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 suppressmulti-user interference

(MUI) via beamforming or by using ”dirty-paper”

codes. It also allows us to performmost 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 formulti-userMIMO

systems. The performance of these techniques is assessed via

simulations on statistical channelmodels, and on channels generated

by the IlmProp, a geometry-based channel model that

generates realistic correlations in space, time, and frequency.