Better Clock Synchronization From Simultaneous Two Skew Estimations

Hisa-Aki Tanaka, Youjie Ouyang, Yoji Yabe, Isao Nishikawa, and Kazuki Nakada
Nonlinear Theory and Its Applications, IEICE Vol. 7, Oct.2016


clock synchronization, crystal oscillators, wireless sensor network, skew estimation, FTSP


An improvement for clock synchronization in wireless sensor networks (WSNs) is presented, which is obtained by analyzing a temporal frequency variation observed in internal clock circuits. Clock synchronization is an essential building component in WSNs for distributed sensing. Flooding time synchronization protocol (FTSP) is one of the highest-precision synchronization protocols for WSNs, which has been implemented on certain WSN testbeds. We carry out systematic experiments of FTSP with a Mica2Dot testbed to understand how synchronization precision is affected by a dynamic frequency variation in the clock circuit with a button battery. Our observations clarify that the following two elements are essential for better clock synchronization; (i) a short-term frequency variation in the clock circuit, and (ii) the resulting error in clock drift (i.e., skew) estimation from the linear regression in FTSP. Based on these findings, we propose a simplistic improvement for robust and more precise clock synchronization, utilizing two sets of simultaneous estimations of skew between sender and receiver nodes. Through systematic experiments and analysis, we confirm this improvement realizes a higher synchronization precision in a stable network environment, while it maintains robustness of time synchronization even in a worst case of unstable networks.

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