Communication control method, user equipment, and processor

Abstract

To provide a communication control method for implementing enhanced multicast and broadcast services.SOLUTION: A communication control method in a first aspect is a communication control method performed by user equipment in a mobile communication system providing a multicast broadcast service (MBS) from a network to the user equipment and includes performing, in an RRC (Radio Resource Control) idle state or an RRC inactive state, monitoring a group notification that is a notification indicating an enabled state of an MBS multicast session in which the user equipment is participating and that is transmitted from the network to a group to which the user equipment belongs; performing, in response to receiving the group notification, transition to an RRC connected state for reception of the MBS multicast session; and performing control not to perform monitoring the group notification when the user equipment has left the MBS multicast session.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a communication control method used in a mobile communication system. [Background technology]

[0002] In recent years, the fifth generation (5G) mobile communication system has been attracting attention. NR (New Radio), the radio access technology (RAT) of the 5G system, has features such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), the fourth generation radio access technology. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP technical specification "3GPP TS 38.300 V16.3.0 (2020-09)" Summary of the Invention

[0004] A communication control method according to a first aspect is a communication control method executed by a user device in a mobile communication system that provides a multicast service from a network to the user device, and includes the steps of: monitoring a group notification in an RRC idle state or an RRC inactive state, the group notification being a notification indicating the activation of a multicast session in which the user device is participating, and being sent from the network to a group to which the user device belongs; transitioning to an RRC connected state in response to receiving the group notification to receive the multicast session; and controlling not to perform the monitoring process or the transition process when the user device loses interest in the multicast session in the RRC idle state or the RRC inactive state, wherein performing the monitoring process includes monitoring the group notification when the user device is interested in the multicast session, and performing the transition process includes transitioning to the RRC connected state in response to receiving the group notification when the user device is interested in the multicast session.

[0005] A communication control method according to a second aspect is a communication control method executed in a mobile communication system that provides a multicast service from a network to a user device, and includes the user device managing a COUNT value as a PDCP (Packet Data Convergence Protocol) variable, wherein the managing includes obtaining a PDCP SN (Sequence Number) included in a header of a PDCP packet that is first received by multicast from the network, and using the obtained PDCP SN as part of the COUNT value.

[0006] A communication control method according to a third aspect is a communication control method executed in a mobile communication system that provides a multicast service from a network to a user device, and includes the steps of the user device, after joining a multicast session, receiving, in an RRC inactive state, a paging message including a Temporary Mobile Group Identity (TMGI) of the multicast session in which the user device is participating, and transitioning to an RRC connected state in response to receiving the paging message including the TMGI.

[0007] A communication control method according to a fourth aspect is a communication control method executed in a mobile communication system that provides multicast services from a network to a user device, and includes a base station transmitting a paging message including a TMGI as a group notification, and the user device monitoring the paging message at paging opportunities for the user device, and the transmitting includes transmitting the paging message including the TMGI at a timing based on a paging request from an AMF (Access and Mobility Management Function).

[0008] A communication control method according to a fifth aspect is a communication control method executed in a mobile communication system that provides a multicast broadcast service (MBS) from a base station to a user device, and includes the base station transmitting MBS data in an MBS session transmitting an initial value of at least one of a PDCP variable and an RLC variable to be used by the user device to receive the MBS data.

[0009] A communication control method according to a sixth aspect is a communication control method executed by a user device in a mobile communication system that provides multicast services from a network to the user device, and includes the steps of: performing a session join procedure for a multicast session with the network; obtaining period information from the network indicating a period during which the user device will remain joined to the multicast session; if the user device is interested in the multicast session, performing the session join procedure or the session continuation procedure with the network before or at the expiration of the period indicated by the period information; and if the user device is not interested in the multicast session, controlling so that the session join procedure or the session continuation procedure is not performed with the network before or at the expiration of the period indicated by the period information.

[0010] A communication control method according to a seventh aspect is a communication control method executed in a mobile communication system that provides a multicast service from a network to a user device, and includes the steps of the user device performing a random access procedure with a base station included in the network in an RRC idle state or an RRC inactive state, the user device transmitting a notification to the base station during the random access procedure indicating a session leave of a multicast session in which the user device is participating, and the user device terminating the random access procedure without transitioning to an RRC connected state. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating a configuration of a UE (user equipment) according to an embodiment. [Figure 3] A diagram showing the configuration of a gNB (base station) according to one embodiment. [Figure 4]FIG. 10 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. [Figure 5] FIG. 1 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). [Figure 6] FIG. 2 is a diagram illustrating a correspondence relationship between downlink logical channels and transport channels according to an embodiment. [Figure 7] FIG. 1 is a diagram illustrating a method for distributing MBS data according to an embodiment. [Figure 8] FIG. 1 illustrates a split MBS bearer according to one embodiment. [Figure 9] FIG. 2 is a diagram showing a basic operation in a first operation pattern of a mobile communication system according to an embodiment. [Figure 10] FIG. 2 is a diagram showing an example of a first operation pattern of the mobile communication system according to an embodiment. [Figure 11] FIG. 10 is a diagram showing another example of the first operation pattern of the mobile communication system according to an embodiment. [Figure 12] FIG. 10 is a diagram illustrating an example of a second operation pattern of the mobile communication system according to an embodiment. [Figure 13] FIG. 10 is a diagram illustrating an example of a third operation pattern of the mobile communication system according to an embodiment. [Figure 14] FIG. 10 is a diagram illustrating an operation according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] The introduction of multicast and broadcast services into the 5G system (NR) is being considered. The NR multicast and broadcast services are expected to provide improved services compared to the LTE multicast and broadcast services.

[0013] Therefore, an object of the present disclosure is to provide a communication control method that realizes improved multicast / broadcast services.

[0014] 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.

[0015] (Configuration of a mobile communication system) First, the configuration of a mobile communication system according to an embodiment will be described. Fig. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. This mobile communication system conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following description, 5GS will be taken as an example, but the mobile communication system may also be at least partially applied to an LTE (Long Term Evolution) system. Furthermore, the mobile communication system may also be at least partially applied to a 6th Generation (6G) system.

[0016] As shown in FIG. 1, the mobile communication system includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20.

[0017] The UE 100 is a mobile wireless communication device. The UE 100 may be any device used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a laptop 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).

[0018] The NG-RAN 10 includes a base station (called a "gNB" in a 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, 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 that performs wireless communication with a UE 100. One cell belongs to one carrier frequency.

[0019] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-base station interface.

[0020] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 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 UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0021] FIG. 2 is a diagram showing a configuration of a UE 100 (user equipment) according to an embodiment.

[0022] As shown in FIG. 2, the UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit .

[0023] 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.

[0024] 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.

[0025] The control unit 130 performs various controls in the UE 100. 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 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.

[0026] FIG. 3 is a diagram showing the configuration of a gNB200 (base station) according to one embodiment.

[0027] As shown in FIG. 3, the gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240.

[0028] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission 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.

[0029] 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.

[0030] The control unit 230 performs various controls in the gNB 200. 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 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.

[0031] The backhaul communication unit 240 is connected to neighboring base stations via an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF 300 via a base station-core network interface. Note that the gNB is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and both units may be connected via an F1 interface.

[0032] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0033] As shown in Figure 4, 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.

[0034] 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 the UE 100 and the PHY layer of the gNB 200 via a physical channel.

[0035] 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 UE100 and the MAC layer of gNB200 via transport channels. The MAC layer of gNB200 includes a scheduler, which determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0036] The RLC layer transmits data to the RLC layer on the receiving side 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 logical channels.

[0037] The PDCP layer performs header compression / decompression and encryption / decryption.

[0038] The SDAP layer maps IP flows, which are the units for Quality of Service (QoS) control by the core network, to radio bearers, which are the units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP is not necessary.

[0039] 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).

[0040] As shown in FIG. 5, the protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer shown in FIG.

[0041] 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.

[0042] The NAS layer, which is positioned 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 300.

[0043] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0044] (MBS) Next, an MBS according to one embodiment will be described. The MBS is a service that enables broadcast or multicast data transmission, i.e., point-to-multipoint (PTM) data transmission, from the NG-RAN 10 to the UE 100. The MBS may also be called an MBMS (Multimedia Broadcast and Multicast Service). Note that use cases (service types) of the MBS include public safety communications, mission-critical communications, V2X (Vehicle to Everything) communications, IPv4 or IPv6 multicast distribution, IPTV (Internet Protocol Television), group communications, and software distribution.

[0045] There are two types of MBS transmission methods in LTE: MBSFN (Multicast Broadcast Single Frequency Network) transmission and SC-PTM (Single Cell Point To Multipoint) transmission. Fig. 6 is a diagram showing the correspondence relationship between downlink logical channels and transport channels according to one embodiment.

[0046] As shown in Figure 6, the logical channels used for MBSFN transmission are the MTCH (Multicast Traffic Channel) and the MCCH (Multicast Control Channel). The transport channel used for MBSFN transmission is the MCH (Multicast Channel). MBSFN transmission is primarily designed for multi-cell transmission, and in an MBSFN area consisting of multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0047] The logical channels used for SC-PTM transmission are the SC-MTCH (Single Cell Multicast Traffic Channel) and SC-MCCH (Single Cell Multicast Control Channel). The transport channel used for SC-PTM transmission is the DL-SCH (Downlink Shared Channel). SC-PTM transmission is primarily designed for single-cell transmission, and transmits data on a cell-by-cell basis by broadcast or multicast. The physical channels used for SC-PTM transmission are the PDCCH (Physical Downlink Control Channel) and PDSCH (Physical Downlink Shared Channel), which enable dynamic resource allocation.

[0048] In the following, an example in which an MBS is provided using a method similar to the SC-PTM transmission method will be mainly described, but an MBS may also be provided using the MBSFN transmission method. Also, an example in which an MBS is provided by multicast will be mainly described. Therefore, MBS may be read as multicast. However, an MBS may also be provided by broadcast.

[0049] Furthermore, MBS data refers to data provided by the MBS. The MBS control channel refers to the MCCH or SC-MCCH. The MBS traffic channel refers to the MTCH or SC-MTCH. However, MBS data may also be transmitted by unicast. The MBS data may also be called an MBS packet or MBS traffic.

[0050] A network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a Temporary Mobile Group Identity (TMGI) and a session identifier, and at least one of these identifiers is called an MBS session identifier. Such an MBS session identifier may also be called an MBS service identifier or a multicast group identifier.

[0051] FIG. 7 is a diagram showing a method for distributing MBS data according to an embodiment.

[0052] As shown in Fig. 7, MBS data (MBS Traffic) is distributed from a single data source (application service provider) to multiple UEs. A 5G CN (5GC) 20, which is a 5G core network, receives the MBS data from the application service provider, creates a copy of the MBS data (replication), and distributes the data.

[0053] From the 5GC20 point of view, two delivery methods are possible: Shared MBS Traffic delivery and Individual MBS Traffic delivery.

[0054] In shared MBS data delivery, a connection is established between NG-RAN 10, which is a 5G radio access network (5G RAN), and 5GC 20, and MBS data is delivered from 5GC 20 to NG-RAN 10. Hereinafter, such a connection (tunnel) will be referred to as an "MBS connection."

[0055] The MBS connection may be referred to as a Shared MBS Traffic delivery connection or a shared transport. The MBS connection terminates in the NG-RAN 10 (i.e., the gNB 200). The MBS connection may have a one-to-one correspondence with the MBS session.

[0056] gNB200 selects either PTP (Point-to-Point: unicast) or PTM (Point-to-Multipoint: multicast or broadcast) transmission method at its own discretion, and transmits MBS data to UE100 using the selected transmission method.

[0057] On the other hand, in individual MBS data delivery, a unicast session is established between the NG-RAN 10 and the UE 100, and the MBS data is delivered individually from the 5GC 20 to the UE 100. Such a unicast may be called a PDU (Protocol Data Unit) session. The unicast (PDU session) terminates at the UE 100.

[0058] (Split MBS bearer) Next, a split MBS bearer according to one embodiment will be described.

[0059] The gNB200 can set an MBS bearer separated into a PTP communication path and a PTM communication path (hereinafter referred to as a "split MBS bearer" as appropriate) to the UE100. This allows the gNB200 to dynamically switch the transmission of MBS data to the UE100 between PTP (PTP communication path) and PTM (PTM communication path). Alternatively, the gNB200 can improve reliability by dual-transmitting the same MBS data using both PTP (PTP communication path) and PTM (PTM communication path).

[0060] The predetermined layer that terminates splitting is the MAC layer (HARQ), the RLC layer, the PDCP layer, or the SDAP layer. In the following, an example in which the predetermined layer that terminates splitting is the PDCP layer will be mainly described, but the predetermined layer may be the MAC layer (HARQ), the RLC layer, or the SDAP layer.

[0061] 8 is a diagram showing a split MBS bearer according to one embodiment. Hereinafter, a PTP communication path is referred to as a PTP leg, and a PTM communication path is referred to as a PTM leg. Furthermore, a functional unit corresponding to each layer is referred to as an entity.

[0062] 8, each of the PDCP entity of the gNB 200 and the PDCP entity of the UE 100 separates an MBS bearer, which is a bearer (data radio bearer) used for MBS, into a PTP leg and a PTM leg. Note that a PDCP entity is provided for each bearer.

[0063] Each of the gNB 200 and the UE 100 has two RLC entities, one MAC entity, and one PHY entity, each of which is provided for each leg. A PHY entity may be provided for each leg. In the case of dual connectivity in which the UE 100 communicates with two gNBs 200, the UE 100 may have two MAC entities.

[0064] The PHY entity transmits and receives data of the PTP leg using a Cell Radio Network Temporary Identifier (C-RNTI) that is assigned one-to-one to the UE 100. The PHY entity transmits and receives data of the PTM leg using a Group Radio Network Temporary Identifier (G-RNTI) that is assigned one-to-one to the MBS session. The C-RNTI is different for each UE 100, but the G-RNTI is a common RNTI for multiple UEs 100 receiving one MBS session.

[0065] In order to perform PTM transmission (multicast or broadcast) of MBS data from gNB200 to UE100 using a PTM leg, a split MBS bearer must be set from gNB200 to UE100 and the PTM leg must be activated. In other words, even if a split MBS bearer is set to UE100, gNB200 cannot perform PTM transmission of MBS data using this PTM leg if the PTM leg is in a deactivation state.

[0066] Furthermore, in order for the gNB200 and the UE100 to perform PTP transmission (unicast) of MBS data using a PTP leg, a split MBS bearer must be set from the gNB200 to the UE100, and the PTP leg must be activated. In other words, even if a split MBS bearer is set to the UE100, the gNB200 cannot perform PTP transmission of MBS data using this PTP leg if the PTP leg is in an inactive state.

[0067] In a state in which the PTM leg is activated, the UE 100 monitors a PDCCH (Physical Downlink Control Channel) to which a G-RNTI associated with the MBS session is applied (i.e., the UE 100 performs blind decoding of the PDCCH using the G-RNTI). The UE 100 may monitor the PDCCH only at a scheduling opportunity for the MBS session.

[0068] When the PTM leg is deactivated, UE 100 does not monitor the PDCCH to which the G-RNTI associated with the MBS session is applied (i.e., does not perform blind decoding of the PDCCH using the G-RNTI).

[0069] UE 100 monitors a PDCCH to which a C-RNTI is applied when a PTP leg is activated. When discontinuous reception (DRX) is configured in a PTP leg, UE 100 monitors the PDCCH during a configured on validity period (OnDuration). When a cell (frequency) associated with an MBS session is specified, UE 100 may monitor the PDCCH of the cell even if the cell is deactivated.

[0070] In a state in which the PTP leg is deactivated, the UE 100 may monitor a PDCCH to which a C-RNTI is applied in preparation for normal unicast downlink transmission other than MBS data. However, when a cell (frequency) associated with an MBS session is specified, the UE 100 may not monitor the PDCCH for the MBS session.

[0071] It is assumed that the split MBS bearer described above is set up by an RRC message (e.g., an RRC Reconfiguration message) sent by the RRC entity of gNB200 to the RRC entity of UE100.

[0072] (Mobile communication system operation) Next, the operation of the mobile communication system 1 according to one embodiment will be described.

[0073] In the following, it is mainly assumed that the UE 100 in the RRC connected state receives MBS data (i.e., multicast data) transmitted by multicast from the gNB 200. For this reason, it is assumed that the MBS session is a multicast session. It is also assumed that the MBS session identifier is a multicast session identifier (e.g., TMGI, Session ID, or G-RNTI). The multicast session is mapped to a PTM leg or a PTM bearer (multicast bearer). The MBS traffic channel (MTCH) is used to transmit the multicast data from the gNB 200 to the UE 100.

[0074] In the following, it is assumed that UE 100, after participating in a multicast session, transitions to an RRC idle state or an RRC inactive state and waits for the start of the multicast session. UE 100 receives, in the RRC idle state or the RRC inactive state, a group notification indicating the activation of the multicast session in which UE 100 is participating, which is transmitted from the network to the group to which UE 100 belongs. In response to receiving the group notification, UE 100 transitions to an RRC connected state and receives multicast data of the multicast session from gNB 200.

[0075] FIG. 9 is a diagram showing basic operations in the first operation pattern of the mobile communication system 1. Hereinafter, the gNB 200 and the AMF 300 will be collectively referred to as the "network" as appropriate. The AMF 300 is an example of a core network (CN) device. The AMF 300 manages MBS sessions (multicast sessions) in cooperation with a session management device. The session management device is another example of a CN device.

[0076] As shown in Fig. 9, in step S101, the UE 100 is in an RRC connected state. The UE 100 is assumed to have an interest in a certain multicast session (hereinafter referred to as a "target multicast session"). "Interested in a multicast session" means that an upper layer of the UE 100 requests or desires to receive the multicast session. The upper layer includes a NAS layer. The upper layer may further include an application.

[0077] In step S102, UE 100 (NAS entity) performs a multicast session join procedure with the network to join the targeted multicast session. For example, UE 100 joins the targeted multicast session by sending a first NAS message to AMF 300 requesting participation in the targeted multicast session and receiving a second NAS message from AMF 300 approving participation in the targeted multicast session. "Joining the targeted multicast session" means registering UE 100 with the CN device as a member of a UE group (multicast group) that receives the multicast session. Note that participation in a multicast session may be performed when the multicast session is in an enabled state (transmitting). Also, participation in a multicast session may be performed when the multicast session is in an disabled state (waiting for transmission to start or transmission suspended).

[0078] In step S103, UE 100 transitions to an RRC idle state or an RRC inactive state. Specifically, UE 100 transitions to the RRC idle state or the RRC inactive state by receiving an RRC release message from gNB 200. Prior to step S103, UE 100 may transmit to gNB 200 an RRC message (e.g., a UE Assistance Information message) including an information element prompting UE 100 to transition to the RRC idle state or the RRC inactive state. gNB 200 may determine to transition UE 100 to the RRC idle state or the RRC inactive state depending on whether a multicast session in which UE 100 is interested is in an invalid state.

[0079] In step S104, the UE 100 starts monitoring for a group notification from the gNB 200. The group notification may be a paging message transmitted from the gNB 200. Alternatively, the group notification may be a message transmitted from the gNB 200 on a multicast control channel (MCCH). The group notification may be transmitted in response to a multicast session being enabled from a disabled state. The group notification may notify the start of a multicast session. In the following, it is mainly assumed that the group notification is a paging message. The UE 100 monitors for the group notification at a paging occasion (PO) of a paging frame (PF) that is set periodically.

[0080] In step S105, the gNB 200 transmits a group notification addressed to a group including the UE 100 or a group in which the UE 100 is interested. The gNB 200 may transmit a group notification (paging message) to the UE 100 in response to a paging request from the AMF 300. The group notification may include at least one of a multicast session identifier indicating the group, an identifier of each UE belonging to the group, and a multicast session identifier associated with the identifier. The UE 100 that receives the group notification including its own identifier can recognize that the target multicast session in which it has joined has been activated. "The target multicast session has been activated" may mean that transmission of multicast data has started in the target multicast session. Furthermore, "the target multicast session has been activated" may mean that the target multicast session is in a state where transmission of multicast data can be started.

[0081] In step S106, UE100 performs a random access procedure with gNB200 to receive the target multicast session.

[0082] In step S107, the UE 100 transitions to an RRC connected state by a random access procedure.

[0083] In step S108, in the RRC connected state, the UE 100 receives multicast data of the target multicast session from the gNB 200. Before receiving the data, the gNB 200 may perform a setting for the UE 100 to receive the target multicast session. The setting is, for example, an RRC Reconfiguration message including an MRB (Multicast Radio Bearer) setting.

[0084] In this basic operation, after transitioning to the RRC idle state or the RRC inactive state in step S103, the UE 100 may lose interest in the target multicast session. "Losing interest in the target multicast session" means that the upper layers of the UE 100 no longer request or desire to receive the target multicast session. For example, this corresponds to a case where the user closes an IPTV application. In such a case, the UE 100 may transition to the RRC connected state and then perform a multicast session leave procedure to leave the target multicast session. "Leaving the target multicast session" means deregistering the UE 100 from the CN device as a member of the UE group (multicast group) that receives the multicast session. For example, the UE 100 leaves the target multicast session by transmitting a third NAS message to the AMF 300 requesting leave from the target multicast session and receiving a fourth NAS message from the AMF 300 approving the leave from the target multicast session.

[0085] Here, if UE 100, which has lost interest in the target multicast session, performs a group notification monitoring process or transitions to the RRC connected state, this increases the power consumption of UE 100 and reduces the utilization efficiency of radio resources. For example, transitioning to the RRC connected state just to perform a multicast session leave procedure is inefficient. For example, it is more efficient to transition to the RRC connected state when unicast data communication is required later and perform the multicast session leave procedure at that time.

[0086] (1) First operation pattern Next, a first operation pattern of the mobile communication system 1 according to an embodiment will be described.

[0087] In the first operation pattern, UE 100 performs a process of monitoring a group notification, which is a notification indicating the activation of a multicast session in which UE 100 participates (a target multicast session) and is transmitted from the network to a group to which UE 100 belongs or a group in which UE 100 is interested, in an RRC idle state or an RRC inactive state. In response to receiving the group notification, UE 100 performs a process of transitioning to an RRC connected state to receive the multicast session. However, if UE 100 loses interest in the multicast session in the RRC idle state or the RRC inactive state, UE 100 controls not to perform the process of monitoring the group notification or the process of transitioning to the RRC connected state. This can prevent UE 100 from performing inefficient operations.

[0088] 10 is a diagram showing an example of the first operation pattern of the mobile communication system 1. Here, differences from the basic operation described above will be mainly explained.

[0089] As shown in FIG. 10, in step S111, it is assumed that UE 100 in an RRC connected state has an interest in a certain multicast session (hereinafter referred to as a "target multicast session").

[0090] In step S112, the UE 100 (NAS entity) performs a multicast session join procedure to the network (AMF 300) to join the target multicast session.

[0091] In step S113, the UE 100 transitions to an RRC idle state or an RRC inactive state.

[0092] In step S114, UE100 (AS entity) starts monitoring for a group notification from gNB200. The AS entity may be an RRC entity. The group notification may be a paging message transmitted from gNB200. The group notification may also be a message transmitted from gNB200 on a multicast control channel (MCCH). In the following, it is mainly assumed that the group notification is a paging message. UE100 monitors for the group notification at paging occasions (PO) of paging frames (PF) that are periodically set. That is, UE100 periodically monitors for the group notification.

[0093] In step S115, it is assumed that UE 100 is no longer interested in the target multicast session. In UE 100, the NAS entity may notify an AS entity (for example, an RRC entity) that UE 100 is no longer interested in the target multicast session.

[0094] In step S116, UE 100 (AS entity) stops periodic monitoring for the group notification. For example, in UE 100, control unit 130 controls receiving unit 110 not to monitor the group notification. This reduces the processing load and power consumption of UE 100. Note that when paging is used as the group notification and the reception (transmission) opportunity for the group notification and normal paging (paging for unicast communication) is the same, the control not to monitor the group notification means that UE 100 omits reception processing related to the group notification at the reception opportunity. Omitting reception processing includes, for example, one or more of the following: not monitoring the RNTI dedicated to the group notification, not demodulating the message portion dedicated to the group notification, and not checking information elements related to the group notification in the paging message (e.g., multicast session identifiers or a list thereof). In addition, when the reception (transmission) opportunity for the group notification and the reception (transmission) opportunity for the normal paging are different, UE 100 does not perform reception operation (does not wake up) at the reception opportunity for the group notification. Note that even when monitoring of the group notification is stopped, monitoring of normal paging should continue.

[0095] For example, when paging (group paging) is used as group notification, there are two possible configurations for the PF / PO that monitors group paging: 1) a PF / PO dedicated to group paging (separate from unicast paging), and 2) the same PF / PO as for normal paging. In the case of 1), UE 100 can stop monitoring the PF / PO for group paging. In the case of 2), the PF / PO becomes the same as for normal paging, so UE 100 does not monitor only the part related to group paging. For example, UE 100 may not monitor an RNTI dedicated to group paging (for example, GP-RNTI) if it is defined, or may not check (the list of) group identifiers in a paging message.

[0096] Then, in step S117, UE100 performs a random access procedure with gNB200 for a purpose other than receiving a multicast session, for example, because uplink data to be transmitted has occurred or because downlink data to be received has occurred (i.e., because normal / unicast paging has been received).

[0097] In step S118, the UE 100 transitions to the RRC connected state.

[0098] In step S119, the UE 100 (NAS entity) performs a session leave procedure for the target multicast session with the network (AMF 300). This enables the session leave procedure to be performed efficiently.

[0099] 11 is a diagram showing another example of the first operation pattern of the mobile communication system 1. Here, differences from the basic operation described above will be mainly explained.

[0100] As shown in FIG. 11, in step S121, it is assumed that UE 100 in an RRC connected state has an interest in a certain multicast session (hereinafter referred to as a "target multicast session").

[0101] In step S122, the UE 100 (NAS entity) performs a multicast session join procedure to the network (AMF 300) to join the target multicast session.

[0102] In step S123, the UE 100 transitions to an RRC idle state or an RRC inactive state.

[0103] In step S124, UE100 starts monitoring for group notifications from gNB200.

[0104] In step S125, it is assumed that UE 100 is no longer interested in the target multicast session. In UE 100, the NAS entity may notify an AS entity (for example, an RRC entity) that UE 100 is no longer interested in the target multicast session.

[0105] In step S126, the gNB 200 transmits a group notification addressed to a group including the UE 100. The gNB 200 may transmit a group notification (paging message) to the UE 100 in response to a paging request from the AMF 300. The group notification may include an identifier of each UE belonging to the group and a multicast session identifier associated with the identifier. The UE 100 that receives the group notification including its own identifier can recognize that the target multicast session in which the UE 100 has joined has been activated.

[0106] In step S127, the AS entity (access stratum entity) of UE 100 performs control so as not to transition to the RRC connected state even when it receives a group notification addressed to itself. The AS entity may be an RRC entity. In UE 100, the AS entity may notify the NAS entity of the multicast session identifier (specifically, the multicast session identifier associated with the identifier of UE 100) included in the group notification addressed to UE 100. If the NAS entity determines that it is not interested in the multicast session indicated by the notified multicast session identifier, it does not request the AS entity to execute processing to transition to the RRC connected state. On the other hand, if it determines that it is interested in the multicast session indicated by the notified multicast session identifier, the NAS entity may request the AS entity to execute processing to transition to the RRC connected state.

[0107] Then, in step S128, UE100 performs a random access procedure with gNB200 for a purpose other than receiving a multicast session, for example, because uplink data to be transmitted has occurred or because downlink data to be received has occurred (i.e., because normal / unicast paging has been received).

[0108] In step S129, the UE 100 transitions to the RRC connected state.

[0109] In step S130, the UE 100 (NAS entity) performs a session leave procedure for the target multicast session with the network (AMF 300). This enables the session leave procedure to be performed efficiently.

[0110] (2) Second operation pattern Next, a second operation pattern of the mobile communication system 1 according to an embodiment will be described.

[0111] As described above, even if the CN device recognizes that the UE 100 is participating in the target multicast session, it is possible that the UE 100 is no longer interested in the target multicast session. That is, there is a concern that a mismatch may occur between the interest state and participation state of the UE 100. However, explicitly performing session withdrawal requires transmission of a NAS message, which leads to the inefficient operation described above. Therefore, in the second operation pattern, an operation that enables the UE 100 to implicitly (automatically) withdraw from the session will be described. Furthermore, this operation can solve the above-mentioned problem of mismatch even when the UE 100 moves out of service or is powered off.

[0112] In the second operation pattern, UE 100 performs a session join procedure for the target multicast session with the network. UE 100 acquires, from the network (AMF 300), period information indicating a period during which UE 100 maintains its participation in the target multicast session. Such a valid period may be called a valid period or a participation duration (duration), but will be referred to as a valid period hereinafter.

[0113] If UE 100 is interested in the target multicast session, UE 100 performs a session join procedure or a rejoin procedure with AMF 300 before the validity period indicated by the validity period information expires or at the expiration of the validity period. On the other hand, if UE 100 is not interested in the target multicast session, UE 100 controls so as not to perform a session join procedure or a rejoin procedure with AMF 300 before the validity period indicated by the validity period information expires or at the expiration of the validity period. This allows UE 100 that has lost interest in the target multicast session to implicitly (automatically) leave the target multicast session by not performing a session join procedure or a rejoin procedure.

[0114] 12 is a diagram showing an example of the second operation pattern of the mobile communication system 1. Here, differences from the basic operation described above will be mainly explained.

[0115] As shown in FIG. 12, in step S201, it is assumed that the UE 100 in the RRC connected state has an interest in a certain multicast session (target multicast session).

[0116] In steps S202 and S203, the UE 100 (NAS entity) performs a multicast session join procedure to the network (AMF 300) to join the target multicast session.

[0117] Specifically, in step S202, UE 100 (NAS entity) transmits a NAS message (first NAS message) requesting participation in a target multicast session to AMF 300. The first NAS message may include an identifier of UE 100 and a multicast session identifier of the target multicast session. UE 100 may transmit the first NAS message including information indicating a validity period desired by UE 100.

[0118] In step S203, in response to receiving the first NAS message, AMF 300 transmits a second NAS message to UE 100 (NAS entity) approving participation in the target multicast session. AMF 300 may transmit the second NAS message by including validity period information. When information indicating a validity period desired by UE 100 is included in the first NAS message, AMF 300 may determine the validity period based on the information, and transmit the second NAS message by including validity period information indicating the determined validity period.

[0119] The validity period information may be a timer value indicating the validity period. The validity period information may be information indicating the end of the validity period in absolute time. In the following, it is assumed that the validity period information is a timer value.

[0120] In step S204, when UE 100 (NAS entity) acquires the validity period information (timer value) from the network, for example, when it acquires the validity period information (timer value) from the second NAS message, it starts a timer in which the timer value is set. Note that the timer may be started and operated only when UE 100 is in the CM_IDLE state. The CM_IDLE state refers to a state in which UE 100 does not have a NAS signaling connection. After receiving the second NAS message, the timer may be started or restarted (reset and started) in response to UE 100 transitioning to CM_IDLE. The timer may be stopped in response to transitioning to CM_CONNECTED.

[0121] In step S205, the timer expires. The processes of steps S206 to S209 described below may be performed before step S205.

[0122] In step S206, the UE 100 (NAS entity) determines whether it is interested in the target multicast session.

[0123] If it is determined that the UE 100 is interested in the target multicast session (step S206: YES), in steps S207 and S208, the UE 100 (NAS entity) performs a multicast session join / continue procedure with the network (AMF 300) to join (or continue participating in) the target multicast session.

[0124] Specifically, in step S207, UE 100 (NAS entity) transmits a NAS message (first NAS message) requesting participation (or continued participation) in the target multicast session to AMF 300. The first NAS message may include an identifier of UE 100 and a multicast session identifier of the target multicast session. UE 100 may transmit the first NAS message including information indicating a validity period desired by UE 100.

[0125] In step S208, in response to receiving the first NAS message, AMF 300 transmits a second NAS message to UE 100 (NAS entity) approving participation (or continued participation) in the target multicast session. AMF 300 may transmit the second NAS message by including validity period information. When information indicating the validity period desired by UE 100 is included in the first NAS message, AMF 300 may determine the validity period based on the information, and may transmit the second NAS message by including validity period information indicating the determined validity period.

[0126] The validity period information may be a timer value indicating the validity period, or may be information indicating the end of the validity period in absolute time.

[0127] In step S209, when UE 100 (NAS entity) acquires the validity period information (timer value) from the network, for example, when it acquires the validity period information (timer value) from the second NAS message, it starts a timer to which the timer value is set. Note that, as described above, the timer may be started and operated only when UE 100 is in the CM_IDLE state. Also, if the validity period information (timer value) is not included in the second NAS message of the continuation approval in step S208, the value already acquired in the second NAS message of the initial approval in step S203 may be applied.

[0128] In this way, if the UE 100 is still interested in the target multicast session, the validity period is updated, and the state in which the UE 100 participates in the target multicast session continues.

[0129] On the other hand, if it is determined that UE 100 is no longer interested in the target multicast session (step S206: NO), UE 100 does not perform the multicast session join / continue procedure. If there is no multicast session join / continue request from UE 100 within the validity period or within a predetermined time after the expiration of the validity period, AMF 300 assumes that UE 100 is no longer interested in the target multicast session (or UE 100 has moved out of range or been turned off), and manages UE 100 as having left the target multicast session.

[0130] (3) Third movement pattern Next, a third operation pattern of the mobile communication system 1 according to an embodiment will be described.

[0131] As described above, it is inefficient for UE 100 to transition to the RRC connected state just to notify session leave. In the third operation pattern, UE 100 notifies session leave during the random access procedure and ends the random access procedure without transitioning to the RRC connected state, thereby making the notification of session leave more efficient.

[0132] In the third operation pattern, the UE 100 performs a random access procedure with the gNB 200 in an RRC idle state or an RRC inactive state. During the random access procedure, the UE 100 transmits to the gNB 200 a notification indicating session withdrawal of the multicast session in which the UE 100 participates (target multicast session). Then, the UE 100 ends the random access procedure without transitioning to an RRC connected state.

[0133] The random access procedure includes transmitting a random access preamble to the gNB 200 using a PRACH (Physical Random Access Channel) resource. The UE 100 may transmit the random access preamble using the PRACH resource for session leave to the gNB 200 as a notification indicating session leave. The gNB 200 identifies the UE 100 that sent the notification indicating session leave, and notifies the CN device (AMF 300) of the session leave of the UE 100.

[0134] 13 is a diagram showing an example of the third operation pattern of the mobile communication system 1. Here, differences from the basic operation described above will be mainly explained.

[0135] As shown in FIG. 13, in step S301, it is assumed that UE 100 in an RRC connected state has an interest in a certain multicast session (target multicast session).

[0136] In step S302, the UE 100 (NAS entity) performs a multicast session join procedure to the network (AMF 300) to join the target multicast session.

[0137] In step S303, the UE 100 transitions to an RRC idle state or an RRC inactive state.

[0138] In step S304, it is assumed that the UE 100 (NAS entity) is no longer interested in the target multicast session. In the UE 100, the NAS entity may notify the AS entity (e.g., RRC entity) that it is no longer interested in the target multicast session.

[0139] In step S305, the UE 100 (AS entity) receives PRACH information indicating the configuration of PRACH resources from the gNB 200. The PRACH information may be broadcast in system information from the gNB 200. For example, some of the configured PRACH resources may be a resource region (e.g., a dedicated resource region) for session leave notification. The resource region for session leave notification may include multiple sub-resource regions partitioned for each multicast session identifier.

[0140] In step S306, the UE 100 (AS entity) selects a PRACH resource included in a resource region for session leave notification from among the PRACH resources indicated by the PRACH information. Here, the UE 100 (AS entity) may select a sub-resource region associated with the multicast session identifier of the target multicast session.

[0141] In step S307, UE 100 (AS entity) uses the PRACH resource selected in step S306 to transmit a random access preamble (Msg1) to gNB 200. Since the PRACH resource for session leave notification is applied to the random access preamble, gNB 200 determines that UE 100, which transmitted the random access preamble, has notified session leave.

[0142] In step S308, gNB200 transmits a random access response (Msg2) to UE100.

[0143] In step S309, in response to receiving the random access response (Msg2), the UE 100 transmits a connection request message (Msg3) to the gNB 200. The connection request message (Msg3) may be an RRC Setup Request message or an RRC Resume Request message. The connection request message (Msg3) may include at least one of an identifier of the UE 100, information notifying that the UE 100 has left the multicast session, and a multicast session identifier of the target multicast session. The gNB 200 identifies the UE 100 and recognizes that the UE 100 has left the multicast session based on the information included in the connection request message (Msg3). The gNB 200 may identify the UE 100 after contention resolution using Msg4, which will be described later. If the connection request message (Msg3) is an RRC Resume Request message, i.e., if the UE 100 is in an RRC inactive state, the gNB 200 may identify the UE context of the UE 100 that it holds.

[0144] In step S310, the gNB 200 transmits an RRC release message as Msg4 to the UE 100. As a result, the UE 100 maintains the RRC idle state or the RRC inactive state. However, if there is another data transmission / reception for the UE 100, the gNB 200 may cause the UE 100 to transition to the RRC connected state by transmitting an RRC Setup message or an RRC Resume message as Msg4.

[0145] In step S311, the gNB 200 notifies the AMF 300 of the UE 100's departure from the multicast session. For example, the gNB 200 performs the notification by an NG-AP message transmitted on the NG interface. The gNB 200 may generate a NAS message on behalf of the UE 100 and perform the notification by the NAS message. Such a message may include an identifier of the UE 100 and a multicast session identifier of the target multicast session. Note that the processing of step S311 may be performed before step S310.

[0146] Although a four-step random access procedure has been exemplified in this operation pattern, a two-step random access procedure may also be used. In the two-step random access procedure, the UE 100 collectively transmits Msg1 and Msg3 to the gNB 200 as MsgA, and the gNB 200 collectively transmits Msg2 and Msg4 to the UE 100 as MsgB.

[0147] (Example of changes to the operation of a mobile communication system) Next, we will explain a modified example of the operation of the mobile communication system 1. This modified example is not limited to multicast but may also be applied to broadcast MBS services.

[0148] The PDCP entity of the UE 100 sets and updates PDCP variables according to the PDCP sequence number (PDCP SN) included in the PDCP packet received from the gNB 200. Normally, the UE 100 sets the initial value of the PDCP variable to zero and updates (increments, counts up) the PDCP variable as packets are received from the gNB 200. The PDCP entity of the UE 100, which joined an MBS session from the beginning, can sequentially update the PDCP variables to the latest state. The PDCP variables include the PDCP SN and the hyperframe number (HFN). The HFN is incremented when the PDCP SN wraps around. In other words, the HFN is a value that is counted up each time the PDCP SN wraps around. For example, the UE 100 and the gNB 200 manage a COUNT, which is a count value consisting of the PDCP SN and the HFN.

[0149] The PDCP entity of the UE 100 that joined the MBS session midway through cannot correctly perform a predetermined PDCP operation because it does not know the current PDCP variables (especially the HFN part). The predetermined PDCP operation is at least one of receive window control and packet reordering. The PDCP variable used for receive window control may be at least one of RX_NEXT and RX_DELIV. RX_NEXT includes the sequence number of the PDCP SDU expected to be received next. RX_DELIV includes the sequence number of the oldest PDCP SDU waiting to be received but not yet provided to the upper layer. Typically, the initial values ​​of RX_NEXT and RX_DELIV are "0." The PDCP variable used for packet reordering may be RX_REORD. RX_REORD is the sequence number of the PDCP SDU that started the timer indicating the maximum time to wait for packet reordering. For example, if the sequence number of a received packet is smaller than RX_REORD, the UE 100 discards the packet. The PDCP variable (COUNT value) is also used to encrypt PDCP packets for security purposes.

[0150] In particular, the initial value of RX_DELIV is 0, and in the case of unicast, both the gNB 200 and the UE 100 increment the HFN based on the initial value each time the PDCP SN wraps around, thereby synchronizing the HFNs of the gNB 200 and the UE 100. In the case of multicast, it is uncertain from which RX_DELIV the UE 100 will start receiving PDCP packets, so the valid HFN (i.e., the HFN managed by the gNB 200) cannot be determined by looking at the received PDCP packet alone. Note that the header of a PDCP PDU contains the PDCP SN but not the HFN. In the following, the PDCP variable is defined as at least one of the HFN and COUNT value.

[0151] In this modified example, the gNB 200, which transmits MBS data in an MBS session, transmits, by multicast or broadcast, PDCP variable initial values ​​to be used by a UE 100 that joins the MBS session midway to receive the MBS data. That is, the gNB 200 transmits the current PDCP variables during MBS data transmission (MBS traffic channel). The gNB 200 may periodically transmit, by multicast or broadcast, PDCP variable initial values ​​to be used by a UE 100 that joins the MBS session midway to receive the MBS data. In response to receiving the PDCP variable initial values ​​from the gNB 200, the UE 100 that joins the MBS session midway performs reception processing of the MBS data using the received PDCP variable initial values. This makes it possible for UE 100 that joins the MBS session midway to perform PDCP processing appropriately.

[0152] FIG. 14 is a diagram showing the operation according to this modified example.

[0153] As shown in Figure 14, the gNB 200 starts transmitting MBS data for a certain MBS session. The gNB 200 updates the PDCP variables while transmitting the MBS data.

[0154] In step S402, UE 100 joins the MBS session late (joins mid-session). However, because UE 100 does not know the current COUNT value (especially the HFN part), it cannot perform PDCP processing on the data packets (PDCP packets) that make up the MBS data. UE 100 may obtain the PDCP SN included in the header of the PDCP packet that it first receives from gNB 200, and use the obtained PDCP SN as part of the COUNT value that it manages itself.

[0155] In step S403, the gNB 200 periodically transmits, by multicast or broadcast, the COUNT value (or HFN) of the MBS data packet (PDCP packet) currently being transmitted or the COUNT value (or HFN) of the MBS data packet (PDCP packet) to be transmitted next. Specifically, the gNB 200 transmits the current COUNT value (or HFN) on the MBS traffic channel using the G-RNTI. For example, the gNB 200 transmits at least one of a MAC Control Element (CE), an RLC Control PDU, and a PDCP Control PDU, including a PDCP variable initial value. When using a MAC CE, the gNB 200 may transmit a set of a multicast session identifier (TMGI) and a COUNT value. When using a PDCP / RLC Control PDU, the UE 100 can identify the COUNT value as the COUNT value of the bearer / LCH to which the PDCP / RLC Control PDU belongs. Here, when a lower layer (for example, MAC) receives the COUNT value (or HFN), the lower layer notifies the upper layer (for example, PDCP) of the COUNT value (or HFN).

[0156] In step S404, UE100 (PDCP entity) sets the PDCP variables notified by gNB200 as the initial values ​​of the PDCP variables it manages.

[0157] In step S405, gNB200 transmits the MBS data packet (PDCP packet) by multicast or broadcast.

[0158] In step S406, UE100 performs PDCP processing on the MBS data packet (PDCP packet) received from gNB200 using the PDCP variables it manages, and updates the PDCP variables it manages.

[0159] Note that the operation according to this modified example may be applied to the operation of RLC, and "PDCP" may be read as "RLC." The PDCP variable initial value may be an RLC variable initial value. Furthermore, in this modified example, an example has been described in which UE100, which joins an MBS session midway, transmits PDCP variable initial values ​​to be used for receiving MBS data in the MBS session by multicast or broadcast, but gNB200 may also transmit the PDCP variable initial values ​​by broadcast using system information (SIB).

[0160] (Other embodiments) 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. Some steps of one operational flow may be replaced with some steps of another operational flow.

[0161] In the above embodiment, an example in which the base station is an NR base station (gNB) has been described, but the base station may also be an LTE base station (eNB). 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 (Distributed Unit) of the IAB node.

[0162] A program may be provided that causes a computer to execute each process performed by UE100 or gNB200. The program may be recorded on a computer-readable medium. The computer-readable medium can be used to install the program 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 UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a Chip).

[0163] As used in this disclosure, the terms "based on" and "depending on" 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 "based only on" and "at least in part on." Furthermore, "obtain" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may also mean including only the listed items or including additional items in addition to the listed items. Furthermore, as used in this disclosure, the term "or" 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, reference to first and second elements does not imply that only two elements may be employed therein or that the first element must precede the second element in some manner. 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.

[0164] 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.

[0165] This application claims priority to U.S. Provisional Application No. 63 / 186512 (filed May 10, 2021), the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0166] 10:NG-RAN (5G RAN) 20:5GC(5G CN) 100:UE 110: Receiving unit 120: Transmitter 130: Control unit 200 :gNB 210: Transmission unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. A communication control method executed by a user device in a mobile communication system that provides a broadcast / multicast service (MBS) from a network to the user device, comprising: monitoring, in an RRC (Radio Resource Control) idle state or an RRC inactive state, a group notification indicating an activation of an MBS multicast session in which the user device is participating, the group notification being sent from the network to a group to which the user device belongs; transitioning to an RRC connected state for receiving the MBS multicast session in response to receiving the group announcement; When the MBS multicast session is terminated, the group notification is not monitored. Communication control method.

2. 1. A user equipment supporting reception of broadcast / multicast services (MBS), comprising: monitoring, in an RRC (Radio Resource Control) idle state or an RRC inactive state, a group notification indicating the activation of an MBS multicast session in which the user device is participating, the group notification being transmitted from the network to a group to which the user device belongs; a control unit that transitions to an RRC connected state in response to receiving the group notification to receive the MBS multicast session; The control unit controls the group notification so as not to monitor the group notification when the MBS multicast session is terminated. User equipment.

3. 1. A processor for controlling a user equipment supporting reception of broadcast / multicast services (MBS), comprising: A process of monitoring a group notification, which indicates the activation of an MBS multicast session in which the user device is participating and is transmitted from the network to a group to which the user device belongs, in an RRC (Radio Resource Control) idle state or an RRC inactive state; In response to receiving the group notification, transitioning to an RRC connected state for receiving the MBS multicast session; When the MBS multicast session is terminated, the group notification is not monitored. Processor.

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