# Radio Frequency Interference, Its Mitigation and Its Implications for the Civil Aviation Industry
## 3 Literature Review  
RFI is a very broad yet interesting topic; however, when it comes to its implications for the aviation industry, the sourcing of recent research work becomes quite challenging. A lot of effort was put into finding relevant and recent research papers for consideration in this review of the literature (see the citation references at the end of this document). [PERSON] et al. [15] examine the significant concerns about interference of fifth generation (5G) telecommunications technology with aviation altimeters, particularly due to the overlap of frequency bands. This interference poses serious risks to flight operationsand navigational accuracy, potentially compromising aviation safety. In response to these challenges, regulatory authorities around the world have enacted various measures, including the issuance of Airworthiness Directives (AD) and restrictions on the effective isotropic radiated power (EIRP) of 5G base stations near airports. In addition, exclusion zones have been established to mitigate the potential risks associated with 5G operations in proximity to aviation activities. The paper advocates for a collaborative approach among regulators, industry stakeholders, and researchers to develop compatible technologies and regulatory frameworks. It emphasizes the need for ongoing research to better understand interference dynamics and to create comprehensive guidelines that balance the advancement of 5G technology with the critical requirements of aviation safety. Figure 1 shows the proposed Aircraft's altimeter in boresight of a 5G antenna. The orange ellipse in the diagram represents the zone of maximum interference, where the main beam of the 5G interfering signal overlaps with the aircraft's approach path and altimeter signal. This region signifies the critical spatial area in which radio altimeter receivers are most vulnerable to potential signal corruption or degradation due to high-power emissions from 5G base stations. The intersection of the interfering signal's main beam with the aircraft's glide slope and altitude measurement path highlights the likelihood of interference during final approach, especially in low-visibility or instrument landing conditions. [PERSON] et al. [16] highlight the substantial interference that 5G base stations can cause to radar altimeters operating within the 4.2-4.4 GHz frequency band, raising significant safety concerns for aviation. A detailed mathematical model is created to systematically assess this interference in various environments, including rural, suburban, and urban areas. The model takes into account different altitudes and operational scenarios to accurately evaluate the interference-to-noise ratio experienced by radar altimeters. In addition, the study examines the impact of two types of antennas--ommidirectional and multiple input-multiple output (MIMO) antennas--on interference dynamics. This analysis is crucial to understanding how antenna design influences interference. The results emphasize the need for effective mitigation strategies to ensure the safe and reliable coexistence of 5G communication systems and radar altimeters. Figure 1: Aircraft’s altimeter in boresight of 5G antenna used by [PERSON] et al. [14]. [PERSON] [17] investigates the potential interference between 5G systems operating within the 3.7-4.0 GHz frequency band and aeronautical radio altimeters operating in the adjacent 4.2-4.4 GHz band in South Korea. This analysis is crucial because South Korea plans to extend the 5G spectrum into the 3.7-4.0 GHz range. The primary objective of the research is to establish technical conditions that ensure compatibility between 5G systems and radio altimeters. This involves evaluating the interference impact of 5G base stations on altimeter operations. The researchers propose an interference analysis scenario and methodology grounded in Monte Carlo simulations. These simulations are designed to replicate real-world conditions, including Aircraft approaches and 5G network deployments.