Regularized adaptive detectors for code-division multiple-access signals

This paper presents the development of regularized adaptive detectors for code-division multiple-access (CDMA) wireless-communication systems. Multiuser CDMA detection is formulated as an inverse problem in the presence of channel-induced interference and noise and the estimation of the detector parameters is accomplished using elements of regularization theory. The regularized solutions are derived by minimizing objective functions formed as a linear combination of a term representing the estimation error and a term representing a smoothness constraint. The smoothness constraint is determined by data-dependent procedures developed to reduce the effect of noise and the impact of interfering users on the performance of the resulting detector. The proposed adaptive detector is evaluated and compared with existing multiuser CDMA detectors in terms of their robustness to noise, resistance to the near-far problem, and ability to handle multipath signals.