Test of the Filter Design Effect on Evil Waveform Monitoring in SBAS for Galileo E1 and E5a Signals

Abstract

Evil Waveforms (EWF) are non-nominal distortions that can be observed on satellite signals and cause additional bias on the estimated user position. A Threat Model (TM) has been proposed by ICAO for GPS L1 C/A to describe the possible distortions that can be observed on the GPS signals [1]. This Threat model is also adopted for Galileo E1-C and E5a-Q signals. A previous paper focused on the Signal Quality Monitoring (SQM) design and compliance test for Galileo signals. In the present paper, the effect of the pre-correlation filter design applied at the aircraft and reference station receivers on the EWF induced bias and SQM compliance test is assessed. Two aspects of the filter design are considered: the filter center frequency shift due to temperature variation or electronic component aging, and the filter gain roll-off out of the filter bandwidth. The obtained results of EWF differential biases and SQM test in [2] are considered as the baseline results used to evaluate the effect on the tested filter parameters. This paper concludes on the tolerable center frequency offset and gain roll-off based on the comparison of the obtained EWF results for Galileo E1 and E5a to the baseline one.