Adaptive clock synchronization in sensor networks

Recent advances in technology have made low cost, low power wireless sensors a reality. Clock synchronization is an important service in any distributed system, including sensor network systems. Applications of clock synchronization in sensor networks include data integration in sensors, sensor reading fusion, TDMA medium access scheduling, and power mode energy saving. However, for a number of reasons, standard clock synchronization protocols are unsuitable for direct application in sensor networks. In this paper, we introduce the concept of adaptive clock synchronization based on the need of the application and the resource constraint in the sensor networks. We describe a probabilistic method for clock synchronization that uses the higher precision of receiver-to-receiver synchronization, as described in Reference Broadcast Synchronization (RBS) protocol. This deterministic protocol is extended to provide a probabilistic bound on the accuracy of the clock synchronization, allowing for a tradeo between accuracy and resource requirement. Expressions to convert service specifications (maximum clock synchronization error and confidence probability) to actual protocol parameters (minimum number of messages and synchronization overhead) are derived. Further, we extend this protocol for maintaining clock synchronization in a multihop network.