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Sensors 2017, 17(4), 909; doi:10.3390/s17040909

Homomorphic Filtering for Improving Time Synchronization in Wireless Networks

1
Department of Computer Technology, University of Alicante, Carretera San Vicente del Raspeig, S/N, 03690 Alicante, Spain
2
Department of Computer Architecture, Electronics and Electronic Technology, Universidad de Córdoba, Campus de Rabanales, 14001 Córdoba, Spain
3
PRINIA Research Group, Universidad de Córdoba, Campus de Rabanales, 14001 Córdoba, Spain
*
Author to whom correspondence should be addressed.
Received: 31 January 2017 / Revised: 17 April 2017 / Accepted: 18 April 2017 / Published: 20 April 2017
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2016)
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Abstract

Wireless sensor networks are used to sample the environment in a distributed way. Therefore, it is mandatory for all of the measurements to be tightly synchronized in order to guarantee that every sensor is sampling the environment at the exact same instant of time. The synchronization drift gets bigger in environments suffering from temperature variations. Thus, this work is focused on improving time synchronization under deployments with temperature variations. The working hypothesis demonstrated in this work is that the clock skew of two nodes (the ratio of the real frequencies of the oscillators) is composed of a multiplicative combination of two main components: the clock skew due to the variations between the cut of the crystal of each oscillator and the clock skew due to the different temperatures affecting the nodes. By applying a nonlinear filtering, the homomorphic filtering, both components are separated in an effective way. A correction factor based on temperature, which can be applied to any synchronization protocol, is proposed. For testing it, an improvement of the FTSP synchronization protocol has been developed and physically tested under temperature variation scenarios using TelosB motes flashed with the IEEE 802.15.4 implementation supplied by TinyOS. View Full-Text
Keywords: clock skew; WSN; synchronization; temperature; oscillators; tuning-fork; homomorphic filtering; TelosB; 802.15.4; TinyOS clock skew; WSN; synchronization; temperature; oscillators; tuning-fork; homomorphic filtering; TelosB; 802.15.4; TinyOS
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Castillo-Secilla, J.M.; Palomares, J.M.; León, F.; Olivares, J. Homomorphic Filtering for Improving Time Synchronization in Wireless Networks. Sensors 2017, 17, 909.

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