Single carrier frequency domain equalizer for underwater wireless communication

Single carrier modulation with frequency domain equalizer is proposed for underwater acoustic channel. An unique training sequence, viewed as cyclic prefix, is inserted into transmitted sequences so that low complexity minimum mean square error (MMSE) frequency domain equalization (FDE) is used for combating the inter-symbol interference in the receivers. Maximum likelihood estimation for robust initial phase error and Doppler shift are derived by using training sequence. The receiver estimates the initial phase error, Doppler shift and underwater acoustic channel block-by-block. Compare to zero padding or cyclic prefix of single carrier modulation, training sequence has the potential to provide more accurate estimation than decision-directed methods and alleviate the time-scale effect caused by significant Doppler shift for wideband acoustic signal. The proposed UWA communication system with single transmitter and single receiver has been tested in practical South China Sea on June 2007. At a distance of 30 km, the data rates of 450 bps and 900 bps are achieved with uncoded bit error rates of 4 out of 8333 (BPSK) and 103 out of 16666 (QPSK).