rm factor. These main factors impacting the cell range are listed in Figure 4.6. Figure 4.7 illustrates path loss measurements in the LOS case with different frequen- cies from 2 to 38 GHz. There is a constant difference between the frequencies regardless of the distance. The path loss is approximately 26 dB higher at 28 GHz VS. 2 GHz, and 2 dB more at 38 GHz. These values clearly illustrate that the path loss at millimeter wave is considerably higher than at low band, and it will impact the cell range. When there are obstacles between the transmitter and receiver, the signal attenua- tion increases further, and the impact increases generally as a function of the frequency. Figure 4.8 illustrates the outdoor to indoor penetration loss at 28 GHz for residential family houses. The measurements compare the path loss when the receiver is outside by the window and indoors 1.5 m from the window. The median measured loss is 9 dB in the case of a plain glass window. The loss increases to 15 dB with low-emissivity win- dows and to 17 dB with foil-backed wall insulation. The building material was based on wood in these measurements. The penetration losses would be even higher if the device were deeper inside the building and if the building material were concrete. Propagation deeper into the building will increase the loss due to internal walls, furniture, and SO on. 4.3 Mid-Band Spectrum at 3.3-5.0 GHz and at 2.6 GHz Indoor penetration loss at 28 GHz [dB] Plain glass window Low loss building Foil-backed insulation material and and low-emissivity low-emissivity windows windows Figure 4.8 Measured outdoor to indoor penetration loss at 28 GHz in wooden building [2]. This additional loss appears to be rather weakly frequency dependent but rather strongly dependent on the composition of the interior of the building. The observed losses were 0.2-2 dB/m over the 2-60 GHz range. The total indoor penetration loss could increase to 30-40 dB in the case of concrete building material. Frequencies around 60 GHz experience some absorpt