Performance of high-rate adaptive equalization on a shallow water acoustic channela)

Multipath propagation in underwater acoustic channels causes intersymbol interference in the transmission of digital communication signals. An increase of the transmission rate on a multipath channel results in longer intersymbol interference, which ultimately limits the performance of a phase-coherent digital communication system. Recent experimental results, however, show a seemingly surprising result: an increase in transmission rate resulted in improved system performance. An explanation for this phenomenon is found in the time variation of the ocean multipath. In strongly fluctuating shallow water channels, higher transmission rates allow for more frequent sampling of the rapidly varying channel, thus resulting in a better tracking capability of the receiver. Experimental results obtained in shallow water show a substantial improvement in performance of QPSK coherent detection over a 1-mile range, as the data rate is increased from 5 to 20 kilobits per second. A theoretical analysis based on stochastic channel modeling supports the experimental observations. © 1996 Acoustical Society of America.