MU-MIMO Decomposition Transmission with Limited Feedback

Downlink multi-user multiple-input multiple-output (MU-MIMO) transmission techniques have gained much attention recently because of their potential to significantly increase system capacity compared to single-user transmission by separating multiple users in the space domain through appropriate signal processing. Unfortunately, these techniques require accurate channel state information at the transmitter (CSIT) for their proper operation. In practice however perfect CSIT is hard to obtain due to capacity-limited feedback channel in FDD systems for example. In this paper we investigate systems employing MU-MIMO decomposition transmission in the downlink with limited feedback. In particular, the essential information that enables the scheme to deal with inter-user interference is identified and the optimal codebook design in terms of minimizing the residual inter-user interference power is derived. Simulation results show that in general limited feedback has a significant impact on the mutual information achieved by MU-MIMO decomposition transmission.