Study on the ISB existence among BDS orbit types and the influence on precise point positioning performance

With the development of the BeiDou Navigation Satellite System (BDS), the BDS-2 and BDS-3, which feature hybrid satellite orbits, will coexist for an extended period. However, little research has been conducted on the Inter-System Bias (ISB) caused by BDS orbit types. This study proposed a new Precise Point Positioning (PPP) approach that accounts for the ISB among BDS orbit types and subsequently analyzes the characteristics of the BDS ISB. The study shows that the ISB difference among BDS orbit types reaches a maximum of 3.6 ns at the investigated stations, which is non-negligible in precise data processing. The PPP solution results from the Multi-GNSS Experiment, covering Day of Year 100 to 300 in 2023, demonstrate that the strategy considering the ISB between BDS-2, BDS-3, and orbit types (S4) achieves the fastest average convergence time of 16.3 min, compared to 16.9 min with only considering the ISB between BDS-2 and BDS-3 (S2), 18.0 min with only considering the ISB among orbit types (S3), and 18.2 min with ignoring the ISB (S1). The S4 strategy shows a 12.3% faster convergence compared to S1, a 4.2% improvement over S2, and a 10.9% improvement over S3. In terms of positioning accuracy, the Root Mean Square (RMS) for S4 is 22.9/13.5/31.6 mm in the E/N/U directions, showing improvements of 7.9/15.6/15.2% compared to S1 (24.7/15.6/36.4 mm), 2.2/14.8/6.6% over S2 (23.4/15.5/33.7 mm), and 3.1/8.1/9.5% better than S3 (23.6/14.6/34.6 mm).