Saddlepoint approximation to the outage capacity of MIMO channels

We put forth a saddlepoint approximation for the outage capacity of multiple-input multiple-output (MIMO) systems using the exact moment generating function of the capacity. We consider both uncorrelated and spatially correlated Rayleigh-fading channels. Our results show that the saddlepoint method gives a remarkably accurate approximation to the outage capacity even at extremely low outage probabilities