## 5 Conclusions  
In this paper, we have addressed the sensitivity analysis of the satellite forward budget link in multi-orbit systems according to the digital modulation schemes and error correction codes, highlighting the significant impact of these schemes on the overall performance of the satellite communication system. We have shown that the use of some modulation schemes, such as those in the DPSK or OFDM family, can provide an optimal balance between spectral efficiency and robustness to noise, essential for maximizing communications capacity and reliability, depending on the implementation case.  
At the same time, optimization of link parameters plays an important role in ensuring an adequate link budget. The correct choice of modulation scheme, depending on the specific operating conditions and application requirements, can significantly improve the performance and efficiency of satellite communication systems.  
Regarding the design of the link, the obtained results emphasize the importance of meticulous planning and a detailed analysis of all the components involved, at both the emission and reception, as well as the consideration and adequate predictions on the propagation part. In our analysis, we considered various multi-orbital scenarios, including a discussion on Starlink satellites.  
In the future, we propose to address this issue in the context of satellite constellations so that we can observe the impact and usefulness of different types of modulations in the inter-satellite connections. Another point of interest is the identification of the effects of scenarios that include the integration of 5G networks or the influence of advanced error correction algorithms on link performance.  
Conceptualization, D.S.; methodology, D.S.; software, D.S.; validation, A.B.; formal analysis, A.B.; investigation, A.B.; resources, D.S.; data curation, A.B.; writing--original draft preparation, D.S.; writing--review and editing, A.B.; visualization, A.B.; supervision, D.S.; project administration, D.S. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Article** & **Scenario** & **Modulation** & **Error Code** \\ \hline \multirow{8}{*}{Our paper} & & BPSK, QPSK, 8 PSK, & \\  & & 16 PSK, 32 PSK & \\  & Ground—GEO & BDPSK, QDPSK, & \\  & LEO—MEO & 8 DPSK, 16 DPSK, & Hard convolutional, \\  & LEO—GEO & 4 QAM, 8 QAM, & LDPC, \\  & MEO—GEO & 16 QAM, 32 QAM, & Reed-Solomon, \\  & LEO-LEO (Starlink) & 64 QAM, 128 QAM, & Golay \\  & & OFDM with BPSK, & \\  & & QPSK, 16 QAM and & \\  & & 64 QAM subcarriers & \\  & Ground—LEO & BPSK, MSK & Not mentioned \\  & Ground—GEO & QPSK, 8 PSK, 16 APSK & The not specified \\  & & Ground—GEO & QPSK & Turbo code \\  & Ground—LEO & BPSK, QPSK, 8 FSK & Mentioned, but \\  & LEO—LEO & BPSK, QPSK, 8 FSK & type not specified \\ \hline \hline \end{tabular}
\end{table}
Table 14: Comparison between different existing studies.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflicts of interest.