3. A device-to-device user equipment (D2D UE), comprising:a controller configured to select a system timing indicator to be included into a D2D synchronization signal (D2DSS) for synchronization of D2D communication, from among a first indicator and a second indicator,
wherein the first indicator indicates that the D2DSS is derived from a base station or derived from another D2D UE being in coverage of the base station, and
the second indicator indicates that the D2DSS is derived from another D2D UE being out of coverage of the base station;
a transmitter configured to transmit the D2DSS including the selected system timing indicator;
the controller further configured to determine whether the D2D UE is in coverage of the base station; and
the transmitter further configured to transmit a coverage indicator indicating whether the D2D UE is in coverage of the base station.