On The Analysis Of Beidou Observations' Characteristics And Its Application In PPP Integer Ambiguity Resolution

The technology of precise point positioning (PPP) is widely used, for its efficiency in computation and flexibility in fieldwork. In the study of PPP, the main concerns of the scholars both at home and abroad could be categorized into several aspects, such as the refinement of the error models, PPP integer ambiguity resolution, the integration of inertial navigation system, and PPP with single-frequency observables. Based on the traditional PPP, the concept of PPP-RTK generates corrections from regional or global reference network, and applies them to recover the integer features of ambiguity parameters. With the integer ambiguity resolution, both the precision and convergence speed are expected to be improved. The construction, development and wide applications of BeiDou Navigation Satellite System (BDS) make it of great scientific value and practical significance, to conduct the study of PPP integer ambiguity resolution with BDS observables.Considering the differences of BDS in components of constellation and frequencies used, comprehensive investigation of the characters of BDS observables is the prerequisite to the study of PPP integer ambiguity resolution with BDS. Aiming at the PPP integer ambiguity resolution, the fundamental principles and methods were introduced systematically. Different PPP-RTK models were compared and their consistency was theoretically proved. With the help of tools such as spectral analysis, correlation and wavelet, the behaviors of MW combinations, code multipath combinations and geometry-free ionosphere-free combinations were investigated compared with GPS, GLONASS and Galileo. The PPP integer ambiguity resolution of BDS was implemented and validated through both static and kinematic PPP experiments. In addition, the PPP integer ambiguity resolution with B1/B3 ionosphere-free combination was also studied. The main contributions of the dissertation are as follows.The status quo and trends of PPP study both at home and abroad were combed, and the importance of PPP integer ambiguity resolution was elaborated.Based on the fundamental theories and methods of GNSS, the mathematical models of PPP and PPP-RTK were described. The analytical solutions for reference and user sides of two different models were deduced. Despite the differences in S-bases and correction vectors for different models, they could be transformed mutually, suggesting that the different models of PPP-RKT are theoretically equivalent.The MW combinations time series of BDS showed periodical behaviors. The daily average of fractional parts of MW combinations for GEO satellites are relatively stable, with a fluctuation of about 0.2 cycles and accidental jumps. The case for MEO satellites is not as good, and the fluctuation could reach 0.5 cycles.Periodicity is also shown in the code multipath combinations of BDS, with an amplitude of about 2 m. Spectral analysis and correlation analysis show that the period is about 1 sidereal day for GEO and IGSO satellites, and about 7 sidereal days for MEO ones, coinciding with their sub-track repeating periods. The multipath combinations of IGSO and MEO satellites are significantly correlated with the elevation angles, while those of GEO ones are not. The periodical biases in multipath combinations of GEO satellites could be extracted and corrected with wavelet decomposition. After correction, the precision of single-point positioning could be improved by 0.5 m. The elevation-dependent bias in the multipath combinations of IGSO and MEO satellites could be remarkably reduced through between-station differencing, suggesting it might come from the satellite end. It could be corrected with proper elevation model.In geometry-free ionosphere-free combination of BDS phase observables, periodical biases with an amplitude of about 2 cm could also be seen. It may also come from the satellites, since it could be reduced through between-station differencing. The variation of solar radiation and the earth eclipse significantly affected the periodical biases in the geometry-free ionosphere-free combination.A regional reference network was employed to generate FCB product, with which PPP integer ambiguity resolution was conducted at the user station in both static and kinematic mode. The RMS's for the fixed solution of static PPP are 0.8 cm, 0.7 cm and 2.1 cm in E, N and U components, respectively. Compared with the float solution, the RMS's in E and U are improved by 11.1% and 4.5%, respectively. For kinematic PPP, the RMS's are improved by 30.4%,20.7% and 10.8%, reaching 1.6 cm,2.3 cm and 5.8 cm, in E, N and U components, respectively.The RMS's for fixed solution of BDS/GPS static PPP are 0.4 cm,0.4 cm and 0.6 cm. For kinematic PPP, the RMS's for fixed solution are 1.3 cm,1.1 cm and 3.2 cm, improved, with respect to the float solution, by 23.5%,15.4% and 8.6%, respectively.Generally, integer ambiguity resolution improves the precision of kinematic PPP more significantly, especially in E components. Besides, the integer ambiguity resolution also accelerates the convergence of PPP. For BDS-only scenario, the convergence for static and kinematic PPP is accelerated by 4.3% and 13.5%, respectively. For BDS/GPS scenario, the convergence for static and kinematic PPP is accelerated by 16.7% and 16.1%, respectively.The combination of B1/B3 is outperformed by that of B1/B2. With the DCB corrected, the precision of PPP with B1/B3 combination is significantly improved. The integer ambiguity resolution could marginally improve the precision of PPP with B1/B3 combination.