Blind asynchronous multiuser CDMA receivers for ISI channels usingcode-aided CMA

摘要

A code-aided constant modulus algorithm (CMA) based approach isnpresented for blind detection of asynchronous short-code DS-CDMA (directnsequence code division multiple access) signals in intersymbolninterference (ISI)/multipath channels. Only the spreading code of thendesired user is assumed to be known; its transmission delay may benunknown. A linear equalizer is designed by minimizing the Godard/CMAncost function of the equalizer output with respect to the equalizerncoefficients subject to the fact that the equalizer lies in a subspacenassociated with the desired user's code sequence. Constrained CMA leadsnto the extraction of the desired user's signal whereas unconstrainednminimization leads to the extraction of any one of the active users. Thenresults are further improved by using unconstrained CMA initialized bynthe results of the code-aided CMA. Identifiability properties of thenapproach are analyzed. Illustrative simulation examples are provided