Communication control method, user equipment and processor

Abstract

A communication control method according to a first aspect of the present invention is a communication control method executed by a user equipment in a mobile communication system in which a multicast service is provided from a network to the user equipment. The communication control method includes: performing a monitoring process of a group notification in a radio resource control (RRC) idle state or an RRC inactive state, the group notification being a notification indicating an enabled multicast session in which the user equipment is participating and being transmitted from the network to a group to which the user equipment belongs; performing a transition process to an RRC connected state to receive the multicast session in response to receiving the group notification; and performing control so that the monitoring process or the transition process is not performed when the user equipment is no longer interested in the multicast session in the RRC idle state or the RRC inactive state. The monitoring process includes monitoring the group notification when the user equipment is interested in the multicast session. The transition process includes transitioning to the RRC connected state in response to receiving the group notification when the user equipment is interested in the multicast session.

Description

Technical Field

[0001] This disclosure relates to a communication control method used in a mobile communication system. Background Technology

[0002] In recent years, fifth-generation (5G) mobile communication systems have attracted much attention. As the radio access technology (RAT) for 5G systems, New Radio (NR) features high speed, large capacity, high reliability, and low latency compared to Long Term Evolution (LTE), the fourth-generation radio access technology.

[0003] Reference List

[0004] Non-patent literature

[0005] Non-patent document 1: 3GPP technical specification "3GPP TS 38.300 V16.3.0 (2020-09)" Summary of the Invention

[0006] In a first aspect, a communication control method is a communication control method performed by a user equipment in a mobile communication system that provides multicast services from a network to a user equipment, and includes: performing a process of monitoring a group notification in an RRC idle state or an RRC inactive state, the group notification being a notification indicating the enabled state of a multicast session in which the user equipment is participating, the group notification being sent from the network to the group to which the user equipment belongs; performing a process of transitioning to an RRC connected state to receive the multicast session in response to receiving the group notification; and performing control to prevent the monitoring process or the transition process from being performed when the user equipment loses interest in the multicast session in the RRC idle state or the RRC inactive state. The monitoring process includes monitoring the group notification when the user equipment is interested in the multicast session. The transition process includes transitioning to an RRC connected state in response to receiving the group notification when the user equipment is interested in the multicast session.

[0007] In a second aspect, a communication control method is a communication control method performed in a mobile communication system that provides multicast services from a network to a user equipment, and includes: the user equipment managing a COUNT value as a Packet Data Convergence Protocol (PDCP) variable. Management includes: acquiring a PDCP sequence number (SN) included in the header of a PDCP packet initially received from the network via multicast; and using the acquired PDCP SN as part of the COUNT value.

[0008] In a third aspect, a communication control method is a communication control method performed in a mobile communication system that provides multicast services from a network to a user equipment, and includes: receiving a paging message by a user equipment that is in an RRC inactive state after participating in a multicast session, the paging message including the TMGI (Temporary Mobile Group Identifier) ​​of the multicast session in which the user equipment is participating; and switching to an RRC connected state in response to receiving the paging message including the TMGI.

[0009] In a fourth aspect, a communication control method is a communication control method performed in a mobile communication system that provides multicast services from a network to a user equipment, and includes: a base station sending a paging message including a TMGI as a group notification; and a user equipment monitoring the paging message at the time of paging by the user equipment. The sending includes: sending the paging message including the TMGI at a timed interval based on a paging request from the Access and Mobility Management Function (AMF).

[0010] In a fifth aspect, a communication control method is a communication control method performed in a mobile communication system that provides multicast broadcast service (MBS) from a base station to a user equipment, and includes: sending initial values ​​of PDCP variables and / or RLC variables to be used by the user equipment to receive MBS data by the base station transmitting MBS data in the MBS session.

[0011] In a sixth aspect, a communication control method is a communication control method performed by a user equipment in a mobile communication system that provides multicast services from a network to a user equipment, and includes: performing a session participation process for a multicast session on the network; obtaining time period information from the network, the time period information indicating a time period in which the user equipment remains in a state of participating in the multicast session; performing a session participation process or a session continuation process on the network before or when the time period indicated in the time period information expires, when there is interest in the multicast session; and performing control to prevent the session participation process or session continuation process from being performed on the network before or when the time period indicated in the time period information expires, when there is no interest in the multicast session.

[0012] In a seventh aspect, a communication control method is a communication control method performed in a mobile communication system that provides multicast services from a network to a user equipment, and includes: a user equipment in an RRC idle state or an RRC inactive state performing a random access procedure to a base station included in the network; during the random access procedure, the user equipment sending a notification to the base station indicating withdrawal from a session in a multicast session in which the user equipment is participating; and the user equipment terminating the random access procedure without transitioning to an RRC connected state. Attached Figure Description

[0013] Figure 1 This is a diagram illustrating the configuration of a mobile communication system according to an embodiment.

[0014] Figure 2 This is a diagram illustrating the configuration of a user equipment (UE) according to an embodiment.

[0015] Figure 3 This is a diagram illustrating the configuration of a base station (gNB) according to an embodiment.

[0016] Figure 4 This is a diagram illustrating the configuration of the protocol stack for the user plane radio interface that processes data.

[0017] Figure 5 This is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0018] Figure 6 This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0019] Figure 7 This is a diagram illustrating a method for delivering MBS data according to an embodiment.

[0020] Figure 8 This is a diagram illustrating the split MBS bearer according to an embodiment.

[0021] Figure 9 This is a diagram illustrating the basic operations in a first operating mode of a mobile communication system according to an embodiment.

[0022] Figure 10 This is a diagram illustrating an example of a first operating mode of a mobile communication system according to an embodiment.

[0023] Figure 11 This is a diagram illustrating another example of a first operating mode of a mobile communication system according to an embodiment.

[0024] Figure 12 This is a diagram illustrating an example of a second operating mode of a mobile communication system according to an embodiment.

[0025] Figure 13 This is a diagram illustrating an example of a third operating mode of a mobile communication system according to an embodiment.

[0026] Figure 14 This is a diagram showing the operations based on the variant. Detailed Implementation

[0027] Research is underway on introducing multicast broadcast services to 5G systems (NR). Compared to LTE multicast broadcast services, NR multicast broadcast services are expected to provide enhanced services.

[0028] In view of this, this disclosure provides a communication control method for implementing enhanced multicast and broadcast services.

[0029] A mobile communication system according to an embodiment is described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are indicated by the same or similar reference numerals.

[0030] Configuration of mobile communication system

[0031] First, the configuration of the mobile communication system according to an embodiment is described. Figure 1 This diagram illustrates the configuration of a mobile communication system according to an embodiment. The mobile communication system conforms to the 3GPP standard for a fifth-generation (5GS) system. The following description uses 5GS as an example; however, a Long Term Evolution (LTE) system can be applied at least partially to this mobile communication system. A sixth-generation (6G) system can also be applied at least partially to this mobile communication system.

[0032] like Figure 1 As shown, the mobile communication system includes user equipment (UE) 100, 5G radio access network (next-generation radio access network (NG-RAN)) 10 and 5G core network (5GC) 20.

[0033] UE 100 is a mobile wireless communication device. UE 100 can be any device, as long as it is used by a user. Examples of UE 100 include mobile phone terminals (including smartphones), and / or tablet terminals, laptop PCs, communication modules (including communication cards or chipsets), sensors or devices mounted on sensors, vehicles or devices mounted on vehicles (vehicle UE), or flying objects or devices mounted on flying objects (airborne UE).

[0034] NG-RAN 10 includes base stations (referred to as "gNBs" in 5G systems) 200. gNBs 200 are interconnected via an Xn interface, which is an inter-base station interface. Each gNB 200 manages one or more cells. gNBs 200 perform wireless communication with UEs 100 that have established connections to cells connected to them. gNBs 200 have Radio Resource Management (RRM) functions, user data routing functions (hereinafter referred to as "data"), measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to represent the smallest unit of a wireless communication area. "Cell" is also used as a term to represent the functions or resources used to perform wireless communication with UEs 100. A cell belongs to one carrier frequency.

[0035] Note that a gNB can connect to the Evolved Packet Core (EPC) corresponding to the LTE core network. LTE base stations can also connect to the 5GC. LTE base stations and gNBs can connect via an inter-base station interface.

[0036] The 5GC 20 includes Access and Mobility Management Functions (AMF) and User Plane Functions (UPF) 300. The AMF performs various types of mobility control for the UE 100. The AMF manages the mobility of the UE 100 by communicating with it using Non-Access Stratum (NAS) signaling. The UPF controls data transmission. The AMF and UPF are connected to the gNB 200 via the NG interface, which is the interface between the base station and the core network.

[0037] Figure 2 This is a diagram illustrating the configuration of a user equipment (UE) 100 according to an embodiment.

[0038] like Figure 2 As shown, UE 100 includes receiver 110, transmitter 120 and controller 130.

[0039] Receiver 110 performs various types of reception under the control of controller 130. Receiver 110 includes an antenna and a receiving device. The receiving device converts the radio signals received through the antenna into baseband signals (received signals) and outputs the resulting signals to controller 130.

[0040] Transmitter 120 performs various types of transmissions under the control of controller 130. Transmitter 120 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 130 into a radio signal and transmits the obtained signal through the antenna.

[0041] Controller 130 performs various types of control within UE 100. Controller 130 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be processed by the processor. The processor may include a baseband processor and a central processing unit (CPU). The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0042] Figure 3 This is a diagram illustrating the configuration of a base station (gNB) 200 according to an embodiment.

[0043] like Figure 3 As shown, gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communicator 240.

[0044] Transmitter 210 performs various types of transmissions under the control of controller 230. Transmitter 210 includes an antenna and a transmitting device. The transmitting device converts the baseband signal (transmit signal) output by controller 230 into a radio signal and transmits the obtained signal through the antenna.

[0045] Receiver 220 performs various types of reception under the control of controller 230. Receiver 220 includes an antenna and a receiving device. The receiving device converts the radio signals received through the antenna into baseband signals (received signals) and outputs the resulting signals to controller 230.

[0046] The controller 230 performs various types of control over the gNB 200. The controller 230 includes at least one processor and at least one memory. The memory stores programs to be executed by the processor and information to be processed by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, encoding and decoding of baseband signals, etc. The CPU executes programs stored in the memory, thereby performing various types of processing.

[0047] The backhaul communicator 240 is connected to the adjacent base station via the inter-base station interface. The backhaul communicator 240 is also connected to the AMF / UPF 300 via the interface between the base station and the core network. Note that the gNB may include a central unit (CU) and a distributed unit (DU) (i.e., functions are divided), and these two units may be connected via the F1 interface.

[0048] Figure 4 This is a diagram illustrating the configuration of the protocol stack for the user plane radio interface that processes data.

[0049] like Figure 4 As shown, the user plane radio interface protocol includes the physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, and service data adaptation protocol (SDAP) layer.

[0050] The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Data and control information are transmitted between the PHY layer of UE 100 and the PHY layer of gNB 200 via physical channels.

[0051] The MAC layer performs data priority control, retransmission processing via Hybrid ARQ (HARQ: Hybrid Automatic Repeat Request), and random access procedures. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of gNB 200 via the transport channel. The MAC layer of gNB 200 includes a scheduler. The scheduler determines the transmission format (transmission block size, modulation and coding scheme (MCS)) in the uplink and downlink and the resource blocks to be allocated to UE 100.

[0052] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC and PHY layers. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of gNB 200 via logical channels.

[0053] The PDCP layer performs header compression and decompression, as well as encryption and decryption.

[0054] The SDAP layer performs the mapping between IP flows, which are the unit of Quality of Service (QoS) control in the core network, and radio bearers, which are the unit of QoS control in the access layer (AS). Note that SDAP is not required when the RAN is connected to the EPC.

[0055] Figure 5 This is a diagram showing the configuration of the protocol stack of the radio interface of the control plane that processes signaling (control signals).

[0056] like Figure 5 As shown, the protocol stack of the control plane's radio interface includes a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer, replacing... Figure 4 The SDAP layer is shown.

[0057] RRC signaling for various configurations is transmitted between the RRC layer of UE 100 and the RRC layer of gNB 200. The RRC layer controls logical channels, transport channels, and physical channels based on the establishment, reconstruction, and release of radio bearers. When a connection exists between the RRC of UE 100 and the RRC of gNB 200 (RRC connection), UE 100 is in an RRC connected state. When a connection does not exist between the RRC of UE 100 and the RRC of gNB 200 (RRC connection), UE 100 is in an RRC idle state. When the connection between the RRC of UE 100 and the RRC of gNB 200 is suspended, UE 100 is in an RRC inactive state.

[0058] The NAS layer, which is above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE 100 and the NAS layer of AMF300.

[0059] Note that UE 100 includes the application layer in addition to the radio interface protocol.

[0060] MBS

[0061] This describes the MBS according to an embodiment. MBS is a service that NG-RAN 10 can provide to UE 100 via broadcast or multicast (i.e., point-to-multipoint (PTM) data transmission). MBS may be referred to as Multimedia Broadcast and Multicast Service (MBMS). Note that use cases (service types) for MBS include public safety communications, mission-critical communications, vehicle-to-everything (V2X) communications, IPv4 or IPv6 multicast delivery, Internet Protocol Television (IPTV), group communications, and software delivery.

[0062] MBS transmission in LTE includes two schemes: Multicast Broadcast Single Frequency Network (MBSFN) transmission and Single Cell Point-to-Multipoint (SC-PTM) transmission. Figure 6 This is a diagram illustrating the correspondence between downlink logical channels and downlink transport channels according to an embodiment.

[0063] like Figure 6 As shown, the logical channels used for MBSFN transmission are the Multicast Service Channel (MTCH) and the Multicast Control Channel (MCCH). The transport channel used for MBSFN transmission is the Multicast Channel (MCH). MBSFN transmission is primarily designed for multi-cell transmission, and in an MBSFN area comprising multiple cells, each cell synchronously transmits the same signal (the same data) in the same MBSFN subframe.

[0064] The logical channels used for SC-PTM transmission are the Single Cell Multicast Service Channel (SC-MTCH) and the Single Cell Multicast Control Channel (SC-MCCH). The transport channel used for SC-PTM transmission is the Downlink Shared Channel (DL-SCH). SC-PTM transmission is primarily designed for single-cell transmission and corresponds to broadcast or multicast data transmission on a cell-by-cell basis. The physical channels used for SC-PTM transmission are the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Shared Channel (PDSCH), and dynamic resource allocation is implemented.

[0065] Although the following descriptions will primarily focus on examples of providing MBS using schemes that are the same as and / or similar to the SC-PTM transport scheme, MBS can also be provided using the MBSFN transport scheme. The examples of providing MBS using multicast will be described primarily. Therefore, MBS can be interpreted as multicast. Note that broadcast can also be used to provide MBS.

[0066] MBS data refers to data provided by MBS. The MBS control channel refers to MCCH or SC-MCCH. The MBS traffic channel refers to MTCH or SC-MTCH. Note that MBS data can be sent via unicast. MBS data can be referred to as MBS packets or MBS traffic.

[0067] The network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a Temporary Mobile Group Identifier (TMGI) or a session identifier, and at least one of these identifiers is called an MBS session identifier. This MBS session identifier can be referred to as an MBS service identifier or a multicast group identifier.

[0068] Figure 7 This is a diagram illustrating a method for delivering MBS data according to an embodiment.

[0069] like Figure 7 As shown, MBS data (MBS service) is delivered from a single data source (application service provider) to multiple UEs. The 5G CN (5GC) 20, which serves as the 5G core network, receives MBS data from the application service provider and performs replication of the MBS data to deliver the results.

[0070] From the perspective of 5GC 20, two delivery methods are possible: shared MBS data delivery (shared MBS service delivery) and separate MBS data delivery (separate MBS service delivery).

[0071] In shared MBS data delivery, a connection is established between NG-RAN 10 and 5GC 20, which serve as the 5G radio access network (5G RAN), to deliver MBS data from 5GC 20 to NG-RAN 10. This connection (tunnel) is referred to below as the "MBS connection".

[0072] MBS connections can be referred to as shared MBS service delivery connections or shared transport. MBS connections terminate at NG-RAN 10 (i.e., gNB 200). MBS connections can correspond to MBS sessions on a one-to-one basis.

[0073] Based on its own judgment, gNB 200 selects either point-to-point (PTP: unicast) or point-to-multipoint (PTM: multicast or broadcast) transmission scheme and sends MBS data to UE 100 through the selected transmission scheme.

[0074] On the other hand, in separate MBS data delivery, a unicast session is established between NG-RAN 10 and UE 100 to deliver MBS data separately from 5GC 20 to UE 100. This unicast can be referred to as a Protocol Data Unit (PDU) session (PDU session). The unicast (PDU session) terminates at UE 100.

[0075] Split MBS bearer

[0076] The split MBS bearer according to an embodiment is described.

[0077] The gNB 200 can be configured for UE 100 to split the MBS bearer into a PTP communication path and a PTM communication path (hereinafter referred to as "split MBS bearer" where appropriate). This allows the gNB 200 to dynamically switch the transmission of MBS data to UE 100 between the PTP (PTP communication path) and PTM (PTM communication path). The gNB 200 can perform duplicate transmission of the same MBS data using both the PTP (PTP communication path) and PTM (PTM communication path) to improve reliability.

[0078] The predetermined layer for terminating a split is the MAC layer (HARQ), RLC layer, PDCP layer, or SDAP layer. Although the following description primarily uses the PDCP layer as the predetermined layer for terminating a split, the predetermined layer can be the MAC layer (HARQ), RLC layer, or SDAP layer.

[0079] Figure 8 This diagram illustrates the split MBS bearer according to an embodiment. In the following text, the PTP communication path is referred to as a PTP branch, and the PTM communication path is referred to as a PTM branch. The functional unit corresponding to each layer is referred to as an entity.

[0080] like Figure 8 As shown, each of the PDCP entities in gNB 200 and UE 100 splits the MBS bearer (which is the bearer used for MBS (data radio bearer)) into PTP tributaries and PTM tributaries. Note that the PDCP entity is set up for each bearer.

[0081] Each of the gNB 200 and UE 100 includes two RLC entities, one MAC entity, and one PHY entity configured for each tributary. The PHY entity may be configured per tributary. Note that in dual connectivity where UE 100 communicates with two gNB 200s, UE 100 may include two MAC entities.

[0082] The PHY entity uses the cell RNTI (Cell Radio Network Temporary Identifier (C-RNTI)) assigned to UE 100 on a one-to-one basis to transmit and receive data in the PTP tributary. The PHY entity uses the group RNTI (Group Radio Network Temporary Identifier (G-RNTI)) assigned to the MBS session on a one-to-one basis to transmit and receive data in the PTM tributary. The C-RNTI is different for each UE 100, but the G-RNTI is a common RNTI for multiple UE 100s receiving data in one MBS session.

[0083] To perform PTM transmission (multicast or broadcast) of MBS data from gNB 200 to UE 100 using the PTM tributary, it is necessary to configure the split MBS bearer for UE 100 from gNB 200 and to activate the PTM tributary. In other words, even if the split MBS bearer is configured for UE 100, gNB 200 cannot use the PTM tributary to perform PTM transmission of MBS data if the PTM tributary is in an inactive state.

[0084] In order for gNB 200 and UE 100 to perform PTP (unicast) transmission of MBS data using the PTP tributary, it is necessary to configure the MBS bearer to be split for UE 100 from gNB 200 and to activate the PTP tributary. In other words, even if the MBS bearer is configured to be split for UE 100, gNB 200 cannot use the PTP tributary to perform PTP transmission of MBS data when the PTP tributary is in an inactive state.

[0085] When the PTM tributary is active, UE 100 monitors the Physical Downlink Control Channel (PDCCH) to which the G-RNTI associated with the MBS session is applied (i.e., performs blind decoding of the PDCCH using G-RNTI). UE 100 can monitor the PDCCH only during the scheduling of the MBS session.

[0086] When the PTM tributary is in a deactivated state, the UE 100 does not monitor the PDCCH to which the G-RNTI associated with the MBS session is applied (i.e., it does not perform blind decoding of the PDCCH using G-RNTI).

[0087] When the PTP tributary is active, UE 100 monitors the PDCCH to which C-RNTI applies. When Discontinuous Receiver Optimization (DRX) is configured in the PTP tributary, UE 100 monitors the PDCCH for the configured OnDuration period. When a cell (frequency) associated with an MBS session is specified, UE 100 can still monitor the PDCCH for that cell even if the cell is deactivated.

[0088] When the PTP tributary is in an inactive state, the UE 100 can monitor the PDCCH to which the C-RNTI is applied in order to prepare for normal unicast downlink transmission of data other than MBS data. Note that when a cell (frequency) associated with an MBS session is specified, the UE 100 does not need to monitor the PDCCH for the MBS session.

[0089] Note that it is assumed that the above-mentioned split MBS bearer is configured via an RRC message (e.g., an RRC reconfiguration message) sent by the RRC entity of gNB 200 to the RRC entity of UE 100.

[0090] Operation of mobile communication systems

[0091] The operation of the mobile communication system 1 according to an embodiment will be described.

[0092] In the following description, it is primarily assumed that UE 100, in an RRC connected state, receives MBS data (i.e., multicast data) transmitted from gNB 200 via multicast. Therefore, it is assumed that the MBS session is a multicast session. It is 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 tributary or PTM bearer (multicast bearer). The MBS traffic channel (MTCH) is used to transmit multicast data from gNB 200 to UE 100.

[0093] In the following description, it is assumed that after participating in a multicast session, UE 100 transitions to an RRC idle state or an RRC inactive state and waits for the multicast session to begin. While in the RRC idle or RRC inactive state, UE 100 receives a group notification indicating the enabled status of the multicast session in which UE 100 is participating, and this notification is sent 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 from gNB 200 in the multicast session.

[0094] Figure 9 This diagram illustrates the basic operations in the first operating mode of the mobile communication system 1. In the following text, gNB200 and AMF 300 are collectively referred to as the "network" where appropriate. AMF 300 is an example of a core network (CN) device. AMF 300 works in conjunction with a session management device to manage MBS sessions (multicast sessions). The session management device is another example of a CN device.

[0095] like Figure 9 As shown, in step S101, UE 100 is in an RRC connection state. Assume UE 100 is interested in a certain multicast session (hereinafter referred to as the "target multicast session"). "Interested in a multicast session" means that UE 100's upper layer requests or expects to receive that multicast session. The upper layer includes the NAS layer. The upper layer may also include applications.

[0096] In step S102, UE 100 (NAS entity) performs a multicast session participation procedure on the network to participate in a target multicast session. For example, UE 100 sends a first NAS message requesting participation in the target multicast session to AMF 300 and receives a second NAS message approving participation from AMF 300, thereby participating in the target multicast session. "Participating in the target multicast session" means registering UE 100 as a member of the UE group (multicast group) receiving the multicast session in the CN device. Note that participation in a multicast session can be performed when the multicast session is enabled (during transmission). Participation in a multicast session can also be performed when the session is disabled (during waiting for transmission to start or during transmission interruption).

[0097] In step S103, UE 100 transitions to an RRC idle state or an RRC inactive state. Specifically, UE 100 transitions to an RRC idle state or an RRC inactive state in response to receiving an RRC release message from gNB 200. Prior to step S103, UE 100 may send an RRC message (e.g., a UE assistance information message) to gNB 200, which includes information elements prompting UE 100 to transition to an RRC idle state or an RRC inactive state. gNB 200 may determine to transition UE 100 to an RRC idle state or an RRC inactive state in response to the disabled state of a multicast session of interest to UE 100.

[0098] In step S104, UE 100 begins monitoring for group notifications from gNB 200. The group notification can be a paging message sent from gNB 200. The group notification can also be a message sent from gNB 200 on the multicast control channel (MCCH). The group notification can be sent in response to a multicast session being enabled from a disabled state. The group notification can also notify of the start of a multicast session. In the following text, it is primarily assumed that the group notification is a paging message. UE 100 monitors for group notifications at paging opportunities (PO) in periodically configured paging frames (PF).

[0099] In step S105, gNB 200 sends a group notification addressing a group that includes UE 100 or a group that UE 100 is interested in. gNB 200 may send a group notification (paging message) to UE 100 in response to a paging request from AMF 300. The group notification may include at least one selected from a group consisting of: a multicast session identifier indicating the group, an identifier for each UE belonging to the group, and a multicast session identifier associated with that identifier. Upon receiving a group notification including the identifier of UE 100, UE 100 may recognize that a target multicast session in which UE 100 has participated has been enabled. “Target multicast session enabled” may mean that multicast data transmission has begun in the target multicast session.

[0100] In step S106, UE 100 performs a random access procedure on gNB 200 to receive data in the target multicast session.

[0101] In step S107, UE 100 is switched to RRC connection state due to the random access procedure.

[0102] In step S108, UE 100 receives multicast data from the target multicast session from gNB 200 while in RRC connection state. Before receiving the data, gNB 200 may perform configuration on UE 100 to enable target multicast session reception. For example, such configuration may be an RRC reconfiguration message including multicast radio bearer (MRB) configuration.

[0103] In this basic operation, after UE 100 transitions to the RRC idle state or RRC inactive state in step S103, it may lose interest in the target multicast session. "Loss of interest in the target multicast session" means that the upper layer of UE 100 no longer requests or expects to receive in the target multicast session. For example, this corresponds to the case where a user closes an IPTV application. In this case, UE 100 can transition to the RRC connected state and then perform a multicast session exit procedure to exit the target multicast session. "Exiting the target multicast session" means that UE 100 is deregistered from the CN device as a member of the UE group (multicast group) receiving the multicast session. For example, UE 100 can exit the target multicast session by sending a third NAS message requesting to exit the target multicast session to AMF 300 and receiving a fourth NAS message approving the exit from AMF 300.

[0104] Here, when UE 100 performs monitoring group notification processing or transitions to RRC connected state after losing interest in the target multicast session, UE 100's power consumption may increase and radio resource utilization efficiency may decrease. For example, transitioning to RRC connected state solely for the purpose of performing a multicast session exit procedure is inefficient. A more efficient approach, for instance, is to transition to RRC connected state when unicast data communication is required later and then perform the multicast session exit procedure at that time.

[0105] (1) First operating mode

[0106] A first operating mode of the mobile communication system 1 according to an embodiment will be described.

[0107] In the first operating mode, UE 100 performs the monitoring of group notifications while in RRC idle or RRC inactive state. These group notifications are notifications indicating the enabled status of the multicast session (target multicast session) in which UE 100 is participating, and are sent from the network to the group to which UE 100 belongs or to a group of interest to UE 100. Upon receiving a group notification, UE 100 performs the process of transitioning to RRC connected state to receive data in the multicast session. Note that in RRC idle or RRC inactive state, when interest in the multicast session is lost, UE 100 performs control measures that prevent the monitoring of group notifications or the transition to RRC connected state from being performed. This suppresses inefficient operation of UE 100.

[0108] Figure 10 This is a diagram illustrating an example of a first operating mode of the mobile communication system 1. Here, the differences from the basic operation described above will be primarily described.

[0109] like Figure 10 As shown, in step S111, it is assumed that UE 100, which is in RRC connection state, is interested in a certain multicast session (hereinafter referred to as "target multicast session").

[0110] In step S112, UE 100 (NAS entity) performs a multicast session participation procedure on the network (AMF 300) to participate in the target multicast session.

[0111] In step S113, UE 100 transitions to RRC idle state or RRC inactive state.

[0112] In step S114, UE 100 (AS entity) begins monitoring group notifications from gNB 200. The AS entity can be an RRC entity. The group notification can be a paging message sent from gNB 200. The group notification can also be a message sent from gNB 200 on the multicast control channel (MCCH). In the following text, it is primarily assumed that the group notification is a paging message. UE 100 monitors group notifications at the paging timing (PO) of periodically configured paging frames (PF). That is, UE 100 periodically monitors group notifications.

[0113] In step S115, it is assumed that UE 100 has lost interest in the target multicast session. In UE 100, the NAS entity can notify the AS entity (e.g., the RRC entity) of the loss of interest in the target multicast session.

[0114] In step S116, UE 100 (AS entity) stops periodic monitoring of group notifications. For example, in UE 100, controller 130 controls receiver 110 not to monitor group notifications. This reduces the processing load and power consumption of UE 100. Note that when paging is used as a group notification and the group notification is the same as normal paging (paging for unicast communication) in terms of reception (transmission) timing, the control of not monitoring group notifications corresponds to UE 100 omitting the reception processing associated with the group notification reception timing. For example, the omission of reception processing includes at least one of the following: not monitoring the RNTI dedicated to group notifications, not demodulating the message portion dedicated to group notifications, and not checking information elements related to group notifications in the paging message (e.g., multicast session identifiers or multicast session identifier lists). Furthermore, when group notifications differ from normal paging in terms of reception (transmission) timing, the omission of reception processing means that UE 100 does not perform a reception operation (do not wake up) at the reception timing of the group notification. Note that even when monitoring of group notifications is stopped, monitoring of normal paging continues.

[0115] For example, when paging (group paging) is used as group notification, the following two configurations are possible for the PF / PO used to monitor group paging: 1) a PF / PO dedicated to group paging (different from unicast paging) and 2) the same PF / PO as the normal paging PF / PO. In case 1), UE 100 can stop monitoring the PF / PO for group paging. In case 2), since the PF / PO is the same as the normal paging PF / PO, UE 100 only omits monitoring of the group paging-related parts. For example, UE 100 can do the following: not monitor an RNTI (e.g., GP-RNTI) that is defined specifically for group paging, not check the group identifier (list) in the paging message, etc.

[0116] Subsequently, in step S117, for example, due to the generation of uplink data to be sent or the generation of downlink data to be received (i.e., normal paging / reception intended for unicast paging), UE 100 performs a random access procedure on gNB 200 for purposes other than reception in a multicast session.

[0117] In step S118, UE 100 switches to RRC connection state.

[0118] In step S119, UE 100 (NAS entity) performs a session exit procedure for the target multicast session on the network (AMF 300). This allows for efficient execution of the session exit procedure.

[0119] Figure 11 This is a diagram illustrating another example of the first operating mode of the mobile communication system 1. Here, the differences from the basic operation described above will be mainly described.

[0120] like Figure 11 As shown, in step S121, it is assumed that UE 100, which is in RRC connection state, is interested in a certain multicast session (hereinafter referred to as "target multicast session").

[0121] In step S122, UE 100 (NAS entity) performs a multicast session participation procedure on the network (AMF 300) to participate in the target multicast session.

[0122] In step S123, UE 100 transitions to RRC idle state or RRC inactive state.

[0123] In step S124, UE 100 begins monitoring group notifications from gNB 200.

[0124] In step S125, it is assumed that UE 100 has lost interest in the target multicast session. In UE 100, the NAS entity can notify the AS entity (e.g., the RRC entity) of the loss of interest in the target multicast session.

[0125] In step S126, gNB 200 sends a group notification addressing to a group including UE 100. gNB 200 may send a group notification (paging message) to UE 100 in response to a paging request from AMF 300. The group notification may include an identifier for each UE belonging to the group and a multicast session identifier associated with that identifier. Upon receiving the group notification including the identifier of UE 100, UE 100 can recognize that the target multicast session in which UE 100 has participated has been enabled.

[0126] In step S127, even when a group notification addressed to UE 100 is received, the access stratum entity (AS entity) of UE 100 can still perform control without transitioning to the RRC connection state. The AS entity can be an RRC entity. In UE 100, the AS entity can notify the NAS entity of the multicast session identifier included in the group notification addressed to UE 100 (specifically, the multicast session identifier associated with the identifier of UE 100). When the NAS entity determines that it is not interested in the multicast session indicated by the notified multicast session identifier, the NAS entity does not request the AS entity to perform the process of transitioning to the RRC connection state. On the other hand, when it determines that it is interested in the multicast session indicated by the notified multicast session identifier, the NAS entity can request the AS entity to perform the process of transitioning to the RRC connection state.

[0127] Subsequently, in step S128, for example, due to the generation of uplink data to be sent or the generation of downlink data to be received (i.e., normal paging / reception intended for unicast paging), UE 100 performs a random access procedure on gNB 200 for purposes other than reception in a multicast session.

[0128] In step S129, UE 100 switches to RRC connection state.

[0129] In step S130, UE 100 (NAS entity) performs a session exit procedure for the target multicast session on the network (AMF 300). This allows for efficient execution of the session exit procedure.

[0130] (2) Second operating mode

[0131] A second operating mode of the mobile communication system 1 according to an embodiment will be described.

[0132] As described above, even when the CN device identifies that UE 100 is participating in the target multicast session, it can still be assumed that UE 100 has lost interest in the target multicast session. In other words, a mismatch can occur between UE 100's interest state and UE 100's participation state. However, NAS message transmission is required to explicitly perform session exit, leading to the aforementioned inefficient operation. Therefore, in the second operating mode, an operation that enables UE 100 to implicitly (automatically) perform session exit will be described. Through this operation, the aforementioned mismatch problem can be resolved even when UE 100 moves out of the service area or is powered off.

[0133] In the second operating mode, UE 100 performs a session participation procedure for the target multicast session with the network. UE 100 obtains time period information from the network (AMF 300), which indicates the time period during which UE 100 remains in the state of participating in the target multicast session. Such a valid time period may also be referred to as a valid time period or participation duration (continuation) time, but will be referred to as a valid time period hereinafter.

[0134] When interested in the target multicast session, UE 100 performs a session participation or re-participation procedure with AMF 300 before or when the valid period indicated in the valid period information expires. Conversely, when not interested in the target multicast session, UE 100 performs control without performing a session participation or re-participation procedure with AMF 300 before or when the valid period indicated in the valid period information expires. Therefore, UE 100, having lost interest in the target multicast session, can implicitly (automatically) exit the target multicast session by not performing a session participation or re-participation procedure.

[0135] Figure 12 This is a diagram illustrating an example of a second operating mode of the mobile communication system 1. Here, the differences from the basic operation described above will be primarily described.

[0136] like Figure 12 As shown, in step S201, it is assumed that UE 100, which is in RRC connection state, is interested in a certain multicast session (target multicast session).

[0137] In steps S202 and S203, UE 100 (NAS entity) performs a multicast session participation procedure on the network (AMF 300) to participate in the target multicast session.

[0138] More specifically, in step S202, UE 100 (NAS entity) sends a NAS message (first NAS message) to AMF 300 requesting participation in the target multicast session. The first NAS message may include the identifier of UE 100 and the multicast session identifier of the target multicast session. UE 100 may send information in the first NAS message indicating the effective time period expected by UE 100.

[0139] In step S203, in response to receiving the first NAS message, the AMF 300 sends a second NAS message to the UE 100 (NAS entity) approving participation in the target multicast session. The AMF 300 may send valid time period information in the second NAS message. When the first NAS message includes information indicating the valid time period desired by the UE 100, the AMF 300 may determine the valid time period based on that information and send valid time period information indicating the determined valid time period in the second NAS message.

[0140] The valid time period information can be a timer value indicating the valid time period. The valid time period information can also be information indicating the end of the valid time period in absolute time. In the following text, we assume the valid time period information is a timer value.

[0141] In step S204, when obtaining valid time period information (timer value) from the network, for example, when obtaining valid time period information (timer value) from the second NAS message, UE 100 (NAS entity) starts the timer configured with that timer value. Note that the timer can only be started or run when UE 100 is in the CM_IDLE state. The CM_IDLE state refers to the state where UE 100 has no NAS signaling connection. The timer can be started or restarted (reset and started) in response to UE 100 transitioning to CM_IDLE after receiving the second NAS message. The timer can be stopped in response to transitioning to CM_CONNECTED.

[0142] In step S205, the timer expires. The processes described below from steps S206 to S209 can be performed before step S205.

[0143] In step S206, UE 100 (NAS entity) determines whether it is interested in the target multicast session.

[0144] When it is determined that there is interest in the target multicast session (step S206: Yes), in steps S207 and S208, UE 100 (NAS entity) performs a multicast session participation / continuation procedure with the network (AMF 300) to participate in (or continue participating in) the target multicast session.

[0145] More specifically, in step S207, UE 100 (NAS entity) sends a NAS message (first NAS message) to AMF 300 requesting to participate in (or continue participating in) the target multicast session. The first NAS message may include the identifier of UE 100 and the multicast session identifier of the target multicast session. UE 100 may send information in the first NAS message indicating the effective time period expected by UE 100.

[0146] In step S208, in response to receiving the first NAS message, the AMF 300 sends a second NAS message to the UE 100 (NAS entity) approving participation (or continued participation) in the target multicast session. The AMF 300 may send valid time period information in the second NAS message. When the first NAS message includes information indicating the valid time period desired by the UE 100, the AMF 300 may determine the valid time period based on that information and send valid time period information indicating the determined valid time period in the second NAS message.

[0147] The valid time period information can be a timer value indicating the valid time period. The valid time period information can also be information indicating the end of the valid time period in absolute time.

[0148] In step S209, when obtaining valid time period information (timer value) from the network, for example, when obtaining valid time period information (timer value) from the second NAS message, UE 100 (NAS entity) starts a timer configured with that timer value. Note that, as mentioned above, the timer can only be started or run when UE 100 is in the CM_IDLE state. When the second NAS message approving continuation in step S208 does not include valid time period information (timer value), the value already obtained through the second NAS message used for the first approval in step S203 can be used.

[0149] As described above, when UE 100 is still interested in the target multicast session, the valid time period is updated, and the state of UE 100 participating in the target multicast session continues.

[0150] On the other hand, when it is determined that the UE 100 is not interested in the target multicast session (step S206: No), the UE 100 does not perform the multicast session participation / continuation procedure. When the UE 100 does not provide a multicast session participation / continuation request within the valid time period or within a predetermined time after the valid time period has passed, the AMF 300 considers that the UE 100 is not interested in the target multicast session (or the UE 100 has moved out of the service area or the power has been turned off), and manages the UE 100 as being in a state of having exited the target multicast session.

[0151] (3) Third operating mode

[0152] A third operating mode of the mobile communication system 1 according to an embodiment will be described.

[0153] As mentioned above, UE 100 is inefficient in transitioning to the RRC connected state merely to notify of session exit. In the third operating mode, UE 100 notifies of session exit during the random access procedure and terminates the random access procedure without transitioning to the RRC connected state, thereby achieving efficient session exit notification.

[0154] In the third operating mode, UE 100 performs a random access procedure to gNB 200 while in RRC idle or RRC inactive state. During the random access procedure, UE 100 sends a notification to gNB 200 indicating that it is leaving the multicast session (target multicast session) in which UE 100 is participating. Then, UE 100 terminates the random access procedure without transitioning to RRC connected state.

[0155] The random access procedure includes sending a random access preamble to gNB 200 using Physical Random Access Channel (PRACH) resources. UE 100 can also send a random access preamble to gNB 200 using PRACH resources designated for session termination as a notification indicating session termination. gNB 200 identifies UE 100 that has sent a notification indicating session termination and notifies CN device (AMF300) of UE 100's session termination.

[0156] Figure 13 This is a diagram illustrating an example of a third operating mode of the mobile communication system 1. Here, the differences from the basic operation described above will be primarily described.

[0157] like Figure 13 As shown, in step S301, it is assumed that UE 100, which is in RRC connection state, is interested in a certain multicast session (target multicast session).

[0158] In step S302, UE 100 (NAS entity) performs a multicast session participation procedure on the network (AMF 300) to participate in the target multicast session.

[0159] In step S303, UE 100 transitions to RRC idle state or RRC inactive state.

[0160] In step S304, it is assumed that UE 100 (NAS entity) has lost interest in the target multicast session. In UE 100, the NAS entity can notify the AS entity (e.g., RRC entity) of the loss of interest in the target multicast session.

[0161] In step S305, UE 100 (AS entity) receives PRACH information from gNB 200 indicating the configuration of PRACH resources. The PRACH information may be broadcast in system information from gNB 200. For example, a portion of the configured PRACH resources may correspond to a resource area (e.g., a dedicated resource area) used to notify session exit. The resource area used to notify session exit may include multiple separate sub-resource areas for the corresponding multicast session identifier.

[0162] In step S306, UE 100 (AS entity) selects the PRACH resources included in the resource area used to notify session exit from the PRACH resources indicated in the PRACH information. Here, UE 100 (AS entity) can select a sub-resource area associated with the multicast session identifier of the target multicast session.

[0163] In step S307, UE 100 (AS entity) sends a random access preamble (Msg1) to gNB 200 using the PRACH resource selected in step S306. Since the PRACH resource used to notify session exit is used for the random access preamble, gNB 200 considers that UE 100, which has sent the random access preamble, has notified session exit.

[0164] In step S308, gNB 200 sends a random access response (Msg2) to UE 100.

[0165] In step S309, in response to receiving a random access response (Msg2), UE 100 sends a connection request message (Msg3) to gNB 200. The connection request message (Msg3) can be an RRC establishment request message or an RRC recovery request message. The connection request message (Msg3) can include at least one selected from the group consisting of: the identifier of UE 100, information notifying of exit from a multicast session, and the multicast session identifier of the target multicast session. Based on the information included in the connection request message (Msg3), gNB 200 identifies UE 100 and recognizes the exit from the multicast session. gNB 200 may identify UE 100 after contention resolution using Msg4 described below. When the connection request message (Msg3) is an RRC recovery request message (i.e., when UE 100 is in an RRC inactive state), gNB 200 may identify the UE context of UE 100 maintained by gNB 200.

[0166] In step S310, gNB 200 sends an RRC release message as Msg4 to UE 100. Therefore, UE 100 remains in an RRC idle or RRC inactive state. Note that when performing another data transmission and reception with UE 100, gNB 200 can switch UE 100 to an RRC connected state by sending an RRC establishment message or RRC recovery message as Msg4.

[0167] In step S311, gNB 200 notifies AMF 300 of UE 100's exit from the multicast session. For example, gNB 200 performs the notification by sending an NG-AP message on the NG interface. gNB 200 (instead of UE 100) can generate a NAS message and use that NAS message to perform the notification. This message may include the identifier of UE 100 and the multicast session identifier of the target multicast session. Note that the processing in step S311 can be performed before step S310.

[0168] In this operating mode, a four-step random access procedure is described; however, a two-step random access procedure can also be used. In the two-step random access procedure, UE 100 sends Msg1 and Msg3 as MsgA to gNB 200, and gNB 200 sends Msg2 and Msg4 as MsgB to UE 100.

[0169] Variations in the operation of mobile communication systems

[0170] A variation of the operation of mobile communication system 1 will be described. This variation applies not only to multicast but also to broadcast MBS services.

[0171] The PDCP entity of UE 100 configures and updates PDCP variables based on the PDCP sequence number (PDCP SN) included in the PDCP packets received from gNB 200. Typically, UE 100 configures the PDCP variables with an initial value of zero and updates (increments, counts up) the PDCP variables in response to packets received from gNB 200. The PDCP entity of UE 100, which has participated in a particular MBS session from the beginning, can sequentially update the PDCP variables to keep them up-to-date. PDCP variables include the PDCP SN and the superframe number (HFN). The HFN increments when the PDCP SN wraps around. In other words, the HFN is the value counted up each time the PDCP SN wraps around. For example, UE 100 and gNB 200 manage the COUNT, which is a count value that includes both the PDCP SN and HFN.

[0172] The PDCP entity of UE 100, which participates in an MBS session midway, is unaware of the current PDCP variables (specifically the HFN portion) and cannot successfully execute the scheduled PDCP operation. The scheduled PDCP operation is receive window control and / or packet reordering. The PDCP variables used for receive window control can be RX NEXT and / or 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 can be RXREORD. RX REORD is the sequence number of the PDCP SDU for which a timer indicating the maximum waiting time for packet reordering has been started. For example, when the sequence number of a received packet is less than RX REORD, UE 100 discards the packet. PDCP variables (COUNT values) are also used for security purposes to encrypt PDCP packets.

[0173] Specifically, the initial value of RX_DELIV is 0, and in the unicast case, both gNB 200 and UE 100 increment the HFN based on the initial value for each wrapback of the PDCP SN. This synchronizes the HFNs of gNB 200 and UE 100. In the multicast case, the RX DELIV at which UE 100 begins receiving PDCP packets is indeterminate. Therefore, the valid HFN (i.e., the HFN managed by gNB 200) cannot be determined solely by examining the received PDCP packets. Note that the header of the PDCP PDU includes the PDCP SN but not the HFN. In the following text, PDCP variables refer to the HFN and / or COUNT values.

[0174] In this variant, the gNB 200, which transmits MBS data during an MBS session, sends the initial values ​​of the PDCP variables that the UE 100, which will use to receive MBS data, via multicast or broadcast within the MBS session. That is, the gNB 200 sends the current PDCP variables during MBS data transmission (MBS service channel). The gNB 200 can periodically send the initial values ​​of the PDCP variables that the UE 100, which will use to receive MBS data, via multicast or broadcast. In response to receiving the initial values ​​of the PDCP variables from the gNB 200, the UE 100, which is participating in the MBS session, performs MBS data reception processing using the received initial values ​​of the PDCP variables. This allows even the UE 100, which is participating in the MBS session, to successfully perform PDCP operations.

[0175] Figure 14 This is a diagram illustrating the operation according to this variant.

[0176] like Figure 14 As shown, gNB 200 initiates MBS data transmission for a specific MBS session. gNB 200 updates the PDCP variable when sending MBS data.

[0177] In step S402, UE 100 joins the MBS session relatively late (joins the MBS session midway). Note that UE 100 is unaware of the current COUNT value (especially the HFN portion), and therefore cannot perform PDCP processing on the data packets (PDCP packets) that constitute the MBS data. UE 100 can obtain the PDCP SN included in the header of the PDCP packet initially received from gNB 200 and use the obtained PDCP SN as part of the COUNT value managed by UE 100.

[0178] In step S403, the gNB 200 periodically transmits the COUNT value (or HFN) of the currently transmitted MBS data packet (PDCP packet) or the COUNT value (or HFN) of the next MBS data packet (PDCP packet) to be transmitted via multicast or broadcast. Specifically, the gNB 200 transmits the current COUNT value (or HFN) on the MBS traffic channel using G-RNTI. For example, the gNB 200 transmits the initial value of the PDCP variable from at least one of the following groups: MAC control element (CE), RLC control PDU, and PDCP control PDU. When using MAC CE, the gNB 200 may transmit a set of multicast session identifier (TMGI) and COUNT values. When using PDCP / RLC control PDU, the UE 100 may identify the COUNT value as the COUNT value of the bearer / LCH to which the PDCP / RLC control PDU belongs. Here, when the lower layer (e.g., MAC) receives the COUNT value (or HFN), the lower layer notifies the upper layer (e.g., PDCP) of the COUNT value (or HFN).

[0179] In step S404, UE 100 (PDCP entity) configures the PDCP variable notified from gNB 200 to the initial value of the PDCP variable managed by UE 100.

[0180] In step S405, gNB 200 sends MBS data packets (PDCP packets) via multicast or broadcast.

[0181] In step S406, UE 100 uses the PDCP variables managed by UE 100 to perform PDCP processing on the MBS data packets (PDCP packets) received from gNB 200, and updates the PDCP variables managed by UE 100.

[0182] Note that the operations according to this variant can be applied to RLC operations, and "PDCP" can be interpreted as "RLC". The initial value of the PDCP variable can be the initial value of the RLC variable. In this variant, the following example has been described: the initial value of the PDCP variable to be used by the UE 100, which is participating in the MBS session midway, to receive MBS data is sent in the MBS session via multicast or broadcast; however, the gNB 200 can send the initial value of the PDCP variable by broadcasting using System Information (SIB).

[0183] Other embodiments

[0184] The above operational procedures can be implemented independently or by combining two or more procedures. For example, certain steps in one operational procedure can be applied to another. Alternatively, certain steps in one operational procedure can be replaced by certain steps in another.

[0185] In the above embodiments, an example of an NR base station (i.e., gNB) was described; however, the base station can be an LTE base station (i.e., eNB). The base station can be a relay node, such as an Integrated Access and Backhaul (IAB) node. The base station can be a Distributed Unit (DU) of an IAB node.

[0186] A program may be provided that enables a computer to execute each process performed by UE 100 or gNB 200. The program may be recorded on a computer-readable medium. The computer-readable medium allows the program to be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. There are no particular limitations on the non-transitory recording medium, and it may be, for example, a recording medium such as a CD-ROM or DVD-ROM. Circuitry for executing each process performed by UE 100 or gNB 200 may be integrated, and at least a portion of UE 100 or gNB 200 may be configured as a semiconductor integrated circuit (chipset or system-on-chip (SoC)).

[0187] Unless otherwise specified, the phrases “based on” and “depending on” as used in this disclosure do not mean “based on only” and “depending on only”. The phrase “based on” means both “based on only” and “at least partially based on”. Similarly, the phrase “depending on” means both “depending on only” and “at least partially dependent on”. “Obtaining” or “acquiring” can mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating information. The terms “comprising,” “including,” and variations thereof do not mean “including only the said items,” but rather mean “may include only the said items” or “may include not only the said items but also other items.” The term “or” as used in this disclosure is not intended to be “exclusive or.” Furthermore, any reference to elements in this disclosure using names such as “first” and “second” does not generally limit the number or order of these elements. These names may be used herein as a convenient method of distinguishing between two or more elements. Therefore, references to the first and second elements do not mean that only two elements may be used herein, or that the first element needs to precede the second element in some way. For example, when English articles such as “a,” “an,” and “the” are added in this disclosure by translation, these articles include plural forms unless otherwise explicitly stated in the context.

[0188] Although various embodiments have been described in detail above with reference to the accompanying drawings, the specific configurations are not limited to those described above, and various design changes can be made without departing from the spirit of this disclosure.

[0189] This application claims priority to U.S. Provisional Patent Application No. 63 / 186512 (filed May 10, 2021), the entire contents of which are incorporated herein by reference.

Claims

1. A communication control method executed by a user equipment in a mobile communication system, the mobile communication system being configured to provide broadcast / multicast service (MBS) from a network to the user equipment, the communication control method comprising: Monitoring group notifications during Radio Resource Control (RRC) idle or inactive states, where the group notification is an indication of the enabled status of an MBS multicast session in which the user equipment is participating, and the group notification is sent from the network to the group to which the user equipment belongs; In response to receiving the group notification, switch to the RRC connection state to receive the MBS multicast session; as well as In the event of exiting the MBS multicast session, control is implemented to prevent the monitoring of group notifications.

2. A user equipment supporting the reception of Broadcast / Multicast Service (MBS), the user equipment comprising: The controller is configured as follows: Monitoring group notifications during Radio Resource Control (RRC) idle or inactive states, where the group notification is an indication of the enabled status of an MBS multicast session in which the user equipment is participating, and the group notification is sent from the network to the group to which the user equipment belongs; as well as In response to receiving the group notification, the connection switches to the RRC connection state to receive the MBS multicast session, wherein, The controller is configured to control the group notifications not to be monitored when exiting the MBS multicast session.

3. A processor for controlling a user equipment, the user equipment supporting receiving a broadcast / multicast service (MBS), the processor being configured to perform the following processes: Monitoring group notifications during Radio Resource Control (RRC) idle or inactive states, where the group notification is an indication of the enabled status of an MBS multicast session in which the user equipment is participating, and the group notification is sent from the network to the group to which the user equipment belongs; In response to receiving the group notification, switch to the RRC connection state to receive the MBS multicast session; as well as In the event of exiting the MBS multicast session, control is implemented to prevent the monitoring of group notifications.

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