COMMUNICATION METHOD, USER EQUIPMENT, NETWORK NODE, CHIP SET, PROGRAM, AND MOBILE COMMUNICATION SYSTEM

Abstract

This communication method executed by a UE 100 in a mobile communication system for providing a multicast / broadcast service (MBS) comprises: a step for, when in an RRC idle state or RRC inactive state in a serving cell, receiving or having an interest in receiving an initial bandwidth part of the serving cell or an MBS session provided in an adjacent cell; and a step for transmitting an MBS interest indication relating to the MBS session to the serving cell when the state shifts from the RRC idle state or the RRC inactive state to an RRC connected state. The MBS interest indication does not include an MBS session identifier indicating the MBS session but includes frequency information relating to the initial bandwidth part or a cell identifier of the adjacent cell.

Description

[Technical field]

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

[0002] The 3GPP (3rd Generation Partnership Project) standard defines the technical specifications of NR (New Radio), which is a fifth-generation (5G) wireless access technology. Compared with LTE (Long Term Evolution), which is a fourth-generation (4G) wireless access technology, NR has features such as high speed, large capacity, high reliability, and low latency. Discussions are underway in 3GPP to formulate technical specifications for 5G / NR multicast broadcast service (MBS) (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP contribution: RP-201038, “WID revision: NR Multicast and Broadcast Services” Summary of the Invention

[0004] It is expected that 5G / NR multicast broadcast services will provide improved services over 4G / LTE multicast broadcast services.

[0005] Therefore, an object of the present disclosure is to provide a communication method that enables an improved multicast broadcast service to be realized.

[0006] A communication method according to a first aspect is a communication method executed by a user equipment in a mobile communication system providing a multicast broadcast service (MBS), comprising the steps of: receiving or becoming interested in receiving an MBS session provided in an initial bandwidth portion of a serving cell or a neighboring cell when in an RRC idle state or an RRC inactive state in the serving cell, and transmitting an MBS interest notification regarding the MBS session to the serving cell when transitioning from the RRC idle state or the RRC inactive state to an RRC connected state. The MBS interest notification does not include an MBS session identifier indicating the MBS session, but includes frequency information regarding the initial bandwidth portion or a cell identifier of the neighboring cell.

[0007] A communication method according to a second aspect is a communication method executed by a user equipment in a mobile communication system providing a multicast broadcast service (MBS), and includes the steps of receiving or becoming interested in receiving a broadcast session when in an RRC idle state or an RRC inactive state in a serving cell, if the broadcast session is provided from the serving cell, transmitting an MBS interest notification regarding the broadcast session to the serving cell upon transition from the RRC idle state or the RRC inactive state to an RRC connected state, and if the broadcast session is provided from a non-serving cell, omitting the transmission of the MBS interest notification to the serving cell upon the transition to the RRC connected state.

[0008] A communication method according to a third aspect is a communication method executed by a user equipment in a mobile communication system that provides a multicast broadcast service (MBS), and includes the steps of receiving or becoming interested in receiving a broadcast session transmitted in an initial bandwidth portion of a serving cell when in an RRC idle state or an RRC inactive state in the serving cell, receiving a message from the serving cell for setting a dedicated bandwidth portion different from the initial bandwidth portion in the user equipment when transitioning from the RRC idle state or the RRC inactive state to an RRC connected state, and continuing to use the initial bandwidth portion even after receiving the message without applying the setting of the dedicated bandwidth portion. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a configuration of a mobile communication system according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a configuration of a UE (user equipment) according to an embodiment. [Diagram 3] A diagram showing the configuration of a gNB (base station) according to an embodiment. [Figure 4] A diagram showing the configuration of a protocol stack of a wireless interface of a user plane that handles data. [Diagram 5] FIG. 2 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 showing an overview of MBS traffic distribution according to an embodiment. [Figure 7] FIG. 13 is a diagram illustrating a distribution mode according to the embodiment. [Figure 8] FIG. 2 is a diagram showing an example of internal processing related to MBS reception in a UE according to an embodiment. [Figure 9] FIG. 11 is a diagram showing another example of internal processing related to MBS reception of the UE according to the embodiment. [Figure 10] FIG. 1 is a diagram for explaining a CFR. [Figure 11] FIG. 2 is a diagram illustrating an example of the operation of the mobile communication system according to the embodiment. [Figure 12] FIG. 11 is a diagram illustrating an example of the operation of a UE according to the first modification. [Figure 13] FIG. 11 is a diagram illustrating an example of the operation of a mobile communication system according to a second modification. [Figure 14] FIG. 11 is a diagram illustrating an example of the operation of a mobile communication system according to a third modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] (Configuration of a mobile communication system) FIG. 1 is a diagram showing a configuration of a mobile communication system according to an embodiment. The mobile communication system 1 complies with the 3GPP standard 5th Generation System (5GS). In the following description, 5GS is taken as an example, but the mobile communication system may be at least partially applied to a Long Term Evolution (LTE) system. Also, the mobile communication system may be at least partially applied to a sixth generation (6G) system.

[0012] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. The 5GC 20 may be simply referred to as the core network (CN) 20.

[0013] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 is a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0014] The NG-RAN 10 includes a base station (called "gNB" in the 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0015] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0016] 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 Non-Access Stratum (NAS) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0017] 2 is a diagram showing a configuration of a UE 100 (user equipment) according to an embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 configure a wireless communication unit that performs wireless communication with the gNB 200.

[0018] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0019] The transmission unit 120 performs various transmissions under the control of the control unit 130. The transmission 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.

[0020] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processes 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.

[0021] 3 is a diagram showing a configuration of a gNB 200 (base station) according to an embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that performs communication with the CN 20.

[0022] 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.

[0023] The receiving unit 220 performs various receptions 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.

[0024] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes of each layer described below. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processes 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.

[0025] The backhaul communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 may be configured (i.e., functionally divided) with a CU (Central Unit) and a DU (Distributed Unit), and both units may be connected to each other via an F1 interface, which is a fronthaul interface.

[0026] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0027] 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.

[0028] The PHY layer performs coding / 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. The PHY layer of the UE 100 receives downlink control information (DCI) transmitted from the gNB 200 on a physical downlink control channel (PDCCH). Specifically, the UE 100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires the successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from the gNB 200 has CRC parity bits scrambled by the RNTI added thereto.

[0029] 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 a transport channel. The MAC layer of gNB200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be assigned to UE100.

[0030] The RLC layer transmits data to the RLC layer on the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0031] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0032] The SDAP layer maps IP flows, which are units for QoS (Quality of Service) control by the core network, to radio bearers, which are units for QoS control by the AS (Access Stratum). Note that if the RAN is connected to the EPC, the SDAP is not necessary.

[0033] 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).

[0034] 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.

[0035] Between the RRC layer of the UE 100 and the RRC layer of the gNB 200, RRC signaling for various settings is transmitted. The RRC layer controls logical channels, transport channels, and physical channels in response to establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of the UE 100 and the RRC of the gNB 200, the UE 100 is in an RRC idle state. When the connection between the RRC of the UE 100 and the RRC of the gNB 200 is suspended, the UE 100 is in an RRC inactive state.

[0036] The NAS layer, which is located above the RRC layer, performs session management, mobility management, and the like. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. The UE 100 has an application layer and the like in addition to the radio interface protocol. The layer below the NAS layer is called the AS layer.

[0037] (Overview of MBS) An overview of the MBS according to the embodiment will be described. The MBS is a service that enables broadcast or multicast, i.e., point-to-multipoint (PTM) data transmission from the NG-RAN 10 to the UE 100. Possible use cases (service types) of the MBS include public safety communication, mission-critical communication, V2X (Vehicle to Everything) communication, IPv4 or IPv6 multicast distribution, IPTV (Internet protocol television), group communication, and software distribution.

[0038] The broadcast service provides a service to all UEs 100 within a specific service area for applications that do not require highly reliable QoS. An MBS session used for the broadcast service is called a broadcast session.

[0039] The multicast service provides services not to all UEs 100 but to a group of UEs 100 participating in the multicast service (multicast session). The MBS session used in the multicast service is called a multicast session. The multicast service allows the same content to be provided to a group of UEs 100 in a more wirelessly efficient manner than the broadcast service.

[0040] FIG. 6 is a diagram showing an overview of MBS traffic delivery according to the embodiment.

[0041] MBS traffic (MBS data) is distributed from a single data source (application service provider) to multiple UEs. A 5G core network, 5G CN (5GC) 20, receives the MBS data from the application service provider, creates a copy of the MBS data (replication), and distributes it.

[0042] From the 5GC20 perspective, two multicast delivery methods are possible: 5GC Shared MBS Traffic delivery and 5GC Individual MBS Traffic delivery.

[0043] In the 5GC individual MBS traffic delivery method, the 5GC 20 receives a single copy of MBS data packets and delivers individual copies of those MBS data packets to individual UEs 100 via a PDU session for each UE 100. Therefore, one PDU session for each UE 100 needs to be associated with the multicast session.

[0044] In the 5GC shared MBS traffic delivery method, the 5GC 20 receives a single copy of MBS data packets and delivers the single copy of those MBS packets to a RAN node (i.e., the gNB 200). The gNB 200 receives the MBS data packets via an MBS tunnel connection and delivers them to one or more UEs 100.

[0045] From the perspective of the RAN (5G RAN) 10, there are two possible delivery methods for transmitting MBS data over the air in the 5GC shared MBS traffic delivery method: PTP (Point-to-Point) and PTM (Point-to-Multipoint). PTP stands for unicast, and PTM stands for multicast and broadcast.

[0046] In the PTP distribution method, the gNB 200 distributes individual copies of the MBS data packets wirelessly to each UE 100. On the other hand, in the PTM distribution method, the gNB 200 distributes a single copy of the MBS data packet wirelessly to a group of UEs 100. The gNB 200 can dynamically determine whether to use PTM or PTP as the distribution method for MBS data to one UE 100.

[0047] The PTP distribution method and the PTM distribution method are mainly related to the user plane. There are two control modes for MBS data distribution: a first distribution mode and a second distribution mode.

[0048] FIG. 7 is a diagram showing a distribution mode according to the embodiment.

[0049] The first delivery mode (Delivery mode 1: DM1) is a delivery mode that can be used by the UE 100 in the RRC connected state, and is a delivery mode for high QoS requirements. The first delivery mode is used for a multicast session among MBS sessions. However, the first delivery mode may also be used for a broadcast session. The first delivery mode may also be available to the UE 100 in the RRC idle state or the RRC inactive state.

[0050] The setting of MBS reception in the first distribution mode is performed by UE-dedicated signaling. For example, the setting of MBS reception in the first distribution mode is performed by an RRC Reconfiguration message (or an RRC Release message), which is an RRC message transmitted by unicast from the gNB 200 to the UE 100.

[0051] The MBS reception configuration includes MBS traffic channel configuration information (hereinafter referred to as "MTCH configuration information") related to the configuration of an MBS traffic channel that transmits MBS data. The MTCH configuration information includes MBS session information (including an MBS session identifier described later) related to an MBS session, and scheduling information of the MBS traffic channel corresponding to this MBS session. The scheduling information of the MBS traffic channel may include a discontinuous reception (DRX) configuration of the MBS traffic channel. The discontinuous reception configuration may include one or more parameters of a timer value (On Duration Timer) that defines an on-duration (On Duration: reception period), a timer value (Inactivity Timer) that extends the on-duration, a scheduling interval or DRX cycle (Scheduling Period, DRX Cycle), an offset value of the start subframe of the scheduling or DRX cycle (Start Offset, DRX Cycle Offset), a start delay slot value of the on-duration timer (Slot Offset), a timer value (Retransmission Timer) that defines the maximum time until retransmission, and a timer value (HARQ RTT Timer) that defines the minimum interval until DL allocation of HARQ retransmission.

[0052] The MBS traffic channel is a type of logical channel and may be referred to as an MTCH. The MBS traffic channel is mapped to a Down Link-Shared CHannel (DL-SCH), which is a type of transport channel.

[0053] The second delivery mode (Delivery mode 2: DM2) is a delivery mode that can be used by UE 100 in the RRC connected state as well as UE 100 in the RRC idle state or RRC inactive state, and is a delivery mode for low QoS requirements. The second delivery mode is used for a broadcast session among MBS sessions. However, the second delivery mode may also be applicable to a multicast session.

[0054] The setting of MBS reception in the second distribution mode is performed by broadcast signaling. For example, the setting of MBS reception in the second distribution mode is performed by a logical channel broadcast from the gNB 200 to the UE 100, such as a broadcast control channel (BCCH) and / or a multicast control channel (MCCH). The UE 100 can receive the BCCH and MCCH using a dedicated RNTI predefined in the technical specifications, for example. The RNTI for BCCH reception may be SI-RNTI, and the RNTI for MCCH reception may be MCCH-RNTI.

[0055] In the second distribution mode, UE 100 may receive MBS data in the following three procedures. First, UE 100 receives MCCH setting information by a SIB (MBS SIB) transmitted on a BCCH from gNB 200. Second, UE 100 receives an MCCH from gNB 200 based on the MCCH setting information. The MCCH transmits MTCH setting information. Third, UE 100 receives an MTCH (MBS data) based on the MTCH setting information. Hereinafter, MTCH setting information and / or MCCH setting information may be referred to as MBS reception setting.

[0056] In the first distribution mode and the second distribution mode, the UE 100 may receive the MTCH using a group RNTI (G-RNTI) assigned by the gNB 200. The G-RNTI corresponds to an RNTI for MTCH reception. The G-RNTI may be included in the MBS reception setting (MTCH setting information).

[0057] 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 Identity (TMGI), a source-specific IP multicast address (consisting of a source unicast IP address of an application function or application server, etc., and an IP multicast address indicating a destination address), a session identifier, and a G-RNTI. At least one of the TMGI, the source-specific IP multicast address, and the session identifier is called an MBS session identifier. The TMGI, the source-specific IP multicast address, the session identifier, and the G-RNTI are collectively called MBS session information.

[0058] Fig. 8 is a diagram showing an example of an internal process related to MBS reception of the UE 100 according to the embodiment. Fig. 9 is a diagram showing another example of an internal process related to MBS reception of the UE 100 according to the embodiment.

[0059] One MBS Radio Bearer (MRB) is one radio bearer that transmits a multicast session or a broadcast session. That is, there are cases where a multicast session is associated with an MRB and cases where a broadcast session is associated with an MRB.

[0060] The MRB and corresponding logical channels (e.g., MTCH) are configured in the UE 100 from the gNB 200 by RRC signaling. The MRB configuration procedure may be separated from the data radio bearer (DRB) configuration procedure. In the RRC signaling, one MRB can be configured with "PTM only", "PTP only", or "both PTM and PTP". The type of such an MRB can be changed by RRC signaling.

[0061] In FIG. 8, an example is shown in which a multicast session and a dedicated traffic channel (DTCH) are associated with MRB#1, a multicast session and MTCH#1 are associated with MRB#2, and a broadcast session and MTCH#2 are associated with MRB#3. That is, MRB#1 is an MRB with PTP only, MRB#2 is an MRB with PTM only, and MRB#3 is an MRB with PTM only. Note that DTCH is scheduled using the cell RNTI (C-RNTI). MTCH is scheduled using the G-RNTI.

[0062] The PHY layer of the UE 100 processes user data (received data) received on a PDSCH, which is one of the physical channels, and transmits the data to a downlink shared channel (DL-SCH), which is one of the transport channels. The MAC layer (MAC entity) of the UE 100 processes data received on the DL-SCH, and transmits the received data to a corresponding logical channel (corresponding RLC entity) based on a logical channel identifier (LCID) included in a header (MAC header) included in the received data.

[0063] In FIG. 9, an example is shown in which a DTCH and an MTCH are associated with an MRB associated with a multicast session. Specifically, one MRB is split into two legs, one leg is associated with a DTCH, and the other leg is associated with an MTCH. The two legs are combined in the PDCP layer (PDCP entity). That is, the MRB is an MRB for both PTM and PTP. Such an MRB is sometimes called a split MRB.

[0064] (MBS Interest Notification) A UE 100 receiving or interested in receiving an MBS session in an RRC connected state can transmit an MBS Interest Indication (MII) to a serving cell (gNB 200). The MBS Interest Indication may be transmitted by a UE Assistance Information message, which is a type of RRC message. The MBS Interest Indication may also be transmitted by a newly defined message (MBS Interest Indication message).

[0065] For example, UE100 initiates an MBS interest notification procedure when a connection is successfully established, when entering or leaving a broadcast service area, when an MBS broadcast session is started or stopped, when MBS interest changes, when the priority between MBS broadcast reception and unicast reception changes, or when changing to a cell (primary cell) that broadcasts SIBs for MBS service continuity.

[0066] The MBS interest notification may include at least one of an MBS frequency list, which is a list of MBS frequencies that UE100 is receiving or is interested in receiving, priority information indicating whether to prioritize receiving all listed MBS frequencies or receiving a unicast bearer, and a TMGI list, which is a list of MBS sessions that UE100 is receiving or is interested in receiving.

[0067] (BWP) In 5G / NR, a bandwidth part (BWP) is defined to reduce the power consumption of the UE 100 and to effectively utilize the wideband carrier. The UE 100 to which the BWP is set can perform communication in a frequency band narrower than the bandwidth of the cell. There are initial BWPs (initial DL BWP and initial UL BWP) and dedicated BWPs (dedicated DL BWP and dedicated UL BWP). Here, DL refers to the downlink, and UL refers to the uplink. The initial BWP is a BWP used at least for initial access, and is used commonly by multiple UEs 100. The dedicated BWP is a BWP that is dedicated (UE-specific) to a certain UE 100. Up to four DL BWPs and up to four UL BWPs are set in a certain serving cell in accordance with the UE 100's capabilities. In the following, when the DL BWP and the UL BWP are not distinguished from each other, they are simply referred to as BWPs.

[0068] The initial BWP is a BWP used at least for initial access, and is used in common by a plurality of UEs 100. The initial DL BWP and the initial UL BWP are each specified with a bwp-id, which is a BWP identifier, of "0". There are two types of initial BWP: an initial BWP derived and set by a master information block (MIB) transmitted on a PBCH, and an initial BWP set by a system information block (SIB), specifically, a system information block type 1 (SIB1). Until the UE 100 receives a message 4 (MSG4) in the random access procedure in the initial access, the UE 100 uses the initial BWP set by the MIB, that is, the bandwidth based on CORESET #0, for the initial BWP. After receiving MSG4, the UE 100 uses the bandwidth set by locationAndBandwidth in SIB1 for the initial BWP. Note that MSG4 may be an RRCSetup message, an RRCResume message, or an RRCReestablishment message. By such initial access (random access procedure), the UE 100 transitions, for example, from an RRC idle state to an RRC connected state.

[0069] The dedicated BWP is a BWP that is set for a specific UE 100 (specific to the UE). A bwp-id other than "0" may be set for the dedicated BWP. For example, the Se in the RRC message, which is dedicated signaling transmitted from the gNB 200 to the UE 100, r Based on the information elements BWP-Downlink and BWP-Uplink included in vingcellConfig, a dedicated DL BWP and a dedicated UL BWP are respectively configured.

[0070] The gNB200 can notify the UE100 of a BWP (i.e., an active BWP) to be used for communication with the gNB200 among one or more configured BWPs. For example, the gNB200 can transmit to the UE100 a BWP identifier indicating a BWP to be activated when the configuration is performed, i.e., a BWP to be used first for communication with the gNB200. In addition, for controlling switching from an active BWP to a BWP that is not an active BWP (hereinafter, an inactive BWP) and switching from an inactive BWP to an active BWP, for example, switching by a PDCCH (DCI), an RRC signaling, a MAC control element (MAC CE), or a timer is used.

[0071] Considering such BWP operation, MBS introduces MBS common frequency resource (CFR) that allows multiple UEs 100 to commonly perform MBS reception. FIG. 10 is a diagram for explaining CFR. As shown in FIG. 10, in the case of broadcast session reception supporting all RRC states, it is desirable that the CFR for receiving PDCCH and PDSCH (i.e., MCCH and MTCH) common to the broadcast session is limited within the initial BWP. However, the bandwidth of the CFR may be the same as, smaller than, or larger than the bandwidth of the initial BWP (or CORESET#0). The CFR may overlap partly with the initial BWP (or CORESET#0), may overlap entirely, or may not overlap entirely.

[0072] (Mobile communication system operation) Assume a scenario in which a UE 100 that is receiving or is interested in receiving a broadcast session in an RRC idle state or an RRC inactive state transitions to an RRC connected state. The above-mentioned second delivery mode is applied to this scenario. In the following, BWP mainly means DL BWP.

[0073] When the UE 100 transitions to the RRC connected state, the dedicated BWP may be set from the gNB 200. For example, when the UE 100 transitions from the RRC inactive state to the RRC connected state, the dedicated BWP may be set from the gNB 200 by MSG4 (RRC Resume) of the random access procedure. When the UE 100 transitions from the RRC idle state to the RRC connected state, the dedicated BWP may be set from the gNB 200 by RRC reconfiguration after the random access procedure.

[0074] Here, since the gNB 200 does not receive an MBS interest notification from the UE 100 during the random access procedure, it cannot grasp the MBS interest of the UE 100. Therefore, the gNB 200 may set a dedicated BWP that does not cover the CFR for the UE 100 that is receiving or is interested in receiving the broadcast session. If a dedicated BWP that does not cover the CFR is set for the UE 100, there is a problem that the UE 100 cannot receive the broadcast session.

[0075] In addition, the security setting of the UE 100 is not activated during the random access procedure. Therefore, it is difficult for the UE 100 to transmit the MBS interest notification during the random access procedure. Specifically, since the TMGI list in the MBS interest notification may correspond to personal information requiring security, it is considered that the transmission of the TMGI list is not permitted before the security setting is activated.

[0076] After the security setting of the UE 100 is activated, the UE 100 can transmit an MBS interest notification to the gNB 200, so that the gNB 200 can learn the MBS interest of the UE 100 and set and activate a dedicated BWP covering the CFR in the UE 100. However, before the security setting of the UE 100 is activated, the UE 100 cannot receive the desired broadcast session.

[0077] Therefore, the UE 100 according to the embodiment performs the following operations. First, when the UE 100 is in an RRC idle state or an RRC inactive state in a serving cell, the UE 100 receives or is interested in receiving a broadcast session provided in the CFR (or initial BWP) of the serving cell. Second, when the UE 100 transitions from an RRC idle state or an RRC inactive state to an RRC connected state, the UE 100 transmits an MBS interest notification regarding the broadcast session to the serving cell (specifically, the gNB 200 that manages the serving cell). The MBS interest notification does not include an MBS session identifier (TMGI) indicating the broadcast session, but includes frequency information regarding the CFR (or initial BWP).

[0078] In this way, since the UE 100 transmits the MBS interest notification not including the TMGI to the serving cell when transitioning to the RRC connected state, the MBS interest notification can be transmitted to the gNB 200 at an early stage before the security setting is activated. For example, the UE 100 transmits the MBS interest notification in MSG3 or MSG5 of the random access procedure. When transitioning from the RRC inactive state to the RRC connected state, the MSG3 may be an RRC resume request message, and the MSG5 may be an RRC resume complete message. When transitioning from the RRC idle state to the RRC connected state, the MSG3 may be an RRC setup request message, and the MSG5 may be an RRC setup complete message. In addition, since the MBS interest notification includes frequency information related to the CFR (or the initial BWP), it becomes easy for the gNB 200 to set the initial BWP or a dedicated BWP covering the CFR to the UE 100. As a result, the UE 100 can receive a broadcast session in the CFR.

[0079] FIG. 11 is a diagram showing an example of the operation of the mobile communication system 1 according to the embodiment.

[0080] In step S101, the UE 100 is in an RRC idle state or an RRC inactive state. The UE 100 uses an initial BWP set by the gNB 200.

[0081] In step S102, the UE 100 in an RRC idle state or an RRC inactive state receives or is interested in receiving a broadcast session. When the UE 100 receives a broadcast session, the UE 100 receives the MCCH and MTCH transmitted in CFR.

[0082] In step S103, UE100 initiates a random access procedure and transmits a random access preamble (MSG1) to gNB200.

[0083] In step S104, in response to receiving the random access preamble (MSG1), gNB200 transmits a random access response (MSG2) to UE100.

[0084] In step S105, in response to receiving the random access response (MSG2), UE100 transmits an RRC Setup Request message or an RRC Resume Request message (MSG3) to gNB200.

[0085] In step S106, in response to receiving the RRC Setup Request message or the RRC Resume Request message (MSG3), gNB200 transmits an RRC Setup message or an RRC Resume message (MSG4) to UE100.

[0086] In step S107, in response to receiving the RRC Setup message or the RRC Resume message (MSG4), the UE 100 transmits an RRC Setup Complete message or an RRC Resume Complete message (MSG5) to the gNB 200. Note that MSG1 to MSG5 configure a random access procedure.

[0087] In step S108, the UE 100 transitions to an RRC connected state by such a random access procedure.

[0088] During the random access procedure, the UE 100 transmits an MBS interest notification for a broadcast session that the UE 100 is receiving or is interested in receiving to the gNB 200 by MSG3 or MSG5. The MBS interest notification may include frequency information for the CFR (or initial BWP) without including an MBS session identifier (TMGI) indicating the broadcast session. The frequency information includes at least one of an identifier of the initial BWP, an identifier of a common frequency resource, an identifier indicating a frequency or resource block corresponding to the initial BWP, and an identifier indicating a frequency or resource block corresponding to the common frequency resource. The identifier indicating the frequency may be an ARFCN (Absolute radio-frequency channel number) (and a bandwidth). The identifier indicating the resource block may be a resource block number (and a resource block number). The gNB 200 may configure (and activate) a dedicated BWP covering the initial BWP or CFR for the UE 100 by MSG4 or an RRC Reconfiguration message based on such frequency information. Even if the MBS interest notification does not include the frequency information, the gNB200 can understand that the UE100 is receiving (or is interested in receiving) a broadcast session, and can therefore take measures such as refraining from setting a dedicated BWP.

[0089] The UE 100 may transmit an MBS interest notification to the gNB 200 in MSG5 (RRC setup complete message or RRC resume complete message). If the UE 100 already has content (such as frequency information) to be reported in the MBS interest notification and is receiving an MBS session (broadcast session), the UE 100 may transmit an MBS interest notification to the gNB 200 in MSG5 (RRC setup complete message or RRC resume complete message). The MBS interest notification may include, as frequency information, a list of MBS frequencies that the UE 100 is receiving or is interested in receiving (MBS frequency list). The MBS interest notification may include priority information indicating which of the reception of the MBS frequencies in the list and the reception of the unicast bearer is prioritized. The gNB 200 may set (and activate) the initial BWP or the dedicated BWP covering the CFR to the UE 100 based on the MBS interest notification. Alternatively, the gNB 200 may control not to set (or activate) the dedicated BWP in the UE 100 based on the MBS interest notification. The MBS interest notification may be transmitted in the same message as Msg3 or Msg5. In this case, the MBS interest notification may be encapsulated and transmitted in Msg3 or Msg5, or an information element of the MBS interest notification may be stored in Msg3 or Msg5 and transmitted. The MBS interest notification may be transmitted at the same timing as Msg3 or Msg5. In this case, the MBS interest notification is transmitted as a message different from Msg3 or Msg5.

[0090] (Modification 1 of the operation of the mobile communication system) In the above embodiment, a scenario was assumed in which the UE 100 receives a broadcast session provided from a serving cell. However, the UE 100 may receive a broadcast session provided from a non-serving cell (neighboring cell). When receiving a broadcast session from a non-serving cell, even if a dedicated BWP that does not cover the CFR is configured in the serving cell, the reception of the broadcast session is not affected.

[0091] In this modification, UE 100 operates as follows. First, UE 100 receives or is interested in receiving a broadcast session when in an RRC idle state or an RRC inactive state in a serving cell. Second, when the broadcast session is provided from a serving cell, UE 100 transmits an MBS interest notification regarding the broadcast session to the serving cell at the time of transition from an RRC idle state or an RRC inactive state to an RRC connected state. Here, when the broadcast session is provided from a non-serving cell (neighbor cell), UE 100 omits transmission of an MBS interest notification to the serving cell at the time of transition to an RRC connected state.

[0092] FIG. 12 is a diagram showing an example of the operation of UE 100 according to this modification.

[0093] In step S201, the UE 100 in an RRC idle state or an RRC inactive state receives or is interested in receiving a broadcast session. The UE 100 may identify a neighboring cell that provides a broadcast session of interest (TMGI) from neighboring cell information included in the MCCH.

[0094] In step S202, the UE 100 determines whether a broadcast session that the UE 100 is receiving or is interested in receiving is provided from a serving cell.

[0095] If the broadcast session is provided from the serving cell (step S202: YES), in step S203, the UE 100 transmits an MBS interest notification to the serving cell (gNB 200) during the random access procedure. The UE 100 may transmit the MBS interest notification to the serving cell based on the criterion that the broadcast session can be received only from the serving cell. Receivable only from the serving cell may mean, for example, that the broadcast session is provided only from the serving cell, or that the broadcast session cannot be received from a non-serving cell depending on the capability of the UE 100. The MBS interest notification may be an MBS interest notification similar to the above-mentioned embodiment. In this modification, the MBS interest notification may be flag information indicating that the broadcast session is being received or is interested in receiving. The MBS interest notification may be transmitted to the serving cell in MSG1. For example, the MBS interest notification may be a special preamble sequence indicating that the broadcast session is being received or is interested in receiving, or a random access preamble transmitted in a special PRACH resource.

[0096] On the other hand, if the broadcast session that UE100 is receiving or is interested in receiving is provided from a non-serving cell (neighboring cell) (step S202: NO), or if the broadcast session can be received from a non-serving cell, in step S204, UE100 does not send an MBS interest notification to the serving cell (gNB200) during the random access procedure.

[0097] (Modification 2 of the operation of the mobile communication system) In this modified example, UE100 is capable of receiving a broadcast session in the initial BWP (CFR) by not applying the dedicated BWP setting from the serving cell (gNB200).

[0098] Specifically, in this modification, the UE 100 operates as follows. First, when the UE 100 is in an RRC idle state or an RRC inactive state in the serving cell, the UE 100 receives or is interested in a broadcast session transmitted in the CFR (or initial BWP) of the serving cell. Second, when the UE 100 transitions from the RRC idle state or the RRC inactive state to the RRC connected state, the UE 100 receives a message (MSG4 or RRC Reconfiguration message) from the serving cell for setting a dedicated BWP different from the CFR (or initial BWP) for the UE 100. Third, even if the UE 100 receives the message, the UE 100 does not apply the setting of the dedicated BWP, and continues to use the initial BWP (or receive the broadcast session in the CFR). The UE 100 may transmit a notification indicating that the setting of the dedicated BWP by the message is not applied to the serving cell.

[0099] 13 is a diagram showing an example of the operation of the mobile communication system 1 according to the present modification. Here, an example will be described in which the message used to set up the dedicated BWP is MSG4, but the message used to set up the dedicated BWP may be an RRC Reconfiguration message.

[0100] In step S301, the UE 100 is in an RRC idle state or an RRC inactive state. The UE 100 uses an initial BWP set by the gNB 200.

[0101] In step S302, the UE 100 in an RRC idle state or an RRC inactive state receives or is interested in receiving a broadcast session. When the UE 100 receives a broadcast session, the UE 100 receives the MCCH and MTCH transmitted in CFR.

[0102] In step S303, UE100 initiates a random access procedure and transmits a random access preamble (MSG1) to gNB200.

[0103] In step S304, in response to receiving the random access preamble (MSG1), gNB200 transmits a random access response (MSG2) to UE100.

[0104] In step S305, in response to receiving the random access response (MSG2), UE100 transmits an RRC Setup Request message or an RRC Resume Request message (MSG3) to gNB200.

[0105] In step S306, in response to receiving the RRC Setup Request message or the RRC Resume Request message (MSG3), the gNB 200 transmits an RRC Setup message or an RRC Resume message (MSG4) to the UE 100. Here, the gNB 200 sets a dedicated BWP for the UE 100.

[0106] In step S306, when the dedicated BWP makes it impossible to receive the broadcast session, that is, when the dedicated BWP does not cover the CFR, the UE 100 suspends (or cancels) the dedicated BWP configuration. Here, the UE 100 may maintain the initial BWP in an active state.

[0107] The UE 100 may notify the gNB 200 that the dedicated BWP setting has been suspended. The UE 100 may notify the gNB 200 that the initial BWP is to be maintained in an active state. Such a notification may be an RRC message (MBS interest notification, UAI, etc.) or a MAC CE (Control Element). The notification may include an identifier of the suspended BWP. The notification may also include an identifier of the BWP (initial BWP, etc.) that is actually applied.

[0108] When gNB200 recognizes based on the notification that the setting of the dedicated BWP is suspended, it will not transmit or receive using the dedicated BWP (it will not activate the dedicated BWP).

[0109] In step S307, in response to receiving the RRC Setup message or the RRC Resume message (MSG4), UE100 transmits an RRC Setup Complete message or an RRC Resume Complete message (MSG5) to gNB200.

[0110] In step S308, the UE 100 transitions to an RRC connected state by a random access procedure.

[0111] In addition, after the security configuration is activated, the UE 100 may transmit an MBS interest notification including an MBS session identifier (TMGI) to the gNB 200. As a result, the gNB 200 may de-configure the dedicated BWP from the UE 100.

[0112] (Modification 3 of the Operation of the Mobile Communication System) In the above-described embodiment, it is mainly assumed that the gNB 200 sets a dedicated BWP to the UE 100. In this modified example, it is mainly assumed that the gNB 200 sets carrier aggregation to the UE 100. As described above, the UE 100 may receive a broadcast session from a non-serving cell (neighboring cell). Therefore, if the gNB 200 can identify a non-serving cell (neighboring cell) that provides a broadcast session that the UE 100 is receiving or is interested in receiving, it becomes easy for the gNB 200 to set the non-serving cell (neighboring cell) as part of the carrier aggregation (specifically, a secondary cell).

[0113] Specifically, in this modification, UE 100 operates as follows. First, when UE 100 is in an RRC idle state or an RRC inactive state in a serving cell, UE 100 receives or is interested in receiving an MBS session (e.g., a broadcast session) provided in a neighboring cell. Second, when UE 100 transitions from an RRC idle state or an RRC inactive state to an RRC connected state, UE 100 transmits an MBS interest notification regarding the MBS session to the serving cell. Here, the MBS interest notification does not include an MBS session identifier (TMGI) but includes a cell identifier of the neighboring cell. When UE 100 transmits MSG5 (an RRC setup complete message or an RRC resume complete message) to the serving cell, UE 100 may transmit an MBS interest notification including a cell identifier of the neighboring cell to the serving cell.

[0114] FIG. 14 is a diagram showing an example of the operation of the mobile communication system 1 according to this modification.

[0115] In step S401, the UE 100 is in an RRC idle state or an RRC inactive state. The UE 100 uses an initial BWP set by the gNB 200.

[0116] In step S402, the UE 100 in the RRC idle state or the RRC inactive state receives or is interested in receiving a broadcast session. The UE 100 may identify a neighboring cell that provides a broadcast session of interest (TMGI) from neighboring cell information included in the MCCH.

[0117] In step S403, UE100 initiates a random access procedure and transmits a random access preamble (MSG1) to gNB200.

[0118] In step S404, in response to receiving the random access preamble (MSG1), gNB200 transmits a random access response (MSG2) to UE100.

[0119] In step S405, in response to receiving the random access response (MSG2), UE100 transmits an RRC Setup Request message or an RRC Resume Request message (MSG3) to gNB200.

[0120] In step S406, in response to receiving the RRC Setup Request message or the RRC Resume Request message (MSG3), gNB200 transmits an RRC Setup message or an RRC Resume message (MSG4) to UE100.

[0121] In step S407, in response to receiving the RRC Setup message or the RRC Resume message (MSG4), the UE 100 transmits an RRC Setup Complete message or an RRC Resume Complete message (MSG5) to the gNB 200. Here, the UE 100 transmits an MBS interest notification including a cell identifier of a neighboring cell that provides a broadcast session that the UE 100 is receiving or is interested in receiving to the gNB 200. The MBS interest notification does not include a TMGI.

[0122] In step S408, the UE 100 transitions to an RRC connected state by a random access procedure. When the gNB 200 configures the UE 100 with carrier aggregation by the initial RRC Reconfiguration for the UE 100, the gNB 200 may configure the UE 100 with the neighboring cell notified by the MBS interest notification as a secondary cell.

[0123] In this modification, the MBS interest notification transmitted during the random access procedure has been mainly described, but the MBS interest notification including the cell identifier may be transmitted by the UE 100 even after the random access procedure. In that case, the MBS interest notification may include an MBS session identifier (TMGI).

[0124] (Other embodiments) In the above-described embodiment and its modified example, the random access procedure may be a two-step random access procedure. In the two-step random access procedure, the UE 100 may transmit a set of a random access preamble (MSG1) and the above-described MSG3 as MSGA to the gNB 200. The gNB 200 may transmit a set of a random access response (MSG2) and the above-described MSG4 as MSGB to the UE 100.

[0125] The above-mentioned operational flows are not limited to being implemented separately and independently, but can be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow.

[0126] In the above-mentioned embodiment and example, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may be a DU of the IAB node. The UE 100 may be an MT (Mobile Termination) of the IAB node.

[0127] A program may be provided that causes a computer to execute each process performed by UE100 or gNB200. The program may be recorded in a computer-readable medium. Using the computer-readable medium, it is possible to install the program in a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. In addition, a circuit that executes 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).

[0128] As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless otherwise specified. 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 "based at least in part on." Additionally, "obtain / acquire" may mean obtaining information from stored information, from information received from other nodes, or by generating information. The terms "include," "comprise," and variations thereof do not mean including only the items listed, but may include only the items listed, or may include additional items in addition to the items listed. Additionally, the term "or" as used in this disclosure is not intended to be an exclusive or. Additionally, any reference to elements using designations such as "first," "second," etc., as used in this disclosure is not intended to 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 a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some manner. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles are intended to include the plural unless the context clearly indicates otherwise.

[0129] 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, etc. are possible without departing from the spirit of the invention.

[0130] This application claims priority to U.S. Provisional Application No. 63 / 296,237 (filed January 4, 2022), the entire contents of which are incorporated herein by reference.

[0131] (Additional Note) 1. Introduction A revised work item for NR Multicast and Broadcast Services (MBS) was approved in RAN2#88. Significant progress was made in RAN2#116e on the details of the MBS Notice of Interest (MII).

[0132] This appendix considers the remaining issues regarding MBS notices of interest.

[0133] 2. Discussion 2.1. Message Definition The currently ongoing CR of TS38.331 includes the following items requiring further consideration:

[0134] Further study is required as to whether MII (MBMS Interest Indication) will be reported in UE Assistance Information or in a new RRC message, and whether the MII information will use a separate IE or be directly included in the RRC message structure.

[0135] In LTE, the MBMS Interest Indication (MII) is separated from the UAI (UE Assistance Information). This is because the preconditions are different: the acquisition of SIB15 for the MII and RRC Connection Reconfiguration for the UAI. On the other hand, the In-device Coexistence Indication (IDC), which was a separate message in LTE, is integrated into the UAI in NR. This is considered feasible because the preconditions for IDC and UAI are the same in LTE (and NR), namely RRC Connection Reconfiguration.

[0136] Observation 1: Whether MBS Interest Notification can be integrated with UE Assistance Information depends on whether the preconditions are consistent between the two messages.

[0137] In NR MBS, neighboring frequency information in the SIB is required to generate an MBS interest notification message including the above IE. In addition, if the UE can obtain the SIB from the serving cell, the transmission of the MBS interest notification is permitted, but this is already known in the approved CR under the condition "if SIBx1 is broadcast from the PCell", as in LTE eMBMS. Therefore, it does not match the RRC Reconfiguration, which is a precondition of the UAI. Therefore, the MBS interest notification should be a separate message from the UAI, as in LTE eMBMS.

[0138] Proposal 1: RAN2 should agree to define the MBS Interest Notification as a new message, i.e., separate from the UAI.

[0139] Proposal 2: RAN2 should agree to allow the UE to send an MBS interest notification if it can obtain an MBS-specific SIB (i.e., SIBx1) from the serving cell (i.e., as a pre-condition).

[0140] 2.2.Other triggers and network controls The following issues requiring further consideration have been incorporated into the current implementation CR:

[0141] Other triggers and network controls require further consideration.

[0142] In RAN2#116e, various triggers for MBS interest notifications have been agreed upon. The UE confirms that it can initiate MII procedures upon successful connection establishment, upon entering or leaving a broadcast service area, upon starting or stopping an MBS broadcast session, upon change of interest, upon change of priority between MBS broadcast reception and unicast reception, and upon change to PCell broadcast SIBx1. Other triggers and network controls require further study.

[0143] Regarding additional triggers, it is considered necessary to send an MBS interest notification when the frequency list is changed. In RAN2#116e, the following was agreed upon regarding the detailed operation of the method for setting the frequency of interest.

[0144] During MII, the UE is required to report only the set of MBS frequencies that the UE can simultaneously receive, i.e., the UE supports at least one band combination and is capable of receiving the indicated set of frequencies.

[0145] The UE shall not consider the currently configured serving frequency when evaluating the simultaneously receivable frequencies for reporting in the MII, i.e., it shall only consider the MBS frequencies it is interested in receiving, regardless of whether they can be received together with the current serving cell.

[0146] According to the above agreement, when the carrier aggregation configuration is updated (e.g., adding or removing an SCell), the frequency list may be changed since it may affect the combination of bandwidths that the UE can currently operate on. In this case, it may be necessary to report the latest interest frequency to the serving cell if it is different from the frequency list reported in the previous MBS interest notification. Therefore, the RAN2 needs to consider whether to send an MBS interest notification when the frequencies of the serving cell and non-serving cells are changed due to a change in the configuration of the serving cell.

[0147] Proposal 3: RAN2 should consider whether to send an MBS interest notification when the UE's interested frequency changes due to a serving cell configuration change.

[0148] For network control, it would certainly be useful to manage the transmission of MBS interest notifications from a large number of UEs to avoid network congestion. Issues that cause resource overload include "spikes" of MBS interest notifications and "frequent" MBS interest notifications.

[0149] Observation 2: If many UEs send MBS interest notifications suddenly, or if a UE sends MBS interest notifications too frequently, network congestion may occur.

[0150] The transmission surge occurs when a huge number of UEs transmit MBS interest notifications at the same time. Since this is a common event for all UEs interested in the MBS broadcast session, a possible trigger for this issue could be "MBS broadcast session start or stop". In particular, if the session stops, the gNB already knows that the MBS broadcast session was stopped by the CN, so it can determine that the UE is no longer interested in this TMGI even without the MBS interest notification. Considering these scenarios, network control could be to spread the MBS interest notification in the time and / or frequency domain (e.g., session start) or to turn on / off the MBS interest notification at this event (e.g., session stop).

[0151] Frequent transmission occurs when the UE frequently changes its interests due to user preferences, etc. Possible triggers for this problem include "changes in interests" and "changes in priority between MBS broadcast reception and unicast reception." A possible network control is to set a prohibition timer in the UE.

[0152] As for the other triggers, i.e. "successful connection establishment", "entering or leaving the broadcast service area", "changing to the PCell broadcasting SIBx1", it can be assumed that they are sufficiently randomized (in time) or already controlled by the network, so they do not pose any major issues.

[0153] Given the above discussion, it has been confirmed that different triggers may require different control methods, i.e., spreading, on / off, inhibit timers, and furthermore, other triggers may not require any enforcement. Therefore, RAN2 needs to discuss whether network control should be considered and, if so, which triggers require what kind of network control.

[0154] Proposal 4: RAN2 should discuss network control to prevent UE from making sudden and frequent transmissions due to MBS interest notification.

[0155] Proposal 5: RAN2 should discuss whether to apply different network control methods to different triggers of MBS interest notification.

[0156] 2.3.Early notification to improve BWP switching behavior This consideration has been incorporated in the current running CR based on the RAN2 agreement that "MBS interest notifications are sent after security activation (it can still be discussed whether additional optimizations are needed for better BWP switching behavior)." Further investigation is required to determine whether additional optimizations are necessary to improve the switching behavior of the BWP.

[0157] Further investigation is required as to whether further optimization is required for better BWP switching behavior.

[0158] The service continuity problem occurs when the UE transitions to the connected state. Specifically, if the serving cell configures the UE with a dedicated BWP that is not aligned with the CFR, the UE cannot continue to receive the broadcast session. Although such a configuration can be avoided after the MBS interest notification, the problem occurs due to the configuration made before the MBS interest notification, i.e. before the activation of AS security.

[0159] It has been noted that an inactive UE can set up a dedicated BWP in Msg4 (RRC Resume), and it has been proposed to provide a one-bit indication in Msg3 to inform the serving cell that the UE is receiving the MBS broadcast session. The serving cell has the UE context for the inactive UE, which includes the previously reported MBS interest indication. Although this interest information is not up-to-date, the serving cell is expected to predict whether a UE moving from inactive to connected is receiving the broadcast session. Therefore, it is not important to extend Msg3, given that the message size is limited.

[0160] It is proposed to introduce an early "broadcast reception" indication in Msg5, which is information for the serving cell to set up a dedicated BWP at the next RRC Reconfiguration. This solution is a simple extension, but it is useful.

[0161] According to the LS from SA3, they are only concerned about reporting the TMGI list before AS security activation. Moreover, it explicitly states that other information (frequency list and priority information) can be reported before AS security activation. Therefore, it is considered that the UE can send an early MBS interest notification, which is sent with Msg5 and contains full content other than the TMGI list, i.e., frequency list and priority information instead of the 1-bit indication above. When the gNB receives the early MBS interest notification in Msg5, it can determine whether this UE is receiving a broadcast session because the MBS interest notification is for the second delivery mode. Also, the full content may be useful for the gNB to determine the appropriate configuration for different frequencies (e.g., SCell configuration) even if the TMGI that the UE is interested in is not yet known. Since these contents are finally reported after AS security activation, there is no signaling overhead if they are reported in the early MBS interest notification.

[0162] Furthermore, it is worth considering whether additional information is required in the early MBS interest notification. For example, the UE reports the CFRs on which it is receiving the MBS broadcast session of interest in the early MBS interest notification. The CFR information may be used by the gNB to determine the appropriate dedicated BWP, for example, such that such CFRs are part of the dedicated BWP. As another example, the UE reports the Cell ID on which the MBS broadcast session of interest is provided in the early MBS interest notification.

[0163] Proposal 6: RAN2 should consider whether to send an early MBS interest notification with Msg5 containing full content other than the TMGI list, i.e., frequency list and priority information.

[0164] Proposal 7: RAN2 should further discuss whether it would be useful for additional information to be reported in the Early MBS Interest Notification, e.g., CFR or Cell ID of interest.

[0165] 2.4. MBS Interest Notification for Multicast Sessions RAN2 currently assumes that MBS Interest Notification is supported for broadcast sessions and not for multicast sessions. RAN2#115e agreed on the basic contents of MBS Interest Notification, i.e. MBS frequency list, priority, and TMGI list.

[0166] For multicast sessions, it is considered common understanding that the core network informs the gNB of the UE's interest because there is a session join procedure at the higher layers. The UE's interest is considered to apply to MBS services. Also, the gNB may know the frequency of the MBS of the UE's interest and the cell providing the MBS service. However, the priority between MBS reception and unicast may not be provided by the core network because it is purely AS-related information. In other words, it is strange for the UE to convey priority information to the core network in the session join procedure.

[0167] Observation 3: In a multicast session, the core network provides the MBS service of interest to the UE to the gNB, and the gNB may know the MBS frequency / cell, but the core network and the gNB may not know the UE’s AS priority between the MBS and unicast.

[0168] The priority information is also useful for the gNB for scheduling and handover decisions, as well as for LTE eMBMS, and is considered relevant for service continuity. Therefore, the UE needs to notify the gNB of its priority information also for multicast sessions. In this sense, RAN2 should agree that MBS interest notification should be supported also for multicast services / first delivery mode.

[0169] Proposal 8: RAN2 should agree that MBS interest notification is also supported in multicast sessions / first delivery mode, at least for the UE to inform the gNB of the priority between MBS reception and unicast reception. [Explanation of symbols]

[0170] 1: Mobile communication systems 10:RAN 20 :CN 100:UE 110: Receiving unit 120: Transmitter 130: Control section 200: gNB 210: Transmission unit 220: Receiving unit 230: Control section 240: Backhaul communication unit

Claims

1. A communication method performed by a user equipment in a mobile communication system providing a multicast broadcast service (MBS), comprising: sending an MBS interest notification to a serving cell for the MBS session; the MBS session is a broadcast session; the MBS interest notification does not include an MBS session identifier indicating the MBS session, and includes information regarding a common frequency resource for receiving the MBS session; The MBS interest notification includes information about a non-serving cell that provides the MBS session. Communication methods.

2. The MBS interest notification includes at least one of an identifier of an initial bandwidth portion, an identifier of the common frequency resource, an identifier indicating a frequency or resource block corresponding to the initial bandwidth portion, and an identifier indicating a frequency or resource block corresponding to the common frequency resource. The communication method according to claim 1 .

3. The transmitting of the MBS interest notification includes transmitting the MBS interest notification to the serving cell when transmitting an RRC setup complete message or an RRC resume complete message to the serving cell. The communication method according to claim 1 or 2.

4. The MBS interest notification includes a list of MBS frequencies that the user equipment is receiving or is interested in receiving. The communication method according to claim 1 or 2.

5. The MBS interest notification further includes priority information indicating whether to prioritize reception of the MBS frequency in the list or reception of a unicast bearer. The communication method according to claim 4.

6. receiving or being interested in receiving the MBS session when in an RRC idle state or an RRC inactive state; The transmitting of the MBS interest notification includes transmitting the MBS interest notification to the serving cell when transitioning from the RRC idle state or the RRC inactive state to an RRC connected state. The communication method according to claim 1 .

7. Receiving or being interested in receiving the MBS session includes receiving or being interested in receiving the MBS session provided in a neighboring cell; The transmitting of the MBS interest notification includes transmitting the MBS interest notification to the serving cell, the MBS interest notification including a cell identifier of the neighboring cell, when transmitting an RRC setup complete message or an RRC resume complete message to the serving cell. The communication method according to claim 6.

8. A user device, a transmitter for transmitting a Multicast Broadcast Service (MBS) interest notification for an MBS session to a serving cell; the MBS session is a broadcast session; the MBS interest notification does not include an MBS session identifier indicating the MBS session, and includes information regarding a common frequency resource for receiving the MBS session; The MBS interest notification includes information about a non-serving cell that provides the MBS session. User equipment.

9. A network node, a receiving unit for receiving a Multicast Broadcast Service (MBS) interest notification from a user device for a MBS session; the MBS session is a broadcast session; the MBS interest notification does not include an MBS session identifier indicating the MBS session, and includes information regarding a common frequency resource for receiving the MBS session; The MBS interest notification includes information about a non-serving cell that provides the MBS session. Network node.

10. A chipset for a user equipment, comprising: performing a process of sending a Multicast Broadcast Service (MBS) interest notification for an MBS session to a serving cell; the MBS session is a broadcast session; the MBS interest notification does not include an MBS session identifier indicating the MBS session, and includes information regarding a common frequency resource for receiving the MBS session; The MBS interest notification includes information about a non-serving cell that provides the MBS session. Chipset.

11. A user device includes: sending a Multicast Broadcast Service (MBS) interest notification to a serving cell for an MBS session; the MBS session is a broadcast session; the MBS interest notification does not include an MBS session identifier indicating the MBS session, and includes information regarding a common frequency resource for receiving the MBS session; The MBS interest notification includes information about a non-serving cell that provides the MBS session. program.

12. A mobile communication system providing a multicast broadcast service (MBS), comprising: A user equipment (100) configured to transmit an MBS interest notification for an MBS session to a serving cell (102); the MBS session is a broadcast session; the MBS interest notification does not include an MBS session identifier indicating the MBS session, and includes information regarding a common frequency resource for receiving the MBS session; The MBS interest notification includes information about a non-serving cell that provides the MBS session. Mobile communication system.

13. A communication method performed by a user equipment in a mobile communication system providing a multicast broadcast service (MBS), comprising: receiving or being interested in receiving a broadcast session while in an RRC idle or RRC inactive state in a serving cell; If the broadcast session is provided from the serving cell, sending an MBS interest notification regarding the broadcast session to the serving cell upon transition from the RRC idle state or the RRC inactive state to an RRC connected state; If the broadcast session is provided from a non-serving cell, omitting transmission of the MBS interest notification to the serving cell upon the transition to the RRC connected state. Communication methods.

14. A communication method performed by a user equipment in a mobile communication system providing a multicast broadcast service (MBS), comprising: receiving or being interested in receiving a broadcast session transmitted in an initial bandwidth portion of a serving cell when in an RRC idle state or an RRC inactive state in the serving cell; receiving a message from the serving cell to configure the user equipment with a dedicated bandwidth portion different from the initial bandwidth portion when transitioning from the RRC idle state or the RRC inactive state to an RRC connected state; and continuing to use the initial bandwidth portion without applying the setting of the dedicated bandwidth portion even when the message is received. Communication methods.

15. and transmitting a notification to the serving cell indicating that the configuration of the dedicated bandwidth portion by the message is not to be applied. The communication method according to claim 14.

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