Abstract
Most of wireless sensor networks require time synchronization to wake up sensor nodes at scheduled time. It helps accomplish coordinated communications among the nodes to save energy. Wireless sensor nodes are often equipped with a low-cost clock oscillator with large clock drift. Thus, it is important to correct the long-term synchronization error caused by clock drift. This paper introduces a low power protocol for long-term synchronization called fast scheduling and accurate drift compensation for time synchronization (FADS). It chooses a minimal sequence of synchronization steps by estimating the density of the neighbor nodes. FADS achieves low power synchronization by reducing the number of message exchanges and increasing the synchronization interval (the period in which each node needs to perform synchronization). To evaluate the performance of FADS, we implemented it in real wireless networks with sensor hardware and conducted extensive tests. This paper demonstrates that FADS achieves substantially fewer messages and less delays in the scheduling phase than a previous technique, Density Table-based Synchronization (DTSync). Simulation results show that FADS reduces the number of messages by 50 times and reduces the delay by 4 times compared with DTSync for large networks. In addition, experiments with actual sensor devices demonstrate that it allows significantly less frequent synchronization 195 times improvement compared with DTSync.