New blind equalization techniques based on improved square contour algorithm

New blind equalization techniques for QAM signaling are presented in this paper. These schemes are based on the improved square contour algorithm (ISCA) which employs the estimated outputs from the decision device in the cost function guiding equalizer outputs to reside on multiple zero error square moduli. This mechanism reduces the misadjustment between transmitted constellation and the new cost function in an efficient manner, which leads to a noteworthy increase in convergence speed and inter symbol interference (ISI) suppression. For further diminution of misadjustment, some modifications have been suggested in ISCA cost function by presenting a new scheme named as constellation matched square contour algorithm (CM-SCA), which makes the multiple zero error square moduli of the ISCA collinear with the source constellation contours. To achieve better performance in severe channel conditions or equalizing higher order QAM signals, a fusion of SCA and CM-SCA, named as modified constellation matched square contour algorithm (MCM-SCA) is proposed. The convergence characteristics of the proposed schemes demonstrated by the simulation results for 16- and 64-QAM signal constellations reveal the effectiveness of new blind equalizers over the existing square contour algorithm (SCA) and recently proposed modified square contour algorithm (MSCA).