Communication system, mobile terminal, program, and communication method

Abstract

The communication system (100) of the present invention includes a base station (130), a relay UE (110A), and a remote UE (110B). When the relay UE (110A) is within range of being able to communicate with the base station (130), it receives MBS data as MBS data from the base station (130) and extracts the TMGI information contained in the MBS data. When the remote UE (110B) is within range of being unable to communicate with the base station (130) but being able to communicate with the relay UE (110A), it obtains the TMGI information from the relay UE (110A) and receives MBS from the base station (130) using the relay function of the relay UE (110A). If the relay UE (110A) does not receive MBS data within a predetermined period, it terminates the MBS relay.

Description

Technical Field

[0001] This disclosure relates to communication systems, mobile terminals, programs, and communication methods. Background Technology

[0002] 3GPP (3rd Generation Partnership Project), the standardization organization for mobile communication systems, is studying services that support the use of SL (Side Link) communication (also known as PC5 communication) in EPS (Evolved Packet System) and 5G (5th Generation) core systems. Furthermore, this service can also be provided through applications.

[0003] In SL communication, communication takes place between UEs (User Equipment) that act as communication terminals or mobile terminals. Services that utilize SL communication include, for example, V2X (Vehicle-to-everything) services and proximity services.

[0004] In SL communication, not only is direct communication between UEs proposed, but also communication between a UE and the NW (network) via a relay is proposed. The UE with this relay function will be referred to as a UE-to-Network relay or U2N relay.

[0005] In 3GPP, in order to extend the coverage of a cell by utilizing SL communication, the function of U2N relay is specified to provide relay connections to the 5G network to other UEs located outside the coverage of the cell via SL communication (see, for example, Non-Patent Document 1). In addition, 3GPP also specified the relay method for MBMS (Multimedia Broadcast and Multicast Service). While 5G has introduced MBS (Multicast and Broadcast Service) to replace MBMS, the relay method used for MBMS can be considered applicable to MBS as well.

[0006] In Non-Patent Document 1, a UE located outside the coverage area of ​​a base station that receives an MBMS needs to perform the following steps: establish a unicast communication with the base station via a U2N relay and identify the required MBMS. Existing technical documents Non-patent literature

[0007] Non-patent document 1: 3GPP TS23.303 V17.1.0 Summary of the Invention The technical problem that the invention aims to solve

[0008] However, when the UE is an IoT (Internet of Things) device, its functionality is limited. If the user does not need to communicate unicastly with the base station but only wants to receive MBMS or MBS, the above relay method requires extra steps, takes a long time to receive MBMS or MBS, and increases the UE's battery consumption.

[0009] Therefore, one of the objectives of one or more aspects of this disclosure is to enable the UE to receive MBS without unicast communication with the base station. Technical means for solving technical problems

[0010] One aspect of this disclosure relates to a communication system comprising a base station, a first mobile terminal, and a second mobile terminal. The system is characterized in that, when the first mobile terminal is within range of the base station capable of communicating with it, it receives MBS data (Multicast Service) data from the base station and extracts TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data. When the second mobile terminal is within range of the base station but unable to communicate with it, it obtains the TMGI information from the first mobile terminal and receives the MBS from the base station using the relay function of the first mobile terminal. If the first mobile terminal does not receive the MBS data within a predetermined period, it terminates the MBS relay.

[0011] One aspect of this disclosure relates to a mobile terminal characterized by comprising: a communication unit that, when within range capable of communicating with a base station, receives MBS data as MBS (Multicast Service) data from the base station; and a control unit that extracts TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data, appends the TMGI information to an SL (Side Link) communication message containing the TMGI information, causes the communication unit to send the message, and terminates MBS relay if the MBS data is not received within a predetermined period.

[0012] One aspect of the program disclosed herein is characterized in that it enables a computer to function as: a communication unit that, when within range of being able to communicate with a base station, receives MBS data as MBS (Multicast Service) data from the base station; and a control unit that extracts TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data, appends the TMGI information to a SL (Side Link) communication message, causes the communication unit to send the message, and terminates the MBS relay if the MBS data is not received within a predetermined period.

[0013] The communication method according to one aspect of this disclosure is characterized in that, when within range of being able to communicate with a base station, MBS data as MBS (Multicast Service) data is received from the base station, TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data is extracted, the TMGI information is appended to a message of SL (Side Link) communication and sent, and if the MBS data is not received within a predetermined period, the relay of the MBS is terminated. Invention Effects

[0014] According to one or more aspects of this disclosure, the UE is able to receive MBS without unicast communication with the base station. Attached Figure Description

[0015] Figure 1 This is a block diagram schematically illustrating the structure of the communication system involved in embodiments 1 and 2. Figure 2 This is a block diagram schematically illustrating the structure of the UE in embodiments 1 and 2. Figure 3 (A) and (B) are block diagrams illustrating examples of hardware structures. Figure 4 This is a block diagram schematically illustrating the structure of the base station in embodiments 1 and 2. Figure 5 This is a block diagram schematically illustrating the structure of the host device in embodiments 1 and 2. Figure 6 This is a sequence diagram illustrating the steps for relaying MBS to a UE in the communication system according to Embodiment 1. Figure 7 This is a schematic diagram illustrating a configuration example of the relay UE, remote UE, and base station 130 in Implementation 1. Figure 8 This is a sequence diagram illustrating the steps for relaying MBS to the UE via multi-hop relay in the communication system according to Embodiment 2. Figure 9This is a schematic diagram illustrating a configuration example of the first relay UE, the second relay UE, the remote UE, and the base station in Implementation Method 2. Detailed Implementation

[0016] Implementation method 1. Figure 1 This is a block diagram schematically illustrating the structure of the communication system 100 according to Embodiment 1. The communication system 100 includes a UE 110 as a mobile terminal, a base station 130 as a base station device, and a host device 160.

[0017] UE110 can communicate wirelessly with base station 130 to transmit and receive signals. In addition, UE110 can also communicate with each other via SL communication and can also communicate via relay.

[0018] Base station 130 constitutes a wireless access network. Here, we assume that the wireless access network is a fifth-generation (hereinafter also referred to as "5G") wireless access system for explanation, but it is not limited to this example.

[0019] When the radio access network (RAN) is the 5G approach discussed in 3GPP, it is called NG-RAN (Next Generation Radio Access Network). In this case, base station 130 is called gNB (NG-RAN NodeB), and the core network is called 5G Core. Conversely, when the RAN is the LTE approach discussed in 3GPP, it is called E-UTRAN (Evolved Universal Terrestrial Radio Access Network). In this case, base station 130 is called eNB (E-UTRAN NodeB).

[0020] Furthermore, a system consisting of the EPC (Evolved Packet Core) as the core network and the E-UTRAN as the radio access network is called EPS (Evolved Packet System). Sometimes, the EPC as the core network and the E-UTRAN as the radio access network are collectively referred to as the "network".

[0021] The base station 130 is connected to the host device 160 via the S1 interface, which functions as an MME (Mobility Management Entity), S-GW (Serving Gateway), or an MME / S-GW that includes both an MME and an S-GW, and communicates control information between the base station 130 and the host device 160.

[0022] A single base station 130 can connect to multiple host devices 160. Multiple base stations 130 are connected via the X2 interface to communicate control information among them.

[0023] The host device 160 is specifically a host node that controls the connection between the base station 130 and the UE 110. The host device 160 constitutes the EPC as the core network.

[0024] Base station 130 can form one cell or multiple cells. Each cell has a predetermined range as its coverage area, and wireless communication with UE 110 is conducted within the coverage area. When one base station 130 forms multiple cells, each cell is configured to communicate with UE 110.

[0025] Figure 2 This is a block diagram schematically representing the structure of UE110. UE110 includes a terminal-side communication unit 111, an application unit (hereinafter referred to as AP unit) 120, a protocol processing unit 121, a control unit 122, and a storage unit 123.

[0026] First, let’s explain the transmission process of UE110. Control data from the protocol processing unit 121 or user data from the AP unit 120 is provided to the terminal-side communication unit 111.

[0027] The terminal-side communication unit 111 converts data into a transmission signal for wireless communication and transmits the transmission signal to the destination via one or more antennas.

[0028] Next, the reception processing of UE110 will be explained. The terminal-side communication unit 111 receives wireless signals from a transmitting source via one or more antennas as received signals, and generates control data or user data based on the received signals. Then, the terminal-side communication unit 111 sends the control data to the protocol processing unit 121 and the user data to the AP unit 120.

[0029] The series of processes in UE110 described above are controlled by control unit 122. Although not shown, control unit 122 is connected to terminal-side communication unit 111, AP unit 120 and protocol processing unit 121. In addition, the number of antennas used for transmitting on UE110 can be the same as or different from the number of antennas used for receiving.

[0030] Storage unit 123 stores the programs and data required for processing in UE110.

[0031] As described above, part or all of the AP unit 120, protocol processing unit 121, and control unit 122, for example, Figure 3 As shown in (A), it can be composed of a memory 10 and a processor 11, such as a CPU (Central Processing Unit), that executes a program stored in the memory 10. Such a program can be provided via a network or recorded on a recording medium. That is, such a program can be provided, for example, as a program product. In other words, UE110 can be implemented using a computer equipped with a processor 11 and a memory 10.

[0032] Additionally, part or all of the AP unit 120, protocol processing unit 121, and control unit 122, for example, Figure 3 As shown in (B), it can also be composed of processing circuits 12 such as single circuits, composite circuits, processors that operate according to programs, parallel processors that operate according to programs, ASICs (Application Specific Integrated Circuits) or FPGAs (Field Programmable Gate Arrays). As described above, the AP unit 120, the protocol processing unit 121, and the control unit 122 can be implemented through a processing circuit network.

[0033] Furthermore, the terminal-side communication unit 111 can be implemented through a wireless communication interface, which serves as an interface for wireless communication. Storage unit 123 can be implemented using storage devices such as non-volatile memory, HDD (Hard Disk Drive) or SSD (Solid State Drive).

[0034] Figure 4 This is a block diagram schematically showing the structure of base station 130. The base station 130 includes a station-side communication unit 131, a communication processing unit 140, a protocol processing unit 144, a control unit 145, and a storage unit 146. The communication processing unit 140 includes: a 5GC communication unit 141 for data transmission and reception with the 5GC; an EPC communication unit 142 for data transmission and reception with EPCs (Evolved Packet Cores) such as the MME (Mobility Management Entity); and other base station communication units 143 for data transmission and reception with other base stations. Furthermore, the 5GC communication unit 141, the EPC communication unit 142, and the other base station communication units 143 exchange information with the protocol processing unit 144.

[0035] First, let's explain the transmission processing of base station 130. Control data from the protocol processing unit 144, or user data or control data from the 5GC communication unit 141, the EPC communication unit 142, or other base station communication units 143, are provided to the station-side communication unit 131.

[0036] The station-side communication unit 131 converts data into a transmission signal for wireless communication and transmits the transmission signal to the destination via one or more antennas.

[0037] Next, the receiving and processing of base station 130 will be explained. The station-side communication unit 131 receives wireless signals from a transmitting source via one or more antennas as received signals, and generates control data or user data based on the received signals. Then, the station-side communication unit 131 sends the control data to the protocol processing unit 144, the 5GC communication unit 141, the EPC communication unit 142, or other base station communication units 143, and sends the user data to the 5GC communication unit 141, the EPC communication unit 142, or other base station communication units 143.

[0038] The series of processes in the base station 130 described above are controlled by the control unit 145. Although not shown, the control unit 145 is connected to the station-side communication unit 131, the communication processing unit 140, and the protocol processing unit 144. In addition, the number of antennas used for transmitting and the number of antennas used for receiving in base station 130 may be the same or different. In addition, the number of antennas of UE110 can be the same as or different from the number of antennas of base station 130.

[0039] Storage unit 146 stores the programs and data required for processing in base station 130.

[0040] As described above, part or all of the communication processing unit 140, protocol processing unit 144, and control unit 145 are, for example, Figure 3As shown in (A), it can be composed of a memory 10 and a processor 11, such as a CPU, that executes a program stored in the memory 10. Such a program can be provided via a network or recorded on a recording medium. That is, such a program can be provided, for example, as a program product.

[0041] Additionally, part or all of the communication processing unit 140, protocol processing unit 144, and control unit 145, for example, Figure 3 As shown in (B), it can also be composed of a single circuit, a composite circuit, a processor that operates according to a program, a parallel processor that operates according to a program, an ASIC, or an FPGA, etc., processing circuit 12. As described above, the communication processing unit 140, the protocol processing unit 144, and the control unit 145 can be implemented through a processing circuit network.

[0042] Furthermore, the station-side communication unit 131 can be implemented through a wireless communication interface, which serves as an interface for wireless communication. The storage unit 126 can be implemented using storage devices such as non-volatile memory, HDD or SSD.

[0043] Figure 5 This is a block diagram schematically representing the structure of the host device 160. In this embodiment, since 5G is used as the wireless access network, the host device 160 is also referred to as 5GC (5G Core).

[0044] Figure 5 It shows in Figure 1 The host device 160 shown includes structures such as AMF (Access and Mobility Management Function), SMF (Session Management Function), and UPF (User Plane Function). The host device 160 includes a data network communication unit 161, a base station communication unit 162, a user plane communication unit 163, a session management unit 164, a control plane control unit 165, and a control unit 169.

[0045] The data network communication unit 161 performs data transmission and reception between the host device 160 and the data network. The base station communication unit 162 performs data transmission and reception between the host device 160 and the base station 130 via the NG interface. When the data received from the data network is user data, the user data is sent from the data network communication unit 161 to the base station communication unit 162 via the user plane communication unit 163, and then from the base station communication unit 162 to the base station 130. When the data from base station 130 is user data, the user data is sent from base station communication unit 162 to data network communication unit 161 via user plane communication unit 163, and then sent from data network communication unit 161 to data network.

[0046] When the data from the data network is control data, the control data is sent from the data network communication unit 161 to the session management unit 164 via the user plane communication unit 163. Session management unit 164 sends control data to control plane control unit 165. When the data from base station 130 is control data, the control data is sent from base station communication unit 162 to control plane control unit 165. Control plane control unit 165 then sends the control data to session management unit 164.

[0047] The control unit 165 performs overall processing on the control surface (hereinafter, sometimes also referred to as C-Plane). The control plane control unit 165 includes a NAS (Non-Access Stratum) security unit 166, a PDU session control unit 167, and an idle state mobility management unit 168.

[0048] The NAS Security Department 166 handles the secure processing of NAS messages, etc. The PDU session control unit 167 manages the PDU session between the UE110 and the host device 160, etc. The idle state mobility management unit 168 performs mobility management in standby mode, generation and control of paging signals in standby mode, addition, deletion, updating and retrieval of tracking areas for one or more UEs 110 within the coverage area, and tracking area list management. Standby mode is also known as idle mode, RRC_IDLE mode, or simply idle.

[0049] The series of processes of the host device 160 are controlled by the control unit 169. Although not shown, the control unit 169 is connected to the data network communication unit 161, the base station communication unit 162, the user plane communication unit 163, the session management unit 164, and the control plane control unit 165.

[0050] Data network communication unit 161, base station communication unit 162, user plane communication unit 163, session management unit 164, control plane control unit 165, and control unit 169 may be part or all of the following: Figure 3As shown in (A), the system comprises a memory 10 and a processor 11, such as a CPU, that executes the program stored in the memory 10. Such a program can be provided via a network or recorded on a recording medium. That is, such a program can be provided, for example, as a program product.

[0051] Additionally, some or all of the data network communication unit 161, base station communication unit 162, user plane communication unit 163, session management unit 164, control plane control unit 165, and control unit 169 may, for example, be as follows: Figure 3 As shown in (B), it consists of a processing circuit 12, such as a single circuit, a composite circuit, a processor that operates according to a program, a parallel processor that operates according to a program, an ASIC, or an FPGA. As described above, the data network communication unit 161, the base station communication unit 162, the user plane communication unit 163, the session management unit 164, and the control plane control unit 165 can be implemented through a circuit network.

[0052] Figure 6 This is a sequence diagram showing the steps for relaying MBS to UE110 in the communication system 100 according to Embodiment 1. Figure 6 The sequence diagram shown is in Figure 7 The steps are as shown. like Figure 7 As shown, the following are present: UE110, which provides a relay connection to the 5G network via SL communication, i.e., relay UE110A, which functions as a U2N relay; UE110B, which wants to receive MBS via relay, i.e., remote UE110B; and base station 130. In addition, the relay UE110A is also called the first mobile terminal, and the remote UE110B is also called the second mobile terminal.

[0053] In step S10, the control unit 122 of the relay UE110A establishes communication with the base station 130, which is a gNB, via the protocol processing unit 121 and the terminal-side communication unit 111, and is in the RRC_CONNECTED state.

[0054] In step S11, the control unit 122 of the relay UE 110A queries the base station 130 and the upper-level device 160 (which is the core network) via the protocol processing unit 121 and the terminal-side communication unit 111 to inquire whether the relay function of the MBS is available. The control plane control unit 165 of the upper-level device 160 notifies the relay UE 110A whether the relay function of the MBS is available via the session management unit 164, the user plane communication unit 163, and the base station communication unit 162. Conditions for the unavailability of the relay function may include geographical conditions or relay restrictions caused by limitations of each service (application). Here, we will assume that the relay function is available for explanation.

[0055] In step S12, since the relay function is available, the control unit 122 of the relay UE110A begins to receive MBS data via the protocol processing unit 121 and the terminal-side communication unit 111. When the relay UE110A's control unit 122 receives MBS data, it extracts the TMGI (Temporary Mobile Group Identity) information contained in the MBS data and stores it in the storage unit 123 as a list of MBS that can be relayed. Furthermore, the relay UE110A's control unit 122 prepares a timer for relaying for each MBS service and starts the timer when MBS data is received. In step S11, when the control unit 122 of the relay UE110A receives notification from the base station 130 of the list information of MBS that are allowed to be relayed, it can use this list information as the initial value of the list of MBS that can be relayed.

[0056] In step S13, the control unit 122 of the remote UE110B searches for a connectable relay UE110A via the protocol processing unit 121 and the terminal-side communication unit 111, according to the SL communication discovery procedure. The control unit 122 of the relay UE110A attaches relay information and the TMGI information of the available MBS that was obtained in advance in step S12 to the discovery message or discovery solicitation message it sends.

[0057] In step S14, the control unit 122 of the remote UE110B parses the acquired TMGI information and determines whether the desired MBS exists. Here, we will assume that the desired MBS exists for explanation.

[0058] In step S15, in the case of multicast service, a direct connection session is established between the remote UE110B and the relay UE110A. Here, the control unit 122 of the remote UE110B and the control unit 122 of the relay UE110A communicate via the protocol processing unit 121 and the terminal-side communication unit 111, respectively, thereby establishing the session. Even in the case of broadcast service, session establishment can be performed.

[0059] In step S16, in the case of multicast service, the control unit 122 of the relay UE110A notifies the base station 130 via the protocol processing unit 121 and the terminal-side communication unit that the remote UE110B receives multicast via the relay.

[0060] In step S17, the control unit 145 of the base station 130 sends MBS data via the protocol processing unit 144 and the station-side communication unit 131. If the relay service is permitted in step S11, the control unit 122 of the relaying UE110A forwards the received MBS data to all remote UEs 110B that wish to relay the MBS data via SL communication through the protocol processing unit 121 and the terminal-side communication unit 111. The forwarding method can be either unicast communication or multicast communication.

[0061] In step S18, the control unit 122 of the relay UE110A resets the timer associated with the received MBS service.

[0062] In step S19, when the timer reaches a certain fixed threshold, the control unit 122 of the relay UE110A considers the corresponding service to have ended, and deletes the TMGI information from the subsequent discovery message or discovery request message via the protocol processing unit 121 and the terminal-side communication unit 111. By receiving this updated message, the control unit 122 of the remote UE110B can recognize that the MBS data is not being relayed. As described above, if the relay UE110A does not receive MBS data within a predetermined period, the MBS relay will terminate.

[0063] Alternatively, the control unit 122 of relay UE110A may use multicast of SL communication to replace the discovery message and immediately broadcast the TMGI information to be terminated to the surrounding UE110. The threshold of the comparison timer can be determined by the control unit 122 of the relay UE110A, or it can be determined based on an instruction from the base station 130. Furthermore, the threshold can be uniform for all services, or it can be different for each service.

[0064] In step S20, during the multicast service, when the timer expires or the remote UE110B ends receiving in step S19, the control unit 122 of the relay UE110A and the control unit 122 of the remote UE110B release unnecessary direct connections and end the session.

[0065] Furthermore, the control unit 122 of the remote UE110B can determine its own location using GNSS (Global Navigation Satellite System) or similar methods, and send the location information representing its location to the relay UE110A in step S15. The control unit 122 of the relay UE110A can send the received location information from the remote UE110B to the base station 130 via the protocol processing unit 121 and the terminal-side communication unit 111 to check if relaying is possible. Alternatively, in step S11, it can obtain map information of the relay-prohibited area from the base station 130, determine whether relaying is possible, and notify the remote UE110B of the result. This enables relay control based on higher-precision location information. Additionally, the relay-prohibited area is an area where relay functionality is prohibited.

[0066] Consider the scenario where relay UE110A moves outside the coverage area of ​​base station 130 and switches to another base station 130, resulting in different MBS (Mobile Base Service). If remote UE110B is receiving multicast, it can obtain and identify the handover information through unicast communication with relay UE110A. However, in the case of broadcast, it can be assumed that there is no unicast communication between remote UE110B and relay UE110A. Furthermore, it can be assumed that relay UE110A does not know which UE110 is receiving the relayed broadcast data. This problem can be resolved by having the control unit 122 of relay UE110A use multicast communication via SL (Single Streaming) to broadcast the handover to surrounding areas, prompting remote UE110B to reset its held receivable TMGI (Transmitted Memory Gauge Information). Thus, the handover situation of relay UE110A can be addressed.

[0067] As described above, when the relay UE110A is within range of the base station 130, it receives MBS data as MBS data from the base station 130 and extracts the TMGI information contained in the MBS data. Then, when the remote UE110B is within range of the relay UE110A but cannot communicate with the base station 130, it obtains the TMGI information from the relay UE110A and uses the relay function of the relay UE110A to receive MBS from the base station 130.

[0068] Alternatively, relay UE110A only needs to append TMGI information to the SL communication message and send it. Either a discovery message or a discovery request message can be used here.

[0069] In addition, the relay UE110A queries the base station 130 whether the MBS relay function can be used. If the MBS relay function can be used, it can receive MBS data from the base station 130.

[0070] Additionally, relay UE110A begins measuring time upon receiving MBS data. When the measured time reaches a predetermined threshold, the relay function of MBS is stopped. When the relay function of MBS is stopped, relay UE110A does not provide TMGI information to remote UE110B.

[0071] Through the above steps, MBS data can be received via relay UE110A without establishing (normal) unicast communication between remote UE110B and base station 130 via relay UE110A, which simplifies remote UE110B and reduces power consumption.

[0072] Additionally, the remote UE110B can also send location information indicating its location to the relay UE110A. The relay UE110A can then notify the base station 130 of this location information, inquiring whether the MBS relay function can be used. If the location indicated by the location information is not within the area where the MBS relay function is prohibited, the base station 130 will respond to the relay UE110A indicating that the MBS relay function can be used. Therefore, it is possible to more accurately determine whether a relay can be performed.

[0073] In addition, the remote UE110B can also send location information indicating the location of the remote UE110B to the relay UE110A. When the location indicated by the location information is not included in the range where the relay function of MBS is prohibited, the relay UE110A can relay MBS data from the base station 130 to the remote UE110B.

[0074] In addition, when relay UE110A switches to a neighboring base station (not shown) that is adjacent to base station 130, it can send a switching information indicating that a switch has been performed to remote UE110B by using the multicast function of SL communication, thereby enabling the relay of the MBS corresponding to the switch.

[0075] Implementation method 2. In addition to the features of Implementation 1, it is believed that the MBS arrival distance can be further extended by using U2U relay (UE-to-UE relay), which is studied in 3GPP for relaying direct communication between terminals. In Implementation 2, the structure that enables this processing will be described.

[0076] like Figure 1 As shown, the communication system 200 involved in Embodiment 2 includes a UE 210, a base station 130, and a host device 160. The base station 130 and the host device 160 of the communication system 200 involved in Embodiment 2 are the same as the base station 130 and the host device 160 of the communication system 100 involved in Embodiment 1.

[0077] like Figure 2 As shown, the UE210 in Embodiment 2 includes a terminal-side communication unit 111, an AP unit 120, a protocol processing unit 121, a control unit 222, and a storage unit 123. The terminal-side communication unit 111, AP unit 120, protocol processing unit 121, and storage unit 123 of UE210 in Embodiment 2 are the same as those of UE110 in Embodiment 1.

[0078] In Embodiment 2, the control unit 220 performs the same processing as in Embodiment 1, and also performs U2U relay processing to implement direct communication between terminals, which is studied in 3GPP.

[0079] Figure 8 This is a sequence diagram showing the steps for relaying MBS to UE210 via multi-hop relay in the communication system 200 according to Embodiment 2. Figure 8 The sequence diagram shown is in Figure 9 The steps are as shown. like Figure 9 As shown, the following are present: UE210, which provides a relay connection to the 5G network via SL communication, i.e., the first relay UE210A, which functions as a U2N relay; UE210, which functions as a U2U relay for direct inter-terminal communication under study in 3GPP, i.e., the second relay UE210B; UE210, which wants to receive MBS via relay, i.e., the remote UE210C; and base station 130. Here, the first relay UE210A is also referred to as the first mobile terminal, the second relay UE210B is also referred to as the second mobile terminal, and the remote UE210C is also referred to as the third mobile terminal.

[0080] In step S30, the control unit 222 of the first relay UE210A establishes communication with the base station 130, which is a gNB, via the protocol processing unit 121 and the terminal-side communication unit 111, and is in the RRC_CONNECTED state.

[0081] In step S31, the control unit 222 of the first relay UE210A queries the base station 130 and the upper-level device 160 (which is the core network) via the protocol processing unit 121 and the terminal-side communication unit 111 to inquire whether the relay function of the MBS is available. The control plane control unit 165 of the upper-level device 160 notifies the first relay UE210A whether the relay function of the MBS is available via the session management unit 164, the user plane communication unit 163, and the base station communication unit 162. Here, it is assumed that the relay function is available for explanation.

[0082] In step S32, the control unit 222 of the second relay UE210B searches for U2N relays connected to the base station 130 via the protocol processing unit 121 and the terminal-side communication unit 111. At this point, the first UE210A is already connected to the base station 130 and is functioning as a U2N relay.

[0083] Therefore, in step S33, the control unit 222 of the second relay UE210B establishes a communication session with the first relay UE210A via the protocol processing unit 121 and the terminal-side communication unit 111.

[0084] In step S34, the control unit 222 of the second relay UE210B receives the relay from the first relay UE210A via the protocol processing unit 121 and the terminal-side communication unit 111, and queries the base station 130 and the upper-level device 160 (which is the core network) whether the relay function of the MBS is available. The control plane control unit 165 of the upper-level device 160 notifies the second relay UE210B via the first relay UE210A whether the relay function of the MBS is available via the session management unit 164, the user plane communication unit 163, and the base station communication unit 162. Here, it is assumed that the relay function is available for explanation.

[0085] In step S35, the relay function is available, and the control unit 222 of the first relay UE210A begins to receive MBS data via the protocol processing unit 121 and the terminal-side communication unit 111. When the control unit 222 of the first relay UE 210A receives MBS data, it extracts the TMGI information contained in the MBS data and stores it in the storage unit 123 as a list of MBS that can be relayed. In addition, the control unit 222 of the first relay UE 110A prepares a relay timer for each MBS service and starts the timer when MBS data is received. Furthermore, the control unit 222 of the second relay UE210B, via the protocol processing unit 121 and the terminal-side communication unit 111, accepts the relay from the first relay UE210A and begins receiving MBS data. In addition, the relay method between the first relay UE210A and the second relay UE210B can be performed via multicast from the first relay UE210A, or via unicast communication already established. When the control unit 222 of the second relay UE210B receives MBS data, it extracts the TMGI information contained in the MBS data and stores it in the storage unit 123 as a list of relayable MBS. Furthermore, the control unit 222 of the second relay UE210B prepares a relay timer for each MBS service and starts the timer when MBS data is received.

[0086] In step S36, the control unit 222 of the remote UE210C searches for connectable relay UEs via the protocol processing unit 121 and the terminal-side communication unit 111, following the SL communication discovery process. Here, we will assume that the second relay UE210B is connectable. The control unit 222 of the second relay UE210B adds relay information and the TMGI information of the available MBS that was pre-acquired in step S35 to the discovery message or discovery request message it sends.

[0087] In step S37, the control unit 222 of the remote UE210C parses the acquired TMGI information and determines whether the desired MBS exists. Here, we will assume that the desired MBS exists for explanation.

[0088] In step S38, in the case of multicast service, a direct connection session is established between the remote UE210C and the second relay UE210B. Here, the control unit 222 of the remote UE210C and the control unit 222 of the second relay UE210B communicate via the protocol processing unit 121 and the terminal-side communication unit 111, respectively, thereby establishing the session. Session establishment can also be performed in the case of broadcast service.

[0089] In step S39, in the case of multicast service, the control unit 222 of the second relay UE210B notifies the base station 130 via the protocol processing unit 121 and the terminal-side communication unit that the remote UE210C is receiving multicast via the relay.

[0090] In step S40, the control unit 145 of the base station 130 sends MBS data via the protocol processing unit 144 and the station-side communication unit 131. In the case where relay service is permitted in step S31, the control unit 222 of the first relay UE210A forwards the received MBS data to all UEs210 that wish to relay the MBS data via SL communication through the protocol processing unit 121 and the terminal-side communication unit 111. Here, the MBS data is forwarded to the second relay UE210B. The forwarding method can be either unicast communication or multicast communication. Furthermore, in the case where relay service is permitted in step S34, the control unit 222 of the second relay UE210B forwards the received MBS data to all UEs210 that wish to relay the MBS data via SL communication through the protocol processing unit 121 and the terminal-side communication unit 111. Here, the MBS data is forwarded to the remote UE210C. The forwarding method can be either unicast communication or multicast communication.

[0091] In step S41, the control unit 222 of the first relay UE210A resets the timer associated with the service of the received MBS. Additionally, in step S42, the control unit 222 of the second relay UE210B resets the timer associated with the service of the received MBS.

[0092] In step S43, when the timer reaches a certain fixed threshold, the control unit 222 of the first relay UE210A considers the corresponding service to have ended, and deletes the TMGI information from subsequent discovery messages or discovery request messages via the protocol processing unit 121 and the terminal-side communication unit 111. By receiving this updated discovery message, the control unit 222 of the second relay UE210B can identify that MBS data is not being relayed. As described above, the first relay UE210A terminates MBS relay when it does not receive MBS data within a predetermined period.

[0093] Alternatively, the control unit 222 of the first relay UE210A may use multicast of SL communication instead of discovery messages to immediately broadcast the TMGI information to be terminated to the surrounding UE210s. The threshold of the comparison timer can be determined by the control unit 222 of the first relay UE210A, or it can be determined based on an instruction from the base station 130. Furthermore, the threshold can be uniform for all services, or it can be different for each service.

[0094] Furthermore, in step S44, when the timer reaches a certain fixed threshold, the control unit 222 of the second relay UE210B considers the corresponding service to have ended, and deletes the TMGI information from subsequent discovery messages or discovery request messages via the protocol processing unit 121 and the terminal-side communication unit 111. By receiving this updated discovery message, the control unit 222 of the remote UE210C can identify that MBS data is not being relayed. In addition, if the second relay UE210B does not receive MBS data within the predetermined period, it will also terminate the MBS relay.

[0095] Alternatively, the control unit 222 of the second relay UE210B may use multicast of SL communication instead of discovery messages to immediately broadcast the TMGI information to be terminated to the surrounding UE210s. The threshold of the comparison timer can be determined by the control unit 222 of the second relay UE210B, or it can be determined according to the instruction of the base station 130. In addition, the threshold can be uniform for all services, or it can be different for each service.

[0096] In step S45, during the multicast service, when the timer expires or the second relay UE210B ends receiving data in step S41, the control unit 222 of the first relay UE210A and the control unit 222 of the second relay UE210B release unnecessary direct connections and terminate the session.

[0097] Additionally, in step S46, during the multicast service, when the timer expires or the remote UE210C ends receiving in step S42, the control unit 222 of the second relay UE210B and the control unit 222 of the remote UE210B release unnecessary direct connections and terminate the session.

[0098] In implementation 2, the first relay UE210A and the second relay UE210B have the following characteristics: regardless of the number of UE210s connected to the U2U relay and functioning as remote UE210C, the number of sessions is always one. This is achieved through PTM (Point-to-Multi) communication, which replicates MBS data at the U2U relay and performs relaying and transmission. This effectively prevents an increase in communication data volume and ensures scalability, especially in SL communication with limited communication bandwidth. Furthermore, the connection between the remote UE210 and the relay UE210 can be either multicast or broadcast.

[0099] As described above, when the remote UE210C is within a range where it cannot communicate with the base station 130 and the first relay UE210A, but can communicate with the second relay UE210B, it obtains TMGI information from the second relay UE210B and uses the relay function of the second relay UE210B and the relay function of the first relay UE210A to receive MBS from the base station 130.

[0100] Here, the second relay UE210B uses the PTM communication method of copying MBS data from the first relay UE210A and relaying the copied MBS data to the remote UE210C, thereby enabling the relay device to have only one session.

[0101] As shown in the steps above, by extracting TMGI information from both the U2U and U2U relays for MBS data, attaching it to its own discovery message and broadcasting it, MBS can be relayed in a multi-hop relay manner. Label Explanation

[0102] 100, 200 Communication System; 110, 210 UE; 111 Terminal-side Communication Department; 120 AP Department; 121 Protocol Processing Department; 122, 222 Control Department; 123 Storage Department; 130 Base Station; 131 Station-side Communication Department; 140 Communication Processing Department; 144 Protocol Processing Department; 145 Control Department; 146 Storage Department; 160 Host Device; 161 Data Network Communication Department; 162 Base Station Communication Department; 163 User Plane Communication Department; 164 Session Management Department; 165 Control Plane Control Department; 169 Control Department.

Claims

1. A communication system comprising a base station, a first mobile terminal, and a second mobile terminal, characterized in that, When the first mobile terminal is within range of the base station capable of communicating with it, it receives MBS data as MBS (Multicast Service) data from the base station and extracts the TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data. When the second mobile terminal is within a range where it cannot communicate with the base station but can communicate with the first mobile terminal, it obtains the TMGI information from the first mobile terminal and, using the relay function of the first mobile terminal, receives the MBS from the base station. If the first mobile terminal does not receive the MBS data within a predetermined period, the MBS relay will be terminated.

2. The communication system as described in claim 1, characterized in that, The first mobile terminal appends the TMGI information to the SL (sidelink) communication message and sends it.

3. The communication system as described in claim 2, characterized in that, The message is a discovery message or a discovery request message.

4. The communication system as described in any one of claims 1 to 3, characterized in that, The first mobile terminal queries the base station to see if it can utilize the relay function of the MBS. If it can utilize the relay function of the MBS, it receives the MBS data from the base station.

5. The communication system as described in claim 4, characterized in that, The second mobile terminal sends location information indicating the location of the second mobile terminal to the first mobile terminal. The first mobile terminal notifies the base station of the location information and inquires whether the relay function of the MBS can be utilized. When the location indicated by the location information is not within the range where the relay function of the MBS is prohibited, the base station responds to the first mobile terminal that the relay function of the MBS can be used.

6. The communication system as described in claim 4, characterized in that, The second mobile terminal sends location information indicating the location of the second mobile terminal to the first mobile terminal. When the location indicated by the location information is not within the range where the relay function of the MBS is prohibited, the first mobile terminal relays the MBS data from the base station to the second mobile terminal.

7. The communication system as described in any one of claims 1 to 6, characterized in that, When the first mobile terminal receives the MBS data, it starts measuring time. If the measured time reaches a predetermined threshold, the relay function of the MBS is stopped.

8. The communication system as described in claim 7, characterized in that, If the first mobile terminal stops the relay function of the MBS, it will not provide the TMGI information to the second mobile terminal.

9. The communication system as described in any one of claims 1 to 8, characterized in that, It also includes neighboring base stations that are adjacent to the base station. When the first mobile terminal switches to the adjacent base station, it uses the multicast function of the SL communication to send a handover message to the second mobile terminal indicating that a handover has taken place.

10. The communication system as described in any one of claims 1 to 9, characterized in that, It also includes third mobile terminals, When the third mobile terminal is in a range where it cannot communicate with the base station and the first mobile terminal, but can communicate with the second mobile terminal, it obtains the TMGI information from the second mobile terminal and receives the MBS from the base station using the relay function of the second mobile terminal and the relay function of the first mobile terminal.

11. The communication system as described in claim 10, characterized in that, If the third mobile terminal does not receive MBS data within a predetermined period, the MBS relay will be terminated.

12. The communication system as described in claim 10 or 11, characterized in that, The second mobile terminal uses a PTM (point-to-multipoint) communication method to copy the MBS data from the first mobile terminal and relay the copied MBS data to the third mobile terminal.

13. A mobile terminal, characterized in that, include: The communication unit, when within range of being able to communicate with the base station, receives MBS data from the base station as MBS (Multicast Broadcast Service) data; as well as The control unit extracts the TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data, appends the TMGI information to an SL (Side Link) communication message containing the TMGI information, causes the communication unit to send the message, and terminates the MBS relay if the MBS data is not received within a predetermined period.

14. A program, characterized in that, To enable a computer to function as the following components: The communication unit, when within range of being able to communicate with the base station, receives MBS data from the base station as MBS (Multicast Broadcast Service) data; as well as The control unit extracts the TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data, appends the TMGI information to the SL (Side Link) communication message, causes the communication unit to send the message, and terminates the MBS relay if the MBS data is not received within a predetermined period.

15. A communication method, characterized in that, When within range of the base station capable of communicating with it, MBS data, which is received from the base station as MBS (Multicast Broadcast Service) data, is received. Extract the TMGI (Temporary Mobile Group Identifier) ​​information contained in the MBS data, append the TMGI information to the SL (Side Link) communication message, and send it. If no MBS data is received within the predetermined period, the MBS relay is terminated.

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