Shallow-Water Acoustic Communications in Strong Multipath Propagation Conditions

A phenomenon that has a strong impact on signal transmission conditions in Underwater Acoustic Communication (UAC) systems is multipath propagation. As a result of multipath propagation, the transmitted signal undergoes time dispersion which results in inter-symbol interference observed on the receiving side. Time dispersion is large, especially in horizontal channels in shallow waters which significantly limits the transmission capabilities of UAC systems operating in these channels. In particularly difficult propagation conditions, such as observed in very shallow-water channel, it may be impossible to obtain reliable data transmission without using a matched filtering algorithm in the receiver. The paper presents the results of data transmission tests using three kinds of signals that require the matched filters in the receiver, namely: Direct-Sequence Spread Spectrum (DSSS) waveforms, Linear Frequency Modulated (LFM) waveforms, and Multi-LFM waveforms. The tests were performed with the use of impulse responses of the UAC channel measured during the experiment in a very shallow water in a configuration where the receiving transducer is located at the bottom of the reservoir.