Blind predictive decision-feedback equalization via the constant modulus algorithm

The noise predictive structure of DFE is attractive for the equalization of the coded modulation signals. In this paper, a blind predictive constant modulus (CM) decision feedback equalizer (PCM-DFE) is presented and analysed. The PCM-DFE employs the CM linear equalizer as its forward filter and a feedback filter that optimizes the CM cost of the decision variable. It is shown that for any fixed forward filter with reasonable small residue intersymbol interference, the CM cost function for the feedback filter is approximately convex and its global minimum can be approximated in closed form. We demonstrate that the convergence rate of the feedback filter is similar to the least mean square (LMS) algorithm used in the nonblind design. We show that the PCM-DFE performs better than the nonblind linear MMSE equalizer in simulations.