Limited Feedback for MIMO Multiuser Systems

In multiple input multiple output (MIMO) downlink systems, if all users send their channel state information (CSI) to the base station, the base station can schedule users whose channels are good and send them information to obtain high system throughout. However, when the number of users in the systems grows quickly, large quantity of feedback information will lead the overflow of the feedback channel. In this paper, we propose a limited feedback strategy based on user rank. In this strategy, only those users whose signal interference and noise ratio (SINR) above a predetermined threshold will send their channel direction information (CDI) and their user ranks to the base station and other users will send nothing to the base station, resulting in the greatly reduced feedback load. Theoretical analysis and computer simulation show the feedback load can be greatly reduced by this method and MIMO downlink systems can achieve multiplexing and multiuser diversity gain at the same time.