Blind multi-user access interference cancellation for CDMA based PCS/cellular using antenna arrays

Abstract

We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access interference and optimally combines multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference spatio-frequency correlation matrix during that portion of the bit interval where the fingers of the RAKE occur, and the interference alone spatio-frequency correlation matrix during that portion of the bit interval away from the fingers. The weight vector yielding the optimum signal to interference plus noise ratio for bit decisions is the largest generalized eigenvector of the resulting matrix pencil. However, even when the number of elements comprising the array is relatively small, this spatio-frequency correlation matrix pencil is of large dimension. In addition to detracting from the real-time applicability of the scheme, this slows up the time to convergence. A reduced complexity scheme is presented based on a data adaptive transformation to a beamspace of dimension equal to the effective number of spatial degrees of freedom taken up by the desired user's multipath.