Underwater communication goes cognitive

Underwater acoustic channel is the most challenging channel in the world due to its time varying and frequency-selective characters. These facts obstruct the realization of most of intelligent and high bit rate underwater communication systems. Cognitive underwater communication systems build up rules of modulation method and receiver algorithm over time through learning from continuous experiential interactions with the underwater environment. Underwater acoustic channel can be proved to be a comb filter where passband and stopband appear alternately. The transmitter can intelligently chooses sub-channels whose SNR exceed a certain threshold which can be called as the passband of the channel to carry information and otherwise the stopband of the channel to carry little or null. But it also has some technical bottlenecks like the need of feedback channel. In future applications, Transform-domain communication system (TDCS) and blind receiver will be adopted to improve system performance.