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.
Phase-coherent digital communications for underwater acoustic channels
Phasenkohärente digitale Kommunikation für akustische Unterwasserkanäle
IEEE Journal of Oceanic Engineering ; 19 , 1 ; 100-111
1994
12 Seiten, 17 Quellen
Article (Journal)
English
Schallempfänger , Digitalübertragung , Doppler-Effekt , Entzerrung , Intersymbolstörung , Methode der kleinsten Quadrate , Optimierung , PLL (Phasenregelkreis) , Unterwasserschall , Phasenumtastung , Diversity-Übertragung , Digitalsignal , Nachrichtenkanal , Unterwassernachrichtentechnik , kohärente Phasenumtastung , Synchronisierung , akustische Signalverarbeitung , Signalerkennung , Maximum-Likelihood-Schätzung , Flachwasser , Tiefsee
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