## 7 Simulation Results with ITU-R P.452-17  
The ITU-R P.452-17 simulations were carried out using the CHIRplus_BC software 7.5.1.1. This software is commonly used for coverage planning and radio network analysis and includes a built-in implementation of the ITU-R P.452-17 model. However, users should be aware that the results may be influenced by the characteristics of the simulator, such as the resolution of terrain data, the numerical methods applied for diffraction and atmospheric attenuation, and internal model approximations. The model-specific parameters were selected as follows: the time percentage was set to \(p=50\%\), the prediction type was set to an average year, the temperature to 20 \({}^{\circ}\)C, the atmospheric pressure to 1013.25 hPa, and the water vapor density to \(\rho=8.0\) g/m\({}^{3}\). Gaseous attenuation was calculated according to the ITU-R P.676-12 model, with \(N_{0}=330\) N-units and \(\Delta N=-45\) N/km. The receiver height was again set to 10 m, while the technical parameters of the base stations and the locations of the test points remained unchanged. Figure 23 shows the simulated field strength distribution for the 3.6 GHz band around all three base stations. It can be seen that the coverage areas differ due to topographic features, particularly in hilly environments. Similarly, Figure 24 presents the corresponding results at 6 GHz. When comparing these two figures, a general reduction in field strength is visible for the higher frequency, particularly in non-line-of-sight (NLOS) areas. To illustrate this difference quantitatively, Figure 25 provides a differential map, where blue regions highlight stronger attenuation at 6 GHz compared to 3.6 GHz. Based on the obtained results, the field strength values at 6 GHz are typically 1-3 dB lower than those at 3.6 GHz, which is generally the expected outcome due to the increased attenuation associated with higher frequencies. A more detailed examination of the figures reveals that in test points with significant terrain obstruction, the signal level is consistently lower at 6 GHz than at 3.6 GHz. However, it is also clearly visible--particularly in the case of base station TestBS_2--that the model calcula  
Figure 24: Field strength level values around the base stations (ITU-R P452-17, 6 GHz). Figure 23: Field strength level values around the base stations (ITU-R P452-17, 3.6 GHz). nal at 6 GHz than at 3.6 GHz. At first glance, this might seem counterintuitive, as the free-space propagation formula alone would suggest a frequency-related difference of \(20\log_{10}(6000/3600)\approx 4.4\) dB. One possible explanation for this apparent contradiction lies in the first-order Fresnel zone, more precisely in its frequency dependence. Its radius is given by \(r_{F1}\approx 0.5\sqrt{\lambda\frac{d_{t}d_{r}}{d_{t}+d_{r}}}\), where \(d_{t}\) and \(d_{r}\) denote the distances from the obstacle to the transmitter and receiver, respectively. It is evident that the smaller the wavelength (\(\lambda\)), the smaller this zone becomes. This implies two important consequences:  
* If an obstacle partially intrudes into the wave's path under given geometric conditions, the higher-frequency (smaller \(\lambda\)) wave may pass beside it, whereas the lower-frequency wave may still intersect the zone and experience attenuation. * If the obstacle causes significant obstruction, the longer wavelength may diffract around it more effectively, resulting in lower loss, while the shorter wavelength tends to remain \"in the shadow\" behind the object. This seemingly paradoxical duality can be observed in the case of the test points associated with TestBS_2. To better understand the statistical distribution of signal levels, Figure 26 shows the boxplot and scatter plot for 3.6 GHz. It reveals high variability, particularly in shadowed regions. Figure 27 presents the same analysis for 6 GHz, where attenuation is more severe and the variability is slightly lower due to limited diffraction in obstructed zones.