Performance study of MIMO systems in a clustered multipath channel

Fading correlation is one of the fundamental limits on the performance of multi-antenna systems. Accurate modeling of the angular power distribution (pdf) is essential for accurate prediction of correlation. Previous studies were limited to the case of single-cluster distribution or uniform pdf. Measurements indicate that multipath often arrives in several angular clusters and with a non-uniform angular cluster pdf. We begin with the popular Salz-Winters model and extend it to the case of a multi-cluster channel and to the case of a non-uniform cluster pdf. The generic model, as well as various approximations which result in compact closed-from expressions, are studied in detail. It is shown that the correlation in a two clusters channel has an oscillatory behavior as antenna spacing increases, regardless of multipath AOA distributions; the envelope of correlation is determined by a single cluster angular spread while the oscillations within the envelope are determined by the inter-cluster angular spread. There exist two types of correlation zeros, which can be beneficially used in system design. The cluster angular pdf has negligible impact on the MIMO capacity and, hence, a simpler uniform model can be used without degradation in accuracy.