## 3 Results and Discussion  
### Simulation Results  
From all the 3D-RL simulation results, the relevant E-field and power density characterization, impact and behavior patterns were obtained:  
Firstly, Figures 10-12 present the Cumulative Density Function (CDF) for the received E-field and power density values in V/m and W/m\({}^{2}\), respectively, at the XY bi-dimensional plane of a 1.6-m height, which corresponded with the head height of the seated active users at the first floor of the library. First, Figure 10 presents the results for Case I, in which we considered that 100% of the users in the library were connected to 5G and no one to WLAN 802.11 ay. In Figure 9(a), an assessment between the 5G UL and DL connections was done, with different user densities (i.e., MD and HD). It could be seen that the, in the  
Figure 8: Transmitter antenna beamforming and radials of the receiver measurement points for the 28 and 60 GHz operating frequencies when the transmitter is placed on the first floor. Figure 9: Transmitter antenna beamforming and receiver measurement points for the 28 and 60 GHz operating frequencies when the transmitter is placed on the second floor: (a) 3D view and (b) 2D view. higher user density scenario, both UL and DL had higher E-field and power density values than the MD scenario in the order of 0.1-0.2 V/m or 0.005-0.01 W/m\({}^{2}\), approximately. In addition, it was observed that the DL connection results presented, on average, more E-field levels than UL for this case. This was due to the fact that we considered 70% of active users as using DL and 30% UL. Although the analyzed height was closer to the active user in the UL, the influence of the E-field/power density levels by nearby users due to UL was lower in average than the DL from the access points in the order of 0.1 V/m or 0.005 W/m\({}^{2}\). In order to have insight into the differences of both UL and DL in the different user densities considered, Figure 10b shows the CDF for the total E-field and power density values received at the same height in the scenario. As stated before, in order to calculate the realistic maximum exposure, \(F_{\rm TDD}\) was applied to calculate these results considering the ratio of the DL transmission time to UL transmission time. It could be seen that the total E-field exposure was higher for HD yet lower than 2 V/m for all user locations in the considered scenario. The same trend could be seen for the power density values, obtaining higher values for HD yet lower than 0.1 W/m\({}^{2}\) for all cases. Secondly, Figure 11 presents the results for Case II, in which we considered that 100% of the users in the library were connected to WLAN 802.11 ay and none to 5G. Following the same E-field and power density pattern than in the previous case, it could be seen that higher E-field and power density levels were obtained for the HD case yet remained for all cases below 2 V/m and 0.1 W/m\({}^{2}\), respectively. In comparison with Case I, the increasing frequency up to 60 GHz resulted in slightly lower exposure levels (in the order of 0.1-0.2 V/m for the E-field and 0.005-0.01 W/m\({}^{2}\) for the power density) than in a 28 GHz 5G system, as can be observed in Figure 11b, where the maximum exposure was  
Figure 10: CDF of the received E-field and power density for Case I at the XY bi-dimensional plane at head height when the people were working on the first floor of the library: (**a**) UL and DL comparisons for HD and MD and (**b**) the total E-field exposure and power density for HD and MD. calculated for Case II. This phenomenon was the result of the higher signal attenuation at higher frequencies. Finally, Figure 12 presents the most realistic case, where both systems coexisted (i.e., 30% of the users were connected to 5G and 70% to WLAN 802.11 ay). In Figure 12a, the difference of the maximum exposure values considering the ratio of DL transmission time to UL transmission time for the different systems and user densities is shown.