CMA and Soft Decision-Directed Scheme for Semi-Blind Beamforming of QAM Systems

We propose a semi-blind adaptive beamforming approach for wireless systems that employ high-throughput quadrature amplitude modulation signalling schemes. A minimum number of training symbols, equal to the number of receive antenna-array´s elements, are first utilised to provide a rough initial least squares estimate of the beamformer´s weight vector. A concurrent constant modulus algorithm and soft decision- directed scheme, originally developed for single-user blind channel equalisation, is then applied to adapt the beamformer. It is demonstrated that this semi-blind adaptive beamforming scheme is capable of converging fast to the minimum mean-square-error beamforming solution.