Multicarrier Acoustic Communications in Multiuser and Interference-Limited Regimes

In this article, we address the design of a multicarrier communication system based on orthogonal frequency-division multiplexing and direct sequence spread spectrum. The design targets operation in the low-signal-to-noise-ratio regimes and multiuser settings. Specifically, coding is employed across carriers such that channel estimation and signal detection are coupled. We consider both coherent and differentially coherent detection and extend the principles to multichannel reception. A custom-designed frequency synchronization technique is proposed to counteract the motion-induced Doppler frequency shifting effect. Using the recordings from the 2010 Mobile Acoustic Communication Experiment, where signals were transmitted in the 10.5-15.5-kHz acoustic band in shallow water, with relative motion up to 1.5 m/s, we demonstrate the system performance in terms of the mean squared error and bit error rate in data detection. Further employing Polar and low-density parity-check coding, we show that the proposed methods provide excellent performance while maintaining low computational complexity, making them suitable for a practical implementation.