Noise cancelling performance of an adaptive receiver for underwater communications

Acoustic communication with autonomous underwater vehicles (AUVs) is complicated by the vehicles self-noise, particularly on AUVs with on-board active acoustic systems. Fortunately, active emissions generated on-board the AUV provide a convenient reference signal characterizing the self-noise. This paper addresses the use of such reference signals to improve the performance of acoustic communication systems. To this end, two methods of noise cancellation are examined both theoretically and experimentally. The first, called the cascade method, makes use of a conventional adaptive noise cancellation algorithm followed by a receiver with adaptive equalization. The second, called the noise cancellation method, involves a recently-proposed multi-channel adaptive receiver algorithm. It is shown that the multi-channel receiver can operate reliably in a signal-to-noise ratio of -3 dB or worse, a gain of about 10 dB over a conventional receiver for the codes and data-rates used. The cascade method, however, has a performance inferior to that of the multi-channel receiver due to adaptation noise.