Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Apr 20;17(4):909.
doi: 10.3390/s17040909.

Homomorphic Filtering for Improving Time Synchronization in Wireless Networks

José María Castillo-Secilla  1 , José Manuel Palomares  2 , Fernando León  3 , Joaquín Olivares  4
Affiliations

Homomorphic Filtering for Improving Time Synchronization in Wireless Networks

José María Castillo-Secilla et al. Sensors (Basel). .

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.

Keywords: 802.15.4; TelosB; TinyOS; WSN; clock skew; homomorphic filtering; oscillators; synchronization; temperature; tuning-fork.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Measured temperature at Node #2.
Figure 2
Figure 2
Comparative between skew cut, skew tempand correction factor without temperature variation.
Figure 3
Figure 3
Temperature for the real-world experiment.
Figure 4
Figure 4
Comparative skew cut using different window sizes (ranging from 4–256).
Figure 5
Figure 5
Comparative skew temp obtained from skew cut using different window sizes (ranging from 4–256).
Figure 6
Figure 6
Comparative between skew cut, skew temp and correction factor with temperature variation.
Figure 7
Figure 7
Obtained skewtemp compared to expected skewtemp.
Figure 8
Figure 8
Low temperature results. (a) Temperature variation. (b) Average synchronization error.
Figure 9
Figure 9
Medium temperature results. (a) Temperature variation. (b) Average synchronization error.
Figure 10
Figure 10
High temperature results. (a) Temperature variation. (b) Average synchronization error.
See this image and copyright information in PMC

References

    1. Buratti C., Conti A., Dardari D., Verdone R. An Overview on Wireless Sensor Networks Technology and Evolution. Sensors. 2009;9:6869–6896. doi: 10.3390/s90906869. - DOI - PMC - PubMed
    1. Akyildiz I., Melodia T., Chowdhury K. A survey on Wireless Multimedia Sensor Networks. Comput. Netw. 2007;51:236–255. doi: 10.1016/j.comnet.2006.10.002. - DOI
    1. Soro S., Heinzelmann W. A Survey of Visual Sensor Networks. Adv. Multimed. 2009;2009:1–21. doi: 10.1155/2009/640386. - DOI
    1. Atzoria L., Ierab A., Morabitoc G. The Internet of Things: A survey. Comput. Netw. 2010;54:2787–2805. doi: 10.1016/j.comnet.2010.05.010. - DOI
    1. Deshpande A., Guestrin C., Madden S.R., Hellerstein J.M., Hong W. Model-driven Data Acquisition in Sensor Networks; Proceedings of the Thirtieth International Conference on Very Large Data Bases—Volume 30. VLDB Endowment, (VLDB ’04); Toronto, ON, Canada. 31 August–3 September 2004; pp. 588–599.

LinkOut - more resources