This thesis report describes a wireless sensor network (WSN), which uses an acoustic distance measurement to determine the distance between the sensor nodes. The system uses the method known as TDOA (Time Difference of Arrival) for distance measurement. The principle of the operation is that a sensor node transmits an acoustic and radio signal at the same time, meanwhile an observer node measures the arrival time difference between these two signals.
The localization algorithm was implemented on Berkley micaz motes. Some software modules were also developed in MATLAB in order to control the operation of the sensor network and process the measurement data on PC.
Since the measurements are often perturbed by errors, special emphasize was put on the identification and elimination of the potential error sources as far as possible.
The measurements carried out on the system show that the distance measurement can be performed with precision 10 20 cm or better within the distance 1-2 m, and the precision degrades considerably above this distance. In this case, the system can be used to obtain qualitative information, e.g., whether a sensor node is in the vicinity of an other node or not.