Single user random beamforming in Gaussian MIMO broadcast channels

This paper proposes a new transmitting scheme for a multi-antenna (MIMO) Gaussian broadcast channel. The transmitter exploits multiuser diversity using a small amount of feedback information from the receivers. The feedback information consists of the maximum achievable rate for each user and the necessary power distribution profile across the spatial dimensions that the transmitter should use to achieve that rate. The receivers use the iterative water-filling algorithm to maximize the achievable rate. The new scheme serves a single user at each transmission, hence the name Single User Random Beamforming (SUBF) scheme. The proposed scheme maximizes the average sum rate under a TDMA environment (i.e., supporting a single user at a time) with the partial channel state information (CSI) feedback constraint.