Research On Precise Velocity Determination Based On GNSS Integration

Velocity determination using GNSS(Global Navigation Satellite System)plays an important role in the early warning of earthquake,development of aerospace engineering,hydrological survey,airborne gravimetry and missile launching.However,most of the researches on GNSS velocities are based on single-system or dual-system using post-precision ephemeris.Moreover,Researches on broadcast ephemeris based on integration of different navigation satellite system,such as GPS,BDS,GLONASS,are still inadequate.Thereby,this paper established a novel mathematical model of GNSS integration based on broadcast ephemeris to realize real-time and high-precision velocity measurement.The major contributions of this thesis are highlighted as follows.(1)An improved cycle-slip detection method is proposed for dual-frequency GNSS receiver.In this method,The GF phase combination and MW combination are used for cycle slip detection.LAMBDA algorithm is applied to searching the fixed solution of cycle slips,and Ratio is used to test whether it is reliable.The Ratio based test confirms the superior reliability of the proposed method compared with the traditional TurboEdit algorithm.In addition,the experimental results show that the proposed method can detect and repair the circle slips larger than 1 circle.(2)The high precision GNSS integration(GPS/BDS/GLONASS)Doppler velocity measurement model is established,including stand-alone velocity model and relative velocity model.Based on the presented measurement model,the velocity solution accuracies using real-time broadcast ephemeris and post-precision ephemeris are compared.The experimental results show that this method is insensitive to the ephemeris.In addition,the comparison experiments between stand-alone GNSS velocity and relative GNSS velocity measurement models are also conducted.It is shown that in dynamic environments,although the RMS of stand-alone velocity is lower than that of relative velocity,both the methods achieve the accuracy at sub-centimeter/s to cm/s level when using raw Doppler and they can achieve at mm/s level when using carrier phase-derived Doppler.While in low-dynamic environments,both stand-alone velocity and relative velocity can achieve the accuracy at dm/s level when using raw Doppler,and they can achieve at cm/s level when using high-frequency carrier phase-derived Doppler.(3)Single-system,dual-system combined and GNSS integration Doppler velocity measurement models are thoroughly investigated based on test data.The compared experimental results show that the GNSS integration can use more satellites and the geometric structures of the satellite are improved.Consequently,the GNSS integration based method obtained the best accuracy and reliability.(4)The stochastic models of GNSS integration(GPS/BDS/GLONASS)Doppler velocity are systematically studied.On the basis of detailed introduction of the equal weight,height angle and Helmert variance components estimation models,experiments based on stand-alone velocity model are carried out with the raw Doppler data.The result shows that the integration of height angle and Helmert variance estimation models produces the highest accuracy of velocity determination,followed by the height angle model and equal weight model orderly.