Limits of multi-user MIMO systems using scheduling and rate feedback

In this paper, we investigate the throughput of downlink multi-user multiple-input multiple-output (MIMO) communication systems when cross-layer processing, such as rate-aware scheduling and rate feedback, is used. Specifically, we derive the probability density function of the mutual information between transmitted and received complex signals over spatially correlated Rayleigh distributed flat fading channels with complex Gaussian additive noise. Using this density, we derive the probability density function of the mutual information between basestation transmitted and best user (good channel condition) received complex signals. Then we analyze the expected throughput gains due to rate-aware scheduling and rate feedback. Numerical results show how the throughput gain varies with the finite number of transmit and receive antennas, the finite number of users and the channel spatial correlation at the receiver end (mobile unit). We also analyze the number of bits needed for rate feedback.