Coherent communications performance in environments with strong multi‐pathing: Model/data comparison.

Coherent underwater communications is hampered by the time spread caused by multi‐pathing and the Doppler spread caused by the rapidly changing shallow water environment. In practice, a time‐varying impulse response model will retain only a finite number of paths as useful signal and will be updated to compensate for the changing environment at a finite rate. In the present study, communications performance is examined as a function of the number of retained paths and the model‐update interval. Results are quantified in terms of the mean squared error in the soft demodulation output. A physics‐based performance model is developed. The model uses as input acoustic quantities like the Rayleigh parameter and environmental quantities like the significant wave height and the dominant period for surface waves. Model predictions for performance are compared to experimental results for data collected near the Hawaiian Island of Kauai. [Work supported by ONR.]