## 6 The ITU-R P.452-17 Wave Propagation Model  
The ITU-R P.452-17 recommendation provides a widely adopted propagation model with a broad range of applications, primarily developed for estimating interference between terrestrial stations. It is applicable across a wide frequency range, covering the radio spectrum from 100 MHz to 50 GHz, and is therefore suitable for the frequencies considered in our study, namely 3.6 GHz and 6 GHz. The distance limit of the model is 10,000 km. The model is explicitly intended for outdoor scenarios involving antenna heights close to the ground, making it appropriate for assessing interference between base stations in land mobile service systems [56]. As the model is designed for stations operating within the surface layer, it is not applicable to systems with extremely high antenna elevations, nor is it suitable for aeronautical systems. The purpose of the model is to determine the minimum expected propagation path loss between two terrestrial stations. As this minimum path loss corresponds to the highest potential interfering signal level, the model is primarily used for worst-case interference estimation. It is therefore particularly suitable for analyzing frequency band sharing scenarios, where different telecommunications services or systems operate within the same or adjacent frequency bands in geographically nearby areas. This propagation model takes into consideration multiple propagation mechanisms, which are classified into two main categories: long-term propagation mechanisms and short-term mechanisms associated with anomalous conditions. The classification of these propagation mechanisms is presented in Figures 19 and 20 as well as in Table 6.  
Figure 19: Long-term propagation mechanisms of ITU-R P.452-17. Figure 20: Short-term propagation mechanisms of ITU-R P.452-17. The ITU-R P.452-17 model estimates the basic transmission loss based on the following key input parameters. The frequency \(f\) [GHz], the polarization, and the great-circle distance \(d\) [km] define the radio path, and the time percentage \(p\) [%] determines the statistical reliability level for which the loss is evaluated. Antenna heights above sea level are given by \(h_{ts}\) and \(h_{ts}\) [m], and the corresponding antenna gains in the path direction are \(G_{t}\) and \(G_{r}\) [dBi]. Geographic coordinates \((\phi_{t},\psi_{t})\) and \((\phi_{r},\psi_{r})\) locate the transmitter and receiver, and the terrain elevation data and the land/sea path fraction \(\omega\) are also required. Radio-climatic parameters, including the average refractivity lapse rate \(\Delta N\), the surface refractivity at sea level \(N_{0}\), and the time percentage \(\beta_{0}\) associated with anomalous propagation conditions, are derived from ITU-R climate maps [57]. The algorithm of the model first determines the free-space path loss based on the input parameters, augmented by a term representing the attenuation caused by atmospheric gases. This can be considered the basis of the model, so we will also review its equations within the framework of the article. The equation takes the following form:  
\[L_{\rm bfsg}=92.45+20\log_{10}(f)+20\log_{10}(d_{\rm fs})+A_{g}(d_{\rm fs}), \tag{37}\]  
where \(d_{\rm fs}\) [km] is the distance between the transmitting and receiving antennas:  
\[d_{\rm fs}=\sqrt{d^{2}+\left(\frac{h_{\rm fs}-h_{\rm rs}}{1000}\right)^{2}}, \tag{38}\]  
and \(A_{g}(d_{\rm fs})\) denotes the total gaseous attenuation, calculated as follows:  
\[A_{g}(d_{\rm fs})=d_{\rm fs}[\gamma_{0}+\gamma_{w}(\rho)]. \tag{39}\]  
In the expression for gaseous attenuation, \(\gamma_{0}\) and \(\gamma_{w}\) represent the specific attenuation due to dry air and water vapor, respectively. These quantities should be determined using the equations provided in ITU-R Recommendation P.676 [58]. In the equation, \(\rho\) denotes the water vapor density, which can be calculated using the formula \(\rho=7.5+2.5\omega\) [g/m\({}^{3}\)], where \(\omega\) represents the proportion of the total propagation path that lies over water.