Underwater acoustic transmission of low-rate digital data

An acoustic data communication system capable of transmitting and receiving multiplexed low-rate digital information through water is described. Although the system presented was designed specifically for real-time monitoring of a free-swimming diver's physiology, the design could be adapted for many other applications of underwater monitoring and control. The Paper describes possible multiplexing methods and transmission formats, and presents the design of a frequency shift keyed (FSK) system capable of achieving reliable communications in the presence of echo signals.