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Low Power, Accurate Time Synchronization MAC Protocol for Real-Time Wireless Data Acquisition

The issues of real-time wireless data acquisition networks, i.e., the design and management of large scale sensor networks distributed over a vast geographical area, have received more attention during the last few years. This paper proposes a real-time wireless data acquisition media access control (MAC) protocol fulfilling the requirements of high throughput, low end-to-end latency, low energy consumption and accurate time synchronization. A hybrid approach, combining the advantages of Time Division Multiple Access (TDMA) and Frequency Hopping Spread Spectrum (FHSS), is adopted for anti-jamming and collision prevention. The packets of commands and data are delivered in a “bucket brigade”-like manner for optimum bandwidth utilization and low end-to-end latency. Correspondingly, we propose a novel time synchronization approach which is tightly coupled with TDMA scheme. As the non-determinism of timestamp is removed from the transmission path, the frequency difference between local clock and parent's clock is accurately estimated by periodically receiving beacons. The results show that our algorithm provides a hop-to-hop latency of 14 milliseconds and synchronization accuracy within 0.6 microseconds under an acceptable power consumption of 34.61 mW.