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Abstract

Precise point positioning (PPP) is one of the most widely used analysis techniques for high precision GNSS applications. Fast centimeter-level results are possible through carrier-phase ambiguity resolution at the user receiver in a PPP-RTK processing mode. Without external atmospheric corrections, however, times-to-first-fix the ambiguities between some tens of minutes for GPS-only dual-frequency solutions and still several minutes for multi-GNSS solutions with three or more frequencies are generally reported. The goal of this contribution is to investigate the limits of the positioning capabilities that can be achieved with PPP-RTK using the current GNSS constellations, where we focus on the feasibility of instantaneous solutions using only a single epoch of observations. We consider different combinations of the systems GPS, Galileo, BDS2+3, and QZSS with up to five frequencies. The MSE-optimal best integer-equivariant (BIE) estimator is employed, which does not 'fix' the ambiguities to integers, but weights different candidates. As the BIE results are always at least as good as the ambiguity-float and any ambiguity-fixed results, they can be used to analyze the best possible performance of a given model. Simulations are used to show that when combining all four systems, we can expect a horizontal precision of better than 3 cm with three frequencies and on the sub-centimeter level with five frequencies. These results are confirmed with real GNSS data, where horizontal RMS positioning errors of 7-8 mm are obtained during an exemplary day for a receiver in the area of Perth, Australia, when combining all four systems with three and five frequencies.