Clock Synchronization with Deterministic Accuracy Guarantee

Accuracy is one of the most important performance metrics in clock synchronization. While state-of-the-art synchronization protocols achieve µsec-order average accuracy, they usually do not focus on the worst case accuracy and do not have any deterministic guarantees. This lack of accuracy guarantee makes it hard for sensor networks to be incorporated into larger systems that require more reliability than e.g., typical environmental monitoring applications do. In this paper, we present a clock synchronization algorithm with deterministic accuracy guarantee. A key observation is that the variability of oscillation frequency is much smaller in a single crystal than between different crystals. Our algorithm leverages this to achieve much tighter accuracy guarantee compared to the interval-based synchronization methods mostly proposed in the literature of distributed systems. We designed an algorithm to solve a geometric problem involving tangents to convex polygons, and implemented that in TinyOS. Experimental results show the deterministic error bound less than 9.2 clock ticks (280 µsec) on average at the first hop, which is close to the simulation results. Further, by a combination with previously proposed synchronization algorithms, it achieves the estimation error of 1.54 ticks at 10 hop distance, which is more than 40% better than FTSP, while giving deterministic error bounds.