Projection multiuser detectors for hierarchical cell structures in CDMA cellular systems

CDMA-only microcell/macrocell cellular systems have traditionally suffered from the near-far problem in the microcells located near the macrocell boundary. Strong macrocell interference in these microcells disables conventional single user detectors. We present techniques for multiuser receiver design that address this problem. The pre-processing stage, called the projection stage, which projects the received signal onto the space orthogonal to the subspace spanned by macrocell users signature sequences, is introduced. It is followed by the stage employing conventional multiuser detection techniques. This class of detectors, called projection multiuser detectors, solves the near-far problem in microcells located at the macrocell boundary, and provides equal treatment to all microcells, regardless of their location within the macrocell. We provide expressions for error probabilities and perform the performance comparison between different projected single user detector and the projected decorrelator.