Research On Several Key Technologies Of BDS/GNSS Data Preprocessing And Positioning

The BDS-2 navigation satellite system has provided services in the Asia-pacific region at the end of 2012,and its accurate positioning,navigation and timing services provided a firm foundation for the positioning of multiple GNSS systems.Meanwhile,with the construction of BDS-3 system and Galileo system,as well as the modernization of other navigation satellite systems,the research on high-precision positioning based on BDS/GNSS has turned into the focus of Chinese scholars.However,there are some key technologies for data preprocessing and high-precision positioning of BDS/GNSS that need to be further studied,which can not only improve the positioning accuracy and efficiency of civil applications,but also avoid the risk of relying on GPS system in the military field.Therefore,several key technologies of data preprocessing and high precision positioning of BDS/GNSS systems have been studied in this dissertation,focus on the tri-frequency cycle slip detecting and repairing,decorrelation algorithm assessment criterion,satellite repeat shift time of GNSS and carrier phase multipath mitigation.the main research contents and contributions for this dissertation are as follows:Considering the problems of detection accuracy and algorithm complexity of the existing cycle slip detection and repair algorithm,WPAT cycle slip detection and repair algorithm based on three-frequency combination is proposed.The core idea of the algorithm is as follows: 1)from the perspective of observation value,wavelet packet transform is used to pre-process the detection for denoising,so as to improve the precision of the detection for cycle slip.At the same time,considering the particularity of BDS navigation system,the accuracy of the observation values is improved by correcting the pseudorange deviation at the BDS satellite,and the precision of the combined observation values of the cycle slip detection is further improved to ensure the success rate of cycle slip detection.2)from the detection threshold,an adaptive detection threshold strategy is designed for satellites with different orbital types and different data sampling rates,so as to adaptively adjust the detection threshold of detection value,further improve the detection accuracy and reduce the error rate of cycle slip detection.Experiments show that the proposed WPAT method can accurately detect and repair various cycle slips,and the computational efficiency of the algorithm is further improved.Aiming at the assessment criterion of decorrelation algorithm,this dissertation studies and analyzes the theoretical derivation of common assessment criteria of decorrelation algorithm,and uses three commonly used decorrelation algorithms to carry out reverse validation analysis on different assessment criteria.Based on the simulation and experimental data,the assessment criteria of the existing algorithms are compared and analyzed,and the three algorithms are compared and analyzed by the number of candidate values.The simulation and experimental results show that the assessment method of decorrelation coefficient and condition number can accurately reflect the decorrelation performance of GAUSS and Cholesky algorithms,but it is difficult for these two assessment criteria to accurately reflect the decorrelation performance of LLL algorithm.In addition,from the perspective of the number of candidate values,although the efficiency of the three algorithms is similar for the simulation data,the experimental results shows that the algorithms based on GAUSS and Cholesky have better decorrelation performance than that based on LLL algorithm.In this dissertation,two methods for calculating the repeat period of satellites are studied and analyzed,and three commonly used methods of calculating the orbit repeat shift time of satellites are discussed: the broadcast ephemeris method(BEM),the correlation coefficient method(CCM)and the aspect repeat time method(ARTM).At the same time,the three methods are used to analyze the performance of the orbit repeat shift time of GPS,BDS and Galileo.Based on the experimental data of MGEX data center station,the experimental results show that: even for the same navigation system,the repeat shift time of each satellite is obviously different.In addition,the difference between the maximum value and the minimum of the system is also different because of the difference of the system,so the deviation caused by this factor must be fully considered when using the sidereal day filtering method to correct the multipath error.The correlation between carrier phase multipath error and carrier-to-noise ratio(CNR)is studied and analyzed,and the theoretical feasibility of detecting carrier phase multipath error based on CNR observations is verified.A multi-resolution CNR model(receiver type,satellite and frequency)is established by the GPS dataset from 230 IGS stations around the world for 30 consecutive days(2019.06.01-2019.06.30).Futher more,the multi-resolution CNR model of different receiver types and different satellites based on satellite altitude angle is established.Then,the multi-resolution CNR model is combined with the inter-frequency CNR difference adaptive double statistical test strategy,which can effectively detect multipath.For the detected epoch,the weight reduction strategy based on CNR is used to reduce the influence of multipath on the positioning results.The experimental results of real-time dynamic precise point positioning show that this method can effectively detect multipath,and the detection rate is 92.58%.For the improvement of positioning results,the positioning accuracy in the three directions of East,North and Up is 19.95%,17.89% and23.07% higher than before,respectively.