Objectives The global BeiDou-3 navigation satellite system (BDS-3) along with regional BeiDou navigation satellite system (BDS-2) is providing users with high-precision positioning, navigation and timing services on three or more frequency signals. To deeply integrate the triple-frequency observations of BDS-2 and BDS-3, we establish the BDS-2/BDS-3 joint triple-frequency precise point positioning (PPP) models and analyze the characteristics of biases arisen in these models.
Methods Using the linear combinations of raw observations, the triple-frequency ionosphere-free and uncombined PPP models are developed. In particular, the mathematical expressions of receiver inter-frequency bias (IFB) and time delay bias (TDB) between BDS-2 and BDS-3 are derived.
Results The experimental results show that BDS-3 can significantly enhance the PPP performance. In static mode, the BDS-2/BDS-3 joint PPP is able to achieve the positioning accuracy of 1.2/1.0/1.8 cm after the convergence time of 15.8/7.3/22.3 min in the east/north/up components. As for kinematic PPP, the convergence time and converged positioning accuracy are 27.3/10.3/33.8 min and 2.2/1.7/4.4 cm, respectively.
Conclusions The convergence performance and positioning accuracy of triple-frequency ionosphere-free and uncombined PPP models are comparable, and the third frequency signal makes a marginal contribution to positioning performance. Both IFB and TDB show the good intra-day stability. The intra-day standard deviations (STD) of IFB can reach 7.9 and 3.6 cm for BDS-2 and BDS-3 signals, respectively, and the intra-day STD of TDB can reach 8.8 cm.
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