Spatially greedy scheduling in multi-user MIMO wireless systems

This paper considers the benefit of opportunistic channel state dependent scheduling in a multi-user MIMO wireless system. Channel state dependent scheduling can provide significant performance gains for wireless networks by exploiting the independence of fading statistics across the user population. While opportunistic schedulers typically pick the single "best" user for transmission, MIMO systems can support transmissions to multiple users simultaneously. Consequently, greedy schedulers in MIMO systems can either transmit only to a single-user transmission or allow multiple users to transmit simultaneously. This paper analytically characterizes the performance gains achieved by both single-user and multi-user MIMO schedulers in a dynamic scenario with a time-varying number of users. In particular, the relation between throughput (or equivalently, ergodic capacity) and user experienced file-transfer delay for both single-user and multi-user MIMO schedulers are evaluated. Our main result indicates that multi-user greedy MIMO scheduling lead to lower average user experienced delays compared to single- user greedy scheduling.