Analysis of 5G Base Station RF EMF Exposure Evaluation Methods in Scattering Environments

The International Electrotechnical Commission (IEC) develops and validates methods for assessing radio frequency electromagnetic field (RF EMF) exposure due to base stations (BS). When the assessment is performed in- situ, it is recommended to extrapolate the maximum level of exposure from measurement of stable signals, such as broadcast signal with BS of the 5^th generation (5G) of mobile communication systems (gNodeB). A comparative statistical analysis of extrapolation methods based on nominal antenna pattern (as measured in an anechoic chamber) and effective antenna pattern (as measured in scattering environment) of gNodeB is presented in this paper. This theoretical analysis shows that extrapolation with nominal antenna pattern may lead to significant overestimation of the maximum RF EMF exposure (up to 5.4 dB) in case of scattering environment or non-line-of-sight (NLOS) conditions. This overestimation is expected to be reduced by using effective antenna pattern in order to better represent the actual propagation conditions, such as those found in urban or dense urban areas. Therefore, it is recommended to perform extrapolation of the maximum exposure based on joint modeling of antenna beam pattern and representative value of the angular spread (AS) for the targeted deployment conditions. This conclusion was obtained from the observed consistence between two different approaches for determination of effective antenna gain. The first approach assumes statistical simulations with full three-dimensional (3D) channel model, especially distribution function of AS. The second approach enables simpler calculation of the effective antenna gain in scattering environment or NLOS conditions by considering only representative values from the full range of AS distribution function. The proposed simple method, if used with representative realistic values of AS, could reduce overestimation of RF EMF exposure resulting from an extrapolation factor based on nominal antenna gains of broadcast and traffic beams.