Simplified time synchronization for underwater acoustic sensor networks with high propagation latency

Time synchronization is of great significance in underwater acoustic (UWA) networks. Many functions, such as network protocol stack, sleep-scheduling, and localization, are based on time synchronization. Because underwater sound speed is comparatively slow, synchronization protocols encounter a long propagation latency problem, which differs from those in terrestrial sensor networks. As a result, protocols omitting propagation latency, including reference-broadcast synchronization (RBS) and timing-sync protocol for sensor networks (TPSN), are inappropriate underwater. Time synchronization for high latency acoustic networks (TSHL) is a two-phase protocol dealing with the considerable propagation time and performs better than TPSN and RBS. In this paper, a simplified time synchronization protocol based on tiny-sync is introduced. Tiny-sync features low complexity in network bandwidth, storage and processing, and achieves good accuracy in terrestrial networks. However, tiny-sync is time-consuming in UWA networks. We improve the traditional tiny-sync protocol by intensively scheduling message exchange to overcome high propagation latency problem. Simulation results show that improved tiny-sync has better performance in synchronization time than previous protocols, as well as retaining the advantage of small storage requirement in traditional tiny-sync.