Multipath-cluster-wise joint equalization method for long-range deep-sea single-element underwater acoustic communication

By exploiting the multipath characteristics of long inter-cluster time delay and simple intra-cluster structure in long-range deep-sea underwater acoustic (UWA) channels, a low-complexity multipath-cluster-wise (MCW) joint equalization method is proposed for long-range deep-sea single-element UWA communications. Firstly, an m sequence is inserted into the data frame without guard time to detect sparse multipath clusters and achieve frame synchronization. Secondly, a low-complexity sparse equalizer based on the proportionate fast a posteriori error sequential technique (PFAEST) is designed for each multipath cluster signal, soft demodulation output of which is then time delay-aligned for maximum ratio combining (MRC) combination according to the time delay of each multipath cluster. Finally, the channel decoder is adopted to further improve performance. Compared with the traditional equalization approaches, the proposed method decomposes the equalization process into several multi-path-cluster-wise joint equalizers corresponding to each multipath cluster. Multipath cluster diversity gain is exploited to enable low-complexity equalization that further incorporates Polar channel coding to enhance demodulation performance. Simulation and deep-sea experiment results show that the proposed method exhibits significantly improvement in terms of output and bit error rate compared to the single-element and two-element conventional equalization approaches. Specifically, the error-free communication performance with a data rate of 4000 bit/s at a distance of 30 km is achieved. The above results show that the proposed MCW joint equalization method is capable of being applied for long-range deep-sea single-element UWA communications.