Measured channel characteristics and the corresponding performance of an underwater acoustic communication system using parametric transduction

The authors present the results of experiments carried out in the Mediterranean Sea using parametric sonar to establish underwater acoustic communication. Short duration, pulsed carrier signals were used to estimate the impulse response of the channel and these observations were related to the performance of a parametric communication system operating under the same conditions. The statistical characteristics and spectra of the amplitude and phase fluctuations were used to analyse the pulsed response over short observation periods. Two distinctive types of channels were encountered during the experiment: one characterised by highly fluctuating multipath, the other predominantly a single path. Typically, the amplitude fluctuations experienced by the main path were Rician in nature with a spectral content in the sub-Hertz range, whilst the phase fluctuations tended towards more Gaussian-like behaviour with a comparable frequency spectrum. Under these conditions a high data rate differential phase shift keyed (DPSK) telemetry link was established over a 1.7 km path. The ensuing performance of the communication system, characterised by the bit error rate for various symbol rates, is presented and demonstrates the viability of a parametric telemetry system