## 5 Conclusions  
The results of this study show that the absorption of energy by the human brain, resulting from exposure to the 3.6-GHz band, is reduced by a factor of \(>\)6 for the tissue-averaged SAR when compared to mobile networks operating at \(<\)1 GHz, and by a factor of \(>\)2 when compared to the frequency bands at 1.8-2 GHz. For deep brain regions, the reduction is much larger. The dose of these regions is reduced as a result of lower penetration depths at higher frequencies. Exposure close to surface structures, e.g., eyes, testicles, etc., can be higher. At the most exposed surface of the grey matter, the values remain approximately \(\pm\)3 dB over all frequencies, whereas the area of high exposure is reduced.  
The results of the Monte Carlo analysis show that for all users (except non-users), total exposure is dominated by a person's own mobile device. Compared to a non-user, the exposure is increased for a light user (with 100 MByte uplink data per day) by 6-10 dB (or by a factor 4-10), for a moderate user (with 1 GByte uplink data per day) by 13-25 dB (or by a factor of 20- \(>\) 300), and for a heavy user by 25-40 dB (or a factor of 300- \(>\) 10000). The peak exposure of non-users is, furthermore, not defined by exposure to surrounding base stations but by the mobile devices of close bystanders in urban areas, resulting in up to a 6 dB (or a factor of four) higher exposure than from a nearby base station antenna. Reducing the size of the mobile cell leads to a decreased overall exposure by a factor of 2-10 for people who actively use their mobile devices. At the same time, the reduction in cell size might lead to a small increase by a factor of \(<\)2 in the exposure of non-users. The exposure of active users can be reduced by factors ranging from 4-600 by increasing indoor network coverage, which, in turn, will be linked to the increased exposure of non-users by a factor of 2-10. However, this increase is at a level that is a factor of 1000 lower than the typical absolute exposure of active users.  
Since data from real networks with MIMO were not available, the effect of adaptive beam-forming antennas on the dose could only be discussed in this study and need to be quantitatively analyzed when 5G networks are fully established, and realistic data becomes available.  
**Author Contributions:** Conceptualization, S.K. and N.K.; methodology, S.K. and S.P.; software, S.P.; validation, S.K., S.P. and N.K.; formal analysis, S.K; investigation, S.K.; resources, N.K.; data curation, S.P.; writing--original draft preparation, S.K.; writing--review and editing, S.K.; visualization, S.P.; supervision, N.K.; project administration, S.K.; funding acquisition, S.K. and N.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Swiss Federal Office for the Environment.  
**Acknowledgments:** The review and advice of [PERSON] (Swisscom), [PERSON] (Telecom Paristech), [PERSON] (University of Maryland), and [PERSON] (Sr Scientific).  
**Conflicts of Interest:** The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.