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

Abstract

To provide a communication method and user equipment that enable an improved multicast and broadcast service.SOLUTION: A communication method is performed by user equipment (UE) 100 in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a multicast and broadcast service (MBS). The communication method includes the steps of receiving system information (SI) scheduling information broadcast by a neighboring cell belonging to a desired MBS frequency associated with a desired MBS service, and prioritizing the desired MBS frequency over other frequencies in a cell re-selection procedure when the SI scheduling information indicates that the neighboring cell has a capability of providing an MBS system information block.SELECTED DRAWING: Figure 12

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) (registered trademark; hereinafter the same) standard specifies the technical specifications of NR (New Radio), a fifth-generation (5G) wireless access technology. Compared with LTE (Long Term Evolution), a fourth-generation (4G) wireless access technology, NR has features such as high speed, large capacity, high reliability, and low latency. Discussions are underway in 3GPP to formulate technical specifications for 5G / NR multicast and broadcast services (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] 5G / NR multicast and broadcast services are expected to provide improved services over 4G / LTE multicast and broadcast services.

[0005] Therefore, an object of the present disclosure is to provide a communication method and user equipment that enable improved multicast / broadcast services.

[0006] A communication method according to a first aspect is a communication performed by a user equipment in a Radio Resource Control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a Multicast and Broadcast Service (MBS), comprising the steps of receiving system information (SI) scheduling information broadcast by a neighboring cell belonging to a desired MBS frequency associated with a desired MBS service, and prioritizing the desired MBS frequency over other frequencies in the cell reselection procedure if the SI scheduling information indicates that the neighboring cell has the capability to provide MBS system information blocks.

[0007] A communication method according to a second aspect is communication performed by a user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a multicast broadcast service (MBS). The communication method includes a step of selecting one of broadcast information provided by a network in an RRC layer by broadcast and higher layer information provided by the network in a layer higher than the RRC layer, and a step of prioritizing a desired MBS frequency associated with a desired MBS service so as to be given priority over other frequencies in a cell reselection procedure. Each of the broadcast information and the higher layer information is information indicating a correspondence between an MBS service and a frequency. The step of prioritizing includes a step of prioritizing based on the one of the information selected in the step of selecting.

[0008] A communication method according to a third aspect is a communication performed by a user equipment in a Radio Resource Control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a Multicast and Broadcast Service (MBS), comprising the steps of: identifying at least one cell for which a result of a measurement on at least one cell belonging to a desired MBS frequency associated with a desired MBS service satisfies a predetermined criterion; and prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure if the user equipment determines that the identified cell broadcasts an MBS system information block.

[0009] A communication method according to a fourth aspect is a communication performed by a user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a multicast and broadcast service (MBS). The communication method includes the steps of: prioritizing a desired MBS frequency in a cell reselection procedure over other frequencies when the user equipment determines that at least one cell belonging to a desired MBS frequency associated with a desired MBS service broadcasts an MBS system information block; identifying a candidate cell from the desired MBS frequency based on a measurement result for the desired MBS frequency; and reselecting the candidate cell if the identified candidate cell is included in the at least one cell.

[0010] A communication method according to a fifth aspect is communication performed by a user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a multicast and broadcast service (MBS). The communication method includes the steps of: reselecting a cell belonging to a desired MBS frequency associated with a desired MBS service by prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure; determining whether the cell provides the desired MBS service based on a multicast control channel transmitted from the cell; and redoing the cell reselection procedure if it is determined in the determining step that the cell does not provide the desired MBS service.

[0011] A communication method according to a sixth aspect is communication performed by a user equipment in a Radio Resource Control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a Multicast Broadcast Service (MBS). The communication method includes the steps of receiving system information broadcast by a neighboring cell belonging to a desired MBS frequency associated with a desired MBS service, the system information including information on whether the MBS service provision in the neighboring cell is restricted or not, and prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure in response to the system information indicating that the MBS service provision is not restricted, the system information being a system information block type 1 or a master information block. [Brief description of the drawings]

[0012] [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] 2 is a diagram showing an example of internal processing related to MBS reception of the UE 100 according to the embodiment. FIG. [Figure 9] FIG. 11 is a diagram showing another example of the internal processing related to MBS reception of the UE 100 according to the embodiment. [Figure 10] FIG. 1 is a diagram for explaining an overview of a cell reselection procedure according to an embodiment. [Figure 11] FIG. 1 is a diagram showing a schematic flow of a cell reselection procedure according to an embodiment. [Figure 12] FIG. 2 is a diagram showing an example of operation of the mobile communication system according to the first embodiment. [Figure 13] FIG. 11 is a diagram illustrating a first operation example according to the second embodiment. [Figure 14] FIG. 11 is a diagram illustrating a second operation example according to the second embodiment. [Figure 15] FIG. 13 is a diagram illustrating an example of the operation of a cell reselection procedure according to the third embodiment. [Figure 16] FIG. 13 is a diagram showing a cell reselection procedure according to a modification of the third embodiment. [Figure 17] FIG. 13 is a diagram illustrating an example of the operation of a cell reselection procedure according to the fourth embodiment. [Figure 18] FIG. 13 is a diagram showing a cell reselection procedure according to a modification of the fourth embodiment. [Figure 19] FIG. 13 is a diagram showing one-step setting of the second distribution mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] [First embodiment] (Configuration of a mobile communication system) FIG. 1 is a diagram showing a configuration of a mobile communication system according to a first 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 an LTE (Long Term Evolution) system. Also, the mobile communication system may be at least partially applied to a 6th Generation (6G) system.

[0015] 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.

[0016] 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).

[0017] 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").

[0018] 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.

[0019] 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.

[0020] 2 is a diagram showing a configuration of a UE 100 (user equipment) according to the first 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 3 is a diagram showing the configuration of the gNB200 (base station) according to the first embodiment. The gNB200 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 CN20.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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.

[0039] 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.

[0040] (Overview of MBS) An overview of the MBS according to the first 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.

[0041] 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.

[0042] The multicast service provides a service to a group of UEs 100 participating in the multicast service (multicast session), rather than to all UEs 100. An MBS session used in the multicast service is called a multicast session.

[0043] FIG. 6 is a diagram showing an overview of MBS traffic delivery according to the first embodiment.

[0044] 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.

[0045] From the 5GC20 perspective, two multicast delivery methods are possible: 5GC Shared MBS Traffic delivery and 5GC Individual MBS Traffic delivery.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] FIG. 7 is a diagram showing distribution modes according to the first embodiment.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] In the second distribution mode, the UE 100 may receive MBS data in the following three procedures. First, the UE 100 receives MCCH setting information by an MBS system information block (MBS SIB) transmitted on the BCCH from the gNB 200. Second, the UE 100 receives the MCCH from the gNB 200 based on the MCCH setting information. The MCCH transmits MTCH setting information. The MCCH may include neighboring cell information indicating whether the currently provided MBS session is also provided in a neighboring cell. Third, the UE 100 receives the MTCH (MBS data) based on the MTCH setting information. Hereinafter, the MTCH setting information and / or the MCCH setting information may be referred to as MBS reception setting. In the following embodiment, a case where the UE 100 receives an MBS session distributed in the second distribution mode will be mainly described.

[0059] 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).

[0060] 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.

[0061] Fig. 8 is a diagram showing an example of internal processing related to MBS reception of the UE 100 according to the first embodiment. Fig. 9 is a diagram showing another example of internal processing related to MBS reception of the UE 100 according to the first embodiment.

[0062] 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.

[0063] 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 RRC signaling, one MRB can be configured with "PTM only", "PTP only", or "both PTM and PTP". The bearer type of such an MRB can be changed by RRC signaling.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] (Overview of cell reselection procedure) An overview of the cell reselection procedure will now be described. Fig. 10 is a diagram for explaining an overview of the cell reselection procedure.

[0068] UE100 in the RRC idle state or the RRC inactive state performs a cell reselection procedure to transition from a current serving cell (cell #1) to a neighboring cell (any of cells #2 to #4) as it moves. Specifically, UE100 identifies a neighboring cell on which it should camp by the cell reselection procedure, and reselects the identified neighboring cell. A case where the frequency (carrier frequency) of the current serving cell and the neighboring cell is the same is called intra-frequency, and a case where the frequency (carrier frequency) of the current serving cell and the neighboring cell is different is called inter-frequency. The current serving cell and the neighboring cell may be managed by the same gNB200. Also, the current serving cell and the neighboring cell may be managed by different gNB200s.

[0069] FIG. 11 shows a schematic flow diagram of a cell reselection procedure.

[0070] In step S1, the UE 100 performs frequency prioritization processing based on the priority for each frequency specified by the gNB 200, for example, by a system information block or an RRC release message. Specifically, the UE 100 manages the frequency priority specified by the gNB 200 for each frequency. Although details will be described later, the UE 100 that is receiving an MBS service or is interested in receiving an MBS service may perform prioritization so as to give priority to an MBS frequency associated with the MBS service over other frequencies.

[0071] The term "MBS service" means an MBS session, but is not limited to this, and may mean an MBS service area. Similarly, the term "MBS service identifier" means an MBS session identifier (e.g., TMGI), but is not limited to this, and may mean an MBS service area identifier (MBS SAI). Furthermore, the term "frequency" means a carrier frequency, but is not limited to this, and may mean a cell. Hereinafter, an MBS service that UE 100 is receiving or is interested in receiving is referred to as a "desired MBS service", and a frequency associated with the desired MBS service is referred to as a "desired MBS frequency".

[0072] In step S2, the UE 100 performs a measurement process to measure radio quality for each of the serving cell and the neighboring cell. The UE 100 measures the reception power and reception quality of reference signals transmitted by each of the serving cell and the neighboring cell, specifically, CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, the UE 100 always measures radio quality for a frequency having a higher priority than the priority of the frequency of the current serving cell. In addition, for a frequency having a priority equal to or lower than the priority of the frequency of the current serving cell, the UE 100 measures the radio quality of the frequency having the same priority or lower priority when the radio quality of the current serving cell falls below a predetermined quality.

[0073] In step S3, the UE 100 performs a reselection process of reselecting a cell on which the UE 100 camps based on the measurement result in step S2. For example, when the frequency priority of the neighboring cell is higher than the priority of the current serving cell, and the neighboring cell satisfies a predetermined quality standard (i.e., a minimum required quality standard) for a predetermined period, the UE 100 may perform cell reselection to the neighboring cell. When the frequency priority of the neighboring cell is the same as the priority of the current serving cell, the UE 100 may rank the radio quality of the neighboring cell and perform cell reselection to the neighboring cell having a higher rank than the rank of the current serving cell for a predetermined period. When the frequency priority of the neighboring cell is lower than the priority of the current serving cell, and the radio quality of the current serving cell is lower than a certain threshold and the radio quality of the neighboring cell is higher than another threshold, the UE 100 may perform cell reselection to the neighboring cell.

[0074] (Mobile communication system operation) As described above, the UE 100 that is receiving an MBS or is interested in receiving an MBS performs a frequency prioritization process to prioritize a desired MBS frequency associated with a desired MBS service over other frequencies. For example, the UE 100 determines the frequency priority of the desired MBS frequency to be the highest priority (e.g., a priority higher than any priority that the network can specify). This makes it easier for the desired MBS service to be continuously provided to the UE 100.

[0075] Currently, it is assumed that the UE 100 prioritizes the desired MBS frequency over other frequencies, provided that the neighboring cell belonging to the desired MBS frequency provides an MBS SIB (i.e., an SIB that transmits an MCCH configuration). However, unlike the minimum system information (Minimum SI) that each cell constantly broadcasts, specifically, the Master Information Block (MIB) and the System Information Block Type 1 (SIB1), the MBS SIB may be an on-demand SI that is broadcast upon request from the UE 100. Therefore, even if a cell has the ability to provide the MBS SIB by broadcast, it does not necessarily provide the MBS SIB.

[0076] Therefore, if a neighboring cell belonging to the desired MBS frequency is required to provide an MBS SIB as a condition for prioritizing the desired MBS frequency over other frequencies, the UE 100 may need to request each neighboring cell to transmit an MBS SIB for the cell reselection procedure. Such an operation increases the power consumption and MBS reception delay of the UE 100, and is not efficient.

[0077] In the first embodiment, a UE 100 in an RRC idle state or an RRC inactive state receives system information (SI) scheduling information broadcast by a neighboring cell belonging to a desired MBS frequency associated with a desired MBS service. The SI scheduling information is an information element included in SIB1. If the SI scheduling information indicates that the neighboring cell has the capability to provide an MBS SIB, the UE 100 prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure.

[0078] That is, in the first embodiment, the UE 100 performs frequency prioritization processing according to whether the neighboring cell has the ability to provide the MBS SIB, not whether the neighboring cell broadcasts the MBS SIB. Specifically, even if the neighboring cell belonging to the desired MBS frequency does not broadcast the MBS SIB, if the neighboring cell has the ability to provide the MBS SIB, the UE 100 performs prioritization so that the desired MBS frequency is given priority over other frequencies in the cell reselection procedure. This eliminates the need for the UE 100 to request each neighboring cell to transmit the MBS SIB, thereby making the cell reselection procedure more efficient.

[0079] FIG. 12 is a diagram showing an example of the operation of the mobile communication system 1 according to the first embodiment.

[0080] In step S101, AF (Application Function) / MBSF (Multicast Broadcast Service Function) 500 provides USD to UE 100. USD is an example of higher layer information provided from a network in a layer higher than the RRC layer (specifically, an application layer). USD may be called service announcement information. USD may be information indicating a correspondence between an MBS service and a frequency. USD may include at least one set of an MBS service identifier and frequency information. USD may include at least one of an MBS session identifier for identifying an MBS session, information on start and end times of the MBS session, an SAI indicating an MBS service area in which the MBS session is provided, and information on a frequency in which the MBS session is provided. UE 100 stores USD provided by AF / MBSF 500.

[0081] In step S102, the UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0082] In step S103, the UE 100 may receive a service continuation SIB from the cell #1, which is the current serving cell. The service continuation SIB is a type of SIB different from the MBS SIB, and is an example of broadcast information provided by broadcast from the network in the RRC layer. The service continuation SIB may be information indicating a correspondence relationship between an MBS service and a frequency. For example, the service continuation SIB may include at least one set of an MBS service identifier and information on a frequency.

[0083] In step S104, the UE 100 identifies a desired MBS frequency associated with the desired MBS service based on the USD (higher layer information) provided in step S101 or the SIB (broadcast information) for service continuation provided in step S103.

[0084] In step S105, the UE 100 receives the SIB1 from the neighboring cell #2 that belongs to the desired MBS frequency identified in step S104.

[0085] In step S106, the UE 100 determines whether the neighbor cell #2 has the capability to provide the MBS SIB based on the SI scheduling information in the SIB1 received in step S105. For example, the UE 100 determines that the neighbor cell #2 has the capability to provide the MBS SIB in any of the following cases: · The SIB type information (SIB-TypeInfo) in the SI scheduling information includes an MBS SIB; · The SI broadcast status (si-BroadcastStatus) in the SI scheduling information is set to "broadcasted" for the MBS SIB or "not broadcasted" for the MBS SIB.

[0086] The UE 100 may determine that the neighbor cell #2 does not have the capability to provide the MBS SIB if any of the following occurs: · The SIB type information (SIB-TypeInfo) in the SI scheduling information does not include the MBS SIB; · The SI broadcast status (si-BroadcastStatus) in the SI scheduling information is not set to "broadcasted" for the MBS SIB or "not broadcasted" for the MBS SIB.

[0087] When it is determined that the neighboring cell #2 has the capability of providing the MBS SIB (step S106: YES), in step S107, the UE 100 determines the frequency priority of the desired MBS frequency to be the highest priority.

[0088] In step S108, the UE 100 performs a measurement process and a cell reselection process to reselect the neighboring cell #2 as a new serving cell.

[0089] In step S109, the UE 100 may transmit a transmission request to the cell #2 to request transmission of the MBS SIB. The transmission request may be a random access preamble transmitted on a special physical random access channel (PRACH) resource.

[0090] In step S110, the UE 100 receives the MBS SIB from the cell #2.

[0091] In step S111, the UE 100 receives the MCCH from the cell #2, based on the MCCH setting information in the MBS SIB received in step S110.

[0092] In step S112, the UE 100 receives the MTCH (ie, MBS data) from the cell #2 based on the MTCH setting information in the MCCH received in step S111.

[0093] [Second embodiment] The second embodiment will be described mainly with respect to the differences from the above-mentioned first embodiment.

[0094] As described above, the UE 100 may acquire two types of information indicating the correspondence between the MBS service and the frequency: USD, which is higher layer information provided by a higher layer, and broadcast information (SIB for service continuation) provided by a RAN (specifically, an RRC layer) corresponding to the gNB 200. Note that the broadcast information is not limited to the SIB for service continuation and may be neighboring cell information in the MCCH. An example in which the broadcast information is the SIB for service continuation will be described below.

[0095] Here, there may be cases where the correspondence between the MBS service and the frequency indicated by the USD does not match the correspondence between the MBS service and the frequency indicated by the SIB for service continuation. For example, there may be cases where the frequency (and the corresponding MBS service) indicated by the USD is not indicated by the SIB for service continuation.

[0096] In such a case, the RAN may intentionally remove information on a certain frequency from the SIB for service continuation due to, for example, the inability to provide an MBS service on the current frequency. In such a scenario, it is not preferable for the UE 100 to specify a desired MBS frequency based on USD. On the other hand, for example, when the MBS service is provided uniformly in all cells on a certain frequency, it is not necessary for the RAN to provide dynamic frequency information, and it is considered that there are cases in which frequency information for the MBS service is efficiently provided only by USD (by providing information only once). In such a scenario, it is preferable for the UE 100 to specify a desired MBS frequency based on USD. However, it is difficult for the UE 100 to determine which of these two scenarios is the case.

[0097] In the second embodiment, the UE 100 in the RRC idle state or the RRC inactive state selects one of the following information: a service continuation SIB provided by the network in the RRC layer by broadcasting, and higher layer information provided by the network in a layer higher than the RRC layer. The UE 100 prioritizes the desired MBS frequency associated with the desired MBS service over other frequencies in the cell reselection procedure based on the one information selected in the selecting step.

[0098] In the second embodiment, the UE 100 acquires selection information provided from the network. The selection information is information on whether or not the USD is prioritized over the SIB for service continuation. That is, the selection information indicates one or more of the following states: prioritizing the USD, prioritizing the SIB for service continuation, not prioritizing the USD, and not prioritizing the SIB for service continuation. The UE 100 selects information on either the SIB for service continuation or the USD based on the selection information. The UE 100 may receive selection information broadcast from the network. The UE 100 may acquire selection information included in the USD.

[0099] 13 is a diagram showing a first operation example according to the second embodiment. In this operation example, the gNB 200 notifies the UE 100 by broadcast whether or not to perform cell reselection using USD.

[0100] In step S201, the UE 100 receives a USD from the AF / MBSF 500.

[0101] In step S202, the UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0102] In step S203, UE100 receives a SIB for service continuity broadcast from gNB200 (serving cell).

[0103] In step S204, the UE 100 receives selection information broadcast from the gNB 200 (serving cell). The selection information may be included in the service continuation SIB, the MBS SIB, the SIB1, or the MCCH. The selection information may be information indicating that the frequency indicated by the USD is prioritized (permitted to be prioritized) in the cell reselection procedure. Here, "prioritizing" may mean that, when the USD has information on a frequency not indicated in the service continuation SIB, the frequency indicated by the USD can be specified as a desired MBS frequency. Alternatively, "prioritizing" may mean that, when the USD has information on a frequency indicated by the service continuation SIB, the frequency indicated by the USD can be specified as a desired MBS frequency. Alternatively, "prioritizing USD" may mean not acquiring the service continuation SIB. Alternatively, "not prioritizing USD" may mean not confirming (reading) the contents of the USD when the service continuation SIB can be acquired. The selection information may be notified to the UE 100 in association with an MBS service identifier (MBS session identifier).

[0104] Then, when the selection information indicates a priority grant of USD, the UE 100 may specify the frequency indicated in USD as the desired MBS frequency for the desired MBS service, regardless of the frequency indicated in the SIB for service continuation.

[0105] Alternatively, even if the selection information indicates priority permission for USD, when UE100 receives a SIB for service continuation, it may identify the frequency indicated in the SIB for service continuation as the desired MBS frequency for the desired MBS service.

[0106] When the selection information does not indicate a priority grant of USD, UE 100 may specify a frequency indicated in the SIB for service continuation as a desired MBS frequency for the desired MBS service, regardless of the frequency indicated in the USD.

[0107] 14 is a diagram showing a second operation example according to the second embodiment. In this operation example, the AF / MBSF 500 provides the UE 100 with a USD including selection information indicating whether or not to prioritize a frequency when the SIB for service continuation does not have information on the frequency indicated by the USD.

[0108] In step S211, the UE 100 receives a USD including selection information from the AF / MBSF 500.

[0109] In step S212, the UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0110] In step S213, UE 100 receives a SIB for service continuity broadcast from gNB 200 (serving cell). Here, UE 100 confirms that frequency information (mapping information between a frequency and the MBS service) for the desired MBS service is not included in the SIB for service continuity.

[0111] When the selection information indicates a priority grant of USD, the UE 100 identifies the frequency indicated by USD as the desired MBS frequency for the desired MBS service.

[0112] On the other hand, if the selection information does not indicate preferential permission for USD, the UE 100 does not specify the frequency indicated by USD as the desired MBS frequency for the desired MBS service.

[0113] [Modification of the second embodiment] In the above-described second embodiment, an example has been described in which the gNB 200 (serving cell) broadcasts the SIB for service continuity to the UE 100. However, it is also possible that the gNB 200 (serving cell) does not broadcast the SIB for service continuity (specifically, does not have the capability to provide the SIB for service continuity).

[0114] In this modification, UE100 determines whether gNB200 (serving cell) has the capability to provide SIB for service continuation, and selects one of USD and SIB for service continuation as information for identifying a desired MBS frequency based on the determination result. When UE100 determines that gNB200 (serving cell) does not have the capability to provide SIB for service continuation, UE100 selects USD as information for identifying a desired MBS frequency. On the other hand, when UE100 determines that gNB200 (serving cell) has the capability to provide SIB for service continuation, UE100 selects SIB for service continuation as information for identifying a desired MBS frequency.

[0115] Here, the serving cell not being capable of providing a SIB for service continuity may mean any of the following: · The serving cell has not sent a SIB for service continuity; In the SI scheduling information of SIB1 of the serving cell, there is no information indicating a SIB for service continuity, for example, neither “broadcasted” nor “not broadcasted” is set; · The serving cell is not transmitting the MBS SIB; · There is no information indicating MBS SIB in the SI scheduling information of SIB1 of the serving cell; · The serving cell is not transmitting MCCH; -SIB1, etc., does not have an identifier indicating support for the MBS function (or the function for transmitting SIBs for service continuity).

[0116] On the other hand, the serving cell's ability to provide a SIB for service continuity may mean either: · The serving cell is sending a SIB for service continuity; In the SI scheduling information of SIB1 of the serving cell, information indicating a SIB for service continuation, for example, “broadcasted” or “not broadcasted”, is set; · The serving cell is transmitting an MBS SIB; ·In the SI scheduling information of SIB1 of the serving cell, there is information indicating an MBS SIB; · The serving cell is transmitting MCCH; -SIB1, etc., has an identifier indicating that the MBS function (or the function for transmitting SIB for service continuity) is supported.

[0117] When it is determined that the serving cell does not have the capability of providing the SIB for service continuity, the UE 100 reads information on a desired MBS service and a corresponding frequency from the USD, and identifies the frequency as a desired MBS frequency.

[0118] On the other hand, when it is determined that the serving cell has the capability of providing the SIB for service continuation, the UE 100 receives the SIB for service continuation from the serving cell. Here, when the serving cell has the capability of providing the SIB for service continuation but does not provide the SIB for service continuation, the UE 100 may receive the SIB for service continuation after requesting the serving cell to transmit the SIB for service continuation. When the information on the frequency associated with the desired MBS service is included in the SIB for service continuation, the UE 100 may determine that the MBS service of interest is provided in the frequency, and may specify the frequency as the desired MBS frequency. On the other hand, when the information on the frequency associated with the desired MBS service is not included in the SIB for service continuation, the UE 100 determines that the desired MBS service is not provided in the current frequency and / or another frequency. In this case, the UE 100 may perform a cell reselection procedure using normal frequency priority. Also, the UE 100 may consider the current serving frequency to be the highest priority.

[0119] [Third embodiment] The third embodiment will be described mainly focusing on the differences from the first and second embodiments.

[0120] As described above, a UE 100 that is receiving or is interested in receiving an MBS prioritizes the desired MBS frequency over other frequencies if a neighboring cell that belongs to the desired MBS frequency provides an MBS SIB (e.g., has the capability to provide an MBS SIB).

[0121] However, after performing such a prioritization process, the UE 100 may reselect a cell different from the neighboring cell as a result of the measurement process and the cell reselection process. In such a case, if the different cell does not provide the MBS SIB (e.g., does not have the capability to provide the MBS SIB), the UE 100 cannot receive the MBS.

[0122] Therefore, in the third embodiment, the UE 100 determines whether to provide an MBS SIB for a neighboring cell having good wireless quality among neighboring cells belonging to a desired MBS frequency. By determining whether to provide an MBS SIB for a neighboring cell having good wireless quality, it is possible to increase the possibility that the neighboring cell will be reselected as a result of the subsequent measurement process and cell reselection process, and therefore it is possible to facilitate the UE 100 to receive the MBS.

[0123] Specifically, the UE 100 according to the third embodiment identifies at least one cell for which a result of measurement on at least one cell belonging to a desired MBS frequency associated with a desired MBS service satisfies a predetermined criterion. If the UE 100 determines that the identified cell provides an MBS SIB, the UE 100 prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure.

[0124] FIG. 15 is a diagram showing an example of an operation of a cell reselection procedure according to the third embodiment.

[0125] In step S301, a UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0126] In step S302, the UE 100 identifies a desired MBS frequency associated with a desired MBS service based on the USD or the SIB for service continuation.

[0127] In step S303, the UE 100 performs a measurement process including measurement on the desired MBS frequency identified in step S302.

[0128] In step S304, the UE 100 identifies at least one cell whose measurement result in step S303 satisfies a predetermined criterion. Here, the predetermined criterion may be a condition that the cell has the best wireless quality. In this case, the UE 100 identifies one cell with the best wireless quality in step S304.

[0129] Alternatively, the predetermined criterion may be a condition that the radio quality of the cell is equal to or higher than a minimum required quality standard (a certain threshold). Also, the predetermined criterion may be a condition that the radio quality of the cell is the best and that the difference in radio quality between the cell and the best radio quality is within a certain threshold. In this case, the UE 100 identifies one or more cells in step S304. The threshold may be provided by the gNB 200 via an SIB or the like.

[0130] UE 100 may determine the predetermined criterion taking into consideration its own moving speed. For example, UE 100 may identify the cell with the best wireless quality in step S304 when not moving, identify a small number of cells with high quality in step S304 when moving at a low speed, and identify a large number of cells with high quality in step S304 when moving at a high speed. Here, the small number or large number may be determined by changing a constant value (threshold) of the wireless quality.

[0131] In step S305, the UE 100 determines whether or not at least one cell identified in step S304 provides an MBS SIB. This determination may be performed in the same manner as in the first embodiment described above.

[0132] When it is determined that at least one cell identified in step S304 provides an MBS SIB (step S305: YES), in step S306, the UE 100 determines the frequency priority of the desired MBS frequency to be the highest priority.

[0133] In step S307, the UE 100 performs the measurement process as described above.

[0134] In step S308, the UE 100 performs the cell reselection process as described above.

[0135] [Modification of the third embodiment] In this modification, when the UE 100 determines that at least one cell belonging to a desired MBS frequency associated with a desired MBS service provides an MBS SIB, the UE 100 prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure. The UE 100 identifies a candidate cell from the desired MBS frequency based on a measurement result for the desired MBS frequency. If the identified candidate cell is included in the at least one cell (i.e., a cell providing an MBS SIB), the UE 100 reselects the candidate cell.

[0136] On the other hand, when the identified candidate cell is not included in the at least one cell, the UE 100 determines whether the candidate cell provides broadcast information. When it is determined that the candidate cell provides broadcast information, the UE 100 reselects the candidate cell.

[0137] In this way, in the frequency prioritization process, UE100 confirms that at least one cell belonging to the desired MBS frequency provides an MBS SIB, and then, when a cell other than the cell confirmed to provide an MBS SIB becomes a candidate for reselection, UE100 confirms whether the candidate cell provides an MBS SIB.

[0138] FIG. 16 is a diagram showing a cell reselection procedure according to this modification.

[0139] In step S331, the UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0140] In step S332, the UE 100 identifies a desired MBS frequency associated with the desired MBS service, based on the USD or the SIB for service continuation.

[0141] In step S333, the UE 100 determines whether or not the cell belonging to the desired MBS frequency identified in step S332 provides an MBS SIB. This determination may be performed in the same manner as in the first embodiment described above.

[0142] When it is determined that the cell belonging to the desired MBS frequency provides the MBS SIB (step S333: YES), in step S334, the UE 100 stores a cell identifier of each of the at least one cell determined to provide the MBS SIB.

[0143] In step S335, the UE 100 determines the frequency priority of the desired MBS frequency to be the highest priority.

[0144] In step S336, the UE 100 performs the measurement process as described above.

[0145] In step S337, the UE 100 performs the cell reselection process as described above. Here, the UE 100 identifies a candidate cell that satisfies a condition for cell reselection, and checks the cell identifier of the candidate cell.

[0146] In step S338, the UE 100 determines whether or not the cell identifier of the candidate cell identified in step S337 is included in the cell identifiers stored in step S334.

[0147] If the cell identifier of the candidate cell identified in step S337 is included in the cell identifier stored in step S334 (step S338: YES), in step S339, the UE 100 assumes that the candidate cell identified in step S337 provides an MBS SIB, and reselects the candidate cell. In this way, by making a determination based on the stored cell identifier, efficient operation is possible.

[0148] On the other hand, if the cell identifier of the candidate cell identified in step S337 is not included in the cell identifiers stored in step S334 (step S338: NO), in step S340, UE 100 determines whether or not the candidate cell identified in step S337 provides an MBS SIB. This determination may be performed in the same manner as in the above-described first embodiment. If it is determined that the candidate cell identified in step S337 provides an MBS SIB (step S340: YES), in step S339, UE 100 reselects the candidate cell.

[0149] When it is determined that the candidate cell identified in step S337 does not provide an MBS SIB (step S340: NO), in step S341, UE 100 stops regarding the desired MBS frequency as the highest priority and redoes the cell reselection procedure. Note that UE 100 may not perform the process of step S340, and may stop regarding the desired MBS frequency as the highest priority and redo the cell reselection procedure if "NO" is determined in step S338.

[0150] [Fourth embodiment] The fourth embodiment will be described mainly focusing on the differences from the first and second embodiments.

[0151] It is assumed that the MBS SIB that transmits the MCCH configuration of the cell does not have information indicating the MBS service (MBS session) provided by the cell. Therefore, unless the UE 100 receives the MCCH, it cannot know whether the cell actually provides the desired MBS service (desired MBS session).

[0152] However, since the UE 100 identifies the desired MBS frequency that provides the desired MBS service based on the USD or the SIB for service continuation, it is considered that the cell belonging to the desired MBS frequency provides the desired MBS service. However, since each cell (gNB 200) has the authority to decide resource allocation for the NR MBS, it is considered that the MBS service is not provided (temporarily) due to cell circumstances such as congestion or overload.

[0153] In the fourth embodiment, the UE 100 reselects a cell belonging to a desired MBS frequency by prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure. The UE 100 determines whether the cell provides the desired MBS service based on the MCCH transmitted from the cell. If the UE 100 determines that the cell does not provide the desired MBS service, the UE 100 repeats the cell reselection procedure. Here, the UE 100 may stop considering the desired MBS frequency as a preferred frequency (highest priority).

[0154] FIG. 17 is a diagram showing an example of an operation of a cell reselection procedure according to the fourth embodiment.

[0155] In step S401, a UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0156] In step S402, the UE 100 identifies a desired MBS frequency associated with a desired MBS service based on the USD or the SIB for service continuation.

[0157] In step S403, the UE 100 determines whether or not the cell belonging to the desired MBS frequency identified in step S402 provides an MBS SIB. This determination may be performed in the same manner as in the first embodiment described above.

[0158] In step S404, the UE 100 determines the frequency priority of the desired MBS frequency to be the highest priority.

[0159] In step S405, the UE 100 performs the measurement process as described above.

[0160] In step S406, the UE 100 performs the cell reselection process as described above.

[0161] In step S407, the UE 100 receives the MBS SIB from the cell reselected in step S406, and then receives the MCCH from the cell based on the MBS SIB.

[0162] In step S408, the UE 100 determines, based on the MCCH received in step S407, whether the cell reselected in step S406 provides the desired MBS service.

[0163] If it is determined in step S406 that the reselected cell does not provide the desired MBS service (step S408: NO), in step S409, the UE 100 stops considering the desired MBS frequency as the highest priority, and starts the cell reselection procedure again.

[0164] [Modification of the fourth embodiment] If the MBS SIB provided by a cell is configured to include an identifier of each MBS service (each MBS session) provided by the cell, it is possible to prevent a situation in which a desired MBS service is not provided after cell reselection. However, since the MBS SIB is expected to be provided on demand, making a transmission request for the MBS SIB in the cell reselection procedure is not preferable in terms of delay and power consumption.

[0165] Although it is possible to include an identifier of each MBS service (each MBS session) in SIB1, the message size of SIB1 is limited, and it is difficult to include an identifier of each MBS service (each MBS session) in SIB1. Therefore, in this modification, the gNB 200 notifies, in SIB1 (or MIB), one bit of information indicating whether or not there is a restriction on the provision of MBS services.

[0166] In this modification, the UE 100 receives SIB1 (or MIB) broadcast by a neighboring cell belonging to the desired MBS frequency, the SIB1 (or MIB) including information on whether the MBS service provision in the neighboring cell is restricted. In response to the SIB1 (or MIB) indicating that the MBS service provision is not restricted, the UE 100 prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure.

[0167] In this modification, each cell (gNB200) is assumed to grasp the correspondence between the frequency and MBS service provided to UE100 by USD and SIB for service continuation, and to recognize the MBS service to be provided in its own cell (the frequency to which it belongs). "MBS service provision is restricted" in a cell means that at least one of the MBS services to be provided in the cell is (temporarily) suspended. When each cell (gNB200) is not providing even one MBS service to be provided by itself, it may include an identifier indicating that the MBS service is restricted in SIB1 (or MIB). When each cell (gNB200) is not providing even one MBS service to be provided by itself, it may include an identifier of the MBS service not provided in SIB1 (or MIB). When each cell (gNB200) is providing all MBS services to be provided by itself, it may include an identifier indicating that the MBS service is not restricted in SIB1 (or MIB). In addition, if each cell (gNB200) is providing all the MBS services that it should provide, it does not need to include the identifier in SIB1 (or MIB).

[0168] FIG. 18 is a diagram showing a cell reselection procedure according to this modification.

[0169] In step S431, the UE 100 in an RRC idle state or an RRC inactive state is receiving or is interested in receiving an MBS.

[0170] In step S432, the UE 100 identifies a desired MBS frequency associated with the desired MBS service, based on the USD or the SIB for service continuation.

[0171] In step S433, the UE 100 determines whether or not the cell belonging to the desired MBS frequency identified in step S432 provides an MBS SIB. This determination may be performed in the same manner as in the first embodiment described above.

[0172] When it is determined that the cell belonging to the desired MBS frequency provides the MBS SIB (step S433: YES), in step S434, the UE 100 checks the SIB1 (or MIB) provided by the cell, and determines whether or not there is a restriction on the MBS service provided by the cell. The SIB1 (or MIB) check may be performed during the cell reselection process (before step S437 or in step S437). That is, the UE 100 performs the check on the cell with the best radio quality (best cell) in the frequency. If there is a restriction on the MBS service provided by the cell, the UE 100 excludes the frequency from the highest priority targets. If there is no restriction on the MBS service provided by the cell, the UE 100 reselects the cell.

[0173] If it is determined that there is a limit to the MBS service provided in the cell (step S434: YES), the desired MBS frequency is excluded from the highest priority targets.

[0174] On the other hand, when it is determined that there is no restriction on the MBS service provided in the cell (step S434: NO), in step S435, the UE 100 determines the frequency priority of the desired MBS frequency to be the highest priority.

[0175] In step S436, the UE 100 performs the measurement process as described above.

[0176] In step S437, the UE 100 performs the cell reselection process as described above.

[0177] [Other embodiments] 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.

[0178] 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 user equipment may be an MT (Mobile Termination) of the IAB node.

[0179] 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).

[0180] 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.

[0181] 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.

[0182] This application claims priority to U.S. Provisional Application No. 63 / 257,215 (filed October 19, 2021), the entire contents of which are incorporated herein by reference.

[0183] [Note] 1. Introduction The revised work item for NR Multicast and Broadcast Services (MBS) was approved in RAN#88. Two delivery modes were agreed for RAN2: a first delivery mode for multicast sessions received by connected UEs and a second delivery mode for broadcast sessions received by UEs in all RRC states.

[0184] For the second distribution mode, the following agreements have been reached in RAN2#115-e:

[0185] When idle / inactive The UE is allowed to prioritize an MBS frequency of interest if the cell of that MBS frequency provides an MBS SIB carrying the MCCH configuration as in LTE SC-PTM. As an LTE SC-PTM, if the UE can only receive MBS service by camping on the MBS frequency, the UE is allowed to prioritize the MBS frequency of interest.

[0186] When idle / inactive. -The UE may consider a cell reselection candidate frequency on which the MBS service cannot be received during an MBS session as the lowest priority as LTE SC-PTM. -Work premise: Mapping of frequencies and MBS service IDs (e.g., SAI) is provided in higher layer signaling (e.g., USD) as LTE SC-PTM (detailed information included in higher layers is provided as LTE SC-PTM). (Detailed information included in higher layers (e.g., USD) is left to the discretion of other WGs.) -As an LTE SC-PTM, send LS to SA2 and SA4 to check whether frequency and MBS service ID (e.g., SAI) mapping is provided by higher layer signaling (e.g., USD). - The mapping between frequencies and MBS service IDs (e.g. SAI) is provided in the SIB as LTE SC-PTM. Detailed mapping awaits feedback from other WGs. -Mapping of frequencies and MBS service IDs (e.g., SAI) is permitted to be transmitted in cells that do not broadcast MBS services as LTE SC-PTM. -Mapping between frequency and MBS service ID (e.g., SAI) is provided in a new SIB different from the MBS SIB that provides MCCH configuration as LTE SC-PTM. - MBS service IDs (e.g. SAI) are provided in SIB and USD as LTE SC-PTM. Details of IDs are pending feedback from other WGs. -As an LTE SC-PTM, send LS to SA2, SA4, and RAN3 to check whether the MBS service ID (e.g., SAI) can be provided in SIB and USD. - As an LTE SC-PTM, further consideration is required as to whether the gNB can indicate a list of neighboring cells in which an ongoing broadcast MBS service provided in the current cell is provided. -Additional offset to cells (providing MBS services) for cell ranking criteria is not supported in Rel-17.

[0187] For connected -(As LTE SC-PTM) The UE reports the following MBS interest information: MBS Frequency List Priority between receiving all listed MBMS frequencies and receiving any unicast bearers TMGI List -If reporting of MBS frequencies is permitted, the MBS frequencies reported by the UE are sorted in order of interest as LTE SC-PTM. - Sending LS to SA3 to check whether the UE can report MBS interest information before security activation. Further consideration is needed as to whether the MII is reported via UE Assistance Information or a new RRC message.

[0188] This appendix discusses the remaining issues of broadcast service continuity and common control plane aspects for the two delivery modes.

[0189] 2. Consideration 2.1.Neighboring cell information RAN2 agreed to the following outstanding items: Further study is required as to whether the gNB can indicate a list of neighboring cells in which the broadcast MBS service provided in the current cell is available, as in LTE SC-PTM.

[0190] In LTE SC-PTM, the serving cell provides information about neighboring cells via the SC-MCCH, so that the UE knows which cells are providing the MBMS services it is interested in. This information eliminates the need for the UE to obtain the SC-MCCH from neighboring cells during cell reselection, which, from the UE's perspective, reduces latency and power consumption and improves service continuity.

[0191] In NR MBS, the situation may be worse than in LTE SC-PTM if the network does not provide neighbor cell information because NR supports the on-demand SI mechanism: during cell reselection, the UE needs to request each neighbor cell to provide an MBS-specific SIB that is “not broadcasted” and obtain the MCCH scheduling information. After that, the UE needs to obtain the MCCH to check whether each neighbor cell provides the interested MBS service.

[0192] Observation 1: If neighboring cell information is not provided, the UE may need to request on-demand SI to obtain MCCH scheduling information and, during the cell reselection procedure, acquire the MCCH to check whether the interested MBS service is provided in each neighboring cell.

[0193] In the discussion of RAN2#115-e, it is argued that it is very complicated for the network to provide neighbor cell information, especially when the start / stop of MBS sessions is dynamically determined by the cell. However, since this condition is no different from LTE SC-PTM, it is not considered that the network cannot provide neighbor cell information. It is up to RAN3 whether coordination with the network is required or whether it can be handled by OAM.

[0194] There is also the option for higher layers (e.g. USD) to provide neighbor cell information, but this has proven difficult for networks to implement, so it is not a viable option.

[0195] Therefore, to reduce cell reselection latency and UE power consumption, the network needs to provide neighbor cell information, similar to LTE SC-PTM.

[0196] Proposal 1: RAN2 should agree that the gNB will provide via MCCH a list of neighboring cells where the broadcast MBS service is provided continuously.

[0197] If proposal 1 is accepted, it is correct that the UE is allowed to use this information for cell reselection priority processing in addition to the information provided in SIBy.

[0198] Proposal 2: If Proposal 1 is agreeable, then RAN2 should agree that during the cell reselection priority process, the UE is allowed to use the list of neighbor cells provided in the MCCH.

[0199] 2.2. Cell reselection priority processing 2.2.1. MBS SIB check during cell reselection RAN2 has agreed on the UE behavior regarding cell reselection priority handling as follows:

[0200] When idle / inactive. -The UE is allowed to prioritize an MBS frequency of interest if the cell of the MBS frequency provides an MBS SIB carrying an MCCH configuration as in LTE SC-PTM. -If the UE can receive MBS service only by camping on the MBS frequency as LTE SC-PTM, the UE is allowed to prioritize the MBS frequency of interest.

[0201] When idle / inactive -The UE may consider a cell reselection candidate frequency on which the MBS service cannot be received during an MBS session as the lowest priority as LTE SC-PTM.

[0202] These UE behaviors reuse the LTE eMBMS specifications. However, one difference between NR MBS and LTE eMBMS is that NR supports the On-demand SI mechanism. With On-demand SI, the gNB can decide whether to “broadcast” or “not broadcast” a SIB. “Not broadcast” SIBs are provided on demand, i.e. in response to an On-demand SI request from the UE.

[0203] In the case of on-demand SI, the agreement "when a cell on an MBS frequency provides an MBS SIB with an MCCH configuration" is problematic because it has two possible interpretations:

[0204] Interpretation 1: The UE checks whether the MBS SIB is actually broadcast from a neighboring cell. In this case, if the MBS SIB is "not broadcast" during cell reselection, the UE considers the frequency for that cell as not preferred or sends an on-demand SI request to that cell.

[0205] Interpretation 2: The UE checks whether the MBS SIB is broadcastable by the neighboring cell. In this case, the UE checks SIB1 only if the MBS SIB is available, whether the MBS SIB is "broadcast" or "not broadcast".

[0206] In our understanding, interpretation 1 does not make sense because it is different from the intended behavior. Also, if the UE needs to send an on-demand SI request in each neighboring cell, the UE's power consumption and cell reselection delay will be large.

[0207] On the other hand, Interpretation 2 is consistent with the intended behavior, but is not properly expressed in the contract. Therefore, the specification should clearly capture the intended behavior based on Interpretation 2.

[0208] Proposal 3: RAN2 should agree that the phrase "if a cell on the MBS frequency provides an MBS SIB" in the agreement means that the MBS cell can provide it regardless of whether it is "broadcast" or "not broadcast" by on-demand SI.

[0209] 2.2.2. Priority of information between SIBy / MCCH and USD The currently ongoing CR is described as follows: Further consideration is required as to whether USD frequencies should also be checked if the serving cell's SIBy indicates one or more IDs (e.g. SAI) for that frequency.

[0210] Further consideration is required as to whether the UE can prioritize frequencies indicated in USD when SIBy is broadcast but no mapping for the service is provided.

[0211] In general, it is considered that the UE should follow the information provided by the gNB, because the gNB is in charge of frequency management and can handle the latest information compared to the USD. For example, if a neighboring cell of the gNB cannot provide MBS service due to lack of resources, the gNB knows such operational information and decides to provide it in SIBy (or MCCH). Considering that the UE is in an idle / inactive state, the USD may not be updated because it is provided by a message of a higher layer. Therefore, if the frequency of interest is provided in SIBy (and / or if agreed, the neighboring cell of interest is provided in MCCH), the UE does not need to check the frequency in USD. Such an operation can avoid the complication of the specification, for example, what the UE should do if the frequency of interest in USD does not match the frequency of interest in SIBy. Note that it is not intended to have a strict requirement that a UE cannot use USD if SIBy is broadcast.

[0212] Observation 2: In general, the frequency information in USD may be out of date, so the UE should follow the latest information provided by the gNB.

[0213] Proposal 4: RAN2 should agree that if the frequency of interest is provided in SIBy, the UE does not need to check the frequency information in USD.

[0214] However, the UE behavior in case that information is not provided in SIBy (and MCCH) but is provided in USD needs to be carefully considered. For frequencies indicated in USD, the following cases can be considered as reasons why a gNB does not provide frequency information in SIBy (and / or neighbor cell information on MCCH if agreed):

[0215] If gNB intentionally conceals certain frequency information Case 1: The gNB wants to prevent the UE from prioritizing a frequency because it knows that a neighboring frequency / cell does not provide the MBS service due to congestion or other reasons; or -Case 2: The gNB intends for the UE to use USD to determine the frequency of interest, for example because, as a deployment policy, all cells on the frequency provide the MBS service.

[0216] gNBs are unaware of operational information in their neighborhoods. -Case 3: The gNB has no information about the UE (no OAM configuration or signaling exchange between gNBs).

[0217] Considering these cases, it is difficult to define a single deterministic UE behavior, since which case should be applied depends on various gNB implementations and deployment policies. It is clear that the UE cannot know the gNB's intentions and deployment policies in any case. Therefore, the UE needs to be indicated in USD whether it is allowed to use the frequency of interest preferentially. Whether such an indication should be provided in SIB or USD needs further study.

[0218] Proposal 5: RAN2 should discuss whether a UE, if indicated (e.g. in SIB), should be allowed to prioritize frequencies of interest in USD when no frequencies are offered in SIBy.

[0219] 2.2.3. Cease of Frequency Prioritization The currently ongoing CR is described as follows: Further consideration is required as to whether the UE should stop frequency priority when the SIBx is no longer scheduled in the serving cell (reselected cell).

[0220] The case intended above occurs when the UE prioritizes a frequency (i.e., based on frequency information in the USD or SIBy from the source cell) but the reselected cell does not provide SIBx. Such a mismatch in cell reselection procedures is likely to occur because the specification assumes that the priority process, measurement process, and cell reselection process are performed sequentially, and therefore frequency information is only used in the priority process, while the measurement process and cell reselection process are performed as is in legacy.

[0221] Considering that the UE has confirmed the cell providing SIBx before reselection, i.e., once it has confirmed that the cell can provide MBS services, this case is caused by one of the following conditions: Condition 1: The UE checks the SIBx of a non-best cell; or - Condition 2: When the UE moves from a cell broadcasting SIBx to a cell not broadcasting SIBx after frequency prioritization.

[0222] Condition 1 can be easily resolved by a simple specification restriction (or annotation), such as performing the SIBx check on the best cell. However, it can also be considered that it depends on the UE implementation.

[0223] Condition 2 can be resolved by another simple restriction (or annotation), such as performing the SIBx check on a candidate cell that takes into account the mobility of the UE. However, this can be considered to be dependent on the implementation of the UE.

[0224] Proposal 6: RAN2 should discuss whether to specify (or add a note to) that the UE checks the SIBx of the best cell (or a higher cell if required for the UE's mobility).

[0225] A similar scenario could be that after cell reselection, the UE finds that the reselected cell does not offer the MBS service of interest. This could happen because the UE only checks if the SIBx is broadcast, i.e., the SIBx does not inform the UE of the currently available MBS services (e.g., TMGI). Therefore, the UE gets the MCCH after cell reselection to that cell, but the MCCH may not contain the MBS service of interest.

[0226] It is important to consider that the problem may be a subset of this scenario, in which case it is natural for the UE to no longer consider this cell's frequency as the most preferred, in order to solve both problems.

[0227] Even if a frequency is mapped to MBS service in SIBy, it is believed that whether or not MBS service will ultimately be provided depends on the implementation of gNB, so it is possible that a cell on a certain frequency may not provide MBS service.

[0228] Proposal 7: RAN2 agrees that if the reselected cell does not provide the MBS service of interest, the UE should stop prioritizing the frequency.

[0229] 2.3.MBS Interest Indication 2.3.1. Message Definition RAN2 agreed on the basic content of MBS Interest Indication and outstanding issues as follows: -(As LTE SC-PTM) The UE reports the following MBS interest information: MBS Frequency List Priority between receiving all listed MBMS frequencies and receiving any unicast bearers TMGI List Further consideration will be given to whether MII is reported in UE Assistance Information or a new RRC message.

[0230] In LTE, MBMS Interest Indication (MII) is separated from UE Assistance Information (UAI). This is because the preconditions for MII are different, that is, acquisition of SIB15, and for UAI, RRC connection setup. On the other hand, In-device Coexistence Indication (IDC), which was a separate message in LTE, is integrated into UAI in NR. This is considered feasible because the preconditions for IDC and UAI are the same in LTE (and NR), that is, RRC connection setup.

[0231] Observation 3: The ability to integrate MBSMBS Interest Indication with UE Assistance Information depends on whether the preconditions are consistent between the two messages.

[0232] In NR MBS, in order to generate an MBS Interest Indication message having the above IE, MBS-specific SIB or neighboring frequency information of MCCH is required. Also, MBS Interest Indication is expected to be configured by MBS-specific SIB (or MCCH) as in LTE eMBMS. Therefore, it does not match RRC Reconfiguration, which is a prerequisite for UAI. Therefore, MBS Interest Indication needs to be a separate message from UAI, as in LTE eMBMS.

[0233] Proposal 8: RAN2 should agree to define MBS Interest Indication as a new message, i.e., separate from UE Assistance Information.

[0234] Proposal 9: RAN2 should agree to allow the UE to transmit MBS Interest Indication if it can obtain an MBS-specific SIB from the serving cell (i.e., as a pre-condition).

[0235] 2.4. MBS Interest Indication for Multicast Sessions RAN2 currently assumes that MBS Interest Indication is supported for broadcast sessions and not for multicast sessions. RAN2#115e agreed on the basic contents of MBS Interest Indication cited in the previous section, i.e. MBS frequency list, priority, and TMGI list.

[0236] It is a common understanding that for multicast sessions, 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 also applies to MBS services. And 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 that the UE conveys the priority information to the core network in the session join procedure.

[0237] Observation 4: 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.

[0238] The priority information is considered to be useful for the gNB for scheduling and handover decisions as well as for LTE eMBMS and is relevant for service continuity. Therefore, the UE needs to inform the gNB of its priority information also for multicast sessions. In this sense, RAN2 should agree that MBS Interest Indication should be supported also for multicast services / first delivery mode.

[0239] Proposal 10: RAN2 should agree that MBS Interest Indication 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.

[0240] 2.5. Dedicated MCCH (from the viewpoint of service continuity) RAN2 agreed to postpone discussion on whether a dedicated MCCH is required until RAN1 has made progress on the BWP / CFR for the MCCH. It is expected that a dedicated MCCH will be provided, for example by RRC configuration, if supported.

[0241] Observation 5: A dedicated MCCH can be interpreted as MCCH being provided by RRC reconfiguration rather than on a broadcast basis.

[0242] On the other hand, a dedicated MCCH can be considered from the perspective of broadcast service continuity. In RAN2, it is already agreed that "we assume that connected UEs can reuse LTE SC-PTM mechanisms to receive PTM configuration in NR MBS second delivery mode, i.e. in a broadcast-based manner." This assumption is for intra-cell configuration, but not for inter-cell service continuity, i.e. handover.

[0243] Observation 6: RAN2 agreed to provide MCCH in a broadcast manner in intra-cell configuration, but not for inter-cell service continuity.

[0244] In LTE SC-PTM, it is assumed that the UE acquires the SIB20 and MCCH of the target cell in some way before, during or after the handover, which could be considered as the baseline for the NR MBS second delivery mode. However, this means that there is a risk of service interruption, since the UE may miss or be late in acquiring the MCCH of the neighboring cell, e.g. in busy conditions. In particular, the MCCH of the target cell (at least the MTCH scheduling information of interest) needs to be provided by the RRC Reconfiguration with sync, i.e. the handover command. This solution ensures service continuity after the handover.

[0245] Proposal 11: RAN2 should agree to provide the MCCH and at least the interesting MTCH scheduling information of the target cell during the handover procedure, i.e., by RRC Reconfiguration with sync, to ensure inter-cell service continuity for the UE in RRC Connected.

[0246] 2.6. Multicast Sessions in Progress Using the Second Delivery Mode NR MBS is expected to support various types of use cases, as cited from the WID below: It is confirmed that NR MBS should be well designed for various requirements, from lossless applications like software distribution to UDP type streaming like IPTV, from delay-sensitive applications like mission-critical and V2X to delay-tolerant applications like IoT, in addition to other dimensional requirements. It is confirmed that in practice, not all multicast services require "high QoS".

[0247] The purpose of SA2 SI is to enable general MBS services over 5GS, and use cases that can benefit from this capability include (but are not limited to) public safety and mission-critical, V2X applications, transparent IPv4 / IPv6 multicast distribution, IPTV, over-the-air software distribution, group communications, and IoT applications.

[0248] Of these services, those with "low QoS requirements" could potentially be covered by the second delivery mode, while other services with "high QoS requirements" would require the first delivery mode. Furthermore, LTE eMBMS can deliver multicast sessions, which are considered as a baseline for NR MBS. In this sense, it is beneficial for gNBs to have the option to use the second delivery mode for multicast sessions. This issue was left for further study in RAN2#112-e to RAN2#114-e, but in general, there seems to be no technical reason to restrict it from our point of view.

[0249] In addition, RAN2 prioritizes "RRC connected mode". RAN2 prioritizes support for active multicast in RRC connected mode in Rel-17. If time permits, multicast support for RRC inactive can be considered later (when multicast and broadcast solutions for connected mode are more mature)." However, since the agreement was made in the context of the first distribution mode, it does not exclude multicast sessions using the second distribution mode for UEs in connected mode.

[0250] Proposal 12: It should be agreed that RAN2 can use the second delivery mode for multicast sessions at least for RRC connected UEs in addition to broadcast sessions.

[0251] 2.7.Details of MBS-dedicated SIB We understand that it is up to the NW implementation whether MBS services are provided by PTP or PTM, and by the first or second delivery mode. This allows a good balance between service reliability and spectrum efficiency. However, from the UE's perspective, especially for idle / inactive UEs and late-joining UEs, the UE needs to know whether it needs to initiate connection establishment to obtain the MBS service of interest. It can be considered that if the UE first checks the MCCH and the MCCH does not contain the MTCH scheduling information for the desired MBS service, the UE knows that the MBS service is only provided via RRC connected, i.e., PTP, first delivery mode or unicast (PDU session). However, such a process can be burdensome for the UE and may cause some delay before obtaining the MBS service. So it is worth considering whether the MBS-specific SIB provides information on whether the UE needs to be connected to receive the MBS service.

[0252] Proposal 13: RAN2 should discuss whether the MBS-specific SIB should provide information to associate MBS services with their delivery modes.

[0253] RAN2 agreed to introduce MBS Interest Indication, but it is currently assumed to be used for broadcast sessions. Also, from the UE's point of view, it is unclear whether the gNB can obtain information about MBS. Also, from the UE's point of view, it is unclear whether the gNB can obtain information about MBS services that the UE is interested in (AMF may provide it in multicast sessions and not in broadcast sessions). As a result, the UE does not know whether it should send MBS Interest Indication for the MBS services that it is interested in. Therefore, it would be useful for the UE if the gNB provided information about whether MBS Interest Indication is allowed for each MBS service. In other words, which MBS services require MBS Interest Indication. Therefore, RAN2 needs to consider whether such additional information is necessary.

[0254] Proposal 14: RAN2 should discuss whether to provide information on whether to allow transmission of MBS Interest Indication for each MBS service in an MBS-specific SIB.

[0255] 2.8. One-Step Configuration Another possibility is to integrate MCCH into BCCH, i.e. one-step configuration as shown in Fig. 19. For example, SIB provides MTCH scheduling information directly, i.e. without MCCH. It would provide optimization for delay tolerant services and / or power sensitive UEs. For example, UEs can request SIB (on demand) and gNB can start providing SIB and corresponding services after requests from multiple UEs. These UEs do not need to monitor the repeatedly broadcasted MCCH.

[0256] Proposal 15: RAN2 should agree as a configuration option to support multicast reception without MCCH (i.e. one-step configuration), e.g. the SIB providing MTCH scheduling information directly.

[0257] 2.9. Idle / Inactive Counting It has been agreed that for NR MBS, MBS Interest Indication is supported in RRC Connected but not in Idle / Inactive, and based on this, it seems worthy of consideration as an extension on top of LTE eMBMS.

[0258] In LTE eMBMS, even though many UEs receive broadcast services in RRC idle, neither MII nor Counting can collect information from idle UEs. This is one of the remaining challenges for LTE eMBMS from the viewpoint of session control and resource efficiency.

[0259] Observation 7: For broadcast sessions, a large proportion of UEs receiving the MBS service may be in RRC idle / inactive.

[0260] In NR MBS, the same problem may exist for idle / inactive UEs, i.e. the second delivery mode of the broadcast session. For example, the network does not know if idle / inactive UEs are no longer receiving / interested in the broadcast service. Thus, the network may continue to provide PTM transmissions even if there are no UEs receiving the service. Such unnecessary PTM transmissions should be avoided if the gNB knows what the idle / inactive UEs are interested in. Conversely, stopping PTM while there are still idle / inactive UEs receiving the service may result in a large number of UEs sending connection requests at the same time, which is also undesirable.

[0261] It is therefore worth considering whether to introduce a mechanism to collect UE assistance information (especially MBMS Counting) from idle / inactive UEs. Obviously, it would be desirable for these idle / inactive UEs to be able to report information without going RRC Connected. This could be achieved, for example, if PRACH resource partitioning related to MBS services were introduced for such reporting.

[0262] Since there is no MCE in NR MBS, the MCE function will be integrated into the gNB. Therefore, regardless of what RAN3 decides from the network interface perspective, RAN2 decides whether Counting is required for NR MBS.

[0263] Proposal 16: RAN2 should discuss whether MBS Counting will be introduced and whether it will also be collected from the UE during idle / inactivity. [Explanation of symbols]

[0264] 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 Radio Resource Control (RRC) idle state or an RRC inactive state in a mobile communication system supporting a Multicast and Broadcast Service (MBS), comprising: receiving broadcast information including frequency mapping information indicating a correspondence between MBS services and frequencies; When the broadcast information includes the frequency mapping information, even if the broadcast information does not include frequency mapping information for a desired MBS service, a desired MBS frequency associated with the desired MBS service is prioritized over other frequencies in a cell reselection procedure in response to the desired MBS frequency being included in higher layer information provided in a layer higher than an RRC layer to which the broadcast information is provided. Communication methods.

2. The prioritizing includes prioritizing the desired MBS frequency over the other frequencies in the cell reselection procedure in response to the desired MBS frequency being included in the higher layer information even when the broadcast information is not provided. The communication method according to claim 1 .

3. receiving system information (SI) scheduling information broadcast by a serving cell; and determining that the broadcast information is not provided in response to the SI scheduling information not including information of the broadcast information. The communication method according to claim 2 .

4. The method further comprises receiving system information (SI) scheduling information broadcast by a cell belonging to the desired MBS frequency; The prioritizing includes prioritizing the desired MBS frequency over the other frequencies in the cell reselection procedure in response to the SI scheduling information including information of an MBS system information block. The communication method according to claim 1 .

5. A user equipment for use in a mobile communication system supporting a Multicast and Broadcast Service (MBS), comprising: In a Radio Resource Control (RRC) idle state or an RRC inactive state, receiving broadcast information including frequency mapping information indicating a correspondence between MBS services and frequencies; and a control unit that executes a process of prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure in response to a desired MBS frequency associated with the desired MBS service being included in higher layer information provided in a layer higher than an RRC layer to which the broadcast information is provided, even if the frequency mapping information does not include frequency mapping information for the desired MBS service when the broadcast information includes the frequency mapping information. User equipment.

6. A device for use in a user equipment for carrying out the communication method according to claim 1. Chipset.

7. The communication method according to claim 1 is executed by a user device. program.

8. The user equipment according to claim 5 and a network node. Mobile communication system.

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