Adaptive and Efficient Nonlinear Channel Equalization for Underwater Acoustic Communication

TL;DR

This paper presents a hierarchical, adaptive nonlinear equalization method for underwater acoustic channels that significantly improves bit error rate performance while maintaining computational efficiency.

Contribution

It introduces a novel hierarchical, adaptive piecewise linear equalizer that learns the structure and adapts in real-time for challenging underwater channels.

Findings

Significant BER performance improvement over linear equalizers.

Efficient polynomial complexity adaptive algorithm.

Validated through realistic underwater acoustic channel simulations.

Abstract

We investigate underwater acoustic (UWA) channel equalization and introduce hierarchical and adaptive nonlinear channel equalization algorithms that are highly efficient and provide significantly improved bit error rate (BER) performance. Due to the high complexity of nonlinear equalizers and poor performance of linear ones, to equalize highly difficult underwater acoustic channels, we employ piecewise linear equalizers. However, in order to achieve the performance of the best piecewise linear model, we use a tree structure to hierarchically partition the space of the received signal. Furthermore, the equalization algorithm should be completely adaptive, since due to the highly non-stationary nature of the underwater medium, the optimal MSE equalizer as well as the best piecewise linear equalizer changes in time. To this end, we introduce an adaptive piecewise linear equalization algorithm that not only adapts the linear equalizer at each region but also learns the complete hierarchical structure with a computational complexity only polynomial in the number of nodes of the tree. Furthermore, our algorithm is constructed to directly minimize the final squared error without introducing any ad-hoc parameters. We demonstrate the performance of our algorithms through highly realistic experiments performed on accurately simulated underwater acoustic channels.