Hybrid Algorithm for Blind Equalization of QAM Signals

In digital communication systems, blind equalizers are used to combat inter-symbol interference (ISI), by only exploiting some statistical and geometrical properties of the transmitted signals. One of the first schemes of blind equalization is the constant modulus algorithm (CMA) which is known to be robust and requires simple hardware implementation. However, for quadrature amplitude modulations (QAM), used in high data-rate communications, the CMA leads to not sufficiently low residual errors. Our contribution presents a hybrid scheme based on the combination of the extended constant modulus algorithm (ECMA) and a modified version of a Gaussian criterion matched to the alphabet of the QAM symbols. The derived algorithm is tested on 512-QAM signals, where significant improvements in terms of mean square error (MSE) are obtained.