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The performance of coherent acoustic communication systems involving moving platforms (e.g., underwater vehicles and ships) is adversely effected by Doppler shift resulting from relative motion of the transmitter and receiver. This paper presents a series of innovations which, together, dramatically improve the response to Doppler shift of a widely-used adaptive receiver algorithm. The innovations include a frequency-shift estimator, time-scale interpolator and robust phase-locked loop (PLL). These techniques reduce the computational load of the coherent equalizer and provide accurate Doppler tracking. Results from at-sea testing are presented to illustrate the performance of the combined algorithm.

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