## 2 Review
### Radio Astronomy and RFI  
Radio astronomy relies on a minimally contaminated radio spectrum to observe the universe [74]. Detecting and estimating weak celestial signals arriving from far away galaxies are particularly required in achieving the key science goals of the next-generation radio telescopes, i.e., the Square Kilometre Array (SKA) ([[https://www.skao.int/accessed](https://www.skao.int/accessed)]([https://www.skao.int/accessed](https://www.skao.int/accessed)) on 24 July 2024) [75], the 2030 Atacama Large Millimeter/sub-millimeter Array--Wideband Sensitivity Upgrade (ALMA-WSU) ([[https://science.nrao.edu/facilities/alma/science_sustainability/wideband-sensitivity-upgrade](https://science.nrao.edu/facilities/alma/science_sustainability/wideband-sensitivity-upgrade)]([https://science.nrao.edu/facilities/alma/science_sustainability/wideband-sensitivity-upgrade](https://science.nrao.edu/facilities/alma/science_sustainability/wideband-sensitivity-upgrade)) accessed on 24 July 2024) [76], and the next-generation Very Large Array ngVLA ([[https://ngvla.nrao.edu/](https://ngvla.nrao.edu/)]([https://ngvla.nrao.edu/](https://ngvla.nrao.edu/)) accessed on 24 July 2024) [77]. Despite being located at remote sparsely populated regions in the world, the increasing intensity, frequency, bandwidth, and occurrences of RFI are threatening the utility of the next-generation radio telescopes [78]. RFI from the global navigation satellite system (GNSS) [79], terrestrial and airborne wireless communications systems, satellite mega constellations [80], and other technologies is encroaching on the spectra that have been exclusively used by radio astronomers, making it harder to distinguish faint celestial signals from RFI. The International Telecommunication Union (ITU) ([[https://www.itu.int/en/Pages/default.aspx](https://www.itu.int/en/Pages/default.aspx)]([https://www.itu.int/en/Pages/default.aspx](https://www.itu.int/en/Pages/default.aspx)) accessed on 24 July 2024) and the FCC ([[https://www.fcc.gov/](https://www.fcc.gov/)]([https://www.fcc.gov/](https://www.fcc.gov/)) accessed on 24 July 2024) have important roles in protecting the spectrum for radio astronomy and other passive users. The ITU, through its radio communication sector (ITU-R), is responsible for developing international regulations and recommendations for the use of radio frequencies. It recognizes the significance of protecting the spectrum for passive services, such as radio astronomy, Earth exploration satellite services, and meteorological satellite services. The ITU-R identifies specific frequency bands for these passive services and establishes regulatory provisions to ensure their protection from harmful interference. These provisions include coordination procedures, power limits, and frequency separation requirements to safeguard the sensitive observations and measurements conducted by radio astronomers and other passive users [81; 82]. Similarly, the FCC in the United States recognizes the importance of protecting the spectrum for radio astronomy and other passive services. The FCC's Office of Engineering and Technology (OET) formulates policies and rules to prevent harmful interference with these services. It establishes technical standards and licensing conditions that take into account the needs of passive users, including radio astronomers. Also, the FCC works closely with the National Science Foundation (NSF) and other relevant agencies to coordinate spectrum usage and protect the integrity of scientific observations. However, both organizations are under relentless pressure from the industry and governments for more commercial utilization of the spectrum that has been previously allocated for the non-commercial users. Therefore, ideally, awareness of the key characteristics of RFI (i.e., frequency range, modulation scheme, source locations, intensity, etc.) would help radio telescope operators with planning and scheduling observations.