On the feedback error in adaptive turbo equalization

In this paper we analyze the decision feedback error propagation in the adaptive turbo equalization with a decision feedback loop. We derive the exact mathematical expression for the feedback error probability density function (pdf) with the assumption that the soft outputs of channel decoder are identical independent distributed (i.i.d) Gaussian random variables with known mean value and variance. We also find a new set of turbo equalizer coefficients based on the feedback error pdf and MMSE criterion. New turbo equalizer is shown to outperform the conventional one (assuming no feedback error propagation) in terms of bit error rate (BER). The achieved improvement is up to 4 dB for severe frequency-selective channels. The analysis is applicable to other turbo detection methods employing the feedback loop