Real-time redundancy allocation for time-varying underwater acoustic channels

In this paper, we jointly address reliability and spectral efficiency in underwater acoustic (UWA) communications by proposing optimal redundancy allocation over time-varying conditions in a communication link. To do so, we use recent results on tight approximation of codeword error probability in the finite block-length regime. First, we propose and evaluate an optimization framework. Then, we design a real-time algorithm, able to allocate the redundancy in a point-to-point link, without adding control messages. We evaluate the performance of the proposed algorithm by considering both rapidly and slowly time-varying experimental channel conditions. Finally, we compare the performance of our algorithm with that obtained with constant length codewords. Results show that the proposed redundancy allocation scheme is more efficient than constant allocation schemes under different channel conditions.