This paper analyzes statistical characteristics of underwater acoustic channels estimated by ocean experimental data. The baseband complex channel impulse responses (CIRs) are estimated by a time-domain least square method with sliding windows applied to long probing sequences. The probability density functions (PDF) of the real part, imaginary part, magnitude, and phase of the CIR are evaluated, and the two-sample Kolmogorov-Smirnov test is used to measure fitness of the magnitude PDF to the Gamma, Rayleigh, and compound-K distributions. The second-order statistics of the channel are also investigated in terms of autocorrelation function, channel coherence time, and scattering function. The experimental results demonstrate that underwater channels are often worse than Rayleigh fading channels.
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