## 4 Simulation Methodology  
The simulations were done using MATLAB and STK platforms. The methodology used in this study uses Monte-Carlo simulation to calculate interference level from IMT terrestrial networks to the GSO FSS uplink operating in the 6425-7125 MHz frequency band and then estimating degradation of the composite link taking into account downlink operation in the frequency band 3400-4200 MHz. One of the most challenging things in estimating interference from large areas of terrestrial networks towards GSO satellites is to understand the deployment density of terrestrial interfering stations inside the satellite footprint. ITU-R for that purpose developed a methodology to determine the density of the interfering stations. For the implementation of the methodology two parameters were developed, the first one is Ra which is the ratio of coverage areas to areas of cities/built areas/districts, the second is Rb which is the ratio of built areas to the total area of the region in study. The values of Ra and Rb depend on the region size and are presented in Table 3.  
Figure 6: EIRP distribution in azimuth and elevation plane of 5G base stations (**a**) Urban deployment; (**b**) Suburban deployment. Total number of the 5G base stations inside the footprint may be calculated using the following expression:  
\[\mathrm{DI_{ur/sub}}=\mathrm{Ds_{ur/sub}}*\mathrm{Ra_{ur/sub}}*\mathrm{Rb} \tag{1}\]  
where Ds is a density of simultaneously active BS transmitters per km\({}^{2}\) for the reviewed coverage area, this value is provided in Table 2; Ra (%) is a ratio of coverage areas to areas of cities/built areas/districts; Rb (%) is a ratio of built areas to the total area of the region in study. Given that this study involved large areas where mixed environments of urban, suburban, and rural are involved inside a satellite footprint, it may not be appropriate to assume that 5G base stations will be deployed with the same density as shown above across the entire footprint area. Thus, the deployment density values may need to be adjusted. This adjustment should be justified by the results of studies, e.g., by providing population density data and assumptions on coverage in less populated areas using the considered band. It is proposed to quantify such an assumption with the factor Rc, described below. To consider the deployment of the rural case, factor Rc could be defined as the ratio of coverage areas to the areas in a rural environment. This factor could be applied in the following equation:  
\[\mathrm{DI_{ru}}=\mathrm{Ds_{ru}}*\mathrm{Rc}*\mathrm{(100\text{-Rb})} \tag{2}\]  
The total number of BS on the surface of the study is then based on the association of each DI for each environment:  
\[\mathrm{DI_{tot}}=\mathrm{DI_{ur}}+\mathrm{DI_{sub}}+\mathrm{DI_{ru}} \tag{3}\]  
Finally, the total number of BS in the footprint could be expressed as:  
\[\mathrm{DI}=\mathrm{(Ds_{ur}}*\mathrm{Ra_{ur}}+\mathrm{Ds_{sub}}*\mathrm{Ra_{ sub}})*\mathrm{Rb}+\mathrm{Ds_{ru}}*\mathrm{Rc}*\mathrm{(100\text{-Rb})} \tag{4}\]  
where Ds \(\mathrm{ur/sub}\) is a density of simultaneously active BS transmitters per km\({}^{2}\) for the reviewed coverage area with urban and suburban deployment; Ra\(\mathrm{{}_{ur/sub}}\) (%) is a ratio of coverage areas to areas of cities/built areas/districts in urban (ur) or suburban (sub); Rb (%) is a ratio of built areas to the total area of the region in the study; Rc (%) is a ratio of coverage areas to rural areas. By definition Rc (%) is a ratio of coverage areas to rural areas:  
\[\mathrm{Rc}\left(\%\right)=\mathrm{S_{coverage}/S_{\mathrm{ rural}}} \tag{5}\]  
Ra (%) is a ratio of coverage areas to areas of cities/built areas/districts or  
\[\mathrm{Ra}\left(\%\right)=\mathrm{S_{coverage}/S_{built\text{-in}}} \tag{6}\]  
From (2):  
\[\mathrm{S_{coverage}}=\mathrm{Ra}\left(\%\right)*\mathrm{S_{built\text{-in}}} \tag{7}\]