Low complexity equalizer with iterative interference cancellation for OTFS underwater acoustic communications

Orthogonal Time–Frequency Space (OTFS) has emerged as a promising two-dimensional modulation technique that multiplexes information symbols in the delay-Doppler (DD) domain, demonstrating significant robustness in rapidly time-varying channels. In this paper, we propose a low-complexity equalizer with iterative interference cancellation (LC-IC) for OTFS-based underwater acoustic (UWA) communications. The proposed method employs a two-stage process: initial symbol estimation using the least-squares minimum residual (LSMR) algorithm, followed by iterative interference cancellation for symbol-wise refinement. Through reformulation of the interference cancellation process and efficient utilization of the LSMR algorithm, the proposed method achieves significant computational complexity reduction. Furthermore, the integration of soft estimation and decision-statistic combining (DSC) ensures rapid convergence and enhanced system performance. Extensive simulation and experimental results validate that the proposed LC-IC equalizer maintains excellent performance while substantially reducing computational complexity compared to conventional methods, making it particularly suitable for OTFS-based UWA communication systems. In a real-world UWA communication scenario with a communication distance of 1.5 km, error-free transmission is achieved at a data rate of 5.79 kbps.