Dispersive properties of the underwater acoustic channel

The underwater acoustic propagation channel is dispersive in time, frequency, and space. The channel connecting a sound source and receiver can be modeled as a finite set of sparsely distributed scatterers with fluctuating reflection parameters. This paper examines the fluctuation characteristics of the frequency selective fading in terms of the channel transfer function for a time spread channel with random path lengths. The first and second moments of the channel transfer function are determined. The effect of path length randomness on the first and second moments of the channel transfer function is clearly separated from the effect of the nominal multipath structure. The conditions under which the coherence bandwidth of the multi-path channel is a meaningful concept are examined. All of the results can be used for the mathematically dual problem of a frequency spread channel.