SIC-Based UAMP Detection for MIMO-OTFS Under Fractional Delay-Doppler Channel

Orthogonal Time Frequency Space (OTFS) has proven to be an effective solution for transmission in high-speed mobile scenarios. The combination of multiple input multiple output and OTFS (MIMO-OTFS) can obtain advantages in transmission rate and spectral efficiency. However, the spatial coupling interference present in MIMO-OTFS poses a challenge to signal detection. This letter focuses on the symbol detection of MIMO-OTFS systems under fractional delay-Doppler channels. Aiming at the spatial coupling interference and inter-symbol interference (ISI) existing in the system, we propose a unitary transform approximate message passing detection algorithm based on serial interference cancellation (SIC-UAMP). It conducts cyclic redundancy check (CRC) on the decoded data streams and feeds back the correctly decoded part to the detector to eliminate the interference. Additionally, we introduce an empirical extrinsic information transfer (E-EXIT) chart to offer a more precise depiction of the iterative detection compared to the traditional EXIT chart. Simulation results under fast fading Rayleigh channels show that SIC-UAMP performs better than UAMP, especially in the medium to high signal-to-noise ratio (SNR) range.