Adaptive Error-Correction Coding Scheme for Underwater Acoustic Communication Networks

Underwater acoustic communication networks (UWANs) have recently attracted much attention in the research community. Two properties that set UWANs apart from most radio-frequency wireless communication networks are the long propagation delay and the possible sparsity of the network topology. This in turn offers opportunities to optimize throughput through time and spatial reuse. In this paper, we propose a new adaptive coding method to realize the former. We consider time-slotted scheduling protocols, which are a popular solution for contention-free and interference-free access in small-scale UWANs, and exploit the surplus guard time that occurs for individual links for improving transmission reliability. In particular, using link distances as side information, transmitters utilize the available portion of the time slot to adapt their code rate and increase reliability. Since increased reliability trades off with energy consumption per transmission, we optimize the code rate for best tradeoff, considering both single and multiple packet transmission using the incremental redundancy hybrid automatic repeat request (IR-HARQ) protocol. For practical implementation of this adaptive coding scheme, we consider punctured and rateless codes. Simulation results demonstrate the gains achieved by our coding scheme over fixed-rate error-correction codes in terms of both throughput and consumption of transmitted energy per successfully delivered packet. We also report results from a sea trial conducted at the Haifa harbor, which corroborate the simulations.