Development of a Physical Layer for Adaptive Underwater Acoustic Communications

For underwater acoustic modems to operate in a time-varying environment, in-mission adaptation is desirable. A physical layer has been designed that supports mechanisms for ad-hoc configuration changes based on (in-situ and indirectly obtained) channel and noise conditions. Coded preambles are used to instruct the receiver of a configuration change. To support indirect link feedback, a fixed bit-allocation scheme is proposed that provides a field for link quality information. Performance of the coded preambles versus payload delivery are studied in replay simulation. Eventually, thresholds for rate switching based on indirect link feedback of the output SNR are presented.