# Electromagnetic Field-Aware Radio Resource Management for 5G and Beyond: A Survey
## 4 EMF Exposure Level and 5G Technologies
### EMF Exposure and 5G Radio Access Technologies
The results showed that the EMF exposure exceeded the limits set by the FCC guidelines for the maximum PD at a compliance distance below 6 m and the maximum SAR at a compliance distance below 2 m. Thus, the authors suggested that the minimum distance for human safety should be maintained at least 6 m in cellular communications at high frequencies such as 28 GHz. The authors of [40] proposed a pencil beamforming technique by minimizing the beamwidth of a transmitted beam. The authors considered seven cells, where each cell was divided into three sectors, and there were 64 radiating elements per sector on the antenna. The impacts of this technique were evaluated in terms of EMF exposure and throughput. EMF exposure was evaluated based on the point-source model proposed in [41] by computing the PD at a measurement spot. This pencil beamforming approach was compared to two other reference solutions, namely beamforming with a fixed beam width [42] and without beamforming [41]. The proposed pencil beamforming showed a reduced EMF exposure level in comparison with the reference solutions. The authors concluded that the EMF exposure tended to be further reduced as the localization uncertainty (difference in distance between the actual and the estimated UE locations) decreased due to the narrower beam widths being synthesized. Although the technique proposed in [40] resulted in an EMF strength that was lower than the limits set by the ICNIRP [10], two research gaps were observed. These gaps are summarized as follows:  
* The authors did not consider the effects of practical beamforming abnormalities, such as the presence of dual main beams, on the EMF evaluation level. The pencil beam considered was perfectly directed toward the estimated location of the UE (with perfect precoding weights). * EMF exposure was evaluated using the PD metric only. However, based on [32], the PD metric is not effective enough to evaluate health risks, especially when the users are close to the measurement spots at high frequencies. The EMF evaluation procedure in [40] is applicable to an ideal beamformer. However, for a practical beamforming technique such as hybrid beamforming, this approach may not be accurate. EMF exposure due to hybrid beamforming has not been adequately investigated in the literature. For 4G and pre-5G radio systems, mobile network operators have begun pushing for denser networks and heterogeneous deployments. It can be observed that more and more BSs have been installed in surrounding areas on walls, rooftops of buildings, and low antenna masts to support increased service requirements. These network deployment trends increase the possibility of the general public being in close proximity to radio BS antennas. As a result, the level of EMF exposure experienced by users will be higher. A measurement study carried out by the authors of [12] for 2G/3G systems found that EMF levels exceeded the limits in 15.6% of the locations considered. In [43], the authors measured the EMFs generated by different 2G/3G/4G BSs located in Poland and found a case where the total EMF generated by multiple operators exceeded the maximum limit. Experimental assessments of EMF exposure in real-world environments due to 5G networks are still lacking in the literature compared to EMF exposure assessments that are based on statistical and simulation approaches. Next, previous studies that have evaluated EMF exposure based on experimental approaches in 5G networks were reviewed. In [44], the authors tested a 16 \(\times\) 8 MIMO testbed in eight beamforming scenarios for indoor downlink communication with multiple users at various locations. The authors acquired a heatmap of the received power for each beamforming scenario utilizing an isotropic triaxial field probe. Finally, the heatmap was converted into an RF-EMF heat map. The authors conducted this experiment to study the impact of the number of users, the position of users, and environmental fluctuation on RF-EMF exposure from a 5G BS.