Optimized Assessment Procedure for Maximal RF Exposure to 5G Massive MIMO Base Stations in Non-Line-of-Sight Scenarios - Part 1: Theoretical and Numerical Investigations

The evaluation of the maximal human RF exposure to 5G base stations acquires a specific extrapolation procedure due to the massive MIMO antennas. Up to now, large misestimations of up to 15 dB of the extrapolated maximal RF exposure compared to the reference value were found at measurement points under non-line-of-sight conditions. One possible cause is the incorrectly determined gain correction factor based on free space assumptions which is used for extrapolating the measured signalization exposure to the maximal possible exposure. This gain correction factor may differ greatly between line-of-sight and non-line-of-sight scenarios. In this paper, considerations based on geometrical optics are used to identify such causative scenarios. Here, the measurement points are in multipath environments, where the resulting field distributions and the corresponding gain correction factors are not identical compared to the free space. Numerical simulations with ray tracing confirm this assumption as the determined gain correction factor in the multipath scenario is significantly lower compared to the free space case. Verification of these considerations by measurement is done in the accompanying paper "Part 2".