Proximity synchronization for mobile wireless sensor networks

Wireless sensor networks are designed to be used in any situation that requires monitoring of widely-dispersed geographic areas. They are capable of providing automated monitoring with high precision at low cost over long periods of time. In order to achieve the conflicting goals of high precision at low cost, software techniques can be employed to enhance the precision of important metrics. In particular, this investigation introduces an improved protocol for synchronizing the clocks of different sensor nodes, for the purpose of improving the accuracy of time-sensitive data acquisition. In the course of our initial investigation, several weaknesses and deficiencies exhibited by existing synchronization protocols were identified, particularly with respect to mobile sensor networks. To address these issues a new protocol was developed. The protocol is based on the Network- wide Time Synchronization in sensor networks protocol, modified to use a restricted tree-based hierarchy arranged as a minimum spanning tree. A key feature of the improved protocol is that it distributes the work of synchronization, thereby eliminating potential bottleneck constraints. In extensive testing, it was also shown to reduce the number of message collisions to which larger networks are prone. When compared to the original protocol, these improvements resulted in lower clock synchronization error across the network and substantially reduced sensor power consumption. In addition, the improved protocol is more robust, in that it has the ability to dynamically reconnect and resynchronize as mobile nodes move in and out of communication range.