Modelling of a hydroacoustic modem for underwater communications

The paper discusses results of designing of an underwater communication device. The MSK modulation type is more preferable as it provides with narrow spectrum density of signals. The article describes a simulation program that allows one to model signal distortions and choose the best-fit method of detection. Three demodulation algorithms are tested. Simulation of signal propagating in underwater medium showed that the most effective is cross correlation detecting for which bit error rate was 5·10-4 at signal-to-noise ratio of 6 dB. Signal distortions were modelled with additive white noise, phase drift and superimposed re-reflections. For a piezoceramic antenna with a resonant frequency of 55 kHz and 6 kHz bandpass, the transmission frequencies of "0" and "1" are defined as 54 kHz and 56 kHz respectively, bitrate is 4000 bauds. During experimental testing in conditions of a natural reservoir all electronic devices demonstrated stability, the maximum range of reliable transmitting was 250 m.