Detection of millimeter movements using ultrasonic ranging and precise time synchronization in wireless sensor networks

In this work, we present a wireless sensor network platform that detects two-dimensional movements with sub-millimeter accuracy in a controlled environment. This was achieved through the use of omnidirectional ultrasonic ranging, cross-correlation of ultrasonic pulses, and precise time synchronization between sensor nodes. The synchronization protocol is based on IEEE 1588, and was adapted for implementation in a wireless sensor network. Experiment results show that the sensor nodes can maintain a worst-case synchronization error of 1μs relative to the reference clock. This enables the system to detect movements with sub-millimeter accuracy, at initial distances of up to one meter between sensor nodes.