On space-time RAKE receiver structures for WCDMA

Adaptive space-time RAKE receivers use diversity combining and multi-user interference suppression to obtain a considerable increase in performance in DS-CDMA systems such as wideband CDMA (WCDMA). We compare the structure and performance of different space-time RAKE receivers for WCDMA. After a review of the decoupled space-time RAKE and the joint space-time RAKE, we present a new joint space-time RAKE with spatial and temporal compression matrices. Here, the spatial compression matrix is calculated from spatial covariance matrices that can be averaged over several time slots, since the change of the spatial characteristics is much slower than the fast fading. It has more degrees of freedom than the decoupled space-time RAKE, but less than the joint space-time RAKE. Finally, Monte-Carlo simulations demonstrate the performance of several space-time RAKE structures for different scenarios. It turns out that if good spatio-temporal channel estimates are available (e.g., in case of a small Doppler), more degrees of freedom can be exploited by the space-lime RAKE receiver structure.