Scheduling for Multiuser MIMO Downlink Channels With Ranking-Based Feedback

The authors consider a multi-antenna broadcast channel with more single-antenna receivers than transmit antennas and partial Channel State Information at the Transmitter (CSIT). They propose a novel type of CSIT representation for the purpose of user selection, coined as ranking-based feedback. Each user calculates and feeds back the rank, an integer between 1 and W + 1, of its instantaneous Channel Quality Information (CQI) among a set of Wpast CQI measurements. Apart from reducing significantly the required feedback load, ranking-based feedback enables the transmitter to select users that are on the highest peak (quantile) with respect to their own channel distribution, independently of the distribution of other users.