Improvements in equalization of multiuser CDMA systems: oversampling and nonuniqueness

Major challenges in the design of new generation wireless systems are the suppression of multiuser interference (MUI) and inter-symbol interference (ISI) within a single user resulting from frequency selective propagation. Both of these, problems were addressed successfully in the recent design of a mutually-orthogonal usercode-receiver (AMOUR) for CDMA systems. An attractive property of AMOUR is that it guarantees user separation and the existence of simple zero-forcing equalizers (ZFE) regardless of the channels. However, these ZFEs can amplify the noise significantly and, in this paper we propose a method aimed at improving their performance. First, we note that oversampling at the receiver yields additional degrees of freedom in the ZFE design. This redundancy is then used to construct the solution that minimizes the noise power at the detector. The method is tested in computer simulations.