Multi-directional decision feedback equalization for orthogonal time frequency space underwater acoustic communication system

Orthogonal time frequency space (OTFS) modulation is widely recognized for its superior performance in time-varying channels, making it particularly effective in rapidly changing underwater acoustic (UWA) environments. This paper introduces a two-dimensional (2D) adaptive multichannel decision feedback equalization (DFE) technique with a multi-directional structure, specifically designed for OTFS-based UWA communication system. Two distinct multi-directional architectures are designed, each capitalizing on the 2D modulation characteristics of OTFS to mitigate error propagation across different directions, resulting in diverse error patterns and locations. The first architecture employs a parallel combination approach, consolidating outputs from multi-directional DFEs to enhance performance by exploiting the low correlation among different directional DFEs. Optimal weight factors for this multi-directional setup are derived. The second architecture adopts a serial approach, in which the outputs from other directional DFEs inform the symbol decision process of the current directional equalizer, thereby accelerating the convergence of the equalization process. Simulation and experimental results conducted in lake environments validate the efficacy of the proposed multi-directional 2D DFE algorithm. Comparative analyses reveal its significant outperformance over traditional 2D DFE methods, demonstrating superior symbol detection capabilities relative to other equalization strategies, especially under conditions characterized by limited pilot resources and channel estimation accuracy.