Abstract
The low-cost crystal oscillators in wireless sensor networks are prone to be affected by their working conditions such as voltage, temperature, and humidity. Such effect is often ignored by existing time synchronization solutions that typically assume the frequency error of a given node to be constant and hence adopt frequent timestamp exchanges, resulting in high energy consumptions. We propose a novel voltage-aware time synchronization (VATS) scheme that is inspired by the fact that the clock skew is highly correlated to voltage supplies. VATS features a two-phase process: (i) it first estimates the clock skew and updates the frequency error autonomously based on the local voltage level; (ii) it then adjusts the resynchronization intervals dynamically according to a given synchronization error controlling factor and the synchronization error accumulating rate to balance the calibration accuracy and cost. Since VATS leverages voltage measurements to assist clock skew estimation, it does not require frequent timestamp exchanges as in traditional schemes. Extensive simulation results illustrate the superior performance of the proposed method in terms of calculation accuracy, robustness, and reduced timestamp exchanges for energy saving.
Highlights
Time synchronization is one of the most fundamental and widely employed middle-ware services in wireless sensor networks (WSNs)
We have proposed a novel voltage-aware time synchronization (VATS) scheme for wireless sensor networks
The VATS scheme is based on the fact that clock skew is highly correlated to the voltage supply
Summary
Time synchronization is one of the most fundamental and widely employed middle-ware services in wireless sensor networks (WSNs). To address the above issues, an emerging type of solutions has been recently proposed which makes use of the environmental information as a common reference These schemes mainly focus on the estimation and compensation of clock skew, which is the inherent and dominant reason causing clock desynchronization. In TCTS [8], temperature is used to autonomously calibrate the local oscillator Both of these two schemes utilize the temperature information to autonomously calibrate the clock skew, which prolongs the resynchronization period without losing synchronization precision, reducing the energy consumption. A novel clock synchronization scheme called VATS is proposed, which allows network nodes to estimate the clock skew by referring to the current supply voltage of the node. (ii) Based on the observation of the skew-voltage experiment, we introduce a novel voltage-aware time synchronization scheme for autonomously skew estimation, which substantially improves the clock accuracy and reduces the energy consumption. The voltage data contain considerably lower noise than the environmental data measurement
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