Adaptive control-based clock synchronization in wireless sensor networks

This paper presents PISync, a novel distributed synchronization algorithm based upon a Proportional-Integral (PI) controller for Wireless Sensor Networks (WSNs). PISync synchronizes each sensor node by applying a proportional feedback (P) and an integral feedback (I) on the relative synchronization error with respect to the received reference time which allow to simultaneously compensate both clock offset and frequency differences. We highlight the benefits of this approach in terms of improved steady state error and scalability as compared to least-squares based time synchronization, and we also propose an on-line adaptive strategy for the design of the integrator gain to further improve performance. We present practical flooding-based and fully-distributed protocol implementations of the PISync algorithm and show through real-world experiments that it has considerably better performance over FTSP, the de-facto time synchronization protocol in WSNs, in terms of both rate of convergence and steady-state error with the additional advantage of minimal resource requirement.