Linear Estimation of Clock Frequency Offset for Time Synchronization Based on Overhearing in Wireless Sensor Networks

The overhearing mechanism in time synchronization has been an active research area for wireless sensor networks (WSNs), for it can save a significant amount of energy by exploiting the wireless medium broadcast property. Recently, based on acknowledgment (ACK) mechanism, a synchronization scheme has been proposed for practical WSNs that the timestamps can be directly inserted into the data frame and the corresponding ACK, instead of dedicated synchronization packet. Consequently, the overhead of time synchronization could be further reduced. Motivated by this, in this letter, we analyze the synchronization of inactive nodes overhearing the pairwise synchronization on the basis of ACK mechanism, and present a linear estimation algorithm of clock frequency offset with the nodes' clock adjusted at every synchronization. Furthermore, assuming Gaussian delays, the linear estimation for frequency offset and the corresponding Cramer-Rao lower bound are derived. Simulation results verify that the estimator is efficient.