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ROBUST ACOUSTIC COMMUNICATIONS OVER DELAY-LIMITED UNDERWATER CHANNELS

Two coded modulation schemes with the same bit-rate and decoding complexity are designed and compared. The first scheme combines Trellis Coded Modulation (TCM), symbol interleaving, and orthogonal frequency-division multiplexing (OFDM). The second system combines bit-interleaved coded modulation (BICM), based on a convolutional code, with OFDM. Both systems are combined with a space-time block code (STBC) when three projectors are used at the transmitter. Testing the aforementioned systems using both simulated and experimental data during the Rescheduled Acoustic Communications Experiment (RACE‘08), the following result was obtained: coded modulation schemes emphasizing higher Hamming distance (e.g., BICM) yield a lower bit-error-rate (BER) when there is no option for many transmit and/or receive hydrophones. On the other hand, coded modulation schemes emphasizing higher free Euclidean distance (e.g., TCM) obtain a lower BER when many transmit and/or receive hydrophones are available.