The high frequency underwater acoustic channel

Underwater acoustic communication systems usually operate at frequencies below 40 kHz, which have low absorption rates that in turn enable long link distances. These links suffer from channel effects including multi-path, fading and doppler. Cellular and multi-hop strategies have been proposed that would use shorter path lengths, so would tolerate much higher absorption rates, and hence could work at higher frequencies. The short-range, high-frequency channel is not well documented. This paper reports on initial measurements of the short-range, high-frequency underwater acoustic channel. Re-examining the basic theory indicates that the short-range high-frequency channel should not suffer from the same multi-path or fading issues as the longer-range lower-frequency channel in common use. Initial collected and processed field data supports this conclusion. The implication is that relatively simple modems should provide adequate performance on the high-frequency channel. Coupled with large available bandwidth, these high frequency modems should offer data communication rates well in excess of those generally available.