Hybrid Energy-Aware Synchronization Algorithm in Wireless Sensor Networks

We present a time synchronization scheme for wireless sensor networks that aims to conserve sensor battery power while maintaining network connectivity for as long as possible. The proposed method creates a hierarchical tree by flooding the sensor network from a designated source point. It then uses a hybrid algorithm derived from the Timing-sync protocol for sensor networks (TSPN) and the reference broadcast synchronization method (RBS) to periodically synchronize sensor clocks by minimizing the number of required transmissions. In multi-hop ad-hoc networks, a depleted sensor will drop information from all other sensors that route data through it, decreasing the physical area being monitored by the network. It is therefore imperative that time synchronization schemes are aware of the number of sensors being used at any given time. The proposed method uses several techniques and thresholds to maintain network connectivity. A new source point is chosen when the current one's battery power reaches a designated energy threshold. The network is also re-flooded whenever the number of used sensors drops below another threshold. We implement and show that our scheme can provide significant power savings over both TPSN and RBS; the power reduction is even more drastic in large multi-hop sensor networks. The method also improves upon these algorithms by maintaining a large area of coverage even when some sensors lose power.