or macrocell links, cell densification has already reduced the required link distance to a substantially smaller range in urban areas, and the densification process will continue to reduce cell sizes. For a link distance of approximately 200 m, the path loss of a 60 GHz link in heavy rain con- dition is less than 3 dB. Fig. 3.4 illustrates the impact of rainfall and oxygen absorption throughout the nmWave transmission. A more serious issue than free-space loss for nmWave signals is their limited penetration through materials and limited diffraction. In the urban environment, coverage for large cells could be particularly challenging; how- ever, cell densification can be used to achieve the ambitious 5G capacity goals. Atmospheric effects such as oxygen and water vapor absorption as well as fog and precipi- tation can scale exponentially with the link distance. Limiting to distances below 1 km, attenuation caused by atmospheric gases can be neglected up to 50 GHz, as shown in Fig. 3.4. However, above 50 GHz, it becomes important to consider the oxygen absorption peak of approximately 13 dB/km at 60 GHz and the water vapor resonance peak at 183 GHz of approximately 29 dB/km for relative humidity of 44% under standard Gaseous H2O and O2 Free space Frequency (GHz) Figure 3.4 Comparison of gaseous H2O + O2, rain, and free-space attenuation (propagation distance 1 km, rain rate of 95 mm/h, and dry air pressure is 1013 hPa and the water vapor density is 7.5 g/m³. New Radio Access Physical Layer Aspects (Part 1) 301 conditions. Note that neither fog nor rain is relevant for frequencies below 6 GHz. At fre- quencies above 80 GHz, dense fog related to a visibility of less than 70 m has a noticeable impact dB/km) and becomes severe above 200 GHz ( > 10 dB/km). Drizzle and steady rain are not a substantial issue for distances up to 1 km (3.0-4.4 dB/km above 70 GHz). However, as shown in Fig. 3.4, heavy rain attenuation increases up to 10-15 dB/km, and for downpours, up to 40 dB/km can be experienced. In summary, atmospheric 