# Enhancing Communication Security in Drones Using QRNG in Frequency Hopping Spread Spectrum
## 6 Application to a Drone Cloud with Ring Topology
### Synchronization and Key Management  
To establish communication, drones must initially synchronize their RPUs to ensure that the frequency hopping sequences are correctly aligned. This synchronization can be achieved using GPS time stamps or a dedicated synchronization signal.  
Each drone pair must securely exchange an initial key or synchronization data to coordinate the start of the frequency hopping sequence. Public-key cryptography can be used for this purpose, providing a secure means of distributing the necessary information.  
Figure 3: Diagram of the drone cloud with ring topology implementing FHSS with true random frequency hopping.  
Given the potential for clock drift or other synchronization issues, drones periodically resynchronize their frequency hopping sequences. This can be achieved through a resynchronization protocol, possibly using reserved channels or a periodic synchronization beacon.  
While it is true that an initial secure and reliable channel is used for exchanging keys and synchronization data between drones, the primary purpose of this channel is to establish the parameters necessary for secure communication. However, relying solely on this channel for all communication would expose the system to vulnerabilities associated with fixed-frequency transmissions, such as jamming, interception, and eavesdropping.  
The use of Frequency Hopping Spread Spectrum (FHSS) for the main communication channel offers several critical advantages:  
* Resistance to Jamming: FHSS systems are inherently resistant to jamming attacks because the frequency changes rapidly in a pattern known only to the communicating parties. An adversary attempting to jam the communication would need to jam all possible frequencies simultaneously, which is often impractical.
* Enhanced Security: By hopping frequencies in a true random sequence, the communication becomes extremely difficult to predict or intercept without knowledge of the hopping pattern. This significantly reduces the risk of eavesdropping and unauthorized access.
* Interference Mitigation: FHSS helps in mitigating interference from other devices operating in the same frequency band. Since the communication frequency changes rapidly, the impact of any interference on a particular frequency is minimized.
* Robustness in Adverse Environments: Drones often operate in environments where the communication channel conditions can vary rapidly due to movement, obstacles, or other factors. FHSS provides robustness against such variations, maintaining reliable communication.
* Scalability: In a network of multiple drones, FHSS allows for better spectrum utilization and reduces the likelihood of collisions, as different pairs can use different hopping patterns.  
The initial secure channel is typically a narrowband communication link used specifically for key exchange and synchronization due to its simplicity and lower resource requirements. It is not designed to handle the bandwidth and security requirements of continuous drone communication, especially in hostile or dynamic environments. By transitioning to an FHSS-based communication channel after the initial setup, the system leverages the benefits of spread spectrum techniques to enhance overall communication security and reliability.  
Therefore, while the initial secure channel is essential for setting up communication parameters, the use of FHSS for ongoing communication is critical for protecting against threats and ensuring the robustness of the drone network in real-world operating conditions.