New results on blind asynchronous CDMA receivers using code-constrained CMA

A code-constrained constant-modulus approach (CMA) was presented recently in Li et al., (2000) for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. The equalizer was determined by minimizing the Godard/CMA cost function of the equalizer output with respect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. We analyze the identifiability properties of this approach. Global minima and some of the local minima of the cost function are investigated. These aspects were not discussed in Li. More extensive simulation comparisons with existing approaches are also provided.