Apparatus and method for configuring synchronization signal for d2d communication

A user equipment (UE) comprising:

• a processor;
• and
• memory storing instructions that, when executed by the processor, cause the UE to:
• synchronize with a synchronization source based on a synchronization signal received from the synchronization source;
• determine, based on the synchronization source and from two integer values X and Y, a root index to generate a primary D2D synchronization signal (PD2DSS), wherein each of the integer value X and integer value Y is not an element of a set {25, 29, 34};
• generate, based on the determined root index, the PD2DSS;
• determine one of two different modes;
• map a secondary D2D synchronization signal (SD2DSS) in two Single Carrier-Frequency Division Multiplexing (SC-FDM) symbols in a same subframe, wherein the mapping comprises mapping, based on the one of the two different modes, a first m-sequence of the SD2DSS to first sub-carriers of the two SC-FDM symbols or to second sub-carriers of the two SC-FDM symbols;
• and
• transmit, to a second UE, a D2D synchronization signal, the D2D synchronization signal comprising the PD2DSS and the SD2DSS,
• wherein indexes of the first sub-carriers are even numbers;
• and
• wherein indexes of the second sub-carriers are odd numbers.

A user equipment (UE) comprising:

• a processor;
• and
• memory storing instructions that, when executed by the processor, cause the UE to:
• receive a device-to-device (D2D) synchronization signal transmitted from a second UE, the D2D synchronization signal comprising a primary D2D synchronization signal (PD2DSS);
• determine, based on the received PD2DSS, a root index used for the received PD2DSS, wherein the root index used for the received PD2DSS has one of two integer values X and Y, and wherein each of the integer value X and integer value Y is not an element of a set {25, 29, 34};
• select the second UE to be a synchronization source of the UE;
• generate, using the root index used for the received PD2DSS, a PD2DSS to be transmitted to a third UE;
• map a secondary D2D synchronization signal (SD2DSS) in two Single Carrier-Frequency Division Multiplexing (SC-FDM) symbols in a same subframe, wherein the mapping comprises mapping, based on one of two different modes, a first m-sequence of the SD2DSS to first sub-carriers of the two SC-FDM symbols or to second sub-carriers of the two SC-FDM symbols;
• and
• transmit, to the third UE, the generated PD2DSS and the SD2DSS,
• wherein indexes of the first sub-carriers are even numbers;
• and
• wherein indexes of the second sub-carriers are odd numbers.