A Markov Chain Monte Carlo (MCMC) Gibbs Sampler Augmented with Zero Forcing Detection for OTFS Reception

The Orthogonal Time Frequency Space (OTFS) is a two-dimensional modulation scheme that operates in the Delay-Doppler domain and is robust in the presence of wireless channels experiencing a high Doppler spread. The OTFS converts a fast-varying doubly-dispersive wireless channel in the time-frequecy domain to a near-static channel in the Delay-Doppler domain. The informative symbols are transmitted in this Delay-Doppler domain with the effect that the transmitted symbols experience a channel fade that changes comparatively slowly with time. In this paper, we propose an enhanced Markov Chain Monte Carlo Markov Chain (MCMC) based Gibbs sampling scheme for the detection of transmitted symbols at the OTFS receiver. A novelty of our proposal is to combine the Zero Forcing Detection (ZFD) with the MCMC-Gibbs algorithm. We show that the proposed joint Gibbs-ZFD method avoids a performance loss that the Gibbs method exhibits at a high signal to noise ratios (SNRs). We conduct a simulation-based evaluation of our proposed approach over a range of the UE (User Equipment) speeds and for Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) modulation schemes. The numerical results show that our proposal offers an improved probability of symbol detection error compared to the two alternative OTFS receivers, namely the Gibbs method and the ZFD.