Soft Direct-Adaptation Based Bidirectional Turbo Equalization for MIMO Underwater Acoustic Communications

摘要

This paper proposes a soft direct-ad-aptation based bidirectional turbo equalizer for multiple-input multiple-output underwater acoustic communication systems. Soft, rather than hard, direct-adaptation based equalizer combined with the fast self-optimized least mean square algorithm is employed to achieve a faster convergence rate, and the second-or-der phase-locked loop is embedded into the equalizer to track the time-varying channel. Meanwhile, by utilizing a weighted linear combining scheme, the conventional soft di-rect-adaptation based equalizer is combined with the time-reversed soft direct-adaptation based equalizer to exploit bidirectional diver-sity and mitigate error propagation. Both the simulation and experimental results demon-strate that the soft direct-adaptation based bidirectional turbo equalizer outperforms the single-direction soft direct-adaptation based turbo equalizer, and achieves a faster con-vergence rate than the hard direct-adaptation based bidirectional turbo equalizer.