Research on bandwidth efficient underwater acoustic communications

An important research area in underwater acoustic (UWA) communication is the development of bandwidth efficient modulation and demodulation techniques with low complexity. Over the past two decades, single carrier with time domain equalization (SC-TDE) and orthogonal frequency division multiplexing (OFDM) were used for high data rate underwater information transmission. The performance of high data rate SC-TDE system is severely limited by large spread inter-symbol interference (ISI) and sophisticated receiver algorithms with high complexity are required. OFDM based UWA communication systems exhibit two inherent shortcomings high peak to average power ratio (PAPR) and sensitivity to Doppler. Another difficult challenge on OFDM is the preservation of orthogonal subcarriers under relative high Doppler shift at acoustic wavelength. Our group conducted bandwidth efficient UWA communication research in the past several years, including SC-TDE and OFDM. Recently, we proposed single carrier with frequency domain equalization (SC-FDE) for bandwidth efficient UWA communication. The complexity of SC-FDE is comparable to that of OFDM while avoiding the drawbacks associated with OFDM and SC-TDE. In this paper, the achievements of three modulation techniques are presented, and their performances are compared.