Novel exact low complexity MMSE turbo equalization

In this paper we analyze low complexity turbo equalization that combines interference canceling and Soft-Input Soft-Output (SISO) decoding. We derive a new, exact MMSE solution for the equalization part taking into account the cross-correlation between the linear equalizer output and the soft decisions in the turbo equalization feedback loop as well as the auto-correlation function of the decoder output. Also, this solution implicitly takes into account the error propagation in the feedback loop of the turbo equalizer. We also introduce a non-linear element in the feedback loop that suppresses less reliable soft decisions. The level of suppression depends on the reliability of a soft decision, which is directly proportional to its absolute value. The simulation results for a common scenario show that the proposed solution outperforms all previously known turbo equalizers of similar computational complexity.