Direct-Adaptive Turbo Equalization Based on Interference Reconstruction for OTFS Underwater Acoustic Communication System

Orthogonal time frequency space (OTFS) modulation has recently gained recognition as a promising modulation scheme for high-mobility communication systems. It offers significant advantages in terms of error performance compared to orthogonal frequency division multiplexing in time-varying channels. In this article, we apply OTFS modulation to mobile underwater acoustic (UWA) communication. We propose an adaptive turbo equalization technique with a 2-D decision feedback equalizer to address the issue of 2-D interference. To mitigate the performance degradation caused by phase flipping and circular convolution in the delay-Doppler domain, we further propose a 2-D DA-TEQ based on interference reconstruction. An adaptive channel estimation based on the improved proportionate normalized least mean squares algorithm is proposed to reconstruct the interference. To validate the proposed OTFS UWA communication schemes, a lake experiment was conducted in Danjiangkou Lake, Henan, China, in July 2022. The experimental results demonstrate that the proposed scheme achieves satisfactory performance at a speed of 4.5 knots, with a data rate of 5.79 kbps. This experiment confirms the effectiveness of OTFS modulation for mobile UWA communication.