Iterative Block Detection for Non-Cyclic-Prefix SEFDM-based OTFS

Orthogonal time frequency space (OTFS) modulation has attracted considerable attention for its reliable communication over doubly selective channels. However, improving spectral efficiency (SE) remains a key challenge due to redundant reference signals and guard intervals. To enhance the SE of OTFS, in this paper, a novel spectrally efficient frequency division multiplexing (SEFDM)-based OTFS system is proposed by compressing the subcarrier spacing in the time-frequency domain. From the perspectives of non-orthogonality-induced interference and noise characteristics, we establish the superiority of time-domain detection over delay-Doppler (DD) domain detection. Based on this, we first introduce an time-domain iterative block detection algorithm for cyclic prefix (CP) SEFDM-based OTFS, which partitions the detection problem to further mitigate the ill-conditioning inherent in SEFDM modulation. To further improve the SE, a novel low-complexity iterative block detection scheme for non-cyclic-prefix (NCP) SEFDM-based OTFS is proposed. Simulation results show that time-domain detection outperforms DD-domain detection. Furthermore, the proposed low-complexity NCP SEFDM-OTFS system achieves up to 56% SE improvement with only a 1.5 dB BER loss relative to standard CP-OTFS.