Abstract
The use of tightly spaced orthogonal tones for communication through shallow water allows for diverse modulation strategies, from moderately efficient noncoherent on–off keying to fully coherent signaling. Critical to the effectiveness of orthogonal frequency division multiplexed (OFDM) schemes is the estimation of both source dilation, due to source–receiver relative motion, and the channel tranfer function. A dilation process estimator based on a spline model of dilation is presented and when coupled with decision directed channel estimation communication reliability is improved. The method is tested on OFDM signaling schemes at 18 kHz center frequency and 4 kHz bandwidth under diverse source motion scenarios and ranges during MREA(03) experiements off the north coast of Elba, Italy. Channel probing experiments characterize the environment in terms of coherence time, multi-path delay and angle spread. The quantitative effect of frequency selectivity and coherence time on the performance of OFDM signaling is addressed. Bit error rates are reported. [Work supported by ONR.]