Experimental study of the space-time properties of acoustic channels for underwater communications

In this paper, we present an analysis of the space-time correlation and power-delay profile (PDP) properties of the underwater acoustic channel in the nearabouts of the Pianosa Island, off the north-western coast of Italy. Our data has been collected during sea trials which took place from May to September 2009. Using the results from this evaluation, we compare the measured bit error rates affecting the transmission of Frequency-Hopping Binary Frequency Shift Keying (FH-BFSK) against those obtained by simulating the same digital modulation scheme over synthesized channels whose spread in time has the same statistical properties as those found in the trials, and whose channel taps are Rayleigh-distributed. The results show a generally good accordance of the simulated performance with the outcomes of the experiments. Moreover, given the absence of a widely agreed upon underwater channel model, and the recent interest in incorporating more accurate propagation simulators into network simulators, we compare the measured channel impulse responses against those obtained through the ray tracing tool Bellhop, and give some observations about the suitability of the tool for the purpose of reproducing realistic channel traces.