Terminal device, communication method, and communication system

1 . A terminal device having a relay function of relaying a signal received from a first peripheral terminal among peripheral terminals, which are other terminal devices available for direct communication with the terminal device, to a second peripheral terminal among the peripheral terminals, the terminal device comprising:

a processor, and

a memory to store a program which, when executed by the processor, causes the processor to control the terminal device to perform processes of:

detecting the peripheral terminals;

holding peripheral terminal information that is information on each of the detected peripheral terminals in the memory;

transmitting a first notification message to the other terminal devices for notifying the other terminal devices of information on the terminal device, wherein the transmitted first notification message includes the information on the terminal device, and the peripheral terminal information held by the memory, the transmitted first notification message further including a parameter indicating peripheral terminals to which the terminal device can relay signals;

when receiving another notification message transmitted by one of the other terminal devices, extracting other peripheral terminal information included in the received other notification message, storing, in the memory, second peripheral terminal information including the extracted other peripheral terminal information in association with information on the one of the other terminal devices that is a source of the received other notification message;

transmitting a second notification message from the terminal device to the other terminal devices, wherein the second notification message includes the second peripheral terminal information held in the memory; and

when performing a terminal-to-terminal communication with one of the other terminal devices via the second peripheral terminal among the peripheral terminals, transmitting a direct communication request message for requesting initiation of the terminal-to-terminal communication to the second peripheral terminal, the direct communication request message including a parameter indicating a third peripheral terminal among the plurality of peripheral terminals that is a counterpart terminal device of the terminal-to-terminal communication.

2 . The terminal device according to claim 1 , wherein

the terminal device sets an announcement message for notifying the other terminal devices of presence of the terminal device as the notification message to be transmitted.

3 . The terminal device according to claim 1 , wherein

the terminal device receives a message for discovering a relay station that performs signal relay processing between two of the terminal devices, and sets, as the notification message to be transmitted, a response message that is transmitted when the terminal device is operable as the relay station.

4 . The terminal device according to claim 1 , wherein

the terminal device transmits the direct communication request message including a resource designation parameter that designates a radio resource to be used in a communication path between the third peripheral terminal and the counterpart terminal.

5 . The terminal device according to claim 4 , wherein

the terminal device transmits the notification message including, in the notification message, a resource pool notification parameter that indicates a resource pool available to each of the peripheral terminals indicated by the peripheral terminal information held in the memory, and

the terminal device selects the radio resource designated by the resource designation parameter from the resource pool indicated by the resource pool notification parameter included in the other notification message received from each of the peripheral terminals.

6 . The terminal device according to claim 1 , wherein

when there is a plurality of paths to the counterpart of the terminal-to-terminal communication,

the terminal device transmits the direct communication request message to one of the peripheral terminals forming a path different from a path being used in the terminal-to-terminal communication when quality of communication of the path being used in the terminal-to-terminal communication is reduced, and initiates the terminal-to-terminal communication using a new communication line.

7 . The terminal device according to claim 6 , wherein

after initiating the terminal-to-terminal communication using the new communication line, the terminal device transmits a disconnection request message to the peripheral terminal forming the path in which the quality of communication is reduced, and disconnects a communication line that is used until then.

8 . A communication method to be executed by a terminal device having a relay function of relaying a signal received from a first peripheral terminal among peripheral terminals, which are other terminal devices available for direct communication with the terminal device, to a second peripheral terminal among the peripheral terminals, the communication method comprising:

detecting the peripheral terminals;

transmitting a first notification message to the other terminal devices for notifying the other terminal devices of information on the terminal device, wherein the transmitted first notification message includes the information on the terminal device, and peripheral terminal information held by a memory of the terminal device, the transmitted first notification message further including a parameter indicating peripheral terminals to which the terminal device can relay signals

extracting, when receiving a second notification message transmitted by one of the other terminal devices, information on a peripheral terminal that is information on each of the peripheral terminals detected and included in the received second notification message;

storing the extracted information on the peripheral terminal in association with information on one of the other terminal devices that is a source of the received second notification message, and updating the held peripheral terminal information;

transmitting a third notification message to the other terminal devices for notifying the other terminal devices of the information on the terminal device, wherein the transmitted third notification message includes the information on the terminal device, and the updated peripheral terminal information, the transmitted third notification message further including the parameter indicating peripheral terminals to which the terminal device can relay signals; and

relaying a signal received to the second peripheral terminal when (1) receiving the signal that is directed toward the second peripheral terminal from the first peripheral terminal or (2) receiving a signal that is directed toward one of the other terminal devices, which is available for communication via the second peripheral terminal, from the first peripheral terminal, and relaying the signal directed toward one of the other terminal devices to at least one of the other terminal devices.

9 . A communication system including a plurality of terminal devices, the terminal devices having a function of directly communicating with other terminal devices, wherein

the plurality of the terminal devices each comprises:

a processor, and

a memory storing a program which, when executed by the processor, causes the processor to control the terminal device to perform processes of:

detecting peripheral terminals that are the other terminal devices available for direct communication;

holding peripheral terminal information that is information on each of the detected peripheral terminals in the memory;

transmitting a first notification message to the peripheral terminals for notifying the peripheral terminals of information on the terminal device, wherein the transmitted first notification message includes the information on the terminal device, and the peripheral terminal information held by the memory, the transmitted first notification message further including a parameter indicating peripheral terminals to which the terminal device can relay signals;

when receiving a second notification message transmitted by one of the other terminal devices, the terminal device extracts peripheral terminal information included in the received second notification message, stores, in the memory, the extracted peripheral terminal information in association with information on one of the other terminal devices that is a source of the received second notification message and updates the held peripheral terminal information;

transmitting a third notification message to the other terminal devices for notifying the other terminal devices of the information on the terminal device, wherein the transmitted third notification message includes the information on the terminal device, and the updated peripheral terminal information, the transmitted third notification message further including the parameter indicating peripheral terminals to which the terminal device can relay signals; and

relaying a signal received to a second peripheral terminal among the peripheral terminals when (1) receiving the signal that is directed toward the second peripheral terminal from a first peripheral terminal among the peripheral terminals or (2) receiving a signal that is directed toward one of the other terminal devices, which is available for communication via the second peripheral terminal, from the first peripheral terminal, and relaying the signal directed toward one of the other terminal devices to at least one of the other terminal devices.