A Blind Decision Feedback Equalizer for QAM Signals based on the Constant Modulus Algorithm

This paper presents a blind adaptive decision feedback equalization (DFE) scheme for QAM signals, which uses block processing and is based on the constant modulus algorithm (CMA). A two-phase scheme is proposed in which the equalizer switches from the blind mode to decision feedback mode after the blind scheme has converged. If the error level is low and the equalizer output is reliable then DFE is successful and all intersymbol interference (ISI) can be removed by this scheme. The block DFE scheme is tested with two blind equalization schemes (i) CMA and (ii) CMA+AMA. Their performance is compared to the original CMA/AMA scheme, and to each of the blind equalization schemes operating alone. The convergence behavior of the AMA cost function is used to evaluate performance of the different schemes. In addition, the average symbol error rate (SER) is compared for the different schemes by Monte Carlo simulation