Objectives China's BeiDou satellite navigation system 3 (BDS-3) is capable of providing high-accuracy positioning services for global clients at the end of July 2020.
Methods To fully exploit BDS-3 multi-frequency positioning ability, BDS-3 traditional B1I, B3I and new B2a signals are integrated to employ triple-frequency PPP ambiguity resolution (AR). First, BDS-3 raw float ambiguities are utilized to calculate extra-wide lane (EWL), wide lane (WL) and narrow lane (NL) undifferenced uncalibrated phase delay (UPD). Subsequently, based on the high-accuracy UPD products, the EXL-WL-NL ambiguity sequential fixing at the user side is employed to perform BDS-3 triple-frequency PPP AR. Especially, the performance difference of BDS-3 triple-frequency undifferenced and uncombined PPP AR with different scale UPD products are evaluated. Then two experiments are designed to validate PPP AR. Experiment I: Data from the day of year 310 to 324 in 2021, of 160 MGEX stations are utilized to perform UPD determination and another 12 MGEX stations are used as users for the PPP ambiguity fixing with UPD products. Experiment II: Data from the day of year 310 to 324 on 2021, of 15 EUREF permanent network (EPN) stations are utilized to generate UPD products and another 5 MGEX stations are regarded as clients to validate PPP AR algorithm.
Results Experimental results demonstrate that BDS-3 EWL, WL and NL UPDs exhibit high stability with average standard derivations better than 0.04 cycles. The stability and accuracy of UPD products from the EPN regional network are ahead of that of the MGEX global network. In the MGEX experiments, BDS-3 triple-frequency PPP AR achieves the best convergence performance (25.1 min), which is much shorter than dual-frequency float solutions (39.7 min) and dual-frequency PPP AR (36.3 min), with an improvement of about 36.7% and 30.0%. In the EPN experiments, BDS-3 triple-frequency PPP AR reduced the convergence time from 39.7 min of the dual-frequency float solutions and 30.8 min of the dual-frequency PPP AR to 25.1 min, with a decrease of about 36.8% and 18.5%. Finally, the common stations of the MGEX and EPN networks are utilized to validate the performance of BDS-3 triple-frequency PPP AR based on the two different UPD products.
Conclusions BDS-3 triple-frequency PPP AR using the EPN regional UPD products exhibits a significantly better positioning performance than MGEX UPDs. The possible reasons can be owned to following two aspects. One is that the UPD products from MGEX global stations shall cause a precision loss in some areas with sparse stations. The other is that the precision of the UPD determination may be dependent on receiver types. MGEX global stations are equipped with complex receivers, and hence the UPD estimation may be contaminated.
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