Achieving maximum space‐time‐frequency diversity in shallow water acoustic channels: System design and experimental results.

Abstract

This work sheds light on the individual impact of coded modulation and diversity in achieving reliable underwater acoustic (UWA) communications. Two systems with the same bit‐rate and complexity but different diversity order are designed and compared. The “conventional” system combines trellis coded modulation (TCM), symbol interleaving and an 8PSK signal set. The “alternative” or bit‐interleaved coded modulation (BICM) system combines a convolutional code, bit interleaving, and a 16QAM signal set. Both systems are coupled with orthogonal frequency division multiplexing (OFDM) to cope with the intersymbol interference (ISI). When two or three projectors are used, the above coding schemes are concatenated with space‐time block codes (STBC). Bit‐error rates using data recorded during the RACE’08 off the coast of Narragansett, USA are computed demonstrating the superiority of BICM schemes relative to their TCM counterparts over an extensive collection of shallow water channels, thus proving that BICM is a promising technique towards achieving reliable UWA communications. In particular, by using BICM and 4 kHz of bandwidth, we have successfully accomplished a 7150 b/s transmission rate over 1 km range.