Low-Complexity Soft-Decision Feedback Turbo Equalization for MIMO Systems With Multilevel Modulations

Many communication systems today encounter the problem of data transmission over a channel with intersymbol interference (ISI). The purpose of this paper is to develop a low-complexity iterative soft-decision feedback equalization (SDFE) receiver for severe frequency-selective ISI channels in multiple-input-multiple-output (MIMO) communication systems. The proposed SDFE algorithm offers a novel approach to combat error propagation. In addition, its computational complexity only linearly grows with the number of equalizer coefficients, compared with the quadratic complexity of minimum mean square error (MMSE)-based linear turbo equalizer with time-varying coefficients. The performance of the proposed detection scheme is verified through simulations using different signal constellations. In addition, convergence properties of the proposed SDFE algorithm are also analyzed using an extrinsic information transfer (EXIT) chart and verified by simulations in a severe ISI channel. Simulation results show that our proposed algorithm has significant improvement over the Approximate MMSE linear turbo equalizer proposed by Tüchler et al. Moreover, we show that the performance of the proposed equalization scheme significantly improves when higher order constellations are used for digital modulation.