| Precise Point Positioning?PPP?is another technological revolution after Real-Time Kinematic?RTK?of satellite positioning technology,which integrats the advantages of standard single point positioning and relative positioning.With the upgrading of GPS and GLONASS,the rapid construction of BDS and Galileo,and the Multi-GNSS Experiment?MGEX?project launched by IGS,PPP has developed toward multi-constellation,real-time,ambiguity-fixed solutions with the advantages of rapidity,high precision,and high reliability.In order to obtain complete navigation parameters,an integrated navigation system integrating positioning,velocity measurement,and attitude determination is constructed by combining inertial navigation system?INS?.Compared with the carrier-phase based DGNSS/INS combination system,PPP/INS integrated system has the advantages of unlimited working distance and low system cost,which will have broad application prospects.This paper focuses on GNSS multi-constellation PPP and INS integrated algorithm to carry out the related research.The main work is as follows:1.By introducing the inter-system bias?ISB?,the PPP model of GNSS multi-constellation fusion is deduced.The correctness of the algorithm is verified by using IGS station data and the performance of multi-constellation PPP is analyzed.Multi-constellation PPP experiments show that,compared with GPS single-constellation PPP,dual-constellation PPP can improve positioning accuracy by 20%-35%,improve positioning stability by 25%-40%,and shorten convergence time by 35%-45%.The contribution of BDS and Galileo in multi-constellation is comparable,and the performance of the triple-constellation PPP is further improved.The BDS and Galileo static PPP comparison experiments show that,the positioning accuracy and convergence speed of the two are similar in the horizontal components.The performance of BDS PPP in the vertical components is poor.The vertical positioning accuracy and three-dimensional convergence time of BDS are 6 cm and 70.26 min,respectively,while corresponding term of Galileo are 5 cm and 49.50 min,respectively.Heterogeneous constellation of BDS increases system availability and observation continuity.2.By introducing correlation coefficient to determine the Intrinsic Mode Function?IMF?component in which the noise signal is the dominant mode,the denoising method of jointing Empirical Mode Decomposition?EMD?and wavelet threshold is improved.It avoids the problem of signal distortion caused by directly removing high-frequency IMF components.The denoising experiments of static inertial data show that,the fitting of Allan Variance curve is better after joint denoising.The angle random walk error coefficient of gyro is reduced from 0.199deg?h-0.5to0.102deg?h-0.5,and corresponding term of accelerometer is reduced from 2.98 e-3m?s-1.5to8.01 e-4m?s-1.5.The denoising experiments of dynamic inertial data show that,the long-time navigation accuracy of pure inertial navigation solution is higher after joint denoising.The error accumulation amplitude is reduced by about 20%after 300 s solution.The joint method has good denoising effect on static and dynamic data,and the wavelet threshold method has a slightly effect on denoising of dynamic data.3.Based on the lever arm correction equations and inertial error equations,a PPP/INS integrated filtering model based on the result domain is deduced.Two sets of vehicle experiments show that the position accuracy of the integrated algorithm is comparrable to the PPP-only solution,velocity accuracy is increased by one order of magnitude,and higher precision attitude parameters can be provided.The correctness of the integrated navigation algorithm is verified.Robust adaptive filtering is applied to the PPP/INS integrated filtering.Experiments show that,robust process and adaptive process has a certain inhibitory effect on gross error in observation and abnormality in state prediction,respectively.The joint effect of robust adaptive filter needs to balance the contribution between the two. |
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