High-rate Phase Coherent Acoustic Communication: a Review of a Decade O F Research and a Perspective on Future Challenges

Slightly more than 10 years ago the Woods Hole Oceanographic Institution and Northeastern University published a new algorithm for multi-channel adaptive equalization along with results of using that algorithm to successfully decode long-range, high-rate, acoustic communication transmissions. In the years since the authors have built on this foundation to improve and adapt the core algorithm for different acoustic environments and applications, incorpo rating Doppler compensation, selectable filter update algorithms, and error-correction capability. The resulting structures are used as the core for receivers operating in a multi-user environment, and for reception of multiple, simultaneous data streams in a MIMO environment. Significant challenges remain, in particular, selection of equalizer parameters (for example, the number of filter taps) based on acoustic channel conditions to optimize receiver performance in a time-varying environment. New approach es to receivers include channel estimation with the goal of both faster adaptation and receiver parameter self-optimization.