 16.

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

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

[0070] Each entry in the list (secondaryCellGroupCandidateList) contains a secondaryCellGroup (or mrdc-SecondaryCellGroup), which is the configuration information of the SCG candidate (target SCG). Each entry in the list (secondaryCellGroupCandidateList) may further include at least one of an SCG identifier (SCG-ID) and 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, specifically, the threshold of the minimum required quality for the SCG when selecting the SCG.

[0071] According to this Configuration Example 1, it is possible to appropriately set a plurality of SCG candidates for the UE100.

[0072] (4.3.2) Message Configuration Example 2 FIG. 13 is a diagram showing Configuration Example 2 of an RRC message according to an embodiment. The gNB200 (MN) transmits an RRC message (RRC Reconfiguration message) for simultaneously performing CHO and CPAC (CPC, CPA) to the UE100. The RRC Reconfiguration message includes Conditional Reconfiguration-r16 as an information element.

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

[0074] condRRCReconfig-r16 (RRCReconfiguration) includes the 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 with respect to the SCG (SN). Each entry (CondReconfigToAddMod-r16) of the condReconfigToAddModList-r16 corresponds to a second conditional RRC reconfiguration. The CondReconfigToAddMod-r16 includes condRRCReconfig-r16, and condRRCReconfig-r16 encapsulates the RRCReconfiguration to be applied when the execution condition is met. The RRCReconfiguration includes the SCG candidate setting (secondaryCellGroup or mrdc-SecondaryCellGroup) which is the setting information of the SCG candidate (target SCG). Further, the CondReconfigToAddMod-r16 further includes condExecutionCond-r16 (not shown) which is condition information indicating the execution conditions that need to be met to trigger the execution of the corresponding conditional reconfiguration.

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

[0076] According to this Configuration Example 2, it becomes possible to appropriately set a plurality of SCG candidates for the UE100. Also, according to this Configuration Example 2, it becomes possible to set the execution conditions for each SCG candidate for the UE100.

[0077] (4.4) An example of the operation flow An example of the operation flow of UE100 according to the embodiment will be described. FIG. 14 is a diagram showing an example of the operation flow of UE100 according to the embodiment.

[0078] In step S1, UE100 receives from gNB200 (MN) an RRC message (RRC Reconfiguration message) for simultaneously performing CHO and CPAC (CPC, CPA). The RRC message has the configuration of Message Configuration Example 1 or Message Configuration Example 2 described above.

[0079] In step S2, UE100 performs radio quality measurement and determines whether the execution conditions (i.e., the execution conditions for CHO) set for the target MCG are satisfied. Such execution conditions for CHO may be, for example, condEventA3 or condEventA5 defined in the 3GPP technical specifications. Also, in the case of Message Configuration Example 1 described above, UE100 may determine whether the corresponding radio quality threshold is satisfied for each SCG candidate. In the case of Message Configuration Example 2 described above, UE100 may determine whether the corresponding execution conditions (i.e., the execution conditions for CPAC) are satisfied for each set SCG candidate. Such execution conditions for CPAC may be, for example, condEventA3, condEventA4, or condEventA5 defined in the 3GPP technical specifications. Note that even if an SCG candidate satisfies the execution conditions, UE100 does not access (holds) the SCG candidate at this point.

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

[0081] When a SCG candidate that meets the specified selection criteria is selected as the target SCG (step S5: YES), in step S6, UE100 starts accessing the target MCG (PCell). Also, UE100 starts accessing the selected target SCG. Here, the description will proceed assuming success in such access.

[0082] In step S7, UE100 may send an identifier related to the SCG candidate selected as the target SCG in step S4 to the target MCG. Here, UE100 may send the identifier to the target MCG when access to the target SCG is successful. Also, UE100 may send the identifier to the target MCG regardless of the success or failure of access to the target SCG. Thereby, the target MCG (new MN) can grasp whether UE100 has selected the target SCG. Note that UE100 may send 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 (SCG-ID) in the above-described message configuration example 1. Also, in response to successful access to the target MCG and / or in response to successful access to the target SCG, UE100 may apply the SCG configuration and discard the SCG configurations other than the said SCG.

[0083] On the other hand, if the UE 100 fails to select an SCG candidate that meets the specified selection criteria as the target SCG (step S5: NO), in step S8, the UE 100 starts accessing the target MCG (PCell). Here, the description will proceed assuming that such access is successful. Then, in step S9, the UE 100 may send information indicating that it did not select the SCG to the target MCG. That is, in response to the non-existence of an SCG candidate that meets the selection criteria, the UE 100 may send information indicating that it cannot select the target SCG to the target MCG without selecting the target SCG. As a result, the target MCG (new MN) can be aware that the UE 100 failed to select the target SCG. Note that the UE 100 may send an RRC Reconfiguration Complete message including such information to the target MCG. Also, in response to the successful access to the target MCG and / or in response to not selecting the target SCG, the UE 100 may discard the SCG configuration. Or, the UE 100 may not discard the SCG configuration and continue to determine the radio measurements and trigger conditions of the SCG according to the SCG configuration. That is, the UE 100 behaves in the same way as when the CPAC configuration is performed (falls back to CPAC). The UE 100 may select whether to discard the SCG configuration or continue to determine the radio measurements and trigger conditions of the SCG according to the SCG configuration without discarding the SCG configuration according to the settings from the gNB 200.

[0084] In this operation flow, an example of transmitting an identifier related to the SCG candidate selected as the target SCG from the UE 100 to the target MCG has been described. However, the target SCG (SN) accessed from the UE 100 may notify the target MCG (new MN) of such access (and the identifier).

[0085] (4.5) SCG Selection Process The SCG selection process according to the embodiment, that is, the details of step S4 in FIG. 14 will be described. The UE 100 performs the SCG selection process by 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 configured SCG candidates according to a selection criterion of selecting in descending order of radio quality. Thereby, the UE 100 can select an appropriate target SCG.

[0087] When an execution condition (that is, an execution condition in CPAC) is set for each of the plurality of SCG candidates, the UE 100 may select, as the target SCG, the SCG candidate with the best radio quality among the SCG candidates for which the execution condition is satisfied.

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

[0089] (4.5.2) Option 2 In Option 2 of the SCG selection process, UE100 selects a target SCG from among a plurality of configured SCG candidates according to a selection criterion that selects in descending order of the priority specified by gNB200 (MN). This enables the network to lead the UE100 to select an appropriate target SCG.

[0090] When execution conditions (i.e., execution conditions in CPAC) are set for each of the plurality of SCG candidates, UE100 may select, as target SCG201S, the SCG candidate with the highest priority among the SCG candidates for which the execution conditions are satisfied. Alternatively, when a minimum required radio quality threshold is set for each of the plurality of SCG candidates, UE100 may select, as target SCG201S, the SCG candidate with the highest priority among the SCG candidates for which the radio quality threshold is satisfied.

[0091] In this Option 2, gNB200 sets a plurality of SCG candidates for UE100 in its order of preference. For example, the priority may be considered higher in the order of the entries in the list for setting the plurality of SCG candidates. Specifically, the first entry in the list would be the highest priority. Alternatively, the priority may be considered higher in the order of the IDs (SCG-IDs) of the above-mentioned SCG candidates. Alternatively, gNB200 may attach an IE indicating the priority so as to explicitly specify the priority for the SCG candidate setting (list).

[0092] UE100 checks whether the execution conditions (or radio quality threshold) are satisfied for the SCG (PSCell) with the highest priority specified by gNB200. If satisfied, UE100 selects the SCG (PSCell); if not, UE100 checks whether the execution conditions (or radio quality threshold) are satisfied for the SCG with the next highest priority. If there are multiple SCGs (PSCells) with the highest priority, UE100 may select the SCG (PSCell) with better radio quality.

[0093] (4.5.3) Option 3 Option 3 of the SCG selection process is an option assuming the CPC. In this Option 3, the UE 100 selects the target SCG 201S from among a plurality of configured SCG candidates according to the selection criteria that preferentially selects the SCG 201S with which it is currently communicating. Thereby, it is possible for the UE 100 to perform efficient target SCG selection.

[0094] For example, in a plurality of configured SCG candidates (a plurality of PSCell candidates), if the SCG (PSCell) with which the UE 100 is currently communicating (being used / being configured) exists, the UE 100 tentatively selects the SCG (PSCell). Then, if the tentatively selected SCG (PSCell) satisfies the execution condition (or radio quality threshold), the UE 100 selects the SCG (PSCell), and if it does not satisfy the execution condition (or radio quality threshold) or if the SCG with which it is currently communicating does not exist among the candidates, the UE 100 executes Option 1 or 2 above.

[0095] (4.5.4) Option 4 Option 4 of the SCG selection process is an exception operation when the UE 100 cannot select an SCG. If, as a result of applying Options 1 to 3 above, the UE 100 cannot select an SCG (when none of the SCG candidate settings satisfy the execution condition (or radio 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 the target SCG 201S from among a plurality of configured SCG candidates according to the selection criteria that selects an SCG whose radio quality satisfies the minimum quality standard. For example, the UE 100 may be used in combination with Option 1 above and select the SCG with the best radio quality from among the SCGs that satisfy the minimum quality threshold. The UE 100 may also include only the SCGs that satisfy the minimum quality threshold as selection targets.

[0097] (5) Other Embodiments In the above embodiments, the DC in which the UE 100 communicates with the MCG and the SCG has been described, but it may also 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-mentioned (4.5) SCG selection process. For example, when selecting two SCGs, the SCG with the best radio quality and the SCG with the second-best radio quality may be selected. Also, the SCG with the highest priority and the SCG with the second-highest priority may be selected. The gNB 200 may set the number of SCGs to be selected (which may be the number of selectable or permitted selections) for the UE 100. The UE 100 may specify the number of SCGs to be selected according to the setting by the gNB 200. This setting may be performed only in the case of MC. That is, in the case of DC, this setting may not be performed. The UE 100 accesses the selected SCG in the same manner as in the above-described embodiments. Note that the UE 100 may perform access to the selected SCG even if the number of selected SCGs has not reached the number of SCGs to be selected. For example, 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 still executed.

[0098] The above-described operation flows are not limited to being implemented separately and independently, and two or more operation flows can be combined and implemented. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

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

[0100] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. By using the computer-readable medium, it is possible to install the program on the 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. Also, a circuit that executes each process performed by the UE 100 or the gNB 200 may be integrated, and at least a part of the UE 100 or the gNB 200 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip).

[0101] As used in this disclosure, the terms "based on" and "depending on" do not mean "only based on" or "only depending on" unless otherwise specified. The term "based on" means both "only based on" and "at least partially based on". Similarly, the term "depending on" means both "only depending on" and "at least partially depending on". Also, the terms "include", "comprise", and their variants do not mean to include only the listed items, but may include only the listed items or may include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to be an exclusive disjunction. Further, any reference to an element using designations such as "first", "second", etc. used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Thus, a reference to a first and a second element does not mean that only two elements can be employed there or that the first element must precede the second element in some form. In this disclosure, for example, when articles are added by translation, such as a, an, and the in English, these articles shall be construed to include plural ones unless the context clearly indicates otherwise.

[0102] As described above in detail with reference to the drawings, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

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

[0104] (Appendix) Append the features regarding the above embodiments.

[0105] (1) A communication method in which a user equipment communicates with a master cell group (MCG) and a secondary cell group (SCG), a master node that manages the master cell group (MCG) transmits 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 an SCG candidate setting for each of a plurality of SCG candidates associated with the target MCG; the user equipment receives the RRC message; when execution conditions in the CHO are satisfied, the user equipment selects any one of the plurality of SCG candidates as a target SCG. Communication method.

[0106] (2) further comprising, when the execution conditions are satisfied, starting access to the target MCG and starting access to the selected target SCG. The communication method according to (1) above.

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

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

[0109] (5) The list includes the second conditional RRC reset for each of the plurality of SCG candidates, The second conditional RRC reset, includes condition information indicating execution conditions for the corresponding SCG candidate, and the SCG candidate setting for the corresponding SCG candidate. The communication method according to any one of (1) to (4) above.

[0110] (6) The selecting step includes selecting the target SCG from among the plurality of SCG candidates according to a selection criterion of selecting in descending order of high radio quality. The 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 selecting, as the target SCG, the SCG candidate having the best radio quality among the SCG candidates for which the execution conditions are satisfied. The communication method according to any one of (1) to (6) above.

[0112] (8) The selecting step includes selecting the target SCG from among the plurality of SCG candidates according to a selection criterion of selecting in descending order of the priority specified by the master node. The 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 selecting, as the target SCG, the SCG candidate having the highest priority among the SCG candidates for which the execution conditions are satisfied. The communication method according to any one of (1) to (8) above.

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

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

[0116] (12) The user equipment further has a step of transmitting an identifier regarding the SCG candidate selected as the target SCG to the target MCG. The communication method according to any one of (1) to (11) above.

[0117] (13) The user equipment further has a step of transmitting, to the target MCG, information indicating that the target SCG cannot be selected without selecting the target SCG in response to the non-existence of an SCG candidate satisfying the selection criterion. The communication method according to any one of (6) to (11) above.

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

[0119] (15) A base station that operates as a master node for managing a master cell group (MCG) used by a user equipment, A transmission unit that transmits a radio resource control (RRC) message including a target MCG setting for performing a conditional handover (CHO) to a target MCG and each SCG candidate setting of a plurality of secondary cell groups (SCGs) associated with the target MCG to the user equipment is provided. Base station.

Explanation of symbols

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

Claims

1. A communication method in which a user device communicates with a master cell group (MCG) and a secondary cell group (SCG), wherein a master node that manages the master cell group (MCG) transmits a radio resource control (RRC) message to the user device, the 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; the user device receives the RRC message; and the user device executes a PCell change involving addition / change of a PSCell based on the RRC message, wherein executing the PCell change involving addition / change of the PSCell includes holding execution of the CHO involving addition / change of the PSCell until both the execution condition for the PCell and the execution condition for the PSCell are satisfied. Communication method.

2. A user device that communicates with a master cell group (MCG) and a secondary cell group (SCG), comprising: a receiving unit 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 addition / change of a PSCell based on the RRC message, wherein the control unit holds execution of the CHOs involving addition / change of the PSCell until both the execution condition for the PCell and the execution condition for the PSCell are satisfied. User device.

3. A processor for controlling a user device that communicates with a master cell group (MCG) and a secondary cell group (SCG), A process of receiving 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, from a master node that manages the master cell group (MCG). Based on the RRC message, perform a process of executing a PCell change involving PSCell addition / change. The process of executing a PCell change involving PSCell addition / change includes a process of suspending the execution of the CHO involving PSCell addition / change until both the execution condition for the PCell and the execution condition for the PSCell are satisfied. 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 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, from a master node that manages the master cell group (MCG). Based on the RRC message, cause the user equipment to execute a process of executing a PCell change involving PSCell addition / change. The process of executing a PCell change involving PSCell addition / change includes a process of suspending the execution of the CHO involving PSCell addition / change until both the execution condition for the PCell and the execution condition for the PSCell are satisfied. Program.

5. A system including the user equipment according to claim 2 and a master node.

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