Global Navigation Satellite Systems (GNSS) have become ubiquitous in many daily activities, whether professional or personal. The signals transmitted by satellites in Medium Earth Orbits (MEO) 20000 km from the surface of the Earth are weak — actually below thermal noise levels. Jamming is the trivial activity of emitting a signal in the frequency band allocated to GNSS — 1575.42 MHz for the most commonly used L1 band — and prevent the receiver from processing the modulated signal to identify its position. More subtle, spoofing means generating a signal that looks genuine but might contain erroneous timing or positioning information. Our objective in this workpackage is identifying computationally efficient means of assessing jamming and spoofing of GNSS receivers [1], and possibly adding some spoofing immunity to the receivers. Spoofing is addressed by measuring the phase between multiple antennas: while a genuine constellation exhibits some diversity in azimuth and elevation leading to different phases while each satellite is characterized by a characteristic Doppler shift, a spoofer can generate the Doppler shifts but being located at a single point, is unable to trick the receiver in believing the the phases between antennas vary. If all phases are the same for all satellites, spoofing is detected.

Genuine GNSS constellation phase-frequency plot demonstrating the diversity of phases as the satellites are located at different azimuth and elevations.
Phase-Doppler chart of a spoofing signal: all phases between antennas are the same since the spoofing emitted is located in a single position and generates the signals representative of the whole constellation.

Based on these preliminary results, we completed a full real time software defined radio based GPS spoofing and jamming cancellation system based on the free, opensource gnss-sdr software framework as described in [2] and available at [3].

[1] G. Goavec-Merou, J.-M Friedt, F. Meyer, Leurrage du GPS par radio logicielle, MISC HS (Feb. 2019) [in French], also presented as Spoofing GPS, FOSDEM 2019 (Free Software Radio devroom: proceeding manuscript)

[2] W. Feng, J.-M Friedt, G. Goavec-Merou, F. Meyer, Software Defined Radio Implemented GPS Spoofing and Its Computationally Efficient Detection and Suppression, IEEE Aerospace and Electronic Systems Magazine 36 (3), March 2021


Auteur : JeanMichel | Date : 16/02/2019