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; the same applies hereinafter) standard defines the technical specifications for NR (New Radio), a fifth-generation (5G) radio access technology. Compared to LTE (Long Term Evolution), a fourth-generation (4G) radio access technology, NR features high speed, large capacity, high reliability, and low latency. Discussions are underway within 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 compared to 4G / LTE multicast and broadcast services.

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

[0006] A first aspect of the present invention relates to a communication method performed by a user equipment (UE) 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 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, if the SI scheduling information indicates that the neighboring cell has the capability to provide MBS system information blocks, prioritizing the desired MBS frequency over other frequencies in the cell reselection procedure.

[0007] A communication method according to a second aspect is communication performed by a user equipment (UE) 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 selecting either broadcast information provided by a network via broadcast at an RRC layer or higher layer information provided by the network at a layer higher than the RRC layer, and prioritizing a desired MBS frequency associated with a desired MBS service so that the desired MBS frequency is given priority over other frequencies in a cell reselection procedure. Each of the broadcast information and the higher layer information indicates a correspondence between MBS services and frequencies. The prioritizing step includes prioritizing the desired MBS frequency based on the one of the information selected in the selecting step.

[0008] A third aspect of the present invention relates to a communication method performed by a user equipment (UE) 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 comprising the steps of: identifying at least one cell for which a measurement result for at least one cell belonging to a desired MBS frequency associated with a desired MBS service satisfies a predetermined criterion; and, if the user equipment determines that the identified cell broadcasts an MBS system information block, prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure.

[0009] A fourth aspect of the present invention relates to a communication method performed by a user equipment (UE) 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: prioritizing a desired MBS frequency in a cell reselection procedure 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 measurement results 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 fifth aspect of the present invention relates to a communication method performed by a user equipment (UE) 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: 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, if it is determined in the determining step that the cell does not provide the desired MBS service, restarting the cell reselection procedure.

[0011] A sixth aspect of the present invention relates to a communication method performed by a user equipment (UE) 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 that belongs to a desired MBS frequency associated with a desired MBS service, the system information including information on whether provision of the MBS service in the neighboring cell is restricted or not, and, in response to the system information indicating that provision of the MBS service is not restricted, prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure, wherein the system information is a System Information Block Type 1 or a Master Information Block. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] 1 is a diagram illustrating a configuration of a UE (user equipment) according to an embodiment. [Figure 3] A diagram showing the configuration of a gNB (base station) according to an embodiment. [Figure 4]FIG. 10 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data. [Figure 5] FIG. 1 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals). [Figure 6] FIG. 1 is a diagram illustrating an overview of MBS traffic distribution according to an embodiment. [Figure 7] FIG. 10 is a diagram illustrating a distribution mode according to the embodiment. [Figure 8] FIG. 2 is a diagram illustrating an example of internal processing related to MBS reception of the UE 100 according to the embodiment. [Figure 9] FIG. 10 is a diagram showing another example of 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 illustrating a schematic flow of a cell reselection procedure according to an embodiment. [Figure 12] FIG. 2 is a diagram illustrating an example of operation of the mobile communication system according to the first embodiment. [Figure 13] FIG. 10 is a diagram illustrating a first operation example according to the second embodiment. [Figure 14] FIG. 10 is a diagram illustrating a second operation example according to the second embodiment. [Figure 15] FIG. 11 is a diagram illustrating an example of the operation of a cell reselection procedure according to the third embodiment. [Figure 16] FIG. 11 is a diagram illustrating a cell reselection procedure according to a modification of the third embodiment. [Figure 17] FIG. 11 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. 10 is a diagram illustrating one-step setting of the second distribution mode. DETAILED DESCRIPTION OF THE INVENTION

[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 the configuration of a mobile communication system according to a first embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). In the following description, 5GS is used as an example, but the mobile communication system may also be at least partially applied to an LTE (Long Term Evolution) system. Furthermore, the mobile communication system may also be at least partially applied to a 6th Generation (6G) system.

[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 may be a mobile phone terminal (including a smartphone), a tablet terminal, a laptop PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[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 a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with a UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0018] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-base station interface.

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

[0020] 2 is a diagram showing the 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 constitute a wireless communication unit that performs wireless communication with the gNB 200.

[0021] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0022] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0023] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer, which will be described later. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used 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 types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0027] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer, which will be described later. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used 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 neighboring 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 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 encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has CRC parity bits scrambled by the RNTI added.

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

[0033] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via logical channels.

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

[0035] The SDAP layer maps IP flows, which are the units for Quality of Service (QoS) control by the core network, to radio bearers, which are the units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP is not necessary.

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

[0039] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the AMF 300A. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, the layer below the NAS layer is called the AS layer.

[0040] (MBS Overview) 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 communications, mission-critical communications, V2X (Vehicle to Everything) communications, IPv4 or IPv6 multicast distribution, IPTV (Internet protocol television), group communications, and software distribution.

[0041] The broadcast service is for applications that do not require highly reliable QoS, and provides service to all UEs 100 within a specific service area. 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 for the multicast service is called a multicast session.

[0043] FIG. 6 is a diagram showing an outline of MBS traffic distribution 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 (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 packet 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 for 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 for the MBS traffic channel corresponding to this MBS session. The MBS traffic channel scheduling information may include discontinuous reception (DRX) configuration for the MBS traffic channel. The discontinuous reception configuration may include one or more parameters: a timer value (On Duration Timer) that defines the 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 (Start Offset, DRX Cycle Offset) of the start subframe of the scheduling or DRX cycle, a start delay slot value (Slot Offset) for the on-duration timer, 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 for HARQ retransmission.

[0055] The MBS traffic channel is a type of logical channel and is sometimes 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 not only by the UE 100 in the RRC connected state but also by the UE 100 in the RRC idle state or the 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 the MCCH using, for example, a dedicated RNTI predefined in a technical specification. 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 configuration information from the 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 configuration information. The MCCH transmits MTCH configuration 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 configuration information. Hereinafter, the MTCH configuration information and / or the MCCH configuration information may be referred to as an MBS reception configuration. In the following embodiments, 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 configuration (MTCH configuration 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, application server, etc., and an IP multicast address indicating the 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] An MBS Radio Bearer (MRB) is a radio bearer that carries a multicast session or a broadcast session. That is, an MRB may be associated with a multicast session or a broadcast session.

[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] 8 shows an example 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 a PTP-only MRB, MRB#2 is a PTM-only MRB, and MRB#3 is a PTM-only MRB. 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 the 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] 9 shows an example 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 associated with a DTCH and the other leg 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 outline of the cell reselection procedure will now be described. Fig. 10 is a diagram for explaining an outline 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 the 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. When the current serving cell and the neighboring cell have the same frequency (carrier frequency), this is called intra-frequency, and when the current serving cell and the neighboring cell have different frequencies (carrier frequencies), this is called inter-frequency. The current serving cell and the neighboring cell may be managed by the same gNB200. Alternatively, the current serving cell and the neighboring cell may be managed by different gNB200s.

[0069] FIG. 11 is a diagram showing a general flow 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. As will be described in detail 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" refers to an MBS session, but is not limited to this, and may refer to an MBS service area. Similarly, the term "MBS service identifier" refers to an MBS session identifier (e.g., TMGI), but is not limited to this, and may refer to an MBS service area identifier (MBS SAI). The term "frequency" refers to a carrier frequency, but is not limited to this, and may refer to a cell. Hereinafter, an MBS service that UE 100 is currently 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, UE 100 performs a measurement process to measure the radio quality of each of the serving cell and the neighboring cell. UE 100 measures the received power and received 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, UE 100 always measures the radio quality of a frequency having a higher priority than the frequency priority of the current serving cell. Furthermore, for a frequency having a priority equal to or lower than the frequency priority of the current serving cell, UE 100 measures the radio quality of the frequency having the same priority or a lower priority when the radio quality of the current serving cell falls below a predetermined quality.

[0073] In step S3, UE 100 performs a reselection process to reselect a cell on which UE 100 will camp based on the measurement result in step S2. For example, if the frequency priority of a neighboring cell is higher than the priority of a current serving cell and the neighboring cell satisfies a predetermined quality standard (i.e., a minimum required quality standard) for a predetermined period, UE 100 may perform cell reselection to the neighboring cell. If the frequency priority of the neighboring cell is the same as the priority of the current serving cell, UE 100 may rank the radio qualities of the neighboring cells and perform cell reselection to the neighboring cell having a higher rank than the rank of the current serving cell for a predetermined period. If 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, UE 100 may perform cell reselection to the neighboring cell.

[0074] (Mobile communication system operation) As described above, 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 the desired MBS service over other frequencies. For example, 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 can be specified by the network). This makes it easier for the desired MBS service to be continuously provided to UE 100.

[0075] Currently, it is assumed that UE 100 prioritizes the desired MBS frequency over other frequencies, provided that a neighboring cell belonging to the desired MBS frequency provides an MBS SIB (i.e., an SIB transmitting 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 UE 100. Therefore, even if a cell has the capability to broadcast an MBS SIB, it does not necessarily provide the MBS SIB.

[0076] Therefore, if a condition for prioritizing a desired MBS frequency over other frequencies requires that neighboring cells belonging to the desired MBS frequency provide an MBS SIB, the UE 100 may need to request transmission of an MBS SIB from each neighboring cell for the cell reselection procedure. Such an operation increases the power consumption and MBS reception delay of the UE 100, and is inefficient.

[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 that belongs 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, UE 100 performs frequency prioritization processing not based on whether a neighboring cell broadcasts an MBS SIB but based on whether the neighboring cell has the capability to provide the MBS SIB. Specifically, even if a neighboring cell belonging to a desired MBS frequency does not broadcast an MBS SIB, UE 100 prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure if the neighboring cell has the capability to provide the MBS SIB. This eliminates the need for UE 100 to request each neighboring cell to transmit an MBS SIB, thereby improving the efficiency of the cell reselection procedure.

[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, the application layer). USD may be referred to as service announcement information. USD may be information indicating the correspondence between MBS services and frequencies. 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 that identifies an MBS session, information on the start and end times of the MBS session, an SAI that indicates the MBS service area in which the MBS session is provided, and information on the frequency in which the MBS session is provided. UE 100 stores the USD provided by AF / MBSF 500.

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

[0082] In step S103, the UE 100 may receive a service continuity SIB from cell #1, which is the current serving cell. The service continuity 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 continuity SIB may be information indicating a correspondence relationship between an MBS service and a frequency. For example, the service continuity SIB may include at least one set of an MBS service identifier and frequency information.

[0083] In step S104, UE100 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, UE 100 determines whether neighboring cell #2 has the capability to provide MBS SIB based on the SI scheduling information in SIB1 received in step S105. For example, UE 100 determines that neighboring cell #2 has the capability to provide 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 MBS SIB broadcasting or "not broadcasted" for non-broadcasting.

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

[0087] If it is determined that the neighboring cell #2 has the capability to provide 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 (that is, 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 focusing on the differences from the first embodiment described above.

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

[0096] In such a case, the RAN may intentionally remove information about a certain frequency from the service continuity SIB, for example, because the MBS service cannot be provided on that frequency. In such a scenario, it is not preferable for the UE 100 to identify 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, the RAN does not need to provide dynamic frequency information, and it is considered that there may be cases where 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 identify a desired MBS frequency based on USD. However, it is difficult for the UE 100 to determine which of these two scenarios applies.

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

[0098] In the second embodiment, the UE 100 acquires selection information provided from the network. The selection information is information regarding whether or not the USD is prioritized over the SIB for service continuity. That is, the selection information indicates one or more of the following states: prioritizing the USD, prioritizing the SIB for service continuity, not prioritizing the USD, and not prioritizing the SIB for service continuity. The UE 100 selects information on either the SIB for service continuity 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 illustrating 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 the RRC idle state or the 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 continuity SIB, the MBS SIB, the SIB1, or the MCCH. The selection information may be information indicating that a frequency indicated by a USD is prioritized (or permitted to be prioritized) in a cell reselection procedure. Here, "prioritizing" may mean that, when the USD has information on a frequency not indicated in the service continuity SIB, the frequency indicated by the USD can be identified as a desired MBS frequency. Alternatively, "prioritizing" may mean that, when the USD has information on a frequency indicated in the service continuity SIB, the frequency indicated by the USD can be identified as a desired MBS frequency. Alternatively, "prioritizing USD" may mean not acquiring the service continuity SIB. Alternatively, "not prioritizing USD" may mean not checking (reading) the contents of the USD when the service continuity 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] When the selection information indicates a priority grant of USD, the UE 100 may specify the frequency indicated by 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 a priority grant 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 priority permission for USD, UE 100 may specify the frequency indicated in the SIB for service continuation as the desired MBS frequency for the desired MBS service, regardless of the frequency indicated in USD.

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

[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 the RRC idle state or the RRC inactive state is receiving or is interested in receiving an MBS.

[0110] In step S213, UE 100 receives a service continuity SIB 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 service continuity SIB.

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

[0112] On the other hand, when the selection information does not indicate priority 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 modified example, UE100 determines whether gNB200 (serving cell) has the capability to provide a SIB for service continuity, and based on the determination result, selects one of USD and SIB for service continuity as information for specifying a desired MBS frequency. If UE100 determines that gNB200 (serving cell) does not have the capability to provide a SIB for service continuity, it selects USD as information for specifying a desired MBS frequency. On the other hand, if UE100 determines that gNB200 (serving cell) has the capability to provide a SIB for service continuity, it selects SIB for service continuity as information for specifying a desired MBS frequency.

[0115] Here, the serving cell not being able to provide 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; ·In the SI scheduling information of SIB1 of the serving cell, there is no information indicating MBS SIB; · The serving cell is not transmitting MCCH; -SIB1, etc., does not have an identifier indicating that the MBS function (or the function to send SIBs for service continuity) is supported.

[0116] On the other hand, the serving cell's ability to provide 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, such as "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 that indicates support for the MBS function (or the function for transmitting SIBs for service continuity).

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

[0118] On the other hand, if it is determined that the serving cell has the capability to provide the service continuity SIB, the UE 100 receives the service continuity SIB from the serving cell. Here, if the serving cell has the capability to provide the service continuity SIB but does not provide the service continuity SIB, the UE 100 may request the serving cell to transmit the service continuity SIB and then receive the service continuity SIB. If information on a frequency associated with a desired MBS service is included in the service continuity SIB, the UE 100 may determine that the MBS service of interest is provided on that frequency and identify that frequency as a desired MBS frequency. On the other hand, if information on a frequency associated with the desired MBS service is not included in the service continuity SIB, the UE 100 may determine that the desired MBS service is not provided on the current frequency and / or another frequency. In this case, the UE 100 may perform a cell reselection procedure using normal frequency priority. Furthermore, 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 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 the desired MBS frequency. By determining whether to provide an MBS SIB for a neighboring cell having good wireless quality, the possibility that the neighboring cell will be reselected as a result of the subsequent measurement process and cell reselection process can be increased, thereby facilitating the UE 100 to receive an MBS.

[0123] Specifically, the UE 100 according to the third embodiment identifies at least one cell for which a measurement result for 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 illustrating an example of the 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 greater than a minimum required quality standard (a certain threshold). The predetermined criterion may also 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 its own moving speed into consideration. 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 slowly, and identify a large number of cells with high quality in step S304 when moving quickly. Here, whether the number is small or large may be determined by changing the fixed 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] If 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 measurement results for the desired MBS frequency. If the identified candidate cell is included in the at least one cell (i.e., a cell that provides 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 the UE 100 determines 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, if 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 the RRC idle state or the 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 made 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 the cell identifier of each of 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 the 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 identifiers stored in step S334 (step S338: YES), in step S339, 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 identifiers, 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 the candidate cell identified in step S337 provides an MBS SIB. This determination may be made in the same manner as in the first embodiment described above. 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] If 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 restarts the cell reselection procedure. Note that UE 100 may stop regarding the desired MBS frequency as the highest priority and restart the cell reselection procedure if the result of step S338 is "NO" without performing the process of step S340.

[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 a 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 service continuation SIB, 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 may not be 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 restarts 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 the 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 made 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 regarding 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, requesting transmission of the MBS SIB during the cell reselection procedure is not desirable from the viewpoint of delay and power consumption.

[0165] Although it is possible to include an identifier for each MBS service (each MBS session) in SIB1, the message size of SIB1 is limited, making it difficult to include an identifier for 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) broadcasted by a neighboring cell belonging to the desired MBS frequency, the SIB1 (or MIB) including information on whether the neighboring cell is restricted from providing MBS services. In response to the SIB1 (or MIB) indicating that the MBS service is not restricted, the UE 100 prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure.

[0167] In this modified example, each cell (gNB200) is assumed to understand the correspondence between the frequencies provided to UE100 in USD and service continuity SIBs and MBS services, and to recognize the MBS services to be provided in its own cell (the frequency to which it belongs). "MBS service provision is restricted" in a cell means that provision of at least one of the MBS services to be provided in the cell is (temporarily) suspended. If a cell (gNB200) is not providing any of the MBS services it should provide, it may include an identifier indicating that the MBS services are restricted in SIB1 (or MIB). Furthermore, if a cell (gNB200) is not providing any of the MBS services it should provide, it may include an identifier of the MBS service that is not provided in SIB1 (or MIB). If a cell (gNB200) is providing all of the MBS services it should provide, it may include an identifier indicating that the MBS services are not restricted in SIB1 (or MIB). Furthermore, if each cell (gNB200) is providing all of the MBS services 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 the RRC idle state or the 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 made in the same manner as in the first embodiment described above.

[0172] If it is determined that the cell belonging to the desired MBS frequency provides an 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 targets of highest priority. 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, if 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 independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow.

[0178] In the above-described 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 also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The user equipment may also 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 on a computer-readable medium. The computer-readable medium can be used to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[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 can be made within the scope that does not deviate from the gist 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 expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "based only on" and "at least in part on." Furthermore, "obtain" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may also mean including only the listed items or including additional items in addition to the listed items. Furthermore, as used in this disclosure, the term "or" is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, reference to first and second elements does not imply that only two elements may be employed therein or that the first element must precede the second element in some manner. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0182] This application claims priority to U.S. Provisional Application No. 63 / 257215 (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 upon in 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] Regarding the second distribution mode, the following agreement has been reached in RAN2#115-e:

[0185] If 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 an MBS frequency, the UE is allowed to prioritize MBS frequencies of interest.

[0186] When idle / inactive. -The UE may consider a cell reselection candidate frequency that cannot receive the MBS service during the MBS session as the lowest priority as LTE SC-PTM. -Working premise: The mapping between 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 is subject to 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. -The mapping between the frequency and the MBS service ID (e.g., SAI) is provided in a new SIB different from the MBS SIB that provides the MCCH configuration as LTE SC-PTM. - MBS service IDs (e.g., SAI) are provided in SIB and USD as LTE SC-PTM. We are waiting for feedback from other WGs on the details of IDs. -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 needed 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 MBS frequency reporting is permitted, the MBS frequencies reported from the UE are sorted in order of interest as LTE SC-PTM. - Sending LS to SA3 to check whether UE can report MBS interest information before security activation. Further consideration is needed as to whether the MII is reported via UEAssistanceInformation 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 issues: Further study is needed to determine whether the gNB can indicate a list of neighboring cells that offer the broadcast MBS service offered in the current cell, as in LTE SC-PTM.

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

[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. That is, during cell reselection, the UE needs to request each neighbor cell to provide a "not broadcast" MBS-specific SIB and acquire the MCCH scheduling information. Then, the UE needs to acquire the MCCH to check whether each neighbor cell provides the MBS service of interest.

[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 MBS service of interest 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 the same as 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] Another option is for higher layers (e.g. USD) to provide neighbor cell information, but this has proven difficult for networks, 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 in its cell reselection priority process in addition to the information provided in SIBy.

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

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

[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 like LTE SC-PTM. -If the UE can receive MBS service only by camping on an MBS frequency as LTE SC-PTM, the UE is allowed to prioritize MBS frequencies of interest.

[0201] If idle / inactive -The UE may consider a cell reselection candidate frequency that cannot receive the MBS service during the 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" SIBs. "Non-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 can be broadcast by a neighboring cell. In this case, the UE checks SIB1 only if the MBS SIB is available, regardless of 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 increase.

[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 an MBS SIB 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 current CR is described as follows: Further consideration is needed as to whether the 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 study is needed to determine whether the UE can prioritize the frequency indicated in USD if SIBy is broadcast but no mapping for the service is provided.

[0211] In general, a UE should follow the information provided by the gNB, since the gNB is responsible for frequency management and can handle the latest information compared with the USD. For example, if a neighboring cell of the gNB cannot provide MBS service due to resource shortage, the gNB knows such operational information and decides to provide it on SIBy (or MCCH). Considering that a UE is in an idle / inactive state, the USD may not be updated because it is provided by a higher layer message. Therefore, if the frequency of interest is provided on SIBy (and / or if agreed, the neighboring cell is provided on MCCH), the UE does not need to check the frequency on USD. This behavior avoids complex specifications, such as what the UE should do if the frequency of interest on USD does not match the frequency of interest on SIBy. Note that it is not intended to impose a strict requirement that UEs cannot use USD when 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, UE behavior when 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 knows that the neighboring frequency / cell does not provide the MBS service due to congestion or other reasons, and therefore wants to prevent the UE from prioritizing the frequency; 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 do not know the operational information of their neighbors. -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 because 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 or deployment policies in any case. Therefore, the UE needs to be indicated in the USD whether it is permitted to use the frequency of interest preferentially. Whether such an indication should be provided in the SIB or USD requires further study.

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

[0219] 2.2.3. Frequency Prioritization Deactivation The current CR is described as follows: Further consideration is needed as to whether the UE should stop prioritizing the frequency 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 prescribes that the priority process, measurement process, and cell reselection process are performed sequentially, and it is assumed that frequency information is only used in the priority process, while the measurement process and cell reselection process are performed as is in legacy mode.

[0221] Considering that the UE confirmed the cell providing the SIBx before reselection, i.e., confirmed that the cell can provide MBS service, 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 this depends on the UE implementation.

[0223] Condition 2 can be resolved by a 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 also be considered to depend 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 is when, after cell reselection, the UE discovers that the reselected cell does not offer the MBS service of interest. This can occur because the UE only checks whether the SIBx is broadcast; that is, the SIBx does not inform the UE of currently available MBS services (e.g., TMGI). Therefore, the UE obtains 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 its highest priority, in order to solve both problems.

[0227] Even if a frequency is mapped to MBS service in SIBy, whether or not MBS service will ultimately be provided is considered to depend on the implementation of the 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 and outstanding issues of MBS Interest Indication 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 UEAssistanceInformation or a new RRC message.

[0230] In LTE, MBMS Interest Indication (MII) is separated from UE Assistance Information (UAI). This is because the prerequisites for MII are different: SIB15 acquisition for MII and RRC connection setup for UAI. 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 prerequisites for IDC and UAI are the same in LTE (and NR), namely, 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, neighboring frequency information of an MBS-specific SIB or MCCH is required to generate an MBS Interest Indication message with the above IE. Furthermore, MBS Interest Indication is expected to be configured by an MBS-specific SIB (or MCCH), similar to 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, similar to 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 transmission of MBS Interest Indication if the UE can obtain 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 but 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 commonly understood that for multicast sessions, the core network notifies the gNB of the UE's interest because there is a session join procedure at the upper layer. The UE's interest also applies to MBS services. The gNB may know the frequency of the MBS of the UE's interest and the cell providing the MBS service. However, the priority between MBS reception and unicast may not be provided by the core network because it is purely AS-related information. In other words, it is strange for the UE to convey priority information to the core network during the session join procedure.

[0237] Observation 4: In a multicast session, the core network provides the MBS service of interest 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 MBS and unicast.

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

[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 perspective of service continuity) RAN2 agreed to postpone the discussion on whether a dedicated MCCH is required until RAN1 has made progress on the BWP / CFR of 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 being broadcast based.

[0242] On the other hand, the dedicated MCCH can be considered from the perspective of broadcast service continuity. In RAN2, it has already been agreed that "it is assumed that connected UEs can reuse the LTE SC-PTM mechanism to receive PTM configuration in the 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 configurations, but not for inter-cell service continuity.

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

[0245] Proposal 11: RAN2 should agree to provide the MCCH, or 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 session in progress using the second delivery mode NR MBS is expected to support various types of use cases, as quoted from the WID below. It has been confirmed that NR MBS should be well-designed for a variety of requirements, from lossless applications like software distribution to UDP-type streaming like IPTV, as well as delay-sensitive applications like mission-critical and V2X to delay-tolerant applications like IoT, in addition to other dimensional requirements. In practice, it has been confirmed that 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 communication, and IoT applications.

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

[0249] RAN2 prioritizes "RRC Connected Mode." RAN2 prioritizes support for active multicast in RRC Connected Mode in Rel-17. It was agreed that "time permitting, support for multicast in 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 delivery mode, it does not preclude multicast sessions using the second delivery mode for UEs in Connected Mode.

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

[0251] 2.7.Details of MBS-dedicated SIB We understand that whether MBS services are provided via PTP or PTM, and via primary or secondary delivery mode, is up to the network implementation. This allows for a good balance between service reliability and spectral 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. If the UE first checks the MCCH and the MCCH does not contain MTCH scheduling information for the desired MBS service, it can be assumed that the UE recognizes that the MBS service is only available via RRC Connected, i.e., PTP, primary delivery mode, or unicast (PDU session). However, this process can be burdensome for the UE and may result in some delay before the MBS service can be obtained. Therefore, it is worth considering whether an 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 that it will be used for broadcast sessions. Furthermore, from the UE's perspective, it is unclear whether the gNB can obtain MBS information. Furthermore, from the UE's perspective, it is unclear whether the gNB can obtain information about MBS services that the UE is interested in (AMF may provide this information in multicast sessions but not in broadcast sessions). As a result, the UE does not know whether it should send MBS Interest Indication for MBS services of interest. Therefore, it would be useful for the UE if the gNB provided information about whether MBS Interest Indication is permitted for each MBS service. In other words, which MBS services require MBS Interest Indication. Therefore, RAN2 must 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 the MCCH into the BCCH, i.e., a one-step configuration as shown in Figure 19. For example, the SIB provides MTCH scheduling information directly, i.e., without the MCCH, which would provide optimization for delay-tolerant services and / or power-sensitive UEs. For example, a UE can request the SIB (on-demand), and the gNB can start providing the SIB and the corresponding services after requests from multiple UEs. These UEs do not need to monitor the repeatedly broadcast MCCH.

[0256] Proposal 15: RAN2 should agree as a configuration option to support multicast reception without MCCH (i.e., one-step configuration), e.g., 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. Based on this, it seems worth considering an extension on top of LTE eMBMS.

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

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

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

[0261] Therefore, it is worth considering whether to introduce a mechanism to collect UE assistance information (especially MBMS Counting) from idle / inactive UEs. Needless to say, it would be desirable for these idle / inactive UEs to be able to report information without transitioning to RRC Connected. For example, this would be possible if PRACH resource partitioning related to MBS services were introduced for such reporting.

[0262] Since NR MBS does not have an MCE, the MCE function will be integrated into the gNB. Therefore, regardless of what RAN3 decides from the network interface perspective, RAN2 will decide whether NR MBS requires counting.

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

[0264] 1: Mobile communication system 10:RAN 20 :CN 100:UE 110: Receiving unit 120: Transmitter 130: Control unit 200 :gNB 210: Transmission unit 220: Receiving unit 230: Control unit 240: Backhaul communication unit

Claims

1. 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 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, prioritizing the desired MBS frequency over other frequencies in a cell reselection procedure in accordance with 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, receiving system information (SI) scheduling information broadcast by a cell belonging to the desired MBS frequency; The prioritizing step 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 the MBS system information block even if the cell does not provide the MBS system information block. Communication method.

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 to be provided in response to the SI scheduling information not including information on the broadcast information. The communication method according to claim 2 .

4. 1. A user equipment for use in a mobile communication system supporting a multicast broadcast service (MBS), comprising: In a Radio Resource Control (RRC) idle state or an RRC inactive state, a receiving unit for receiving broadcast information including frequency mapping information indicating a correspondence relationship between an MBS service and a frequency; a control unit that, when the broadcast information includes the frequency mapping information, prioritizes the desired MBS frequency over other frequencies in a cell reselection procedure even if the frequency mapping information does not include frequency mapping information for a desired MBS service, 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; The receiver receives system information (SI) scheduling information broadcast by a cell belonging to the desired MBS frequency; The control unit prioritizes the desired MBS frequency over the other frequencies in the cell reselection procedure in response to the SI scheduling information including information of the MBS system information block even if the cell does not provide the MBS system information block. User equipment.

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

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

7. A user equipment according to claim 4 and a network node. Mobile communication system.

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