Improved multi-hop time synchronization for Underwater Acoustic Networks

Time synchronization is important for many distributed applications in Underwater Acoustic Networks (UANs) with large propagation delay, such as precise scheduling, target tracking and energy conservation. In this paper, we prove that the accuracy of time skew estimation increases as the number of overheard packet exchange from other neighboring nodes increases, and propose a light-weighted synchronization algorithm for multi-hop UANS, named as Improved Multi-hop time Synchronization for Underwater Acoustic Networks(IMSUAN). IMSUAN consists of three parts. The first one is to establish a time synchronization tree with the reference node as the root, and assign each node a tree level as low as possible. The second one is to synchronize with the parent node by dedicated three-time handshake and overhear exchange packets from parent and neighboring nodes. The third is to filter the inaccurate time-stamps of the overheard synchronization packets. In the paper, we establish a simulation platform in OPNET to evaluate the performance of IMSUAN. Simulation results show that the performance of extended Tri-message, MSUAN and IMSUAN are the same when no overhearing exists. However, when overhearing is possible in a random topology, the performance of IMSUAN can be 60% better than extended Tri-Message and 40% better than MSUAN.