Performance of Galileo multi-signal measurements in satellite product determination and PPP-AR applications

Kurzfassung

Galileo satellites transmit microwave signals on five frequencies assigned by the International Telecommunication Union (ITU) for radio Navigation Satellite Services (RNSS). By assessing the carrier-to-noise (C/N0) ratios and pseudorange noise (multipath errors) of multi-signal measurements from different sites, we confirm that E1, E5a, E5b and E6 observations have similar measurement quality. The combined E5 AltBOC tracking is superior as a result of a very large signal bandwidth. The manufacturer-provided frequency-specific satellite Phase center offsets (PCOs) are proven to be consistent with each other, with the largest difference of 4.7 cm in the Z direction between E1/E5b and E1/E6 ionosphere-free linear combination. The major part of this difference generates a constant bias that can be absorbed by satellite biases in the multi-frequency processing. Satellite phase biases of individual signals in accord with E1/E5a satellite clock offsets are in general constant over time. Only phase biases of the E6 signal from the early IOV (In-Orbit-Validation) satellites show a drift of about 25 mm/d. Considering the daily STD value of this drift (about 6 mm) to the wavelength (about 20 cm) of each phase ambiguity, it is still reasonable to estimate daily constant phase biases for E6 phase signals. Based on these preconditions, Galileo satellite products determined from multi-frequency (signal) measurements show clear higher precision than those from dual-frequency measurements when using a small ground network (15 or 20 stations). For instance, the ambiguity fixing rate is 80 % in the multi-frequency solution while it is less than 40 % in the dual-frequency solution if a 15-station network is used. With multi-frequency Galileo satellite products, kinematic PPP-AR solutions are more robust and more precise (5-10 %) than those computed from dual-frequency observations.