Homomorphic Filtering for Improving Time Synchronization in Wireless Networks

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.

ARS: Adaptive Robust Synchronization for Underground Coal Wireless Internet of Things

“…It explores the minimum number of synchronization messages by means of a smart clock update strategy with the requirement to keep low energy consumption. Castillo-Secilla et al, (2017) focused on improving time synchronization under deployments with temperature variations [ 18 ]. The clock skew of two nodes is composed of a multiplicative combination of two main components: the cut of the crystal of each oscillator and the different temperatures affecting the nodes.…”

GTSO: Global Trace Synchronization and Ordering Mechanism for Wireless Sensor Network Monitoring Platforms

“…On the other hand, in [ 21 ] another issue was detected: the clock rate is not always stable, even when a high quality clock source is used. The influence of environmental factors—for example the temperature—over clocks skew have been analyzed [ 16 , 22 ]. Figure 3 shows the scatter diagram of measured drifts of the clocks of four nodes with the same hardware for both low quality and high quality timing sources.…”

“…The time synchronization between nodes in a DS is a classical problem that has been widely studied. Internal clocks can suffer deviations due to hardware issues or environmental conditions such as temperature [ 16 ]. Mechanisms focused on nodes’ clocks synchronization may be applicable, however, this solution is not always the best.…”