Sparse linear equalizers for turbo equalizations in underwater acoustic communication

Underwater acoustic channels are characterized by a time-varying multipath structure with a long delay spread. The multi path is usually very sparse. Direct-adaptation based turbo equalizer is a low-complexity and effective method to combat the inter-symbol interference caused by the time-varying multi path. This paper studies the determinations of the tap positions of the linear equalizers in the direct-adaptation multichannel turbo equalizer. A multiple threshold and retraining scheme is proposed to determine the sparse position of direct-adaptive equalizer in turbo equalization. The length of the training can be less than the number of the full taps. The performance of the proposed scheme is comparable to that of the scheme based on the orthogonal matching pursuit (OMP) algorithm, but much simpler. The proposed scheme is verified in the shallow ocean experiments at a distance of 5.3 km to transmit a bit rate of 4 bps.