Signal Quality Monitoring for New GNSS Signals

In the context of GNSS signals and associated augmentation systems modernization, new modulations are envisaged. More precisely Galileo E1C, the pilot component of the E1 Open Service signal (CBOC(6,1,1/11) modulation), Galileo E5a and GPS L5 (BPSK(10) modulation) are signals that will be used by civil aviation airborne receivers for pseudorange computation. To meet stringent requirements defined for civil aviation GNSS receivers, the characterization of distortions which could affect a GNSS signal in a hazardous way is required. In particular, expected signal distortions generated at payload level are described by Threat Models (TM). Distortions incorporate in the TM are also called Evil Waveform (EWF). These TMs, and their associated parameter ranges, referred to as Threat Space (TS) are powerful and necessary tools to design and test the performance of Signal Quality Monitor (SQM). The SQM is a mean to detect the presence of dangerous signal distortions and is necessary to protect users with high requirements in terms of integrity, accuracy, availability, and continuity (for example civil aviation users). Nowadays, this monitoring task is performed by GBAS and SBAS reference station for GPS L1 C/A to warn the user in a timely manner. In this paper SQMs for Galileo E1C and Galileo E5a will be designed and compared by mean of an innovative representation inspired from [ 1]. From this representation, SQM performance is assessed based on the highest differential tracking error entailed by a signal distortion included in the TM and not detected by the SQM within allocated P-ffd and P-md. It is noteworthy that performance of SQM is dependent on several parameters and in particular on the C/N-0 at which the reference station is operating. One of the advantage of the proposed representation is that performances of the SQM can be assessed for different equivalent C/N-0 from one figure. Using this representation, different SQMs are compared and an optimized SQM is proposed to monitor signal distortions on Galileo E5a and Galileo E1C signals.