# A Survey on Satellite Communication System Security
## 5 Defense in Satellite Communication Systems
### Solutions for Availability  
Anti-Jamming  
Anti-jamming in SCSs refers to the techniques and strategies used to protect satellite signals from intentional interference or jamming attacks. These methods aim to ensure the integrity and availability of SCSs by mitigating the effects of jamming. Anti-jamming can involve a variety of approaches, such as using spread spectrum technologies, frequency hopping, signal encryption, and implementing robust error-correcting codes. These techniques enhance the resilience of SCSs against deliberate attempts to disrupt or degrade the signal quality. An overall summary of anti-jamming and its pros and cons is shown in Table 4.  
**Game Theoretic Approaches:** Mitigating a jamming attack using a game-theoretic approach in SCSs involves formulating the interaction between a jammer (attacker) and a communication system (defender) as a strategic game. In this framework, each participant is considered a player with specific strategies. The goal is to analyze and predict the behaviors of the jammer and the defender, with the aim of finding optimal strategies for the defender to minimize the impact of jamming. [PERSON] et al. [77] apply game theory to address FHSS satellite jamming. They formulate the minimization of the damaging effect of satellite jamming attacks as a two-player asymmetric zero-sum game framework, where the payoff is modeled as the channel capacity of the defender under white additive Gaussian noise. Also, ref. [78] presents a two-stage anti-jamming scheme for satellite internet communication. This scheme integrates a deep-reinforcement-learning-based routing algorithm with a fast response anti-jamming algorithm, using Stackelberg game theory for dynamic and uncertain environments. **Filtering-based Approaches:** Mitigating a jamming attack using a filter-based approach in SCSs involves implementing specific filtering techniques to isolate and remove the jamming signal from legitimate communication signals. This approach typically uses advanced signal processing algorithms to distinguish between the noise introduced by the jammer and the genuine satellite signals. Figure 14: Key exchange process in QKD. The authors of [79] discuss a range of anti-jamming strategies for small satellites. They cover modulation adjustments, wave filtering, spread spectrum techniques, smart antenna technology, and methods to counter broadband interference, emphasizing an integrated approach for enhanced system robustness against jamming. Similarly, ref. [39] also introduces an anti-jamming technique that is a dual-filter approach combining the augmented-state approximate conditional mean filter and discrete wavelet transform filter to mitigate FM jamming in GPS receivers. This method is effective for both single and multiple FM jammers, with simulations demonstrating its efficacy, especially in high jammer-to-signal scenarios. DoS/DDoS Mitigation  
DoS and DDoS attacks aim to neutralize or halt the function of devices. Typically, these types of attacks can be countered in various ways, such as detecting intrusions in the network or verifying changes. In SCS networks, defending against DoS and DDoS attacks usually involves ground-satellite integrated systems and detection from the ground, as computational costs are high in satellite systems. Therefore, this solution is approached by dividing it into four categories: blockchain-based solutions, secure routing-based solutions, SDN-based solutions, and collaborative-based solutions. An overall summary of DoS and DDoS attack mitigation and its pros and cons is shown in Table 5.  
**Blockchain-based Mitigation:** Blockchain technology has recently emerged and allows for transparent information sharing within a network. Typically, a blockchain database stores data in sequentially linked blocks, making them detectable by other users if any chain is altered or deleted without network consensus. This ensures the blocks in a blockchain maintain temporal consistency, guaranteeing the immutability and unchangeability of transactions [11].