## 4 Discussion  
This study's results are limited due to the network data that were used and the definition of the total dose, as stated in the Introduction. The results are also based on the currently relatively limited knowledge about the actual deployment and development of 5G. In this study, we do not consider the effect of upcoming massive multiple-input multiple-output (MIMO) and multi-user MIMO systems in 5G networks. MIMO usage is likely to improve link throughput in 5G networks and hence reduce local exposure for heavy users. However, due to space limitations in realistic handsets, we do not expect MIMO implementations with more than four antennas (4 \(\times\) 4 MIMO) at frequencies \(<\)6 GHz, i.e., with a theoretical throughput increase of 6 dB in the uplink. In the downlink, massive MIMO configurations will be implemented. Locally, beam-steering in the downlink will result in temporal fluctuations \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Location**} & \multirow{2}{*}{**Bystander**} & \multirow{2}{*}{\(N\)} & \multicolumn{3}{c}{**Cell Edge**} & \multirow{2}{*}{**0 MB/d**} & \multirow{2}{*}{**100 MB/d**} & \multirow{2}{*}{**1 GB/d**} & \multirow{2}{*}{**10 GB/d**} & \multirow{2}{*}{**10 GB/d**} \\  & & & **Reduction** & & & & \\  & & & **0 dB** & & & & \\ \hline rural-macro & \(r=25\) m & [0] & [0] & 0 & 7.9 & 20.0 & 33.0 \\ rural-macro & \(r=25\) m & [0.8] & [0] & \(-\)0.9 & 4.0 & 13.9 & 26.4 \\ suburban-macro & \(r=10\) m & [0] & [0] & 0 & 11.0 & 25.0 & 37.8 \\ suburban-macro & \(r=10\) m & [0.8] & [0] & 2.0 & 8.1 & 18.0 & 30.9 \\ urban-macro & \(r=5\) m & [0] & [0] & 0 & 15.6 & 30.4 & 42.5 \\ urban-macro & \(r=5\) m & [0.8] & [0] & 3.0 & 12.0 & 24.0 & 35.4 \\ urban-macro & \(r=1\) m & [0] & [0] & 0 & 11.2 & 25.2 & 37.3 \\ urban-macro & \(r=1\) m & [0.8] & [0] & \(-\)0.2 & 6.2 & 18.6 & 30.2 \\ urban-mini & \(r=5\) m & [0] & [0] & 0 & 10.0 & 22.6 & 36.1 \\ urban-mini & \(r=5\) m & [0.8] & [0] & 4.0 & 8.0 & 16.8 & 29.3 \\ urban-mini & \(r=1\) m & [0] & [0] & 0 & 7.8 & 19.5 & 33.5 \\ urban-mini & \(r=1\) m & [0.8] & [0] & 1.5 & 5.5 & 14.0 & 26.4 \\ urban-micro & \(r=5\) m & [0] & [0] & 0 & 7.1 & 18.3 & 30.3 \\ urban-micro & \(r=5\) m & [0.8] & [0] & 11.0 & 12.0 & 16.1 & 24.5 \\ urban-micro & \(r=1\) m & [0] & [0] & 0 & 6.2 & 17.3 & 29.4 \\ urban-micro & \(r=1\) m & [0.8] & [0] & 10.0 & 10.3 & 15.0 & 23.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Total dose change (in dB) as a function of the data usage relative to the non-user without indoor coverage (i.e., values for \(N=80\%\) have been normalized to the scenario for \(N=0\) with no data usage). Displayed are the 95 th percentile values for all four user types (light user (100 MBtyte/day), moderate user (1 GByte/day), heavy user (10 GByte/day), and non-user (0 MBtyte/day)). Situations have been analyzed for \(N=0\) (i.e., no additional indoor coverage) and \(N=80\%\), i.e., rather strong indoor coverage. of the incident field strength. Preliminary experiments suggest that the peak-to-average ratio is approximately 6 dB in 5G MIMO downlink scenarios [9]. WLAN [30] is not considered in this study, as WLAN indoor infrastructure can reduce the exposure to electromagnetic fields in ways similar to indoor 5G infrastructure by reducing the path loss between the access point and the user equipment. However, due to technological and deployment limitations, the exposure reduction by WLAN use is limited, and in fact, to date, WLAN is still a major source of exposure [31]. The use of millimeter-wave frequencies in 5G mobile networks is not considered in this study. However, the use of millimeter waves would dramatically change the exposure compared to the current sub-6 GHz implementation: (i) millimeter waves would require a much denser base station network, (ii) exposure would be mainly superficial, of mainly the skin tissues, and (iii) it is further expected that the strong directivity and beamforming capability of handset antenna arrays would reduce the exposure due to one's own device.