Graph colouring MAC protocol for underwater sensor networks

Employing contention-based MAC protocols in underwater sensor networks are typically costly. This is mainly due to the unique characteristics of its acoustic channels such as long propagation delay, high bit error rate, and limited bandwidth. As a consequence, handshake-based and random access-based MAC protocols do not perform as well as expected. The collision-free approach is therefore considered to achieve a better performance by efficiently addressing spatial-temporal uncertainty, hidden/exposed terminal problems, and near-far effect at MAC layer, thus collisions and retransmissions are properly avoided in order to reduce the energy cost and also to improve the throughput and fairness across the network. In this paper, we propose a novel energy-conserving and collision-free graph colouring MAC protocol, called GC-MAC, for UWSNs. It employs a TDMA-like principle by assigning separate time slots to every individual colour in the network. Nodes with the same colours can thus transmit concurrently without any collision. GC-MAC also does not require CDMA or power adjustment for collision resolution. Our extensive simulation study reveals that our proposed protocol can efficiently handle the traffic contention to achieve significant improvement in terms of throughput, energy consumption, and fairness index under varying offered loads.