Real-time RFI Mitigation Techniques in Radio Astronomy and Their Practical Limitations

TL;DR

This chapter addresses the escalating challenge of radio frequency interference (RFI) in radio astronomy by presenting a structured catalogue of real-time mitigation techniques spanning analog front-end solutions, digital processing in the F-engine and beamformer, and proactive coordination strategies. It discusses existing implementations and surveys prospective approaches such as satellite boresight avoidance, tunable notch filters, reconfigurable intelligent surfaces, cyclic spectroscopy, UV-domain flagging, spatial filtering, AI/ML-based methods, and sample frequency offset sampling. Key contributions include a taxonomy of techniques, maturity assessments, and practical considerations (e.g., impact on system temperature, data loss, and computational requirements), illustrating how real-time excision and proactive strategies can preserve sensitivity in crowded spectra. The work emphasizes that combining technical mitigation with spectrum management and cooperative scheduling is essential for sustaining radio astronomy capabilities and enabling future discoveries. Overall, the chapter provides a roadmap for integrating real-time RFI mitigation into telescope design and operations, balancing data integrity, sensitivity, and observational efficiency in an increasingly interfered radio landscape.

Abstract

Radio astronomy is facing critical challenges due to an ever-increasing human-made signal density filling up the radio spectrum. With the rise of satellites, mobile networks, and other wireless technologies, radio telescopes are struggling with radio frequency interference (RFI), which can masquerade, block or distort astronomical signals. In this chapter, we explain where RFI comes from, how it affects observations, and discuss different ways to reduce or remove interference. The techniques presented here reflect the state of the art in real-time RFI mitigation at the time of publication and include methods such as filtering, digital processing, and optimal scheduling. The proposed catalogue also explores new ideas like satellite avoidance through scheduling, the use of intelligent surfaces to block interference, and advanced computer algorithms to clean up data. The chapter also highlights the need for strong cooperation between astronomers and spectrum regulators to protect radio frequencies for future discoveries. By combining technical solutions and better policies, we can help ensure that radio astronomy continues to provide important insights into the universe.

Figures (4)

• Figure 1: Spectrogram of upgraded Giant Metrewave Radio Telescope (uGMRT) gupta2017upgraded antenna showing broadband (powerline RFI) and narrowband (communication transmitters) RFI in the 250-500 MHz band. Broadband powerline RFI is seen to be repeated every 10ms (submultiple of 50Hz powerline frequency). Note that the astronomical signal is buried below the noise floor and cannot be identified in this plot.
• Figure 2: One of the 5-s periodic bursts received from a radar system. The burst is a group of many periodic short impulses, sparse in time, but broad.
• Figure 3: SNR versus data loss in a typical telescope receiver system
• Figure 8: The proposed RFI threshold detector/flagger (from ska_mid_cbf_rfi_2019).