## 4 Conclusions  
In this work, environmental RF-EMF exposure was assessed from an empirical and modeling approach in a complex heterogeneous indoor environment when considering dense personal mobile communications operating at 28 and 60 GHz. For that purpose, an enhanced in-house deterministic 3D-RL simulation tool for a RF-EMF exposure assessment was proposed, allowing E-field and incident power density level characterizations in different complex heterogenous scenarios of increased complexity. Realistic operation conditions were considered, as well as different user distributions and densities, emulating advanced mmWave communication systems with directive antennas and MIMO beamforming techniques.  
From the obtained results, a discussion regarding the contribution, impact and health effects of the coexistence of multiple heterogeneous networks and services was provided. The main conclusion that must be stated is that wireless communication systems operating at both the 28 and 60 GHz frequency bands considering realistic and worst-case scenarios in terms of user densities, as well as directive antennas and beamforming techniques, generated environmental E-field exposure levels lower than 2 V/m and incident power  
Figure 16: Experimental measurements and 3D-RL simulation comparisons at the 28 and 60 GHz frequencies along the different points depicted in Figure 9.  
density levels lower than 0.1 W/m\({}^{2}\) for all the analyzed cases. Therefore, the compliance with the current established international regulation limits with the exposure levels for the general population far below the aforementioned limits (10 W/m\({}^{2}\)[54]) was verified even in the worst-case conditions and, at the same time, denying the hypothesis of an increase in the total RF-EMF exposure by the use of mmWave frequencies or directive antennas in complex dense heterogeneous indoor environments. In this sense, these results guaranteed that E-field distributions and received power levels within the complete scenario under analysis were below the thresholds and, hence, complied with the current regulatory frameworks in relation with the health assessment.  
Moreover, the proposed simulation methodology was validated with a complete empirical campaign of measurements, showing good agreement with the experimental results. Thus, the obtained measurement datasets and simulation estimations, along with the presented enhanced 3D-RL simulation tool, could be a reference approach for the design, deployment and exposure assessment of the current and future wireless communication systems, where complex context aware scenarios with massive high-node density heterogenous networks are expected in the mmWave frequency range.  
Conceptualization, M.C.-E., F.A.R.-C. and L.A.; methodology, M.C.-E., F.A.R.-C., L.A., P.L.-L., V.R., R.M.S. and F.F.; software, M.C.-E. and F.A.R.-C.; validation, M.C.-E., F.A.R.-C. and L.A.; formal analysis, M.C.-E. and L.A.; investigation, M.C.-E., F.A.R.-C., L.A., P.L.-L. and M.A.; resources, M.C.-E., F.A.R.-C. and L.A.; data curation, M.C.-E.; writing--original draft preparation, M.C.-E.; writing--review and editing, M.C.-E., L.A., V.R., F.F., R.M.S., P.L.-I. and M.A.; visualization, M.C.-E. and F.A.R.-C.; supervision, L.A., F.F. and R.M.S.; project administration, L.A., F.F. and R.M.S. and funding acquisition, L.A., F.F. and R.M.S. All authors have read and agreed to the published version of the manuscript.  
The authors declare no conflict of interest. The statements made herein are solely the responsibility of the authors.