STETS: A novel energy-efficient time synchronization scheme based on embedded networking devices

Time synchronization is essential in the implementation of large-scale Wireless Sensor Networks (WSNs). However, many approaches of time synchronization suffer from high communication overheads when pursuing high accuracy. Such overheads cause significant shrinkage of the lifetime of WSNs since frequent data communications consume much energy which is extremely limited in each sensor node. The energy consumption increases rapidly with the growth of WSNs density. In this paper, we present a Spanning Tree-based Energy-efficient Time Synchronization (STETS) which effectively incorporates two time synchronization schemes: Sender to Receiver Protocol (SRP) and Receiver to Receiver Protocol (RRP). It reduces the communication overheads while still maintaining high accuracy. In our approach, backbone sensor nodes form a spanning tree and they get synchronized layer by layer through SRP. Other nodes get synchronized through RRP by only listening to the communication between backbone sensor nodes. We evaluated the performances by simulating our approach on NS-2 and implementing it on embedded networking devices STM32W108 with simple MAC protocol stack. The experiment results show that our approach is efficient in both energy consumption and accuracy of time synchronization. Especially, it can get better performances in densely connected WSNs.