Measurements and modeling comparisons of underwater communications performance at three shallow-water sites

Large differences in performance of underwater acoustic communications were found when looking at results from three shallow water sites. Using acoustic modeling, these channel responses are simulated and communications performance predictions are made. Ray based modeling is used to determine the mechanisms in the environment causing differences in bit error rates. Experimental results for the non-coherent Multi-Frequency Shift Keying (MFSK) signaling method showed better performance in very shallow water (about 5 m) with a lossy seabed compared to deeper water (about 80-150 m) with a more reflective seabed. The modeling shows that while interfering multi-path is an important mechanism for bit errors in the deeper water sites, the performance at the shallow water site depends mainly on the surface roughness, volume attenuation and ambient noise level. In this paper, simple acoustic modeling is used to capture the most important channel characteristics. The emphasis is on modeling the mulitpath arrival pattern and on the comparison between modeled and measured communications performance.