Research On GNSS Asynchornous Differential Kinematic Precise Relative Positioning Theory,Method And Application

Taking high-speed scenarios such as Intelligent Traffic Control,Unmanned Vehicle,Aircraft Automatic Landing,Ship Automatic Landing,Aircrft Aerial Refueling and Spacecraft Rendezvous and Docking as the application background,and in order to break through the GNSS low-latency precise relative positioning navigation and attitude determination technology,this dissertation develops a fast high-dimensional ambiguity resolution algorithm for multi-frequency multi-GNSS,static-reference asynchronous differential low-latency precise relative positioning,moving-reference asynchronous differential low-latency precise relative positioning and single-difference carrier phase attitude determination based on a common-clock receiver.In order to solve the key problems of static-reference,moving-reference data link transmitting delay and colored receiver hardware delay,the corresponding solutions are put forward and verified by real experiments.In order to further validate the engineering practice of the GNSS low-latency precise relative positioning technology,a GNSS vehicle semi-automatic navigation system was developed,and a vehicle semi-automatic navigation test was carried out.The main research results and conclusions are as follows:(1)A fast high-dimensional ambiguity resolution algorithm for multi-frequency multi-GNSS is studied.A stepwise algorithm for integer ambiguity resolution based on the ultra-wide lane/wide-lane operator is proposed,which avoids the traditional float ambiguity caculation way of returning to the carrier phase observation equations secondly.It can save storage space and improves the computational efficiency.It is proved that the wide-lane/ultra-wide-lane operator model and wide-lane/ultra-wide-lane observation models are equivalent for the wide-lane and ultra-wide-lane ambiguity resoluntion in case of single epoch.The single-epoch ambiguity resolution is equivalent to substituting the baseline vector obtained by least squares of pseudo-range information int the carrier phase obaervation equations to resolve each ambiguity paramenter one by one.The experimental results show that the efficiency of stepwise single-frequency ambiguity resolution is about one order of magnitude higher than the direct ambiguity resolution way.Compared with the three-step search strategy,the efficiency of the improved three-step solution based on direct mapping BDS ultra-wide-lane ambiguity is about 10% higher.The influence of different objective functions on the performance of ambiguity resolution is analyzed based on the commonly used pseudo-range and wide-lane carrier phase observation equations of a short baseline.The results of GPS static test show that the sum of square residuals of two frequencies carrier phase is superior to the quadratic form of residual error between the float ambiguity solution and the true solution on the correctness,reliability and availability.(2)The static-reference asynchronous differential low-latency precise relative positioning method is studied.Firstly,the RCPP/SRTK low-latency precise relative positioning algorithm is studied,and the equivalence of the non-difference and single-difference carrier phase prediction in the RCPP/SRTK patent is proved by continuous observations.It is shown that the multipath error only affects the zero-order term coefficients of the polynomial fitting in RCPP,so that the RCPP error introduced by the multipath error of the historical time does not increase with the increase of the forecast time.Based on the RCPP error propagation model,combined with the observed data processing and analysis,we found that the RCPP error mainly comes from the polynomial function model error.The results of BDS/GPS data show that the accuracy of RCP /SRTK is about 10 cm and the maximum error is about 0.5m when the prediction time is 15 s.PDOT/SRTK real-time relative positioning error mainly comes from the PDOT positioning error accumulation.The higher the update rate or the longer the reference observation data transmitting delay,the relative positioning accuracy is poorer of PDOT/SRTK.The results of BDS/GPS data processing show that the PDOT/SRTK positioning noise is seriously accumulated at high update rate.The maximum error is more than 10 cm when the update rate is 20 Hz and the reference observation data transmitting delay is 15 s.In order to avoid the RCPP error inRCPP/SRTK and PDOT positioning noise accumulation in PDOT/SRTK,an asynchronous RTK(ARTK)low-latency precise relative positioning method is proposed.The ARTK method uses the observation data of the base station at the historical moment and the observation data of the mobile station at the present time to establish the asynchronous difference observation positioning model between stations.The asynchronous double-difference integer ambiguity is obtained according to the invariance of the integer ambiguity.Then,the precise relative position is directly obtained by the asynchronous-difference observation model and least squares.A real-time relative positioning error analysis model of ARTK was established.In short time delay,ARTK relative positioning error mainly comes from the broadcast ephemeris satellite velocity error and "inverted ephemeris error".The results show that the real-time relative positioning precision of ARTK is about 3cm when the observation data tranmitting delay is 15 s,which is in accordance with the measured data.The advantages and disadvantages of RCPP/SRTK,PDOT/SRTK and ARTK real-time relative positioning methods are compared.It theoretically proves that the ARTK real-time relative positioning accuracy is better than PDOT/SRTK in a short fixed time-delay.The results of 20 Hz high update-rate static,dynamic test and 1Hz low-update rate long time static experiment show that ARTK real-time relative positioning accuracy is better than PDOT/SRTK under different update rate and reference observation data transmitting delay.The accuracy of ARTK relative positioning accuracy is more significant under the condition of high update rate,for example,when the reference observation data transmitting delay is 0.5s and the update rate is 20 Hz,the maximum down error 6.6cm of PDOT/SRTK relative positioning results is decreased to 1cm.A calibration algorithm in observation or position domain for ARTK real-time relative positioning systemmatic error introduced by broadcast ephemeris is proposed.The algorithm uses the latent SRTK precise relative positioning results to calculate the asynchronous difference phase error rate or the relative positioning error rate of ARTK.The error of the asynchronous difference phase error or the relative positioning result at the current time is compensated with time-sliding window linear fitting and forecasting in the observation or position domain.The results of BDS/GPS data processing show that under the condition of 5s,10 s and 15 s observation data transmitting delay,compared with uncompensated ARTK real-time relative positioning algorithm,the compensation algorithm improves the positioning accuracy with 2 and 1.6 times in plane and down,respectively.In case of a longer refercence station observation data transmitthing delay,the compensation algorithm in the observation domain is better than the position domain.(3)The kinematic relatving positioning methods in the case of moving-reference are studied.A combination ARTK and moving-reference prediction and ARTK/PDOT are proposed,which can sovle the moving-reference data link transmitting delay.Based on the relative navigation simulation data,the influence between the moving-reference positioning error and relative positioning error is analyzed.In order to improve the accuracy of moving-reference single point positioning,moving-reference relative positioning and moving-reference prediction accuracy,a new method based on a combination of single point positioning and PDOT positioning results is proposed.The results of relative navigation simulation show that the method can reduce the relative positioning error of the long-distance segment and improve the relative positioning accuracy.The result of static long-period test shows that this method can reduce the pseudo-range single point positioning noise significantly,and the positioning error is stable and smooth,and also improves the accuracy of single point positioning.The real-time combination positiong algorithm of ARTK and moving-refernce prediction uses the historical moving-reference observation data and current mobile observation data to carry on the ARTK relative positing,obtaining the relative lacation between the historical moving-refernce and the current mobile.And then a sliding window polynomial is used to predict the position increment of the moving-reference to obtain current the relative position.The results of the two dynamic vehicles test show that the positioning accuracy of the method is mainly determined by the accuracy of the moving-reference prediction.The higher the dynamic benchmark,the accuracy of the moving-reference predciton and relative positioning is worse.The real-time positioning accuracy of the method is 1cm and 6cm respectively under 0.2s and 1s data transmitting delay.The ARTK/PDOT real-time positiong algorithm improves the relative positioning accuracy in the case of a long moving-reference data link transmitting delay.The algorithm uses ARTK to obtain the relative position between the historical moving-reference and the current mobile,and obtains the current relative position with the high update rate PDOT position increment of moving-reference.The results of two dynamic vehicles show that the precision of down positioning is better than 1cm,and the plane precision is better than 5mm under the conditions of 10 s delay.(4)The real-time single-difference carrier phase attitude determination method based on a common-clock receiver is studied,which mainly solves the problem that the accuracy of the attitude determination is decreased or even abnormal due to the hardware delay variation.According to the hardware delay time series analysis of each visible satellite,it is confirmed that the long period slow change characteristic comes from the hardware itself,regardless of the multipath long period variation.Aiming at the problem of hardware delay time-varying characteristic,which can not be used as constant compensation,a semi-parametric filter single-difference carrier phase attitude determination method based on ARMA prediction and single-difference attitude determination method based on moving-average constant compensation are proposed.The main idea of semi-parametric filter single-difference carrier phase attitude determination method based on ARMA prediction is to establish the system equation with hardware delay as state parameter and the single-difference carrier phase measurement update procedure.The system equations and the measurement update equations are used to semi-parametrically filter the hardware delay while estimating the baseline vector.The main idea of the single-difference attitude determination method based on moving-average constant compensation is to obtain the hardware delay based on the double-difference carrier phase solution.Then a sliding window average is used to estimate the hardware delay,compensated by the single-difference carrier phase observation equation.The semi-parametric filtering model and double-difference model and constant compesation model are compared.The attitude determination of constant compesation model is the highest,and fllowed by the semi-parametric filtering model,the double-difference model.But the semi-parametric filtering model is suitable for practical application.The zero-baseline static test results show that the constant model and the moving-average constant compensation model can improve the accuracy of down positioning while the plane accuracy is slightly decreased.The semi-parametric filtering model improves the three dimensional positioning accuracy,and the BDS and GPS accuracy are improved by about 40% and 50%,respectively.The results of the short baseline test showed that the constant model decreased the attitude determination accuracy.The moving-average constant compensation and semi-parametric filtering model both improved the accuracy of attitude determination.The accuracy of BDS and GPS pitch angle were increased by about 30% and 48%,respectively.Moving-average constant compensation attitude determination method must select an appropriate sliding window;otherwise it will decrease the attitude accuracy.(5)A vehicle semi-automatic navigation test system and multi-mode GNSS real-time kinamtic precise relative positioning software are designed.Completing the integration of semi-automatic navigation system and carring out the high-speed semi-automatic navigation crossing obstacle test,verify the accuracy and feasibility of the static-reference low-latency precise relative positioning technology.The multi-mode GNSS real-time kinematic relative positioning software can realize the precise relative positioning in case of B1B2,B1B3,L1L2,B1B2B3,B1B2/L1L2,B1B3/L1L2 and B1B2B3/L1L2.The positioning accuracy can reach mm or even cm level.The experimental results show that,even if the static-reference data link transmitting delay is unstable,the GNSS low-delay precise relative positioning method is correct and feasible.Its positioning accuracy and output latency can meet the requirements of high-speed vehicle precise navigation applications.