Efficient multi-user MIMO downlink precoding and scheduling

Space division multiple access (SDMA) promises high gains in the system throughput of wireless multiple antenna systems. If SDMA is used on the downlink of a multi-user MIMO system, either long-term or short-term channel state information has to be available at the base station (BS) to faciliate the joint precoding of the signals intended for the different users. Precoding is used to efficiently eliminate or suppress multi-user interference (MUI) via beamforming or by using ”dirty-paper” codes. It also allows us to perform most of the complex processing at the BS which leads to a simplification of the mobile terminals. In this paper, we provide an overview of efficient linear and non-linear precoding techniques for multi-user MIMO systems. The performance of these techniques is assessed via simulations on statistical channel models, and on channels generated by the IlmProp, a geometry-based channel model that generates realistic correlations in space, time, and frequency.