Statistical characteristics of sound channel in shallow water

Abstract

In shallow water under the influence of sea bottom and complicated construction of sound speed profile on sound signal propagation, the system characteristics of channel appear strong time-frequency varied characteristics. In this paper several very efficient measuring methods for obtaining the channel characteristics are developed. For example, a method called pulse-to-pulse correlation is used for measuring long time time-variation characteristics of the sound channel, a linear frequency modulated signal, and a pseudo-random coded signal are used for measuring channel system functions as a response function, transfer function, and scattering function. Among these functions, the scattering function is more important from the point of view of the channel match in under water acoustic signal processing. In this paper, the statistical study of measured scattering functions shows that shallow water sound channel meets the requirement of WSSUS (wide sense stationary uncorrelation scattering) channel. In the case of multipath channel, if the difference of time delays among paths is over the time duration of the code chip, an intersymbol interference will occur. To overcome the ISI a quite simple coherent accumulation of different arriving paths is realized. In the case of shallow water acoustic communication the coherent accumulation shows its efficiency obviously.