Wideband monopulse spatial filtering for large receiver arrays for reverberant underwater communication channels
Underwater acoustic communication (ACOMMS) is critical for many applications including marine science, oceanographic exploration, offshore surveying/drilling, and military uses. ACOMMS data rates are usually limited by multiple propagation paths with different time delays and Doppler characteristics. It is often difficult to coherently recombine all paths, especially in shallow water, leaving incoherent paths that interfere with the receiver. One way to suppress unwanted paths is with a directional receiving array. Indeed, many existing large, directional acoustic arrays could be used as ACOMMS receivers. In a number of these arrays, wideband monopulse outputs could be made available. These directional beam outputs, in monopulse pairs, can selectively suppress, or even null, offending multipath when combined with a simple scalar weight. Using an experimental system, we show how a relatively short equalizer, using as inputs the wideband monopulse beam outputs of a large array, can form the backbone of an ACOMMS system that performs effectively in a multipath-limited environment. Our contributions include (i) a multipath-Doppler channel model validated by experimental results, (ii) a receiver design that utilizes monopulse processing, and (iii) an analysis of its performance using simulated and experimental data.