Impact of Very Shallow Underwater Channel on Performance of MFSK System

Abstract

The shallow water underwater acoustic channel can be expressed as a frequency selective fast fading channel due to multipath, sea surface roughness, propagation medium and so on change with time and space. In addition the nature of fading varies as communication frequency change for a given channel environment. Therefore the nature of fading changes with time, space, and frequency. The receiving signal amplitude varies with range from transmitter to receiver and therefore fading statistics also changes. Inherent factor of this fading change is a constructive or destructive interference. In this study, multipath, temporal coherence and fading statistics are analyzed using linear frequency modulation (LFM) and pseudo noise (PN) signals. Based on these results, the performance of non-coherent M-ary frequency-shift-keying (MFSK) system is examined and found that the underwater acoustic channel fading depends strongly on carrier frequency and transmitter to receiver range if there are strong coherent multipath and scattering.