Capacity improvement of CDMA-based mobile communication systems using linear antenna arrays - theoretical and experimental results

The interference suppression capability of the uniform linear array (ULA) is analyzed within a DS-CDMA space-time processing framework. In literature the simplifying assumption of 'spatially white' interference is often made in order to obtain analytical results. In this case the output SNIR of space-time matched filter becomes independent of the array geometry. However, considering the special geometry of the ULA, spatially white interference corresponds to a large number of interferers distributed with cosine-shaped probability density function. For all other distributions, the expected array performance depends on the look direction of the main beam. This is analytically proven and illustrated with numerical simulations. We derive an analytical expression, which estimates the SNIR in case of uniformly distributed interferers. The results provide new insight into the problem of spatial filtering with linear arrays and show its theoretical limitations.