# Enhancing Communication Security in Drones Using QRNG in Frequency Hopping Spread Spectrum
## 4 Methodology and System Architecture  
In this section, we present our methodology to enhancing the security and robustness of FHSS systems by integrating a Randomness Processing Unit (RPU) to generate truly random frequency hopping sequences. The core idea of our methodology is to use the RPU to produce a sequence of true random numbers that are used to determine the hopping frequencies. Both the transmitter and receiver have access to this same sequence of random numbers, enabling them to stay synchronized during communication. This is achieved through secure key distribution or pre-sharing the random sequence prior to communication. By using true random numbers, the frequency hopping pattern becomes entirely unpredictable to an adversary, significantly enhancing security against eavesdropping and jamming attacks. Unlike traditional FHSS systems that rely on pseudo-random number generators (PRNGs) and shared seeds, which can be potentially predicted or replicated by attackers, our system's use of true randomness ensures that the hopping sequence cannot be reproduced without direct knowledge of the random numbers generated by the RPU. The synchronization between the transmitter and receiver does not depend on generating the same sequence independently but on both parties accessing the same random sequence securely. Secure key distribution mechanisms, such as public-key cryptography or pre-shared keys, are employed to share the random sequence or the necessary keys to access it. This approach maintains synchronization and ensures that only authorized parties can participate in the communication, thereby enhancing overall system security. Figure 2 illustrates the overall system architecture, highlighting the key components and their interactions within the proposed method. In FHSS, the carrier frequency is changed according to a predefined sequence [25; 26], hopping between different frequencies in a seemingly random fashion. This method spreads the signal over a wider bandwidth, providing robustness against narrowband interference and eavesdropping. The sequence of frequency hops is traditionally generated  
Figure 2: Diagram illustrating the methodology of using a Randomness Processing Unit (RPU) for true random frequency hopping in an FHSS system. using pseudo-random number generators (PRNGs), which, while complex, are ultimately deterministic and potentially predictable [27; 28]. Next, we provide a detailed explanation of how each component interacts and the data flow between them. 1. Randomness Processing Unit (RPU): The RPU generates a stream of true random numbers by exploiting inherent physical phenomena such as quantum noise or thermal fluctuations. These random numbers form the basis of the frequency hopping sequence and are critical for ensuring unpredictability in the system. 2. True Random Frequency Sequence Generator: The random numbers produced by the RPU are processed to generate a sequence of frequencies \(\{f_{o}\}\). This involves mapping the random numbers to specific frequencies within the available frequency band \(F\). The mapping ensures a uniform probability distribution over \(F\), maximizing entropy. The frequency sequence generator interfaces directly with the RPU to receive the random numbers and with the FHSS modulator to provide the frequency sequence. 3. FHSS Modulator: The FHSS modulator receives the true random frequency sequence from the frequency sequence generator. It modulates the carrier signal according to the frequency \(f_{o}\) specified for each time interval \([t_{o},t_{o+1})\). The modulator also incorporates the data to be transmitted, applying appropriate modulation techniques (e.g., frequency shift keying or phase shift keying). The modulated signal is then passed to the transmitter. 4. Transmitter: The transmitter amplifies the modulated signal and broadcasts it over the wireless channel. It ensures that the signal conforms to regulatory standards for transmission power and spectral occupancy.