Ultrawideband Underwater Acoustic Communication Channels

Traditional channel models for communications research are designed for narrowband systems. Underwater acoustic communication systems use a bandwidth that is not small compared with the center frequency of the signal and qualify as ultrawideband (UWB) in a relative sense. In this paper, measurements and analysis of acoustic propagation effects demonstrate the shortcomings of narrowband channel models. These effects are frequency-dependent fluctuation rates and frequency-dependent attenuation, where the frequency dependence of the attenuation differs between paths. This frequency selectivity of the medium violates the assumption of uncorrelated taps and requires a UWB channel model. It is also shown that correlative channel sounders preserve wideband properties, which renders them suitable for UWB channel simulation based on the principle of direct replay.