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.
Highlights
IntroductionThe rapid growth of Wireless Sensor Networks (WSN) is leading to numerous research projects [1]
The rapid growth of Wireless Sensor Networks (WSN) is leading to numerous research projects [1].Their increase involves the development of wireless embedded devices, communication technologies and distributed computing
The above-mentioned results have empirically demonstrated that clock skew is: (i) a multiplicative combination of, at least, two components; (ii) the skewcut shows a very stable behavior without any response to temperature variation; (iii) the skewtemp is highly correlated with any change in temperature; it includes all of the effects of temperature; and (iv) the proposed multiplication factor works instantly, helping the skew to reach the correct value faster than using skewtemp
Summary
The rapid growth of Wireless Sensor Networks (WSN) is leading to numerous research projects [1]. Their increase involves the development of wireless embedded devices, communication technologies and distributed computing. This work focuses on the challenge represented by distributed sensors, which triggers the need for synchronization schemes among the embedded devices that form the entire network. One specific field of application is Wireless Multimedia Sensor Networks (WMSNs) [2]. The availability of low-cost hardware, such as cameras and microphones, has fostered the range of applications suitable to use in WMSNs. Among the concept of WMSNs emerge the Visual Sensor Networks (VSNs)
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