Characterization and Modeling of Underwater Acoustic Communications Channels for Frequency-Shift-Keying Signals

In a fading channel, bit error rate for frequency-shift-keying signals is determined predominantly by the envelope amplitude fading statistics of the signal. The narrowband envelope amplitude distributions are measured from the TREX04 data (as a function of frequency) using M-sequence signals centered at 17 kHz with a 5 kHz bandwidth. The results do not fit the Rayleigh, Rician, Nakagami m-distributions. In contrast, we find that the data are fitted well by a K-distribution. We also analyze the data in terms of long-term and short-term statistics. The long-term and short-term fading statistics are well fitted by the lognormal distribution and Rayleigh distribution respectively, choosing the average time scale to be ~0.2 sec. The joint probability distribution function of a lognormal and the Rayleigh distribution is approximately the K-distribution