Adaptive optimization of OFDM Underwater Acoustic communication parameters based on on-board channel simulations

Abstract

Self-configuration of modems is a key enabler to improve efficiency and robustness of digital communications in underwater channels. The aim of this work is to develop a method for the transmitter to automatically adapt its parameters based only on the information of the transmission geometry: transmitter/receiver depth, range, water depth and relative velocity. The modem uses a CP-OFDM waveform. We seek to optimize the number of subcarriers (Nsub) and cyclic-prefix length (TCP) that should be used, given some constraints on the overhead induced by TCP. Based on the transmission geometry, the proposed method runs an on-board wideband ray-tracer to predict the power-delay profile, and a maximum-entropy based model to generate a Doppler power spectrum. The outputs of this simulated channel are then used to predict the interblock-interference and intercarrier-interference expected at reception for each pair (Nsub , TCP). The optimal pair is the one that minimizes the total predicted interference. Performance of the proposed approach is tested in shallow-water environments using Watermak simulator. In this scenario, the OFDM parameters of our optimization method match most of parameter pairs that minimize the bit-error-rate. The benefit of the proposed approach is to provide adaptive waveform optimization having only the knowledge of channel geometry.