Back-of-the-envelope evaluation of the prevalence of RIMP or LOS propagation as a function of frequency

The performance of 5G wireless communication systems, employing Massive-MIMO at millimeter-wave frequencies, is most likely measured only in Over-The-Air (OTA) setups. It is proposed to perform OTA measurements in two limiting environments of Rich Isotropic MultiPath (RIMP) and Random Line-of-Sight (Random-LOS) instead of a typical or representative channel. In the present paper, we present a back-of-the envelope investigation of the impact of scattering on the frequency dependence of the signal fading statistics in the 500 MHz-100 GHz band. We introduce a simple model for a generic scattering environment by using randomly distributed resonant scatterers to investigate the impact of the size of the scattering environment, the scatterer density, and the number of scatterers on the signal variability in terms of the Rician K-factor as a function of frequency. The simplified model is also verified against full-wave simulation using the Method of Moments (MoM).