Communication methods, user devices, processors, programs, and systems

Abstract

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

Description

Technical Field

[0001] The present disclosure relates to a communication method, a user 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 for 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] A communication method according to the first embodiment is a communication method for a user device to communicate with a master cell group (MCG) and a secondary cell group (SCG), comprising the steps of: a master node managing the master cell group (MCG) sending a radio resource control (RRC) message to the user device 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 device receiving the RRC message; and the user device selecting one of the SCG candidates from the plurality of SCG candidates as the target SCG if the execution conditions in the CHO are met.

[0006] The user device according to the second embodiment is a user device that communicates with a master cell group (MCG) and a secondary cell group (SCG), and includes a receiving unit that receives a radio resource control (RRC) message from a master node that manages the master cell group (MCG) that includes 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, and a control unit that, when the execution conditions in the CHO are met, selects one of the SCG candidates from the plurality of SCG candidates as the target SCG.

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

[0008] [Figure 1]This diagram shows the configuration of a mobile communication system according to an embodiment. [Figure 2] This diagram shows the configuration of the UE (User Equipment) according to the embodiment. [Figure 3] This diagram shows the configuration of the gNB (base station) according to the embodiment. [Figure 4] This diagram shows the protocol stack configuration of the user plane wireless interface that handles data. [Figure 5] This diagram shows the protocol stack configuration of the wireless interface of the control plane that handles signaling (control signals). [Figure 6] This is a diagram illustrating the outline of DC according to the embodiment. [Figure 7] This is a diagram illustrating the CHO according to the embodiment. [Figure 8] This is a diagram illustrating the CPC according to an embodiment. [Figure 9] This is a diagram illustrating the CPA according to the embodiment. [Figure 10] This is a diagram illustrating the operation related to the simultaneous execution of CHO and CPC according to the embodiment. [Figure 11] This is a diagram illustrating the operation related to the simultaneous implementation of CHO and CPA according to the embodiment. [Figure 12] This figure shows an example of the configuration of an RRC message according to the embodiment. [Figure 13] This figure shows an example of the configuration of an RRC message according to the embodiment (2). [Figure 14] This figure shows an example of the operation flow of the UE according to the embodiment. [Modes for carrying out the invention]

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

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

[0011] The mobile communication system 1 comprises User Equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereafter, NG-RAN 10 may be simply referred to as RAN 10, and 5GC 20 may be simply referred to as core network (CN) 20.

[0012] A UE100 is a mobile wireless communication device. A UE100 can be any device used by a user. For example, a UE100 can be a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device attached to a sensor, a vehicle or a device attached to a vehicle (Vehicle UE), or an aircraft or a device attached to an 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 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. A "cell" is used as a term indicating the smallest unit of a wireless communication area. A "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 an AMF (Access and Mobility Management Function) and a 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] FIG. 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 a program executed by the processor and information used for the processing 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 program 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 types of reception 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 control and processing in the gNB200. Such processing includes processing in 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 processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing.

[0024] The backhaul communication unit 240 is connected to an adjacent base station via the Xn interface, which is an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF300 via the NG interface, which is an inter-base station-core network interface. The gNB200 may consist of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally separated), and the two units may be connected by the F1 interface, which is a fronthaul interface.

[0025] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0026] The user plane radio interface protocol consists of 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. Data and control information are transmitted between the UE100's PHY layer and the gNB200's PHY layer via a physical channel. The UE100's PHY layer receives downlink control information (DCI) transmitted from the gNB200 over the physical downlink control channel (PDCCH). Specifically, the UE100 performs blind decoding of the PDCCH using a Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from the gNB200 has a CRC parity bit added, which is scrambled by the RNTI.

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

[0029] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the UE100's RLC layer and the gNB200's RLC layer via a logical channel.

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

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

[0032] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

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

[0034] RRC signaling for various settings is transmitted between the RRC layer of the UE100 and the RRC layer of the gNB200. 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. If there is a connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC idle state. If the connection between the RRC of the UE100 and the RRC of the gNB200 is suspended, the UE100 is in the RRC inactive state.

[0035] The NAS, located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the UE100's NAS and the AMF300A's NAS. The UE100 also has application layers in addition to the wireless interface protocol. Layers below the NAS are called AS (Access Stratum).

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

[0037] In the data center, UE100 communicates simultaneously with the master cell group (MCG) 201M managed by the master node (MN) 200M and the secondary cell group (SCG) 201S managed by the secondary node (SN) 200S. MN200M may be an NR base station (gNB) or an LTE base station (eNB). MN200M is also referred to as the master base station. SN200S may be an NR base station (gNB) or an LTE base station (eNB). SN200S is also referred to as the secondary base station. MN200M and SN200S may be 6G base stations. The following explanation will primarily focus on an example where MN200M and SN200S are both NR base stations (gNBs).

[0038] For example, DC is initiated when the MN200M sends a predetermined message (e.g., an SN Addition Request message) to the SN200S via the network interface between the MN200M and the SN200S, and the MN200M sends an RRC Reconfiguration message to the UE100. The UE100, in the RRC connected state, is allocated radio resources from the schedulers of the MN200M and SN200S, and performs wireless communication using the radio resources of the MN200M and SN200S. The network interface between the MN200M and SN200S may be an Xn interface (or an X2 interface). The MN200M and SN200 communicate with each other via this network interface.

[0039] The MN200M may have a control plane connection to the core network. The MN200M provides the primary wireless resources for the UE100. The MN200M manages the MCG201M, which 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 configuration for the UE100.

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

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

[0042] (3.1) Conditional Handover (CHO) In CHO, the conditions for executing a handover are pre-set in UE100, and the handover is executed when the set conditions are met in UE100. Figure 7 is a diagram illustrating a CHO according to an embodiment.

[0043] Figure 7 shows an example 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. However, these cells may be managed by a single base station. Also, although two candidate cells (candidate cell #1 and candidate cell #2) are shown as an example, there may be one candidate cell or three or more. UE100 is in an RRC connected state in the source cell.

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

[0045] In STEP 2, UE100 begins accessing the candidate cell (in this case, candidate cell #1) whose execution conditions were met, depending on whether the conditions set in STEP 1 were met. Note that UE100 does not need to monitor the source cell from the moment it starts synchronizing with candidate cell #1.

[0046] In STEP 3, if UE100 successfully accesses candidate cell #1, it switches the connection from the source cell to candidate cell #1. This completes the handover. UE100 then communicates with candidate cell #1 using the candidate cell settings (configuration information for candidate cell #1) received in STEP 1.

[0047] (3.2) Conditional PSCell Modification (CPC) In CPC, the execution conditions for PSCell changes are pre-set in UE100, and the PSCell change is executed when the set execution conditions are met in UE100. Figure 8 is a diagram illustrating a CPC according to an embodiment. UE100 is assumed to have connections with MN gNB200M (MCG201M) and SN gNB200S-1 (SCG201S-1) and to be using DC communication.

[0048] CPCs include intra-SN CPCs, which change PSCells from one cell to another within a single SN200S, and inter-SN CPCs, which change PSCells from one cell in one SN200S to another. The following description will mainly focus on inter-SN CPCs, but the embodiments are not limited to inter-SN CPCs and may also be intra-SN CPCs.

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

[0050] In STEP 2, UE100 initiates access to the PSCell of SCG candidate 201S-2, which has met the execution conditions set in STEP 1.

[0051] In STEP 3, if UE100 successfully accesses SCG candidate 201S-2 (PSCell), it switches the PSCell from SCG201S-1 (gNB200S-1) to SCG201S-2 (gNB200S-2). This completes the PSCell change. UE100 then communicates with SCG201S-2 using the SCG candidate settings (SCG201S-2 configuration information) received in STEP 1.

[0052] (3.3) Conditional PSCell Addition (CPA) In CPA, the execution conditions for adding a PSCell are pre-set in UE100, and the PSCell is added when the set execution conditions are met in UE100. Figure 9 is a diagram illustrating a CPA according to an embodiment. UE100 is in the RRC connected state in MCG201M.

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

[0054] In STEP 2, UE100 starts accessing the PSCell of the SCG candidate (in this case, SCG candidate 201S-1) whose execution conditions have been met, depending on whether the execution conditions set in STEP 1 have been met.

[0055] In STEP 3, if UE100 successfully accesses SCG candidate 201S-1 (PSCell), it will start DC-style communication. UE100 will communicate with SCG201S-1 using the SCG candidate settings (configuration information for SCG201S-1) received in STEP 1.

[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 operation, a potential issue is how the gNB200(MN) sets multiple SCG candidates in the UE100. Furthermore, a potential issue is how the UE100 determines the target SCG from among the multiple SCG candidates.

[0057] In this embodiment, UE100 communicates with MCG201M and SCG201S via DC. Firstly, MN200M, which manages MCG201M, sends an RRC message (specifically, a Conditional Reconfiguration) to UE100 that includes the target MCG settings for performing a CHO to the target MCG, and the SCG candidate settings for each of the multiple SCG candidates associated with the target MCG. UE100 receives this RRC message. Secondly, if the execution conditions (also referred to as "trigger conditions") in the CHO are met, UE100 selects one of the multiple SCG candidates as the target SCG. This makes it possible to perform CHO and CPAC (CPC, CPA) simultaneously. If the execution conditions in the CHO are met, UE100 may start accessing the target MCG and the selected target SCG.

[0058] (4.1) Operations related to the simultaneous implementation of CHO and CPC The operation of the simultaneous execution of CHO and CPC according to the embodiment will be described. Figure 10 is a diagram illustrating the operation of the simultaneous execution of CHO and CPC according to the embodiment. UE100 is assumed to have connections with MN gNB200M-1 (MCG201M-1) and SN gNB200S-1 (SCG201S-1) and to be using DC communication. In Figure 10, one SCG candidate 201S-2 is shown as an example, but it is assumed that there are multiple SCG candidates. In the following explanation, for the sake of simplicity, it is assumed that there is one MCG candidate (target MCG) set in CHO, but there may be multiple MCG candidates set in CHO. Multiple SCG candidates may be set for each of these multiple MCG candidates.

[0059] In STEP 1, the MN, gNB200M-1, sends an RRC Reconfiguration message to UE100, which includes a Conditional Reconfiguration, consisting of CHO and CPC settings. This Conditional Reconfiguration (the first conditional RRC reconfiguration) includes condition information indicating the execution conditions in the CHO, a target MCG setting which is the setting information for the target MCG201M-2, and a list containing the SCG candidate settings for each of the multiple SCG candidates. The target MCG setting includes information necessary for communication with the target MCG201M-2 (PCell). The SCG candidate setting includes information necessary for communication with the corresponding SCG (PSCell). Details of the Conditional Reconfiguration configuration will be described later.

[0060] In STEP 2, UE100 selects a target SCG from among the multiple SCG candidates set in STEP 1, depending on whether the execution conditions for the CHO set in STEP 1 are met. Details of the target SCG selection process will be described later. Then, UE100 starts accessing target MCG201M-2(PCell) and also starts accessing the PSCell of the selected target SCG (in this case, SCG candidate 201S-2). For example, UE100 may start accessing target SCG201S-2(PSCell) after successfully accessing target MCG201M-2(PCell).

[0061] In STEP 3, if UE100 successfully accesses target MCG201M-2(PCell), it switches PCell(MN) from MCG201M-1(gNB200M-1) to MCG201M-2(gNB200M-2). Also, if UE100 successfully accesses target SCG201S-2(PSCell), it switches PSCell(SN) from SCG201S-1(gNB200S-1) to SCG201S-2(gNB200S-2). This completes CHO and CPC. UE100 communicates with MCG201M-2(PCell) using the target MCG settings received in STEP 1. Also, UE100 communicates with SCG201S-2(PSCell) using the SCG settings of the target SCG from among the multiple candidate SCG settings received in STEP 1.

[0062] (4.2) Operations related to the simultaneous administration of CHO and CPA The operation of the simultaneous implementation of CHO and CPA according to the embodiment will be described. Figure 11 is a diagram illustrating the operation of the simultaneous implementation of CHO and CPA according to the embodiment. UE100 has a connection with MN, gNB200M-1 (MCG201M-1).

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

[0064] In STEP 2, UE100 selects a target SCG from among the multiple SCG candidates set in STEP 1, depending on whether the execution conditions for the CHO set in STEP 1 are met. Details of the target SCG selection process will be described later. Then, UE100 starts accessing target MCG201M-2(PCell) and also starts accessing the PSCell of the selected target SCG (in this case, SCG candidate 201S-1). For example, UE100 may start accessing target SCG201S-1(PSCell) after successfully accessing target MCG201M-2(PCell).

[0065] In STEP 3, if UE100 successfully accesses target MCG201M-2(PCell), it switches PCell(MN) from MCG201M-1(gNB200M-1) to MCG201M-2(gNB200M-2). Also, if UE100 successfully accesses target SCG201S-2(PSCell), PSCell(SN) is added to SCG201S-1(gNB200S-1). This completes CHO and CPA. UE100 communicates with MCG201M-2(PCell) using the target MCG settings received in STEP 1. Also, UE100 communicates with SCG201S-1(PSCell) using the SCG settings of the target SCG from among the multiple candidate SCG settings received in STEP 1.

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

[0067] (4.3.1) Message Structure Example 1 Figure 12 shows an example configuration 1 of an RRC message according to the embodiment. The gNB200(MN) sends an RRC message (RRC Reconfiguration message) to the UE100 for simultaneously performing CHO and CPAC (CPC, CPA). The RRC Reconfiguration message includes Conditional Reconfiguration-r16 as an information element. Here, "-r16" means that it is an information element introduced in 3GPP Release 16.

[0068] Conditional Reconfiguration-r16 includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to add or modify with respect to MCG(MN). Each entry in condReconfigToAddModList-r16 (CondReconfigToAddMod-r16) corresponds to the first conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates the RRCReconfiguration that should be applied when the execution conditions are met. CondReconfigToAddMod-r16 also further includes condExecutionCond-r16 (not shown), which is condition information indicating the execution conditions that must be met to trigger the execution of the corresponding conditional reconfiguration.

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

[0070] Each entry in the list (secondaryCellGroupCandidateList) contains a secondaryCellGroup (or mrdc-SecondaryCellGroup), which is configuration information for a candidate SCG (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 that identifies the SCG. The radio quality threshold is the reference signal received power (RSRP) and / or reference signal received quality (RSRQ) used when selecting the SCG, specifically the threshold for the minimum quality required for the SCG to be selected.

[0071] According to this configuration example 1, it becomes possible to appropriately configure multiple SCG candidates in UE100.

[0072] (4.3.2) Example of message structure 2 Figure 13 shows an example of the configuration 2 of an RRC message according to the embodiment. The gNB200(MN) sends an RRC message (RRC Reconfiguration message) to the UE100 for simultaneously performing CHO and CPAC (CPC, CPA). The RRC Reconfiguration message includes Conditional Reconfiguration-r16 as an information element.

[0073] Conditional Reconfiguration-r16 includes condReconfigToAddModList-r16, which is a list of conditional reconfigurations to add or modify with respect to MCG(MN). Each entry in condReconfigToAddModList-r16 (CondReconfigToAddMod-r16) corresponds to the first conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates the RRCReconfiguration that should be applied when the execution conditions are met. CondReconfigToAddMod-r16 also further includes condExecutionCond-r16 (not shown), which is condition information indicating the execution conditions that must be met to trigger the execution of the corresponding conditional reconfiguration.

[0074] condRRCReconfig-r16 (RRCReconfiguration) includes masterCellGroup, which is the target MCG setting. 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 in condReconfigToAddModList-r16 (CondReconfigToAddMod-r16) corresponds to a second conditional RRC reconfiguration. CondReconfigToAddMod-r16 includes condRRCReconfig-r16, which encapsulates an RRCReconfiguration that should be applied when the execution conditions are met, and this RRCReconfiguration includes SCG candidate settings (secondaryCellGroup or mrdc-SecondaryCellGroup), which are the configuration information for the SCG candidate (target SCG). Furthermore, CondReconfigToAddMod-r16 further includes condExecutionCond-r16 (not shown), which is conditional information indicating the execution conditions that must be met to trigger the execution of the corresponding conditional reconfiguration.

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

[0076] According to this configuration example 2, it becomes possible to appropriately configure multiple SCG candidates in UE100. Furthermore, according to this configuration example 2, it becomes possible to set execution conditions for each SCG candidate in UE100.

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

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

[0079] In step S2, UE100 performs a wireless quality measurement and determines whether the execution conditions set for the target MCG (i.e., the execution conditions for CHO) have been met. Such CHO execution conditions may be condEventA3 or condEventA5 as defined in the 3GPP technical specifications. In the case of message configuration example 1 described above, UE100 may also determine whether the corresponding wireless quality threshold has been met for each SCG candidate. In the case of message configuration example 2 described above, UE100 may also determine whether the corresponding execution conditions (i.e., the execution conditions for CPAC) have been met for each set SCG candidate. Such CPAC execution conditions may be condEventA3, condEventA4, or condEventA5 as defined in the 3GPP technical specifications. Note that even if an SCG candidate meets the execution conditions, UE100 does not access that SCG candidate at this point (it is put on hold).

[0080] If it is determined that the execution conditions set for MCG201M (CHO execution conditions) are met (step S3: YES), then in step S4, UE100 selects a target SCG (PSCell) from among the set of multiple SCG candidates. Details of this selection process will be described later. Note that if there are no SCG candidates that meet the predetermined selection criteria, UE100 may fail to select a target SCG (PSCell). In other words, UE100 does not select a target SCG.

[0081] If a candidate SCG that meets the predetermined selection criteria is selected as the target SCG (Step S5: YES), in Step S6, UE100 begins accessing the target MCG (PCell). UE100 also begins accessing the selected target SCG. This explanation will proceed assuming that this access was successful.

[0082] In step S7, UE100 may send an identifier relating 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. Alternatively, UE100 may send the identifier to the target MCG regardless of the success or failure of access to the target SCG. This allows the target MCG (new MN) to know whether UE100 has selected a target SCG. UE100 may also send an RRC Reconfiguration Complete message containing the identifier to the target MCG. The identifier may be at least one of the following: the Cell ID of the PSCell of the selected target SCG, the identifier of the SCG candidate setting of the selected target SCG (condReconfigId-r16), and the ID of the SCG candidate in the message configuration example 1 described above (SCG-ID). Furthermore, UE100 may apply the SCG settings in response to successful access to the target MCG and / or to successful access to the target SCG, and discard the SCG settings for any other SCGs.

[0083] On the other hand, if a candidate SCG that meets the predetermined selection criteria cannot be selected as the target SCG (step S5: NO), in step S8, UE100 starts accessing the target MCG (PCell). Here, we will proceed with the assumption that such access was successful. Then, in step S9, UE100 may send information to the target MCG indicating that it did not select an SCG. That is, UE100 may send information to the target MCG indicating that it could not select a target SCG without selecting one, in response to the absence of a candidate SCG that meets the selection criteria. This allows the target MCG (new MN) to understand that UE100 was unable to select a target SCG. UE100 may also send an RRC Reconfiguration Complete message containing this information to the target MCG. Furthermore, UE100 may discard the SCG setting in response to successful access to the target MCG and / or in response to not selecting a target SCG. Alternatively, UE100 may not discard the SCG setting and continue wireless measurement and trigger condition determination for the SCG according to the SCG setting. In other words, the UE100 behaves as if CPAC settings were configured (it falls back to CPAC). Depending on the settings from the gNB200, the UE100 may choose to discard the SCG settings or to continue wireless measurement and trigger condition determination for the SCG without discarding the SCG settings.

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

[0085] (4.5) SCG selection process The SCG selection process according to the embodiment, i.e., step S4 in Figure 14, will now be described in detail. UE100 performs the SCG selection process using at least one of the following options.

[0086] (4.5.1) Option 1 In option 1 of the SCG selection process, the UE100 selects a target SCG from among several configured SCG candidates according to a selection criterion that prioritizes the highest wireless quality. This allows the UE100 to select an appropriate target SCG.

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

[0088] For example, UE100 first extracts an SCG (PSCell) from among multiple configured SCG candidates (multiple PSCell candidates) that satisfies the execution conditions. Alternatively, UE100 may extract an SCG (PSCell) from among multiple configured SCG candidates (multiple PSCell candidates) that satisfies the minimum required wireless quality threshold. Secondly, UE100 selects the SCG (PSCell) with the best wireless quality among the extracted SCG (PSCell). Note that wireless quality may be RSRP and / or RSRQ measured by UE100. Alternatively, UE100 may first extract the SCG with the best wireless quality from among multiple SCG candidates (multiple PSCell candidates), and secondly, if the extracted SCG satisfies the execution conditions, select that SCG (PSCell).

[0089] (4.5.2) Option 2 In option 2 of the SCG selection process, UE100 selects a target SCG from among multiple configured SCG candidates according to selection criteria that prioritize the most important SCGs specified by gNB200(MN). This allows UE100 to select the appropriate target SCG in a network-driven manner.

[0090] When execution conditions (i.e., execution conditions in CPAC) are set for each of the multiple SCG candidates, UE100 may select the SCG candidate with the highest priority among those that satisfy the execution conditions as Target SCG201S. Alternatively, when a minimum required wireless quality threshold is set for each of the multiple SCG candidates, UE100 may select the SCG candidate with the highest priority among those that satisfy the wireless quality threshold as Target SCG201S.

[0091] In Option 2, gNB200 sets multiple SCG candidates in UE100 in its preferred order. For example, the priority may be set by the order of entries in the list of SCG candidates. Specifically, the first entry in the list would have the highest priority. Alternatively, the priority may be set by the order of the SCG candidate IDs (SCG-IDs). Alternatively, gNB200 may be given an IE indicating priority so that the priority of the SCG candidate settings (list) can be explicitly specified.

[0092] The UE100 checks whether the execution conditions (or wireless quality threshold) are met for the highest priority SCG (PSCell) specified by the gNB200. If the conditions are met, the UE100 selects that SCG (PSCell); otherwise, it checks whether the execution conditions (or wireless quality threshold) are met for the next highest priority SCG. If there are multiple highest priority SCGs (PSCells), the UE100 may select the SCG (PSCell) with better wireless quality.

[0093] (4.5.3) Option 3 Option 3 of the SCG selection process is an option intended for CPC (Communication Processing). In this option 3, UE100 selects the target SCG201S from among multiple SCG candidates according to selection criteria that prioritize the SCG201S with which it is currently communicating. This enables UE100 to perform efficient target SCG selection.

[0094] For example, if UE100 has multiple configured SCG candidates (multiple PSCell candidates) and there is an SCG (PSCell) that is currently communicating (in use or configured), it provisionally selects that SCG (PSCell). Then, if the provisionally selected SCG (PSCell) meets the execution conditions (or wireless quality threshold), UE100 selects that SCG (PSCell). If the execution conditions (or wireless quality threshold) are not met or if there is no SCG currently communicating among the candidates, UE100 executes option 1 or 2 above.

[0095] (4.5.4) Option 4 Option 4 of the SCG selection process is an exception behavior for when UE100 is unable to select an SCG. If, as a result of applying options 1 through 3 above, UE100 is unable to select an SCG (i.e., none of the candidate SCG settings meet the execution conditions (or wireless quality threshold)), it will not select any SCG.

[0096] (4.5.5) Option 5 In option 5 of the SCG selection process, UE100 selects target SCG201S from among multiple SCG candidates according to the selection criteria for selecting an SCG whose wireless quality meets the minimum quality standard. For example, UE100 may, in conjunction with option 1 described above, select the SCG with the best wireless quality from among the SCGs that meet the minimum quality threshold. UE100 may also include only SCGs that meet the minimum quality threshold in its selection.

[0097] (5) Other embodiments In the embodiments described above, a DC in which UE100 communicates with an MCG and an SCG was described, but it may also be applied to multi-connectivity (MC) in which UE100 communicates with an MCG and multiple SCGs. In this case, UE100 may select multiple SCGs in the (4.5) SCG selection process described above. For example, when selecting two SCGs, UE100 may select the SCG with the best wireless quality and the SCG with the second best wireless quality. Alternatively, UE100 may select the SCG with the highest priority and the SCG with the second highest priority. gNB200 may set the number of SCGs to be selected (which may be the number of selectable SCGs or the number of permitted SCGs) for UE100. UE100 may specify the number of SCGs to be selected according to the setting by gNB200. This setting may only be performed in the case of MC. That is, in the case of DC, this setting may not be performed. UE100 accesses the selected SCGs in the same manner as in the embodiments described above. Note that UE100 may access the selected SCGs even if the number of selected SCGs does not reach 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 SCGs selected is 1, access to the selected SCG will still be performed.

[0098] Each of the above-described operation flows can be performed not only independently, but also in combination of two or more operation flows. 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 embodiment, an example was described in which the base station is an NR base station (gNB), but the base station may also be an LTE base station (eNB) or a 6G base station. Furthermore, the base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of an IAB node. Additionally, the user equipment may be an MT (Mobile Termination) of an IAB node.

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

[0101] The terms “based on” and “depending on” used in this disclosure do not mean “based solely on” or “depending solely on” unless otherwise specified. “Based on” means both “based solely on” and “at least partially on.” Similarly, “depending on” means both “at least partially on” and “at least partially on.” Furthermore, the terms “include,” “comprise,” and variations thereof do not mean that only the listed items are included; they may include only the listed items, or they may include additional items in addition to the listed items. Also, the term “or” used in this disclosure is not intended to mean exclusive OR. Moreover, any reference to elements 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. Therefore, references to the first and second elements do not imply that only two elements may be adopted therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated by the context that they are not.

[0102] Although the embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes can be made without departing from the gist of the invention.

[0103] This application claims priority to U.S. Provisional Application No. 63 / 307248 (filed February 7, 2022), the entirety of which is incorporated into the specification of this application.

[0104] (Note) The features of the above-described embodiment are noted below.

[0105] (1) A communication method by which a user device communicates with a master cell group (MCG) and a secondary cell group (SCG), The steps include: a master node managing the master cell group (MCG) sending a radio resource control (RRC) message to the user device, which includes a target MCG setting for performing a conditional handover (CHO) to the target MCG, and the SCG candidate settings for each of a plurality of SCG candidates associated with the target MCG; The user device receives the RRC message, The user device has the step of selecting one of the SCG candidates from among the plurality of SCG candidates as the target SCG when the execution conditions in the CHO are met. Communication method.

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

[0107] (3) The RRC message includes a first conditional RRC reset, The first conditional RRC reset described above is: Conditional information indicating the execution conditions, The aforementioned target MCG setting, A list including the settings for each of the plurality of SCG candidates, The communication method described in (1) or (2) above.

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

[0109] (5) The aforementioned list includes the second conditional RRC reset for each of the multiple SCG candidates, The second conditional RRC reset described above is: Conditional information indicating the execution conditions for the corresponding SCG candidate, The SCG candidate setting for the corresponding SCG candidate, The communication method described in any of (1) through (4) above.

[0110] (6) The aforementioned selection step includes selecting the target SCG from among the multiple SCG candidates according to a selection criterion that selects them in order of highest wireless quality. The communication method described in any of (1) through (5) above.

[0111] (7) When execution conditions have been set for each of the aforementioned multiple SCG candidates, The aforementioned selection step includes selecting the SCG candidate with the best wireless quality among the SCG candidates that satisfy the execution conditions as the target SCG. The communication method described in any of (1) through (6) above.

[0112] (8) The aforementioned selection step includes selecting the target SCG from among the multiple SCG candidates according to selection criteria that select in descending order of priority as specified by the master node. The communication method described in any of (1) through (7) above.

[0113] (9) When execution conditions have been set for each of the aforementioned multiple SCG candidates, The aforementioned selection step includes selecting the SCG candidate with the highest priority among the SCG candidates that satisfy the execution conditions as the target SCG. The communication method described in any of (1) through (8) above.

[0114] (10) The selection step includes selecting the target SCG from among the multiple SCG candidates in accordance with selection criteria that prioritize the SCG that the user device is currently communicating with. The communication method described in any of (1) through (9) above.

[0115] (11) The aforementioned selection step includes selecting the target SCG from among the multiple SCG candidates in accordance with selection criteria for selecting an SCG whose wireless quality meets the minimum quality standard. The communication method described in any of (1) through (10) above.

[0116] (12) The user device further includes the step of transmitting an identifier relating to the SCG candidate selected as the target SCG to the target MCG. The communication method described in any of (1) through (11) above.

[0117] (13) The user device further includes the step of transmitting information to the target MCG indicating that it cannot select a target SCG, without selecting a target SCG, if no SCG candidate that satisfies the selection criteria exists. The communication method described in any of (6) through (11) above.

[0118] (14) A user device that communicates with a master cell group (MCG) and a secondary cell group (SCG), A receiving unit receives a radio resource control (RRC) message from a master node managing the master cell group (MCG) that includes a target MCG setting for performing a conditional handover (CHO) to a target MCG, and the SCG candidate settings for each of a plurality of SCG candidates associated with the target MCG. The system includes a control unit that, when the execution conditions in the CHO are met, selects one of the multiple SCG candidates as the target SCG. User device.

[0119] (15) A base station that operates as a master node managing the master cell group (MCG) used by user equipment, The system includes a transmission unit that transmits a radio resource control (RRC) message to the user device, which includes a target MCG setting for performing a conditional handover (CHO) to a target MCG, and SCG candidate settings for each of a plurality of secondary cell group (SCG) candidates associated with the target MCG. Base station. [Explanation of Symbols]

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

Claims

1. A communication method by which a user device communicates with a master cell group (MCG) and a secondary cell group (SCG), The master node managing the master cell group (MCG) transmits a radio resource control (RRC) message to the user device, which includes a target MCG setting for performing a conditional handover (CHO) to the target MCG, an SCG setting for a candidate SCG associated with the target MCG, condition information indicating the execution conditions for the primary cell (PCell) in the target MCG, and condition information indicating the execution conditions for the primary cell (PSCell) in the candidate SCG. The user device receives the RRC message, The user device performs PCell modifications, including PSCell additions and modifications, based on the RRC message. Communication method.

2. A user device that communicates with a master cell group (MCG) and a secondary cell group (SCG), A receiving unit receives a radio resource control (RRC) message from a master node managing the master cell group (MCG), which includes a target MCG setting for performing a conditional handover (CHO) to a target MCG, an SCG setting for a candidate SCG associated with the target MCG, condition information indicating the execution conditions for a primary cell (PCell) in the target MCG, and condition information indicating the execution conditions for a primary cell (PSCell) in the candidate SCG. The system includes a control unit that performs a PCell modification, which involves adding or modifying a PSCell, based on the aforementioned RRC message. User device.

3. A processor that controls user devices that communicate with a master cell group (MCG) and a secondary cell group (SCG), Processing to receive a radio resource control (RRC) message from a master node managing the master cell group (MCG), which includes: target MCG settings for performing a conditional handover (CHO) to a target MCG; SCG settings for a candidate SCG associated with the target MCG; condition information indicating execution conditions for a primary cell (PCell) in the target MCG; and condition information indicating execution conditions for a primary cell (PSCell) in the candidate SCG. Based on the RRC message, the process of performing PCell changes that involve adding or modifying PSCell is executed. Processor.

4. A program for controlling user devices that communicate with a master cell group (MCG) and a secondary cell group (SCG), Processing to receive a radio resource control (RRC) message from a master node managing the master cell group (MCG), which includes: target MCG settings for performing a conditional handover (CHO) to a target MCG; SCG settings for a candidate SCG associated with the target MCG; condition information indicating execution conditions for a primary cell (PCell) in the target MCG; and condition information indicating execution conditions for a primary cell (PSCell) in the candidate SCG. Based on the RRC message, the user device is instructed to perform a process that involves adding or modifying PSCell. program.

5. A system comprising the user device and master node described in claim 2.

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