The impact of correlation on multi-antenna system performance: correlation matrix approach

A universal upper bound on the MIMO architecture capacity, which is not limited to a particular scenario, is derived using the correlation matrix approach and the Jensen's inequality. This bound accounts for both transmit and receive branch correlation in such a way that the impact of these branches can be estimated separately, which simplifies the procedure substantially and also allows one to decide which site is responsible for capacity reduction, which is not easy to do using traditional approaches. Further, using the results above and the Salz-Winters (1994) model of fading spatial correlation, it is demonstrated that the correlation has no impact on the MIMO capacity provided that the two-element antenna array beamwidth is smaller than the angle spread of the incoming multipath signals. A fundamental tradeoff between MIMO capacity and diversity order is also pointed out.