305 / 2023-10-12 16:29:54

Uncalibrated phase delay estimation and ambiguity resolution for BDS-3 six-frequency uncombined PPP with legacy B1I/B3I and new B1C/B2a/B2b/B2a+b signals

BDS-3,Six-frequency integration,Precise point positioning,Uncalibrated phase delay,Fast ambiguity resolution

Multi-frequency integration can accelerate the ambiguity resolution (AR) and shorten the convergence time of precise point positioning (PPP). BDS-3 satellites can broadcast legacy B1I/B3I and new B1C/B2a/B2b/B2a+b signals, which facilitates the multi-frequency PPP. An uncalibrated phase delay (UPD) estimation method and a step-by-step AR method with Extra-Wide-Lane (EWL) ambiguities, wide-lane (WL) ambiguities, and N1 ambiguities, are extended for BDS-3 six-frequency uncombined PPP. The data sets on seven consecutive days from 224 globally distributed stations are selected for UPD estimation, and those from 21 stations are employed for PPP AR. The results indicate that the mean daily stability of EWL and WL UPD estimates is better than 0.02 cycles, and that of B1I UPDs is 0.111 cycles. In addition, the ambiguity residuals show the characteristics of normal distribution and the average data usage rate is as high as 94.3% even for narrow-lane (NL) float ambiguities. These results prove the reliability of UPD estimates. Based on the generated UPD products, the BDS-3 multi-frequency PPP AR experiments are carried out. The results indicate that the static convergence time of BDS-3 six-frequency PPP ambiguity-fixed solutions (with a threshold of 10 cm) can reach 8.2, 4.0, and 13.4 min in the east, north, and up directions, respectively, and the three-dimensional (3D) convergence time is shortened by 21.1% and 26.5% compared with the six-frequency ambiguity-float solutions and the dual-frequency ambiguity-fixed solutions, respectively. The time-to-first-fix (TTFF) of six-frequency static PPP AR is 28.6 min and the fixing rate of N1 ambiguities is 90.4%. Compared with the dual-frequency ambiguity-fixed solutions, the two indexes are improved by 34.6% and 7.1%, respectively. The kinematic convergence time of BDS-3 six-frequency PPP ambiguity-fixed solutions can reach 13.0, 7.0, and 33.2 min in three directions, respectively, and the improvement rates are 21.0% and 33.7% compared with the six-frequency ambiguity-float solutions and the dual-frequency ambiguity-fixed solutions, respectively. In terms of the TTFF and fixing rate of N1 ambiguities, the numerical values for six-frequency kinematic PPP AR are 51.2 min and 83.4%, respectively, which are improved by 35.4% and 9.3% compared with the dual-frequency PPP AR, respectively. In addition, the convergence time and TTFF of BDS-3 six-frequency PPP ambiguity-fixed solutions can be slightly shortened even compared with the five-frequency case. The static and kinematic positioning accuracy of BDS-3 six-frequency PPP ambiguity-fixed solutions can reach 4, 3, and 9 mm, and 18, 14, and 38 mm in three directions, respectively, which is slightly better than other cases.