Interference-Free Graph Based TDMA Protocol for Underwater Acoustic Sensor Networks

Underwater acoustic sensor networks (UW-ASNs) have been attracting more and more research interests recently due to their various promising applications. In this paper, we focus on the time division multiple access (TDMA) based media access control (MAC) protocol design for UW-ASNs in order to improve the network performance. Different from existing work, we consider a more general underwater communication scenario, where the communication network topology is modeled as a three-dimensional (3-D) scenario and the mobility of sensor nodes is also taken into consideration. We introduce a dynamic and flexible spatial reuse strategy for the TDMA protocol design, and formulate the interference scenario as a dynamic interference-free graph according to the nodes' current position distribution and a preset interference-free threshold. To achieve high spatial reuse efficiency, we propose two interference-free graph (IG) clustering algorithms, which lead to the optimal IG-TDMA protocol and the heuristic IG-TDMA protocol, respectively. The former can achieve the optimal network throughput but may not be feasible for high traffic networks due to its high computational complexity. The latter can achieve near-optimal network performance with much lower computational complexity and thus is more practical. Simulations verify the benefits of our proposed protocols in comparison with the CSMA/CA protocol and some existing TDMA protocols with and without spatial reuse.