Long-range acoustic communication in deep water using a towed array: Beam diversity

Underwater acoustic communication typically involves vertical arrays that provide spatial diversity to mitigate channel fading and intersymbol interference when the array elements are well-separated. For closely-spaced arrays (e.g., one-half wavelength), an array gain is achieved by a beamforming process provided that the noise is uncorrelated while the signal is coherent across the array. A recent experiment (LRAC10) showed that coherent long-range acoustic communication (200-300 Hz) is feasible in deep water over ~550-km range between a source and a horizontal towed array (~100 m aperture). This paper demonstrates that beam diversity with a larger horizontal array (~200 m aperture) can be exploited to further improve the communication performance, achieving an error-free data rate of 50 bits/s for BPSK modulation at ~550-km range.