# Review of Physical Layer Security in Integrated Satellite-Terrestrial Networks
## 4 Review
### Physical Characteristics
The accurate characterization of these channels is crucial for efficient resource allocation, interference management, and link performance optimization. To address these challenges, researchers are exploring hybrid channel models that combine terrestrial and satellite channel characteristics, leveraging advanced techniques like machine learning and deep learning for model calibration and prediction. While noise can be a powerful tool in PLS, it can also introduce challenges. The goal in PLS is to exploit noise to make eavesdropping difficult, but excessive noise can degrade the signal quality to the point where it becomes unreliable. This can lead to ineffective authentication. Excessive noise can obscure the intended signal, making it difficult for the receiver to accurately decode the transmitted data. This can lead to authentication errors, as the receiver may not be able to verify the sender's identity correctly. Noise can introduce errors that mimic legitimate authentication signals. This can lead to false positives, where unauthorized parties are mistakenly authenticated. Noise can also cause legitimate authentication signals to be missed or misinterpreted. This can lead to false negatives, where authorized parties are denied access. The physical characteristics of communication channels offer unique advantages for achieving PLS in ISTNs. By leveraging factors such as fast fading, slow fading, background noise, forward and reverse link asymmetry, and the differences between terrestrial and  
Figure 8: The AR as a function of the adversary’s signal strength \(\delta\). The results demonstrate the superior performance of the proposed RVSC method in maintaining a high AR even under challenging spoofing conditions. In contrast, the direct detection method exhibits a significantly lower AR, indicating its vulnerability to spoofing attacks. As the adversary’s signal strength increases, the direct detection method’s AR rapidly degrades, while the RVSC method consistently maintains a high level of resistance. Reprinted with permission from ref. [104]. Copyright: 21 October 2024 IEEE. \begin{table}
\begin{tabular}{l l} \hline \hline
**Reference** & **Physical Characteristics** \\ \hline \hline \
\begin{tabular}{l} [107] \\ [104] \\ [103] \\ [108] \\ \end{tabular} &
\begin{tabular}{l} Doppler shift \\ Rapid signal variation \\ Spatio-temporal characteristics of signal \\ Tropospheric scintillation fading \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: References using the physical characteristics of the channel to improve the PLS of the communication network. satellite links, networks can create a more complex and unpredictable environment for potential attackers. While these physical characteristics provide a promising foundation for PLS, their effective exploitation requires accurate channel modeling and reliable parameter estimation. The complex and dynamic nature of ISTN channels, coupled with diverse propagation environments, introduces challenges in accurately characterizing and modeling these channels. Addressing these challenges through hybrid channel models and advanced estimation techniques is crucial for maximizing the effectiveness of PLS in ISTNs. It is important to note that while noise can be a powerful tool for PLS, excessive noise can introduce challenges such as degraded signal quality, authentication errors, and false positives/negatives. Therefore, the careful management of noise levels is essential for ensuring the effectiveness of PLS while maintaining reliable communication. Extensive work is ongoing to develop advanced channel models that capture the unique characteristics of terrestrial and satellite links. Reliable estimation of channel parameters at the transmitter and receiver is essential for exploiting channel variations for security purposes, but it is difficult in this scenario. Techniques need to be robust and adaptable to handle dynamic channel conditions. The physical characteristics of ISTN channels offer a powerful foundation for achieving PLS.