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.

A method for selecting the order in which the users are detected in communication systems employing adaptive successive decision feedback multiuser detection is proposed. Systems employing channel coding without the assumption of perfect decision feedback are analyzed. The method is based on the mean squared error (MSE) measurements during a training period for each user. The analysis' shows that the method delivers BER performance improvement relative to other previously proposed ordering methods.

In this letter, we propose a new turbo decision feedback equalizer (DFE) algorithm that takes into account decision feedback error propagation. We derive the exact mathematical expression for the probability density function (pdf) of soft decision feedback symbols, assuming that soft outputs from channel decoder are independent identically distributed Gaussian random variables with known mean and variance. We find a new set of "imperfect" turbo minimum mean-square error DFE coefficients based on the derived pdf. The proposed turbo detector outperforms other turbo equalization algorithms of similar computational complexity in terms of bit-error rate. The achieved improvement is up to 3.8 dB for severe frequency-selective channels.