BeiDou/GPS Combined Precise Positioning Theory And Algorithm

BDS(BeiDou Navigation Satellite System) is the first heterogeneous constellation and the only currently fully operational tri-band navigation system. It combines curious functions of positioning, timing, user monitoring, and short message communication and could provide 7-9 satellites in China and its surrounding areas. Moreover,it is compatible and interoperation with GPS(Global Positioning System), GLONASS(Global'naya Navigatsionnaya Sputnikovaya Sistema) and Galileo. With its own particular advantages, BDS will help to reduce DOP(Dilution of Precision) values, weaken atmospheric errors, and shorten the time to fix carrier phase integer ambiguity. At present, BDS has an equivalent high precision positioning performance with GPS in the Asia Pacific region. Since BDS starts late the international and domestic market is still dominated by GPS. So BDS and GPS fusion will be a process that BDS enter the international market.In this research,the differences between BDS and GPS in space-time reference frame,constellation structure, signals and data quality are analyzed, the key issues of BDS/GPS high precision relative positioning are studied, and static and dynamic relative positioning algorithm models are proposed. Furthermore, a lot of experiments are carried out as follows:Processing static baselines of railway CPI control network, fast static positioning of CPI control network, and RTK(Real Time Kinematic) positioning at different ranges and in the challenging environmental. These experimental results verify the theories and methods of the study in this dissertation.The main contributions of this dissertation are summarized as follows:1. A refined stochastic model method is proposed to derive proper models for BDS and GPS data processing. Stochastic models express the relationship of BDS/GPS quality indicators and measurement accuracies. To model the relationship, five basic stochastic models about satellite elevation angle and SNR are presented. Moreover, coefficients of these models are refined. We found that SNR stochastic models with same coefficients are improper for BDS and GPS conbined positioning. Stochastic models with an additive constant could model the relationship better. Moreover,the performance of the five models are tested in BDS/GPS independent and combined precise positioning. The results show that: (1) The refined stochastic models could improve the success rate of integer ambiguity single-epoch solutions when compared with empirical models; (2) These stochastic models with an additive constant could also improve the success rate when compared with stochastic models without additive constants. SNR model with an additive constant performs better in BDS/GPS conbined positioning.2. Considering BDS satellite types including GEO(Geostationary Orbit), IGSO(Inclined Geosynchronous Orbit),MEO(Medium Earth Orbit),the carrier phase measurement variance components of three types satellites are calculated,which are proved to be significantly different. Also, their time correlations are various. Hence, a real-time estimating stochastic model is presented for the estimation of different variance components, and a more appropriate stochastic modeling procedure is developed to effectively deal with the heterogeneous variances. Using iterative least square and MINQUE (minimun norm quadratic unbiased estimation) methods, three variance components and accurate position parameters are estimated in the real-time stochastic modeling estimating procedure. To demonstrate its performance, precise relative positioning experiments are carried out using 243-m-length,645-m-length and 10137-m-length baselines, respectively. In contrast to the empirical stochastic model, the real-time estimating stochastic model can improve the performance of BDS precise relative positioning, and improve more significantly for the longest baseline. 10137-m-length baseline test results indicate that the real-time estimating stochastic model can improve mean positioning precision of 41.3%?54.5%?51.6%.3. New atmosphere DOP styles including TrDOP(Troposphere DOP) and IDOP(Ionosphere DOP) in GNSS relative positioning are difined. From DOP standpoint, it is firstly demonstrated that the efficiency of BDS/GPS conbined precise relative positioning are improved. With the attendance of BDS or increasing observing sessions,the values of ADOP,RGDOP and TrDOP decrease efficiently. Moreover, analyzing TrDOP and IDOP values, it indicates that BDS/GPS is favorable to estimate the tropospheric parameter and the ionospheric parameters. Meanwhile, some experiments are carried out to verify the theoretical results.4. BDS and GPS precise relative positioning data processing software is developed,which can be used to processe BDS/GPS static and dynamic data. It is applied to process a railway CPI control network, and the results show that BDS can achieve equivalent precision with GPS, and BDS/GPS fusion could improve qualified rate and precision of baseline solutions. RTK positioning tests show that BDS and GPS short range RTK can achieve 1cm accuracy in N, E horizontal direction and 5cm accuracy in U direction; Medium-long range RTK can achieve 2cm accuracy in N, E horizontal direction and 1dm accuracy in U direction;BDS/GPS fusion can significantly improve the accuracy of U direction; In the challenging environment such as city and corner, BDS/GPS fusion RTK positioning has obvious advantages and improves 50% qualified rate.