Synthetic Undersea Acoustic Transmission Channels
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Achieving effective through-water acoustic digital signaling (telesonar) requires an ability to adaptively accommodate a complex and possibly time-varying acoustic channel. Variable combinations of noise, interference, multipath, and motion impair real-world telesonar channels. When considering any one of these factors individually, performance degradation may be predicted from theory. But the combination of these factors can confound our theoretical predictive capabilities. A computer simulation of the acoustic channel is useful for developing telesonar waveforms and modems. The simulation directly drives the modem receiver with a virtually propagated analog signal, enabling us to test the performance of the synthetic end-to-end telesonar link. We have observed a close correlation between simulation-based performance and observed performance in at-sea channels exhibiting similar characteristics. The fact that telesonar performance is now quite predictable in a wide variety of channels is due, in large measure, to the use of channel simulation. The simulation presented here does not rely on physical modeling of the channel. Rather, it is based on the combination of theoretical multipath models (e.g., a Rician channel) with rapidly time-varying impulse response functions, where the statistics are derived from at-sea experiments or governed by values derived from independent physics-based models (e.g., PC-SWAT, Bellhop, etc). Noise and other additive interference are combinations of theoretical and stored data, and range rate-induced compression and dilation are incorporated.
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