Novel equalizer for shallow water acoustic communications

pp. 185-190, vol. 3, 2000

Y-h. Yoon
University of Victoria, Victoria, Canada

Adam Zielinski
University of Victoria, Victoria, Canada

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Abstract: The signal transmitted through an underwater acoustic channel is corrupted by multipath propagation caused by surface and bottom reflections. This delay spread causes intersymbol interference (ISI). The surface waves produced by wind affect the signal delay spread at the receiver. The delay spread is large for a calm sea and decreases with rough sea agitated by winds. To compensate for distortion introduced by the multipath channel, adaptive equalizers have been utilized to improve the performance of a communication system. These equalizers have been designed to handle the worst case of a signal delay spread condition associated with a calm sea and have a suitable and fixed number of taps. However, it is known that the power consumed by the processor increases with the number of computations performed per time unit. In this paper, we propose a novel equalizer with a variable number of taps which adaptively changes depending on channel conditions in order to conserve power. The proposed equalizer was tested by computer simulations using a model of an underwater acoustic channel. Results indicate savings in computational load up to 54% for a selected case. Power savings were also obtained when a directional receiver is used together with the proposed equalizer. Lower power consumption is particularly desirable for battery operated systems.

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