Research on the Model of BDS-3 Triple-Frequency Carrier-Phase Combination Observations

The BDS-3 satellite navigation system has entered the global coverage stage this year, and it is expected that the service area of the BDS-3 will cover the “the Belt and Road” countries and neighboring countries by the end of 2018. At present, the BDS-3 has released four ICD (Interface Control Document) for the signal B1I, B1C, B2a, and B3I. The optimal linear coefficients with minimal noise are induced with the analytical method considering the wavelength and ionoshperic scale factor of combinations. It is shown that the optimal extrawide lane (EWL) combination of the BDS3 are the linear combination (1,-1,0) of the signals (B1C,B1I,B2a) and (B1C,B1I,B3I), and the optimal wide-lane (WL) combination is the linear combination (1,-3,2) composed with the signals (B1I,B3I,B2a) and (B1C,B3I,B2a), these three combinations are also the best combination among all the BDS-3, BDS-2 and GPS linear combinations. Using the measured data of BDS-3 to select the WL／EWL combinations for double-difference ambiguity resolution under the long and short baseline, not only the conclusion of the combinations of WL and EWL is verified, it is also concluded that the WL combinations (1,-3,2) and EWL combinations (1,-4,3) and (0,1,-1) of triplefrequency signals (B1I,B3I,B2a) and (B1C,B3I,B2a) are applicable to both long and short baseline conditions, and the better WL／EWL combinations of triple-frequency signals (B1C,B1I,B2a) and (B1C,B1I,B3I) are only applicable to the short baseline conditions.