Better Clock Synchronization From Simultaneous Two Skew Estimations

Keyword

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

Abstract

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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References

1. M. Maroti, G. Simon, A. Ledeczi, and J. Sztipanovits, “Shooter localization in urban terrain,” IEEE Computer, vol. 37, no. 8, pp. 60-61, 2004.
2. J. Elson, L. Girod, and D. Estrin, “Fine-grained network time synchronization using reference broadcasts,” in Proc. 5th Symposium on Operating Systems Design and Implementation, pp. 147-163, 2002.
3. S. Ganeriwal, R. Kumar, and M.B. Srivastava, “Timing-sync protocol for sensor networks,” in Proc. 1st ACM Conference on Embedded Network Sensor Systems, pp. 138-149, 2003.
4. J.-H. Chiang and T. Chiueh, “Accurate clock synchronization for IEEE 802.11-based multi-hop wireless networks,” IEEE ICNP'09, pp. 11-20, 2009.
5. A.R. Swain and R.C. Hansdah, “A model for the classification and survey of clock synchronization protocols in WSNs,” Ad Hoc Networks, vol. 27, pp. 219-241, 2015.
6. M. Maroti, B. Kusy, G. Simon, and A. Ledeczi, “The flooding time synchronization protocol,” in Proc. 2nd ACM Conference on Embedded Networked Sensor Systems, pp. 39-49, 2004.
7. C. Lenzen, P. Sommer, and R. Wattenhofer, “PulseSync: an efficient and scalable clock synchronization protocol,” IEEE/ACM Transactions on Networking, vol. 23, no. 3, pp. 717-727, 2015.
8. H.-A. Tanaka, O. Masugata, D. Ohta, A. Hasegawa, and P. Davis, “Fast, self-adaptive timing-synchronization algorithm for 802.11 MANET,” IEE Electronics Letters, vol. 42, no. 16, pp. 932-934, 2006.
9. Crossbow Technology, Available at http://www.xbow.com/Products/ Product_pdf_files/Wireless_pdf/MICA2_Datasheet.pdf.
10. Z. Yang, L. Cai, Y. Liu, and J. Pan, “Environment-aware clock skew estimation and synchronization for wireless sensor networks,” in Proc. 2012 IEEE, INFOCOM, pp. 1017-1025, 2012.
11. J.M. Castillo-Secilla, J.M. Palomares, and J. Olivares, “Temperature-aware methodology for time synchronisation protocols in wireless sensor networks,” IEE Electronics Letters, vol. 49, no. 7, pp. 506-508, 2013.
12. Z. Yang, L. He, L. Cai, and J. Pan, “Temperature-assisted clock synchronization and self-calibration for sensor networks,” IEEE Trans. on Wireless Communications, vol. 13, no. 6, pp. 3419-3429, 2014.
13. K. Takano, M. Motoyoshi, and M. Fujishima, “4.8GHz CMOS frequency multiplier with subharmonic pulse-injection locking,” in Proc. 2007 IEEE Asian Solid-State Circuits Conf., pp. 336-339, 2007.
14. H.-A. Tanaka, A. Hasegawa, H. Mizuno, and T. Endoh, “Synchronizability of distributed clock oscillators,” IEEE Trans. on Circuits Syst. I, vol. 49, no. 9, pp. 1271-1278, 2002.