Evil waveform test-bed design

Several types of failures can occur in the GPS satellites that transmit the ranging signals to the users. Among them, a specific type of failure in the signal generation process aboard the satellite may result in an anomalous waveform being transmitted, called an "evil waveform". Evil waveforms are GPS signals that have a distorted PRN code modulation waveform. The main impact is a rupture of the symmetry of the cross-correlation peak inside the tracking channel, therefore inducing a different measurement error for two receivers that would not have the same architecture. As a consequence, there is a potential for evil waveforms to induce large tracking errors of differential systems if left undetected. Simulations of the impact of these evil waveforms using simplified GPS receiver simulators with harmonized assumptions have been conducted by several teams. This includes simulations of the performance of the ground monitoring techniques and tracking errors induced by these waveforms. Only a small number of practical results were reported about the behavior of real receivers tracking evil waveforms. ESTEC has decided to develop a test-bed to increase the knowledge on the true effect of evil waveforms on real receivers since few results exist on the subject. The test set-up will allow to: