Air Traffic Radar Interference Event in the Galileo E6 Band: Detection, Analysis and Mitigation

Abstract

In this work, the authors report a serious threat to the Galileo E6 users caused by an in-band L-band Air Traffic Control (ATC) radar pulsed interference, which is currently authorized by the International Telecommunications Union radio regulations in Europe. This paper documents the complete sequence of facts in a real environment, from the interference detection, time/frequency analysis, source identification and location to the mitigation of its effects by implementing a real-time pulse blanking algorithm in an open source, software defined GNSS receiver. The vulnerability of general purpose front-ends to strong out-ofband interferences due to lack of selectivity and component non-linearities was also evidenced, which is specially concerning for Software Defined Radio (SDR) receiver users. In order to assess the interference protection options of a receiver, three input filter blocks have been implemented and integrated into the open source GNSS-SDR receiver. These signal processing blocks aim to mitigate two common types of interferences: continuous wave FM modulated and short-time pulsed ones. Two blocks deal with the CW interferences, implementing an adaptive Notch filter interference canceler. The first implementation performs a very effective mitigation of CW interferences even in cases of very fast instantaneous frequency variations. The second implementation requires less computational resources and is valid only when the instantaneous frequency changes relatively slowly. The third block is a Pulse Blanking filter that mitigates pulsed interferences. Both algorithm implementations were tested with real GNSS signals. In case of notch filters, the GNSS signal was contaminated with simulated Continuous Wave FM interferences and, in the case of the pulse blanking algorithm, the performance measurements were obtained using real ATC radar interference captures.