Adaptive Decision Feedback Equalization for Underwater Acoustic OTFS System with Superposition Pilot

Orthogonal time-frequency-space (OTFS) modulation transforms the time-varying channel into the delay-Doppler domain, and the fading coefficient of the channel in the delay-Doppler domain is near constant. OTFS modulation realizes the quantized representation of the channel in the delay dimension and the Doppler dimension, and the system has the good performance of anti-multipath effect and anti-Doppler expansion. Therefore, we extend the two-dimensional decision feedback equalization (2D-DFE) to the OTFS system, and propose a 2D adaptive multichannel DFE for OTFS system with superposition pilot (SP). Based on the superior performance of the algorithm, this paper applies the method to underwater acoustic (UWA) communications to deal with UWA channel with large delay and large Doppler. At the same time, the sparse nature of the delay-Doppler domain channel is exploited to achieve fast convergence and fast tracking using the normalized least mean square (NLMS) algorithm. Simulation results show that the proposed equalizer could achieve more satisfactory BER performance and improve the band utilization.