Improving the Energy Efficiency of a Clock Synchronization Protocol for WSNs Using a TDMA-Based MAC Protocol

Clock synchronization protocols in wireless sensor networks (WSNs) provide a uniform notion of time which is required by both system as well as application level programs of WSNs. Since nodes have limited energy, it is required that the energy consumed by the clock synchronization protocols is as minimum as possible. Synchronous clock synchronization protocols execute their clock synchronization process at each node, roughly during the same real-time interval, called synchronization phase. The energy consumed by these protocols depends on the duration of the synchronization phase and how frequently the synchronization phase is executed. Hence, to minimize the energy consumption by each node, the duration of synchronization phase should be as small as possible, and the interval between consecutive synchronization phases as large as possible. Due to different drift rates of the clocks, the synchronization phases at different nodes drift apart and special techniques are required to keep them in sync. Keeping synchronization phases at neighbouring nodes in sync helps to reduce the synchronization phase. In this paper, we propose a novel technique using TDMA-based MAC protocol to keep the synchronization phases at neighbouring nodes in sync much more tightly than the existing techniques. We have applied the technique in the improved weighted-average based clock synchronization (IWICS) protocol to reduce the synchronization phase considerably and the modified TDMA-based IWICS protocol is named TIWICS protocol. This reduction in energy consumption is achieved without reducing the synchronization accuracy. Simulation results obtained using Castalia network simulator and the experimental results obtained using a test bed of WSN consisting of a few TELUS motes confirm the effectiveness of the approach.