COMMUNICATION METHOD, REMOTE USER EQUIPMENT, RELAY USER EQUIPMENT AND NETWORK NODE

Abstract

This communication method for transferring multicast broadcast service (MBS) data, which belongs to an MBS session, from a base station to a remote UE through a relay UE, comprises: a step in which the remote UE preferentially selects the relay UE which can transfer a desired MBS session for which the remote UE is interested in reception rather than the relay UE which does not transfer the desired MBS session; and a step in which the remote UE receives MBS data, which belongs to the desired MBS session, from the base station through the selected relay UE.

Description

[Technical Field]

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

[0002] The 3GPP (3rd Generation Partnership Project) standard defines the technical specifications 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 offers higher speed, larger capacity, higher reliability, and lower latency. Discussions are underway within 3GPP to formulate technical specifications for 5G / NR multicast broadcast services (MBS) (see, for example, Non-Patent Document 1).

[0003] In addition, 3GPP is currently discussing the development of technical specifications for Sidelink Relay, which uses user equipment (UE) as a relay node. Sidelink Relay is a technology in which a relay node called Relay UE (Relay UE) intervenes in communication between a base station and a remote user equipment (Remote UE) and relays this communication. Here, communication between the base station and the Relay UE is performed on uplink / downlink (also called Uu interface), and communication between the Relay UE and the Remote UE is performed on sidelink (also called PC5 interface). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] 3GPP contribution: RP-201038 Summary of the Invention

[0005] A first aspect of the present invention provides a communication method for transmitting MBS data belonging to a Multicast Broadcast Service (MBS) session from a base station to a remote user equipment (RUE) via a relay user equipment (REE), the communication method comprising the steps of: the remote user equipment selecting, by the RUE, a relay user equipment capable of forwarding a desired MBS session that the remote user equipment is interested in receiving, in preference to a relay user equipment that does not forward the desired MBS session; and the remote user equipment receiving, by the RUE, the MBS data belonging to the desired MBS session from the base station via the selected relay user equipment.

[0006] A second aspect of the present invention provides a communication method for transmitting MBS data belonging to a Multicast Broadcast Service (MBS) session from a base station to a remote user equipment (REE) via a relay user equipment (UE), the communication method comprising the steps of: receiving, by the relay user equipment in an RRC idle state or an RRC inactive state, interest information from the remote user equipment indicating that the remote user equipment is interested in receiving a multicast session; and performing a connection process by the relay user equipment (REE) to establish or resume an RRC connection with the base station in response to receiving the interest information.

[0007] A third aspect of the present invention provides a communication method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a base station to a remote user equipment (UE) via a relay user equipment (RE), the communication method comprising the steps of: transmitting, by the relay user equipment, data received from a first cell supporting sidelink relay functionality to the remote user equipment; causing the remote user equipment to transmit a measurement report to the base station in response to the base station managing the first cell deciding to handover the relay user equipment to a second cell not supporting the sidelink relay functionality; and, by the base station, performing a handover of the remote user equipment prior to the handover of the relay user equipment based on the measurement report.

[0008] A fourth aspect of the present invention provides a communication method for transmitting MBS data belonging to a Multicast Broadcast Service (MBS) session from a base station to a remote user equipment (REE) via a relay user equipment (REE), the communication method comprising the steps of: transmitting, by the relay user equipment, the MBS data received by the relay user equipment from a first cell supporting the MBS function to the remote user equipment; in response to a decision by the base station managing the first cell to handover the relay user equipment to a second cell not supporting the MBS function, causing the remote user equipment to establish a PDU session for unicasting the MBS data to the remote user equipment; and, after the PDU session is established, performing the handover by the base station.

[0009] A fifth aspect of the present invention relates to a communication method for transmitting MBS data belonging to a Multicast Broadcast Service (MBS) session from a base station to a remote user equipment via a relay user equipment, the communication method comprising the steps of: the relay user equipment identifying an MBS session that the remote user equipment is interested in receiving; and the relay user equipment transmitting an identifier indicating the identified MBS session to the base station. [Brief explanation of the drawings]

[0010] [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. 10 is a diagram illustrating an example of internal processing related to MBS reception in a UE according to an embodiment. [Figure 9] FIG. 10 is a diagram illustrating another example of internal processing related to MBS reception in the UE according to the embodiment. [Figure 10] FIG. 1 is a diagram illustrating a side link according to an embodiment. [Figure 11] FIG. 1 illustrates a radio protocol configuration for sidelink communication according to an embodiment. [Figure 12] FIG. 1 illustrates an example of sidelink relay according to an embodiment. [Figure 13] FIG. 10 is a diagram illustrating an example of a user plane protocol stack in sidelink relay according to an embodiment. [Figure 14] FIG. 10 is a diagram illustrating an example of a protocol stack of a control plane in sidelink relay according to an embodiment. [Figure 15] FIG. 1 illustrates an example of MBS forwarding using sidelink relay according to an embodiment. [Figure 16] FIG. 10 is a diagram illustrating a transfer operation of a session start notification according to the embodiment. [Figure 17] FIG. 10 is a diagram illustrating an example of an operation related to transfer of a session start notification according to an embodiment. [Figure 18] 18 is a diagram illustrating a modification of the operation shown in FIG. 17. [Figure 19] FIG. 10 is a diagram illustrating a first operation example of MBS data transmission in a side link according to an embodiment. [Figure 20] FIG. 10 is a diagram illustrating a second operation example of MBS data transmission in a side link according to the embodiment. [Figure 21] FIG. 10 is a diagram illustrating an example of a relay UE selection operation by a remote UE according to an embodiment. [Figure 22] FIG. 10 is a diagram illustrating an example of an operation related to an RRC connection operation of a relay UE according to the embodiment. [Figure 23] FIG. 10 is a diagram illustrating a handover operation of a relay UE according to the embodiment. [Figure 24] FIG. 10 is a diagram illustrating a first operation example of handover of a relay UE according to the embodiment. [Figure 25] FIG. 10 is a diagram illustrating a second operation example of handover of a relay UE according to the embodiment. [Figure 26] FIG. 10 is a diagram illustrating a third operation example of handover of a relay UE according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] It is believed that combining Multicast Broadcast Service (MBS) with sidelink relaying can improve MBS. For example, a relay user equipment (UE) can forward MBS data from a base station to a remote user equipment (RUE), so that even remote user equipment (RUE) outside the base station's coverage area can receive the MBS data via the relay user equipment. However, the current 3GPP technical specifications do not provide a mechanism for combining MBS with sidelink relaying.

[0012] Therefore, an object of the present disclosure is to make it possible to realize an improved multicast broadcast service.

[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] (1) 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 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 an embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 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 a gNB 200 (base station) according to an embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that performs communication with the CN 20.

[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 for the radio interface of the control plane is replaced by the RRC (Radio Relay Control) layer instead of the SDAP layer shown in Figure 4. source It has a Control layer and a Non-Access Stratum (NAS) layer.

[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] (2) Overview of MBS An overview of the MBS according to the embodiment will be described. The MBS is a service that enables broadcast or multicast, i.e., point-to-multipoint (PTM) data transmission from the NG-RAN 10 to the UE 100. Possible use cases (service types) of the MBS include public safety 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] A multicast service provides a service not to all UEs 100 but to a group of UEs 100 participating in the multicast service (multicast session). An MBS session used for a multicast service is called a multicast session. A multicast service can provide the same content to a group of UEs 100 in a more wirelessly efficient manner than a broadcast service.

[0043] FIG. 6 is a diagram illustrating an overview of MBS traffic distribution according to the 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 Protocol Data Unit (PDU) session for each UE 100. Therefore, one PDU session for each UE 100 needs to be associated with a 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 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, UE100 may receive MBS data in the following three procedures. First, UE100 receives MCCH configuration information via an SIB (MBS SIB) transmitted on the BCCH from gNB200. Second, UE100 receives an MCCH from gNB200 based on the MCCH configuration information. The MCCH transmits the MTCH configuration information. Third, UE100 receives an 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 configuration.

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

[0062] An MBS Radio Bearer (MRB) is a radio bearer that transmits 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 as "PTM only," "PTP only," or "both PTM and PTP." The 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 (LC ID) 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] (3) Overview of Side Link An overview of the side link according to the embodiment will be described below. Fig. 10 is a diagram showing the side link according to the embodiment.

[0068] The sidelink is a direct interface between the UEs 100 and is provided on a PC5 interface. The UE 100 may be within the coverage of the gNB 200 (RAN 10). Alternatively, the UE 100 may be out of the coverage of the gNB 200 (RAN 10). The UE 100 may be in any RRC state (RRC connected state, RRC idle state, RRC inactive state).

[0069] The sidelink is used for sidelink communication, which is a method for multiple nearby UEs 100 to communicate data without going through a network node. The sidelink is also used for sidelink discovery, which is a method for a UE 100 to discover other nearby UEs 100. The following mainly describes sidelink communication.

[0070] Sidelink communication can support one of three transmission modes for a pair of Source Layer-2 ID and Destination Layer-2 ID in an AS: unicast transmission, groupcast transmission, and broadcast transmission.

[0071] In unicast transmission, one PC5-RRC connection is supported between two peer UEs that make up a UE pair, and control information and user data are transmitted and received between the peer UEs on the sidelink. A PC5-RRC connection is a logical connection between two UEs for a pair of source Layer 2 identifiers and destination Layer 2 identifiers that is considered established after a corresponding PC5 unicast link is established. There is a one-to-one correspondence between PC5-RRC connections and PC5 unicast links. A UE 100 may have multiple PC5-RRC connections with one or more UEs for different pairs of source Layer 2 identifiers and destination Layer 2 identifiers. In addition, in unicast transmission, sidelink HARQ feedback, sidelink transmit power control, RLC AM (Acknowledge Mode), and radio link failure detection for PC5-RRC connections are supported.

[0072] In groupcast, user data is transmitted and received between UEs belonging to a group on the sidelink, and sidelink HARQ feedback is supported in groupcast.

[0073] In broadcast transmission, user data is transmitted and received between UEs on the sidelink.

[0074] Here, the Source Layer-2 ID is an identifier for identifying the source of data in sidelink communication. For example, the Source Layer-2 ID is 24 bits long and is divided into two bit strings at the MAC layer. One bit string is the LSB part (8 bits) of the Source Layer-2 ID and is transferred to the physical layer on the transmitting side. This is used to identify the source of the target data in the sidelink control information and to filter packets at the physical layer on the receiving side. The other bit string is the MSB part (16 bits) of the Source Layer-2 ID and is transferred in the MAC header. This is used to filter packets at the MAC layer on the receiving side.

[0075] The Destination Layer-2 ID is an identifier used to identify the target of data in sidelink communication. For example, the Destination Layer-2 ID is 24 bits long and is divided into two bit strings at the MAC layer. One bit string is the least significant bit (16 bits) of the Destination Layer-2 ID and is transmitted to the physical layer on the transmitting side. This is used to identify the target of the data in the sidelink control information and to filter packets at the physical layer on the receiving side. The other bit string is the most significant bit (8 bits) of the Destination Layer-2 ID and is transmitted in the MAC header. This is used to filter packets at the MAC layer on the receiving side.

[0076] In sidelink communication, the MAC sublayer is responsible for radio resource selection, packet filtering, prioritization between uplink and sidelink transmissions, and sidelink Channel State Information (CSI) reporting. For packet filtering, an SL-SCH MAC header containing both the source and destination Layer 2 identifiers is added to each MAC Protocol Data Unit (PDU). The LCID included in the MAC subheader uniquely identifies a logical channel within the combination of the source and destination Layer 2 identifiers.

[0077] The following logical channels are used in the sidelink:

[0078] Sidelink Control Channel (SCCH): A sidelink channel for transmitting control information (PC5-RRC messages and PC5-S messages) from one UE to another. The SCCH is mapped to the SL-SCH, a transport channel.

[0079] Sidelink Traffic Channel (STCH): A sidelink channel for transmitting user data from one UE to another. The STCH is mapped to the SL-SCH, a transport channel.

[0080] Sidelink Broadcast Control Channel (SBCCH): A sidelink channel for broadcasting sidelink system information from one UE to other UEs. The SBCCH is mapped to the SL-BCH, a transport channel.

[0081] FIG. 11 is a diagram illustrating a configuration of a radio protocol for sidelink communication according to the embodiment.

[0082] 11(1) shows the protocol stack of the control plane for SCCH for RRC, which is composed of RRC, PDCP, RLC, MAC, and physical (PHY) layers.

[0083] 11(2) shows the control plane protocol stack for SCCH for PC5-S, which is positioned above the PDCP, RLC, MAC, and physical (PHY) layers.

[0084] The control plane protocol stack for SBCCH is shown in (3) of Fig. 11. This protocol stack is made up of the RRC, RLC, MAC, and physical (PHY) layers.

[0085] The user plane protocol stack for STCH is shown in (4) of Figure 11. This protocol stack is composed of the SDAP, PDCP, RLC, MAC, and physical (PHY) layers.

[0086] (4) Overview of sidelink relay An overview of sidelink relay according to an embodiment will be described below. Fig. 12 is a diagram illustrating an example of sidelink relay according to an embodiment.

[0087] In sidelink relaying, a relay UE 100-2 intervenes in communication between a gNB 200-1 and a remote UE 100-1 and relays this communication. The remote UE 100-1 communicates with the gNB 200-1 via the relay UE 100-2. The relay UE 100-2 is located within the coverage of the RAN 10 (specifically, the gNB 200-1). The remote UE 100-1 is located either outside or within the coverage of the RAN 10.

[0088] The remote UE 100-1 performs wireless communication (sidelink communication) with the relay UE 100-2 over a PC5 interface (sidelink), which is an interface between UEs. The relay UE 100-2 performs wireless communication (Uu communication) with the gNB 200-1 over an NR Uu interface. As a result, the remote UE 100-1 indirectly communicates with the gNB 200-1 via the relay UE 100-2. The Uu communication includes uplink communication and downlink communication.

[0089] 13 is a diagram illustrating an example of a user plane protocol stack in sidelink relay according to the embodiment. This diagram also illustrates an example of a user plane protocol stack in relay via a relay UE 100-2, i.e., U2N (UE to Network) relay.

[0090] The gNB200-1 is a Uu-SRAP (S id It has a Uu-Link Relay Adaptation Protocol (UuRLC) layer, a Uu-MAC layer, and a Uu-PHY layer.

[0091] The relay UE 100-2 has a Uu-SRAP layer, a Uu-RLC layer, a Uu-MAC layer, and a Uu-PHY layer used for communication on the NR Uu interface (Uu communication). Also, the relay UE 100-2 has a PC5-SRAP layer, a PC5-RLC layer, a PC5-MAC layer, and a PC5-PHY layer used for communication on the PC5 interface (PC5 communication).

[0092] The remote UE 100-1 has a Uu-SDAP layer and a Uu-PDCP layer used for communication (Uu) on the Uu interface, and also has a PC5-SRAP layer, a PC5-RLC layer, a PC5-MAC layer, and a PC5-PHY layer used for communication (PC5 communication) on the PC5 interface.

[0093] 14 is a diagram illustrating an example of a protocol stack of a control plane in sidelink relay according to an embodiment. This diagram is also an example of a protocol stack of a control plane in U2N relay.

[0094] In the control plane, a Uu-RRC layer is arranged in place of the Uu-SDAP layer of the user plane.

[0095] As shown in Figures 13 and 14, an SRAP layer is arranged on the Uu interface and the PC5 interface. The SRAP layer is an example of a so-called adaptation layer. The SRAP layer exists only in Layer 2 relay and does not exist in Layer 3 relay. The SRAP layer also exists in all of the remote UE 100-1, relay UE 100-2, and gNB 200-1. Furthermore, there are two SRAP layers: PC5-SRAP and Uu-SRAP. The PC5-SRAP and Uu-SRAP have a bearer mapping function. For example, they have the following bearer mapping function. That is, the Uu-SRAP of the remote UE 100-1 and the gNB 200-1 maps the bearer (Uu-PDCP) to the PC5 RLC channel (PC5-RLC). Furthermore, the PC5-SRAP and Uu-SRAP of the relay UE 100-2 perform mapping between the PC5 RLC channel (PC5-RLC) and the Uu RLC channel (Uu-RLC). Furthermore, the Uu-SRAP has a function of identifying the remote UE 100-1.

[0096] As described above, each of the remote UE 100-1 and the relay UE 100-2 may have an RRC layer for PC5. Such an RRC layer is called a "PC5-RRC layer." There is a one-to-one correspondence between the PC5-RRC connection and the PC5 unicast link between the remote UE 100-1 and the relay UE 100-2, and the PC5-RRC connection is established after the PC5 unicast link is established.

[0097] As described above, each of the remote UE 100-1 and the relay UE 100-2 may have a PC5-S (Signaling) protocol layer. The PC5-S protocol layer is a layer above the PDCP layer. Like the PC5-RRC layer, the PC5-S protocol layer is also a layer for transmitting control information.

[0098] (5) MBS transmission using sidelink relay 15 is a diagram illustrating an example of MBS transmission using sidelink relay according to an embodiment.

[0099] In the embodiment, MBS is combined with sidelink relay. For example, the relay UE 100-2 forwards MBS data from the gNB 200 to the remote UE 100-1. This allows the remote UE 100-1, which is outside the coverage of the gNB 200, to receive the MBS data via the relay UE 100-2.

[0100] For MBS data relay, first, the relay UE 100-2 receives MBS data belonging to an MBS session from the gNB 200 over the downlink (Uu interface). The MBS distribution mode between the gNB 200 and the relay UE 100-2 may be a first distribution mode (DM1) or a second distribution mode (DM2). The MBS data from the gNB 200 to the relay UE 100-2 may be PTM, PTP, or a split bearer (split MRB). The MBS data may be transmitted from the gNB 200 to the relay UE 100-2 via a data radio bearer (DRB), i.e., unicast. Second, the relay UE 100-2 transmits (forwards) the MBS data received from the gNB 200 to the remote UE 100-1 over the sidelink (PC5 interface). The sidelink transmission mode from the relay UE 100-2 to the remote UE 100-1 may be unicast, groupcast, or broadcast.

[0101] Various operations in MBS transfer using sidelink relay are described below. Note that, although the following description mainly focuses on an example in which TMGI is used as the MBS session identifier, at least one of a source-specific IP multicast address, a session identifier, and a G-RNTI may also be used as the MBS session identifier.

[0102] (5.1) Session start notification forwarding behavior A transfer operation of a session start notification according to the embodiment will be described below. Fig. 16 is a diagram showing a transfer operation of a session start notification according to the embodiment.

[0103] 16, the relay UE 100-2 receives an MBS session start notification indicating the start of an MBS session from the gNB 200. The relay UE 100-2 transmits MBS session start information based on the MBS session start notification received from the gNB 200 to the remote UE 100-1 on the sidelink. This allows the remote UE 100-1 to know the start of the MBS session based on the MBS session start information.

[0104] The relay UE 100-2 may receive a paging message including an identifier of the MBS session to be started from the gNB 200 as an MBS session start notification. Such a session start notification may be a paging message including a list of TMGIs of the MBS session to be started. Such a paging message may be a paging message used in the first delivery mode (DM1) and may be a message notifying multicast session activation in order to call the UE 100 that will participate in the multicast session as the MBS session. For example, when a multicast session is started (activated), the gNB 200 transmits a paging message including the TMGI of the multicast session. The start (activation) of a multicast session may be when transmission of multicast data has started in the multicast session. Alternatively, the start (activation) of the multicast session may be when the multicast session is in a state where transmission of multicast data can be started.

[0105] Alternatively, the relaying UE 100-2 may receive an MCCH change notification indicating an update of the multicast control channel (MCCH) and the updated MCCH from the gNB 200 as an MBS session start notification. Such an MBS session start notification is used for the second distribution mode (DM2). In response to receiving the MCCH change notification from the gNB 200, the relaying UE 100-2 receives the updated MCCH from the gNB 200. The MCCH includes TMGI as an MBS session identifier. The updated MCCH may include TMGI of the broadcast session to be started.

[0106] Then, the relay UE 100-2 transmits MBS session start information based on the MBS session start notification received from the gNB 200 to the remote UE 100-1 on the sidelink. The MBS session start information may include an identifier of the MBS session to be started. This allows the remote UE 100-1 to identify the MBS session to be started. The relay UE 100-2 may transmit a PC5-RRC message including the MBS session start information to the remote UE 100-1. Furthermore, the relay UE 100-2 may transmit a discovery message including the MBS session start information to the remote UE 100-1.

[0107] In response to receiving the MBS session start information from the relay UE 100-2, the remote UE 100-1 may avoid reselection to a relay UE 100-2 different from the relay UE 100-2. For example, the remote UE 100-1 identifies, based on the MBS session start information, that an MBS session (multicast session or broadcast session) that the remote UE 100-1 is interested in receiving is about to start, and waits for MBS data transfer while maintaining the current relay UE 100-2.

[0108] In response to receiving the MBS session start information from the relay UE 100-2, the remote UE 100-1 may start monitoring the sidelink data transmission from the relay UE 100-2. For example, the remote UE 100-1 may identify, based on the MBS session start information, that an MBS session (multicast session or broadcast session) that the remote UE 100-1 is interested in receiving will be started, and start monitoring the sidelink data transmission from the relay UE 100-2. The remote UE 100-1 may stop monitoring the sidelink data transmission from the relay UE 100-2 until the MBS session that the remote UE 100-1 is interested in receiving is started. This allows the remote UE 100-1 to reduce power consumption and processing load caused by monitoring.

[0109] Note that the relay UE 100-2 may transmit session start information including the TMGI of an MBS session that the remote UE 100-1 is interested in receiving to the remote UE 100-1 only when the MBS session that the remote UE 100-1 is interested in receiving has started. This prevents unnecessary session start information from being transmitted to the remote UE 100-1, thereby reducing the resource load on the side link and the processing load on the remote UE 100-1. For example, the relay UE 100-2 may receive an identifier of a desired MBS session that the remote UE 100-1 is interested in receiving from the remote UE 100-1 or the gNB 200. The relay UE 100-2 may recognize the start of the desired MBS session based on a session start notification received from the gNB 200, and may indicate the start of the desired MBS session to the remote UE 100-1 by using MBS session start information.

[0110] Furthermore, the relay UE 100-2 may not forward all of the information included in the session start notification received from the gNB 200 to the remote UE 100-1, but may forward only part of the information, such as the TMGI, to the remote UE 100-1. For example, the relay UE 100-2 may not forward the MTCH scheduling information received from the gNB 200 on the MCCH to the remote UE 100-1. This reduces the amount of information in the session start information, and reduces the resource load on the side link and the processing load on the remote UE 100-1. Note that the relay UE 100-2 may forward neighboring cell information received from the gNB 200 on the MCCH to the remote UE 100-1 for MBS service continuity.

[0111] Furthermore, the relay UE 100-2 may receive a Layer 2 identifier assigned to the remote UE 100-1 that is interested in receiving the MBS session from the gNB 200. The relay UE 100-2 may transmit MBS session start information to the remote UE 100-1 using the Layer 2 identifier.

[0112] 17 is a diagram illustrating an example of an operation related to transfer of a session start notification according to the embodiment. The relay UE 100-2 may be in an RRC connected state, an RRC inactive state, or an RRC idle state in relation to the gNB 200.

[0113] In step S101, the remote UE 100-1 is interested in receiving an MBS session. In the case of multicast, the remote UE 100-1 may have already joined the multicast session. Note that joining the multicast session may mean that the UE 100 is registered in the CN 20 (CN device) as a member of a UE group (multicast group) that receives the multicast session.

[0114] In step S102a, the remote UE 100-1 may transmit an identifier (TMGI) of an MBS session in which it is interested to the relay UE 100-2 as MBS interest information. For example, the remote UE 100-1 may transmit a PC5-RRC message (or a discovery message) including the identifier (TMGI) of an MBS session in which it is interested to the relay UE 100-2. The relay UE 100-2 may store the TMGI in association with the Layer 2 identifier of the remote UE 100-1.

[0115] In step S102b, the gNB 200 may transmit a message including the Layer 2 identifier of the remote UE 100-1 that is interested in the MBS session to the relay UE 100-2. The relay UE 100-2 may store the TMGI of the MBS session and the Layer 2 identifier of the remote UE 100-1 in association with each other.

[0116] In step S103, the relay UE 100-2 may send a notification to the gNB 200, including an identifier (TMGI) of an MBS session in which the remote UE 100-1 is interested, in order to receive an MBS session start notification (e.g., a paging message). Such a notification may be an MBS Interest Indication (MII). Alternatively, such a notification may be UE Assistance Information. In the case of multicast, the relay UE 100-2 may join the multicast session in which the remote UE 100-1 is interested, in order to receive an MBS session start notification (e.g., a paging message).

[0117] In step S104, the remote UE 100-1 and the relay UE 100-2 wait for the start of an MBS session that the remote UE 100-1 is interested in. The remote UE 100-1 may be in an RRC connected state, an RRC inactive state, or an RRC idle state in relation to the gNB 200. The remote UE 100-1 may be in a PC5-RRC connected state or a PC5-RRC idle state in relation to the relay UE 100-2.

[0118] In step S105, the relaying UE 100-2 receives an MBS session start notification from the gNB 200. In the case of DM1, the relaying UE 100-2 receives a paging message including a TMGI list as the MBS session start notification. On the other hand, in the case of DM2, the relaying UE 100-2 receives the MCCH change notification, then receives the updated MCCH, and confirms that the TMGI (MTCH scheduling information for the TMGI) has been added in the MCCH.

[0119] In step S106, the relay UE 100-2 transmits MBS session start information including the TMGI of the MBS session to be started to the remote UE 100-1. The relay UE 100-2 may include all TMGIs (TMGIs for session start) received in step S105 in the MBS session start information. The relay UE 100-2 may include only the TMGI of the MBS session in which the remote UE 100-1 is interested, from the TMGIs (TMGIs for session start) received in step S105, in the MBS session start information. Here, the relay UE 100-2 may transmit the MBS session start information targeting the Layer 2 identifier of the remote UE 100-1.

[0120] In step S107, in response to receiving, from the relay UE 100-2, MBS session start information indicating the start of an MBS session that the remote UE 100-1 is interested in, the remote UE 100-1 may stop the reselection operation to another relay UE and maintain the currently selected relay UE 100-2. In response to receiving, from the relay UE 100-2, MBS session start information indicating the start of an MBS session that the remote UE 100-1 is interested in, the remote UE 100-1 may start monitoring sidelink data transmission associated with the identifier (TMGI) of the MBS session that the remote UE 100-1 is interested in.

[0121] In step S108, the relay UE 100-2 receives MBS data belonging to the MBS session from the gNB 200 on the downlink (Uu interface). The MBS distribution mode between the gNB 200 and the relay UE 100-2 may be the first distribution mode (DM1) or the second distribution mode (DM2). The MRB from the gNB 200 to the relay UE 100-2 may be PTM, PTP, or a split bearer (split MRB). The MBS data may be transmitted from the gNB 200 to the relay UE 100-2 using a DRB.

[0122] In step S109, the relay UE 100-2 transmits (transfers) the MBS data received from the gNB 200 to the remote UE 100-1 on the sidelink (PC5 interface). Specifically, the relay UE 100-2 transmits the MBS data to the remote UE 100-1 on a sidelink shared channel (SL-SCH). The sidelink transmission mode from the relay UE 100-2 to the remote UE 100-1 may be unicast, groupcast, or broadcast. The remote UE 100-1 receives the MBS data.

[0123] Fig. 18 is a diagram illustrating a modified example of the operation shown in Fig. 17. In the case of multicast, the gNB 200 can grasp the MBS session (TMGI) in which the remote UE 100-1 is interested by acquiring session participation information from the CN 20.

[0124] In this modification, in step S102b, the gNB 200 transmits a message including an identifier (TMGI) of an MBS session of interest to the remote UE 100-1 to the relay UE 100-2. The message may include a Layer 2 identifier of the remote UE 100-1 that is interested in the MBS session.

[0125] (5.2) MBS Data Transmission Operation in Sidelink The MBS data transmission operation in the side link according to the embodiment will be described.

[0126] In the side link communication between the remote UE 100-1 and the relay UE 100-2, the source layer 2 identifier (SRC) and the destination layer 2 identifier (DST) assigned to the SL-SCH are set as follows.

[0127] SRC is the Layer 2 identifier of the transmitting UE, whether unicast, groupcast or broadcast.

[0128] DST is determined by:

[0129] In the unicast case, DST is the Layer 2 identifier of the receiving UE.

[0130] In the case of groupcast, if the ProSe Layer 2 group identifier is configured to an application layer group identifier provided by the application layer, the DST is the ProSe Layer 2 group identifier. In the case of groupcast, if the ProSe Layer 2 group identifier is not configured to an application layer group identifier provided by the application layer, the DST is a conversion value from the application layer group identifier. The transmitting UE selects the DST from the configuration of the mapping between ProSe service types and Layer 2 identifiers.

[0131] In the case of broadcast, the DST is the value set in the transmitting UE, and the DST is set for the ProSe application.

[0132] (5.2.1) First operation example The remote UE 100-1 needs to know the correspondence between the identifier (TMGI) of the MBS session of interest to the remote UE 100-1 and the Layer 2 identifier. Specifically, the remote UE 100-1 needs to know which Layer 2 identifier is associated with a target TMGI in order to receive only the target sidelink transmission (target SL-SCH transmission).

[0133] In the embodiment, the remote UE 100-1 receives, from the relay UE 100-2 or the gNB 200, mapping information that associates an identifier (TMGI) indicating an MBS session (specifically, an MBS session of interest to the remote UE 100-1) with a destination Layer 2 identifier. Based on the mapping information, the remote UE 100-1 receives MBS data belonging to the MBS session from the relay UE 100-2 via the relay UE 100-2. Here, the remote UE 100-1 monitors the SL-SCH using the destination Layer 2 identifier associated with the MBS session. This allows the remote UE 100-1 to appropriately receive only the target sidelink transmission from the relay UE 100-2.

[0134] 19 is a diagram illustrating a first operation example of MBS data transmission in a side link according to the embodiment. In this operation example, it is assumed that the side link transmission mode from the relay UE 100-2 to the remote UE 100-1 is groupcast or broadcast.

[0135] In step S201a, the gNB 200 may transmit, to the remote UE 100-1 via the relay UE 100-2, mapping information that associates an identifier indicating an MBS session (TMGI) with a destination Layer 2 identifier. The mapping information may include one or more sets of TMGI and destination Layer 2 identifier. The gNB 200 may transmit, to the remote UE 100-1 via the relay UE 100-2, an RRC message that includes the mapping information.

[0136] In step S201b, the relay UE 100-2 may transmit, to the remote UE 100-1, mapping information that associates an identifier indicating an MBS session (TMGI) with a destination Layer 2 identifier. The mapping information may include one or more sets of TMGI and destination Layer 2 identifier. The relay UE 100-2 may transmit, to the remote UE 100-1, a PC5-RRC message, a discovery message, or a PC5-S message that includes the mapping information.

[0137] In addition, the gNB 200 or the relay UE 100-2 may transmit association information only to the remote UE 100-1 that is interested in receiving the MBS, based on the MBS interest information described above or below.

[0138] In step S202, the remote UE 100-1 monitors the SL-SCH in which the destination layer 2 identifier (DST) is set in the AS layer (e.g., MAC layer) based on the association information received from the gNB 200 or the relay UE 100-2.

[0139] In step S203, the relaying UE 100-2 receives the MBS data belonging to the MBS session from the gNB 200 on the downlink (Uu interface).

[0140] In step S204, the relay UE 100-2 transmits (transfers) the MBS data received from the gNB 200 to the remote UE 100-1 on the side link (PC5 interface). The remote UE 100-1 receives the MBS data.

[0141] In this operation example, the gNB 200 may transmit association information (mapping information) that associates an identifier indicating an MBS session (TMGI) with a destination Layer 2 identifier to the relay UE 100-2, and the relay UE 100-2 may use the association information. When the remote UE 100-1 is within the coverage of the gNB 200, the gNB 200 may transmit the association information directly to the remote UE 100-1 without going through the relay UE 100-2.

[0142] (5.2.2) Second operation example As mentioned above, when using groupcast in sidelink, the ProSe Layer 2 group identifier is used as the destination Layer 2 identifier (DST). Therefore, the ProSe Layer 2 group identifier may be associated with a TMGI. In this case, it is assumed that all UEs in this group are interested in this TMGI. Similarly, an application layer group identifier may be associated with a TMGI.

[0143] Therefore, a higher layer (NAS, PC5-S, or application layer), specifically, a CN device (e.g., AMF) or a ProSe server device may associate a group identifier (ProSe Layer 2 group identifier or application layer group identifier) ​​with a TMGI and transmit this association information (mapping information) to remote UE 100-1 and / or relay UE 100-2.

[0144] The remote UE 100-1 and / or the relay UE 100-2 receives, from the CN device or the ProSe server device, association information that associates a ProSe Layer 2 group identifier or an application layer group identifier with an identifier indicating an MBS session. The remote UE 100-1 and / or the relay UE 100-2 may identify a destination Layer 2 identifier associated with the MBS session based on the association information.

[0145] 20 is a diagram showing a second operation example of MBS data transmission in the side link according to the embodiment. In this operation example, it is assumed that the side link transmission mode from the relay UE 100-2 to the remote UE 100-1 is groupcast.

[0146] In step S251a, the CN device or the ProSe server device may transmit, to the relay UE 100-2, association information (mapping information) in which a group identifier (a ProSe layer 2 group identifier or an application layer group identifier) ​​is associated with a TMGI. The relay UE 100-2 may transfer the association information to the remote UE 100-1.

[0147] In step S251b, the CN device or the ProSe server device may transmit, to the remote UE 100-1 via the relay UE 100-2, association information (mapping information) that associates a group identifier (ProSe Layer 2 group identifier or application layer group identifier) ​​with a TMGI. The association information may be transmitted to the remote UE 100-1 by NAS signaling.

[0148] An upper layer (e.g., NAS, PC5-S, or application layer) of the remote UE 100-1 (and the relay UE 100-2) may notify the AS layer of the association information as, for example, mapping information between DSTs and TMGIs. The upper layer may notify the AS layer of the association information as an interesting DST (a DST that requests reception).

[0149] In step S252, the remote UE 100-1 monitors the SL-SCH in which the ProSe Layer 2 group identifier (DST) is set.

[0150] In step S253, the relaying UE 100-2 receives the MBS data belonging to the MBS session from the gNB 200 on the downlink (Uu interface).

[0151] In step S254, the relay UE 100-2 transmits (transfers) the MBS data received from the gNB 200 to the remote UE 100-1 on the side link (PC5 interface). The remote UE 100-1 receives the MBS data.

[0152] (5.3) Relay UE Selection Operation by Remote UE A relay UE selection operation by the remote UE 100-1 according to the embodiment will be described.

[0153] Prior to the sidelink relay, the remote UE 100-1 selects a relay UE 100-2 to be used for the sidelink relay from among relay UE candidates. After selecting the relay UE 100-2, the relay UE 100-2 may again select (reselect) another UE 100 as the new relay UE 100-2.

[0154] In this embodiment, in such a relay UE selection operation, the remote UE 100-1 interested in receiving MBS prioritizes the relay UE 100-2 that can transfer the MBS session of interest to the remote UE 100-1. That is, the remote UE 100-1 preferentially selects the relay UE 100-2 that can transfer the desired MBS session of interest to the remote UE 100-1 over the relay UE 100-2 that does not transfer the desired MBS session of interest to the remote UE 100-1. The remote UE 100-1 receives MBS data belonging to the desired MBS session via the selected relay UE 100-2. This allows the remote UE 100-1 interested in receiving MBS to receive the MBS data belonging to the desired MBS session via the appropriate relay UE 100-2.

[0155] 21 is a diagram showing an example of a relay UE selection operation by the remote UE 100-1 according to the embodiment. In FIG. 21, an example is shown in which the relay UE 100-2a is connected to the gNB 200a via the Uu interface, and the relay UE 100-2b is connected to the gNB 200b via the Uu interface. The relay UE 100-2a and the relay UE 100-2b are relay UE candidates for the remote UE 100-1.

[0156] In step S301, each of the relay UE candidates (the relay UE 100-2a and the relay UE 100-2b) may transmit support information indicating whether or not it supports MBS session forwarding on the sidelink. The remote UE 100-1 receives the support information from the relay UE candidates. In step S302, the remote UE 100-1 preferentially selects a relay UE candidate capable of forwarding the desired MBS session based on the received support information. The remote UE 100-1 receives MBS data via a relay UE 100-2 selected from the relay UE candidates. For example, assume that the relay UE 100-2a supports MBS session forwarding and the relay UE 100-2b does not support MBS session forwarding. In this case, the remote UE 100-1 selects the relay UE 100-2a that supports MBS session forwarding based on the support information from each relay UE 100-2, and receives the MBS data via the relay UE 100-2a.

[0157] In step S301, each of the relay UE candidates (the relay UE 100-2a and the relay UE 100-2b) may transmit, on the sidelink, an identifier (TMGI) indicating an MBS session to which it can transfer data. Each of the relay UE candidates (the relay UE 100-2a and the relay UE 100-2b) may transmit a list of identifiers (TMGI) indicating MBS sessions to which it can transfer data. The remote UE 100-1 receives the identifiers (TMGI). In step S302, the remote UE 100-1 preferentially selects the relay UE 100-2 to which it can transfer the desired MBS session based on the received identifiers (TMGI). The remote UE 100-1 receives the MBS data via the relay UE 100-2 selected from the relay UE candidates. For example, assume that the identifier of the desired MBS session of the remote UE 100-1 is TMGI#1, the identifier of the MBS session forwarded by the relay UE 100-2a is TMGI#1, and the identifier of the MBS session forwarded by the relay UE 100-2b is TMGI#2. In this case, the remote UE 100-1 selects the relay UE 100-2a that supports forwarding of the desired MBS session based on the MBS session identifier (TMGI) from each relay UE 100-2, and receives the MBS data via the relay UE 100-2a.

[0158] If none of the relay UE candidates provides the desired MBS session, the remote UE 100-1 may transmit the identifier (TMGI) of the desired MBS session to the relay UE candidates as MBS interest information, as described above.

[0159] In step S301, the relay UE candidate may transmit a PC5-RRC message or a discovery message including support information and / or an MBS session identifier (TMGI) to the remote UE 100-1. The remote UE 100-1 may acquire the support information and / or the MBS session identifier (TMGI) of the relay UE candidate by receiving the PC5-RRC message or the discovery message. Note that the relay UE candidate may also transmit information about other relay UE candidates (support information and / or MBS session identifier (TMGI)) to the remote UE 100-1. For example, the relay UE candidate may acquire information about neighbor relay UE candidates from the gNB 200.

[0160] Prior to step S301, the relay UE candidate may identify a transferable MBS session based on the MBS reception configuration received from the gNB 200. For example, in the case of a broadcast session, the relay UE candidate may identify a transferable MBS session (TMGI) by receiving and checking an MCCH from the gNB 200 (serving cell). In the case of a multicast session, the relay UE candidate may identify a transferable MBS session (TMGI) by receiving an RRC Reconfiguration from the gNB 200 (serving cell) and checking the TMGI of the configured MRB. When the relay UE 100-2 receives MBS data from the gNB 200 via a DRB (unicast), the relay UE candidate may identify the MBS session (TMGI) being received via the DRB.

[0161] In step S302, the remote UE 100-1 preferentially selects a relay UE 100-2 capable of transferring a desired MBS session of interest to the remote UE 100-1. For example, the remote UE 100-1 may select a relay UE from only relay UEs 100-2 capable of transferring the desired MBS session. The remote UE 100-1 may measure the reception quality of a wireless signal from each relay UE candidate and add an offset to the measurement value (e.g., RSRP) to select a relay UE. Specifically, the remote UE 100-1 performs relay UE selection by measuring and comparing the reception quality of a wireless signal (e.g., a sidelink communication signal or a sidelink discovery signal) received from each relay UE candidate. For example, the remote UE 100-1 selects a relay UE candidate with the best reception quality. In this operation, the remote UE 100-1 adds an offset to the reception quality of a relay UE candidate capable of transferring the desired MBS session. This makes it easier to select a relay UE candidate capable of transferring the desired MBS session.

[0162] (5.4) RRC Connection Operation of Relay UE The RRC connection operation of the relay UE 100-2 according to the embodiment will be described.

[0163] If the remote UE 100-1 is interested in the multicast session, the multicast session is delivered in the first delivery mode (DM1), so the relay UE 100-2 may need to receive an MBS reception configuration (MRB configuration) from the gNB 200 in an RRC connected state. Therefore, the relay UE 100-2 in an RRC idle state or an RRC inactive state may need to establish or resume an RRC connection to receive the multicast session.

[0164] In the embodiment, the relay UE 100-2 in the RRC idle state or the RRC inactive state receives interest information (MBS interest information) from the remote UE 100-1, indicating that the remote UE 100-1 is interested in receiving a multicast session. In response to receiving the interest information, the relay UE 100-2 performs a connection process to establish or resume an RRC connection with the gNB 200. This enables the relay UE 100-2 to receive the multicast session from the gNB 200 and transfer MBS data belonging to the multicast session to the remote UE 100-1.

[0165] Here, when performing connection processing for the relay UE 100-2, the gNB 200 cannot distinguish the relay UE 100-2, which is only interested in multicast reception, from a normal UE. Therefore, the gNB 200 may reject the connection processing for the relay UE 100-2, for example, due to network congestion. Since multicast reception requires less resource consumption than a normal UE (i.e., unicast), it is not preferable to reject the connection processing. Therefore, the relay UE 100-2 notifies the gNB 200 that the connection is dedicated to multicast reception during the connection processing. That is, the relay UE 100-2 notifies the gNB 200 that the purpose is to forward a multicast session, using a message transmitted from the relay UE 100-2 to the gNB 200 during the connection processing. This makes it possible to prevent the gNB 200 from rejecting the connection processing.

[0166] Furthermore, since high reliability is required for a multicast MRB (i.e., DM1), it is preferable to ensure reliability in the sidelink as well. Therefore, the relay UE 100-2 maps a multicast radio bearer (MRB) corresponding to a multicast session to a unicast or groupcast transmission in the sidelink between the remote UE 100-1 and the relay UE 100-2. For the sidelink, unicast transmission and groupcast transmission support HARQ feedback, and therefore can ensure higher reliability than broadcast transmission, which does not support HARQ feedback.

[0167] FIG. 22 is a diagram illustrating an example of an operation related to an RRC connection operation of the relay UE 100-2 according to the embodiment.

[0168] In step S401, the relay UE 100-2 is in an RRC idle state or an RRC inactive state. Note that a PC5-RRC connection may be established between the remote UE 100-1 and the relay UE 100-2.

[0169] In step S402, the remote UE 100-1 transmits an identifier (TMGI) of an MBS session of interest to the relay UE 100-2 as MBS interest information. The MBS interest information may include information indicating an interest in receiving a multicast session. For example, the MBS interest information may include information indicating that the TGI corresponds to a multicast session. The relay UE 100-2 determines, based on the MBS interest information, that the remote UE 100-1 is interested in receiving the multicast session, and recognizes that it needs to transition to an RRC connected state.

[0170] In step S403, the relay UE 100-2 starts a connection process with the gNB 200, specifically, a random access procedure. The relay UE 100-2 transmits an RRC Setup Request message or an RRC Resume Request message as message 3 (Msg3) of the random access procedure. Here, the relay UE 100-2 includes in Msg3 a Cause value (for example, "relay-MBS") indicating that the relay UE 100-2 aims to transmit an MBS. The Cause value may be information indicating that the relay UE 100-2 aims to receive an MBS only. The gNB 200 accepts Msg3 (the RRC Setup Request message or the RRC Resume Request message) and transmits Msg4 (the RRC Setup message or the RRC Resume message) to the relay UE 100-2. Alternatively, the relay UE 100-2 may notify the gNB 200 that the relay UE 100-2 aims to transmit an MBS (or receive an MBS) by using a random access preamble as message 1 (Msg1) of the random access procedure. For example, a physical random access channel (PRACH) resource for the notification may be prepared, and the relay UE 100-2 may perform the notification by transmitting a random access preamble on the PRACH resource.

[0171] As a result, in step S404, the relay UE 100-2 establishes or resumes the RRC connection, and transitions to the RRC connected state.

[0172] In step S405, the relay UE 100-2 may transmit to the gNB 200 an MBS interest notification including an identifier (TMGI) of the MBS session (multicast session) that the remote UE 100-1 is interested in receiving.

[0173] In step S406, the gNB 200 transmits to the relaying UE 100-2 an RRC Reconfiguration message including an MBS reception setting (multicast MRB setting, etc.) for the relaying UE 100-2 to receive the multicast session.

[0174] In step S407, the relay UE 100-2 maps the MRB (multicast MRB) configured by the gNB 200 to the sidelink. Specifically, the relay UE 100-2 maps the multicast MRB to a unicast or groupcast MRB of the sidelink. This mapping may be specified to the relay UE 100-2 by the gNB 200 in step S406, for example.

[0175] In step S408, the relaying UE 100-2 receives the MBS data belonging to the multicast session from the gNB 200 on the downlink (Uu interface).

[0176] In step S409, the relay UE 100-2 transmits the MBS data received from the gNB 200 to the remote UE 100-1 on the side link (PC5 interface). Specifically, the relay UE 100-2 transmits the MBS data to the remote UE 100-1 by unicast or groupcast. The remote UE 100-1 receives the MBS data.

[0177] In the above operation, multicast (DM1) is assumed, but in the case of broadcast MRB (DM2), the relay UE 100-2 may map the MRB (broadcast MRB) to a sidelink broadcast because the broadcast MRB does not support HARQ feedback and may be best-effort.

[0178] (5.5) Handover Operation of Relay UE A handover operation of the relay UE 100-2 according to the embodiment will be described below. Fig. 23 is a diagram showing a handover operation of the relay UE 100-2 according to the embodiment.

[0179] A relay UE 100-2, which transfers MBS data from a gNB 200 to a remote UE 100-1, may be handed over from one cell (source cell 201S) to another cell (target cell 201T). Note that the source cell 201S and the target cell 201T may be managed by different gNBs 200. Alternatively, the source cell 201S and the target cell 201T may be managed by the same gNB 200. Such handovers include the following two cases.

[0180] Case 1: The target cell 201T supports the MBS function but does not support the sidelink relay function.

[0181] Case 2: The target cell 201T supports the sidelink relay function but does not support the MBS function.

[0182] In these cases 1 and 2, the remote UE 100-1 may be unable to continue receiving the MBS data in response to the handover of the relay UE 100-2. An example of an operation for the remote UE 100-1 to continue receiving the MBS data will be described below.

[0183] (5.5.1) First operation example The first operation example is an operation example for the above-described case 1, with the aim of appropriately handing over the remote UE 100-1.

[0184] In the first operation example, the relay UE 100-2 forwards data received from a first cell (source cell 201S) that supports the sidelink relay function to the remote UE 100-1. The gNB 200, which manages the first cell, performs a process of causing the remote UE 100-1 to transmit a measurement report to the gNB 200 in response to a decision to handover the relay UE 100-2 to a second cell (target cell 201T) that does not support the sidelink relay function. Based on the measurement report from the remote UE 100-1, the gNB 200 performs a handover of the remote UE 100-1 before the handover of the relay UE 100-2. This avoids the problem that the remote UE 100-1 is unable to continue receiving MBS data due to the handover of the relay UE 100-2. Note that this operation is generally applicable to sidelink relay, regardless of MBS.

[0185] 24 is a diagram showing a first example of handover operation of the relay UE 100-2 according to the embodiment. Prior to this operation, the gNB 200 managing the source cell 201S may acquire information on whether each of the neighboring cells of the source cell 201S supports the MBS and sidelink relay functions. In addition, the remote UE 100-1 (and the relay UE 100-2) may be configured to transmit an event-triggered measurement report.

[0186] In step S501, the relaying UE 100-2 may receive MBS data belonging to the MBS session from the gNB 200 on the downlink (Uu interface).

[0187] In step S502, the relay UE 100-2 may transmit (transfer) the MBS data received from the gNB 200 to the remote UE 100-1 on the side link (PC5 interface).

[0188] In step S503, the relay UE 100-2 may transmit a measurement report including the measurement results of each cell to the source cell 201S (gNB 200), for example, in response to a deterioration in the reception quality of the source cell 201S and / or an improvement in the reception quality of the neighboring cell.

[0189] In step S504, the gNB 200 determines to hand over the relay UE 100-2 to a target cell that does not support sidelink relay functionality. Such a determination may be made by recognizing that the likelihood of handing over the relay UE 100-2 has increased.

[0190] In step S505, the gNB 200 instructs the remote UE 100-1 to transmit the measurement report via the relay UE 100-2. The instruction may be performed by an RRC message. For example, the instruction may be transmitted from the gNB 200 to the relay UE 100-2, and then the relay UE 100-2 may forward it to the remote UE 100-1. The instruction may forcibly trigger the remote UE 100-1 to transmit the configured measurement report. Note that the gNB 200 may request the relay UE 100-2 to transmit the instruction, and the relay UE 100-2 may instruct the remote UE 100-1.

[0191] In step S506, the remote UE 100-1 transmits a measurement report to the gNB 200. The measurement report includes measurement results of each cell measured by the remote UE 100-1.

[0192] In step S507, the gNB200 determines handover of the remote UE100-1 based on the measurement report from the remote UE100-1 and selects an appropriate target cell (or relay UE) as the target. Here, the gNB200 may select a target that supports MBS (and sidelink relay) functionality.

[0193] In step S508, the gNB 200 transmits a handover command instructing a handover to the determined target to the remote UE 100-1 via the relay UE 100-2. The handover command may be transmitted by an RRC message.

[0194] In step S509, the remote UE 100-1 accesses the target (performs a connection process) in accordance with the received handover command, and may receive MBS data from the target.

[0195] In step S510, the gNB 200 transmits a handover command to the relay UE 100-2.

[0196] In step S511, the relay UE 100-2 accesses the target (connection process) in accordance with the received handover command.

[0197] (5.5.2) Second operation example The second operation example is an operation example for enabling the remote UE 100-1 to perform continuous MBS reception in the above-described case 2.

[0198] In the second operation example, the relay UE 100-2 forwards MBS data received by the relay UE 100-2 from a first cell (source cell 201S) that supports the MBS function to the remote UE 100-1. In response to a decision to handover the relay UE 100-2 to a second cell (target cell 201T) that does not support the MBS function, the gNB 200, which manages the first cell, performs a process of establishing a PDU session in the remote UE 100-1 to deliver the MBS data to the remote UE 100-1 by unicast. After establishing the PDU session, the gNB 200 performs handover of the relay UE 100-2. The PDU session allows the MBS data to be received by unicast from the CN 20, as shown in FIG. 6 . Therefore, even if the relay UE 100-2 is handed over to the second cell (target cell 201T) that does not support the MBS function, the remote UE 100-1 can continue receiving the MBS data using the established PDU session.

[0199] 25 is a diagram illustrating a second example of handover operation of the relay UE 100-2 according to the embodiment. Prior to this operation, the gNB 200 managing the source cell 201S may acquire information on whether each of the neighboring cells of the source cell 201S supports the MBS and sidelink relay functions.

[0200] In step S531, the relaying UE 100-2 may receive MBS data belonging to the MBS session from the gNB 200 on the downlink (Uu interface).

[0201] In step S532, the relay UE 100-2 may transmit (transfer) the MBS data received from the gNB 200 to the remote UE 100-1 on the side link (PC5 interface).

[0202] In step S533, the relay UE 100-2 may transmit a measurement report including the measurement results of each cell to the source cell 201S (gNB 200), for example, in response to a deterioration in the reception quality of the source cell 201S and / or an improvement in the reception quality of the neighboring cell.

[0203] In step S534, the gNB 200 determines to hand over the relay UE 100-2 to a target cell that does not support the MBS function. Such a determination may be made by recognizing that the likelihood of handing over the relay UE 100-2 has increased.

[0204] In step S535, the gNB 200 instructs the remote UE 100-1 to establish a PDU session for MBS reception via the relay UE 100-2. The instruction may be sent by an RRC message. For example, the instruction may be transmitted from the gNB 200 to the relay UE 100-2, and then the relay UE 100-2 may forward it to the remote UE 100-1. The instruction may include information (cause information) indicating that the PDU session establishment is due to handover of the relay UE 100-2. The AS of the remote UE 100-1 may notify its own NAS of the instruction.

[0205] In step S536, the remote UE 100-1 establishes a PDU session for receiving the MBS.

[0206] In step S537, the gNB200 transmits a handover command to the relay UE100-2.

[0207] In step S538, the relay UE 100-2 accesses the target (performs a connection process) in accordance with the received handover command. After that, the remote UE 100-1 continues to receive the MBS data using the PDU session established on the relay UE 100-2.

[0208] (5.5.3) Third operation example The third operation example is an operation example for enabling handover of the remote UE 100-1 to the target cell 201T that supports the MBS function in order to avoid the above-mentioned case 2.

[0209] In the third operation example, the relay UE 100-2 identifies an MBS session that the remote UE 100-1 is interested in receiving. The relay UE 100-2 transmits an identifier (TMGI) indicating the identified MBS session to the gNB 200. This allows the gNB 200 to know the MBS session that the remote UE 100-1 is interested in receiving, and therefore allows the gNB 200 to select a target that provides the MBS session as a target for handover of the relay UE 100-2. Note that if multiple remote UEs 100-1 exist under the relay UE 100-2, the relay UE 100-2 may transmit to the gNB 200 the identifiers (TMGI) of the MBS sessions that each remote UE 100-1 is interested in receiving.

[0210] 26 is a diagram illustrating a third operation example of handover of the relay UE 100-2 according to the embodiment. Prior to this operation, the gNB 200 managing the source cell 201S may acquire information on whether each of the neighboring cells of the source cell 201S supports the MBS and sidelink relay functions.

[0211] In step S551, the relaying UE 100-2 may receive MBS data belonging to the MBS session from the gNB 200 on the downlink (Uu interface).

[0212] In step S552, the relay UE 100-2 may transmit (transfer) the MBS data received from the gNB 200 to the remote UE 100-1 on the side link (PC5 interface).

[0213] In step S553, the relay UE 100-2 identifies the identifier (TMGI) of the MBS session in which the remote UE 100-1 is interested. The relay UE 100-2 may perform the identification in step S553 from information (MBS interest information) of the identifier (TMGI) of the MBS session in which the remote UE 100-1 is interested, as described above. The relay UE 100-2 may also perform the identification in step S553 from the identifier (TMGI) of the MBS session that the relay UE 100-2 is currently transferring.

[0214] In step S554, the relay UE 100-2 transmits a message including the identified identifier (TMGI) to the gNB 200. The message may be an MBS Interest Notification (MII). The message may include information indicating that the remote UE 100-1, rather than the relay UE 100-2, is interested in the identifier (TMGI) of the MBS session.

[0215] In step S555, the relay UE 100-2 may transmit a measurement report including the measurement results of each cell to the source cell 201S (gNB 200), for example, in response to a deterioration in the reception quality of the source cell 201S and / or an improvement in the reception quality of the neighboring cell.

[0216] In step S556, based on the identifier (TMGI) received from the relay UE 100-2 in step S554, the gNB 200 determines handover of the relay UE 100-2 to a target that provides the MBS session corresponding to the TMGI.

[0217] In step S557, the gNB 200 transmits a handover command to the relay UE 100-2.

[0218] In step S558, the relay UE 100-2 accesses the target (connection process) in accordance with the received handover command.

[0219] (6) Other embodiments In the above-described embodiment, a single-hop case in which one relay UE 100-2 is interposed between the gNB 200 and the remote UE 100-1 has been assumed. However, the above-described embodiment may also be applied to a multi-hop case in which multiple relay UEs 100-2 are interposed between the gNB 200 and the remote UE 100-1. In the multi-hop case, the remote UE 100-1 may receive the above-described MBS session start notification from the relay UE 100-2. The notification may be a PC5-RRC message including the MBS session start information. Alternatively, the notification may be a discovery message including the MBS session start information.

[0220] 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.

[0221] In the above-described embodiment, 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 UE 100 may also be an MT (Mobile Termination) of the IAB node. Alternatively, in the above-described embodiment, the relay UE may be read as an IAB node (relay node), and the remote UE may be read as a UE.

[0222] 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).

[0223] 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 "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, 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, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. 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.

[0224] 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.

[0225] This application claims priority to U.S. Provisional Application No. 63 / 301,819 (filed January 21, 2022), the entire contents of which are incorporated herein by reference.

[0226] (Addendum) The following additional notes are about the features of the above-described embodiment.

[0227] (1) 1. A communication method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a base station to a remote user equipment via a relay user equipment, comprising: the remote user equipment preferentially selecting the relay user equipment capable of transferring the desired MBS session that the remote user equipment is interested in receiving over the relay user equipment that does not transfer the desired MBS session that the remote user equipment is interested in receiving; and receiving, by the remote user equipment, MBS data belonging to the desired MBS session from the base station via the selected relay user equipment. Communication method.

[0228] (2) the relay user equipment transmitting support information on a side link, indicating whether the relay user equipment supports forwarding of the MBS session; and the remote user equipment receiving the support information from the relay user equipment; The selecting step includes a step of preferentially selecting the relay user equipment capable of transferring the desired MBS session based on the received support information. The communication method described in (1) above.

[0229] (3) the relay user equipment transmitting, on a sidelink, an identifier indicating an MBS session that the relay user equipment is able to forward; and receiving, by the remote user equipment, the identifier from the relay user equipment; The selecting step includes a step of preferentially selecting the relay user equipment capable of transferring the desired MBS session based on the received identifier. The communication method according to (1) or (2) above.

[0230] (4) The method further includes a step of: identifying an MBS session that the relay user equipment can transfer based on an MBS reception configuration that the relay user equipment receives from the base station. The communication method described in (3) above.

[0231] (5) The selecting step includes a step of selecting relay user equipment from only relay user equipment capable of transferring the desired MBS session as candidates. A communication method according to any one of (1) to (4) above.

[0232] (6) the selecting step includes a step of performing relay user equipment selection by the remote user equipment comparing reception qualities of radio signals received from each of a plurality of relay user equipments; The step of selecting a relay user equipment includes a step of adding an offset to the reception quality of a relay user equipment that can transfer the desired MBS session. A communication method according to any one of (1) to (4) above.

[0233] (7) 1. A communication method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a base station to a remote user equipment via a relay user equipment, comprising: the relay user equipment in an RRC idle state or an RRC inactive state receiving interest information from the remote user equipment indicating that the remote user equipment is interested in receiving a multicast session; and performing a connection process by the relay user equipment to establish or resume an RRC connection with the base station in response to receiving the interest information. Communication method.

[0234] (8) The step of performing the connection process includes a step of notifying the base station that the multicast session is to be forwarded using a message transmitted from the relay user equipment to the base station during the connection process. The communication method according to (7) above.

[0235] (9) The method further comprises the step of the relay user equipment, which has established or resumed the RRC connection, forwarding MBS data belonging to the multicast session from the base station to the remote user equipment. The communication method according to (7) or (8) above.

[0236] (10) The relay user equipment that has established or resumed the RRC connection maps a multicast radio bearer (MRB) corresponding to the multicast session to a unicast or groupcast sidelink between the remote user equipment and the relay user equipment. A communication method according to any one of (7) to (9) above.

[0237] (11) 1. A communication method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a base station to a remote user equipment via a relay user equipment, comprising: forwarding, by the relay user equipment, data received from a first cell supporting sidelink relay functionality to the remote user equipment; performing a process of causing the remote user equipment to transmit a measurement report to the base station in response to the base station managing the first cell deciding to handover the relay user equipment to a second cell that does not support the sidelink relay function; and performing a handover of the remote user equipment prior to a handover of the relay user equipment based on the measurement report by the base station. Communication method.

[0238] (12) 1. A communication method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a base station to a remote user equipment via a relay user equipment, comprising: the relay user equipment forwarding the MBS data received by the relay user equipment from a first cell supporting the MBS function to the remote user equipment; In response to the base station managing the first cell deciding to handover the relay user equipment to a second cell that does not support the MBS function, the base station causes the remote user equipment to establish a PDU session for unicasting the MBS data to the remote user equipment; the base station performing the handover after the PDU session is established. Communication method.

[0239] (13) 1. A communication method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a base station to a remote user equipment via a relay user equipment, comprising: the relay user equipment identifying an MBS session that the remote user equipment is interested in receiving; and transmitting, by the relay user equipment, an identifier indicating the identified MBS session to the base station. Communication method. [Explanation of symbols]

[0240] 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 communications method for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a network node to a remote user equipment via a relay user equipment, comprising: the remote user equipment preferentially selecting the relay user equipment capable of transferring the desired MBS session that the remote user equipment is interested in receiving over the relay user equipment that does not transfer the desired MBS session that the remote user equipment is interested in receiving; receiving, by the remote user equipment, MBS data belonging to the desired MBS session from the network node via the selected relay user equipment; The selecting includes the remote user equipment transitioning the relay user equipment in an RRC (Radio Resource Control) idle state or an RRC inactive state to an RRC connected state, and preferentially selecting the relay user equipment to which the desired MBS session can be transferred. Communication method.

2. the relay user equipment transmitting support information on a side link indicating whether the relay user equipment supports forwarding of an MBS session; and the remote user equipment receiving the support information from the relay user equipment; The selecting step includes preferentially selecting the relay user equipment capable of transferring the desired MBS session based on the received support information. The communication method according to claim 1 .

3. the relay user equipment transmitting, on a side link, an identifier indicating an MBS session that the relay user equipment is able to forward; and the remote user equipment receiving the identifier from the relay user equipment; The selecting step includes preferentially selecting the relay user equipment to which the desired MBS session can be transferred based on the received identifier. The communication method according to claim 1 or 2.

4. The method further comprises: the relay user equipment identifying an MBS session that the relay user equipment can forward based on an MBS reception configuration that the relay user equipment receives from the network node. The communication method according to claim 3 .

5. The selecting includes selecting relay user equipment from only relay user equipment capable of transferring the desired MBS session as candidates. The communication method according to claim 1 or 2.

6. the selecting includes performing relay user equipment selection by comparing reception qualities of radio signals received by the remote user equipment from each of a plurality of relay user equipments; The step of selecting a relay user equipment includes adding an offset to the reception quality of a relay user equipment to which the desired MBS session can be transferred. The communication method according to claim 1 or 2.

7. receiving, by the selected relay user equipment in the RRC idle state or the RRC inactive state, interest information from the remote user equipment indicating that the remote user equipment is interested in receiving a multicast session; and performing a connection procedure by the selected relay user equipment to establish or resume an RRC connection with the network node in response to receiving the interest information. The communication method according to claim 1 .

8. The step of performing the connection process includes notifying the network node that the multicast session is to be forwarded using a message sent from the selected relay user equipment to the network node during the connection process. The communication method according to claim 7.

9. The method further comprises the selected relay user equipment that has established or resumed the RRC connection forwarding MBS data belonging to the multicast session from the network node to the remote user equipment.

9. The communication method according to claim 7 or 8.

10. The selected relay user equipment that established or resumed the RRC connection maps a multicast radio bearer (MRB) corresponding to the multicast session to a unicast or groupcast sidelink between the remote user equipment and the selected relay user equipment.

9. The communication method according to claim 7 or 8.

11. forwarding, by the selected relay user equipment, data received from a first cell supporting sidelink relay functionality to the remote user equipment; causing the remote user equipment to transmit measurement reports to the network node in response to the network node managing the first cell deciding to hand over the selected relay user equipment to a second cell that does not support the sidelink relay functionality; and performing a handover of the remote user equipment prior to a handover of the selected relay user equipment based on the measurement report. The communication method according to claim 1 .

12. the selected relay user equipment forwarding to the remote user equipment the MBS data received by the selected relay user equipment from a first cell supporting the MBS function; In response to the network node managing the first cell deciding to handover the selected relay user equipment to a second cell that does not support the MBS function, performing a process of causing the remote user equipment to establish a PDU session for unicasting the MBS data to the remote user equipment; The network node performs the handover after the PDU session is established. The communication method according to claim 1 .

13. the selected relay user equipment identifying an MBS session that the remote user equipment is interested in receiving; the selected relay user equipment transmitting an identifier indicating the identified MBS session to the network node. The communication method according to claim 1 .

14. 1. A remote user equipment in a communication system for transmitting Multicast Broadcast Service (MBS) data belonging to an MBS session from a network node to the remote user equipment via a relay user equipment, comprising: a control unit for preferentially selecting the relay user equipment capable of transferring the desired MBS session that the remote user equipment is interested in receiving over the relay user equipment that does not transfer the desired MBS session that the remote user equipment is interested in receiving; a receiving unit configured to receive MBS data belonging to the desired MBS session from the network node via the selected relay user equipment; The control unit transitions the relay user equipment in an RRC (Radio Resource Control) idle state or an RRC inactive state to an RRC connected state, and preferentially selects the relay user equipment to which the desired MBS session can be transferred. Remote user device.

Images