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.