A penalty function approach to code-constrained CMA for blind multiuser CDMA signal detection

A code-constrained constant-modulus approach (CMA) was presented in Li and Tugnait (2000) for blind detection of asynchronous short-code DS-CDMA 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. An iterative projection approach was used in Li for constrained optimization where at each iteration the equalizer was projected onto the desired subspace. We investigate an alternative, penalty function-based approach to constrained optimization. Global minima and some of the local minima of the cost function are investigated. A simulation example is presented