Blind asynchronous multiuser CDMA receivers for ISI channels using code-aided CMA

A code-aided constant modulus algorithm (CMA) based approach is presented f or blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in intersymbol interference (ISI)/multip ath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. A linear equalizer is designe d by minimizing the Godard/CMA cost function of the equalizer output with r espect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. Const rained CMA leads to extraction of the desired user's signal whereas unconst rained minimization leads to the extraction of any one of the active users. The results are further improved by using unconstrained CMA initialized by the results of the code-aided CMA. Identifiability properties of the appro ach are analyzed. Illustrative simulation examples are provided.