Hydroacoustic communication channel capacity

Objectives. Capacity, describing the maximum rate of information transmission, is an important characteristic of any communication channel. The main purpose of this work isto determine the capacity of a hydroacoustic communication channel with constrained average intensity of the transmitted signal. An additional aim consists in finding the optimal spectrum of a transmitted signal and calculate its boundary frequencies. A model of a single-path channel was considered, which is characteristic of the deep sea with the receiver or transmitter placed at a sufficient depth.

Methods. Concepts of applied hydroacoustics, the theory of random processes, and information theory were used. 

Results. An expression for gain in a hydroacoustic communication channel has been obtained. A novel expression derived for the spectral level of sea noise caused by sea surface waves is based on piecewise linear approximation of the curves of the spectral levels of noise obtained from four sources: turbulence, shipping, sea waves, and the thermal noise of the sea. Dependencies of the hydroacoustic channel capacity on communication distance, intensity of the transmitted signal, and sea state, are characterized. The definition of the optimal spectrum itself is determined along with the lower and upper boundary frequencies of the optimal spectrum of the transmitted signal. The dependence of the bandwidth usage on the intensity of the input signal at various communication distances has been investigated.

Conclusions. On the basis of the Francois–Garrison attenuation coefficient, channel capacity was correlated with the parameters of the marine environment: temperature, salinity, and pH in the study area. At a given intensity of the input signal, channel capacity was shown to decrease significantly with increasing distance and sea wave intensity. It is also shown that the width of the optimal spectrum decreases with increasing distance. Sea wave noise was noted to affect significantly the shape of the optimal spectrum and its boundary frequencies. The possibility of cases where bandwidth usage increases with increasing distance at a given input signal intensity cannot be ruled out.

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