A low overhead multi-hop time-sync protocol for wireless sensor networks

Time synchronization is a fundamental service for both design and application of wireless sensor networks (WSN). This paper concerns more on the aspect of overhead caused by time synchronization and presents a low overhead multi-hop time synchronization protocol (LOTS). In single hop domain, only one-way synchronization beacon is transmitted. MAC layer time stamping and linear regression methods are used to improve the accuracy of the synchronization between pair of nodes. Single hop synchronization spreads hop by hop from the time master node to the whole network. A synchronized node counts the beacons it heard to calculate a wireless connectivity metric. Only the node whose connectivity metric is higher than a certain threshold can broad synchronization beacon. Therefore the overhead and chances of packets collision are reduced. Simulation results show that our idea is effective when nodes are deployed, densely. In addition, we argue that the possibility of synchronization error blowing up with hop distance is very small. This point is verified by experimenting on real sensor networks.