Apparatus and method for configuring synchronization signal for communication between user devices

A first wireless user device comprising:

• at least one processor;
• and
• memory storing instructions that, when executed by the at least one processor, cause the first wireless user device to:
• receive, from a second wireless user device, one or more wireless signals for direct communication between wireless user devices, wherein the one or more wireless signals comprises a primary synchronization signal and a secondary synchronization signal;
• determine, based on the primary synchronization signal, a root index associated with the primary synchronization signal, wherein the root index associated with the primary synchronization signal corresponds to one of a plurality of integer values, wherein each of the plurality of integer values is different from root index values associated with synchronization signals transmitted from one or more base stations, and wherein a type of a synchronization source is associated with the one of the plurality of integer values;
• and
• decode the secondary synchronization signal that is mapped in two symbols in a same subframe by:
• determining, based on one of two different conditions, whether a first m-sequence of the secondary synchronization signal is mapped to first sub-carriers of the two symbols or mapped to second sub-carriers of the two symbols,
• wherein indexes of the first sub-carriers are even numbers and indexes of the second sub-carriers are odd numbers.