Method and apparatus for synchronization for Vehicle-to-X communication

A first user device comprising:

• at least one antenna to transmit and receive at least one wireless signal;
• at least one processor;
• and
• memory storing instructions that, when executed by the at least one processor, cause the first user device to:
• receive, based on a configured sidelink communication mode that supports Global Navigational Satellite Systems (GNSS) timing-based synchronization, a plurality of synchronization signals transmitted from a plurality of synchronization sources, wherein the plurality of synchronization sources comprise at least one of:
• one or more base stations, one or more Global Navigational Satellite Systems (GNSSs), one or more devices capable of synchronizing with the one or more GNSSs, or one or more devices capable of synchronizing with the one or more base stations;
• select, based on prioritization of the plurality of synchronization signals, a synchronization signal of the plurality of synchronization signals, wherein a timing of the selected synchronization signal is associated with a synchronization timing of the one or more GNSSs, and wherein a synchronization signal of a second user device directly synchronized to the one or more GNSSs and a synchronization signal of a third user device directly synchronized to the one or more base stations are prioritized over a synchronization signal of a fourth user device indirectly synchronized to the one or more GNSSs and over a synchronization signal of a fifth user device indirectly synchronized to the one or more base stations;
• map a primary sidelink synchronization signal (PSSS) to first two consecutive symbols in a subframe;
• map a secondary sidelink synchronization signal (SSSS) to second two consecutive symbols in the subframe, wherein the SSSS mapped to the second two consecutive symbols in the subframe is generated based on a selected SSSS mapping scheme of a plurality of SSSS mapping schemes, wherein the selected SSSS mapping scheme is configured to use a first mapping order of sequences of the SSSS, wherein a second SSSS mapping scheme is configured to use a second mapping order of the sequences of the SSSS, and wherein the selected SSSS mapping scheme indicates that the configured sidelink communication mode that supports GNSS timing-based synchronization is associated with the SSSS;
• and
• transmit, using the at least one antenna, the PSSS and the SSSS to at least one wireless user device.