Communication system, mobile terminal, program, and communication method

Abstract

A communication system (100) comprises a base station (130), a relay UE (110A), and a remote UE (110B). When the relay UE (110A) is present in a communicable range with the base station (130), the relay UE (110A) receives MBS data, which is data on an MBS, from the base station (130), and extracts TMGI information included in the MBS data. When the remote UE (110B) is present in a communicable range with the relay UE (110A) but unable to communicate with the base station (130), the remote UE (110B) acquires the TMGI information from the relay UE (110A), and is provided with the MBS from the base station (130) by using the relay function of the relay UE (110A). The relay UE (110A) terminates the MBS relay when the MBS data has not been received for a predetermined period.

Description

Communication system, mobile terminal, program, and communication method

[0001] The present disclosure relates to a communication system, a mobile terminal, a program, and a communication method.

[0002] The 3rd Generation Partnership Project (3GPP), a standardization organization for mobile communication systems, is considering supporting services using Side Link (SL) communication (also referred to as PC5 communication) in both the Evolved Packet System (EPS) and the 5th Generation (5G) core system. Note that this service may be provided by an application.

[0003] In SL communication, communication is performed between UEs (User Equipment) as communication terminals or mobile terminals. Services using SL communication include, for example, a Vehicle-to-Everything (V2X) service and a proximity service.

[0004] In SL communication, not only direct communication between UEs but also communication between a UE and a NW (Network) via a relay has been proposed. A UE having a relay function, which is a function to perform such relaying, is hereinafter referred to as a UE-to-Network relay or U2N relay.

[0005] In order to extend the coverage of a cell using SL communication, 3GPP specifies a U2N relay function that provides a relay connection to a 5G network via SL communication for other UEs outside the coverage of the cell (see, for example, Non-Patent Document 1). 3GPP also specifies a relay method for MBMS (Multimedia Broadcast and Multicast Service). 3GPP newly specifies MBS (Multicast and Broadcast Service) instead of MBMS in 5G, and it is considered that the relay method for MBMS can also be applied to MBS.

[0006] Here, in Non-Patent Document 1, a UE that is outside the coverage area of ​​a base station and that wants to receive MBMS must first establish unicast communication with the base station via a U2N relay and then recognize the desired MBMS.

[0007] 3GPP TS23.303 V17.1.0

[0008] However, when the UE is an IoT (Internet of Things) device or the like, and the UE has limited functionality, and the user does not need unicast communication with the base station but only wants to receive MBMS or MBS, the above relay method requires an extra procedure, which takes time to receive MBMS or MBS and also increases the battery consumption of the UE.

[0009] Therefore, one object of one or more aspects of the present disclosure is to enable a UE to receive an MBS without performing unicast communication with a base station.

[0010] A communication system according to one aspect of the present disclosure is a communication system including a base station, a first mobile terminal, and a second mobile terminal, wherein the first mobile terminal, when present within a range in which it can communicate with the base station, receives MBS data, which is MBS (Multicast and Broadcast Service) data, from the base station and extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, and the second mobile terminal, when present within a range in which it cannot communicate with the base station but can communicate with the first mobile terminal, acquires the TMGI information from the first mobile terminal and uses the relay function of the first mobile terminal to receive the MBS from the base station, and the first mobile terminal terminates relaying of the MBS if it does not receive the MBS data for a predetermined period of time.

[0011] A mobile terminal according to one aspect of the present disclosure is characterized in that it includes: a communication unit that receives MBS data, which is MBS (Multicast and Broadcast Service) data, from a base station when the mobile terminal is within a range where the mobile terminal can communicate with the base station; and a control unit that extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, adds the TMGI information to an SL (Side Link) communication message including the TMGI information, and causes the communication unit to transmit the message; and terminates relaying of the MBS when the mobile terminal does not receive the MBS data for a predetermined period of time.

[0012] A program according to one aspect of the present disclosure causes a computer to function as a communication unit that receives MBS (Multicast and Broadcast Service) data from a base station when the computer is within a range capable of communicating with the base station, and a control unit that extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, adds the TMGI information to an SL (Side Link) communication message, and transmits the message to the communication unit, and terminates relaying of the MBS when the MBS data is not received for a predetermined period of time.

[0013] A communication method according to one aspect of the present disclosure is characterized in that, when a mobile station is within a range capable of communicating with a base station, it receives MBS data, which is data of MBS (Multicast and Broadcast Service), from the base station, extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, adds the TMGI information to an SL (Side Link) communication message, and transmits the message, and if the MBS data is not received for a predetermined period, it terminates relaying of the MBS.

[0014] According to one or more aspects of the present disclosure, a UE can receive an MBS without unicast communication with a base station.

[0015] 1 is a block diagram schematically showing the configuration of a communication system according to embodiments 1 and 2. FIG. 2 is a block diagram schematically showing the configuration of a UE according to embodiments 1 and 2. FIG. 3 is a block diagram showing an example of a hardware configuration. FIG. 4 is a block diagram schematically showing the configuration of a base station according to embodiments 1 and 2. FIG. 5 is a block diagram schematically showing the configuration of a higher-level device according to embodiments 1 and 2. FIG. 6 is a sequence diagram showing a procedure for relaying an MBS to a UE in a communication system according to embodiment 1. FIG. 7 is a schematic diagram showing an example of arrangement of a relay UE, a remote UE, and a base station 130 according to embodiment 1. FIG. 8 is a sequence diagram showing a procedure for relaying an MBS to a UE by multi-hop relay in a communication system according to embodiment 2. FIG. 9 is a schematic diagram showing an example of arrangement of a first relay UE, a second relay UE, a remote UE, and a base station according to embodiment 2.

[0016] 1 is a block diagram showing a schematic configuration of a 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 an upper level device 160.

[0017] The UE 110 can wirelessly communicate with the base station 130 and transmits and receives signals via wireless communication. The UE 110 can also communicate with another UE 110 via SL communication, and can also communicate via a relay.

[0018] The base station 130 configures a radio access network. Here, the radio access network is described as being a fifth-generation (hereinafter also referred to as "5G") radio access system, but is not limited to this example.

[0019] If the radio access network is of the 5G system being discussed in 3GPP, the radio access network is referred to as a Next Generation Radio Access Network (NG-RAN). In this case, the base station 130 is referred to as a gNB (NG-RAN NodeB). The core network is referred to as a 5G Core. Note that if the radio access network is of the LTE system being discussed in 3GPP, the radio access network is referred to as an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). In this case, the base station 130 is referred to as an eNB (E-UTRAN NodeB).

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

[0021] The base station 130 is connected to a higher-level device 160 that functions as an MME (Mobility Management Entity), an S-GW (Serving Gateway), or an MME / S-GW unit including an MME and an S-GW via an S1 interface, and control information is communicated between the base station 130 and the higher-level device 160.

[0022] A plurality of higher-level devices 160 may be connected to one base station 130. The plurality of base stations 130 are connected to each other via an X2 interface, and control information is communicated between the plurality of base stations 130.

[0023] The upper device 160 is specifically an upper node, and controls the connection between the base station 130 and the UE 110. The upper device 160 constitutes the EPC, which is a core network.

[0024] The base station 130 may configure one cell or multiple cells. Each cell has a predetermined range as its coverage, which is a range within which communication with the UE 110 is possible, and performs wireless communication with the UE 110 within the coverage. When one base station 130 configures multiple cells, each cell is configured to be able to communicate with the UE 110.

[0025] 2 is a block diagram showing a schematic configuration of the UE 110. The UE 110 includes a terminal-side communication unit 111, an application unit (hereinafter referred to as an AP unit) 120, a protocol processing unit 121, a control unit 122, and a storage unit 123.

[0026] First, a description will be given of the transmission process of the UE 110. 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 the data into a transmission signal for wireless communication, and transmits the transmission signal to a destination via one or more antennas.

[0028] Next, the reception process of the UE 110 will be described. The terminal-side communication unit 111 receives a wireless signal from a sender as a received signal using one or more antennas, and generates control data or user data from the received signal. The terminal-side communication unit 111 then sends the control data to the protocol processing unit 121 and sends the user data to the AP unit 120.

[0029] The above-described series of processes in UE 110 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. Note that the number of antennas used by UE 110 for transmission and the number of antennas used for reception may be the same or different.

[0030] The storage unit 123 stores programs and data necessary for processing in the UE 110 .

[0031] As shown in FIG. 3A , part or all of the AP unit 120, protocol processing unit 121, and control unit 122 described above can be configured by, for example, 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 may be provided via a network or may be provided by being recorded on a recording medium. That is, such a program may be provided, for example, as a program product. In other words, the UE 110 can be realized by a computer including the processor 11 and the memory 10.

[0032] 3B, the AP unit 120, the protocol processing unit 121, and the control unit 122 may be partially or entirely configured as a processing circuit 12 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array). As described above, the AP unit 120, the protocol processing unit 121, and the control unit 122 may be realized by a processing circuit network.

[0033] The terminal-side communication unit 111 can be realized by a wireless communication interface, which is an interface for wireless communication. The storage unit 123 can be realized by a storage device such as a nonvolatile memory, a hard disk drive (HDD), or a solid state drive (SSD).

[0034] 4 is a block diagram showing a schematic configuration of the 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 that transmits and receives data to and from the 5GC, an EPC communication unit 142 that transmits and receives data to and from an EPC (Evolved Packet Core) such as an MME (Mobility Management Entity), and an other base station communication unit 143 that transmits and receives data to and from other base stations. The 5GC communication unit 141, the EPC communication unit 142, and the other base station communication unit 143 each exchange information with the protocol processing unit 144.

[0035] First, a description will be given of the transmission process of the 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 the other base station communication unit 143 is provided to the station side communication unit 131.

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

[0037] Next, the reception processing of the base station 130 will be described. The station-side communication unit 131 receives a radio signal from a transmission source as a received signal using one or more antennas, and generates control data or user data from the received signal. The station-side communication unit 131 then sends the control data to the protocol processing unit 144, the 5GC communication unit 141, the EPC communication unit 142, or the other base station communication unit 143, and sends the user data to the 5GC communication unit 141, the EPC communication unit 142, or the other base station communication unit 143.

[0038] The above-described series of processes in the base station 130 is 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. Note that the number of antennas used by the base station 130 for transmission and the number of antennas used for reception may be the same or different. Furthermore, the number of antennas of the UE 110 and the number of antennas of the base station 130 may be the same or different.

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

[0040] As shown in FIG. 3A, part or all of the above-described communication processing unit 140, protocol processing unit 144, and control unit 145 can be configured, for example, by a memory 10 and a processor 11 such as a CPU that executes a program stored in the memory 10. Such a program may be provided over a network or may be provided by being recorded on a recording medium. That is, such a program may be provided, for example, as a program product.

[0041] 3B, the communication processing unit 140, the protocol processing unit 144, and the control unit 145 may be configured as a processing circuit 12 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC, or an FPGA. As described above, the communication processing unit 140, the protocol processing unit 144, and the control unit 145 may be realized by a processing circuit network.

[0042] The station side communication unit 131 can be realized by a wireless communication interface, which is an interface for wireless communication. The storage unit 126 can be realized by a storage device such as a nonvolatile memory, an HDD, or an SSD.

[0043] 5 is a block diagram showing a schematic configuration of the higher-level device 160. In this embodiment, since the 5G system is used as the wireless access network, the higher-level device 160 is also referred to as a 5GC (5G Core) unit.

[0044] 5 illustrates a case where an AMF (Access and Mobility Management Function) configuration, an SMF (Session Management Function) configuration, and a UPF (User Plane Function) configuration are included in the higher-level device 160 illustrated in FIG. 1. The higher-level 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 transmits and receives data between the upper device 160 and the Data Network. The Base Station communication unit 162 transmits and receives data between the upper device 160 and the base station 130 via the NG interface. If 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 sent from the base station communication unit 162 to the base station 130. If the data from the base station 130 is user data, the user data is sent from the base station communication unit 162 to the Data Network communication unit 161 via the user plane communication unit 163, and then sent from the Data Network communication unit 161 to the Data Network.

[0046] If 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. The session management unit 164 sends the control data to the control plane control unit 165. If the data from the base station 130 is control data, the control data is sent from the base station communication unit 162 to the control plane control unit 165. The control plane control unit 165 sends the control data to the session management unit 164.

[0047] The control plane control unit 165 performs overall processing for the control plane (hereinafter, sometimes 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 unit 166 performs security of NAS messages, etc. The PDU session control unit 167 performs management of PDU sessions between the UE 110 and the higher-level device 160, etc. The idle state mobility management unit 168 performs mobility management in the standby state, generation and control of paging signals in the standby state, addition, deletion, update and search of tracking areas of one or more UEs 110 under its control, tracking area list management, etc. The standby state is also called an idle state, an RRC_IDLE state, or simply idle.

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

[0050] As shown in FIG. 3A , part 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 can be configured by a memory 10 and a processor 11 such as a CPU that executes a program stored in the memory 10. Such a program may be provided via a network or may be provided by being recorded on a recording medium. That is, such a program may be provided as a program product, for example.

[0051] 3B, part 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 can be configured by a processing circuit 12 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC, or an FPGA. As described above, the data network communication unit 161, base station communication unit 162, user plane communication unit 163, session management unit 164, and control plane control unit 165 can be realized by a circuit network.

[0052] Fig. 6 is a sequence diagram showing a procedure for relaying MBS to UE 110 in communication system 100 according to embodiment 1. The sequence diagram shown in Fig. 6 is a procedure in a situation as shown in Fig. 7. As shown in Fig. 7, here, there are a relay UE 110A functioning as a U2N relay, which is a UE 110 that provides a relay connection to a 5G network via SL communication, a remote UE 110B that is a UE 110 that wants to receive MBS via the relay, and a base station 130. Note that the relay UE 110A is also referred to as a first mobile terminal, and the remote UE 110B is also referred to as a second mobile terminal.

[0053] In step S10, the control unit 122 of the relay UE 110A 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 an RRC_CONNECTED state.

[0054] In step S11, the control unit 122 of the relay UE 110A inquires of the base station 130 and the upper device 160, which is the core network, whether or not the relay function of the MBS can be used, via the protocol processing unit 121 and the terminal-side communication unit 111. The control plane control unit 165 of the upper device 160 notifies the relay UE 110A whether or not the relay function of the MBS can be used, via the session management unit 164, the user plane communication unit 163, and the base station communication unit 162. Possible conditions for the relay function to be unavailable include relay prohibition due to geographical conditions or restrictions on each service (application). Here, the explanation will be given assuming that the relay function is available.

[0055] In step S12, the relay function is enabled, and the control unit 122 of the relay UE 110A starts receiving MBS data via the protocol processing unit 121 and the terminal-side communication unit 111. Upon receiving the MBS data, the control unit 122 of the relay UE 110A extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data and stores it in the storage unit 123 as a list of MBSs that can be relayed. The control unit 122 of the relay UE 110A also prepares a relay timer for each MBS service and starts the timer upon receiving MBS data. In step S11, when the control unit 122 of the relay UE 110A receives notification of list information of MBSs that are permitted to be relayed from the base station 130, the control unit 122 of the relay UE 110A may use the list information as the initial value of the list of MBSs that can be relayed.

[0056] In step S13, the control unit 122 of the remote UE 110B searches for a connectable relay UE 110A in accordance with the Discovery Procedure of SL communication via the protocol processing unit 121 and the terminal-side communication unit 111. The control unit 122 of the relay UE 110A adds the TMGI information of the available MBS previously acquired in step S12 together with the relay information to the Discovery message or Discovery Solicitation message that it sends.

[0057] In step S14, the control unit 122 of the remote UE 110B analyzes the acquired TMGI information and determines whether or not the desired MBS is present. Here, the description will be given assuming that the desired MBS is present.

[0058] In step S15, in the case of the multicast service, a Direct Connection session is established between the remote UE 110B and the relay UE 110A. Here, the control unit 122 of the remote UE 110B and the control unit 122 of the relay UE 110A communicate with each other via the protocol processing unit 121 and the terminal-side communication unit 111, thereby establishing the session. The session may also be established in the case of the broadcast service.

[0059] In step S16, in the case of the multicast service, the control unit 122 of the relay UE 110A notifies the base station 130 via the protocol processing unit 121 and the terminal side communication unit that the remote UE 110B will receive the multicast via the relay.

[0060] In step S17, the control unit 145 of the base station 130 transmits the MBS data via the protocol processing unit 144 and the station-side communication unit 131. If the service is permitted for relaying in step S11, the control unit 122 of the relay UE 110A transfers the received MBS data to all remote UEs 110B that wish to relay the MBS data by SL communication via the protocol processing unit 121 and the terminal-side communication unit 111. The transfer method may be either unicast communication or groupcast communication.

[0061] In step S18, the control unit 122 of the relay UE 110A resets a timer associated with the received MBS service.

[0062] In step S19, when the timer reaches a certain threshold, the control unit 122 of the relay UE 110A determines that the corresponding service has ended, and deletes the TMGI information in the Discovery message or Discovery Solicitation message to be transmitted thereafter via the protocol processing unit 121 and the terminal-side communication unit 111. By receiving such an updated message, the control unit 122 of the remote UE 110B can recognize that the MBS data will not be relayed. As described above, the relay UE 110A ends the relay of the MBS if it does not receive MBS data for a predetermined period of time.

[0063] Alternatively, the control unit 122 of the relay UE 110A may use groupcast of SL communication instead of the Discovery message to immediately broadcast the TMGI information to surrounding UEs 110. The threshold value for comparing the timer may be determined by the control unit 122 of the relay UE 110A or may be determined in response to an instruction from the base station 130. The threshold value may be the same for all services or may differ for each service.

[0064] In step S20, in the Multicast service, if the timer expires or the remote UE 110B ends reception in step S19, the control unit 122 of the relay UE 110A and the control unit 122 of the remote UE 110B release the Direct Connection that is no longer needed and end the session.

[0065] The control unit 122 of the remote UE 110B may determine its own location using a Global Navigation Satellite System (GNSS) or the like, and transmit location information indicating the determined location to the relay UE 110A in step S15. The control unit 122 of the relay UE 110A may transmit the received location information of the remote UE 110B to the base station 130 via the protocol processing unit 121 and the terminal-side communication unit 111 to inquire whether relaying is possible, or may obtain map information of the relay-prohibited area from the base station 130 in step S11, determine whether relaying is possible, and notify the remote UE 110B of the result. This enables relay control using more accurate location information. The relay-prohibited area is an area where the use of the relay function is prohibited.

[0066] When the relay UE 110A moves out of the coverage area of ​​the base station 130 and hands over to another base station 130, the MBS provided may be different. If the remote UE 110B receives multicast, it can acquire and recognize handover information through unicast communication with the relay UE 110A. However, in the case of broadcast, the remote UE 110B may not have unicast communication with the relay UE 110A. Furthermore, the relay UE 110A may not know which UE 110 is receiving the broadcast data being relayed. The above problem can be solved by having the control unit 122 of the relay UE 110A notify the surrounding area that a handover will be performed using groupcast SL communication and prompt the remote UE 110B to reset the receivable TMGI information it holds. This enables the relay UE 110A to handle handovers.

[0067] As described above, when the relay UE 110A is within a range where it can communicate with the base station 130, it receives MBS data, which is data on the MBS, from the base station 130 and extracts the TMGI information included in the MBS data. When the remote UE 110B is unable to communicate with the base station 130 but is within a range where it can communicate with the relay UE 110A, it acquires the TMGI information from the relay UE 110A and uses the relay function of the relay UE 110A to receive MBS from the base station 130.

[0068] The relay UE 110A may add the TMGI information to a message of the SL communication and transmit the message. The message may be either a Discovery message or a Discovery Solicitation message.

[0069] In addition, the relay UE 110A inquires of the base station 130 whether or not it is possible to use the relay function of the MBS, and if it is possible to use the relay function of the MBS, it receives MBS data from the base station 130.

[0070] The relay UE 110A starts measuring time when it receives MBS data, and stops the MBS relay function when the measured time reaches a predetermined threshold. When the relay function of the MBS is stopped, the relay UE 110A does not provide the TMGI information to the remote UE 110B.

[0071] The above procedure makes it possible for the remote UE 110B to receive MBS data via the relay UE 110A without establishing (normal) unicast communication with the base station 130 via the relay UE 110A, thereby enabling simplification of the remote UE 110B and reduction in power consumption.

[0072] The remote UE 110B may transmit location information indicating the location of the remote UE 110B to the relay UE 110A. The relay UE 110A can then notify the base station 130 of the location information and inquire whether the relay function of the MBS can be used. If the location indicated by the location information is not within an area where the use of the MBS relay function is prohibited, the base station 130 responds to the relay UE 110A that the relay function of the MBS can be used. This allows for a more accurate determination of whether relaying is possible.

[0073] In addition, the remote UE 110B may transmit location information indicating the location of the remote UE 110B to the relay UE 110A, and the relay UE 110A may relay MBS data from the base station 130 to the remote UE 110B if the location indicated by the location information is not included in an area where the use of the MBS relay function is prohibited.

[0074] In addition, when the relay UE 110A performs a handover to an adjacent base station (not shown) that is a base station adjacent to the base station 130, handover information indicating that the handover has been performed is sent to the remote UE 110B using the group cast function of SL communication, thereby enabling relay of the MBS corresponding to the handover.

[0075] Embodiment 2. In addition to the features of embodiment 1, it is possible to further extend the reach of the MBS by using a U2U relay (UE-to-UE relay) that relays direct communication between terminals, which is being considered in 3GPP. In embodiment 2, a configuration that enables such processing will be described.

[0076] 1 , the communication system 200 according to the second embodiment 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 according to the second embodiment are similar to the base station 130 and the host device 160 of the communication system 100 according to the first embodiment.

[0077] 2 , UE 210 in the second embodiment includes terminal-side communication unit 111, AP unit 120, protocol processing unit 121, control unit 222, and storage unit 123. Terminal-side communication unit 111, AP unit 120, protocol processing unit 121, and storage unit 123 of UE 210 in the second embodiment are similar to terminal-side communication unit 111, AP unit 120, protocol processing unit 121, and storage unit 123 of UE 110 in the first embodiment.

[0078] The control unit 220 in the second embodiment performs the same processing as in the first embodiment, and also performs processing to realize a U2U relay that relays direct communication between terminals, which is being considered in 3GPP.

[0079] Fig. 8 is a sequence diagram showing a procedure for relaying MBS to UE 210 via a multi-hop relay in communication system 200 according to embodiment 2. The sequence diagram shown in Fig. 8 illustrates a procedure under the circumstances shown in Fig. 9. As shown in Fig. 9, here, there are a first relay UE 210A functioning as a U2N relay, which is a UE 210 that provides a relay connection to a 5G network via SL communication; a second relay UE 210B functioning as a U2U relay that relays direct terminal-to-terminal communication discussed in 3GPP; a remote UE 210C that is a UE 210 that wants to receive MBS via the relay; and a base station 130. Here, the first relay UE 210A is also referred to as a first mobile terminal, the second relay UE 210B is also referred to as a second mobile terminal, and the remote UE 210C is also referred to as a third mobile terminal.

[0080] In step S30, the control unit 222 of the first relay UE 210A 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 an RRC_CONNECTED state.

[0081] In step S31, the control unit 222 of the first relay UE 210A inquires of the base station 130 and the upper device 160, which is the core network, whether or not the relay function of the MBS can be used, via the protocol processing unit 121 and the terminal side communication unit 111. The control plane control unit 165 of the upper device 160 notifies the first relay UE 210A whether or not the relay function of the MBS can be used, via the session management unit 164, the user plane communication unit 163, and the base station communication unit 162. Here, the description will be given assuming that the relay function is available.

[0082] In step S32, the control unit 222 of the second relay UE 210B searches for a U2N relay connected to the base station 130 via the protocol processing unit 121 and the terminal side communication unit 111. Here, the first UE 210A is already connected to the base station 130 and functions as a U2N relay.

[0083] Therefore, in step S33, the control unit 222 of the second relay UE 210B establishes a communication session with the first relay UE 210A 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 UE 210B receives the relay from the first relay UE 210A via the protocol processing unit 121 and the terminal side communication unit 111, and inquires of the base station 130 and the upper device 160, which is the core network, whether or not the relay function of the MBS can be used. The control plane control unit 165 of the upper device 160 notifies the second relay UE 210B, via the first relay UE 210A, whether or not the relay function of the MBS can be used, via the session management unit 164, the user plane communication unit 163, and the base station communication unit 162. Here, the description will be given assuming that the relay function is available.

[0085] In step S35, the relay function is enabled, and the control unit 222 of the first relay UE 210A starts receiving MBS data via the protocol processing unit 121 and the terminal-side communication unit 111. Upon receiving the MBS data, the control unit 222 of the first relay UE 210A extracts TMGI information included in the MBS data and stores it in the storage unit 123 as a list of MBS services that can be relayed. The control unit 222 of the first relay UE 110A also prepares a relay timer for each MBS service and starts the timer upon receiving the MBS data. The control unit 222 of the second relay UE 210B also starts receiving the MBS data upon receiving the relay from the first relay UE 210A via the protocol processing unit 121 and the terminal-side communication unit 111. The relay method between the first relay UE 210A and the second relay UE 210B may be groupcast from the first relay UE 210A, or may be unicast since unicast communication has been established. When the control unit 222 of the second relay UE 210B receives the MBS data, it extracts the TMGI information included in the MBS data and stores it in the storage unit 123 as a list of MBSs that can be relayed. In addition, the control unit 222 of the second relay UE 210B prepares a relay timer for each MBS service and starts the timer upon receiving the MBS data.

[0086] In step S36, the control unit 222 of the remote UE 210C searches for a connectable relay UE in accordance with the Discovery Procedure of SL communication via the protocol processing unit 121 and the terminal-side communication unit 111. Here, it is assumed that the second relay UE 210B is connectable. The control unit 222 of the second relay UE 210B adds the TMGI information of the available MBS previously acquired in step S35 together with the relay information to the Discovery message or Discovery Solicitation message that it sends.

[0087] In step S37, the control unit 222 of the remote UE 210C analyzes the acquired TMGI information and determines whether or not the desired MBS is present. Here, the description will be given assuming that the desired MBS is present.

[0088] In step S38, in the case of the multicast service, a Direct Connection session is established between the remote UE 210C and the second relay UE 210B. Here, the control unit 222 of the remote UE 210C and the control unit 222 of the second relay UE 210B communicate with each other via the protocol processing unit 121 and the terminal-side communication unit 111, thereby establishing the session. The session may also be established in the case of the broadcast service.

[0089] In step S39, in the case of the multicast service, the control unit 222 of the second relay UE 210B notifies the base station 130 via the protocol processing unit 121 and the terminal side communication unit that the remote UE 210C will receive the multicast via the relay.

[0090] In step S40, the control unit 145 of the base station 130 transmits the MBS data via the protocol processing unit 144 and the station-side communication unit 131. If the service is permitted for relaying in step S31, the control unit 222 of the first relay UE 210A forwards the received MBS data to all UEs 210 that wish to relay the MBS data via SL communication, via the protocol processing unit 121 and the terminal-side communication unit 111. Here, the MBS data is forwarded to the second relay UE 210B. The forwarding method may be either unicast communication or groupcast communication. Furthermore, if the service is permitted for relaying in step S34, the control unit 222 of the second relay UE 210B forwards the received MBS data to all UEs 210 that wish to relay the MBS data via SL communication, via the protocol processing unit 121 and the terminal-side communication unit 111. Here, the MBS data is forwarded to the remote UE 210C. The forwarding method may be either unicast communication or groupcast communication.

[0091] In step S41, the control unit 222 of the first relay UE 210A resets a timer associated with the received MBS service. In step S42, the control unit 222 of the second relay UE 210B resets a timer associated with the received MBS service.

[0092] In step S43, when the timer reaches a certain threshold, the control unit 222 of the first relay UE 210A determines that the corresponding service has ended, and deletes the TMGI information in the Discovery message or Discovery Solicitation message to be transmitted thereafter via the protocol processing unit 121 and the terminal-side communication unit 111. By receiving such an updated Discovery message, the control unit 222 of the second relay UE 210B can recognize that the MBS data will not be relayed. As described above, the first relay UE 210A ends the relay of the MBS if it does not receive MBS data for a predetermined period of time.

[0093] Alternatively, the control unit 222 of the first relay UE 210A may use a groupcast of SL communication instead of a Discovery message to immediately broadcast the TMGI information to surrounding UEs 210. The threshold value for comparing the timer may be determined by the control unit 222 of the first relay UE 210A or may be determined in response to an instruction from the base station 130. The threshold value may be the same for all services or may differ for each service.

[0094] In step S44, when the timer reaches a certain threshold, the control unit 222 of the second relay UE 210B determines that the corresponding service has ended, and deletes the TMGI information in the Discovery message or Discovery Solicitation message to be transmitted thereafter via the protocol processing unit 121 and the terminal-side communication unit 111. By receiving such an updated Discovery message, the control unit 222 of the remote UE 210C can recognize that the MBS data will not be relayed. Furthermore, when the second relay UE 210B does not receive MBS data for a predetermined period, it also ends the relaying of the MBS.

[0095] Alternatively, the control unit 222 of the second relay UE 210B may use a groupcast of SL communication instead of a Discovery message to immediately broadcast the TMGI information to surrounding UEs 210. The threshold value for comparing the timer may be determined by the control unit 222 of the second relay UE 210B or may be determined in response to an instruction from the base station 130. The threshold value may be the same for all services or may differ for each service.

[0096] In step S45, in the Multicast service, if the timer expires or the second relay UE 210B ends reception in step S41, the control unit 222 of the first relay UE 210A and the control unit 222 of the second relay UE 210B release the Direct Connection that is no longer needed and end the session.

[0097] In addition, in step S46, in the Multicast service, if the timer expires or the remote UE 210C ends reception in step S42, the control unit 222 of the second relay UE 210B and the control unit 222 of the remote UE 210C release the Direct Connection that is no longer needed and end the session.

[0098] In the second embodiment, the number of sessions between the first relay UE 210A and the second relay UE 210B is one, regardless of the number of UEs 210 functioning as remote UEs 210C connected to the U2U relay. This is achieved by a PTM (Point-to-Multi) communication method in which MBS data is copied and relayed and transmitted by the U2U relay, and is effective in preventing an increase in the amount of communication data and ensuring scalability, particularly in SL communication where the communication bandwidth is limited. Note that the connection between the remote UE 210 and the relay UE 210 may be either Multicast or Broadcast.

[0099] As described above, when the remote UE 210C is unable to communicate with the base station 130 and the first relay UE 210A but is within a range where it can communicate with the second relay UE 210B, it obtains TMGI information from the second relay UE 210B and receives MBS from the base station 130 using the relay function of the second relay UE 210B and the relay function of the first relay UE 210A.

[0100] Here, the second relay UE 210B copies the MBS data from the first relay UE 210A and uses a PTM communication method to relay the copied MBS data to the remote UE 210C, thereby allowing only one session between the relay devices.

[0101] As shown in the above procedure, by extracting TMGI information from MBS data at each U2U relay and adding it to its own Discovery message and broadcasting it, it becomes possible to relay MBS using a multi-hop relay method.

[0102] 100, 200 Communication system, 110, 210 UE, 111 Terminal side communication unit, 120 AP unit, 121 Protocol processing unit, 122, 222 Control unit, 123 Memory unit, 130 Base station, 131 Station side communication unit, 140 Communication processing unit, 144 Protocol processing unit, 145 Control unit, 146 Memory unit, 160 Upper device, 161 Data network communication unit, 162 Base station communication unit, 163 User plane communication unit, 164 Session management unit, 165 Control plane control unit, 169 Control unit.

Claims

1. A communication system comprising a base station, a first mobile terminal, and a second mobile terminal, wherein when the first mobile terminal is within a range where it can communicate with the base station, it receives MBS (Multicast and Broadcast Service) data from the base station, extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, and when the second mobile terminal is not within a range where it can communicate with the base station but is within a range where it can communicate with the first mobile terminal, it obtains the TMGI information from the first mobile terminal, utilizes the relay function of the first mobile terminal, and receives the provision of the MBS from the base station. The first mobile terminal terminates the relay of the MBS when it does not receive the MBS data for a predetermined period. A communication system characterized by the above.

2. The communication system according to claim 1, wherein the first mobile terminal adds the TMGI information to a message of SL (Side Link) communication and transmits it.

3. The communication system according to claim 2, wherein the message is a Discovery message or a Discovery Solicitation message.

4. The communication system according to any one of claims 1 to 3, wherein the first mobile terminal inquires of the base station whether it can utilize the relay function of the MBS, and when it can utilize the relay function of the MBS, it receives the MBS data from the base station.

5. The communication system according to claim 4, wherein the second mobile terminal transmits position information indicating the position of the second mobile terminal to the first mobile terminal. The first mobile terminal notifies the base station of the position information and inquires whether it can utilize the relay function of the MBS. The base station responds to the first mobile terminal that it can utilize the relay function of the MBS when the position indicated by the position information is not included in a range where the utilization of the relay function of the MBS is prohibited.

6. The second mobile terminal transmits position information indicating the position of the second mobile terminal to the first mobile terminal. When the position indicated by the position information is not included in the range where the use of 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. The communication system according to claim 4, characterized in that.

7. The first mobile terminal starts measuring time when receiving the MBS data, and stops the relay function of the MBS when the measured time reaches a predetermined threshold value. The communication system according to any one of claims 1 to 6, characterized in that.

8. When the first mobile terminal stops the relay function of the MBS, the first mobile terminal does not provide the TMCI information to the second mobile terminal. The communication system according to claim 7, characterized in that.

9. The communication system further includes an adjacent base station that is a base station adjacent to the base station. When the first mobile terminal performs a handover to the adjacent base station, the first mobile terminal transmits handover information indicating that the handover has been performed to the second mobile terminal using the groupcast function of the SL communication. The communication system according to any one of claims 1 to 8, characterized in that.

10. The communication system further includes a third mobile terminal. When the third mobile terminal is within a range where it cannot communicate with the base station and the first mobile terminal but can communicate with the second mobile terminal, the third mobile terminal acquires the TMCI information from the second mobile terminal and uses the relay function of the second mobile terminal and the relay function of the first mobile terminal to receive the MBS from the base station. The communication system according to any one of claims 1 to 9, characterized in that.

11. When the third mobile terminal does not receive the MBS data for a predetermined period, the third mobile terminal ends the relay of the MBS. The communication system according to claim 10, characterized in that.

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

13. A mobile terminal, comprising: a communication unit that receives MBS data, which is data of MBS (Multicast and Broadcast Service), from the base station when in a range communicable with the base station; and a control unit that extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, adds the TMGI information to a message of SL (Side Link) communication including the TMGI information, and causes the communication unit to transmit the message, and ends the relay of the MBS when the MBS data is not received for a predetermined period.

14. A program, causing a computer to function as: a communication unit that receives MBS data, which is data of MBS (Multicast and Broadcast Service), from the base station when in a range communicable with the base station; and a control unit that extracts TMGI (Temporary Mobile Group Identity) information included in the MBS data, adds the TMGI information to a message of SL (Side Link) communication, and causes the communication unit to transmit the message, and ends the relay of the MBS when the MBS data is not received for a predetermined period.

15. A communication method, comprising: receiving MBS data, which is data of MBS (Multicast and Broadcast Service), from the base station when in a range communicable with the base station; extracting TMGI (Temporary Mobile Group Identity) information included in the MBS data, adding the TMGI information to a message of SL (Side Link) communication, and transmitting the message; and ending the relay of the MBS when the MBS data is not received for a predetermined period.

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