Signal Quality Monitoring for Protection of GBAS Users Against Evil Waveforms

摘要

Several types of failures can occur in the GPSsatellites that transmit the ranging signals to the users.Among them, a specific type of failure in the signalgeneration process aboard the satellite may result in ananomalous waveform being transmitted, called an ?evilwaveform?. Evil waveforms are GPS signals that have adistorted PRN code modulation waveform. The mainimpact is a rupture of the symmetry of the crosscorrelationpeak inside the tracking channel, thereforeinducing a different measurement error for two receiversthat would not have the same architecture. As aconsequence, there is a potential for evil waveforms toinduce large tracking errors of differential systems if leftundetected.The aim of this paper is to analyze theperformance of the latest proposed ground Signal QualityMonitoring (SQM) techniques, and to present a summaryof the final recommendations adopted by ICAOGNSSPanel.The paper starts with a description of themathematical model of the evil waveform, and itspredicted effect on the GPS receiver is presented.Next, we discuss the rationale for themethodology employed to design the currently proposedground Signal Quality Monitoring (SQM) techniques, anddescribe one of these techniques. Some theoretical andcollected statistics of the test thresholds includingmeasurement noise and multipath level used by thistechnique are then presented.Then, we present simulation results showing thelevel of protection provided by this technique, dependingon the airborne receiver architecture. Observed behaviorsof real receivers tracking one of these evil waveforms isthen shown.We finally conclude with the actualrecommendations formulated by the GNSSP.