The benefits of the MMSE-DFE feedforward filter in reduced-complexity turbo equalization

This paper shows the performance improvement attainable in reduced-complexity turbo equalization schemes when the MMSE-DFE (minimum mean square error - decision feedback equalizer) feedforward filter is used as pre-filter in place of the noise-whitening filter. Performance of two reduced-state soft-input soft-output (RS-SISO) techniques have been compared by computer simulations. In the first technique delayed decision feedback sequence detection, that is normally used for reducing the complexity of maximum likelihood detectors, is used also in the backward recursion. In our implementation, the forward and the backward recursions are calculated by using two different sequences. The second technique is based on the concept of state partitioning.