Spatial-Temporal Multipath Clusters Joint Equalization for Deep-Sea Acoustic Communication in Large Delay Spread Channels

For deep-sea underwater acoustic (UWA) communication, large multipath time delay spread, that caused by spatial divergence effects of acoustic propagation along the deep-sea distance-depth dimension, exert extremely adverse influence on communication performance. Inspired by the fact that the large delay spread deep-sea channels tend to be clustered, and each cluster of which varies independently with respect to receiving element as well as time delay, in this article a multipath clusters (MCs) joint equalization approach is proposed to explore the spatial-temporal diversity of large delay spread deep-sea UWA channels. First we design a compact m-sequence synchronization sequence to extract MCs along different receiving element and time delay while achieving frame synchronization. Then, a sparsity-aware proportionate-type adaptive iterative algorithm is formulated under the recursive least squares (RLS) framework, by which, equalization output of each spatial-temporal-wise MC is aligned and combined to achieve joint equalization gain. Simulation results demonstrate that the proposed approach is capable of yielding superior performance in terms of output signal-to-noise ratio (SNR) and bit error rate (BER) compared to the traditional equalization approaches under large delay spread channels. Finally, in deep-sea trial error-free UWA communication with a maximum data rate of 6000 bps at a distance of 20 km is achieved by a two-element receiver, further demonstrating the effectiveness of the proposed algorithm.