Ray tracing-based analysis of extrapolation factors for RF exposure to 5G massive-MIMO base stations

The assessment of maximal RF exposure to 5G massive-MIMO antennas in non-line-of-sight (NLOS) scenarios may lead to significant misestimations because of incorrect gain correction factors, which are used to extrapolate the measured exposure to the maximal possible state. Preliminary work provided theoretical and measurement-based investigations to clarify the cause, which have now been supplemented by ray tracing-based analyses. For this purpose, a measurement scenario was implemented into a ray tracing software to compute the gain correction factors. These were compared with the measurements and theoretical calculations. The simulated exposure values vary strongly with the exact location of the measurement point and the frequency, especially in the light of multipath propagation effects such as frequency-selective fading. A volume-based assessment, which is usually used during measurements instead of a single point analysis, or the combination of several frequency carriers instead of single-tone excitation deliver results that agree with measured data within a typical measurement uncertainty of ±3 dB.