A low-complexity approximate message passing equalizer for OTFS system

The orthogonal time frequency space (OTFS) modulation has emerged as a potential candidate modulation scheme for high mobility wireless communications. However, OTFS may experience significant inter-Doppler interference (IDI) and inter-symbol interference (ISI) occur in the receiver. To jointly combat both interferences, we propose an efficient improved approximate message passing (AMP) equalizer for OTFS transmission over delay-Doppler channels in this paper. Specifically, a decoupling operation can be performed for joint interference cancellation, and the sparse feature of equivalent channel matrix is utilized in delay-Doppler domain. Then, the posterior mean and variance estimates of the transmitted symbol is reconstructed by the denoising step. Furthermore, a threshold-based convergence scheme is proposed with the purpose of trade-off the computational complexity and performance of the OTFS system. Simulation results demonstrate that the proposed improved AMP equalizer exhibits a better bit error rate (BER) performance with a reduced complexity compared to its conventional counterparts.