Inventors: Shengli Zhou, Baosheng Li, Peter Willett, Milica Stojanovic, and Lee Freitag
Publication No. US7859944 B2
Overview: Underwater acoustic (UWA) communication (the sending and receiving of acoustic signals underwater) is an inherently difficult and complex process. The unique characteristics of water as a propagation medium contribute to the problematic nature of UWA communication. Thus, due to factors like multi-path propagation, time variations of the channel, it is necessary to account for, inter alia, small available bandwidth and strong signal attenuation. Moreover, slow propagation speeds associated with acoustic signals lead to significant Doppler shifts and spreading. Thus, UWA communication systems are often times limited by reverberation and time variability beyond the capability of receiver algorithms.
Technology: The Multi-Carrier Underwater Acoustic Communication System uses a two-step approach to mitigate frequency-dependent Doppler drifts for zero-padded OFDM transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling to convert a “wideband” problem into a “narrowband” problem; and (2) high-resolution uniform compensation on the residual Doppler. The system is based on block-by-block processing and does not rely on channel dependence across OFDM blocks. Thus, the system is applicable for fast-varying UWA channels.