A robust digital communication system for doubly-spread underwater acoustic channels

The performance of underwater acoustic communication systems depends on the timeliness and accuracy of the estimate of the time-varying channel characteristics and the use of an effective algorithm to compensate for the distortion on the received signal caused by the channel. In a previous paper, the authors proposed estimating the characteristics of the doubly-spread underwater channel using a pilot tone in conjunction with a broadband PN pilot sequence and the channel estimate was optimised using an evolutionary algorithm. However, because of frequency selective fading due to multipath propagation, the pilot tone can be severely attenuated, causing unreliable channel estimates. To overcome this, diversity techniques are used here, wherein additional pilot tones are suitably placed to mitigate the frequency selective fading. As a result, both the channel estimates and the overall system performance are more reliable even for the more severe channel being considered here.