Discrete multi-tone loading algorithms for underwater acoustic communication

Underwater acoustic (UWA) channel is characterized as a severe multipath propagation channel due to signal reflections from the surface and bottom of the sea, that is affected by a variety of ambient noise profiles unique to underwater environment. Further the motion of water introduces a Doppler. Multicarrier modulation schemes can be adapted to meet a given Quality of service (QoS) in such environments. In this paper the underwater acoustic channel is modelled using the Thorp and Ainslie-McColm models for absorption and their limitations are analyzed. Signal to noise ratio (SNR) profiles at various distances employing Discrete Multitone Modulation (DMT) are obtained considering different types of ambient noise sources such as shipping, wind, thermal, bubble and turbulence. To meet the QoS different Rate Adaptive and Margin Adaptive Tone loading algorithms are simulated and compared based on system margin, utilizing these SNR profiles.