## 4 Methodology of Simulations
### Methodology of the Simulation of Interference to NTN  
In the realm of satellite communications, the evaluation of throughput losses involves the examination of Modulation and Coding Schemes (MODCOD). These coding schemes are typically outlined in corresponding specifications. However, when it comes to incorporating adaptive modulation and coding schemes into simulations, there exists no universally accepted methodology. In contrast, 3 GPP terrestrial specifications have made significant progress in this area. They have developed a methodology that effectively accommodates adaptive modulation and coding schemes. To achieve this, 3 GPP has introduced link adaption approximations [21], which enable the accurate estimation of modem throughput losses, taking into account the intricacies of adaptive modulation and coding schemes. Given that NTN system D2D systems are designed to use the same waveforms to ensure compatibility with smartphones, these link-level adaptions developed by 3 GPP can be readily applied to the analysis of interference within the NTN system. The subsequent equations serve to approximate throughput over a channel, given a specific signal-to-interference-plus-noise ratio (SINR), measured in dB, when employing link adaptation:  
\[Throughput\ (SINR),\ bps/Hz= \begin{cases}0&for\ SINR<SINR_{MIN}\\ \alpha\cdot S(SINR)&for\ SINR_{MIN}\leq SINR<SINR_{MAX}\\ \alpha\cdot S(SINR_{MAX})&for\ SINR\ \geq\ SINR_{MAX}\end{cases} \]  
where:  
\(S(SINR)\): Shannon bound, \(S(SINR)=\log_{2}(1+10^{SINR/10})\) (\(\text{bps}/\text{Hz}\));  
\(\alpha\): Attenuation factor, representing modem implementation losses;  
\(SINR_{MIN}\): Minimum SINR of the code set, dB;  
\(SINR_{MAX}\): Maximum SINR of the code set, dB. In these equations, the Shannon bound represents the maximum theoretical throughput than can be achieved over an AWGN channel for a given SNIR. The parameters \(\alpha\), \(SINR_{MIN}\), and \(SINR_{MAX}\) can be chosen to represent different modem implementations and link conditions [22]. The parameters from Table 5 represent a typical case, which assumes the following:  
1:1 configuration of the antenna;  
AWGN channel model;  
Link Adaptation;  
No HARQ. Figure 5: Simulation of the single-entry interference from a Starlink satellite to the MSS receiver: (**a**) view from Starlink; (**b**) view from MSS. Based on the above equations, bitrate mapping can be calculated for the uplink and downlink. Figure 6 represents bitrate mappings for the downlink and uplink of the typical NTN system. To determine the throughput loss for both the uplink and downlink in a considered network, the essential steps involve calculating the signal-to-noise ratio (SNR) of all the connections and assessing interference (I) from interfering stations. Next, the interference level should be combined with the background noise level in the analyzed system to compute the signal-to-interference-plus-noise ratio (SINR). These SINR values can then be compared against the reference curves in Figure 6, and the throughput loss can be determined using the following formula:  
\[\text{Throughput}[kbps]=\frac{N_{RB\_per\_UE}}{N_{total\_RBs}}.S_{capacity}~{}( SINR)\cdot B\cdot 1000\]  
where _Throughput[kbps]_ is the maximum throughput of the channel, expressed in bps, \(N_{RB\_per\_UE}\) is the number of resource blocks (RBs) per user, \(N_{total\_RBs}\) the total number of RBs, \(B\) stands for the channel bandwidth, expressed in MHz, and \(S_{capacity}\) is the spectral efficiency, depending on the _SINR_, expressed in bps/Hz. Figure 7 illustrates a simulation depicting interference from a Starlink satellite to the NTN satellite receiver when the NTN satellite is serving a user during a close flyby of the Starlink satellite for a single-entry interference case and for aggregate interference.