Multiuser diversity scheduling in MIMO systems with correlated fading

Previous studies have shown that single-user systems with t antennas at the transmitter and r antennas at the receiver can achieve capacity proportional to min(r, t) assuming a rich scattering environment. In this paper, we study a cellular network with a t-antenna basestation and K r-antenna users. We assume exponentially correlated fading exists either at the basestation or at the users, and the channels of different users change independently. Multiuser diversity is exploited by always allowing the basestation to transmit to the user which channel provides the highest capacity among all users. For this network, we investigate the impact of correlated fading on the network capacity. We find that if both t and r > 1, the impact of correlated fading depends on the signal-to-noise ratio (SNR). At the low SNR regime, the capacity will also increase with the correlation coefficient. However, at the high SNR regime, under the condition that one side of the channel having correlated fading has less antennas than the other side, the increase of the correlation coefficient will reduce the capacity. In addition, we find the closed-form solutions for the mean and variance of single-user multiple-input multiple-output (MIMO) channel capacities for different cases.