Combined Temporal and Spatial Filter Structures for CDMA Systems

CDMA systems are interference limited and therefore efficient interference management is necessary to enhance the capacity of a CDMA system. In this paper; we consider combining two effective receiver based interjerence management strategies: multiuser detection (temporal filtering) and receiver beamfoming (spatial$ltering). We formulate and examine the performunee of several linear filter structures which are all based on minimum mean squared error (MMSE) criteria, but differ in how the MMSEproblems are defined in the temporal and spatial domains, i.e., jointly or in cascade. It is shown that while the joint optimum MMSE filter achieves the maximum signal-to-interference ratio (SIR) among all possible linearfilters, the constrained optimum MMSE filter which results in a single temporal and single spatial filter; outperforms all combined singleuserlmultiple-user approaches and cascaded optimization approaches either uniformly o r asymptotically. The constrained optimum MMSEfrlter is nearfar resistant in all but very highly loaded systems and enjoys low complexity.