MSER-Based Two-Dimensional Adaptive Multi-Branch Joint Sparse Equalization for OTFS Underwater Acoustic Communication

To more effectively suppress inter-Doppler interference (IDI) and inter-symbol interference (ISI), this paper first proposes a two-dimensional (2D) adaptive multi-branch sparse equalization algorithm based on the minimum symbol error rate criterion (TAMSE-MSER) for orthogonal time frequency space (OTFS) underwater acoustic (UWA) communication. Compared to existing methods, the TAMSE-MSER is designed based on the MSER criterion and incorporates a sparse-aware proportional update mechanism. This design can effectively enhance reliability while significantly improving the convergence rate in sparse channels. Furthermore, to address the impact of channel quality differences among branches, an MSER-based 2D adaptive multi-branch joint sparse equalization algorithm (TAMJSE-MSER) is proposed. Unlike the TAMSE-MSER, the weighted coefficient for each branch output is introduced into the TAMJSE-MSER. The TAMJSE-MSER not only enables joint adjustment of the tap coefficient vector (TCV) and the weighted coefficient vector (WCV), but also adaptively adjusts the weighted coefficient according to the corresponding channel quality without requiring channel estimation. Simulation results demonstrate that the proposed TAMSE-MSER outperforms existing approaches in terms of convergence, bit error rate (BER), and output signal-to-noise ratio (SNR) performance. Moreover, the simulation results also validate the effectiveness and feasibility of the TAMJSE-MSER, and demonstrate further improvement in its overall performance compared to the TAMSE-MSER.