Low complexity soft decision feedback equalizer for multilevel modulation

This letter presents a soft decision feedback equalizer (SDFE), for multilevel modulation. In contrast to common turbo principle which only uses the extrinsic information from the decoder, the SDFE can be used in the channel equalizer for calculation of the a posteriori probability (APP) by collecting information of the entire block as in maximum a-posteriori probability (MAP) algorithm. Replaced hard decision with soft decision reduces the effects of the error propagation. Meanwhile, In contrast to common soft DFE for only BPSK, The SDFE can be used for multilevel modulation, such as MPSK or QAM. Simulation results confirm the superiority of the new proposed equalizer comparing with current low complexity Turbo equalizers with hard decision for High-level modulation.