Communication method

Abstract

This communication method is executed by a UE 100 in a mobile communication system that provides a multicast broadcast service (MBS). The communication method comprises: a step for receiving MBS signals transmitted from a plurality of cells constituting a single frequency network (SFN) by using the same identifier; a step for measuring reception quality of MBS signals by setting the MBS signals having the same identifier as measurement targets; and a step for reporting to the network a measurement result obtained in the measurement step.

Description

Technical Field

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

Background Art

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

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] The 5G / NR multicast and broadcast service is desired to provide a service improved over the 4G / LTE multicast and broadcast service.

[0005] Therefore, an object of the present disclosure is to enable an improved multicast and broadcast service.

[0006] The communication method according to the first aspect is a method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS). The communication method includes steps of receiving an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN), measuring the reception quality of the MBS signal with the same identifier as a measurement target, and reporting the measurement result obtained in the measuring step to a network.

[0007] The communication method according to the second aspect is a method executed by a user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system that provides a multicast / broadcast service (MBS). The communication method includes steps of receiving an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN), and performing priority control so as to prioritize the cells constituting the SFN over the cells not constituting the SFN in a cell reselection procedure.

[0008] The communication method according to the third aspect is a method executed by a user equipment in a mobile communication system that provides a multicast / broadcast service (MBS). The communication method includes steps of receiving an MBS reception setting transmitted by dedicated signaling from a network to the user equipment in a radio resource control (RRC) connected state, and performing MBS reception using the MBS reception setting for a predetermined time after transitioning to an RRC idle state or an RRC inactive state.

Brief Description of Drawings

[0009]

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[0010] With reference to the drawings, a mobile communication system according to an embodiment will be described. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] [First Embodiment] (Configuration of Mobile Communication System) FIG. 1 is a diagram showing the configuration of a mobile communication system according to an embodiment. The mobile communication system 1 complies with the 5th Generation System (5GS) of the 3GPP standard. Hereinafter, the 5GS will be described as an example, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system. Further, the 6th Generation (6G) system may be at least partially applied to the mobile communication system.

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

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

[0014] NG-RAN10 includes base stations (referred to as "gNB" in the 5G system) 200. The gNBs 200 are interconnected via the Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its cell. The gNB 200 has functions such as radio resource management (RRM), routing function for user data (hereinafter simply referred to as "data"), and measurement control function for mobility control and scheduling. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

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

[0016] The 5GC 20 includes the AMF (Access and Mobility Management Function) and the UPF (User Plane Function) 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 performs transfer control of data. The AMF and the UPF are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network.

[0017] Figure 2 is a diagram showing the configuration of the UE 100 (user equipment) according to the 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.

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

[0019] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0020] The control unit 130 performs various controls and processes in the UE 100. Such processes include the processes of each layer described later. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of the baseband signal, etc. The CPU executes the programs stored in the memory to perform various processes.

[0021] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to the embodiment. The gNB 200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and a backhaul communication unit 240. The transmitting unit 210 and the receiving unit 220 constitute a radio communication unit that performs radio communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0022] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

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

[0024] The control unit 230 performs various controls and processes in the gNB 200. Such processes include the processes of each layer described later. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for the processing 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, etc. The CPU executes programs stored in the memory to perform various processes.

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

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

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

[0028] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Between the PHY layer of UE100 and the PHY layer of gNB200, data and control information are transmitted via physical channels. Note that the PHY layer of UE100 receives downlink control information (DCI) transmitted on the physical downlink control channel (PDCCH) from gNB200. Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI), and acquires the DCI that has been successfully decoded as DCI addressed to its own UE. The DCI transmitted from gNB200 has CRC parity bits scrambled by the RNTI added thereto.

[0029] The MAC layer performs priority control of data, retransmission processing by hybrid automatic repeat request (HARQ), and random access procedures, etc. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via transport channels. The MAC layer of gNB200 includes a scheduler. The scheduler determines the transport format of the uplink and downlink (transport block size, modulation and coding scheme (MCS)) and the resource blocks allocated to UE100.

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

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

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

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

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

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

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

[0037] (Overview of MBS) The overview of MBS according to the embodiment will be described. MBS is a service that enables broadcast or multicast, that is, one-to-many (PTM: Point To Multipoint) data transmission from the NG-RAN 10 to the UE 100. As use cases (service types) of MBS, public security communication, mission-critical communication, V2X (Vehicle to Everything) communication, IPv4 or IPv6 multicast distribution, IPTV (Internet protocol television), group communication, software distribution, etc. are assumed.

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

[0039] The multicast service provides services not to all UEs 100 but to a group of UEs 100 that participate in the multicast service (multicast session). The MBS session used for the multicast service is called a multicast session.

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

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

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

[0043] In the 5GC Individual MBS Traffic delivery method, 5GC 20 receives a single copy of the MBS data 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 per UE 100 needs to be associated with the multicast session.

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

[0045] From the perspective of the RAN (5G RAN) 10, for the wireless transmission of MBS data in the 5GC Shared MBS Traffic delivery method, there are two delivery methods: PTP (Point-To-Point) and PTM (Point-To-Multipoint). PTP means unicast, and PTM means multicast and broadcast.

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

[0047] The PTP delivery method and the PTM delivery method mainly relate to the user plane. As control modes for MBS data delivery, there are two delivery modes: the first delivery mode and the second delivery mode.

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

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

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

[0051] The MBS reception setting includes MBS traffic channel setting information (hereinafter referred to as "MTCH setting information") regarding the setting of the MBS traffic channel that transmits MBS data. The MTCH setting information includes MBS session information regarding the MBS session (including the MBS session identifier described later) and the scheduling information of the MTCH corresponding to this MBS session. The scheduling information of the MTCH may include the discontinuous reception (DRX) setting of the MTCH. The discontinuous reception setting may include one or more parameters of a timer value (On Duration Timer) that defines the on period (On Duration: reception period), a timer value (Inactivity Timer) that extends the on period, a scheduling interval or DRX cycle (Scheduling Period, DRX Cycle), an offset value (Start Offset, DRX Cycle Offset) of the start subframe of the scheduling or DRX cycle, a slot offset value (Slot Offset) of the start delay slot of the on period timer, a timer value (Retransmission Timer) that defines the maximum time until retransmission, and a timer value (HARQ RTT Timer) that defines the minimum interval until the DL allocation of HARQ retransmission. Note that the MTCH (Multicast Traffic Channel) is a type of logical channel. The MTCH is mapped to a downlink shared channel (DL-SCH: Down Link - Shared CHannel), which is a type of transport channel.

[0052] The second delivery mode (Delivery mode 2: DM2) is a delivery mode that can be used not only by the UE100 in the RRC connected state but also by the UE100 in the RRC idle state or the RRC inactive state, and is a delivery mode for low QoS requirements. The second delivery mode is used for the broadcast session among the MBS sessions. However, the second delivery mode may also be applicable to the multicast session.

[0053] The setting of MBS reception in the second delivery mode is performed by broadcast signaling. For example, the setting of MBS reception in the second delivery mode is performed by a logical channel broadcast from gNB200 to UE100, such as a broadcast control channel (BCCH) and / or a multicast control channel (MCCH). UE100 can receive BCCH and MCCH using, for example, a dedicated RNTI predefined in the technical specifications. The RNTI for BCCH reception may be SI-RNTI, and the RNTI for MCCH reception may be MCCH-RNTI.

[0054] In the second delivery mode, UE100 may receive MBS data in the following three steps. First, UE100 receives MCCH configuration information from the MBS system information block (MBS SIB) transmitted on BCCH from gNB200. Second, UE100 receives MCCH from gNB200 based on the MCCH configuration information. MCCH transmits MTCH configuration information. MCCH may include adjacent cell information indicating whether the currently provided MBS session is also provided in adjacent cells. Third, UE100 receives MTCH (MBS data) based on the MTCH configuration information. Hereinafter, MTCH configuration information and / or MCCH configuration information may be referred to as MBS reception settings.

[0055] In the first and second delivery modes, UE100 may receive MTCH using a group RNTI (G-RNTI) assigned from gNB200. G-RNTI corresponds to the RNTI for MTCH reception. G-RNTI may be included in the MBS reception setting (MTCH configuration information).

[0056] Note that the network can provide different MBS services for each MBS session. An MBS session is identified by at least one of a TMGI (Temporary Mobile Group Identity), a source-specific IP multicast address (which consists of a source unicast IP address such as an application function or an application server, and an IP multicast address indicating a destination address), a session identifier, and a G-RNTI. At least one of the TMGI, the source-specific IP multicast address, and the session identifier is called an MBS session identifier. The TMGI, the source-specific IP multicast address, the session identifier, and the G-RNTI are collectively called MBS session information.

[0057] FIG. 8 is a diagram showing an example of internal processing related to MBS reception of the UE100 according to the embodiment. FIG. 9 is a diagram showing another example of internal processing related to MBS reception of the UE100 according to the embodiment.

[0058] One MBS radio bearer (MRB) is one radio bearer for transmitting a multicast session or a broadcast session. That is, there are cases where a multicast session is associated with the MRB and cases where a broadcast session is associated with the MRB.

[0059] The MRB and the corresponding logical channel (e.g., MTCH) are set from the gNB200 to the UE100 by RRC signaling. The setting procedure of the MRB may be separated from the setting procedure of the data radio bearer (DRB). In RRC signaling, one MRB can be set as "PTM only", "PTP only", or "both PTM and PTP". Such a bearer type of the MRB can be changed by RRC signaling.

[0060] In FIG. 8, an example is shown in which a multicast session and a dedicated traffic channel (DTCH) are associated with MRB#1, a multicast session and MTCH#1 are associated with MRB#2, and a broadcast session and MTCH#2 are associated with MRB#3. That is, MRB#1 is an MRB for PTP only, MRB#2 is an MRB for PTM only, and MRB#3 is an MRB for PTM only. Note that the DTCH is scheduled using the cell RNTI (C-RNTI). The MTCH is scheduled using the G-RNTI.

[0061] The PHY layer of the UE 100 processes the user data (received data) received on the PDSCH, which is one of the physical channels, and sends it to the downlink shared channel (DL-SCH), which is one of the transport channels. The MAC layer (MAC entity) of the UE 100 processes the data received on the DL-SCH and sends the received data to the corresponding logical channel (corresponding RLC entity) based on the logical channel identifier (LCID) included in the header (MAC header) included in the received data.

[0062] In FIG. 9, an example is shown in which a DTCH and an MTCH are associated with an MRB associated with a multicast session. Specifically, one MRB is split into two legs, one leg is associated with the DTCH, and the other leg is associated with the MTCH. The two legs are combined in the PDCP layer (PDCP entity). That is, the MRB is an MRB for both PTM and PTP. Such an MRB may be called a split MRB.

[0063] (Operation according to the first embodiment) FIG. 10 is a diagram for explaining a single frequency network (SFN) according to the first embodiment.

[0064] In the first embodiment, a plurality of cells constitute a single frequency network (SFN) for a certain MBS session. Each cell constituting the SFN simultaneously transmits the same MBS signal at the same frequency. Here, the MBS signal refers to a radio signal including MBS data and / or MBS control information. In the SFN, PTM (multicast / broadcast) transmission is performed using the same G-RNTI from a plurality of cells. A UE 100 located in the overlapping area of the plurality of cells synthesizes and receives radio waves from these plurality of cells. Therefore, even when the UE 100 is located at the cell edge, it is easy to realize good MBS reception.

[0065] Note that not limited to the SFN, in MBS, the network performs PTM transmission using a single cell or a plurality of cells in a certain area, so the cells constituting the SFN can change dynamically to some extent. Also, in MBS, the network performs PTM transmission using a single cell or a plurality of cells for each service (MBS session), so the cells constituting the SFN can be different for each service.

[0066] FIG. 11 is a diagram showing a first operation scenario of the mobile communication system 1 according to the embodiment.

[0067] gNB 200A manages cell C1, and gNB 200B adjacent to gNB 200A manages cell C2. Cell C1 and cell C2 at least partially have overlapping coverage. gNB 200A and gNB 200B are interconnected via an Xn interface which is an interface between base stations. Assume that the inter-base station communication between gNB 200A and gNB 200B is performed on the Xn interface.

[0068] gNB200A provides an MBS session in cell C1. Specifically, gNB200A receives MBS data belonging to the MBS session from UPF300B and transmits the MBS data in PTM (multicast / broadcast) in cell C1. UE100 in the RRC connected state receives (MBS reception) the MBS data transmitted in PTM in cell C1. The reception (MBS reception) of the MBS data transmitted in PTM is also referred to as PTM reception.

[0069] gNB200B provides an MBS session in cell C2. Specifically, gNB200B receives MBS data belonging to the MBS session from UPF300B and transmits the MBS data in PTM in cell C2. Cell C2 constitutes an SFN together with cell C1, and gNB200B provides the same MBS session in cell C2 as the MBS session provided in cell C1.

[0070] FIG. 12 is a diagram showing a second operation scenario of the mobile communication system 1 according to the embodiment.

[0071] The second operation scenario is different from the first operation scenario in that cells C1 and C2 are managed by one gNB200. gNB200 provides an MBS session in each of cells C1 and C2. Specifically, gNB200 transmits MBS data in PTM (multicast / broadcast) in each of cells C1 and C2. Cells C1 and C2 constitute an SFN, and gNB200 provides the same MBS session in cells C1 and C2.

[0072] In the scenario as described above, for example, UE100 in the RRC connected state measures the reception quality of the received signal and reports the measurement result to the network (gNB200). There are the following problems considered regarding the measurement of the SFN.

[0073] In a normal measurement report, measurements and reports are performed on cells. For example, UE100 measures the SSB (Synchronization Signal / PBCH block) transmitted by each cell. The SSB includes a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), a Demodulation Reference Signal (DMRS), and a Physical Broadcast Channel (PBCH). The PBCH transmits the MIB. The received quality to be measured is, for example, the Reference Signal Received Power (RSRP), the reference signal received Quality (RSRQ), and / or the Signal-to-Interference-plus-Noise Ratio (SINR).

[0074] Such cell-based measurements result in a deterioration of the received quality when UE100 moves to the cell edge, even when the serving cell and neighboring cells of UE100 form an SFN. Therefore, the network (gNB200) cannot accurately grasp the reception status of UE100 regarding the PTM transmitted with the SFN based on the measurement report. Thus, there is a problem that the network (gNB200) cannot appropriately perform, for example, the switching from PTM to PTP or network optimization.

[0075] In the first embodiment, UE100 first receives an MBS signal transmitted using the same identifier from a plurality of cells constituting an SFN. The same identifier may be a Group Radio Network Temporary Identifier (G-RNTI), a Temporary Mobility Group Identifier (TMGI), a Multicast Radio Bearer (MRB) identifier, a logical channel identifier (LCID) of a Multicast Traffic Channel (MTCH), or a Multicast Control Channel - Radio Network Temporary Identifier (MCCH-RNTI).

[0076] Second, the UE 100 measures the reception quality of the MBS signal using the same identifier as the measurement target. The reception quality may be RSRP, RSRQ, SINR, bit error rate (BER), frame error rate (FER), or block error rate (BLER). For example, the UE 100 may measure the RSRP, RSRQ, SINR, BER, FER, or BLER of the MBS signal in units of G-RNTI, in units of TMGI, in units of MRB identifier, in units of LCID of MTCH, or in units of MCCH-RNTI. The measurement may be performed when the UE 100 is in the RRC connected state. Also, the measurement may be performed when the UE 100 is in the RRC idle state or the RRC inactive state. The reference signal used for measuring RSRP, RSRQ, and SINR is not limited to the SSB, and may also be a channel state information reference signal (CSI-RS) or a DMRS.

[0077] Third, the UE 100 reports the measurement results obtained by the measurement to the network (gNB 200). The UE 100 may report the same identifier associated with the measurement results to the network together with the measurement results.

[0078] Thereby, the network (gNB 200) can accurately grasp the reception status of the UE 100 with respect to the PTM transmitted in the SFN based on the measurement report from the UE 100. Therefore, the network (gNB 200) can appropriately perform, for example, switching from PTM to PTP and network optimization.

[0079] In the first embodiment, the UE 100 receives from the network (gNB 200) a measurement setting for setting the same identifier (that is, the identifier used for the MBS signal in the SFN) as the measurement target. The UE 100 performs the measurement based on the measurement setting. Thereby, the network (gNB 200) can specify the same identifier to be the measurement target.

[0080] In the first embodiment, the measurement configuration may include a measurement report configuration for setting a measurement report. The measurement report configuration may include a trigger configuration for setting a trigger condition for reporting a measurement result obtained by measuring the same identifier. UE100 may perform reporting (measurement report) in response to the measurement result satisfying the trigger condition. Thereby, the network (gNB200) can specify the identifier to be measured.

[0081] FIG. 13 is a diagram showing a first operation example according to the first embodiment.

[0082] In step S100, UE100 is in the RRC connected state.

[0083] In step S101, the network 50 (gNB200) transmits UE-specific signaling including a measurement configuration related to the measurement of the SFN to UE100. The UE-specific signaling may be an RRC reconfiguration message.

[0084] The measurement configuration includes an identifier to be measured (G-RNTI, MBS session identifier (TMGI), MRB ID, MTCH LCID, or MCCH-RNTI) as a measurement target setting. The measurement configuration may include a specification of a channel such as measuring the MCCH.

[0085] The measurement configuration includes a measurement report configuration for setting a trigger condition for a measurement report. The trigger condition may be for setting an event for measurement reporting by an event trigger. Also, the trigger condition may be for setting a periodic measurement report.

[0086] The event for measurement reporting by an event trigger may be, for example, the following event for the identifier to be measured: · An event that the received quality (e.g., RSRP, RSRQ, or SINR) falls below a threshold or an event that the received quality exceeds the threshold; · An event that MBS reception (PTM reception) fails for a certain period or a certain number of times; · An event that the error rate (BER, FER, or BLER) is below a threshold or an event that the error rate is above the threshold.

[0087] In step S102, UE100 receives an MBS signal from network 50. Prior to receiving the MBS data, it is assumed that UE100 receives MBS reception settings from network 50.

[0088] In step S103, UE100 performs measurements on the set measurement objects according to the measurement settings in step S101. Here, UE100 may perform measurements only during the on-duration in the discontinuous reception (DRX) pattern associated with the measurement object (such as G-RNTI). UE100 may perform measurements only on the G-RNTI etc. that it is interested in receiving or is receiving. Also, UE100 may perform measurements only on the G-RNTI etc. that it is not interested in receiving. In the case of the first delivery mode (DM1), UE100 may perform measurements only on the G-RNTI etc. for which an MRB is set from gNB200.

[0089] In step S104, UE100 determines whether the trigger condition for the measurement report is satisfied. Here, the description will proceed assuming that the trigger condition is satisfied.

[0090] In step S105, UE100 transmits a measurement report including the measurement results obtained in step S103 to network 50. The measurement results (measurement report) include the identifier (G-RNTI, MBS session identifier, MRB ID, MTCH LCID, or MCCH-RNTI) on which the measurement was performed. Identification information such as an identifier that the UE is interested in receiving or is receiving (such as G-RNTI etc.) or an identifier that the UE is not interested in receiving may be assigned to the identifier. The measurement results (measurement report) may also include information indicating the frequency and / or bandwidth part (BWP) on which the measurement was performed.

[0091] The network 50 (gNB200) may change the bearer type from PTM to PTP or adjust the MCS of PTM based on the measurement results (measurement reports) from the UE100.

[0092] FIG. 14 is a diagram showing a second operation example according to the first embodiment. In the second operation example, the UE100 performs a process of recording measurement results (hereinafter referred to as "logging"). Here, the differences from the above-described first operation example will be described.

[0093] In step S151, the network 50 (gNB200) transmits UE-specific signaling including the measurement settings as described above to the UE100. The information included in the measurement settings is the same as the above-described information, but the above-described "trigger condition" may be read as a "logging condition".

[0094] In step S152, the UE100 may transition from the RRC connected state to the RRC idle state or the RRC inactive state.

[0095] In step S153, the UE100 stores (logs) the measurement results obtained in step S103. The UE100 may store the measurement results as a measurement log together with the UE location information and / or the time stamp.

[0096] In step S154, the UE100 may send a log availability notification indicating that it has a measurement log to the network 50. For example, the UE100 may send the notification during the random access procedure to the network 50.

[0097] In step S155, the network 50 (gNB200) may send a log transmission request to the UE100 requesting the transmission of the measurement log.

[0098] The gNB200 that has received the measurement result (measurement log) in step S105 may transfer the received measurement result (measurement log) to OAM (Operations Administration Maintenance).

[0099] [Second Embodiment] Regarding the second embodiment, differences from the above-described first embodiment will be mainly described. The second embodiment is an embodiment related to a cell reselection procedure performed by the UE100 in the RRC idle state or the RRC inactive state in the network 50 configured with an SFN.

[0100] Here, an overview of a general cell reselection procedure will be described. FIG. 15 is a diagram showing a schematic flow of a general cell reselection procedure.

[0101] In step S10, the UE100 performs frequency prioritization processing based on the priority (also referred to as "absolute priority") for each frequency specified by the network 50 (gNB200), for example, by a system information block (SIB) or an RRC release message. Specifically, the UE100 manages the frequency priorities specified by the network 50 (gNB200) for each frequency.

[0102] In step S20, the UE100 performs measurement processing to measure the radio quality for each of the serving cell and the neighboring cells. The UE100 measures the reference signals transmitted by each of the serving cell and the neighboring cells, specifically, the received power and received quality of the CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, the UE100 always measures the radio quality for frequencies having a priority higher than the priority of the frequency of the current serving cell, and for frequencies having a priority equal to or lower than the priority of the frequency of the current serving cell, measures the radio quality of the frequencies having an equal or lower priority when the radio quality of the current serving cell falls below a predetermined quality.

[0103] In step S30, the UE 100 performs a cell reselection process of reselecting the cell on which it camps based on the measurement results in step S20. For example, when the priority of the frequency of an adjacent cell is higher than the priority of the current serving cell and the adjacent cell satisfies a predetermined quality criterion (i.e., the required minimum quality criterion) over a predetermined period, the UE 100 may perform cell reselection to the adjacent cell. When the priority of the frequency of an adjacent cell is the same as the priority of the current serving cell, the UE 100 ranks the radio quality of the adjacent cells and may perform cell reselection to an adjacent cell having a rank higher than the rank of the current serving cell over a predetermined period. When the priority of the frequency of an adjacent 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 adjacent cell is higher than another threshold continuously over a predetermined period, the UE 100 may perform cell reselection to the adjacent cell.

[0104] Under such a premise, in the RRC idle state or the RRC inactive state, MBS reception from the SFN Perform By using the cells constituting the SFN as reselection candidates, the UE 100 can easily perform continuous MBS reception.

[0105] In the second embodiment, the UE 100 receives MBS signals transmitted using the same identifier from a plurality of cells constituting the SFN. The UE 100 in the RRC idle state or the RRC inactive state performs priority control so that the cells constituting the SFN are prioritized over the cells not constituting the SFN in the cell reselection procedure.

[0106] In the second embodiment, the UE 100 may receive a notification indicating that it is permitted to perform priority control from the network 50 (gNB 200). The UE 100 may perform priority control only when it has received the notification from the network 50 (gNB 200).

[0107] In the second embodiment, the UE 100 may receive from the network 50 (gNB 200) SFN information indicating an MBS session provided by the SFN. When the information indicates that the MBS session being received by the UE 100 is provided by the SFN, the UE 100 may determine the frequency to which the current serving cell of the UE 100 belongs as the highest priority among the frequency priorities used in the cell reselection procedure.

[0108] In the second embodiment, the UE 100 may receive from the network 50 (gNB 200) a list including identifiers of each cell constituting the SFN. For example, the UE 100 may receive from a serving cell constituting the SFN a list of adjacent cells constituting the SFN. In the cell reselection procedure, the UE 100 may control cell reselection so as to reselect the cells (adjacent cells) indicated in the list with priority over the cells (adjacent cells) not indicated in the list.

[0109] In the second embodiment, when the UE 100 reselects an adjacent cell constituting the SFN, the UE 100 may skip reception of the MCCH from the adjacent cell and receive the MTCH from the adjacent cell.

[0110] FIG. 16 is a diagram showing an operation example according to the second embodiment.

[0111] In step S201, the network 50 (gNB 200) transmits SFN information related to the SFN to the UE 100. The UE 100 in the RRC connected state, RRC idle state, or RRC inactive state receives the SFN information. The network 50 (gNB 200) may transmit to the UE 100 an SIB, MCCH, RRC Reconfiguration message, or RRC Release message including the SFN information.

[0112] The SFN information may be information (identifier) indicating the MBS sessions constituting the SFN. For example, the SFN information may include an MBS session identifier (e.g., TMGI), an MRB ID, an MTCH LCID, a G-RNTI (hereinafter referred to as "MBS session identifier etc."). The SFN information may be an identifier indicating whether or not it constitutes an SFN in the MRB setting or the MTCH setting information. The SFN information may include a list of MBS session identifiers etc. constituting the SFN. The SFN information may include a cell ID (list) of adjacent cells constituting the SFN for each MBS session identifier etc.

[0113] In step S201, the network 50 (gNB200) may notify the UE100 of information indicating whether or not it is allowed to preferentially reselect cells constituting the SFN. The notification may be an information element explicitly such as "allowed". The notification may implicitly indicate that it is "allowed" by notifying the SFN information.

[0114] In step S202, the UE100 in the RRC idle state or the RRC inactive state may perform MBS reception (PTM reception) from the serving cell.

[0115] When the MBS session being received by the UE100 in the RRC idle state or the RRC inactive state constitutes an SFN, the following processing is performed in the cell reselection procedure.

[0116] The UE100 may determine whether or not preferential reselection of SFN cells is permitted (step S203). If not permitted, the UE100 may perform a normal cell reselection procedure.

[0117] UE100 may consider the frequency priority of the current serving frequency (i.e., the frequency to which the cells constituting the SFN belong) as the highest priority (step S204). As a result, UE100 preferentially reselects inter-frequency cells, i.e., the cells constituting the SFN (step S205).

[0118] UE100 may add an offset in the ranking (ranking) for the current serving cell and / or adjacent cells constituting the SFN (step S204). For example, UE100 adds an offset to the rank (or radio quality value) so that the rank of the cells constituting the SFN becomes higher. The offset value may be set by gNB200 for UE100 in SIB, MCCH, RRC Reconfiguration, or RRC Release.

[0119] After UE100 reselects the adjacent cells constituting the SFN (step S205), it may skip receiving MCCH from the cell.

[0120] [Third Embodiment] Regarding the third embodiment, the differences from the above-described first and second embodiments will be mainly described.

[0121] In the third embodiment, the UE 100 in the RRC idle state or the RRC inactive state receives an MBS session (for example, a multicast session) to which the first delivery mode (DM1) is applied. For example, assume a scenario in which, while the UE 100 is receiving the MBS session in the RRC connected state, the load on the network 50 (gNB 200) increases, and the network 50 (gNB 200) temporarily transitions the UE 100 to the RRC idle state or the RRC inactive state. The UE 100 that has transitioned to the RRC idle state or the RRC inactive state can continue to receive MBS for a certain period (predetermined time) using the settings of the first delivery mode. However, after the elapse of the certain period (predetermined time), the UE 100 may discard the settings of the first delivery mode. In that case, the UE 100 that desires to continue receiving MBS transitions to the RRC connected state and acquires the settings of the first delivery mode from the network 50 (gNB 200).

[0122] In the third embodiment, the UE 100 receives, in the RRC connected state, an MBS reception setting (that is, a setting of the first delivery mode) transmitted by dedicated signaling from the network 50 (gNB 200) to the UE 100. The MBS reception setting may include the above-described MTCH setting information. The UE 100 performs MBS reception using the MBS reception setting for a predetermined time after transitioning to the RRC idle state or the RRC inactive state. The dedicated signaling may include information specifying the predetermined time.

[0123] In the third embodiment, the UE 100 may transition to the RRC connected state in response to the elapse of the predetermined time. After transitioning to the RRC connected state, the UE 100 may receive a new MBS reception setting transmitted by dedicated signaling from the network 50 (gNB 200) to the UE 100.

[0124] FIG. 17 is a diagram showing an operation example according to the third embodiment.

[0125] In step S301, UE100 is in the RRC connected state.

[0126] In step S302, UE100 receives an RRC Reconfiguration message including the setting of the first delivery mode from network 50 (gNB200). UE100 may start PTM reception using the setting of the first delivery mode.

[0127] In step S303, network 50 (gNB200) transmits an RRC Release message to UE100.

[0128] In step S304, in response to receiving the RRC Release message, UE100 transitions to the RRC idle state or the RRC inactive state.

[0129] UE100 may continue to apply the setting received in the RRC Reconfiguration message (step S302) in the RRC idle state or the RRC inactive state for the setting of the first delivery mode. Alternatively, the setting of the first delivery mode may be set for UE100 again in the RRC Release message (step S303). The setting of the first delivery mode includes an expiration date (timer value) corresponding to the above-mentioned predetermined time.

[0130] In step S305, when transitioning to the RRC idle state or the RRC inactive state, UE100 starts a timer set with the expiration date (timer value).

[0131] In step S306, while the timer is running, UE100 continues PTM reception using the setting of the first delivery mode.

[0132] In step S307, UE100 detects the expiration of the timer.

[0133] In step S308, UE100 performs a random access procedure with network 50 (gNB200) in response to the expiration of the timer. Here, UE100 transmits an RRC Setup Request message or an RRC Resume Request message that constitutes message 3 (Msg3) of the random access procedure to request an RRC connection. UE100 may start the random access procedure before the timer expires. Note that there may be two timers, one being the timer that triggers an RRC connection request and the other being the timer that indicates the valid period of the setting of the first delivery mode (triggering setting abandonment).

[0134] Note that when the timer expires, if UE100 has no interest in the MBS service (MBS session), the above request for an RRC connection may not be made. In that case, UE100 may discard the MRB setting and maintain the RRC idle state or the RRC inactive state.

[0135] In step S308, UE100 may notify gNB200 that it requests only an update of the setting of the first delivery mode. For example, UE100 may include an information element (Establishment Cause, Resume Cause) indicating that it requests only an update of the setting of the first delivery mode in the RRC Setup Request message or the RRC Resume Request message. Alternatively, UE100 may notify gNB200 that it requests only an update of the setting of the first delivery mode in message 5 (Msg5) of the random access procedure, or may notify it later in a UE Assistance Information message. When using the Msg5 or UE Assistance Information message, UE100 may further notify the MBS session identifier (TMGI) for which a setting update is desired.

[0136] In step S309, when the network 50 (gNB200) accepts the request, it configures the UE100 with the first delivery mode. The network 50 (gNB200) may reconfigure the first delivery mode. Alternatively, the network 50 (gNB200) may notify the UE100 only of an identifier indicating that the current configuration is to be continued. After this configuration, the network 50 (gNB200) may transition the UE100 back to the RRC idle state or the RRC inactive state again.

[0137] [Other Embodiments] The above-described operation flows are not limited to being implemented separately and independently, and two or more operation flows can be combined and implemented. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0138] In the above-described embodiments and examples, an example where the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. Further, the base station may be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may be the DU of the IAB node. Also, the user equipment may be the MT (Mobile Termination) of the IAB node.

[0139] A program may be provided that causes a computer to execute each process performed by the UE100 or the gNB200. The program may be recorded on a computer-readable medium. By using a computer-readable medium, it is possible 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. Further, circuits that execute each process performed by the UE100 or the gNB200 may be integrated, and at least a part of the UE100 or the gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip).

[0140] As used in this disclosure, the phrases "based on" and "depending on" do not mean "only based on" or "only depending on" unless otherwise specified. The phrase "based on" means both "only based on" and "at least partially based on". Similarly, the phrase "depending on" means both "only depending on" and "at least partially depending on". Also, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from other nodes, or obtaining the information by generating the information. The terms "include", "comprise", and their variants do not mean including only the listed items, but may include only the listed items or may further include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to be an exclusive disjunction. Further, any reference to elements using designations such as "first", "second", etc. used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used in this specification as a convenient way to distinguish between two or more elements. Thus, a reference to a first and a second element does not mean that only two elements may be employed there or that the first element must precede the second element in any form. In this disclosure, for example, when articles are added by translation, such as a, an, and the in English, these articles shall be construed to include pluralities unless the context clearly indicates otherwise.

[0141] As described above in detail with reference to the drawings, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

[0142] This application claims the priority of Japanese Patent Application No. 2021-178062 (filed on October 29, 2021), and all of its content is incorporated into the specification of this application.

Explanation of Reference Signs

[0143] 1: Mobile communication system 10: RAN 20: CN 100: UE 110: Receiver 120: Transmitter 130: Control unit 200: gNB 210: Transmitter 220: Receiver 230: Control unit 240: Backhaul communication unit

Claims

1. A communication method performed by a user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system that provides a multicast broadcast service (MBS), comprising: Receiving an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN); Performing priority control in a cell reselection procedure to prioritize the cells constituting the SFN over the cells not constituting the SFN; Receiving from the network a notification indicating that performing the priority control is permitted; and Performing the priority control includes performing the priority control only when the notification is received from the network. Communication method.

2. 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 that provides a multicast broadcast service (MBS), comprising: Receiving an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN); Performing priority control in a cell reselection procedure to prioritize the cells constituting the SFN over the cells not constituting the SFN; Receiving from the network SFN information indicating an MBS session provided by the SFN; and Performing the priority control includes determining, as the frequency priority used in the cell reselection procedure, that the frequency to which the current serving cell of the user equipment belongs has the highest priority when the SFN information indicates that the MBS session being received by the user equipment is provided by the SFN. Communication method.

3. 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 that provides a multicast broadcast service (MBS), comprising: Receiving an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN); Performing priority control in a cell reselection procedure to prioritize the cells constituting the SFN over the cells not constituting the SFN; Receiving, from a network, a list including identifiers of cells constituting the SFN, Performing the priority control includes controlling cell reselection so that, in the cell reselection procedure, cells indicated by the list are reselected with priority over cells not indicated by the list. Communication method.

4. 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 providing a multicast broadcast service (MBS), Receiving an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN), Performing priority control so that, in a cell reselection procedure, cells constituting the SFN are prioritized over cells not constituting the SFN, When reselection is made to an adjacent cell constituting the SFN, receiving a multicast traffic channel (MTCH) from the adjacent cell while omitting reception of a multicast control channel (MCCH) from the adjacent cell. Communication method.

5. A user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a mobile communication system providing a multicast broadcast service (MBS), A receiving unit that receives an MBS signal transmitted using the same identifier from a plurality of cells constituting a single frequency network (SFN), A control unit that performs priority control so that, in a cell reselection procedure, cells constituting the SFN are prioritized over cells not constituting the SFN, The receiving unit receives, from a network, a notification indicating that permission to perform the priority control is granted, The control unit performs the priority control only when the notification has been received from the network User equipment.

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