Phase-coherent digital communications for underwater acoustic channels

• Published in: IEEE journal of oceanic engineering 1994-01, Vol.19 (1), p.100-111
• Main Authors: Stojanovic, M., Catipovic, J.A., Proakis, J.G.
• Format: Article
• Language: English
• Subjects: Adaptive algorithm; Decision feedback equalizers; Delay; Digital communication; Earth, ocean, space; Exact sciences and technology; External geophysics; Fluctuations; Intersymbol interference; Least squares methods; Marine; Marine optics and underwater sound; Oceans; Physics of the oceans; Underwater acoustics; Underwater communication; Underwater sound
• ISSN: 0364-9059; 1558-1691
• DOI: 10.1109/48.289455

High-speed phase coherent communications in the ocean channel are made difficult by the combined effects of large Doppler fluctuations and extended, time-varying multipath. In order to account for these effects, we consider a receiver which performs optimal phase synchronization and channel equalization jointly. Since the intersymbol interference in some underwater acoustic channels spans several tens of symbol intervals, making the optimal maximum-likelihood receiver unacceptably complex, we use a suboptimal, but low complexity, decision feedback equalizer. The mean squared error multiparameter optimization results in an adaptive algorithm which is a combination of recursive least squares and second-order digital phase and delay-locked loops. The use of a fractionally spaced equalizer eliminates the need for explicit symbol delay tracking. The proposed algorithm is applied to experimental data from three types of underwater acoustic channels: long-range deep water, long-range shallow water, and short-range shallow water channels. The modulation techniques used are 4- and 8-PSK. The results indicate the feasibility of achieving power-efficient communications in these channels and demonstrate the ability to coherently combine multiple arrivals, thus exploiting the diversity inherent in multipath propagation.< >