COMMUNICATION METHOD, USER EQUIPMENT, CHIPSET AND MOBILE COMMUNICATION SYSTEM

Abstract

This communication method, which is performed by a user device in a mobile communication system that provides a multicast / broadcast service (MBS), comprises: a step for receiving, in a radio resource control (RRC) inactive state and from a base station, a paging message including a first list, which is a list of user device identifiers, and a second list, which is a list of MBS session identifiers; a step for commencing RRC connection resumption for transitioning from the RRC inactive state to an RRC connected state, on the basis of a user device identifier of the user device being included in the first list; and a step for recognizing activation of a joined multicast session which the user device has joined and for maintaining the RRC inactive state, on the basis of the MBS session identifier of the joined multicast session being included in the second list.

Description

Communication method and user device

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

[0002] The 3rd Generation Partnership Project (3GPP) has defined 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 has defined the technical specifications for 5G / NR multicast / broadcast services (MBS).

[0003] In 3GPP Release 17, reception of MBS multicast (i.e., multicast reception) is possible only for user equipment in a radio resource control (RRC) connected state (see, for example, Non-Patent Document 1). In contrast, in 3GPP Release 18, the technical specifications are planned to be extended so that user equipment in an RRC inactive state can perform multicast reception.

[0004] 3GPP Technical Specification: TS 38.300 V17.4.0

[0005] A communication method according to a first aspect is a communication method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS), and includes the steps of: receiving, in a radio resource control (RRC) inactive state, a paging message from a network node, the paging message including a first list that is a list of MBS session identifiers and flag information associated with the MBS session identifiers included in the first list; and, if an MBS session identifier of a multicast session in which the user equipment has joined is included in the first list, determining whether to maintain the RRC inactive state based on the flag information associated with the MBS session identifier of the multicast session in which the user equipment has joined.

[0006] A communication method according to a second aspect is a communication method executed by a user equipment in a mobile communication system providing a multicast / broadcast service (MBS), and includes the steps of: receiving, in a radio resource control (RRC) inactive state, a paging message from a network node, the paging message including a first list that is a list of user equipment identifiers and a second list that is a list of MBS session identifiers; initiating an RRC connection resume to transition from the RRC inactive state to an RRC connected state based on the user equipment identifier of the user equipment being included in the first list; and recognizing activation of the joined multicast session and maintaining the RRC inactive state based on the MBS session identifier of the joined multicast session of the user equipment being included in the second list.

[0007] A user equipment according to a third aspect is a user equipment used in a mobile communication system that provides a multicast / broadcast service (MBS), and comprises: a receiving unit that receives, in a radio resource control (RRC) inactive state, a paging message from a network node, the paging message including a first list that is a list of user equipment identifiers and a second list that is a list of MBS session identifiers; and a control unit that initiates an RRC connection resume to transition from the RRC inactive state to an RRC connected state based on the user equipment identifier of the user equipment being included in the first list, and the control unit recognizes activation of the joined multicast session and maintains the RRC inactive state based on the MBS session identifier of the joined multicast session of the user equipment being included in the second list.

[0008] 1 is a diagram showing an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 3 is a diagram showing an example of the configuration of a gNB (base station) according to an embodiment. FIG. 4 is a diagram showing a protocol stack configuration of a radio interface of a user plane that handles data. FIG. 5 is a diagram showing a protocol stack configuration of a radio interface of a control plane that handles signaling (control signals). FIG. 6 is a diagram showing a schematic operation of a UE according to an embodiment. FIG. 7 is a diagram showing an example of the operation of a UE according to a first operation pattern of an embodiment. FIG. 8 is a diagram showing an example of the operation of a UE according to a second operation pattern of an embodiment. FIG. 9 is a diagram showing an example of the operation of a UE according to a third operation pattern of an embodiment. FIG. 10 is a diagram showing an example of the operation of a UE according to a fourth operation pattern of an embodiment. FIG. 11 is a diagram showing an example of the operation of a UE according to a fifth operation pattern of an embodiment. FIG. 12 is a diagram showing an example of the operation of a UE according to a sixth operation pattern of an embodiment. FIG. 13 is a diagram showing an example of the operation of a UE according to a seventh operation pattern of an embodiment. FIG. 14 is a diagram showing an initial setup procedure for an ongoing session (left) and a stopped session (right).

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

[0010] (1) System Configuration Example Fig. 1 is a diagram showing a configuration example of a mobile communication system 1 according to an embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). Although 5GS will be described below as an example, the mobile communication system may be at least partially based on an LTE (Long Term Evolution) system. The mobile communication system may be at least partially based on a 6th Generation (6G) system.

[0011] 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. Furthermore, the 5GC 20 may be simply referred to as the core network (CN) 20. The RAN 10 and the CN 20 constitute the network of the mobile communication system 1.

[0012] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) 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).

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

[0014] 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.

[0015] 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.

[0016] 2 is a diagram illustrating an example 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 configure a wireless communication unit that performs wireless communication with the gNB 200.

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

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

[0019] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer 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.

[0020] 3 is a diagram showing an example of the configuration of a gNB 200 (base station) according to an embodiment. The gNB 200 has 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.

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

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

[0023] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer 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.

[0024] 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.

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

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

[0027] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires 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.

[0028] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of 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.

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

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0031] 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.

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

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

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

[0035] The NAS layer (also simply referred to as "NAS") 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 referred to as the AS layer (also simply referred to as "AS").

[0036] (2) Overview of MBS The mobile communication system 1 can perform resource-efficient distribution using multicast / broadcast services (MBS).

[0037] (2.1) MBS Broadcast 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 session in any of the following states: RRC idle state, RRC inactive state, and RRC connected state.

[0038] Point-to-Multipoint (PTM) delivery is applied to broadcast communication services. In the case of PTM transmission, the gNB 200 delivers a single copy of an MBS packet to a set (group) of multiple UEs 100. For example, the gNB 200 schedules a group-common PDSCH scrambled by a G-RNTI (Group RNTI), which is a group-common RNTI, using a group-common PDCCH having a CRC (Cyclic Redundancy Code) scrambled by the G-RNTI.

[0039] In the case of a broadcast communication service, the UE 100 receives a broadcast session in the following procedure. First, the UE 100 receives a system information block type 20 (SIB20) from the gNB 200. The SIB20 includes a configuration of a multicast control channel (MCCH), which is a type of logical channel. Second, the UE 100 receives the MCCH from the gNB 200 based on the SIB20. The MCCH includes a PTM configuration. The PTM configuration transmits a configuration (MTCH configuration) for a multicast traffic channel (MTCH), which is a type of logical channel, and a broadcast MRB configuration, which is a multicast radio bearer (MRB) for the broadcast session. The information transmitted by the MCCH is sometimes referred to as MBS broadcast control information. Third, the UE 100 receives the MTCH based on the MCCH. The MTCH transmits the broadcast session (specifically, MBS data belonging to the broadcast session).

[0040] 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. The MTCH is a PTM downlink channel for transmitting MBS data of either a multicast session or a broadcast session from the network 10 to the UE 100.

[0041] (2.2) MBS Multicast 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.

[0042] The UE 100 can receive the multicast session only after joining the multicast session (session join). Joining the multicast session may mean being registered in the network 5 (CN 20) as the UE 100 that can receive the multicast session.

[0043] In the case of a multicast communication service, only UEs 100 in an RRC connected state can receive a multicast session in 3GPP Release 17. On the other hand, in 3GPP Release 18, this will be extended so that UEs 100 in an RRC inactive state can also receive a multicast session.

[0044] (2.2.1) Multicast reception in RRC connected state UE100 in the RRC connected state can receive a multicast session (specifically, MBS data belonging to the multicast session) using mechanisms such as PTP (Point-to-Point) and / or PTM (Point-to-Multipoint) delivery.

[0045] In the case of a multicast communication service, the UE 100 in the RRC connected state receives a multicast session in the following procedure. First, the UE 100 receives an RRC Reconfiguration message from the gNB 200. The RRC Reconfiguration message is a message transmitted on a dedicated control channel (DCCH). The RRC Reconfiguration message transmits a setting (MTCH setting) for the MTCH for receiving the multicast session and a setting of a multicast MRB, which is an MRB for the multicast session. Second, the UE 100 receives the MTCH based on the RRC Reconfiguration message. The MTCH transmits the multicast session (specifically, MBS data belonging to the multicast session).

[0046] (2.2.2) Multicast Reception in RRC Inactive State The UE 100 in the RRC inactive state can receive a multicast session (specifically, MBS data belonging to the multicast session) using the PTM distribution mechanism.

[0047] In the case of a multicast communication service, the UE 100 in the RRC inactive state can receive a multicast session in the following procedure. First, the UE 100 in the RRC inactive state receives a newly introduced system information block (also referred to as a "new SIB") from the gNB 200. The new SIB includes a configuration of a newly introduced MCCH (also referred to as a "multicast MCCH"). Second, the UE 100 in the RRC inactive state receives a multicast MCCH from the gNB 200 based on the new SIB. The multicast MCCH includes a PTM configuration. The PTM configuration transmits a configuration (MTCH configuration) related to the MTCH for receiving the multicast session and a configuration of a multicast MRB, which is an MRB for the multicast session. Third, the UE 100 in the RRC inactive state receives the MTCH based on the multicast MCCH. The MTCH transmits the multicast session (specifically, MBS data belonging to the multicast session).

[0048] When gNB200 configures UE100 to receive multicast in the RRC inactive state, it can send PTM configuration to UE100 using an RRC Release message including a suspend configuration. In this case, when UE100 receives an RRC Release message including PTM configuration from gNB200, it transitions to the RRC inactive state and receives the multicast session in the RRC inactive state.

[0049] (2.2.3) Group Notification When there is temporarily no data to transmit to UE 100 in an active multicast session, gNB 200 may transition UE 100 to an RRC inactive state. When the multicast session is deactivated, gNB 200 may transition UE 100 to an RRC idle state or an RRC inactive state.

[0050] A gNB 200 that supports MBS uses a group notification mechanism to notify UEs 100 in an RRC idle state or an RRC inactive state when a multicast session is activated by CN 20. For example, a gNB 200 that supports MBS may use a group notification mechanism to notify UEs 100 in an RRC inactive state when a multicast session has been activated and there is multicast data to be distributed in the gNB 200.

[0051] Upon receiving the group notification (also referred to as "group paging"), the UE 100 reconnects or resumes connection to the network 5 and transitions to the RRC connected state. The group notification is processed in the paging RNTI (P-RNTI) on the PDCCH, and the paging channel is monitored by the UE 100.

[0052] The group notification paging message includes a session identifier (MBS session identifier) ​​used to page all UEs 100 in RRC idle state and RRC inactive state that have joined the associated MBS multicast session. That is, the UEs 100 are not paged individually. The MBS session identifier is, for example, a TMGI (Temporary Mobile Group Identity). The TMGI includes a plmn-Index and a serviceId.

[0053] When UE 100 transitions to the RRC connected state, UE 100 may stop monitoring group notifications related to a particular multicast session. That is, UE 100 stops checking the MBS session ID in paging messages. UE 100 does not monitor group notifications in cases where UE 100 leaves this multicast session, network 5 requests UE 100 to leave, or network 5 releases the multicast session.

[0054] The group notification may be performed using the MCCH or may be performed using an MCCH Change Notification. When the MCCH is used, the determination may be made based on whether or not an MTCH configuration for the MBS session of interest exists in the MCCH. When the MCCH Change Notification is used, the group notification may be notified in a predetermined bit of the DCI.

[0055] (3) Operation According to the Embodiment The operation according to the embodiment will be described below. The operation according to the embodiment is an operation related to the above-mentioned group notification (group paging).

[0056] In the 3GPP Release 17 technical specifications, a paging message can include a paging record list, which is a list of user equipment identifiers (UE-IDs), and a paging group list, which is a list of MBS session identifiers (TMGIs). The paging record list is an example of a first list constituting the UE-ID list, and the paging group list is an example of a second list constituting the TMGI list.

[0057] When paging UE100 in an RRC inactive state, gNB200 generates a paging message (also referred to as a "RAN paging message") and transmits the paging message on a paging channel.

[0058] If the UE 100 in the RRC inactive state has its own UE-ID included in the paging record list in the paging message, the UE 100 starts an RRC connection resume to transition from the RRC inactive state to the RRC connected state.

[0059] In the technical specifications of 3GPP Release 17, when a UE 100 in an RRC inactive state has the TMGI of its joined multicast session included in the paging group list in the paging message, the UE 100 initiates an RRC connection resume to transition from the RRC inactive state to the RRC connected state.

[0060] In 3GPP Release 17, multicast reception is possible only for UE 100 in an RRC connected state. Therefore, UE 100 in an RRC inactive state recognizes activation of its own joined multicast session based on the paging group list, transitions to the RRC connected state by RRC connection resume, and performs multicast reception in the RRC connected state.

[0061] In contrast, the technical specifications of 3GPP Release 18 enable UE 100 to receive multicast data in the RRC inactive state. However, in the conventional paging mechanism, UE 100 in the RRC inactive state resumes the RRC connection if the TMGI of the multicast session in which UE 100 has joined is included in the paging group list in the paging message. Therefore, there is a problem that UE 100 cannot be maintained in the RRC inactive state.

[0062] Therefore, the conventional paging mechanism has a problem that it is not possible to specify for each UE 100 whether to transition to the RRC connected state or maintain the RRC inactive state. In particular, when there is a special UE 100 for which the quality of service (QoS) requirements of the multicast service must be met, when there is a multicast session requiring high QoS, and / or when the load on the gNB 200 is high, there is a need to make it possible for each UE 100 to transition to the RRC connected state or maintain the RRC inactive state.

[0063] 6 is a diagram showing a schematic operation of the UE 100 according to the embodiment. The UE 100 according to the embodiment is assumed to be a Rel-18 UE that complies with the technical specifications of 3GPP Release 18.

[0064] In step S1, UE100 in an RRC inactive state receives a paging message from gNB200, the paging message including a first list (e.g., a paging record list) which is a list of UE-IDs, and a second list (e.g., a paging group list) which is a list of TMGIs.

[0065] In step S2, the UE 100 in the RRC inactive state starts an RRC connection resume for transitioning from the RRC inactive state to the RRC connected state based on the inclusion of its own UE-ID in the first list (as a result, transitioning to the RRC connected state). Also, the UE 100 in the RRC inactive state recognizes the activation of the joined multicast session based on the inclusion of the TMGI of the joined multicast session in the second list, and maintains the RRC inactive state.

[0066] As a result, the UE 100 to be transitioned to the RRC connected state is specified using the first list, and the UE 100 to be maintained in the RRC inactive state can be specified using the second list. Therefore, it is possible to specify for each UE 100 whether to transition to the RRC connected state or to maintain the RRC inactive state.

[0067] (3.1) First Operation Pattern In the first operation pattern of the embodiment, the gNB 200 transmits a new UE-ID list (third list), which is a list different from the paging record list (first list) and is a list of UE-IDs. The UE 100 in the RRC inactive state receives the new UE-ID list (third list) from the gNB 200. The new UE-ID list (third list) is included in the paging message received from the gNB 200. Then, when the TMGI of the UE 100 in the RRC inactive state is included in the paging group list (second list), the UE 100 recognizes the activation of the joined multicast session in response to its UE-ID being included in the new UE-ID list (third list) and maintains the RRC inactive state.

[0068] In this way, in the first operation pattern, a new UE-ID list is added to the paging message. Even when the UE 100 specified in the new UE-ID list receives a paging group list including the TMGI of the multicast session in which the UE 100 has already participated, the UE 100 recognizes the activation of the TMGI but does not transition to the RRC connected state.

[0069] According to the first operation pattern, for multiple RRC inactive UEs participating in the same activated multicast session, UEs 100 not specified in the new UE-ID list can be transitioned to an RRC connected state, while UEs 100 specified in the new UE-ID list can be maintained in an RRC inactive state.

[0070] FIG. 7 is a diagram illustrating an example of an operation of the UE 100 according to the first operation pattern of the embodiment.

[0071] In step S11, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0072] In step S12, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparing for activation of the multicast session. In the first operation pattern, the paging message includes a paging record list (a UE-ID list in 3GPP Release 17), a paging group list (a list of TMGIs in 3GPP Release 17), and a new UE-ID list (which has the same structure as the paging record list and contains UE-IDs).

[0073] In step S13, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list in the paging message.

[0074] If its own UE-ID is included (step S13: YES), in step S14, the UE 100 in the RRC inactive state resumes the RRC connection and transitions to the RRC connected state.

[0075] On the other hand, if its own UE-ID is not included (step S13: NO), in step S15, the UE 100 in the RRC inactive state checks whether or not the TMGI of the multicast session in which the UE 100 has participated is included in the paging group list in the paging message. If the TMGI of the multicast session in which the UE 100 has participated is not included in the paging group list (step S15: NO), the UE 100 does nothing in particular.

[0076] On the other hand, if the TMGI of the multicast session in which the UE has participated is included in the paging group list (step S15: YES), in step S16, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the new UE-ID list in the paging message.

[0077] If its own UE-ID is included in the new UE-ID list (step S16: YES), in step S17, the UE 100 in the RRC inactive state recognizes that the multicast session (joined multicast session) indicated by the TMGI has been activated, and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, it may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, it may start RRC connection resume.

[0078] On the other hand, if the UE-ID of the UE 100 is not included in the new UE-ID list (step S16: NO), in step S14, the UE 100 in the RRC inactive state recognizes that the multicast session indicated by the TMGI (the multicast session in which the UE 100 has already participated) has been activated, and resumes the RRC connection.

[0079] According to this operation example, among multiple UEs 100 participating in the same multicast session, some UEs 100 can transition to an RRC connected state and receive the multicast session, while other UEs 100 can receive the multicast session while remaining in an RRC inactive state.

[0080] In this operation example, the new UE-ID list is a list that specifies the UEs 100 to be maintained in the RRC inactive state. That is, the UE-IDs in the new UE-ID list are the UE-IDs of the UEs 100 to be maintained in the RRC inactive state.

[0081] Conversely, the new UE-ID list may be a list that specifies the UEs 100 to be transitioned to the RRC connected state. That is, the UE-IDs in the new UE-ID list are the UE-IDs of the UEs 100 to be transitioned to the RRC connected state. In this case, the relationship between "YES" and "NO" in step S16 is reversed. For example, when the TMGI of a multicast session in which the UE 100 has joined is included in the paging group list, the UE 100 in the RRC inactive state recognizes the activation of the multicast session in which the UE 100 has joined and maintains the RRC inactive state in response to the fact that the UE-ID of the UE 100 has not been included in the new UE-ID list.

[0082] (3.2) Second Operation Pattern In the second operation pattern of the embodiment, the gNB 200 transmits flag information associated with the UE-ID included in the paging record list (first list). The UE 100 in the RRC inactive state receives the flag information from the gNB 200. The flag information is included in the paging message received from the gNB 200. Then, when the TMGI of the multicast session in which the UE 100 has joined is included in the paging group list (second list), the UE 100 in the RRC inactive state recognizes the activation of the multicast session in which the UE 100 has joined and maintains the RRC inactive state in accordance with the fact that the UE 100's UE-ID is included in the paging record list (first list) and that flag information is associated with the UE 100's UE-ID.

[0083] In this way, in the second operation pattern, flag information (indicator) indicating that the RRC inactive state is maintained is added to each entry of the paging record list in the paging message. Even when the UE 100 corresponding to the entry receives a paging group list including the TMGI of the multicast session in which the UE 100 has joined, the UE 100 recognizes the activation of the TMGI but does not transition to the RRC connected state.

[0084] According to the second operation pattern, for multiple RRC inactive UEs participating in the same activated multicast session, UE 100 that is not designated using flag information can be transitioned to an RRC connected state, while UE 100 that is designated using flag information can be maintained in an RRC inactive state.

[0085] FIG. 8 is a diagram illustrating an example of an operation of the UE 100 according to the second operation pattern of the embodiment.

[0086] In step S21, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0087] In step S22, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparing for activation of the multicast session. In the second operation pattern, the paging message includes a paging record list having a new structure and a paging group list (TMGI list in 3GPP Release 17). The new paging record list has a one-bit flag (RRC inactive state maintain indicator) for each entry in the UE-ID list in 3GPP Release 17. If the flag exists, it indicates that the RRC inactive state is maintained, and if it does not exist, it is the same as the existing operation. Alternatively, the 1 / 0 (True / False) of the flag may indicate whether or not there is an instruction to maintain the RRC inactive state. In this case, "the flag exists" means that a flag of 1 (True) exists.

[0088] In step S23, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list. If its own UE-ID is not included in the paging record list (step S23: NO), the process proceeds to step S25.

[0089] On the other hand, if its own UE-ID is included in the paging record list (step S23: YES), in step S24, the UE 100 in the RRC inactive state checks whether or not a flag associated with its own UE-ID exists. If a flag associated with its own UE-ID does not exist (step S24: NO), in step S26, the UE 100 in the RRC inactive state resumes the RRC connection. On the other hand, if a flag associated with its own UE-ID exists (step S24: YES), the process proceeds to step S25.

[0090] In step S25, the UE 100 in the RRC inactive state checks whether or not the paging group list includes the TMGI of the multicast session that the UE 100 has participated in. If the paging group list does not include the TMGI of the multicast session that the UE 100 has participated in (step S25: NO), the UE 100 does not do anything in particular.

[0091] If the paging group list includes the TMGI of the multicast session in which the UE 100 has joined (step S25: YES), in step S27, the UE 100 in the RRC inactive state checks whether a flag associated with the UE 100's UE-ID is present in the paging record list. If a flag associated with the UE 100's UE-ID is present in the paging record list (step S27: YES), in step S28, the UE 100 in the RRC inactive state recognizes that the joined multicast session indicated by the TMGI has been activated, and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, the UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, the UE 100 may start RRC connection resume.

[0092] If there is no flag associated with its own UE-ID in the paging record list (step S27: NO), in step S26, the UE 100 in the RRC inactive state resumes the RRC connection and transitions to the RRC connected state.

[0093] According to this operation example, among multiple UEs 100 participating in the same multicast session, some UEs 100 can transition to an RRC connected state and receive the multicast session, while other UEs 100 can receive the multicast session while remaining in an RRC inactive state.

[0094] (3.3) Third Operation Pattern In the third operation pattern of the embodiment, the gNB 200 transmits flag information. The UE 100 in the RRC inactive state receives the flag information from the gNB 200. The flag information is included in the paging message received from the gNB 200. Then, when the TMGI of the UE 100's joined multicast session is included in the paging group list (second list), the UE 100 recognizes the activation of the joined multicast session in response to receiving the flag information and maintains the RRC inactive state.

[0095] In this way, in the third operation pattern, a new indicator (1-bit flag) is added to the paging message. When the indicator exists, even if the UE 100 receives a paging group list including the TMGI of the multicast session in which the UE 100 has joined, the UE 100 recognizes the activation of the TMGI but does not transition to the RRC connected state.

[0096] This allows a Rel-18 UE that can interpret flag information (new indicator) to not transition to the RRC connected state (not resume the RRC connection) even when it receives a paging group list that includes the TMGI of a multicast session in which it has already joined.

[0097] FIG. 9 is a diagram illustrating an example of an operation of the UE 100 according to the third operation pattern of the embodiment.

[0098] In step S31, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0099] In step S32, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparing for activation of the multicast session. In the third operation pattern, the paging message includes a paging record list (UE-ID list in 3GPP Release 17), a paging group list (TMGI list in 3GPP Release 17), and a new 1-bit flag (RRC inactive state maintenance indicator). Only one new 1-bit flag exists in the paging message. If the flag exists, it indicates that the RRC inactive state is maintained, and if it does not exist, it is the same as the existing operation. Alternatively, the 1 / 0 (True / False) of the flag may indicate whether or not there is an instruction to maintain the RRC inactive state. In this case, "the flag exists" means that a flag of 1 (True) exists.

[0100] In step S33, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list. If its own UE-ID is included in the paging record list (step S33: YES), in step S34, the UE 100 resumes the RRC connection.

[0101] If the UE-ID of the UE 100 is not included in the paging record list (step S33: NO), in step S35, the UE 100 in the RRC inactive state checks whether the paging group list includes the TMGI of the multicast session that the UE 100 has participated in. If the paging group list does not include the TMGI of the multicast session that the UE 100 has participated in (step S35: NO), the UE 100 does nothing in particular.

[0102] If the paging group list includes the TMGI of the multicast session in which the UE 100 has joined (step S35: YES), in step S36, the UE 100 in the RRC inactive state checks whether or not a new flag is present. If the new flag is present (step S36: YES), in step S37, the UE 100 recognizes that the joined multicast session indicated by the TMGI has been activated, and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, the UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, the UE 100 may start RRC connection resume.

[0103] On the other hand, if the new flag does not exist (step S36: NO), in step S34, the UE 100 in the RRC inactive state recognizes that the joined multicast session indicated by the TMGI has been activated, and resumes the RRC connection.

[0104] In this operation example, an example in which flag information is included in a paging message has been described, but the flag information may be included in a system information block (SIB). In this case, the gNB 200 transmits an SIB including the flag information, and the UE 100 in the RRC inactive state receives the flag information. The SIB may be a system information block type 1 (SIB1). The SIB may be a new type of system information block (specifically, a new SIB including a multicast MCCH reception setting).

[0105] (3.4) Fourth Operation Pattern In the fourth operation pattern of the embodiment, the gNB 200 transmits flag information associated with the TMGI included in the paging group list (second list). The UE 100 in the RRC inactive state receives the flag information from the gNB 200. The flag information is included in the paging message received from the gNB 200. Then, when the TMGI of the UE 100 in the RRC inactive state is included in the paging group list (second list), the UE 100 recognizes the activation of the joined multicast session and maintains the RRC inactive state in accordance with the fact that the flag information is associated with the TMGI of the joined multicast session.

[0106] In this way, in the fourth operation pattern, a new indicator (1-bit flag) is added to each entry of the paging group list of the paging message. For the TMGI of the entry in which the indicator exists, even when the UE 100 receives the paging group list, the UE 100 recognizes the activation of the TMGI, but does not transition to the RRC connected state.

[0107] This makes it possible to transition UE100 (Rel-18 UE) to an RRC connected state for multicast sessions of TMGIs that are not associated with a flag in the paging group list, while maintaining UE100 (Rel-18 UE) in an RRC inactive state for multicast sessions of TMGIs that are associated with a flag in the paging group list.

[0108] FIG. 10 is a diagram illustrating an example of an operation of the UE 100 according to the fourth operation pattern of the embodiment.

[0109] In step S41, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0110] In step S42, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparing for activation of the multicast session. In the fourth operation pattern, the paging message includes a paging record list (UE-ID list in 3GPP Release 17) and a paging group list having a new structure. The new paging group list has a new 1-bit flag (RRC inactive state maintenance indicator) in each entry of the existing TMGI list. If the flag exists, it indicates that the RRC inactive state is maintained, and if it does not exist, it is the same as the existing operation. Alternatively, the 1 / 0 (True / False) of the flag may indicate whether or not there is an instruction to maintain the RRC inactive state. In this case, "the flag exists" means that a flag of 1 (True) exists.

[0111] In step S43, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list. If its own UE-ID is included (step S43: YES), in step S44, the UE 100 resumes the RRC connection.

[0112] If its own UE-ID is not included (step S43: NO), in step S45, the UE 100 in the RRC inactive state checks whether or not the paging group list includes the TMGI of the multicast session that the UE 100 has participated in. If the paging group list does not include the TMGI of the multicast session that the UE 100 has participated in (step S45: NO), the UE 100 does nothing in particular.

[0113] If the paging group list includes the TMGI of the multicast session in which the UE 100 has joined (step S45: YES), in step S46, the UE 100 in the RRC inactive state checks whether or not a flag is present in the entry for the TMGI of the multicast session in which the UE 100 has joined. If the flag is present (step S46: YES), in step S47, the UE 100 recognizes that the joined multicast session indicated by the TMGI has been activated, and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, the UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, the UE 100 may start RRC connection resume.

[0114] On the other hand, if the flag does not exist (step S46: NO), in step S44, the UE 100 in the RRC inactive state recognizes that the joined multicast session indicated by the TMGI has been activated, and resumes the RRC connection.

[0115] In this operation example, the new flag is a flag that designates the UE 100 to be maintained in the RRC inactive state. Conversely, the new flag may be a flag that designates the UE 100 to be transitioned to the RRC connected state. In this case, the relationship between "YES" and "NO" in step S46 is reversed.

[0116] (3.5) Fifth Operation Pattern In the fifth operation pattern of the embodiment, the gNB 200 transmits a new TMGI list (third list), which is a list different from the paging group list (second list) and is a list of TMGIs. The UE 100 in the RRC inactive state receives the new TMGI list (third list) from the gNB 200. The new TMGI list (third list) is included in the paging message received from the gNB 200. Then, when the TMGI of the UE 100's joined multicast session is included in the paging group list (second list), the UE 100 recognizes the activation of the joined multicast session and maintains the RRC inactive state in response to the TMGI of the joined multicast session being included in the new TMGI list (third list).

[0117] In this way, in the fifth operation pattern, a new TMGI list (Paging Group Cancel List) is added to the paging message. For the TMGI of the list, even when the UE 100 receives the paging group list, the UE 100 recognizes the activation of the TMGI, but does not transition to the RRC connected state.

[0118] This makes it possible to transition UE100 (Rel-18 UE) to an RRC connected state for multicast sessions of TMGIs that are not specified in the new TMGI list in the paging group list, while maintaining UE100 (Rel-18 UE) in an RRC inactive state for multicast sessions of TMGIs that are specified in the new TMGI list in the paging group list.

[0119] FIG. 11 is a diagram illustrating an example of an operation of the UE 100 according to the fifth operation pattern of the embodiment.

[0120] In step S51, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0121] In step S52, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparing for activation of the multicast session. In the fifth operation pattern, the paging message includes a paging record list (a UE-ID list in 3GPP Release 17), a paging group list (a TMGI list in 3GPP Release 17), and a new TMGI list (the structure of which is the same as the TMGI list in 3GPP Release 17).

[0122] In step S53, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list. If its own UE-ID is included in the paging record list (step S53: YES), in step S54, the UE 100 resumes the RRC connection.

[0123] If the UE-ID of the UE 100 is not included in the paging record list (step S53: NO), in step S55, the UE 100 in the RRC inactive state checks whether the paging group list includes the TMGI of the multicast session that the UE 100 has participated in. If the paging group list does not include the TMGI of the multicast session that the UE 100 has participated in (step S55: NO), the UE 100 does nothing in particular.

[0124] If the paging group list includes the TMGI of the multicast session in which the UE 100 has joined (step S55: YES), in step S56, the UE 100 in the RRC inactive state checks whether the TMGI is included in the new TMGI list. If the TMGI is included in the new TMGI list (step S56: YES), in step S57, the UE 100 recognizes that the joined multicast session indicated by the TMGI has been activated and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, the UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, the UE 100 may start RRC connection resume.

[0125] If the TMGI is not included in the new TMGI list (step S56: NO), in step S54, the UE 100 in the RRC inactive state recognizes that the joined multicast session indicated by the TMGI has been activated, and resumes the RRC connection.

[0126] In this operation example, an example in which the new TMGI list is included in the paging message has been described, but the new TMGI list may be included in a system information block (SIB). In this case, the gNB 200 transmits an SIB including the new TMGI list, and the UE 100 in the RRC inactive state receives the new TMGI list. The SIB may be a system information block type 1 (SIB1). The SIB may be a new type of system information block (specifically, a new SIB including a multicast MCCH reception setting).

[0127] (3.6) Sixth Operation Pattern In the sixth operation pattern of the embodiment, when the 3GPP Release 18 UE 100 has a TMGI of a multicast session in which it has joined, the UE 100 recognizes the activation of the TMGI but does not transition to the RRC connected state.

[0128] FIG. 12 is a diagram illustrating an example of an operation of the UE 100 according to the sixth operation pattern of the embodiment.

[0129] In step S61, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0130] In step S62, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparation for activating the multicast session. In the fifth operation pattern, the paging message includes a paging record list (a UE-ID list in 3GPP Release 17) and a paging group list (a TMGI list in 3GPP Release 17).

[0131] In step S63, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list. If its own UE-ID is included in the paging record list (step S63: YES), in step S64, the UE 100 resumes the RRC connection.

[0132] If the UE-ID of the UE 100 is not included in the paging record list (step S63: NO), in step S65, the UE 100 in the RRC inactive state checks whether the paging group list includes the TMGI of the multicast session that the UE 100 has participated in. If the paging group list does not include the TMGI of the multicast session that the UE 100 has participated in (step S65: NO), the UE 100 does nothing in particular.

[0133] If the paging group list includes the TMGI of the multicast session in which the UE 100 has joined (step S65: YES), in step S66, the UE 100 in the RRC inactive state recognizes that the joined multicast session indicated by the TMGI has been activated, and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, the UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, the UE 100 may start RRC connection resume.

[0134] In this manner, in this operation example, the paging group list is used only to recognize session activation, and the paging record list is used to determine whether or not to actually transition to the RRC connected state.

[0135] (3.7) Seventh Operation Pattern In the seventh operation pattern of the embodiment, a new TMGI list (Multicast Activation List) for Rel-18 UEs is defined in a paging message, on the assumption that the conventional paging group list (TMGI list of Rel-17) is not included in the paging message. This list notifies only the activation of a multicast session. The new TMGI list corresponds to the second list, which is a list that cannot be deciphered by UEs 100 that do not support multicast reception in the RRC inactive state.

[0136] FIG. 13 is a diagram illustrating an example of an operation of the UE 100 according to the seventh operation pattern of the embodiment.

[0137] In step S71, after joining the multicast session in the RRC connected state, the UE 100 receives an RRC Release message including a suspend setting from the gNB 200 and transitions to an RRC inactive state. The RRC Release message may include a PTM setting for performing multicast reception in the RRC inactive state.

[0138] In step S72, the UE 100 in the RRC inactive state receives a paging message from the gNB 200 that has started preparing for activation of the multicast session. In the seventh operation pattern, the paging message includes a paging record list (a UE-ID list in 3GPP Release 17) and a new TMGI list (a list only for notifying activation of the multicast session). The paging message may include a paging group list (a list of existing TMGIs), but even if the paging group list is included, the UE 100 in 3GPP Release 18 ignores the list.

[0139] In step S73, the UE 100 in the RRC inactive state checks whether its own UE-ID is included in the paging record list. If its own UE-ID is included in the paging record list (step S73: YES), in step S74, the UE 100 resumes the RRC connection.

[0140] If the UE-ID of the UE 100 is not included in the paging record list (step S73: NO), in step S75, the UE 100 in the RRC inactive state checks whether the new TMGI list includes the TMGI of the multicast session that the UE 100 has already participated in. If the new TMGI list does not include the TMGI of the multicast session that the UE 100 has already participated in (step S75: NO), the UE 100 does nothing in particular.

[0141] If the new TMGI list includes the TMGI of the multicast session in which the UE 100 has joined (step S75: YES), in step S76, the UE 100 in the RRC inactive state recognizes that the joined multicast session indicated by the TMGI has been activated, and maintains the RRC inactive state. In this case, for example, if the UE 100 has a multicast reception setting (PTM setting) in the RRC inactive state, the UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception). Note that if the UE 100 does not have the PTM setting, the UE 100 may start RRC connection resume.

[0142] (4) Other Embodiments In the above-described embodiment, an example has been described in which UE 100 recognizes that the joined multicast session indicated by the TMGI has been activated and maintains the RRC inactive state. In this case, it has also been described that UE 100 may start multicast reception processing (MTCH reception and / or MCCH reception) if it has, for example, a multicast reception setting (PTM setting) in the RRC inactive state, and that UE 100 may start RRC connection resume if it does not have the PTM setting. In addition to or instead of these, UE 100 may notify a higher layer (e.g., NAS) of UE 100 of the TMGI from a predetermined layer (e.g., RRC layer) of UE 100. The predetermined layer may notify the higher layer together with information indicating that the RRC inactive state will be maintained and the TMGI will be received. The predetermined layer may also notify the higher layer together with information indicating that the TMGI has been activated. The predetermined layer may notify the upper layer together with information indicating that the multicast reception process will be started / has been started. Also, if the UE 100 does not have the PTM configuration, the predetermined layer may notify the upper layer (e.g., NAS) of the TMGI.

[0143] In the above-described embodiment, an example has been described in which new flag information is included in a paging message (particularly, a paging group list) to indicate whether or not to perform RRC resume when the TMGI of a multicast session to which the UE has joined is included in the paging group list. However, this is not limiting. Instead of the flag information, information indicating behavior when the TMGI of a multicast session to which the UE has joined is included in the paging group list may be included. Such information may be an RRC state, and may indicate, for example, any of the states of RRC connected, RRC inactive, or RRC idle. When the TMGI is included, the UE 100 maintains or restores (or establishes) the RRC state according to the information. Alternatively, such information may be information indicating a release (version) and may indicate behavior conforming to Rel-17 or Rel-18 (or a version other than Rel-17, such as Rel-18 or later). When the TMGI is included, the UE 100 maintains or restores (or establishes) the RRC state according to the information. Specifically, if Rel-17 is indicated, RRC recovery is performed, and if Rel-18 is indicated, RRC inactivity is maintained.

[0144] 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. In the RRC idle state, the above-described RRC resume (Resume) is replaced with RRC establishment (Establishment).

[0145] 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.

[0146] 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.

[0147] That is, the UE 100 may be a terminal function unit (a type of communication module) for a base station to control a repeater that relays signals. Such a terminal function unit is referred to as an MT. Examples of the MT include, in addition to the IAB-MT, an NCR (Network Controlled Repeater)-MT and a RIS (Reconfigurable Intelligent Surface)-MT.

[0148] The term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). A network node may also be configured by a combination of at least a part of a core network device and at least a part of a base station.

[0149] 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).

[0150] The functions performed by the UE 100 or the gNB 200 (network node) may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), CPUs (Central Processing Units), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, or means refers to hardware that is programmed to perform the described functions or hardware that executes them. The hardware may be any hardware disclosed herein or any hardware known to be programmed or capable of performing the described functions. If the hardware is a processor, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0151] 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.

[0152] 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.

[0153] This application claims priority to U.S. Provisional Application No. 63 / 501,473 (filed May 11, 2023), the entire contents of which are incorporated herein by reference.

[0154] (5) Supplementary Note A The following supplementary note is provided regarding the features of the above-described embodiment.

[0155] (Supplementary Note 1) A communication method executed by a user equipment in a mobile communication system providing a multicast / broadcast service (MBS), comprising: receiving, in a radio resource control (RRC) inactive state, a paging message from a network node, the paging message including a first list that is a list of user equipment identifiers and a second list that is a list of MBS session identifiers; initiating an RRC connection resume to transition from the RRC inactive state to an RRC connected state, based on the user equipment identifier of the user equipment being included in the first list; and recognizing activation of the joined multicast session and maintaining the RRC inactive state, based on the MBS session identifier of the joined multicast session of the user equipment being included in the second list.

[0156] (Supplementary Note 2) The communication method according to Supplementary Note 1, further comprising the step of receiving from the network node a third list, the third list being a list of user equipment identifiers, the third list being different from the first list, the third list being included in the paging message received from the network node, and the maintaining step comprising the step of recognizing activation of the joined multicast session and maintaining the RRC inactive state in response to a user equipment identifier of the user equipment being included in the third list or a user equipment identifier of the user equipment being not included in the third list, when an MBS session identifier of the joined multicast session is included in the second list.

[0157] (Supplementary Note 3) The communication method according to Supplementary Note 1, further comprising the step of receiving, from the network node, flag information associated with a user equipment identifier included in the first list, wherein the flag information is included in the paging message received from the network node, and wherein the maintaining step includes the step of recognizing activation of the joined multicast session and maintaining the RRC inactive state in response to the user equipment identifier of the user equipment being included in the first list and the flag information being associated with the user equipment identifier of the user equipment, when an MBS session identifier of the joined multicast session is included in the second list.

[0158] (Supplementary Note 4) The communication method according to Supplementary Note 1, further comprising the step of receiving flag information from the network node, wherein the flag information is included in the paging message or the system information block received from the network node, and wherein the maintaining step includes the step of recognizing activation of the joined multicast session and maintaining the RRC inactive state in response to reception of the flag information if an MBS session identifier of the joined multicast session is included in the second list.

[0159] (Supplementary Note 5) The communication method according to Supplementary Note 1, further comprising the step of receiving from the network node flag information associated with an MBS session identifier included in the second list, wherein the flag information is included in the paging message received from the network node, and wherein the maintaining step includes the step of recognizing activation of the joined multicast session and maintaining the RRC inactive state in response to the flag information being associated with the MBS session identifier of the joined multicast session when the MBS session identifier of the joined multicast session is included in the second list.

[0160] (Supplementary Note 6) The communication method according to Supplementary Note 1, further comprising the step of receiving from the network node a third list, the third list being a list of MBS session identifiers and different from the second list, the third list being included in the paging message or system information block received from the network node, and the maintaining step comprising the step of recognizing activation of the joined multicast session and maintaining the RRC inactive state in response to the MBS session identifier of the joined multicast session being included in the third list when the MBS session identifier of the joined multicast session is included in the second list.

[0161] (Supplementary Note 7) The communication method according to Supplementary Note 1, wherein the second list is a list that cannot be deciphered by a user device that does not support multicast reception in an RRC inactive state.

[0162] (6) Appendix B 1. Introduction The work item on enhanced MBS (eMBS) aims to support multicast reception by UEs in inactive mode and is described as follows: - Specify support for multicast reception by UEs in RRC inactive mode [RAN2, RAN3]. - PTM configuration for UEs receiving multicast in RRC inactive mode [RAN2]. - Investigate the impact of mobility and state transitions for UEs receiving multicast in RRC inactive mode (seamless / lossless mobility is not mandatory) [RAN2, RAN3].

[0163] RAN2 has been discussing this goal and has reached a set of agreements. Building on these agreements, the control plane aspects regarding multicast reception in inactive mode are discussed in this appendix.

[0164] 2. Discussion 2.1. Initial Setup Procedure RAN2#120 reached a consensus to proceed with a "mixed approach."

[0165] In the mixed approach, we recommend the following: 1: If the NW configures the UE to continue multicast reception in inactive state, the NW provides PTM configuration of activated multicast sessions through RRC dedicated signaling, at least for the serving cell (other cases require further study). 2: MCCH is used when PTM configuration needs to be changed or when PTM configuration needs to be indicated during movement beyond the serving cell / gNB. Session status changes and other indications require further study. 3: It is assumed that the UE can receive multicast services only after joining the session. 4: Whether MCCH configuration is initially provided to the UE through dedicated signaling requires further study.

[0166] RAN2#121 agreed to the following: ・The UE needs to join a multicast session before receiving multicast in RR inactive. ・If the network deems it useful, it can configure the UE with the PTM configuration of a (single) serving cell before session activation and the UE can store the configuration. Once the session is activated, the UE can apply the configuration and receive multicast in inactive state without going back to RRC Connected, unless updated by MCCH after configuration. ・If the network configures the UE to receive multicast in inactive state, it can deliver the PTM configuration using an RRC Release message with suspendconfig. No other dedicated RRC message will be used to provide PTM configuration for MBS multicast in inactive. ・A new MCCH logical channel for multicast in inactive will be introduced (different from the broadcast MCCH). ・Multicast MCCH configuration will be provided via a new SIB. Alternatively, multicast MCCH configuration for the serving cell can also be provided by dedicated signaling, which is therefore not optimized for mobility.

[0167] Based on these agreements, the setup procedures for an ongoing (i.e., activated) multicast session and a deactivated (i.e., before activation) multicast session can be seen as shown in FIG. 14.

[0168] 2.1.1 Ongoing (Active) Multicast Session For an ongoing multicast session, the UE configures a multicast MRB for multicast reception in Connected mode via RRC reconfiguration and starts receiving MTCH as in Rel-1. For multicast reception in Inactive mode, the UE configures a broadcast MRB (or a new "multicast inactive MRB") for multicast reception via RRC release.

[0169] Regarding the PTM settings for RRC resume, it is clear that the baseline content (IEs, etc.) is the same as that of Rel-17 MCCH (MBS Broadcast Configuration). However, since RAN2 agreed to "introduce a new MCCH logical channel," the RRC message name must also be different from that of Rel-17 MBS Broadcast Configuration. The same message is transmitted over the new MCCH logical channel.

[0170] Proposal 1: RAN2 should agree to define a new RRC message for PTM configuration in RRC release and define a new "multicast MCCH", e.g., MBSMulticastInactiveConfiguration.

[0171] Proposal 2: RAN2 should agree that the IE of the new RRC message for PTM configuration is the same as Rel-17 MBSBroadcastConfiguration as the baseline.

[0172] When the UE receives an RRCRelease with suspendConfig, the connected multicast MRBs are suspended, just like in Rel-1. The UE continues the same multicast session if the RRC release includes inactive PTM configuration. Service continuity of the multicast session needs to be ensured during / after RRC state transitions. This is similar to legacy-only configurations such as redirectedCarrierInfo, cellReselectionPriorities, deprioritizationReq, and measIdleConfig. The UE needs to start receiving broadcast MRBs as soon as it applies the PTM configuration. Whether a new procedure (i.e., the UE applies PTM configuration and starts receiving MTCH) is performed when the UE applies suspendConfig needs further study.

[0173] Proposal 3: RAN2 should agree that before suspending multicast MRBs, UEs should apply PTM configuration for broadcast MRBs (or new "multicast inactive MRBs") and start receiving the corresponding MCCH.

[0174] 2.1.2. Deactivated Multicast Session (Before Activation) In a deactivated multicast session, the UE performs PTM configuration via RRC release. If Proposal 3 above is acceptable, the UE would immediately start receiving the MTCH, but since the MTCH is not transmitted at this time, the UE should refrain from doing so. Instead, the UE should be notified via RRC release that the multicast session is still inactive, allowing the UE to wait for a multicast session activation notification without receiving the MTCH. Further study is required for detailed operation; for example, it can be decided whether to wait for session activation while applying the PTM configuration.

[0175] Proposal 4: RAN2 should agree to inform the UE via RRC release whether the multicast session has been deactivated so that the UE will not attempt to receive the corresponding MTCH.

[0176] After transitioning to inactive, the UE monitors multicast session activation notifications (i.e., group paging). Prior to multicast session activation, the gNB may change the PTM settings of the session, and such changes constitute a new "multicast MCCH" for the UE in inactive. In this case, the gNB may transmit the "multicast MCCH" before session activation.

[0177] From the UE's perspective, if the UE needs to monitor a new "multicast MCCH" for the deactivated multicast session, the UE's power consumption will increase. Therefore, it is necessary to ensure that the UE does not need to monitor the multicast MCCH before receiving the multicast session activation notification. In other words, the UE only needs to monitor the multicast MCCH once it receives the activation notification for the TMGI of interest. The same operation can be applied to new SIBs (such as SIB20) for MCCH configuration.

[0178] Proposal 5: RAN2 should agree that UEs do not need to monitor the new "multicast MCCH" or new SIBs (such as SIB20) if the corresponding multicast session is deactivated (i.e., before receiving a multicast session notification).

[0179] Upon receiving the multicast activation notification, the UE needs to check whether the MCCH configuration in the new SIB and / or the PTM configuration in the multicast MCCH have been updated if the MCCH configuration and / or the PTM configuration were provided by the RRC release. Unless the configuration has been updated, the saved configuration, i.e., the configuration provided by the RRC release, should be applied. Of course, if the configuration has been updated, the UE needs to acquire the new SIB and / or the multicast MCCH.

[0180] For the new SIB, it is expected that the UE can know whether the new SIB has been updated by checking the value tag of SIB1 as it does now. However, the UE does not know whether the multicast MCCH has been updated before receiving and decoding the MCCH. In this case, even if the MCCH has been configured by RRC release, the UE would still need to decode the MCCH once, which is also meaningless. In this sense, a value tag needs to be introduced into the MCCH so that the UE can know the PTM configuration update without decoding the MCCH. Further study is required on where the MCCH value tag should be placed, whether it should be placed in the new SIB, SIB1, or group paging, etc.

[0181] Proposal 6: RAN2 should agree that an MCCH value tag be introduced that the UE uses to know whether the PTM configuration has been updated from that set by RRC release, without having to decode the MCCH itself.

[0182] 2.2 Configuration Update in Inactivity In Rel-17, there is one MCCH in a cell. In Rel-18, RAN2 agreed to introduce a new MCCH logical channel for multicast in inactivity (different from the broadcast MCCH). The multicast MCCH is used when the PTM configuration needs to be changed or when the PTM configuration needs to be indicated during movement across the serving cell / gNB.

[0183] Observation 1: The multicast MCCH is used to update the PTM configuration of UEs in inactivity.

[0184] In other words, there are two MCCHs in Rel-18 networks: (broadcast) MCCH and multicast MCCH. The motivation for introducing separate MCCHs within a cell is thought to be to handle the different service requirements of different cast types (MBS broadcast and MBS multicast).

[0185] The question is whether different multicast sessions have different service requirements. It is considered that the service requirements for a group multimedia call service and a firmware download service are quite different. For example, the group multimedia call service is a foreground service, so it needs to frequently optimize the PTM settings, while the firmware download service is a background service, so such frequent optimization is not necessary. Considering that the initial PTM settings are provided by RRC release, updating the PTM settings via a multicast MCCH is necessary for some services but not for others. In this sense, introducing multiple multicast MCCHs is efficient for UEs and flexible for the network.

[0186] Proposal 7: RAN2 should discuss whether to introduce multiple multicast MCCHs per cell.

[0187] 2.3 UE Mobility and Service Continuity 2.3.1 Frequency Prioritization RAN2#121bis-e agreed that UE behavior during cell reselection requires further study. Similar to the Rel-17 broadcast reception procedure, the UE acquires new SIBs and multicast MCCH and PTM settings after cell reselection. If the UE reselects to a cell where PTM settings are not available on the multicast MCCH, the UE initiates the RRC resumption procedure for active multicast sessions that it is interested in receiving or continuing to receive. Frequency prioritization may be provided to the UE for cell reselection with RRC inactivity and multicast reception, but the detailed mechanism for identifying frequency information (e.g., SAI, USD, or frequency information provided directly by the network) requires further study. It is not necessary to define a mechanism other than frequency prioritization, i.e., per-cell prioritization for cell reselection, to enable the UE to select an appropriate cell. The neighbor cell list mechanism for multicast reception in RRC inactive can be configured in some aspects to be similar to the Rel-17 NCL mechanism in MBS broadcast, so that it can be used by the UE to resume RRC connection when the service is not available in the reselected cell due to NCL, without reading the MCCH in the reselected cell.

[0188] Regarding frequency information, higher layers can provide information via USD, etc. However, considering that NRMBS transmission is determined on a cell-by-cell basis, USD can only provide static information (especially for inactive UEs), while the RAN may have up-to-date information. Therefore, the RAN should also provide frequency information if possible. Therefore, like SIB21 in the Rel-17 MBS broadcast, the gNB can broadcast frequency information so that the UE can prioritize the appropriate frequency during cell reselection.

[0189] Proposal 8: RAN2 should agree that frequency information will be broadcast by the gNB.

[0190] 2.3.2 Area-Specific PTM Configuration In RAN2#121, area scope for MCCH was discussed. Some companies have proposed enabling PTM configuration in multiple cells to improve service continuity during UE mobility. In the intra-gNB case, PTM configuration for each cell can be easily coordinated (if necessary), but in the inter-gNB case, it becomes more difficult and requires negotiation with the Xn-AP. Finally, RAN2 agreed that area scope does not involve other gNBs, and the intra-gNB case requires further study. ・A serving cell does not provide PTM configuration for neighboring cells from other gNBs. ・Whether the network can provide PTM configuration to intra-gNB cells requires further study.

[0191] For this small enhancement, it is considered acceptable to limit it to the case within the gNB. Therefore, RAN2 should discuss whether the PTM configuration can be applied to multiple cells within the gNB.

[0192] Proposal 9: RAN2 should discuss whether PTM settings can be applied to multiple cells within a gNB.

[0193] 2.3.3 QoS Enforcement RAN2#119e has reached the following agreements related to Case 3: HARQ feedback and PTP are not supported for RRC inactive multicast reception.

[0194] According to the agreement, multicast reception in inactive mode is similar to MBS broadcast reception (so-called Delivery mode 2) specified in Rel-17. MBS broadcast is best-effort type.

[0195] On the other hand, guaranteeing QoS / reliability is an important issue for multicast sessions. SA2 also raised the question of whether there is a difference in quality / reliability of multicast reception between connected and inactive, and RAN2#119bis-e agreed to the following answer:

[0196] RAN2 Q1-a) If there is a large difference in the quality and reliability of MBS data reception between a UE in RRC connected state and a UE in RRC inactive state, the quality and reliability of MBS data reception between a UE in RRC connected state and a UE in RRC inactive state may be different since HARQ feedback and PTP transmission are not supported and seamless / lossless mobility is not required for multicast reception in RRC inactive.

[0197] RAN2#121bis-e agreed to introduce an event-triggered RRC restart mechanism, but the trigger conditions require further study.

[0198] The UE may trigger the resumption of the RRC connection if the reception quality of the multicast data falls below a configured threshold.

[0199] In RAN2#119e, it has been proposed to introduce thresholds for reception quality such as RSRP and BLER, which are thought to be used to ensure a certain level of QoS required for multicast reception.

[0200] Regarding the RSRP threshold, NR MBS assumes a single-cell transmission method and monitors SSB or CSI-RS instead of directly monitoring MTCH. Therefore, it is considered necessary for the UE to transition to Connected whenever it moves to the cell edge or performs cell reselection. This may not be optimal in some deployments from the perspective of network congestion and UE power saving. However, RSRP is one of the basic metrics used to evaluate reception quality and is one of the usual metrics used by gNBs when deciding on handover (i.e., handover is performed after the UE transitions to Connected due to this RSRP threshold).

[0201] Regarding the BLER threshold, it is considered to be more understandable to ensure QoS requirements since it directly monitors the quality of the MTCH, and therefore BLER is worth specifying as the metric.

[0202] Another way is to define a specific event. For example, if the event is set to cell reselection, the UE must always transition to Connected before cell reselection. However, such an event can be emulated by the RSRP threshold mentioned above. Therefore, careful consideration is required when RAN2 defines the events that will be trigger conditions.

[0203] In summary, at least the RSRP threshold and / or the MTCH BLER threshold should be used for event-triggered RRC resumption.

[0204] Proposal 10: RAN2 should agree to introduce an RSRP threshold and / or an MTCH BLER threshold to monitor multicast reception quality and trigger RRC restart.

[0205] 2.4 Notifications 2.4.1 Multicast Session Deactivation In RAN2#121bis-e, the method of notifying UEs of session deactivation is being discussed. Further study is required to determine whether the option of enhanced group paging or enhanced MCCH should be adopted to allow Rel-18 UEs to remain in RRC inactive and stop monitoring the corresponding G-RNTI in the event of session deactivation / temporary no data.

[0206] The above agreement allows for only enhanced group paging or enhanced MCCH, but does not explicitly exclude the new MAC CE. Only the key points of the analysis of these options are summarized in Table 1.

[0207] Of the three options, MAC CE is considered to be the most efficient in terms of UE power consumption (i.e., because it has the shortest latency), but email discussions have shown that this option has few supporters.

[0208] Of the two viable options, enhanced group paging has a slight advantage, even in terms of UE power consumption. Based on legacy operation, the MCCH would need to delete the PTM configuration of the deactivated session. Considering that this multicast session will become active again (because it has not been released), the enhanced MCCH would need to add back the same PTM configuration, and the UE would need to reacquire and apply this configuration. Furthermore, it is unclear what is being enhanced in the enhanced MCCH. Assuming that a deactivation notification is added to the MCCH (a similar notification is added in enhanced group paging), this notification is delayed so that the UE receives it after the session is actually deactivated. Therefore, group paging seems reasonable.

[0209] Proposal 11: RAN2 should agree to enhanced group paging for multicast session invalidation.

[0210] Regarding the details of the group paging enhancement, backward compatibility needs to be considered: since the existing paging group list (i.e., list of TMGIs) is applicable to legacy UEs, group paging needs to add a new TMGI list for invalidation notification to avoid impacting legacy UEs.

[0211] Proposal 12: If proposal 11 can be agreed upon, RAN2 will further discuss whether to create a new paging group list consisting of the TMGIs of the disabled multicast sessions.

[0212] 2.4.2 Multicast Session Activation and Selective Transition RAN2 #119e has arrived at the assumption that the gNB can select a subset of UEs to transition between inactive and connected states. It is assumed that the network can select which UEs receive in the RRC inactive and RRC connected states and can move UEs between states for multicast service reception.

[0213] RAN2#121bis-e agreed to enhance group paging for session activation notification. A Rel-18 UE can remain in RRC inactive state and start monitoring the corresponding G-RNTI when an enhanced group paging occurs (e.g., session activation or data transmission resumption). Details require further study. Legacy group paging (i.e., Rel-17 group paging) can be used to return the UE to RRC Connected state. UE-specific paging (e.g., PagingRecordList) can be used to move a specific MBS multicast UE to RRC Connected (i.e., legacy UE behavior). If a UE receives both enhanced group paging and unicast paging (and both are targeted at this UE), the UE will follow the unicast paging and transition to RRC Connected.

[0214] For the enhancement regarding group paging, considering that a subset of UEs remain in inactive while another subset transitions to Connected, the behavior of the UEs when receiving the current paging message (i.e., UE-specific paging and group paging) is as follows: UE-specific paging: The UE transitions to Connected if its UE-ID is available in the pagingRecordList. Group paging: All UEs transition to Connected when the TMGI of interest is available in the pagingGroupList. Paging messages: The pagingRecordList and pagingGroupList can be set simultaneously (i.e., in one message) from an ASN.1 perspective. In any case, all UEs transition to Connected when a TMGI of interest becomes available in the pagingGroupList, regardless of the pagingRecordList.

[0215] Therefore, the gNB cannot keep a subset of UEs in an inactive state as long as these UEs are interested in the TMGIs available in the pagingGroupList.

[0216] Therefore, the Rel-18 enhancements require a change in the UE behavior when receiving group paging. A simple solution is to cancel the legacy pagingGroupList, which is always required for Rel-17 UEs (i.e., backward compatibility). Since the cancellation needs to be per TMGI, an additional TMGI list is required (e.g., the Paging Group Cancel List is configured in TMGIs). Considering the RAN2 agreement that "if both enhanced group paging and unicast paging are received by a UE (and targeted at this UE), the UE follows unicast paging and becomes RRC connected," the behavior of a Rel-18 UE is as follows:

[0217] Step 1: The UE receives a paging message containing a pagingRecordList, pagingGroupList, and a new TMGI cancellation list. Step 2: Because the pagingGroupList contains the TMGI of interest, the UE considers it has been paged by group paging, as in Rel-17. Step 3: Because the new TMGI cancellation list contains the TMGI of interest (i.e., the same TMGI), the UE considers the group paging to have been canceled. Step 4: Because the pagingRecordList contains the UE-ID, the UE considers it has been paged by UE-specific paging and transitions to Connected, as in Rel-17. Step 5: The gNB configures the UE with multicast MRBs, as in Rel-17.

[0218] Finally, only a subset of UEs transition to Connected for multicast reception.

[0219] Proposal 13: RAN2 should agree to add a new cancellation TMGI list to group paging to cancel Rel-17 group paging.

[0220] Further study is needed for "special UEs" in RAN2#121bis-e. "Special UEs" identified by MBS assistance information from 5GC may be released to RRC inactive (e.g., when a session is deactivated). Further study is needed on how to enable the network to return to RRC connected when such UEs activate a session.

[0221] That is, the pagingRecordList contains the UE-ID of the "special UE", and the pagingGroupList and the new TMGI cancellation list contain the TMGIs of interest for the "special UE", so there is no need to extend it for this purpose.

[0222] Observation 2: The new TMGI cancellation list also works for "special UEs" at session activation.

[0223] 2.4.3. PTM Configuration Update It was agreed in RAN2#120 that MCCH should be used when PTM configuration needs to be updated. A mixed approach is recommended as follows: 5: If the NW configures the UE to continue multicast reception in inactive state, the NW provides PTM configuration for activated multicast sessions through RRC dedicated signaling, at least for the serving cell (other cases require further study). 6: MCCH is used when PTM configuration needs to be changed or when PTM configuration needs to be indicated during movement beyond the serving cell / gNB. Session status changes and other indications require further study. 7: It is assumed that the UE can receive multicast services only after joining the session. 8: Whether MCCH configuration is initially provided to the UE by dedicated signaling requires further study.

[0224] RAN2#121 agreed to use RRC release for PTM configuration (even before session activation) and to introduce a new MCCH (different from the Rel-17 MCCH).

[0225] - A UE needs to join a multicast session before receiving multicast in RRC inactive. - If the network deems it useful, it can configure the UE with the PTM configuration of a (single) serving cell before session activation, and the UE can store the configuration. Once the session is activated, the UE can apply the configuration and receive multicast in inactive state without returning to RRC connected, unless updated by MCCH after configuration. - If the network configures the UE to receive multicast in inactive state, it can deliver the PTM configuration using an RRC release message with suspendconfig. No other dedicated RRC message is used to provide PTM configuration for MBS multicast in inactive. - A new MCCH logical channel for multicast in inactive is introduced (different from broadcast MCCH).

[0226] According to these agreements, there are two cases for PTM configuration update: Case 1: UE in inactive state receiving an already activated multicast session Case 2: UE in inactive state waiting for multicast session activation Note: Case 2 may be further classified depending on whether the PTM configuration was provided by RRC release or not. In such cases, it is desirable that the solution is as common as possible.

[0227] Proposal 14: RAN2 should aim for a common solution for PTM configuration update notification that considers at least two cases: sessions that have already been activated and sessions before activation.

[0228] The motivation for using MCCH is to reduce the signaling overhead during PTM configuration updates, i.e., to allow UEs to remain inactive to obtain updated PTM configurations. Therefore, from the perspective of an inactive UE, the new PTM configuration distribution method in Rel-18 is similar to distribution mode 2 in Rel-17. In this case, it seems reasonable to reuse the existing MCCH change notification to signal PTM configuration updates.

[0229] However, MCCH Change Notification requires the UE to wake up once per MCCH change boundary, which imposes additional burden on top of monitoring paging occasions, and is not efficient, especially for case 2 above (i.e., the UE needs to monitor MCCH Change Notification even if it is only waiting for a multicast session notification to see if the PTM configuration provided by the RRC release has been updated).

[0230] To solve this problem, group paging can be enhanced for notification of PTM configuration updates. The UE only needs to monitor paging opportunities to determine whether the PTM configuration has been updated, regardless of whether the UE is receiving a multicast session or not (i.e., case 1 or case 2 above). Therefore, RAN2 needs to agree to use group paging for this notification. The details of the enhancements require further study.

[0231] Proposal 15: RAN2 should agree to use group paging for PTM configuration updates instead of the existing MCCH change notification.

[0232] 2.5 Service Continuity During RRC Resume It is necessary to consider the possibility that a UE already receiving a multicast session in Inactive (i.e., via a Broadcast MRB or a new MRB for multicast reception in Inactive) is paged and initiates an RRC Resume procedure. After transitioning to Connected, the UE would of course like to continue receiving the same multicast session. However, in this case, the UE has two MRBs for the same multicast session: the Broadcast MRB (or new MRB) configured for multicast reception in Inactive, and the resumed Multicast MRB for multicast reception in Connected.

[0233] In Rel-17, multicast sessions can only be received via multicast MRBs configured by RRC reconfiguration, whereas in Rel-18, it is expected that UEs will be able to receive multicast sessions via Broadcast MRBs (or new MRBs) configured by RRC reconfiguration or a new MCCH.

[0234] The UE should use multicast MRBs for reception after transitioning to Connected (similar to Rel-17). However, it is unclear how the UE should switch between these MRBs, when the UE should discard broadcast MRBs (or new MRBs), and how the UE should behave if the multicast MRB is an AM MRB (i.e., from the perspective of the lossless principle). Therefore, RAN2 needs to discuss the UE behavior upon RRC resumption in terms of MRB handling and service continuity of multicast sessions.

[0235] Proposal 16: RAN2 should discuss UE behavior upon RRC resumption during continuous reception of a multicast session (e.g., handling of broadcast MRBs and multicast MRBs).

[0236] 1: Mobile communication system 5: Network 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. 1. A communication method performed by a user equipment in a mobile communication system providing a multicast / broadcast service (MBS), comprising: receiving, in a Radio Resource Control (RRC) connected state, a multicast reception configuration in an RRC inactive state from a network node; receiving, in the RRC inactive state, a paging message from a network node, the paging message including a first list of MBS session identifiers and flag information associated with the MBS session identifiers included in the first list; and when an MBS session identifier of a multicast session in which the user device has joined is included in the first list and the multicast reception configuration has been received, determining whether to maintain the RRC inactive state based on the flag information associated with the MBS session identifier of the multicast session in which the user device has joined. Communication method.

2. A user device for use in a mobile communication system providing a multicast / broadcast service (MBS), comprising: a receiving unit that receives a multicast reception configuration in a radio resource control (RRC) inactive state from a network node in a radio resource control (RRC) connected state; a control unit, the receiving unit receives, in the RRC inactive state, a paging message from a network node, the paging message including a first list that is a list of MBS session identifiers and flag information associated with the MBS session identifiers included in the first list; When an MBS session identifier of a multicast session in which the user device has joined is included in the first list and the multicast reception setting has been received, the control unit determines whether to maintain the RRC inactive state based on the flag information associated with the MBS session identifier of the multicast session in which the user device has joined. User equipment.

3. A chipset for user equipment used in a mobile communication system providing multicast / broadcast services (MBS), comprising: In a radio resource control (RRC) connected state, receiving a multicast reception configuration in an RRC inactive state from a network node; receiving, in the RRC inactive state, a paging message from a network node, the paging message including a first list of MBS session identifiers and flag information associated with the MBS session identifiers included in the first list; If the MBS session identifier of the multicast session in which the user device has joined is included in the first list and the multicast reception configuration has been received, a process of determining whether to maintain the RRC inactive state based on the flag information associated with the MBS session identifier of the multicast session in which the user device has joined is executed. Chipset.

4. A user device used in a mobile communication system providing a multicast / broadcast service (MBS), comprising: In a radio resource control (RRC) connected state, receiving a multicast reception configuration in an RRC inactive state from a network node; receiving, in the RRC inactive state, a paging message from a network node, the paging message including a first list of MBS session identifiers and flag information associated with the MBS session identifiers included in the first list; and when the MBS session identifier of the multicast session in which the user device has joined is included in the first list and the multicast reception configuration has been received, determining whether to maintain the RRC inactive state based on the flag information associated with the MBS session identifier of the multicast session in which the user device has joined. Chipset.

5. A mobile communication system providing a multicast / broadcast service (MBS), comprising: a user equipment and a network node; The user equipment receives, in a radio resource control (RRC) connected state, a multicast reception configuration in an RRC inactive state from the network node; The user equipment receives, in the RRC inactive state, a paging message from a network node, the paging message including a first list that is a list of MBS session identifiers and flag information associated with the MBS session identifiers included in the first list; When the MBS session identifier of the multicast session in which the user device has joined is included in the first list and the user device has received the multicast reception configuration, the user device determines whether to maintain the RRC inactive state based on the flag information associated with the MBS session identifier of the multicast session in which the user device has joined. Mobile communication system.