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 in place of the noise-whitening feedforward filter. Performance of two reduced-state soft-input soft-output techniques are compared by computer simulations. In the first technique delayed decision feedback sequence detection is used both in the forward and in the backward recursions. In our implementation, the output of the matched filter is passed through a non-causal filter to obtain the sequence used In the forward recursion, while the time-reversed version of the mentioned filter is used for the backward recursion. The second technique is based on the concept of state partitioning.