Random beamforming for MIMO systems with multiuser diversity

For MIMO multiuser systems, random beamforming asymptotically approaches each user's capacity limit through partial feedback. The convergence speed (the closeness of the achievable capacity of one particular user to its capacity limit in terms of the total number of users) and amount of training are two key factors when evaluating the performance of random beamforming, and they are dependent on the receiver design at the mobile stations (MSs). Two kinds of receivers are proposed, a MMSE-based receiver and a QR-based receiver. The new QR-based receiver provides the flexibility to calibrate the ESNRs when the power allocation used in the data transmission mode is different from that in the pilot mode. More importantly, for high the SNR region, when the QR-based receiver is applied, random beamforming approaches coherent beamforming, even when the number of users is small. Evaluation by computer simulation shows that the new receiver has faster convergence than existing receivers for both low and high SNR.