Galileo model of group delay accuracy for advanced RAIM users

Group delays (GDs) are errors affecting Global Navigation Satellite Systems (GNSS) due to non-idealities of the satellite or the receiver hardware and can compromise safety critical applications (eg, advanced receiver autonomous integrity monitoring [ARAIM]) when integrity requirements are at major or even hazardous safety level. The paper shows that GPS uses L1 and L2 signals in the generation of the navigation message, and as a consequence, an L1-L5 dual-frequency user must include the GD contribution in the integrity assessment. For Galileo, whose navigation message refers to the aviation frequencies (E1 and E5), the GDs can be modeled separately from the Signal In Space Accuracy (SISA), because they affect only single-frequency users. This model permits a reduction of User Ranging Accuracy (URA) values with respect to those of GPS, thus improving availability for dual-frequency users. Characterizing the GD of Galileo navigation messages, the paper describes a method to include the GD error model in ARAIM and its potential advantages.