Communication method, user device, mobile communication system, program, and chipset

Abstract

This communication method comprises: a step in which a user device in a wireless resource control (RRC) connected state receives a first multicast configuration including a reference identifier, a fixed parameter value, and a variable parameter value from a network node via a dedicated RRC message; a step in which the user device that has transitioned from the RRC connected state to an RRC inactive state receives a second multicast configuration including the reference identifier and a new variable parameter value from the network node in a multicast control channel (MCCH); and a step in which, on the basis of the reference identifier, the user device in the RRC inactive state updates the variable parameter value received in the dedicated RRC message to the new variable configuration parameter value received in the MCCH.

Description

Communication Method

[0001] The present disclosure relates to a communication method for use in a mobile communication system.

[0002] The 3rd Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter) defines the technical specifications for NR (New Radio), a fifth-generation (5G) wireless access technology. Compared to LTE (Long Term Evolution), a fourth-generation (4G) wireless access technology, NR has features such as high speed, large capacity, high reliability, and low latency. 3GPP defines the technical specifications for 5G / NR multicast / broadcast services (MBS) (see, for example, Non-Patent Document 1).

[0003] 3GPP Technical Specification: TS 38.300 V17.1.0

[0004] A communication method according to a first aspect is a communication method used in a mobile communication system that provides a multicast / broadcast service (MBS), and includes the steps of: a user equipment in a radio resource control (RRC) connected state receiving a first multicast configuration including a reference identifier, a fixed parameter value, and a variable parameter value from a network node (or a network device) in a dedicated RRC message; the user equipment, which has transitioned from the RRC connected state to an RRC inactive state, receiving a second multicast configuration including the reference identifier and a new variable parameter value from the network node on a multicast control channel (MCCH); and the user equipment in the RRC inactive state updating the variable parameter value received in the dedicated RRC message to the new variable configuration parameter value received on the MCCH based on the reference identifier.

[0005] A communication method according to a second aspect is a communication method used in a mobile communication system that provides a multicast / broadcast service (MBS), and includes the steps of: a user equipment in a radio resource control (RRC) connected state and having participated in a multicast session, receiving configuration information from a network node that configures whether the user equipment will monitor a multicast control channel (MCCH) in an RRC inactive state; and the user equipment that has transitioned from the RRC connected state to the RRC inactive state monitoring the MCCH based on the configuration information.

[0006] 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram showing the configuration of a gNB (base station) according to an embodiment. FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram showing an operation for a UE in an RRC inactive state to perform multicast reception. FIG. 7 is a diagram showing an example of operation of a mobile communication system according to an embodiment. FIG. 8 is a diagram showing an example of operation of a mobile communication system according to a modified example.

[0007] 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.

[0008] (System Configuration) Fig. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. The mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. Although 5GS will be described below as an example, the mobile communication system may also be at least partially based on an LTE (Long Term Evolution) system. The mobile communication system may also be at least partially based on a 6th Generation (6G) system.

[0009] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10 (or network 10). The 5GC 20 may be simply referred to as the core network (CN) 20.

[0010] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0011] The NG-RAN 10 includes a base station (called a "gNB" in a 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource for wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0012] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0013] The 5GC20 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 controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0014] 2 is a diagram showing the configuration of a UE 100 (user equipment) according to an 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.

[0015] The receiving unit 110 performs various reception operations under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0016] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0017] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. The operations of the UE 100 described above and below may be operations under the control of the control unit 230. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the 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 baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0018] 3 is a diagram showing the configuration of a gNB 200 (base station) according to an embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0019] 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 a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0020] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0021] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer described below. The operations of the gNB 200 described above and below may be operations under the control of the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0022] The backhaul communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected by an F1 interface, which is a fronthaul interface.

[0023] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0024] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0025] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires the successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC parity bit scrambled by the RNTI added.

[0026] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the gNB 200 via a transport channel. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE 100.

[0027] 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 RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0028] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0029] The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0030] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0031] The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and an NAS (Non-Access Stratum) layer instead of the SDAP layer shown in FIG.

[0032] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0033] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, a layer lower than the NAS layer is called an AS layer.

[0034] (Overview of MBS) The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0035] In the case of a multicast communication service (also referred to as "MBS multicast"), the same service and the same specific content data are simultaneously provided to a specific set of UEs. That is, not all UEs 100 within a multicast service area are permitted to receive the data. The multicast communication service is delivered to the UEs 100 using a multicast session, which is a type of MBS session. The UEs 100 can receive the multicast communication service in an RRC connected state using mechanisms such as Point-to-Point (PTP) and / or Point-to-Multipoint (PTM) delivery. The UEs 100 may also receive the multicast communication service in an RRC inactive (or RRC idle) state. Such a delivery mode is also referred to as "Delivery Mode 1".

[0036] In the case of a broadcast communication service (also referred to as "MBS broadcast"), the same service and the same specific content data are simultaneously provided to all UEs 100 in a geographical area. That is, all UEs 100 within the broadcast service area are permitted to receive the data. The broadcast communication service is delivered to the UEs 100 using a broadcast session, which is a type of MBS session. The UEs 100 can receive the broadcast communication service in any of the RRC idle state, the RRC inactive state, and the RRC connected state. This delivery mode is also referred to as "delivery mode 2".

[0037] The main logical channels used for MBS delivery are the Multicast Traffic Channel (MTCH), the Dedicated Traffic Channel (DTCH), and the Multicast Control Channel (MCCH). The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast or broadcast session from the network 10 to the UE 100. The DTCH is a PTP channel for transmitting MBS data of a multicast session from the network 10 to the UE 100. The MCCH is a PTM downlink channel for transmitting MBS broadcast control information associated with one or more MTCHs from the network 10 to the UE 100.

[0038] Regarding the configuration for MBS broadcast, the UE 100 in the RRC idle state, the RRC inactive state, or the RRC connected state receives the MBS configuration for the broadcast session (e.g., parameters required for MTCH reception) via the MCCH. The parameters required for MCCH reception (MCCH configuration) are provided via system information. Specifically, the system information block type 20 (SIB20) includes the MCCH configuration. Note that the SIB type 21 (SIB21) includes information on service continuity for MBS broadcast reception. The MCCH provides a list of all broadcast services, including ongoing sessions, transmitted on the MTCH. The related information for the broadcast session includes the MBS session ID (e.g., TMGI (Temporary Mobile Group Identity)), related MTCH scheduling information, and information on neighboring cells providing a specific service on the MTCH.

[0039] On the other hand, with regard to MBS multicast, in the current 3GPP technical specifications, UE 100 can only receive multicast session data in the RRC connected state. When UE 100 that has joined a multicast session is in the RRC connected state and the multicast session is activated, gNB 200 transmits an RRC reconfiguration message including MBS configuration for the multicast session to UE 100. Such MBS configuration is also referred to as multicast radio bearer (MRB) configuration, MTCH configuration, or multicast configuration. Such MRB configuration (MRB-ToAddMod) includes other parameters such as an MBS session ID (mbs-SessionId), an MRB ID (mrb-Identity), and a PDCP configuration (pdcp-Config) for the MRB (multicast MRB) to be configured in UE 100.

[0040] In the following embodiment, an operation that enables the UE 100 in the RRC inactive state to perform multicast reception will be mainly described. Fig. 6 is a diagram showing an overview of the operation.

[0041] Possible solutions for the UE 100 in the RRC inactive state to perform multicast reception include a distribution mode 1 based solution shown in FIG. 6( a) and a distribution mode 2 based solution shown in FIG. 6( b).

[0042] In the distribution mode 1-based solution shown in Figure 6 (a), in step S1, gNB200 transmits an RRC Reconfiguration message including an MBS setting (multicast setting) for the multicast session to UE100 in the RRC connected state. UE100 receives multicast data on the MTCH via the multicast session (multicast MRB) based on the multicast setting received in the RRC Reconfiguration message.

[0043] In step S2, the gNB 200 transmits an RRC Release message to the UE 100 in the RRC Connected state to transition the UE 100 to the RRC inactive state. The RRC Release message includes a setting (Suspend Config.) for the RRC inactive state.

[0044] In step S3, in response to the reception of the RRC Release message in step S2, the UE 100 transitions from the RRC connected state to the RRC inactive state.

[0045] In step S4, the UE 100 in the RRC inactive state continues to use the multicast setting in step S1 to receive multicast data on the MTCH via the multicast session.

[0046] This enables the UE 100 in the RRC inactive state to perform multicast reception. Note that although an example of performing multicast configuration using an RRC Reconfiguration message has been described, multicast configuration may also be performed using an RRC Release message.

[0047] The RRC Reconfiguration message and the RRC Release message are both RRC messages transmitted individually to a UE on a Dedicated Control Channel (DCCH), and are hereinafter also referred to as dedicated RRC messages.

[0048] On the other hand, in the distribution mode 2-based solution shown in FIG. 6(b), in step S11, the gNB 200 transmits an RRC Release message to the UE 100 in the RRC connected state to transition the UE 100 to the RRC inactive state. The RRC Release message includes a setting (Suspend Config.) for the RRC inactive state.

[0049] In step S12, in response to the reception of the RRC Release message in step S11, the UE 100 transitions to an RRC inactive (INACTIVE) state.

[0050] In step S13, gNB200 transmits an MCCH including an MBS setting (multicast setting) for the multicast session. UE100 receives the MCCH. Note that UE100 receives SIB20 prior to receiving the MCCH, and receives the MCCH based on SIB20. MCCH transmission (and reception) may be performed before step S11 or simultaneously with step S11.

[0051] In step S14, the UE 100 in the RRC inactive state receives multicast data on the MTCH via the multicast session based on the multicast setting received on the MCCH in step S13. This enables the UE 100 in the RRC inactive state to perform multicast reception.

[0052] (System Operation Example) In the embodiment, a delivery mode 1 based solution and a delivery mode 2 based solution are combined to enable the UE 100 in an RRC inactive state to efficiently receive multicast.

[0053] Specifically, first, when UE 100 is in an RRC connected state, it receives a multicast setting (first multicast setting) in a dedicated RRC message. Second, UE 100 transitions from the RRC connected state to an RRC inactive state. UE 100 in the RRC inactive state may perform multicast reception using the first multicast setting until it receives the second multicast setting. Third, when UE 100 is in an RRC inactive state, it receives a multicast setting (second multicast setting) on ​​an MCCH.

[0054] As described above, MBS multicast can be received only by a specific UE group (a specific UE set). The multicast configuration includes a parameter value such as an identifier of a multicast session (multicast service) received by the specific UE group, for example, at least one of a TMGI (Temporary Mobile Group Identity) and a G-RNTI (Group Radio Network Temporary Identifier).

[0055] Such parameter values ​​are UE group-specific parameters and may require security (and privacy protection). However, since the MCCH is a logical channel that can be received by all UEs, it is not preferable to transmit parameter values ​​that may require security on the MCCH.

[0056] In the embodiment, parameter values ​​requiring security are set in a dedicated RRC message, and parameter values ​​other than the set parameter values ​​are transmitted via the MCCH. That is, parameter values ​​requiring security are not transmitted via the MCCH, and the parameter values ​​transmitted via the dedicated RRC message are continuously used. Hereinafter, the continuously used parameter values ​​are also referred to as fixed parameter values. Meanwhile, parameter values ​​transmitted via the dedicated RRC message and the MCCH and that can be updated are also referred to as variable parameter values.

[0057] 7 is a diagram showing an example of operation of the mobile communication system 1 according to the embodiment. Prior to this operation, it is assumed that the UE 100 has already joined a multicast session. Furthermore, it is assumed that the UE 100 is currently receiving or will soon receive multicast data in an RRC connected state.

[0058] In step S101, the gNB 200 transmits a first multicast setting to the UE 100 in the RRC connected state in a dedicated RRC message, the first multicast setting including a reference identifier, fixed parameter values ​​that are not updated by the MCCH, and variable parameter values ​​that can be updated by the MCCH. That is, the gNB 200 configures the first multicast setting individually for the UE. The UE 100 receives a dedicated RRC message including the first multicast setting from the gNB 200 and stores the first multicast setting. A portion of the first multicast setting may be updated by the MCCH. Therefore, the first multicast setting can be considered a base multicast setting. Note that some or all of the variable parameter values ​​that can be updated by the MCCH may not be included in the first multicast setting. In this case, the multicast setting is not completed until the second multicast setting described below is received. In other words, by receiving the first multicast setting and the second multicast setting, the UE 100 becomes able to receive multicast (MTCH).

[0059] In the illustrated example, the dedicated RRC message including the first multicast configuration is an RRC Reconfiguration message. However, the dedicated RRC message may be an RRC Release message. Alternatively, the fixed parameter values ​​and variable parameter values ​​may be configured in the RRC Reconfiguration message, and the reference identifier may be configured in the RRC Release message.

[0060] The reference identifier is an identifier that can identify a multicast setting and is an identifier other than TMGI and G-RNTI. The reference identifier may be an MRB identifier (MRB ID). However, since the MRB ID is unique to a UE, a new identifier unique to a multicast group may be used as the reference identifier.

[0061] The fixed parameter values ​​include the TMGI and / or G-RNTI associated with the multicast session.

[0062] The variable parameter value includes at least one of a transmission period and a transmission duration of an MTCH associated with the multicast session. The variable parameter value may include a PDSCH setting of the MTCH. The variable parameter value may include at least one of drx-ConfigPTM-List, pdsch-ConfigMTCH, mtch-SSB-MappingWindowList, mtch-SchedulingInfo, pdsch-ConfigIndex, mtch-SSB-MappingWindowIndex, and drx-ConfigPTM, which are defined in the 3GPP technical specifications.

[0063] Here, which parameters (specifically, which information elements in the first multicast setting) are fixed parameters or variable parameters may be specified in advance in the technical specifications, or may be determined by the setting of the gNB 200. In the latter case, the gNB 200 may transmit information specifying at least one of the parameter types of fixed parameters and variable parameters to the UE 100, for example, in step S101. Based on the information, the UE 100 identifies whether each parameter included in the first multicast setting set in the dedicated RRC message is a fixed parameter or a variable parameter.

[0064] In step S102, gNB200 may transmit multicast data on the MTCH via the multicast session based on the first multicast setting of step S101. UE100 may receive multicast data on the MTCH via the multicast session based on the first multicast setting of step S101.

[0065] In step S103, the gNB 200 determines to transition the UE 100 from the RRC connected state to the RRC inactive state, and transmits an RRC Release message including Suspend config. to the UE 100. The UE 100 receives the RRC Release message. Note that the above-described first multicast setting may be included in the RRC Release message. In that case, step S101 may be unnecessary.

[0066] In step S104, in response to the reception of the RRC Release message in step S103, the UE 100 transitions from the RRC connected state to the RRC inactive state.

[0067] In step S105, the gNB 200 may transmit multicast data on the MTCH via the multicast session based on the first multicast setting of step S101. The UE 100 that has transitioned to the RRC inactive state may receive multicast data on the MTCH via the multicast session based on the first multicast setting of step S101.

[0068] In step S106, the gNB 200 determines to update the multicast setting (first multicast setting) set in step S101. For example, the gNB 200 may determine to change the transmission period of the MTCH associated with the multicast session. The gNB 200 may determine to change the transmission duration of the MTCH. The transmission duration refers to the time during which one MTCH transmission according to the transmission period lasts.

[0069] In step S107, the gNB 200 transmits a second multicast configuration including the reference identifier and the new variable parameter value on the MCCH to the UE 100. The UE 100 in the RRC inactive state receives the second multicast configuration.

[0070] The reference identifier in the second multicast setting is an identifier for identifying the above-mentioned first multicast setting, and is an MRB identifier or a newly defined identifier. The new variable parameter values ​​in the second multicast setting are parameter values ​​after updating the variable parameter values ​​of the first multicast setting. However, parameter values ​​that are not updated among the variable parameter values ​​may not be included in the second multicast setting.

[0071] The second multicast configuration does not include fixed parameter values, such as TMGI and / or G-RNTI. This can prevent security issues from occurring. For example, it is easier to prevent UEs 100 that are not participating in a multicast session from attempting to receive the multicast session. In addition, since TMGI has a large number of bits, not transmitting TMGI on the MCCH also contributes to reducing MCCH overhead.

[0072] In step S108, the UE 100 in the RRC inactive state updates the variable parameter value received in the dedicated RRC message (first multicast setting) to the new variable setting parameter value received in the MCCH (second multicast setting) based on the reference identifier (i.e., using the reference identifier as a key). That is, the UE 100 overwrites the stored variable parameter value with the new variable setting parameter value while maintaining the stored fixed parameter value. In this way, when the UE 100 in the RRC inactive state finds that the second multicast setting (MCCH) contains a reference identifier that matches the reference identifier in the currently stored multicast setting, the UE 100 applies the parameters updated in the MCCH to the base multicast setting.

[0073] In step S109, gNB200 may transmit multicast data on MTCH via a multicast session based on the second multicast setting of step S107. UE100 in an RRC inactive state receives multicast data from gNB200 on MTCH via a multicast session based on the second multicast setting of step S107, specifically, the updated multicast setting (fixed parameter values ​​and new variable parameter values) of step S108.

[0074] (Modification of Operation) A modification of the operation according to the above-described embodiment will be described. In the above-described embodiment, it is assumed that the UE 100 in the RRC inactive state monitors the MCCH after multicast configuration is performed using a dedicated RRC message.

[0075] However, in cases where the multicast setting configured in the dedicated RRC message is not subsequently updated, the UE 100 may waste power consumption by monitoring the MCCH. Therefore, in this modification, the gNB 200 is configured to set to the UE 100 whether the UE 100 should monitor the MCCH. Specifically, the gNB 200 sets to the UE 100 whether the UE 100 should monitor the MCCH while receiving multicast in an RRC inactive state.

[0076] 8 is a diagram showing an example of operation of the mobile communication system 1 according to this modification. Prior to this operation, it is assumed that the UE 100 has already joined a multicast session. Furthermore, it is assumed that the UE 100 is currently receiving or will soon receive multicast data in an RRC connected state. Here, redundant explanations of operations similar to those described above will be omitted.

[0077] In step S201, gNB200 transmits multicast settings to UE100 in the RRC connected state in a dedicated RRC message (in the illustrated example, an RRC Reconfiguration message. However, it may also be an RRC Release message (step S203)). UE100 receives the multicast settings in the dedicated RRC message.

[0078] In step S202, gNB200 may transmit multicast data on the MTCH via the multicast session based on the multicast setting of step S201. UE100 may receive multicast data on the MTCH via the multicast session based on the multicast setting of step S201.

[0079] In step S203, gNB200 decides to transition UE100 from the RRC connected state to the RRC inactive state, and transmits an RRC Release message including Suspend config. to UE100. UE100 receives the RRC Release message.

[0080] In the example shown, the gNB 200 includes in the RRC Release message setting information for setting whether the UE 100 monitors the MCCH in the RRC inactive state. That is, the RRC Release message includes setting information that specifies whether or not to perform the MCCH reception operation when performing multicast reception (or waiting) in the RRC inactive state. Note that instead of including the setting information in the RRC Release message (step S203), the setting information may be included in the RRC Reconfiguration message (step S201). Below, an example of including the setting information in the RRC Release message (step S203) will be described. When gNB200 configures UE100 to monitor the MCCH, it may include the MCCH configuration to be transmitted in SIB20 in a dedicated RRC message (RRC Release message or RRC Reconfiguration message) and send it to UE100.

[0081] In step S204, in response to the reception of the RRC Release message in step S203, the UE 100 transitions from the RRC connected state to the RRC inactive state.

[0082] In step S205, the UE 100 in the RRC inactive state checks whether or not it has been set in step S203 to perform MCCH monitoring.

[0083] If MCCH monitoring is configured (step S205: YES), in step S206, UE 100 in the RRC inactive state monitors the MCCH and receives the MCCH (multicast setting). Note that UE 100 receives SIB 20 prior to receiving the MCCH, and monitors and receives the MCCH based on SIB 20. UE 100 receives multicast data on the MTCH via a multicast session based on the received MCCH (step S207). UE 100 may receive the MCCH after receiving the MTCH. That is, MCCH reception (step S206) and MTCH reception (step S207) may be performed in parallel.

[0084] On the other hand, if MCCH monitoring is not configured (step S205: NO), in step S207, UE 100 in the RRC inactive state receives multicast data on the MTCH via the multicast session by continuing to use the multicast setting of step S201 without performing MCCH monitoring.

[0085] This modification may be based on the operation according to the above-described embodiment. That is, the multicast setting in step S201 (first multicast setting) and the multicast setting in step S205 (second multicast setting) may each include a reference identifier, and the second multicast setting may update the variable parameter value of the first multicast setting.

[0086] (Other Embodiments) In the above-described embodiment, multicast reception in the RRC inactive state has been mainly described, but the operation according to the above-described embodiment may be applied to multicast reception in the RRC idle state. That is, the "RRC inactive state" in the operation according to the above-described embodiment and its modified examples may be read as the "RRC idle state." In the case of the RRC idle state, RRC restoration (Resume) is read as RRC establishment (Establishment).

[0087] The above-described operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed.

[0088] In the above-described embodiments and examples, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The UE 100 may also be an MT (Mobile Termination) of the IAB node.

[0089] Also, the term "network node" primarily refers to a base station, but may also refer to a device in the core network or part of a base station (CU, DU, or RU).

[0090] 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. Using a computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the UE 100 or the gNB 200 may be integrated, and at least a portion of the UE 100 or the gNB 200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0091] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0092] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0093] This application claims priority from Japanese Patent Application No. 2022-155399 (filed September 28, 2022), the entire contents of which are incorporated herein by reference.

[0094] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0095] (Supplementary Note 1) A communication method used in a mobile communication system providing a multicast / broadcast service (MBS), comprising: a step of a user equipment in a radio resource control (RRC) connected state receiving a first multicast configuration including a reference identifier, a fixed parameter value, and a variable parameter value from a network node in a dedicated RRC message; a step of the user equipment, which has transitioned from the RRC connected state to an RRC inactive state, receiving a second multicast configuration including the reference identifier and a new variable parameter value from the network node in a multicast control channel (MCCH); and a step of the user equipment in the RRC inactive state updating the variable parameter value received in the dedicated RRC message to the new variable configuration parameter value received in the MCCH based on the reference identifier.

[0096] (Supplementary Note 2) The communication method according to Supplementary Note 1, further comprising the step of the user equipment in the RRC inactive state receiving multicast data from the network node via a multicast session based on the fixed parameter value and the new variable parameter value.

[0097] (Supplementary Note 3) The communication method according to Supplementary Note 1 or 2, further comprising the step of receiving, from the network node, information specifying at least one of a parameter type of a fixed parameter that is not updated by the MCCH and a parameter type of a variable parameter that can be updated by the MCCH.

[0098] (Supplementary Note 4) The communication method according to any one of Supplementary Notes 1 to 3, wherein the fixed parameter value includes at least one of a TMGI (Temporary Mobile Group Identity) and a G-RNTI (Group Radio Network Temporary Identifier).

[0099] (Supplementary Note 5) The communication method according to any one of Supplementary Notes 1 to 4, wherein the variable parameter value includes at least one of a transmission period and a transmission duration of a multicast traffic channel (MTCH).

[0100] (Supplementary Note 6) A communication method used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising the steps of: a user equipment in a radio resource control (RRC) connected state and having joined a multicast session receiving, from a network node, configuration information for configuring whether the user equipment will monitor a multicast control channel (MCCH) in an RRC inactive state; and the user equipment that has transitioned from the RRC connected state to the RRC inactive state monitoring the MCCH based on the configuration information.

[0101] (Supplementary Note 7) The communication method according to Supplementary Note 6, further comprising the step of the user equipment in the RRC connected state transitioning from the RRC connected state to the RRC inactive state in response to receiving an RRC release message from the network node, wherein the configuration information is information included in the RRC release message.

[0102] (Supplementary Note 8) The communication method according to Supplementary Note 6, further comprising the step of the user equipment in the RRC connected state receiving, from the network node, an RRC reconfiguration message including multicast configuration required for receiving the multicast session, wherein the configuration information is information included in the RRC reconfiguration message.

[0103] 1: Mobile communication system 10: RAN 20: CN 100: UE (user equipment) 110: Receiving unit 120: Transmitting unit 130: Control unit 200: gNB (base station) 210: Transmitting unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication method used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: A user equipment that is in a Radio Resource Control (RRC) connected state and has already participated in a multicast session receives an RRC Release message from a network node for permitting reception of the multicast session in an RRC inactive state; The user equipment transitions from the RRC connected state to the RRC inactive state in response to reception of the RRC Release message; When the received RRC Release message does not contain predetermined information, the user equipment that has transitioned to the RRC inactive state receives a multicast control channel from the network node; When the received RRC Release message contains the predetermined information, the user equipment that has transitioned to the RRC inactive state receives a multicast traffic channel from the network node. The communication method.

2. Receiving the multicast traffic channel When the received RRC Release message contains the predetermined information, the user equipment that has transitioned to the RRC inactive state includes receiving the multicast traffic channel without receiving the multicast control channel. The communication method according to Claim 1.

3. A user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), comprising: A receiving unit that receives an RRC Release message from a network node for permitting reception of a multicast session in an RRC inactive state by the user equipment that is in an RRC connected state and has already participated in the multicast session; A control unit that transitions the user equipment from the RRC connected state to the RRC inactive state in response to reception of the RRC Release message. The receiving unit ​ After the user device transitions to the RRC inactive state, if the received RRC Release message does not contain predetermined information, receive a multicast control channel from the network node, After the user device transitions to the RRC inactive state, if the received RRC Release message contains the predetermined information, receive a multicast traffic channel from the network node User device. **Claim 4**: A mobile communication system that provides a multicast / broadcast service (MBS), An RRC Release message for permitting a user device that is in the radio resource control (RRC) connected state and has already participated in a multicast session to receive the multicast session in the RRC inactive state is received from a network node, The user device transitions from the RRC connected state to the RRC inactive state in response to the reception of the RRC Release message, After the user device that has transitioned to the RRC inactive state, if the received RRC Release message does not contain predetermined information, receive a multicast control channel from the network node, After the user device that has transitioned to the RRC inactive state, if the received RRC Release message contains the predetermined information, receive a multicast traffic channel from the network node Mobile communication system. **Claim 5**: In a user device used in a mobile communication system that provides a multicast / broadcast service (MBS), A process of receiving, from a network node, an RRC Release message for permitting a user device that is in the radio resource control (RRC) connected state and has already participated in a multicast session to receive the multicast session in the RRC inactive state, A process of transitioning the user device from the RRC connected state to the RRC inactive state in response to the reception of the RRC Release message, After the user device transitions to the RRC inactive state, if the received RRC Release message does not contain predetermined information, a process of receiving a multicast control channel from the network node, After the user device transitions to the RRC inactive state, if the received RRC Release message contains the predetermined information, a process of receiving a multicast traffic channel from the network node, and causing the execution of Program. **Claim 6**: A chipset of a user device used in a mobile communication system that provides a multicast / broadcast service (MBS), Receiving an RRC Release message from a network node for permitting the user device, which is in the radio resource control (RRC) connected state and has already participated in a multicast session, to receive the multicast session in the RRC inactive state, In response to the reception of the RRC Release message, transitioning the user device from the RRC connected state to the RRC inactive state, After the user device has transitioned to the RRC inactive state, if the received RRC Release message does not contain predetermined information, receiving a multicast control channel from the network node, After the user device has transitioned to the RRC inactive state, if the received RRC Release message contains the predetermined information, receiving a multicast traffic channel from the network node, and executing Chipset.