MULTI-USER MIMO DOWNLINK BEAMFORMING OVER CORRELATED MIMO CHANNELS

Multi-user (MU) multiple-input multiple-output (MIMO) systems provide a high capacity while offering the benefits of space division multiple access. The channel state information (CSI) at the base station(BS)/access point (AP) can be used to precode the signals and to perform most of the complex processing at the BS/AP which results in a simplification of the users’ terminals. If perfect CSI is available at the transmitter it can be used to completely eliminate interference at the BS/AP. In situations when the channel variations are too fast to obtain short-term CSI, the long-term channel state information can be also used to improve the system performance. In this paper we propose a new approach to MU precoding based on long-term CSI. It can be used with previously defined precoding techniques originally requiring perfect CSI at the transmitter. Thereby we exploit the knowledge of the spatial correlation at the transmitter to improve the system throughput. The more antennas there are at the BS/AP, the greater are the benefits of MU MIMO precoding.