Rapid Ambiguity Resolution And Precise Positioning For Medium/Long Baselines With BeiDou Triple-frequency Signals

GNSS precise relative positioning is the first invented precise positioning technique developed in 1980s. After more than thirty years of development, the theoretical and practical issues of GNSS Precise Relative Positioning have been widely researched and successfully resolved. The related norms were also established. Because its high-precision, high-speed, dispensing with intervisible measuring stations, all-climate working and low cost, GNSS Precise Relative Positioning have been widely applied to many areas, such as geomatics, engineering construction and earth science studies and so on. However, there are still some limitations for GNSS Precise Relative Positioning technique. In medium or long distances case, the atmospheric errors can not be eliminated through double-differencing function and can not be precisely extracted rapidly. Therefore, the ambiguities of phase measurements can not be fixed rapidly, which hinders its applications in some cases. It is an important issue that many researchers trying to addressed.The ongoing development of other GNSS systems like BeiDou, Galileo and GLONASS, brings a new opportunity for GNSS Precise Relative Positioning technique and make it become the GNSS research frontier and hotspots again. As a comletedly self-developed system, the performance of BeiDou navigation satellite system has to be assessed urgently. This thesis aims to establish ambiguity resolution and positioning methods/strategies that are suitable for BeiDou observations and can shorten the ambiguity resolution time with triple-frequency BeiDou signals.The main work and contributions of this thesis are as follows:(1) The mathmatical model of precise relative positioning are introduced and the main issues of BeiDou medium/long baseline positioning are extracted. The error effects of precise relative positioning are analyzed and the differences of the error effects between short baselines and long baselines are summarized. Then, the short baseline model and medium/long baseline model are given. The resoving methods are also discussed. Based on the error effects in medium/long baselines and the charateristics of BeiDou signals and constellation, we summarized the main issues of BeiDou medium/long baseline ambiguity resolution.(2) The characteristics and qualities of BeiDou mesurements are analyzed systematically and the stochastic model for BeiDou is formed based on real observations. The mesuremnt residuals of zero-baselines and short baselines are analyzed. The magnitudes of measurement noise and multipath effect are assessed. Then, we analyzed the characteristics and qualities of BeiDou code and phase mesurements with serveral linear combinations. We confirmed that there are systematic biases on BeiDou code mesurements. We also analyzed the characteristics of these biases for different types of mesurements under single- and double-differencing cases. Their influence on wide-lane ambiguity resolution is also evaluated. According to the relation between the characteristics of mesurements residuals and the satellite elevation, we formed the schastic model that is suitable for BeiDou mesurements.(3) A new triple-frequency cycle slip detecting method that is suitable for severe ionospheric condition is proposed. Two extra-wide-lane combinations and one narrow lane combination are formed to detect cycle slip:cycle slips occurred in these two EWL combinations can be detected with high success rate; second-oder time-differencing algorithm is applied to the narrow-lane combination to lower the impact of residual ionospheric delay. The relation between the third combination and the traditional GF combination is analyzed. The detecting success rate of the three combinations is analyzed theoretically. The detecting and repair strategies is given based on the relation the measurement noise and the elevation. Tests with actuall observations indicated that our new cycle slip detecting method performs better than the existing method.(4) A systematic investigation of BeiDou triple-frequency carrier phase linear combination is implemented. Real linear combination is classified based on the error sources. According to the lane number, ionospheric amplification factor and noise amplification factor, triple-frequency carrier phase integer linear combinations are illustrated grafically. The optimal linear combinations that are suitable for general short baselines and long baselines are suggested. A new DGNSS method that is based on wide-lane mesurements derived from triple-frequency signals is proposed. Theoretical analysis and empirical analysis is given of the ambiguity fixing rate and the positioning accuracy of the presented method. The performance is compared with the traditional carrier-smoothed code DGNSS method. The results indicate that our method can realize fast high-precision positioning whereas the carrier-smoothed code differential positioning method needs several hundreds of seconds for obtaining high precision results. Tests with six medium baselines indicate that the precision of our method can achieve 1.5 dm in horizontal direction and 6 dm in up direction.(5) The performance of four classical triple-frequency ambiguity resolution methods is evaluated first time with Beidou real observations. LAMBDA is optimal in both short baseline and medium baseline cases. However, the performances of GB-TCAR and LAMBDA differ slightly for short baselines. Compared with GF-TCAR, which uses the geometry-free model, the GB-TCAR using the geometry-based model improves the AR perfor-mance significantly. Multipath errors on carrier phases will have a significant influence on GIF-TCAR results, which leads to different GIF-TCAR performance for different type of satellites. For GEO (Geostationary Orbit) satellites, the narrow lane ambiguities can barely be correctly fixed because the multipath errors on carrier phases are very systematic. For IGSO (Inclined Geosynchronous Orbit) and MEO (Medium Earth Orbit) satellites, it is suggested to set high cut-off angle. When the elevation cutoff angle is set as 30°, several tens to several hundreds of epochs are needed for correctly fixing the narrow lane ambiguities.(6) Finally, we propose a modified PAR strategy and a piece-wise iono-weighting model to shorten the fixing time in medium/long baselines. The results indicate that the time to first fix (TTFF) can be shortened efficiently. A systematic comparison of the TTFF between GPS+BeiDou combined system and single system is also conducted with real observations, which indicates that the TTFF of GPS+BeiDou combined system is much shorter than that of single system.