# Radio Frequency Interference, Its Mitigation and Its Implications for the Civil Aviation Industry
## 3 Literature Review
Furthermore, the paper stresses achieving EMC through design, manufacturing, maintenance, training, and awareness initiatives for improved technological device usage and maintenance. [PERSON] et al. [21] examine various mechanisms that cause out-of-band interference, which can disrupt GNSS receivers. It identifies key disruptive factors such as saturation, desensitization, reciprocal mixing effects, intermodulation products, aliasing, and in-band emissions. The paper provides detailed explanations of these mechanisms and discusses strategies to mitigate each one. The study is set against the backdrop of the growing dependence on GNSS technology and the susceptibility of GNSS receivers to out-of-band interference. The findings offer a comprehensive understanding of these disruptive mechanisms and effective mitigation strategies, which are essential for enhancing the reliability and accuracy of GNSSs. Monitoring interference is an important topic, and [PERSON] et al. [22] outline a method for monitoring RFI in civil aviation using UAVs, emphasizing four key contributions. Firstly, it introduces an angle-of-arrival (AOA) algorithm that improves the accuracy of RFI location by using directional antennas to determine the azimuth of radio signals. Secondly, it describes the development of a lightweight UAV monitoring platform that meets airworthiness standards, ensuring safe data collection. Thirdly, it details a ground analysis system designed for real-time data processing and the intuitive visualization of RFI locations. Lastly, the method is validated through various test scenarios, showing superior performance in terms of radius monitoring and positioning accuracy compared to traditional ground-based methods. Figure 6 shows the process of [PERSON] et al. [22] for RFI monitoring using a UAV. [PERSON] et al. [23] introduce a monitoring network established in Japan to observe the anomalous propagation (EsAP) of aeronautical VHF radio waves, which are influenced by sporadic layers of E (Es). Operational since May 2019, the network comprises six stations equipped with software-defined radios that capture signals within the 98 to 118 MHz frequency range. This system facilitates near-real-time monitoring, providing essential data for aviation navigation and communication. The network has successfully identified multiple instances of EsAP, with notable variations in signal intensity across different stations. This capability enables the distinction between equipment malfunctions and interference caused by Es, thereby enhancing operational safety. Ongoing efforts to  
Figure 5: Architecture used by [PERSON], [PERSON], and [PERSON] [19] to show emissions. develop algorithms for automatic data analysis aim to further improve the visualization and understanding of Es impacts on VHF communications. [PERSON] et al. [24] explore the growing dangers that RFI poses to Global Navigation Satellite System (GNSS) receivers in commercial Aircraft. They highlight problems such as jamming and spoofing, which can result in navigation failures and safety hazards. To counter these issues, the authors suggest a three-part approach: detecting RFI, accurately measuring the extent of the errors caused, and ensuring that receivers can still provide genuine position information even during interference. Furthermore, the paper stresses the importance of combining GNSS data with other navigation sensors like Inertial Reference Systems (IRSs) and Distance Measuring Equipment (DME) to improve overall navigation integrity and reliability in the face of RFI threats. Figure 7 shows the process of RFI on the GNSS receivers used by the authors. Researchers at MIT [14] discussed three novel techniques to mitigate interference in aeronautical communication: Pulse Blanking, Space Time Block Coding (STBC), and Decision-Directed Noise Estimation (DDNE). Using cognitive radio technology, Aircraft spectrum access was enhanced through dynamic identification and the utilization of available spectral bands, addressing the problem of spectrum scarcity.