Improved PPP ambiguity resolution by COES FCB estimation

Precise point positioning (ppp) integer ambiguity resolution is able to significantly improve the positioning accuracy with the correction of fractional cycle biases (fcbs) by shortening the time to first fix (ttff) of ambiguities. when satellite orbit products are adopted to estimate the satellite fcb corrections, the narrow-lane (nl) fcb corrections will be contaminated by the orbit’s line-of-sight (los) errors which subsequently affect ambiguity resolution (ar) performance, as well as positioning accuracy. to effectively separate orbit errors from satellite fcbs, we propose a cascaded orbit error separation (coes) method for the ppp implementation. instead of using only one direction-independent component in previous studies, the satellite nl improved fcb corrections are modeled by one direction-independent component and three directional-dependent components per satellite in this study. more specifically, the direction-independent component assimilates actual fcbs, whereas the directional-dependent components are used to assimilate the orbit errors. to evaluate the performance of the proposed method, gps measurements from a regional and a global network are processed with the igsreal-time service (rts), igs rapid (igr) products and predicted orbits with $$>$$ 10 cm 3d root mean square (rms) error. the improvements by the proposed fcb estimation method are validated in terms of ambiguity fractions after applying fcb corrections and positioning accuracy. the numerical results confirm that the obtained fcbs using the proposed method outperform those by conventional method. the rms of ambiguity fractions after applying fcb corrections is reduced by 13.2 %. the position rmss in north, east and up directions are reduced by 30.0, 32.0 and 22.0 % on average.