Capacity enhancement scheme for downlink multiuser MIMO systems with limited feedback

Many precoding schemes in downlink multiuser MIMO systems require perfect channel state information of all users at the transmitter, which is hard to realize in practical systems. Random beamforming scheme is a conventional method to reduce the amount of feedback. However, it only enjoys significant performance gains with a large number of users, which limits its practical application. We propose a limited feedback capacity enhancement scheme based upon grassmannian beamforming for downlink multiuser MIMO systems. In order to get better performance when users with multiple receive antennas we also propose a MMSE based scheme to further eliminate multi-user interference. The proposed scheme outperforms conventional random beamforming scheme when the number of users is small or moderate.