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Abstract:
Galileo satellites transmit microwave signals on five frequencies. By assessing the carrier-to-noise ratios and pseudorange noise 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 phase center offsets of Galileo satellites 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 satellites show a drift of about 25 mm/d. Considering the daily STD value of this drift (6 mm) to the wavelength (20 cm) of each phase ambiguity, it is reasonable to estimate daily constant phase biases for E6 signals. Based on these preconditions, Galileo satellite products determined from multi-frequency measurements show higher precision than those from dual-frequency measurements when using a small ground network. 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 precise (5-10 %) than those computed from dual-frequency observations.
