An efficient clock synchronization protocol for wireless sensor networks

In wireless sensor networks (WSNs), it may be necessary to have a unified time reference for all network nodes. Such a necessity may be imposed by the management strategy in the network, e.g., using time based medium access arbitration, or simply due to the dynamic nature of the application, e.g. target tracking. Since each node more or less operates autonomously, the clocks of the individual nodes have to be synchronized. Contemporary clock synchronization protocols introduce significant messaging overhead and thus do not suit the resource-constrained WSNs. In the paper, we propose a novel solution called Synchronization through Piggybacked Reference Timestamps (SPiRT). SRiRT exploits the popularity of two-tier network architectures in WSN, where nodes are grouped into disjoint clusters and each cluster is lead by a cluster-head that aggregates the data from its members. Each cluster-head synchronizes its clock to that of a reference node in the network through message exchange. Since cluster members can overhear the cluster-head transmissions, SPiRT takes advantages of such synchronization traffic to adjust the clock of the cluster members. SPiRT calls for appending the reference timestamps in the cluster-head messages so that a cluster member can estimate their clock adjustment. This cuts on energy consumption and increases the synchronization efficiency of SPiRT. SPiRT is validated through simulation and implementation on a Micaz based testbed. The validation results confirm the effectiveness of SPiRT and show that it outperforms competing schemes in the literature.