A Distributed TDMA Scheduling Algorithm for Target Tracking in Ultrasonic Sensor Networks

Ultrasonic sensors are able to provide highly accurate measurements if they are properly scheduled, otherwise, the intersensor interference (ISI) could greatly deteriorate the performance. In addition, the scheduling scheme should be performed in a distributed and energy-efficient way so that it can be conveniently implemented for a large-scale network. In this paper, for target tracking with multiple ultrasonic sensors, we convert the ISI avoidance problem to the problem of multiple access in a shared channel and adopt the time division multiple access strategy which has the properties of being collision free and energy efficient. Then, by graph theory, the scheduling problem is transformed into a coloring problem which aims at minimizing the number of used colors. Since the original problem has been proved to be NP-hard, we propose a distributed-saturation-degree-based algorithm (DSDA) which can be implemented locally by each node with information collected from its neighbors. Furthermore, we verify that an interference-free schedule is guaranteed to be obtained by DSDA. We derive analytical results for the complexity of this algorithm. Specifically, for different sensor network topologies, we prove that the expected converging time and the expected message transmissions per node are both upper bounded by O(δ), where δ is the maximum neighborhood size in the network. Extensive simulations demonstrate the effectiveness of our algorithm.