Software Defined Radio allows accessing the raw radiofrequency stream through the IQ coefficients digitized by the radiofrequency frontend. Thanks to this raw information, either anti-spoofing/anti-jamming algorithms can be implemented early in the reception chain (Controlled Radiation Pattern Antenna with null-steering -- CRPA) or fine multipath analysis can be performed during the correlation step.
Furthermore, processing GNSS data in the virtual world of SDR is fine, but generating a 1-PPS output to be assessed on a physical frequency counter is better. We have investigated how to steer the clock driving the FPGA acquiring the signal -- the only relevant timestaming information in the SDR processing chain -- with the local clock error signal derived from the Position, Velocity and Time (PVT) solution.
Repositories of these projects can be found at https://github.com/oscimp/gnss-sdr-1pps with all developments relying on the original GNSS-SDR decoding software and the underlying GNU Radio framework.
References:
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 vol 36 num 3, March 2021
D. Rabus, G. Goavec-Merou, G. Cabodevila, F. Meyer, J.-M Friedt, Generating a timing information (1-PPS) from a software defined radio decoding of GPS signals, Joint EFTF/IFCS conference (2021)
External link to the RRaTRAAP project description at Institut Saint Louis (ISL) rratraap