Accurate time synchronization of ultrasonic TOF measurements in IEEE 802.15.4 based wireless sensor networks

This paper discusses the problem of accurate time synchronization of wireless sensor networks (WSNs) used in applications in which a physical phenomenon must be monitored through periodical sampling. In some applications incorrect time synchronization can significantly degrade the system precision. This is for example the case of local positioning systems (LPSs) using ultrasonic time of flight (TOF) measurements for pseudorange estimation. The nodes clock drifts and the random variations of the start time used in each measurement are the two main error sources. In this work a Time Division Multiple Access (TDMA) synchronization algorithm is presented to overcome these problems for WSN using the IEEE 802.15.4 standard. The algorithm is able to compensate for the mentioned error sources in an easy and effective way. Experimental results for an implementation of an ultrasonic pseudorange measurement system between wireless nodes show the effectiveness of the proposed algorithm.