New geometrical interpretation of the decorrelator in multiuser CDMA

Abstract

In this paper we present a new geometrical interpretation of the multiuser CDMA decorrelator. This interpretation relates the output of the decorrelator to the subspace spanned by the spreading codes. The interpretation makes it clear that a decision feedback detector based on the soft outputs from a decorrelator and a multistage detector with a soft output first stage decorrelator do not provide any performance improvement over the single stage decorrelator. These conclusions are confirmed by analytical results.