# Challenges of Using the L-Band and S-Band for Direct-to-Cellular Satellite 5G-6G NTN Systems
## 4 Simulation Methodology  
### Study Assumptions and Protection Criteria  
The evaluation of the interference from the 5G NTN system on incumbent satellite systems was conducted using a simulation that considered the orbital characteristics of the satellites involved. Throughout the simulation, the interference levels and desired signal levels at the victim receiver's input were sampled at regular intervals of 1 s. This step size was chosen to ensure precise results and to observe the variations within the simulated timeframe, including the percentage of time when the interference levels exceeded the threshold levels. The performance degradation of the victim satellite systems due to interference was evaluated based on two criteria. The first criterion focused on the degradation of the carrier-to-noise ratio (_C/N_), which can be expressed as the _C/(N + I)_ ratio. It is widely accepted that a tolerable signal-to-noise degradation is 1 dB, which corresponds to a 10% reduction in spectral efficiency [18; 19]. This criterion is also mentioned in ITU-R Recommendation S.2131, although it was originally defined in the context of the DVB-S2 standard. Nevertheless, it can be applied to other systems as well. The second protection \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Carrier** & **Carrier Power,** & **Carrier Power,** & **Sat. TX Gain** & **ES Type** & **ES Gain (dBi)** & **ES Sidelobe** & **Noise Temp.** \\
**Assignment** & **Max (dBW)** & **Min (dBW)** & **(dBi)** & **ES Type** & **ES Gain (dBi)** & **Formula** & **(K)** \\ \hline
28K0G1W\(-\) & 18 & \(-\)7 & 11 & RTU-1 & 14 & APS & 290 \\
14K0G1W\(-\) & 15 & \(-\)10 & 11 & RTU-1 & 14 & APS & 290 \\
5K60G1W\(-\) & 17 & \(-\)8 & 11 & RTU-1 & 14 & APS & 290 \\
28K0G1W\(-\) & 14 & \(-\)11 & 11 & RTU-1 & 14 & APS & 290 \\
1K40G1W\(-\) & 11 & \(-\)14 & 11 & RTU-1 & 14 & APS & 290 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The link characteristics of the Lyra satellite system. Figure 6: Simulation of the wanted Lyra link (space-to-Earth). criterion is based on the increase in noise temperature at the victim receiver, represented as DeltaT/T. In satellite systems, the commonly used threshold level for DeltaT/T is 6% as a coordination trigger. This value can be expressed in dB as the interference-to-noise ratio (I/N) of \(-12.2\) dB [20]. A typical scenario of NTN satellite interference at an incumbent system Earth station is illustrated below in Figure 7:  
The interference level from the \(i\)-th interfering 5G NTN satellite of the \(j\)-th beam can be calculated using the following expression [17]:  
\[I=P_{\rm NTN}+G_{\rm NTN}(\varphi)+G_{victim}(\varphi)-L_{b}-L_{xpr} \tag{2}\]  
where \(I\) is an interference level from the \(i\)-th NTN transmitting station, \(P_{\rm NTN}\) is the output power of the transmitting NTN station in dBW, adjusted to the victim receiver bandwidth, \(G_{\rm NTN}\) is the gain of the transmitting antenna of an NTN satellite towards the victim receiver direction in dBi, \(G_{victim}\) is the gain of the receiving antenna of the victim receiver station towards the interfering station direction in dBi, \(L_{b}\) is the propagation loss between the interfering NTN transmitter and victim receiver in dB, and \(L_{xpr}\) is the cross-polarization loss. The propagation loss can be found using the free-space formula below:  
The main transmission losses for a space-to-Earth line under clear-sky conditions, not exceeded for \(p\%\) of the time, for one transmitter and one interference receiver, are generally calculated as follows:  
\[L_{b}=L_{bfs}+A_{xp}+A_{gas}+A_{bs}+A_{s}(p)+L_{dtb}(p) \tag{3}\]  
where \(L_{bfs}\) is the free space loss; \(A_{xp}\) is the attenuation due to [PERSON]'s rotation; \(A_{gas}\) represents attenuation in atmospheric gases; \(A_{bs}\) is attenuation due to beam spreading; \(A_{s}(p)\) is attenuation due to either ionospheric or tropospheric scintillation; and \(L_{dtb}(p)\) is the ducting-enhanced diffraction loss.