Chapter 5

Multiuser MIMO Systems

Antti Tölli, Petri Komulainen, Federico Boccardi, Mats Bengtsson and Afif Osseiran

In Multiple-Input Multiple-Output (MIMO) communications, multiple antenna elements are employed both in the transmitter and the receiver, in order to obtain increased data rates or improved reliability compared to single-antenna transmission. In cellular systems, the Base Station (BS) may operate in Single-User (SU)-MIMO mode (see Figure 5.1(a)), that is, to employ point-to-point transmission of data just for one multi-antenna User Equipment (UE) at a time. Alternatively, the BS can perform Multi-User (MU)-MIMO transmission (see Figure 5.1(b)), that is, spatially multiplex data streams intended for different UEs that may be equipped with arbitrary numbers of antenna elements. The use of MU-MIMO mode offers potential system capacity gains especially when the BS employs a large antenna array.