Low complexity space-frequency RAKE receivers for WCDMA

Adaptive space-frequency RAKE receivers use diversity combining and multiuser interference suppression to obtain a considerable increase in performance in DS-CDMA systems such as WCDMA. The main advantages of operation in the space-frequency domain include a reduced computational complexity and an improved noise suppression. To this end, the signal-plus-interference-and-noise (SIN) and the interference-plus-noise (IN) space-frequency covariance matrices are required. The optimum weight vector for symbol decisions is the "largest" generalized eigenvector of the resulting matrix pencil. If we decouple spatial and frequency processing with respect to interfering users, the IN space-frequency covariance matrix can be approximated by the Kronecker product of the frequency and the spatial covariance matrix. That this IN covariance matrix is estimated by using the outputs of the antenna elements before correlation and the output of the conventional RAKE fingers of the antenna elements may be utilized to approximate the SIN covariance matrix. Thus, the required correlations are reduced to the number of RAKE fingers. Moreover, the computational complexity which is required to estimate the optimum weight vector may be reduced significantly.