A frequency domain-based detection technique for digital distortion on GNSS signals

Global Navigation Satellite Systems (GNSS) signal distortions could threaten the position accuracy and integrity of GNSS, especially for safety critical applications. Digital distortion is an important kind of deformations caused by failure inside the baseband generation unit onboard the GNSS satellites. A TMA model in time domain was particularly presented to characterize this deformation. And the multi-correlator technique, as the prevalent Signal Quality Monitoring (SQM) method, was also developed to reliably detect this anomaly and thereby protect airborne users from this integrity threat. However, the conventional multicorrelator technique is unable to estimate the distortion degree quantitatively. While another prevalent method, chip domain observable, has a poor real-time capability so that it cannot meet the stringent TTA (Time To Alarm, for avionics applications this is 6 seconds) requirements. This paper starts with deriving a spectrum form of TMA for digital distortion and proposes a novel SQM algorithm based on IFFT processing. Simulation results show that the IFFT-based method is feasible to perform a quantitative, real-time monitoring against the digital distortion.