Communication method, user equipment, network node, chipset, program, and mobile communication system

Abstract

To provide a communication method and a device that enable an improved multicast broadcast service (MBS).SOLUTION: In a mobile communication system, a method includes a step of receiving or being interested in receiving, by a UE, an MBS session provided in an initial bandwidth portion of a serving cell or in a neighboring cell when the serving cell (specifically, a gNB managing the serving cell) is in an RRC idle state or an RRC inactive state, and a step of 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.SELECTED DRAWING: Figure 12

Description

Technical Field

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

Background Art

[0002] In the 3GPP (3rd Generation Partnership Project) (registered trademark; the same shall apply hereinafter) standard, the technical specifications of NR (New Radio), which is a 5th generation (5G) radio access technology, are defined. NR has characteristics such as high speed, large capacity, high reliability, and low latency compared to LTE (Long Term Evolution), which is a 4th generation (4G) radio access technology. In 3GPP, discussions are being held to formulate the technical specifications of 5G / NR's multicast broadcast service (MBS) (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] It is desired that the 5G / NR multicast broadcast service provides a service improved from the 4G / LTE multicast broadcast service.

[0005] Therefore, an object of the present disclosure is to provide a communication method capable of realizing an improved multicast broadcast service.

[0006] The communication method according to the first aspect is a communication method executed by a user equipment in a mobile communication system that provides a multicast broadcast service (MBS), and when in the RRC idle state or the RRC inactive state in a serving cell, receiving or being interested in receiving an MBS session provided in the initial bandwidth part of the serving cell or an adjacent cell; and when transitioning from the RRC idle state or the RRC inactive state to the RRC connected state, transmitting an MBS interest notification regarding the MBS session to the serving cell. The MBS interest notification includes frequency information regarding the initial bandwidth part or a cell identifier of the adjacent cell without including an MBS session identifier indicating the MBS session.

[0007] The communication method according to the second aspect is a communication method executed by a user equipment in a mobile communication system that provides a multicast broadcast service (MBS), and when in the RRC idle state or the RRC inactive state in a serving cell, receiving or being interested in receiving a broadcast session; when the broadcast session is provided from the serving cell, transmitting an MBS interest notification regarding the broadcast session to the serving cell when transitioning from the RRC idle state or the RRC inactive state to the RRC connected state; and when the broadcast session is provided from a non-serving cell, omitting transmitting the MBS interest notification to the serving cell when making the transition to the RRC connected state.

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

Brief Description of Drawings

[0009]

Figure 1

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Mode for Carrying Out the Invention

[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 Mobile Communication System) FIG. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. The mobile communication system 1 complies with the 5th generation system (5GS: 5th Generation System) of the 3GPP standard. Hereinafter, the 5GS will be described as an example, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system. Further, the 6th generation (6G) system may be at least partially applied to the mobile communication system.

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

[0013] UE100 is a mobile wireless communication device. UE100 can be any device as long as it is used by a user. For example, UE100 can be a mobile phone terminal (including smartphones), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided on a sensor, a vehicle or a device provided on a vehicle (Vehicle UE), an aircraft or a device provided on an aircraft (Aerial UE).

[0014] NG-RAN10 includes base stations (referred to as "gNB" in the 5G system) 200. The gNBs 200 are interconnected via the 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 UE100 that has established a connection with its cell. The gNB 200 has functions such as a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), and a measurement control function for mobility control and scheduling. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0015] Note that the gNB can also be connected to the EPC (Evolved Packet Core) which is the core network of LTE. The base station of LTE can also be connected to the 5GC. The base station of LTE and the gNB can also be connected via an interface between base stations.

[0016] 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls and the like for the UE100. The AMF manages the mobility of the UE100 by communicating with the UE100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB200 via the NG interface, which is an interface between the base station and the core network.

[0017] Figure 2 is a diagram showing the configuration of a UE100 (user equipment) according to an embodiment. The UE100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB200.

[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 the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0019] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmitted 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 UE100. Such processes include the processes of each layer described later. 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 for 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 the programs stored in the memory to perform various processes.

[0021] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to the embodiment. The gNB 200 includes a transmission unit 210, a reception unit 220, a control unit 230, and a backhaul communication unit 240. The transmission unit 210 and the reception unit 220 constitute a radio communication unit that performs radio communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates 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 the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0023] The reception unit 220 performs various receptions under the control of the control unit 230. The reception unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0024] The control unit 230 performs various controls and processes in the gNB 200. Such processes include the processes of each layer described later. 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 for 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 the baseband signal, etc. The CPU executes programs stored in the memory to perform various processes.

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

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

[0027] The radio interface protocol of the user plane has a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0028] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the gNB 200 via a physical channel. Note that the PHY layer of the UE 100 receives downlink control information (DCI) transmitted on the physical downlink control channel (PDCCH) from the gNB 200. Specifically, the UE 100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and obtains the DCI that has been successfully decoded as the DCI addressed to the own UE. The DCI transmitted from the gNB 200 has CRC parity bits scrambled by the RNTI added thereto.

[0029] The MAC layer performs functions such as priority control of data, retransmission processing by Hybrid Automatic Repeat reQuest (HARQ), and random access procedures. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via transport channels. The MAC layer of gNB200 includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) for the uplink and downlink and the resource blocks allocated to UE100.

[0030] The RLC layer uses the functions of the MAC layer and the PHY layer to transmit data to the RLC layer on the receiving side. Between the RLC layer of UE100 and the RLC layer of gNB200, data and control information are transmitted via logical channels.

[0031] The PDCP layer performs functions such as header compression / expansion and encryption / decryption.

[0032] The SDAP layer performs the mapping between the IP flow, which is the unit for the core network to perform Quality of Service (QoS) control, and the radio bearer, which is the unit for the Access Stratum (AS) to perform QoS control. When the RAN is connected to the EPC, the SDAP may not be necessary.

[0033] Figure 5 is a diagram showing the configuration of the protocol stack of the radio interface in the control plane that handles signaling (control signals).

[0034] The protocol stack of the radio interface in the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer shown in Figure 4.

[0035] Between the RRC layer of UE100 and the RRC layer of gNB200, RRC signaling for various settings is transmitted. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in the RRC inactive state.

[0036] The NAS layer located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of UE100 and the NAS layer of AMF300A. Note that UE100 has an application layer etc. in addition to the protocol of the radio interface. Also, the layer below the NAS layer is called the AS layer.

[0037] (Overview of MBS) The overview of MBS according to the embodiment will be described. MBS is a service that enables the NG-RAN10 to transmit data to UE100 in a broadcast or multicast manner, that is, one-to-many (PTM: Point To Multipoint). The use cases (service types) of MBS are assumed to include public security communication, mission-critical communication, V2X (Vehicle to Everything) communication, IPv4 or IPv6 multicast distribution, IPTV (Internet protocol television), group communication, and software distribution, etc.

[0038] The broadcast service provides services to all UEs 100 within a specific service area for applications that do not require high-reliability QoS. The 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 for the multicast service is called a multicast session. According to the multicast service, the same content can be provided to a group of UEs 100 in a more radio-efficient way compared to the broadcast service.

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

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

[0042] From the perspective of 5GC 20, two multicast distribution methods are possible: 5GC Shared MBS Traffic delivery and 5GC Individual MBS Traffic delivery.

[0043] In the 5GC Individual MBS Traffic delivery method, 5GC 20 receives a single copy of the MBS data packet and distributes individual copies of those MBS data packets to individual UEs 100 via a PDU session for each UE 100. Therefore, it is necessary to associate one PDU session with the multicast session for each UE 100.

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

[0045] From the perspective of the RAN (5G RAN) 10, for the wireless transmission of MBS data in the 5GC common MBS traffic distribution method, two distribution methods, PTP (Point-to-Point) and PTM (Point-to-Multipoint), are possible. PTP means unicast, and PTM means multicast and broadcast.

[0046] In the PTP distribution method, the gNB 200 wirelessly distributes individual copies of MBS data packets to individual UEs 100. On the other hand, in the PTM distribution method, the gNB 200 wirelessly distributes a single copy of MBS data packets 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 mainly relate to the user plane. As control modes for MBS data distribution, there are two distribution modes: the first distribution mode and the second distribution mode.

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

[0049] The first delivery mode (Delivery mode 1: DM1) is a delivery mode available to the UE100 in the RRC connected state and is a delivery mode for high QoS requirements. The first delivery mode is used for the multicast session among the MBS sessions. However, the first delivery mode may be used for the broadcast session. The first delivery mode may also be available to the UE100 in the RRC idle state or the RRC inactive state.

[0050] The setting of MBS reception in the first delivery mode is performed by UE-dedicated signaling. For example, the setting of MBS reception in the first delivery mode is performed by an RRC Reconfiguration message (or an RRC Release message), which is an RRC message transmitted unicast from the gNB200 to the UE100.

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

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

[0053] The second delivery mode (Delivery mode 2: DM2) is a delivery mode that can be used not only by the UE100 in the RRC connected state but also by the UE100 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 the broadcast session among the MBS sessions. However, the second delivery mode may also be applicable to the multicast session.

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

[0055] In the second delivery mode, UE 100 may receive MBS data in the following three procedures. First, UE 100 receives MCCH setting information by means of an SIB (MBS SIB) transmitted on BCCH from gNB 200. Second, UE 100 receives MCCH from gNB 200 based on the MCCH setting information. MCCH transmits MTCH setting information. Third, UE 100 receives 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 settings.

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

[0057] Note that the network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a TMGI (Temporary Mobile Group Identity), a source-specific IP multicast address (which consists of a source unicast IP address such as an application function or an application server 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 internal processing related to MBS reception of the UE100 according to the embodiment. FIG. 9 is a diagram showing another example of internal processing related to MBS reception of the UE100 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 the MRB and cases where a broadcast session is associated with the MRB.

[0060] The MRB and the corresponding logical channel (e.g., MTCH) are set from the gNB200 to the UE100 by RRC signaling. The setting procedure of the MRB may be separated from the setting procedure of the data radio bearer (DRB). In RRC signaling, one MRB can be set as "PTM only", "PTP only", or "both PTM and PTP". Such a type of MRB can be changed by RRC signaling.

[0061] In FIG. 8, an example is shown where 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 a PTP only MRB, MRB#2 is a PTM only MRB, and MRB#3 is a PTM only MRB. Note that the DTCH is scheduled using the cell RNTI (C-RNTI). The MTCH is scheduled using the G-RNTI.

[0062] The PHY layer of UE100 processes the user data (received data) received on the PDSCH, which is one of the physical channels, and sends it to the downlink shared channel (DL-SCH), which is one of the transport channels. The MAC layer (MAC entity) of UE100 processes the data received on the DL-SCH and sends the received data to the corresponding logical channel (corresponding RLC entity) based on the logical channel identifier (LCID) included in the header (MAC header) included in the received data.

[0063] In FIG. 9, an example is shown where 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 the DTCH, and the other leg is associated with the 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 may be called a split MRB.

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

[0065] For example, the UE 100 may start the MBS Interest Indication procedure when the connection establishment is successful, when entering or exiting the broadcast service area, at the start or stop of an MBS broadcast session, when there is a change in MBS interest, when there is a change in priority between MBS broadcast reception and unicast reception, or when there is a change to the cell (primary cell) that broadcasts the SIB for MBS service continuity.

[0066] The MBS Interest Indication may include at least one of an MBS frequency list, which is a list of MBS frequencies that the UE 100 is receiving or interested in receiving; priority information indicating whether to prioritize the reception of all the listed MBS frequencies or the reception of unicast bearers; and a TMGI list, which is a list of MBS sessions that the UE 100 is receiving or interested in receiving.

[0067] (BWP) In 5G / NR, bandwidth parts (BWPs) are defined to reduce the power consumption of the UE 100 and to effectively utilize wideband carriers. The UE 100 with a configured BWP can communicate in a frequency band narrower than the cell bandwidth. There are an initial BWP (initial DL BWP and initial UL BWP) and a dedicated BWP (dedicated DL BWP and dedicated UL BWP). Here, DL refers to the downlink and UL refers to the uplink. The initial BWP is at least the BWP used for initial access and is commonly used by multiple UEs 100. The dedicated BWP is a BWP configured specifically (UE-specific) for a certain UE 100. Up to a maximum of four DL BWPs and up to a maximum of four UL BWPs can be configured for a single serving cell in the UE 100 according to its capabilities. Note that hereinafter, when the DL BWP and the UL BWP are not distinguished, they are simply referred to as BWP.

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

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

[0070] gNB 200 can notify UE 100 of the BWP (i.e., the active BWP) used for communication with gNB 200 among the one or more configured BWPs. For example, gNB 200 can send a BWP identifier indicating the BWP to be activated at the time of configuration, i.e., the BWP used first in communication with gNB 200, to UE 100. Also, for controlling the switching from the active BWP to a non-active BWP (hereinafter referred to as a non-active BWP) and from the non-active BWP to the active BWP, for example, PDCCH (DCI), RRC signaling, MAC control element (MAC CE), or timer-based switching is used.

[0071] In consideration of such BWP operations, in MBS, an MBS common frequency resource (CFR) through which a plurality of UEs 100 can commonly perform MBS reception is introduced. FIG. 10 is a diagram for explaining the 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 the PDCCH and PDSCH common to the broadcast session (i.e., MCCH and MTCH) be restricted 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 partially overlap, fully overlap, or not overlap at all with the initial BWP (or CORESET #0).

[0072] (Operation of Mobile Communication System) Assume a scenario in which a UE 100 that is receiving or interested in receiving a broadcast session in the RRC idle state or the RRC inactive state transitions to the RRC connected state. The second delivery mode described above is applied to this scenario. Hereinafter, the BWP mainly means a DL BWP.

[0073] When the UE100 transitions to the RRC connected state, a dedicated BWP can be configured from the gNB200. For example, when the UE100 transitions from the RRC inactive state to the RRC connected state, a dedicated BWP can be configured from the gNB200 by MSG4 (RRC Resume) of the random access procedure. When the UE100 transitions from the RRC idle state to the RRC connected state, a dedicated BWP can be configured from the gNB200 by RRC reconfiguration after the random access procedure.

[0074] Here, since the gNB200 has not received an MBS interest notification from the UE100 during the random access procedure, it cannot grasp the MBS interest of the UE100. Therefore, the gNB200 may configure a dedicated BWP that does not cover the CFR for the UE100 that is receiving or interested in receiving the broadcast session. When a dedicated BWP that does not cover the CFR is configured for the UE100, there is a problem that the UE100 cannot receive the broadcast session.

[0075] Also, during the random access procedure, the security settings of the UE100 are not activated. Therefore, it is difficult for the UE100 to send an MBS interest notification during the random access procedure. Specifically, since the TMGI list in the MBS interest notification may correspond to personal information that requires security, it is considered that the transmission of the TMGI list is not permitted before the security settings are activated.

[0076] After the security settings of the UE100 are activated, by sending an MBS interest notification from the UE100 to the gNB200, it is possible for the gNB200 to grasp the MBS interest of the UE100 and configure and activate a dedicated BWP that covers the CFR for the UE100. However, before the security settings of the UE100 are activated, the UE100 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 the RRC idle state or the RRC inactive state in the serving cell, it receives or is interested in receiving the broadcast session provided 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, it 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 the 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 an MBS interest notification not including the TMGI to the serving cell when transitioning to the RRC connected state, it can transmit the MBS interest notification to the gNB 200 early before the security settings are 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, MSG3 may be an RRC resume request message and MSG5 may be an RRC resume completion message. When transitioning from the RRC idle state to the RRC connected state, MSG3 may be an RRC setup request message and MSG5 may be an RRC setup completion message. Also, since the MBS interest notification includes frequency information regarding the CFR (or initial BWP), it becomes easier for the gNB 200 to set a dedicated BWP covering the initial BWP or CFR for the UE 100. As a result, the UE 100 can receive the broadcast session in the CFR.

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

[0080] In step S101, UE100 is in the RRC idle state or the RRC inactive state. UE100 uses the initial BWP configured by gNB200.

[0081] In step S102, UE100 in the RRC idle state or the RRC inactive state receives or is interested in receiving a broadcast session. When UE100 receives a broadcast session, it receives the MCCH and MTCH transmitted with CFR.

[0082] In step S103, UE100 starts 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), UE100 transmits an RRC Setup Complete message or an RRC Resume Complete message (MSG5) to gNB200. Note that MSG1 to MSG5 constitute the random access procedure.

[0087] In step S108, UE100 transitions to the RRC connected state through such a random access procedure.

[0088] During the random access procedure, UE100 sends an MBS interest notification regarding the broadcast session it is receiving or interested in receiving to gNB200 in MSG3 or MSG5. The MBS interest notification may include frequency information regarding the CFR (or initial BWP) without including the MBS session identifier (TMGI) indicating the broadcast session. The frequency information includes at least one of the identifier of the initial BWP, the identifier of the common frequency resource, the identifier indicating the frequency or resource block corresponding to the initial BWP, and the identifier indicating the 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 bandwidth). The identifier indicating the resource block may be the resource block number (and the number of resource blocks). Based on such frequency information, gNB200 may set (and activate) a dedicated BWP covering the initial BWP or CFR for UE100 by means of an MSG4 or RRC Reconfiguration message. Even when the MBS interest notification does not include the frequency information, since gNB200 can recognize that the UE100 is receiving (or interested in receiving) the broadcast session, it is possible to take measures such as withholding the setting of the dedicated BWP.

[0089] UE100 may send an MBS interest notification to gNB200 in MSG5 (RRC setup complete message or RRC resume complete message). UE100 already has the content to be reported in the MBS interest notification (such as frequency information), and when receiving an MBS session (broadcast session), UE100 may send an MBS interest notification to gNB200 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 (MBS frequency list) that UE100 is receiving or interested in receiving. The MBS interest notification may include priority information indicating which of the reception of the MBS frequencies in the list and the reception of unicast bearers is to be prioritized. Based on the MBS interest notification, gNB200 may set (and activate) a dedicated BWP covering the initial BWP or CFR for UE100. Alternatively, gNB200 may control not to set (or activate) a dedicated BWP for UE100 based on the MBS interest notification. The MBS interest notification may be sent in the same message as Msg3 or Msg5. In this case, the MBS interest notification may be sent encapsulated in Msg3 or Msg5, or the information element of the MBS interest notification may be stored in and sent in Msg3 or Msg5. The MBS interest notification may be sent at the same timing as Msg3 or Msg5. In this case, the MBS interest notification is sent as a message different from Msg3 or Msg5.

[0090] (Example 1 of change in operation of mobile communication system) In the above embodiment, a scenario where UE100 receives a broadcast session provided by a serving cell was assumed. However, UE100 may receive a broadcast session provided by a non-serving cell (adjacent cell). When receiving a broadcast session from a non-serving cell, even if a dedicated BWP that does not cover CFR is set in the serving cell, it does not affect the reception of the broadcast session.

[0091] In this modification example, UE100 operates as follows. First, when in the RRC idle state or the RRC inactive state in the serving cell, UE100 receives or is interested in receiving a broadcast session. Second, when the broadcast session is provided from the serving cell, UE100 transmits an MBS interest notification regarding the broadcast session to the serving cell when transitioning from the RRC idle state or the RRC inactive state to the RRC connected state. Here, when the broadcast session is provided from a non-serving cell (adjacent cell), UE100 omits transmitting the MBS interest notification to the serving cell when transitioning to the RRC connected state.

[0092] FIG. 12 is a diagram showing an operation example of UE100 according to this modification example.

[0093] In step S201, UE100 in the RRC idle state or the RRC inactive state receives or is interested in receiving a broadcast session. UE100 may identify an adjacent cell that provides a broadcast session (TMGI) of its interest from the adjacent cell information included in the MCCH.

[0094] In step S202, UE100 determines whether the broadcast session it is receiving or is interested in receiving is provided from the serving cell.

[0095] When the broadcast session is provided from the serving cell (step S202: YES), in step S203, UE100 transmits an MBS interest notification to the serving cell (gNB200) during the random access procedure. UE100 may transmit the MBS interest notification to the serving cell on the basis of the criterion that the broadcast session can be received only from the serving cell. The fact that it can be received only from the serving cell means, for example, that the broadcast session is provided only from the serving cell, or that the UE100 cannot receive the broadcast session from non-serving cells depending on its capabilities. The MBS interest notification may be the same MBS interest notification as in the above-described embodiment. In this modification example, the MBS interest notification may be flag information indicating that it is receiving or is interested in receiving a broadcast session. The MBS interest notification may be transmitted to the serving cell in MSG1. For example, the MBS interest notification may be a random access preamble transmitted in a special preamble sequence or a special PRACH resource indicating that it is receiving or is interested in receiving a broadcast session.

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

[0097] (Modification Example 2 of the Operation of the Mobile Communication System) In this modification example, UE100 enables reception of a broadcast session in the initial BWP (CFR) by not applying the setting of the dedicated BWP from the serving cell (gNB200).

[0098] Specifically, in this modification example, UE 100 operates as follows. First, when UE 100 is in the RRC idle state or RRC inactive state in the serving cell, UE 100 receives or is interested in receiving the broadcast session transmitted in the CFR (or initial BWP) of the serving cell. Second, when UE 100 transitions from the RRC idle state or RRC inactive state to the RRC connected state, UE 100 receives from the serving cell a message (MSG4 or RRC Reconfiguration message) that sets a dedicated BWP different from the CFR (or initial BWP) for UE 100. Third, even when UE 100 receives the message, UE 100 continues to use the initial BWP (or receive the broadcast session in the CFR) without applying the setting of the dedicated BWP. UE 100 may send a notification to the serving cell indicating that it does not apply the setting of the dedicated BWP according to the message.

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

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

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

[0102] In step S303, UE 100 starts a random access procedure and transmits a random access preamble (MSG1) to gNB 200.

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

[0104] In step S305, in response to receiving a 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 an RRC Setup Request message or an RRC Resume Request message (MSG3), gNB200 transmits an RRC Setup message or an RRC Resume message (MSG4) to UE100. Here, gNB200 configures a dedicated BWP for UE100.

[0106] In step S306, if UE100 cannot receive a broadcast session by means of the dedicated BWP, that is, if the dedicated BWP does not cover the CFR, UE100 suspends (or cancels) the dedicated BWP configuration. Here, UE100 may maintain the initial BWP in an active state.

[0107] UE100 may notify gNB200 that it has suspended the configuration of the dedicated BWP. UE100 may also notify gNB200 that it maintains the initial BWP in an active state. Such notification may be an RRC message (such as an MBS interest notification or a UAI, etc.) or a MAC CE (Control Element). The notification may include an identifier of the suspended BWP. Further, the notification may include an identifier of the actually applied BWP (such as the initial BWP, etc.).

[0108] When gNB200 recognizes based on the said notification that the configuration of the dedicated BWP is suspended, it does not perform transmission and reception using the dedicated BWP (does not activate the dedicated BWP).

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

[0110] In step S308, UE100 transitions to the RRC connected state through a random access procedure.

[0111] Note that after the security configuration is activated (security activation), UE100 may send an MBS interest notification including an MBS session identifier (TMGI) to gNB200. As a result, gNB200 may de-configure the dedicated BWP setting from UE100.

[0112] (Modification Example 3 of the Operation of the Mobile Communication System) In the above-described embodiment, it was mainly assumed that gNB200 configures a dedicated BWP for UE100. In this modification example, it is mainly assumed that gNB200 configures carrier aggregation for UE100. As described above, UE100 can receive a broadcast session from a non-serving cell (adjacent cell). Therefore, if gNB200 can grasp the non-serving cell (adjacent cell) that provides the broadcast session that UE100 is receiving or is interested in receiving, it becomes easy for gNB200 to configure the non-serving cell (adjacent cell) as part of the carrier aggregation (specifically, a secondary cell).

[0113] Specifically, in this modification example, UE 100 operates as follows. First, when UE 100 is in the RRC idle state or the RRC inactive state in the serving cell, it receives or is interested in receiving an MBS session (e.g., a broadcast session) provided in an adjacent cell. Second, when transitioning from the RRC idle state or the RRC inactive state to the 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 the MBS session identifier (TMGI) but includes the cell identifier of the adjacent cell. When transmitting MSG5 (RRC setup complete message or RRC resume complete message) to the serving cell, UE 100 may transmit an MBS interest notification including the cell identifier of the adjacent cell to the serving cell.

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

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

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

[0117] In step S403, UE 100 starts a random access procedure and transmits a random access preamble (MSG1) to gNB 200.

[0118] In step S404, in response to receiving the random access preamble (MSG1), gNB 200 transmits a random access response (MSG2) to UE 100.

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

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

[0121] In step S407, in response to receiving an RRC Setup message or an RRC Resume message (MSG4), UE100 sends an RRC Setup Complete message or an RRC Resume Complete message (MSG5) to gNB200. Here, UE100 sends an MBS interest notification including the cell identifier of an adjacent cell that provides a broadcast session that UE100 is receiving or is interested in receiving to gNB200. The MBS interest notification does not include a TMGI.

[0122] In step S408, UE100 transitions to the RRC connected state through a random access procedure. When gNB200 sets carrier aggregation for UE100 in the first RRC Reconfiguration for UE100, gNB200 may set the adjacent cell notified in the MBS interest notification as a secondary cell for UE100.

[0123] In this modification example, the MBS interest notification sent during the random access procedure has been mainly described. However, the MBS interest notification including a cell identifier may also be sent by UE100 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 embodiments and their modified examples, 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 to the gNB 200 as MSGA. The gNB 200 may transmit a set of a random access response (MSG2) and the above-described MSG4 to the UE 100 as MSGB.

[0125] Each of the above operation flows is not limited to being implemented separately and independently, and two or more operation flows can be combined and implemented. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0126] In the above embodiments and examples, an example where 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. Further, 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. Further, 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 the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. By using the computer-readable medium, it is possible to install the program in the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Also, a circuit that executes each process performed by the UE 100 or the gNB 200 may be integrated, and at least a part of the UE 100 or the gNB 200 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, unless otherwise specified, mean "only based on" or "only depending on". The term "based on" means both "only based on" and "at least partially based on". Similarly, the term "depending on" means both "only depending on" and "at least partially depending on". Also, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from other nodes, or obtaining the information by generating the information. The terms "include", "comprise", and their variants do not mean including only the listed items, but may include only the listed items or may include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to be an exclusive disjunction. Further, any reference to an element using designations such as "first", "second", etc. used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Thus, a reference to a first and a second element does not mean that only two elements can be employed there or that the first element must precede the second element in some form. In this disclosure, for example, when articles are added by translation, such as a, an, and the in English, these articles shall be construed to include plural ones unless the context clearly indicates otherwise.

[0129] As described above in detail with reference to the drawings, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

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

[0131] (Appendix) 1. Introduction The revised work item for NR Multicast and Broadcast Services (MBS) was approved at RAN#88. At RAN2#116e, significant progress was made on the details of the MBS Interest Indication (MII).

[0132] In this appendix, the remaining issues regarding the MBS interest indication are discussed.

[0133] 2. Discussion 2.1. Definition of Messages The currently running CR in TS38.331 incorporates the following matters that require further consideration.

[0134] Regarding whether the MII (MBMS Interest Indication) is reported in the UE Assistance Information or a new RRC message, and whether the MII information uses another IE or is directly included in the RRC message structure, further consideration is required.

[0135] In LTE, the MBMS Interest Indication (MII) is separated from the UE Assistance Information (UAI). This is because the preconditions for obtaining SIB15 in MII and RRC Connection Reconfiguration in UAI are different. On the other hand, the IDC (In-device Coexistence Indication), 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 in LTE (and NR) are the same, namely RRC Connection Reconfiguration.

[0136] Observation 1: Whether the MBS interest notification can be integrated with the UE Assistance Information depends on whether the preconditions match between the two messages.

[0137] In NR MBS, in order to generate the MBS interest notification message containing the above IEs, the neighboring frequency information in the SIB is required. Also, when the UE can obtain the SIB from the serving cell, the transmission of the MBS interest notification is permitted, which, similar to LTE eMBMS, has already been understood under the condition in the approved CR that "if SIBx1 is broadcast from the PCell". Therefore, it does not match the RRC Reconfiguration which is a precondition of UAI. Thus, the MBS interest notification should be a separate message from UAI, like in LTE eMBMS.

[0138] Proposal 1: RAN2 should agree to define the MBS interest notification as a new message, that is, separate from UAI.

[0139] Proposal 2: RAN2 should agree to permit the transmission of the MBS interest notification when the UE can obtain the MBS-specific SIB (i.e., SIBx1) from the serving cell (i.e., as a precondition).

[0140] 2.2. Other Triggers and Network Controls The following matters that require further consideration have been incorporated into the current running CR.

[0141] Regarding other triggers and network controls, further consideration is required.

[0142] In RAN2#116e, agreements have been reached on various triggers of the MBS interest notification. The UE shall confirm that it can initiate the MII procedure when it successfully establishes a connection, enters or exits the broadcast service area, starts or stops an MBS broadcast session, changes its interests, changes the priority between MBS broadcast reception and unicast reception, or changes to PCell broadcast SIBx1. Further consideration is required for other triggers and network controls.

[0143] Regarding additional triggers, it is considered necessary to send an MBS interest notification when the frequency list changes. In RAN2#116e, the following agreement was reached on the detailed operations regarding the method of setting the interested frequencies.

[0144] During the MII, the UE shall only report the set of MBS frequencies that the UE can receive simultaneously. That is, the UE shall support at least one combination of bands and be able to receive the set of indicated frequencies.

[0145] When evaluating the frequencies that can be received simultaneously for reporting in the MII, the UE does not consider the currently configured serving frequency. That is, only the MBS frequencies that the UE is interested in receiving are considered, 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 (such as adding or deleting an SCell), the frequency list may be changed because it may affect the combinations of bandwidths that the UE can currently operate. In this case, if it is different from the frequency list reported in the previous MBS interest notification, it may be necessary to report the latest interested frequencies to the serving cell. Therefore, 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 serving cell configuration.

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

[0148] Regarding network control, it is undoubtedly useful to be able to manage the transmission of MBS interest notifications from a large number of UEs in order to avoid network congestion. The problems that cause resource overload include the "spike" and "frequent" MBS interest notifications.

[0149] Finding 2: If MBS interest notifications increase suddenly from many UEs or are frequently sent from a certain UE, network congestion may occur.

[0150] Regarding the sudden increase in transmission, it occurs when a huge number of UEs send MBS interest notifications simultaneously. Since this is an event common to all UEs interested in the MBS broadcast session, the trigger that may cause this problem may be the "start or stop of the MBS broadcast session". In particular, when the session stops, since the gNB already knows that the MBS broadcast session has been stopped by the CN, even without an MBS interest notification, the UE can determine that it is no longer interested in this TMGI. Considering these scenarios, as network control, it is conceivable to spread the MBS interest notification in the time domain and / or frequency domain (e.g., session start), or turn the MBS interest notification on / off at this event (e.g., session stop).

[0151] Regarding frequent transmission, it occurs when the UE frequently changes its interest due to user preferences, etc. The triggers that may cause this problem include "change of interest", "change in the priority of MBS broadcast reception and unicast reception", etc. As network control, it is conceivable to set a prohibited timer for the UE.

[0152] For other triggers, namely "successful connection establishment", "entry into / exit from the broadcast service area", and "change to the PCell that broadcasts SIBx1", since these are (temporally) sufficiently randomized or already controlled by the network, it can be considered that no major problems will occur.

[0153] Based on the above discussion, it was confirmed that different triggers may require different control methods, namely diffusion, on / off, and prohibited timers, and some other triggers may not require any enhancement. 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 the UE from experiencing a sharp increase and frequent transmissions due to MBS interest notifications.

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

[0156] 2.3 Early Notification for Improving BWP Switching Operations This consideration item is incorporated into the current ongoing CR based on the RAN2 consensus that "MBS interest notifications are sent after security activation (it is still possible to discuss whether additional optimizations are required for better BWP switching operations)". Further consideration is required to determine whether additional optimizations are needed to improve the BWP switching operation.

[0157] Further consideration is required to determine whether additional optimizations are needed for better BWP switching operations.

[0158] The problem of service continuity occurs when the UE transitions to the connected state. Specifically, when the serving cell configures a dedicated BWP that is not in alignment with the CFR for the UE, the UE cannot continue to receive the broadcast session. Such a configuration can be avoided after the MBS interest notification, but 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 pointed out that an inactive UE can configure a dedicated BWP in Msg4 (RRC Resume). To notify the serving cell that the UE is receiving the MBS broadcast session, it has been proposed to provide a 1-bit indication in Msg3. The serving cell has the UE context of the inactive UE, which includes the previously reported MBS interest notification. Although this interest information is not up-to-date, the serving cell is expected to predict whether a UE transitioning from the inactive state to the connected state is receiving the broadcast session. Therefore, considering the limited message size, it is not important to extend Msg3.

[0160] It has been proposed to introduce an early "broadcast reception" indication in Msg5, which is information for the serving cell to configure a dedicated BWP in the next RRC Reconfiguration. This solution is useful while being a simple extension.

[0161] According to the LS from SA3, they are only concerned with reporting the TMGI list before AS security activation. Furthermore, it is explicitly stated that other information (frequency list and priority information) can be reported before the activation of AS security. Therefore, it is considered that the UE can send an early MBS interest notification, which is sent together with Msg5 and contains full content other than the TMGI list, that is, the frequency list and priority information instead of the above 1-bit indication. When the gNB receives the early MBS interest notification in Msg5, since the MBS interest notification is for the second delivery mode, it can determine whether this UE is receiving the broadcast session. Also, even if the TMGI that the UE is interested in is still unknown, the full content may be useful for the gNB to determine the appropriate configuration (e.g., SCell configuration) for different frequencies. Since these contents are finally reported after the activation of AS security, there is no signaling overhead if they are reported in the early MBS interest notification.

[0162] Furthermore, it is also worth considering whether additional information is required for the early MBS interest notification. For example, the UE reports the CFR 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 CFR is part of the dedicated BWP. As another example, the UE reports the Cell ID in which the MBS broadcast session of interest is provided in the early MBS interest notification.

[0163] Proposal 6: RAN2 needs to consider whether to send an early MBS interest notification together with Msg5 that contains full content other than the TMGI list, that is, the frequency list and priority information.

[0164] Proposal 7: RAN2 should further discuss whether it is useful for additional information to be reported in the early MBS interest notification, for example, regarding CFR or the cell ID of interest.

[0165] 2.4. MBS Interest Notification for Multicast Sessions RAN2 currently assumes that MBS interest notification is supported in the broadcast session and not in the multicast session. RAN2 #115e reached an agreement on the basic content of the MBS interest notification, namely the MBS frequency list, priority, and TMGI list.

[0166] In the multicast session, since there is a session participation procedure at the upper layer, it is generally understood that the core network notifies the gNB of the UE's interests. The UE's interests are considered to also apply to MBS services. Also, the gNB may know the frequencies of MBS that the UE is interested in and the cells that provide the MBS services. However, since the priority between MBS reception and unicast is purely AS-related information, it may not be provided by the core network. That is, it is unnatural for the UE to convey priority information to the core network during the session participation procedure.

[0167] Finding 3: In the multicast session, the core network provides the gNB with MBS services that are of interest to the UE. The gNB may know the MBS frequencies / cells, but the core network and the gNB may not know the UE's AS priority between MBS and unicast.

[0168] Priority information is also useful at the gNB, for example, in scheduling and handover decisions, similar to LTE eMBMS, and is considered to be related to service continuity. Therefore, the UE should also notify the gNB of its priority information for the multicast session. In this sense, RAN2 should reach an agreement that MBS interest notification should also be supported for multicast services / primary delivery mode.

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

Description of Signs

[0170] 1: Mobile communication system 10: RAN 20: CN 100: UE 110: Receiver 120: Transmitter 130: Control unit 200: gNB 210: Transmitter 220: Receiver 230: Control unit 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 includes information about a non-serving cell that provides the MBS session. Communication methods.

2. 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 includes information about a non-serving cell that provides the MBS session. User equipment.

3. 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 includes information about a non-serving cell that provides the MBS session. Network node.

4. 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 includes information about a non-serving cell that provides the MBS session. Chipset.

5. 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 includes information about a non-serving cell that provides the MBS session. program.

6. 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 includes information about a non-serving cell that provides the MBS session. Mobile communication system.

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