An improved method for multi-GNSS baseline processing using single difference

Abstract

The rapid development of multi-GNSS (Global Navigation Satellite System) constellations has provided numerous benefits for common PNT (Positioning, Navigation and Timing) services. Generally, DD (Double Difference) observations are used in GNSS baseline processing. However, in traditional DD data processing methods, DD observations are normally not formed between different GNSS systems or the inter-system DD ambiguities are rather difficult to be resolved due to the different wavelength. As a result, DD observations are normally formed in each system or their inter-system ambiguities are left unresolved, which could not be regarded as the optimal baseline processing methods for multi-GNSS. This paper presents an improved algorithm for multi-GNSS short baseline processing where SD (Single Difference) rather than DD observations are formed between two receivers and this method is found to be equivalent to the ideal DD method with inter-system DD observations and resolved inter-system DD ambiguities. Furthermore, an average approach and linear model are proposed to isolate the receiver-dependent Uncalibrated Phase Delays (UPDs) from the SD ambiguities for CDMA (Code Division Multiple Access) and FDMA (Frequency Division Multiple Access) GNSS systems, respectively, to address ambiguity resolution. Experiments show that after removing the UPDs derived by the proposed methods, the fractional parts of the residuals for almost all ambiguities are less than 0.1 cycles for the GPS, BDS, GLONASS and Galileo systems, which confirms the validity of our UPD calibration methods. Experiments also show that the mean differences between the daily solutions derived by GAMIT and the 4-h solutions derived by the proposed SD method are approximately −0.12, −0.33, 1.04 and 0.31cm in the north, east, up and length components, respectively. We also find that the baseline repeatability of the new SD method outperforms that of the DD method with only DD observations formed in each GNSS system by 36% and 26% in the north and up directions, respectively. These improvements are more significant in environments with poor observation conditions. An improvement of 40% and 30% in the north and up directions are, respectively, found when only 5GPS and 4 BDS satellites are available. Therefore, more reliable and precise baselines can be derived with our new baseline processing method in multi-GNSS cases.