Analysis of non-coherent signaling in surf zone acoustic telemetry experiments

This paper presents the statistical analysis of non-coherent signaling performance and the analysis of underwater acoustic channel characteristics from an experiment conducted in the surf zone. The purpose of this experiment was to develop a clear understanding of the ability of very shallow water and surf zone channels to support acoustic communications. The transmitted signal carried 512 bits of information in 530 channel symbols. Two non-coherent modulation techniques were used: a frequency-hopped M-ary frequency-shift keyed (FH/MFSK) and MFSK modulation. The FH/MFSK modulation technique provides a low data rate of 30 bits per second (bps) and the MFSK modulation technique provides a medium data rate of 300 bps. Channel probes including a pseudo-random broadband signal and a tonal probe were embedded in both types of transmitted signals to measure the impulse response and the spectral fading of the time-varying channels. Signals were continuously transmitted for 18 minutes every two hours and received by two hydrophones located at seaward and shoreward sites. The received signals were recorded on digital audiotapes along with time codes for post-analysis. The experiment was performed for several days over a wide range of environmental conditions and consequently provided extensive information on the correlation between signaling performance and channel characteristics