Robust OTFS Detection via MMSE-DFE Equalization for ISAC in Doubly Dispersive Channels

This paper presents a detailed performance evaluation of a proposed Orthogonal Time Frequency Space (OTFS) system for Integrated Sensing and Communications (ISAC) in doubly dispersive wireless channels, characterized by both delay and Doppler spreads. The system is benchmarked against conventional Orthogonal Frequency Division Multiplexing (OFDM) schemes with Linear Minimum Mean Square Error (LMMSE) and Minimum Mean Square Error Decision Feedback Equalizer (MMSE-DFE) receivers. Through extensive simulations, the paper assesses Bit Error Rate (BER) and throughput performance under various Signal-to-Noise Ratios (SNRs), channel estimation error percentages, and multipath conditions. Results indicate that the proposed OTFS system is highly suitable for ISAC scenarios due to its delay-Doppler domain resilience and robustness to mobility, delivering superior BER performance, e.g., 1.25×10−5 at 20 dB SNR with 0% estimation error, compared to 1.10×10−3 for OFDM-LMMSE. It also sustains 64 Mbps throughput under ideal conditions, though it shows sensitivity under severe estimation errors and rich multipath. In contrast, OFDM with LMMSE demonstrates smaller performance variation, maintaining over 61 Mbps throughput even at 100% estimation error and 15 scattered path components. These results suggest that OTFS is an effective waveform for ISAC when accurate channel estimation is available, while the corresponding OFDM with MMSE-DFE remains a robust fallback in highly uncertain environments.