Communication control method and user terminal for selecting synchronization reference of device-to-device (D2D)

A method for performing by a first user terminal, comprising:

• in case that the first user terminal is out of coverage area of a communication network including a plurality of base stations,
• directly receiving device-to-device (D2D) synchronization information from a second user terminal being in the coverage area, the D2D synchronization information including coverage information that indicates that the second user terminal is in the coverage area;
• determining, based on the coverage information, that the second user terminal is in the coverage area;
• selecting the second user terminal as a synchronization reference of the first user terminal in response to determining that the second user terminal is in the coverage area;
• and
• receiving usable resource information broadcasted from the second user terminal that becomes the synchronization reference, the usable resource information indicating D2D usable resources notified from a base station to the second user terminal by broadcast signaling.

A device for controlling a first user terminal, comprising:

• at least one processor and at least one memory, wherein
• in case that the first user terminal is out of coverage area of a communication network including a plurality of base stations, the at least one processor is configured to execute processes of:
• directly receiving device-to-device (D2D) synchronization information from a second user terminal being in the coverage area, the D2D synchronization information including coverage information that indicates that the second user terminal is in the coverage area;
• determining, based on the coverage information, that the second user terminal is in the coverage area;
• selecting the second user terminal as a synchronization reference of the first user terminal in response to determining that the second user terminal is in the coverage area;
• and
• receiving usable resource information broadcasted from the second user terminal that becomes the synchronization reference, the usable resource information indicating D2D usable resources notified from a base station to the second user terminal by broadcast signaling.