A Novel Iterative OTFS Detector Based on Local L-MMSE and Global Message Passing

Orthogonal time frequency space (OTFS) modulation has attracted significant attention due to its robust performance over high-mobility channels. However, conventional detectors, like linear equalizers and message passing (MP), suffer from noise enhancement or fail in complex doubly-selective channels. We propose a hybrid iterative detection framework combining linear minimum mean square error (L-MMSE) estimation with MP. A key novelty is the delay-Doppler commutation precoder (DDCP), which structures the effective channel into sparsely interconnected, locally dense blocks. This enables a hybrid strategy: low-dimensional L-MMSE handles intra-block interference locally, while MP handles sparse inter-block connections globally. The proposed scheme achieves near-optimal error performance with low complexity.