Fault-tolerant cluster-wise clock synchronization for wireless sensor networks

Wireless sensor networks have received a lot of attention recently due to their wide applications, such as target tracking, environment monitoring, and scientific exploration in dangerous environments. It is usually necessary to have a cluster of sensor nodes share a common view of a local clock time, so that all these nodes can coordinate in some important applications, such as time slotted MAC protocols, power-saving protocols with sleep/listen modes, etc. However, all the clock synchronization techniques proposed for sensor networks assume benign environments; they cannot survive malicious attacks in hostile environments. Fault-tolerant clock synchronization techniques are potential candidates to address this problem. However, existing approaches are all resource consuming and suffer from message collisions in most of cases. This paper presents a novel fault-tolerant clock synchronization scheme for clusters of nodes in sensor networks, where the nodes in each cluster can communicate through broadcast. The proposed scheme guarantees an upper bound of clock difference between any nonfaulty nodes in a cluster, provided that the malicious nodes are no more than one third of the cluster. Unlike the traditional fault-tolerant clock synchronization approaches, the proposed technique does not introduce collisions between synchronization messages, nor does it require costly digital signatures.