An effective distributed synchronization method subject to timing error for D2D communication

We study the problem of distributed synchronization for device-to-device(D2D) communication. For D2D out-of-network coverage (ONC) scenario, synchronization among multiple user equipment (UE) is a very important issue due to the fact that synchronization method does not have a common time/frequency standard, so synchronization in self-organized D2D network is adjusting their own time/frequency offset until a group consensus is reached. 3GPP agreed a synchronization method based on multi-hop relays. In this method, UE uses reference signal received power (RSRP) of D2D synchronization signals (D2DSS) as the only criterion for selecting the reference signal and synchronizing with it. However, this method doesn't consider actual timing error of D2DSS, which are accumulated through the previous multi-hop links. Therefore, in this paper, we propose a novel synchronization method where UE selects a reference timing with the smallest RMS error. We examine the problem from system-level perspective, and verify that the proposed method can efficiently make more UE's RMS timing error meet tolerance of SC-FDMA symbols, which means a UE can successfully communicate with its neighbors directly.