Block diagonalization and user selection for MIMO broadcast channels with limited feedback

We consider limited-feedback-based block diagonalization (BD) and user selection for multiple antenna broadcast channels. With limited feedback, the conventional channel norm can not be a good estimate for channel quality of each user, because multiuser interference is not completely eliminated by using BD under limited channel direction information. Therefore, we need an appropriate channel quality indicator (CQI) to increase the diversity gain achieved by multiuser scheduling. To this end, we consider a determinant-based instantaneous channel capacity and propose a new CQI by taking an expectation over precoding matrices that can not be known at the feedback stage. Simulation results show that the sum rate with the proposed CQI is much higher than the sum rate with conventional CQIs.