FLOPSYNC-QACS: quantization-aware clock synchronization for wireless sensor networks

The development of distributed real-time systems often relies on clock synchronization. However, achieving precise synchronization in the field of Wireless Sensor Networks (WSNs) is hampered by competing design challenges, such as energy consumption and cost constraints, e.g., in Internet of Things applications. For these reasons many WSN hardware platforms rely on a low frequency clock crystal to provide the local timebase. Although this solution is inexpensive and allows for a remarkably low energy consumption, it limits the resolution at which time can be measured. The FLOPSYNC synchronization scheme provides low-energy synchronization that takes into account the quartz crystal imperfections. The main limitation of the approach are the effects of quantization. In this paper we propose a clock synchronization scheme that explicitly takes into account quantization effects caused by low frequency clock crystal, thus addressing the clock synchronization issue in cost-sensitive WSN node platforms. The solution adopts switched control for minimizing the effect of quantization, with minimal overhead. We provide experimental evidence that the approach manages to reach a synchronization error of at most 1 clock tick in a real WSN.