Terminal device, communication method and communication system

Abstract

A terminal device (1) has a relay function for relaying a signal received from a first peripheral terminal among peripheral terminals to a second peripheral terminal among peripheral terminals, wherein the peripheral terminal is another terminal device capable of direct communication, and comprises: a detection unit (11) for detecting the peripheral terminal; a storage unit (17) for storing information of the peripheral terminal detected by the detection unit (11), i.e., peripheral terminal information; and an information notification unit (12) for including the peripheral terminal information stored in the storage unit (17) in a notification message for notifying other terminal devices of its own information and sending the information.

Description

Technical Field

[0001] The present disclosure relates to a terminal device having a function of directly communicating with other terminal devices, a communication method, and a communication system. Background Art

[0002] As one of the functions of a terminal device (hereinafter referred to as a terminal) in a wireless communication system, non-patent document 1 discloses a function of directly communicating with other terminals without going through a base station, that is, direct communication between terminals.

[0003] In non-patent document 1, two methods, Model A and Model B, are defined as methods for discovering the terminal of the other party when the terminals start direct communication with each other. In the Model A method, a terminal broadcasts its own information to the surroundings, and other terminals receive the information to discover the terminal of the other party. On the other hand, in the Model B method, a terminal that wants to discover the other party sends information related to the other party, and the terminal that receives the information responds if it can become the other party.

[0004] In addition, in non-patent document 1, the following method is specified: the first terminal in a state where direct communication with the base station cannot be performed and the second terminal connected to the base station (a terminal that can communicate with the base station) use the above-mentioned direct communication between terminals, so that the first terminal communicates with the base station via the second terminal. In the direct communication between terminals in this case, the terminal that desires direct communication between terminals also discovers the terminal of the communication partner through the above-mentioned model A or model B method. In the case of the model A method, the second terminal sends a message including information indicating that signals can be relayed between other terminals and the base station, and the first terminal receives the information, thereby the first terminal can know the existence of the second terminal. In addition, in the case of the model B method, the first terminal in a state where it cannot communicate with the base station sends a message for discovering a terminal that can act as a relay terminal for relaying signals between the base station, and when the second terminal receives the information, it returns a response message, thereby the first terminal can know the existence of the second terminal.

[0005] Furthermore, Non-Patent Document 2 discloses a method in which two terminals that are in a positional relationship whereby they cannot communicate directly communicate with each other via another terminal that can communicate directly with both of the two terminals.

[0006] In the case of communication disclosed in non-patent document 2, each terminal discovers other terminals that can communicate directly through the same steps as the above-mentioned model A method or model B method. After that, when each terminal wants to communicate with a terminal that cannot communicate directly, it sends a message including the information of the terminal of the communication partner, and the terminal that receives the message sends a response message to the received message when it can act as a repeater that relays signals between the terminal of the message source and the terminal of the communication partner. The terminal that receives the response message starts communication via the terminal that can act as a repeater. In addition, in non-patent document 2, a terminal that acts as a repeater that relays signals bidirectionally between two terminals is called "UE-to-UE relay". For convenience, in this specification, "UE-to-UE relay" is referred to as a relay station.

[0007] Prior art literature

[0008] Non-patent literature

[0009] Non-patent document 1: 3GPP TS 23.303, V15.1.0 (2018-06)

[0010] Non-patent document 2: 3GPP TR 23.703, V12.0.0 (2014-02) Summary of the invention

[0011] Problem that the invention aims to solve

[0012] As described above, in the communication method described in Non-Patent Document 2, when two terminals cannot communicate directly and communicate via a relay station, the terminal that is to start communication sends a message including information about the other terminal to the terminals that have been discovered in the vicinity, and receives a response message to the message to understand the terminal that can become a relay station. Therefore, there is a problem that it takes time to select a relay station, establish a communication line, and enable communication.

[0013] The present disclosure has been made in view of the above, and an object of the present disclosure is to obtain a terminal device capable of shortening the time required to establish a communication line between terminal devices that communicate via a relay station.

[0014] Means used to solve problems

[0015] In order to solve the above-mentioned problems and achieve the purpose, the present invention discloses a terminal device, which has a relay function of relaying a signal received from a first peripheral terminal among peripheral terminals to a second peripheral terminal among peripheral terminals, and the peripheral terminal is another terminal device capable of direct communication, and comprises: a detection unit, which detects the peripheral terminal; a storage unit, which stores information about the peripheral terminal detected by the detection unit, i.e., peripheral terminal information; and an information notification unit, which causes the peripheral terminal information stored in the storage unit to be included in a notification message for notifying other terminal devices of their own information and sends it.

[0016] Effects of the Invention

[0017] According to the terminal device of the present disclosure, it is possible to shorten the time required to establish a communication line between terminal devices that communicate via a relay station. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a diagram showing a configuration example of a communication system realized by applying the terminal device of the first embodiment.

[0019] Figure 2 This is a diagram showing an example of a functional block configuration of a terminal device according to Embodiment 1.

[0020] Figure 3 This is a diagram for explaining the operation of the terminal device according to the first embodiment.

[0021] Figure 4 This is a diagram showing an example of a sequence of operations in which a terminal device according to Embodiment 1 performs inter-terminal communication via a relay station.

[0022] Figure 5 This is a diagram showing an example of a sequence of actions in which a terminal device according to Embodiment 2 performs inter-terminal communication via a relay station.

[0023] Figure 6 This is a diagram for explaining the operation of the terminal device according to the third embodiment.

[0024] Figure 7 This is a diagram showing an example of a sequence of actions in which a terminal device according to Embodiment 3 performs inter-terminal communication via a relay station.

[0025] Figure 8 A diagram for illustrating the operation of a terminal device according to a fourth embodiment.

[0026] Fig. 9 This is a diagram showing an example of a sequence of actions in which a terminal device according to Embodiment 4 performs inter-terminal communication via a relay station.

[0027] Fig.10 This is a diagram for explaining the operation of the terminal device according to the fifth embodiment.

[0028] Fig.11 This is a diagram showing an example of a sequence of actions in which a terminal device according to Embodiment 5 performs inter-terminal communication via a relay station.

[0029] Fig.12 This is a diagram for explaining the operation of the terminal device according to the sixth embodiment.

[0030] Fig.13 This is a diagram showing an example of a sequence of actions for switching a communication path when a terminal device according to Embodiment 6 is performing inter-terminal communication via a relay station. DETAILED DESCRIPTION

[0031] Hereinafter, a terminal device, a communication method, and a communication system according to an embodiment of the present disclosure will be described in detail based on the drawings.

[0032] Implementation method 1.

[0033] Figure 1 This is a diagram showing a configuration example of a communication system realized by applying the terminal device of the first embodiment.

[0034] The communication system 100 of the first embodiment is configured to include a terminal device 1 and a base station 3. In addition to the function of communicating with the base station 3 connected to the core network, the terminal device 1 can also perform inter-terminal communication for directly communicating with other terminal devices 1. In addition, the terminal device 1 can communicate with the target terminal device 1 via one or more other terminal devices 1 using the inter-terminal communication. When each terminal device 1 is in a state where it can directly communicate with both of two other terminal devices 1 in a positional relationship where inter-terminal communication is not possible, it can act as a relay station that relays signals bidirectionally between the two other terminal devices 1.

[0035] The terminal device 1 of the first embodiment has a feature in the operation of performing inter-terminal communication via a relay station, and therefore, the description is given for the portion related to the inter-terminal communication via the relay station. In addition, the operation when the terminal device 1 communicates via the base station 3 and the operation when the terminal devices 1 communicate directly with each other are the same as before, and therefore the description is omitted. In addition, in the following description, the terminal device 1 is sometimes referred to as UE (User Equipment).

[0036] Figure 2 1 is a diagram showing an example of a functional block configuration of a terminal device 1 according to Embodiment 1. The terminal device 1 includes a control unit 10 , a wireless communication unit 16 , and a storage unit 17 . The control unit 10 includes a detection unit 11 , an information notification unit 12 , a relay processing unit 13 , and a communication processing unit 14 .

[0037] Here, for the implementation Figure 2 The hardware of each part of the terminal device 1 shown in the figure is described. The control unit 10 is implemented by a CPU (also called a Central Processing Unit, a central processing unit, a processing unit, an arithmetic unit, a processor, a microprocessor, and a microcomputer). That is, the detection unit 11, the information notification unit 12, the relay processing unit 13, and the communication processing unit 14 of the control unit 10 are implemented by the CPU executing a program that describes the processing performed by these parts. The wireless communication unit 16 is implemented by an electronic circuit composed of a modem, an analog-to-digital converter, a digital-to-analog converter, a frequency converter, an amplifier, an antenna, etc. The storage unit 17 is implemented by a RAM (Random Access Memory), a flash memory, etc. In addition, the detection unit 11, the information notification unit 12, and the relay processing unit 13 of the control unit 10 can also be implemented by a dedicated processing circuit such as an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), and a DSP (Digital Signal Processor). Furthermore, part of the detection unit 11 , the information notification unit 12 , the relay processing unit 13 , and the communication processing unit 14 of the control unit 10 may be implemented by a CPU, and the remaining parts may be implemented by a dedicated processing circuit.

[0038] right Figure 2 1 and 1 . The components of the terminal device 1 shown in the figure are described. The detection unit 11 detects other terminal devices 1 that can directly communicate with the terminal device 1, that is, peripheral terminals. The information notification unit 12 sends a message including the information of the peripheral terminals detected by the detection unit 11 and the information of itself (terminal device 1) to the other terminal devices 1. The relay processing unit 13, when operating as a relay station, relays the signal to the other party when receiving a signal sent from one of the two other terminal devices 1 communicating via itself. The communication processing unit 14 sends and receives signals with other terminal devices 1. The wireless communication unit 16 performs reception processing and transmission processing of wireless signals. The storage unit 17 stores various information represented by the information of the peripheral terminals detected by the detection unit 11.

[0039] Next, the operation of each terminal device 1 of the communication system 100 of this embodiment to perform inter-terminal communication via a relay station will be described. Figure 3 The operation shown in FIG. 1 is described below. Specifically, the operation in which UE#2 operates as a relay station (relay) and UE#1 and UE#3 communicate via UE#2 is described below.

[0040] Figure 4 This is a diagram showing an example of a sequence of operations in which the terminal device 1 according to the first embodiment performs inter-terminal communication via a relay station.

[0041] UE#1, UE#2, and UE#3 each send a "Relay Discovery Announcement" or "Discovery Announcement" (steps S11 to S13) as an announcement message for notifying other UEs of their existence at a predetermined time. At this time, each UE broadcasts an announcement message including its own terminal ID (Identification) and information about surrounding terminals maintained by the storage unit 17, namely, the surrounding terminal IDs. In addition, in each UE, the detection unit 11 generates an announcement message and broadcasts it via the wireless communication unit 16. The detection unit 11 includes all the surrounding terminal IDs maintained by the storage unit 17 in the announcement message. When the storage unit 17 does not maintain the surrounding terminal IDs, the detection unit 11 generates and sends an announcement message containing only its own terminal ID. The announcement messages sent by UE#1 to UE#3 in steps S11 to S13, respectively, are examples of notification messages for UEs to notify other UEs of their own information.

[0042] exist Figure 4 In the example shown, UE#1 first sends the announcement message (step S11), followed by UE#3 sending the announcement message (step S12), and finally UE#2 sending the announcement message (step S13). UE#1 and UE#3 have not completed the detection of surrounding terminals at the time of sending the announcement message, and have not retained the surrounding terminal IDs. Therefore, announcement messages that do not include the surrounding terminal IDs are sent in steps S11 and S12.

[0043] When UE#2 receives the announcement message sent in step S11, it extracts the terminal ID of UE#1. Specifically, the detection unit 11 of UE#2 extracts the terminal ID of UE#1 from the received announcement message, and stores it in the storage unit 17 as a peripheral terminal ID. Similarly, when UE#2 receives the announcement message sent in step S12, it extracts the terminal ID of UE#3. Specifically, the detection unit 11 of UE#2 extracts the terminal ID of UE#3 from the received announcement message, and stores it in the storage unit 17 as a peripheral terminal ID. In this way, UE#2 detects UE#1 and UE#3 as peripheral terminals.

[0044] In the subsequent step S13, UE#2 sends an announcement message including its own terminal ID and the terminal IDs of UE#1 and UE#3 as the surrounding terminal IDs, and UE#1 and UE#3 receive the announcement message. Figure 4, an example is shown in which "Relay Service Code", "Relay UE ID" and "Relay-able UE" are included as parameters in the announcement message sent by UE#2. "Relay Service Code" is a parameter indicating the service that UE#2 can relay as a relay station. "Relay UE ID" is a parameter indicating the terminal ID of UE#2. "Relay-able UE" is a peripheral terminal ID maintained by UE#2, and is a parameter indicating a terminal device for which UE#2 can relay signals.

[0045] The announcement messages transmitted by UE#1 to UE#3 in steps S11 to S13 are messages obtained by extending the "Relay Discovery Announcement message" defined in the above-mentioned Non-Patent Document 1 and adding "Relay-able UE" as a new parameter.

[0046] When UE#1 receives the announcement message sent in step S13, it recognizes that UE#3 is included in the peripheral terminals of UE#2, that is, the signal sent to UE#3 can reach UE#3 via UE#2. The announcement message is received by the detection unit 11 of UE#1, and the detection unit 11 extracts the terminal ID of UE#3 from the announcement message and stores it in the storage unit 17 corresponding to the terminal ID of UE#2. Similarly, when UE#3 receives the announcement message sent in step S13, it recognizes that the signal sent to UE#1 can reach UE#1 via UE#2.

[0047] Furthermore, each time UE#1 to UE#3 receive an announcement message, they extract the surrounding terminal ID from the received message and update the surrounding terminal ID (the surrounding terminal ID of the UE that has transmitted the announcement message) stored in the storage unit 17 .

[0048] When UE#1 recognizes that it can communicate with UE#3 via UE#2, it includes the terminal ID of UE#3, the other terminal of the terminal-to-terminal communication via the relay station, in a direct communication request message, i.e., "Direct Communication Request", for requesting the start of terminal-to-terminal communication, and sends it to UE#2 (step S14). The direct communication request message is sent by the communication processing unit 14. Figure 4 In the FD (Final Destination), a parameter indicating a counterpart terminal in inter-terminal communication is expressed, and the counterpart terminal is described after "FD:".

[0049] The direct communication request message transmitted by UE#1 in step S14 is a message having a structure in which "Final Destination" is added as a new parameter by extending the "Direct Communication Request message" defined in the above-mentioned Non-Patent Document 1.

[0050] When UE#2 receives the direct communication request message including the terminal ID of UE#3 indicating FD, it forwards it to UE#3 (step S15). In step S15, the relay processing unit 13 acts as a proxy for UE#1 and sends a direct communication request message that does not include FD, that is, a direct communication request message with the transmission source set to UE#2 and the transmission destination set to UE#3.

[0051] In addition, UE#2 assumes that, when receiving a direct communication request message that does not include FD from UE#1, it determines that UE#1 wishes to communicate directly with itself, and performs processing for starting direct communication with UE#1. The action of UE#2 in this case is the same as the action specified in non-patent document 1 when UEs communicate directly with each other. That is, when UE#2 receives a direct communication request message that does not include FD, it determines that terminal-to-terminal communication with itself (UE#2) is requested, and when receiving a direct communication request message that includes FD, it determines that terminal-to-terminal communication via itself is requested.

[0052] When receiving the direct communication request message from UE#2, UE#3 returns an Ack (Acknowledgement) (step S16 ). The communication processing unit 14 receives the direct communication request message and returns the Ack.

[0053] When receiving the Ack for the direct communication request message transmitted in step S15 , the relay processing unit 13 of UE# 2 transmits the Ack for the direct communication request message received in step S14 to UE# 1 (step S17 ).

[0054] When UE#1 receives the Ack for the direct communication request message sent in step S14, a communication line is established between UE#1 and UE#3 via UE#2 (step S18). Figure 4 In FIG. 1 , the establishment of a communication line via UE#2 is described as “Establishment of Direct Communication (via relay)”. A communication line is sometimes referred to as a link.

[0055] As described above, when the terminal device 1 of implementation mode 1 sends an announcement message for notifying other UEs of its existence, it includes the peripheral terminal ID indicating the peripheral terminal that has been detected at that time point and sends it. As a result, the terminal device 1 that receives the announcement message can simultaneously detect the peripheral terminal and detect other terminal devices 1 that can communicate via the peripheral terminal, and can shorten the time required to establish a communication line when communicating with other terminal devices 1 via the peripheral terminal.

[0056] In this embodiment, the terminal device 1 detects surrounding terminals by changing a part of the steps corresponding to the above-mentioned Model A method described in Non-Patent Document 1. Therefore, the existing method can be retained and inter-terminal communication via a relay station can be realized with a simple change.

[0057] In addition, in this embodiment, an example is shown in which the terminal device 1 detects surrounding terminals by receiving an announcement message, but the method of detecting surrounding terminals is not limited to this. The terminal device 1 may also collect information about surrounding terminals via the base station 3, for example. For example, the base station 3 determines the position of each terminal device 1 in the service area, and based on the determined position, detects the surrounding terminals of each terminal device 1. The base station 3 notifies each terminal device 1 of the surrounding terminals of each terminal device 1.

[0058] Furthermore, when the terminal device 1 communicates with other terminal devices 1 via the peripheral terminal, the terminal device 1 transmits a direct communication request message including the terminal ID (hereinafter referred to as FD-ID) of the other terminal device 1 that is the communication partner to the peripheral terminal that operates as a relay station. Thus, the peripheral terminal that operates as a relay station can determine whether it is performing signal relay processing as a relay station or whether the terminal device 1 that is the source of the direct communication request message requests communication with itself, based on whether the direct communication request message includes the FD-ID.

[0059] In this embodiment, the announcement message includes the peripheral terminal ID indicating the detected peripheral terminal, but may also include other parameters. For example, it may include a parameter indicating whether the peripheral terminal is in a state capable of operating as a relay station.

[0060] Implementation method 2.

[0061] Next, the terminal device of the second embodiment will be described. The configuration of the communication system implemented by applying the terminal device of the second embodiment is the same as that of the first embodiment (see Figure 1 The functional block structure of the terminal device in the second embodiment is also the same as that in the first embodiment (see Figure 2 ). In this embodiment, the parts different from Embodiment 1 are described.

[0062] The operation of each terminal device 1 of the communication system 100 of this embodiment to perform inter-terminal communication via a relay station will be described. Figure 3 The operation shown will be described, that is, the operation in which UE#2 operates as a relay station and UE#1 and UE#3 communicate via UE#2.

[0063] Figure 5 This is a diagram showing an example of a sequence of operations in which the terminal device 1 according to the second embodiment performs inter-terminal communication via a relay station.

[0064] UE#1 and UE#3, which wish to communicate between terminals via the relay station, send a message for discovering other nearby UEs, namely "Discovery Solicitation" (steps S21 and S23), and UE#2, which receives the message, returns a response message (Response) (steps S22 and S24). As a result, UE#1 and UE#3 detect UE#2, which is in the vicinity, as a surrounding terminal. In addition, UE#2 detects UE#1 and UE#3, which are in the vicinity, as surrounding terminals.

[0065] Next, UE#1 sends a message for discovering UEs that can act as relay stations, namely "RelayDiscovery Solicitation" (Relay Station Discovery Request) (step S25). If UE#2 that receives the message can act as a relay station, it sends a response message for notifying that it can act as a relay station, namely "RelayDiscovery Response" (Relay Station Discovery Response) (step S26). At this time, UE#2 sends a response message including its own terminal ID and the surrounding terminal IDs stored in the storage unit 17 to UE#1. Figure 5 , an example is shown in which the response message sent by UE#2 includes "Relay Service Code", "Relay UE ID" and "Relay-able UE" as parameters. These parameters are the same as those described in Implementation Example 1. Figure 4The parameters included in the announcement message sent by UE#2 in step S13 are the same. In addition, when UE#2 receives the "Relay Discovery Solicitation" but cannot act as a relay station, it does not send a response message. Each response message sent by UE#2 in steps S22, S24, and S26 is an example of a notification message for the UE to notify other UEs of its own information. In addition, the response message sent by UE#2 in step S26 is a message that extends the "Relay Discovery Response message" specified in the above-mentioned non-patent document 1 and adds "Relay-able UE" as a new parameter.

[0066] When receiving the response message transmitted by UE#2 in step S26, UE#1 recognizes that UE#3 is included in the peripheral terminals of UE#2, that is, the signal addressed to UE#3 can reach UE#3 via UE#2.

[0067] Steps S27 to S31 after step S26 are the same as those described in the first embodiment. Figure 4 The same processing is performed as in steps S14 to S18 shown.

[0068] Thus, when receiving a message (Relay Discovery Solicitation) for discovering a UE capable of operating as a relay station, the terminal device 1 of the second embodiment sends a response message (Relay Discovery Response) including the peripheral terminal ID indicating the peripheral terminal detected at that time.

[0069] In this embodiment, the terminal device 1 detects surrounding terminals by changing a part of the procedure corresponding to the Model B method described in Non-Patent Document 1. Therefore, the existing method can be retained and inter-terminal communication via a relay station can be realized with a simple change.

[0070] In addition, UE#1 may also include the terminal ID of the communicating party (UE#3 in this embodiment) in the message requesting the discovery of the relay station. In this case, UE#2 that receives the message may send a response message if it has detected the UE of the communicating party (UE#3 in this embodiment), and may not send a response message if this is not the case.

[0071] Implementation method 3.

[0072] Next, the terminal device of the third embodiment will be described. The configuration of the communication system implemented by applying the terminal device of the third embodiment is the same as that of the first embodiment (see Figure 1 The functional block structure of the terminal device in the third embodiment is also the same as that in the first embodiment (see Figure 2 ).

[0073] In Embodiments 1 and 2, inter-terminal communication between two terminal devices 1 via one relay station is described. However, in this embodiment, inter-terminal communication via two or more relay stations is described. Figure 6 The operation in the case of the positional relationship shown will be described. Figure 6 The UE#1 shown is in a state where it can directly communicate only with UE#2, and UE#2 is in a state where it can directly communicate with UE#1 and UE#4. UE#4 is in a state where it can directly communicate with UE#2 and UE#3, and UE#3 is in a state where it can directly communicate only with UE#4. In this case, in order for UE#1 to communicate with UE#3, it is necessary to communicate via UE#2 and UE#4. Therefore, in this embodiment, the action in which UE#2 and UE#4 act as relay stations and UE#1 and UE#3 communicate via UE#2 and UE#4 is described. UE#2 is set as the first relay station (relay#1), and UE#4 is set as the second relay station (relay#2).

[0074] Figure 7 This is a diagram showing an example of a sequence of operations in which the terminal device 1 according to the third embodiment performs inter-terminal communication via a relay station.

[0075] UE#2 and UE#4 each send the announcement message (RelayDiscovery Announcement) described in Implementation Example 1 at a predetermined timing (steps S41 to S42). At this time, each UE broadcasts an announcement message including its own terminal ID and the surrounding terminal IDs stored in the storage unit 17. In addition, UE#1 and UE#3 also broadcast the same announcement message, but Figure 7 Records are omitted. Assume that UE#2 receives the announcement message sent by UE#1 and detects UE#1, and UE#4 receives the announcement message sent by UE#3 and detects UE#3. Therefore, in step S41, UE#4 sends an announcement message including its own terminal ID and the terminal ID of UE#3 (peripheral terminal ID).

[0076] When UE#2 receives the announcement message sent in step S41, it extracts the terminal ID of UE#4 and the terminal ID of UE#3. Specifically, the detection unit 11 of UE#2 extracts the terminal ID of UE#4 and the terminal ID of UE#3, which is the terminal ID of the peripheral terminal of UE#4, from the received announcement message, and stores them in the storage unit 17. Then, UE#2 sends an announcement message including its own terminal ID and the peripheral terminal ID in step S42. At this time, in addition to including the peripheral terminals detected by itself in the announcement message, UE#2 also includes the terminal ID of the peripheral terminal (UE#3) of UE#4 as the peripheral terminal ID in the announcement message. That is, UE#2 sends an announcement message including its own terminal ID and all the peripheral terminal IDs (terminal ID of UE#1, terminal ID of UE#4, terminal ID of UE#3) maintained by the storage unit 17. As a result, UE#1, which receives the announcement message sent in step S42, can recognize that the signal sent to UE#3 can reach UE#3 via UE#2. At this time, the announcement message may also include information about the number of relays used to reach each terminal, for example, Figure 7 The announcement message sent by UE#2 is set to {UE#1(0), UE#4(0), UE#3(1)}, and the communication path with the minimum number of relay times is selected.

[0077] When receiving the announcement message sent in step S42 , UE#1 extracts all terminal IDs (the terminal IDs of UE#2, UE#4, and UE#3) other than its own terminal ID included in the received announcement message, and stores them in the storage unit 17 .

[0078] When UE#1 recognizes that it can communicate with UE#3 via UE#2, it includes the terminal ID of UE#3, the other terminal for terminal-to-terminal communication via the relay station, in a direct communication request message (Direct Communication Request) and sends it to UE#2 (step S43). The direct communication request message sent by UE#1 in step S43 is similar to the one described in Implementation Example 1. Figure 4 The direct communication request message sent in step S14 is the same.

[0079] When UE#2 receives the direct communication request message including the terminal ID of UE#3 as the FD parameter (terminal ID of the communication partner) indicating the communication partner from UE#1, since UE#3 is not included in its peripheral terminals, the direct communication request message is forwarded to UE#4 (step S44). In step S44, the transmission source is set to UE#2, the transmission destination is set to UE#4, and the direct communication request message including the terminal ID of UE#3 as the FD parameter indicating the communication partner is transmitted.

[0080] When UE#4 receives a direct communication request message including the terminal ID of UE#3 as the FD parameter indicating the communication partner from UE#2, it forwards it to UE#3 (step S45). In step S45, the transmission source is set to UE#4, the transmission destination is set to UE#3, and the direct communication request message without the FD parameter indicating the communication partner is sent.

[0081] When UE#3 receives the direct communication request message from UE#4, it returns Ack (step S46). When UE#4 receives the Ack for the direct communication request message sent in step S45, it sends the Ack for the direct communication request message received in step S44 to UE#2 (step S47). When UE#2 receives the Ack for the direct communication request message sent in step S44, it sends the Ack for the direct communication request message received in step S43 to UE#1 (step S48). When UE#1 receives the Ack for the direct communication request message sent in step S43, a communication line is established between UE#1 and UE#3 via UE#2 (relay#1) and UE#4 (relay#2) (step S49). In addition, Figure 7 In the example, the establishment of the communication line via UE#2 and UE#4 is described as "Establishment of Direct Communication (via relay#1+relay#2)".

[0082] In addition, for the sake of simplicity, the case where a single path is used to relay signals between UE#1 and UE#3 is described, but when there are multiple paths, each UE selects a path in consideration of communication quality, etc. When a path selected once cannot be used, for example, when a Nack (Negative Acknowledgement) is received despite sending a direct communication request message, each UE reselects another path and resends the direct communication request message.

[0083] In addition, the case where there are two relay stations performing relay processing between two terminal devices 1 (UE#1, UE#3) performing inter-terminal communication is described, but the operation is the same when there are three or more relay stations. In order to avoid loops, the terminal device 1 operating as a relay station can also confirm whether it is a message that has been relayed in the past when receiving a message, and discard it and return Nack if it has been relayed. The judgment of whether it is a message that has been relayed can also be performed by any method.

[0084] As described above, when the terminal device 1 of implementation mode 3 sends an announcement message for notifying other UEs of its existence, it includes the surrounding terminal ID indicating the surrounding terminal detected at that time point and the surrounding terminal ID indicating the surrounding terminal detected by other terminal devices 1, that is, the surrounding terminal ID notified from other terminal devices 1. As a result, the terminal device 1 that receives the announcement message can identify other terminal devices 1 that can communicate via more than two relay stations. That is, terminal-to-terminal communication via more than two relay stations can be realized.

[0085] In this embodiment, the action of detecting surrounding terminals by modifying the steps described in embodiment 1 to achieve terminal-to-terminal communication via two or more relay stations is described, but the action of detecting surrounding terminals by modifying the steps described in embodiment 2 can also be described.

[0086] Implementation method 4.

[0087] Next, the terminal device of the fourth embodiment will be described. The configuration of the communication system implemented by applying the terminal device of the fourth embodiment is the same as that of the first embodiment (see Figure 1 The functional block structure of the terminal device in the fourth embodiment is also the same as that in the first embodiment (see Figure 2 ).

[0088] In Embodiments 1 and 2, the case where there is a single path for two terminal devices 1 to communicate with each other via a relay station is described. However, in this embodiment, the operation of the terminal device 1 when there are multiple paths for communication with each other is described. Figure 8 The operation in the case of the positional relationship shown will be described. Figure 8 UE#1 is shown as being able to communicate directly with UE#2 and UE#4, and UE#2 is shown as being able to communicate directly with UE#1, UE#4, and UE#3. UE#4 is shown as being able to communicate directly with UE#1, UE#2, and UE#3, and UE#3 is shown as being able to communicate directly only with UE#2 and UE#4. In this case, there are multiple paths that can be used when UE#1 and UE#3 communicate.

[0089] In such Figure 8As shown in the figure, when there are multiple selectable paths in the terminal-to-terminal communication, multiple relay stations are used to simultaneously communicate on the multiple paths, thereby achieving stable and high-quality communication through redundancy of communication. The UE that receives signals through multiple paths selects the best quality received data from multiple received data of each path. The quality is determined based on the signal strength, error rate, etc. The UE can also improve the quality by synthesizing the signals received through multiple paths. At this time, in the mode of using the method of determining the wireless resources used by the UE on the side that starts the communication, a certain relay station and the UE of the other party of the communication (in Figure 8 In the example shown, the wireless resources used for communication with the UE#3) and the wireless resources used for communication between other relay stations and the UE (UE#3) of the communication partner may compete with each other, and the communication efficiency cannot be improved.

[0090] In the present embodiment, a description will be given of a terminal device 1 that can prevent contention for radio resources used in a plurality of paths.

[0091] Fig. 9 This is a diagram showing an example of a sequence of operations in which the terminal device 1 according to the fourth embodiment performs inter-terminal communication via a relay station.

[0092] UE#2 and UE#4 each send the announcement message (RelayDiscovery Announcement) described in Implementation Example 1 at a predetermined timing (steps S51 to S52). At this time, each UE broadcasts an announcement message including its own terminal ID and the surrounding terminal IDs stored in the storage unit 17. In addition, UE#1 and UE#3 also broadcast the same announcement message, but Fig. 9 Records are omitted. Assume that UE#2 and UE#4 receive the announcement message sent by UE#1 and detect UE#1, and receive the announcement message sent by UE#3 and detect UE#3. Therefore, in step S51, UE#2 sends an announcement message including its own terminal ID, the terminal ID of UE#1, the terminal ID of UE#3, and the terminal ID of UE#4. The terminal ID of UE#1, the terminal ID of UE#3, and the terminal ID of UE#4 are surrounding terminal IDs. In addition, in step S52, UE#4 sends an announcement message including its own terminal ID, the terminal ID of UE#1, the terminal ID of UE#2, and the terminal ID of UE#3.

[0093] When UE#1 receives the announcement message sent in step S51 and the announcement message sent in step S52, it recognizes that UE#3 and UE#4 are included in the peripheral terminals of UE#2, and UE#2 and UE#3 are included in the peripheral terminals of UE#4. In other words, UE#1 recognizes that the signal sent to UE#3 can reach UE#3 regardless of whether it passes through UE#2 or UE#4.

[0094] When UE#1 recognizes that it can communicate with UE#3 regardless of whether it is via UE#2 or UE#4, that is, when it recognizes that there are multiple paths that can be used in communication with UE#3, it first sends a direct communication request message (Direct Communication Request) for establishing a communication path via UE#2 (relay#1) to UE#2 (step S53). Thereafter, UE#1 sends a direct communication request message for establishing a communication path via UE#4 (relay#2) to UE#4 (step S58). In addition to the FD parameter (parameter indicating the communication partner) described in Implementation Example 1, each direct communication request message sent by UE#1 also includes an RP parameter (RP#1 or RP#2) for specifying the wireless resources used in the communication between the relay station and the UE (UE#3) of the communication partner. As a result, UE#1 can specify wireless resources in a manner that the wireless resources used in each of the multiple communication paths are different.

[0095] When UE#2 receives the direct communication request message sent in step S53, it uses the wireless resources indicated by the parameters included in the direct communication request message to send the direct communication request message to UE#3 (step S54). In step S54, UE#2 sends a direct communication request message that does not include the FD parameter and the RP parameter, that is, it sends a direct communication request message with the transmission source set to UE#2 and the transmission destination set to UE#3. Steps S55 to S57 after step S54 are the same as those described in Implementation Example 1. Figure 4 The same processing is performed as in steps S16 to S18 shown.

[0096] When UE#4 receives the direct communication request message sent in step S58, it uses the wireless resources indicated by the parameters included in the direct communication request message to send the direct communication request message to UE#3 (step S59). In step S59, UE#4 sends a direct communication request message that does not include the FD parameter and the RP parameter, that is, it sends a direct communication request message with the transmission source set to UE#4 and the transmission destination set to UE#3. Steps S60 to S62 after step S59 are the same as those described in Embodiment 1. Figure 4 The same processing is performed as in steps S16 to S18 shown.

[0097] Alternatively, UE#1 may specify radio resources so that radio resources used for communication between itself and the relay station and radio resources used for communication between the relay station and UE#3 as the communication partner do not compete with each other.

[0098] Thus, when the terminal device 1 of the fourth embodiment performs inter-terminal communication via the relay station, the terminal device 1 sends the following direct communication request message to the relay station, the direct communication request message including the FD parameter indicating the communication partner and the RP parameter, the RP parameter being used to specify the wireless resources used in the communication between the relay station and the terminal device 1 of the communication partner. The relay station that receives the direct communication request message including the FD parameter and the RP parameter uses the wireless resources indicated by the RP parameter when communicating with the terminal device 1 indicated by the FD parameter. Thus, competition for wireless resources used in multiple communication paths can be avoided.

[0099] To simplify the description, in this embodiment, a case is described where two terminal devices 1 communicate with each other via one relay station. However, a direct communication request message including FD parameters and RP parameters can also be sent when two terminal devices 1 communicate with each other via two or more relay stations.

[0100] In addition, in this embodiment, the action of detecting surrounding terminals through the steps described in embodiment 1 and preventing competition for wireless resources when there are multiple selectable paths in terminal-to-terminal communication is described, but the detection of surrounding terminals can also be performed through the steps described in embodiment 2.

[0101] Implementation method 5.

[0102] Next, the terminal device of the fifth embodiment will be described. The configuration of the communication system implemented by applying the terminal device of the fifth embodiment is the same as that of the first embodiment (see Figure 1 The functional block structure of the terminal device in the fifth embodiment is also the same as that in the first embodiment (see Figure 2 ).

[0103] Similar to Embodiment 4, in this embodiment, the operation of the terminal device 1 when there are multiple inter-terminal communication paths is described. Fig.10 The operation in the case of the positional relationship shown will be described. Fig.10UE#1 is shown as being able to communicate directly with UE#2 and UE#4, and UE#2 is shown as being able to communicate directly with UE#1, UE#4, and UE#3. UE#4 is shown as being able to communicate directly with UE#1, UE#2, and UE#3, and UE#3 is shown as being able to communicate directly only with UE#2 and UE#4. In this case, there are multiple paths that can be used when UE#1 and UE#3 communicate. In addition, UE#1 belongs to carrier A, and UE#3 belongs to carrier B.

[0104] exist Fig.10 In the case where UE#1 and UE#3 that perform terminal-to-terminal communication via a relay station as shown in the figure belong to different communication companies, that is, when the communication carrier to which UE#1 belongs is different from the communication carrier to which UE#3 belongs, UE#1 that starts communication according to the actions described in Implementation Examples 1 to 4 does not know the communication between the relay station ( Fig.10 A resource pool that can be used between UE#2 or UE#4) and the communicating party UE#3. Wireless resources cannot be specified when starting inter-terminal communication. A resource pool is a collection of wireless resources that can be used when UEs communicate directly with each other.

[0105] Therefore, in this embodiment, the following actions are described: when the UE (UE#1) that starts terminal-to-terminal communication belongs to a communications company that is different from the communications company to which the other party's UE (UE#3) that communicates with the terminal via the relay station belongs, a resource pool that can be used between the relay station (UE#2, UE#4) and the other party's UE (UE#3) is grasped to conduct terminal-to-terminal communication.

[0106] Fig.11 This is a diagram showing an example of a sequence of operations in which the terminal device 1 according to the fifth embodiment performs inter-terminal communication via a relay station.

[0107] UE#2 and UE#4 respectively send announcement messages (RelayDiscovery Announcement) at predetermined times in the same manner as in Implementation 4 (steps S71 to S72). At this time, each UE sends the following announcement message, which, in addition to the parameters included in the announcement message sent in steps S51 to S52 described in Implementation 4, also includes a resource pool notification parameter (Relay Resource-pool) indicating the resource pool that each of the surrounding terminals can use. That is, in steps S71 and S72, UE#2 and UE#4 send announcement messages including the above-mentioned service code (Relay Service Code), their own terminal ID (Relay UE ID) and the surrounding terminal ID (Relay-able UE) and the resource pool notification parameter (RelayResource-pool). Fig.11 The resource pool notification parameter in the example shown shows the resource pools that can be used by each surrounding terminal represented by the surrounding terminal ID in a form corresponding to the surrounding terminal ID. For example, in the announcement message sent by UE#2 in step S71, the surrounding terminal ID indicates that it can relay to UE#1, UE#3, and UE#4, and the resource pool notification parameter indicates that the resource pools that UE#1 can use are A: RP#1, A: RP#2, and A: RP#3, the resource pools that UE#3 can use are B: RP#1 and B: RP#2, and the resource pools that UE#4 can use are B: RP#1 and B: RP#2. In addition, 'A' and 'B' in the resource pool notification parameter are communication company information, indicating the communication company to which the UE belongs.

[0108] When UE#1 receives the announcement message sent in step S71 and the announcement message sent in step S72, it identifies that the surrounding terminals of UE#2 include UE#3 and UE#4 and that the surrounding terminals of UE#4 include UE#2 and UE#3, and identifies the resource pools that can be used by the surrounding terminals of UE#2 and the resource pools that can be used by the surrounding terminals of UE#4.

[0109] Steps S73 to S82 after steps S71 and S72 are the same as those described in Embodiment 4. Fig. 9 The same processing is performed as in steps S53 to S62 shown above. However, when determining the RP parameter included in the direct communication request message transmitted in steps S73 and S78, UE#1 selects from the resource pool that can be used by the UE (UE#3) of the communication partner.

[0110] Thus, when the terminal device 1 of implementation mode 5 sends an announcement message, it includes the peripheral terminal ID indicating the peripheral terminal detected at that time point and the resource pool notification parameter indicating the resource pool that each detected peripheral terminal can use. In addition, when the terminal device 1 performs terminal-to-terminal communication via a relay station, it sends a direct communication request message including an FD parameter indicating the communication partner and an RP parameter specifying the wireless resources used in the communication between the relay station and the terminal device 1 of the communication partner to the relay station. At this time, the terminal device 1 selects a wireless resource from the resource pool that the communication partner can use, and sets the value indicating the selected wireless resource as the RP parameter. The relay station that receives the direct communication request message including the FD parameter and the RP parameter uses the wireless resource indicated by the RP parameter when communicating with the terminal device 1 indicated by the FD parameter. Thus, even if the terminal devices 1 performing terminal-to-terminal communication via a relay station belong to different communication companies, competition for wireless resources used in multiple communication paths can be avoided.

[0111] To simplify the description, this embodiment describes a case where two terminal devices 1 communicate with each other via one relay station. However, in a case where two terminal devices 1 communicate with each other via two or more relay stations, the terminal device 1 can also send an announcement message including a resource pool notification parameter indicating a resource pool that each detected surrounding terminal can use.

[0112] In addition, in this embodiment, the action of detecting surrounding terminals by modifying the steps described in embodiment 1 to notify the available resource pool is described, but it is also possible to modify the action of detecting surrounding terminals by modifying the steps described in embodiment 2 to notify the available resource pool.

[0113] Implementation method 6.

[0114] Next, the terminal device of the sixth embodiment will be described. The configuration of the communication system implemented by applying the terminal device of the sixth embodiment is the same as that of the first embodiment (see Figure 1 The functional block structure of the terminal device in the sixth embodiment is also the same as that in the first embodiment (see Figure 2 ).

[0115] Similar to Embodiments 4 and 5, in this embodiment, the operation of the terminal device 1 when there are multiple inter-terminal communication paths is described. Fig.12 The operation in the case of the positional relationship shown will be described. Fig.12UE#1 is shown as being able to communicate directly with UE#2 and UE#4, UE#2 is shown as being able to communicate directly with UE#1, UE#4 and UE#3. UE#4 is shown as being able to communicate directly with UE#1, UE#2 and UE#3, and UE#3 is shown as being able to communicate directly with UE#2 and UE#4. Fig.12 In the example, it is assumed that UE#1 and UE#3 are communicating via UE#2, but the communication quality between UE#2 and UE#3 is degraded.

[0116] exist Fig.12 In the state shown, there are a plurality of paths through which UE#1 and UE#3 can communicate. Therefore, when the communication quality of a path in use decreases, it is desirable to switch to another path so as to continue the communication.

[0117] Therefore, in this embodiment, the operation of switching the communication path of the terminal device 1 when a problem occurs in the path being used in inter-terminal communication and it is difficult to continue the communication will be described.

[0118] Fig.13 This is a diagram showing an example of a sequence of operations for switching a communication path in a state where the terminal device 1 according to the sixth embodiment is performing inter-terminal communication via a relay station.

[0119] Assume that UE#1 and UE#3 are performing inter-terminal communication via UE#2 (relay#1) (step S91). At this time, UE#4 transmits the announcement message (Relay Discovery Announcement) described in Embodiment 1 at a predetermined timing (step S92).

[0120] When UE#1, UE#2, and UE#3 receive the announcement message from UE#4, they recognize that the surrounding terminals of UE#4 are UE#1, UE#2, and UE#3. As a result, UE#1 recognizes that UE#4 can relay to UE#3. That is, UE#1 recognizes that it can also communicate with UE#3 via UE#4.

[0121] Afterwards, it is assumed that UE#3 detects that the communication quality with UE#2 (the communication quality of UE#2→UE#3) has decreased. In this case, UE#3 sends a status notification message (Status Report) to UE#2 to notify the decrease in communication quality, and UE#2, which receives the status notification message, relays the status notification message to UE#1 (steps S93, S94).

[0122] The method by which UE#3 detects the decline in communication quality may be any method. For example, UE#3 sets a threshold for the strength of the received power of the signal, the error rate of the data obtained at the physical layer or the upper layer, and determines that the communication quality has declined when the strength of the received power, the error rate, and other indicators used are lower than the threshold. At this time, in order to avoid false detection, UE#3 may also determine that the communication quality has declined when, for example, the number of times the indicator is lower than the threshold exceeds the set upper limit within a certain period of time.

[0123] In addition, Fig.13 In the example shown, it is assumed that UE#3 detects a decrease in communication quality, but UE#3 may also send an indicator (received power strength, error rate, etc.) for detecting a decrease in communication quality to UE#1, and detect a decrease in communication quality between UE#2 and UE#3 on the UE#1 side. The above threshold and upper limit value for detection may be maintained in advance by each UE, or may be notified to each UE from the core network side via the base station 3 at any time.

[0124] When UE#1 receives a status notification message indicating that the communication quality between UE#2 and UE#3 has decreased, in order to switch the communication path, it sends a direct communication request message to UE#4 that can relay the signal sent to UE#3 toward UE#3 (step S95). UE#4 forwards the received direct communication request message to UE#3 (step S96). In step S96, UE#4 sends a direct communication request message that does not include the FD parameter and the RP parameter, that is, a direct communication request message that sets the transmission source to UE#4 and the transmission destination to UE#3. Thereafter, the same steps as described in Implementation Example 4 are performed. Fig. 9 In steps S97 to S98 similar to steps S55 to S56 shown above, a communication line is established between UE#1 and UE#3 via UE#4 (relay#2) (step S99).

[0125] After establishing a new communication line via UE#4, UE#1 sends a disconnection request message "Disconnect Request" to UE#2 (step S100) to disconnect the communication line with degraded communication quality, and disconnects the communication line with UE#2 (step S101).

[0126] UE#2, which has received the disconnection request message from UE#1, transmits a disconnection request message to UE#3, which is the communication partner of UE#1 (step S102), and disconnects the communication line with UE#3 (step S103).

[0127] In addition, in this embodiment, the operation in the case where a decrease in communication quality is detected when there are multiple relay stations that can be used when UE#1 and UE#3 communicate is described, but in the case where a decrease in communication quality is detected when there is only one relay station that can be used, each UE does not perform the processing equivalent to the above-mentioned steps S95 to S103. In other words, each UE continues to maintain communication even if the communication quality decreases when there is no communication path that can be switched.

[0128] In addition, in this embodiment, as an example, the action of switching the communication path when UE#3 detects a decrease in communication quality when UE#1 and UE#3 are communicating between terminals via UE#2 is described, but the action of switching the communication path is not limited to this. For example, even if UE#1 detects a decrease in the communication quality between UE#2 and UE#1, the communication path is switched by the same steps. In this case, when UE#1 detects a decrease in communication quality, it performs a process equivalent to step S95 described above, and each UE performs a process equivalent to subsequent steps S96 to S103 to switch the communication path. In addition, even if UE#2 detects a decrease in communication quality between UE#1 or a decrease in communication quality between UE#3, the communication path is switched by the same steps. In this case, UE#2 sends a status notification message indicating the detection of a decrease in communication quality to UE#1. UE#1 that receives the status notification message performs a process equivalent to step S95 described above, and each UE performs a process equivalent to subsequent steps S96 to S103 to switch the communication path.

[0129] Thus, when the communication quality decreases during inter-terminal communication via a relay station selected from a plurality of available relay stations, the terminal device 1 of Embodiment 6 changes the relay station to be used to switch the communication path. Thus, it is possible to avoid interruption or disconnection of communication and maintain the communication quality, and it is possible to continue inter-terminal communication.

[0130] To simplify the description, this embodiment describes a case where two terminal devices 1 communicate with each other via one relay station. However, even when two terminal devices 1 communicate with each other via two or more relay stations, the communication path can be switched when the communication quality decreases.

[0131] In addition, the communication path is switched when the communication quality is degraded, but in addition, the communication path may be switched when communication is not possible. For example, the communication path may be switched when the time elapsed since the state in which no signal is received in the communication path currently used in the inter-terminal communication reaches a threshold.

[0132] In addition, when two terminal devices 1 are performing terminal-to-terminal communication via a relay station and the terminal device 1 of the relay station relays the communication quality information sent from each terminal device 1, the terminal device 1 of the relay station may also send the communication quality information received from other terminal devices 1 together with the communication quality information generated by itself, or may send them separately.

[0133] The configurations described in the above embodiments are merely examples, and may be combined with other known technologies, the embodiments may be combined with each other, and some configurations may be omitted or changed without departing from the spirit and scope of the invention.

[0134] Description of Reference Numerals

[0135] 1 terminal device, 3 base station, 10 control unit, 11 detection unit, 12 information notification unit, 13 relay processing unit, 14 communication processing unit, 16 wireless communication unit, 17 storage unit, 100 communication system.

Claims

1. A terminal device having a relay function of relaying a signal received from a first peripheral terminal among peripheral terminals to a second peripheral terminal among the peripheral terminals, wherein the peripheral terminals are other terminal devices capable of direct communication, characterized in that: The terminal device comprises: A detection unit, which detects the peripheral terminals; a storage unit that stores information of surrounding terminals detected by the detection unit, that is, surrounding terminal information; and an information notification unit that includes the peripheral terminal information held by the storage unit in a notification message for notifying other terminal devices of the information of the peripheral terminal and transmits the notification message to the other terminal devices, When receiving the notification message sent by the other terminal device, the detection unit extracts the surrounding terminal information contained in the received notification message, and stores the extracted surrounding terminal information and the information of the other terminal device that is the sending source of the received notification message in the storage unit in correspondence, The terminal device also includes a communication processing unit. When performing terminal-to-terminal communication with other terminal devices via a third peripheral terminal among the peripheral terminals, the communication processing unit causes parameters representing the terminal device of the other party of the terminal-to-terminal communication, i.e., the other party terminal, to be included in a direct communication request message for requesting the start of terminal-to-terminal communication and sent.

2. The terminal device according to claim 1, characterized in that The notification message is a bulletin message for notifying other terminal devices of its presence.

3. The terminal device according to claim 1, characterized in that The notification message is a response message that is transmitted when a message for finding a relay station that relays signals between two terminal devices is received and the terminal device is able to operate as the relay station.

4. The terminal device according to claim 1, characterized in that: The communication processing unit includes a resource designation parameter in the direct communication request message and transmits the message, the resource designation parameter designating a wireless resource used in a communication path between the third neighboring terminal and the counterpart terminal.

5. The terminal device according to claim 4, characterized in that: The information notification unit includes a resource pool notification parameter in the notification message and sends the notification message, the resource pool notification parameter indicating a resource pool that can be used by each of the surrounding terminals indicated by the surrounding terminal information held by the storage unit, The communication processing unit selects a wireless resource designated by the resource designation parameter from a resource pool indicated by a resource pool notification parameter included in a notification message received from the surrounding terminal.

6. The terminal device according to claim 1, characterized in that: When there are a plurality of paths to the other party of the inter-terminal communication, When the communication quality in the path currently being used in the inter-terminal communication decreases, the communication processing unit sends the direct communication request message to the peripheral terminal forming a path different from the path currently being used in the inter-terminal communication, and starts the inter-terminal communication using a new communication line.

7. The terminal device according to claim 4, characterized in that: When there are a plurality of paths to the other party of the inter-terminal communication, When the communication quality in the path currently being used in the inter-terminal communication decreases, the communication processing unit sends the direct communication request message to the peripheral terminal forming a path different from the path currently being used in the inter-terminal communication, and starts the inter-terminal communication using a new communication line.

8. The terminal device according to claim 5, characterized in that: When there are a plurality of paths to the other party of the inter-terminal communication, When the communication quality in the path currently being used in the inter-terminal communication decreases, the communication processing unit sends the direct communication request message to the peripheral terminal forming a path different from the path currently being used in the inter-terminal communication, and starts the inter-terminal communication using a new communication line.

9. The terminal device according to any one of claims 6 to 8, characterized in that: After starting the inter-terminal communication using the new communication line, the communication processing unit transmits a disconnection request message to the peripheral terminals forming the path where the communication quality has deteriorated, thereby disconnecting the communication line that has been used so far.

10. A communication method, which is a communication method performed by a terminal device, the terminal device having a relay function of relaying a signal received from a first peripheral terminal among peripheral terminals to a second peripheral terminal among the peripheral terminals, the peripheral terminals being other terminal devices capable of direct communication, characterized in that: The communication method comprises: Step 1, detecting the peripheral terminals; Step 2, storing the information of the surrounding terminals detected in the step 1, i.e., the surrounding terminal information; A third step is to include the peripheral terminal information stored in the second step in a notification message for notifying other terminal devices of the information of the peripheral terminal and transmit the notification message; and In step 4, when a signal for the second peripheral terminal is received from the first peripheral terminal, or a signal for another terminal device that can communicate via the second peripheral terminal is received from the first peripheral terminal, the received signal is relayed to the second peripheral terminal. The first step further includes, when receiving the notification message sent by other terminal devices, extracting the surrounding terminal information contained in the received notification message; the second step further includes storing the extracted surrounding terminal information in correspondence with the information of the other terminal device that is the sending source of the received notification message, The communication method further includes: when performing terminal-to-terminal communication with other terminal devices via a third peripheral terminal among the peripheral terminals, including a parameter indicating a terminal device, i.e., a counterpart terminal, of the counterpart of the terminal-to-terminal communication in a direct communication request message for requesting the start of the terminal-to-terminal communication and sending the message.

11. A communication system, comprising a plurality of terminal devices, wherein each terminal device has a function of directly communicating with other terminal devices, characterized in that: The plurality of terminal devices respectively include: a detection unit that detects other terminal devices that can directly communicate, namely, surrounding terminals; a storage unit that stores information of surrounding terminals detected by the detection unit, that is, surrounding terminal information; An information notification unit configured to include the peripheral terminal information stored in the storage unit in a notification message for notifying the peripheral terminals of the information of the peripheral terminal and transmit the notification message to the peripheral terminals; as well as a relay processing unit that, when receiving a signal from a first peripheral terminal among the peripheral terminals for a second peripheral terminal among the peripheral terminals, or receiving a signal from the first peripheral terminal for another terminal device that can communicate via the second peripheral terminal, relays the received signal to the second peripheral terminal, When receiving the notification message sent by the other terminal device, the detection unit extracts the surrounding terminal information contained in the received notification message, and stores the extracted surrounding terminal information and the information of the other terminal device that is the sending source of the received notification message in the storage unit in correspondence, The plurality of terminal devices also respectively include a communication processing unit, and when performing terminal-to-terminal communication with other terminal devices via the third peripheral terminal among the peripheral terminals, the communication processing unit causes parameters representing the terminal device of the other party of the terminal-to-terminal communication, i.e., the other party terminal, to be included in a direct communication request message for requesting the start of terminal-to-terminal communication and sent.

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