Some Electromagnetic Limitations on the Number of Users in MU-MIMO Communication Systems

The aim of this letter is to analyze some physical limitations in the number of users that can be simultaneously served in multiuser multiple-input-multiple-output (MU-MIMO) communication systems with Zero-Forcing algorithm. The problem of MU-MIMO is reformulated as a spatial interpolation problem. The results show that the maximum number of users that can be simultaneously served with a reasonable signal-to-noise ratio (SNR) is limited by the number of degrees of freedom of the field. This is a further constraint that must be taken into account during the allocation of the resources among the MU-MIMO users.