Enhancing Beidou PPP ambiguity resolution through tight integration between BDS-2 and BDS-3

Abstract Beidou has been complete for several years since 2020; however, the existing discrepancies between BDS-2 and BDS-3 are tricky obstacles that make the two Beidou constellations incompatible. Generally, users assign Beidou satellites from different generations to separate systems in data processing, so that the positioning capabilities beyond those of Beidou cannot be fully exploited. The present contribution concentrates on the approach of tight integration (TI) between BDS-2 and BDS-3 constellations and explores how TI enhances the BDS-only positioning performance. The findings show that inter-system phase bias (ISPB) in Beidou TI is receiver-specific and demonstrates good consistency between homologous receivers. More than 99% of ISPB variations from neighboring epochs in a day are distributed within 0.1 cycles, implying that ISPB can be stable for a long time. After correcting ISPB, the accuracy of the uncalibrated phase delay (UPD) extracted under the TI strategy is significantly improved compared with that of implementing TI without precalibration. The wide-lane UPD residuals distribute from 80.2% within 0.15 cycles to 87.2%, and the narrow-lane UPD residuals increase from 87.9% within 0.15 cycles to 94.8%; these statistics are slightly better than those of the loose integration (LI) strategy. Regarding the precise point positioning ambiguity resolution (PPP-AR) performance in an open area, the TI strategy has certain advantages over the LI strategy in the early stage of convergence, as it is 13.2%, 9.7%, and 7.1% faster in the E/ N/U directions, respectively. Moreover, the advantages of the TI strategy are highlighted in an extremely obstructed scenario. TI can significantly enhance positioning performance and ensure positioning availability, which cannot be achieved in the manner of LI PPP-AR.