Research On Method Of Shortening Ambiguity TTFF For Uncombined Model Of BDS Medium-long Baseline

How to effectively deal with the atmospheric delay error in the long baseline and realize the fast and accurate ambiguity fixation has always been the focus and difficulty of the GNSS relative positioning research based on the single baseline solution model.With the modernization of China's Beidou Satellite Navigation System(BDS),GPS and GLONASS,and the development of Galileo,QZSS and IRNSS systems,the satellite navigation system is entering the era of multi-frequency multi-system,in which the BDS regional system is the first full-constellation broadcast tri-band navigation signal satellite navigation system.This presents new opportunities and challenges for long baseline positioning in GNSS single base stations.In this paper,according to the advantages of the three frequency system of Beidou system,this paper makes a detailed study on the algorithm of ambiguity resolution in the uncombined solution model.The main work and conclusions are as follows:(1)This paper expatiates on the research status of BDS system,the solution of three frequency ambiguity resolution and the rapid fixation of medium and long baseline ambiguities.At the same time,it points out the problems and difficulties in the long baseline solution of BDS.(2)The mathematical model of medium-length baseline solution of BDS precision relative positioning is introduced in detail,and the problems and difficulties in the long-range solution of BDS are summarized.Using the BDS system tri-band advantage,this paper compares the performance of the three-frequency GF algorithm and the GB algorithm of the wide-lane ambiguities in detail.The experimental results show that the performance of GB algorithm and GF algorithm is equivalent,but the combination of the two algorithm is the best.Two kinds of constraint algorithms have different effects in different regions,and the TTFF of the original ambiguity is improved by half an hour.(3)In order to make full use of BDS tri-frequency advantage,two algorithms are proposed.The constraint effect of the two kinds of constraint algorithms is compared and analyzed by using the measured data.The experimental results show that the wide-lane constraint algorithm based on the observed domain constraint is more reliable than the constraint algorithm based on the fuzzy degree domain,but the effect of the constraint is slightly worse.(4)The TCAR-ION algorithm based on tri-band linear combination is proposed.In the TCAR-ION algorithm,we at first solve the initial ionospheric delay by using the combination of the tri-band linear combination(0,-1,1)and(1,-1,0).Then an idea which is similar to carrier-smoothed code through hatch filter is introduced to improve the initial ionospheric delay.At last,we introduce the moving average algorithm to further optimize the algorithm.We use measured data to evaluate the precision of double differential ionospheric delay.The results show that the the double differential ionospheric delay can converge to less than 0.1 m in 20 minutes whic is obtained by TCAR-ION algorithm.(5)In order to solve the problem that the ionospheric delay and the ambiguity parameter separation speed are too slow in the long baseline solution of BDS,the double differential ionospheric delay of TCAR-ION is applied to the ionospheric weighting model.This paper use nine baselines of different latitudes to analysis the performance of the algorithm.The results show that the algorithm can speed up the TTFF of uncombined ambiguities.And it is further improved by half an hour to the wide-Lane constraint algorithm.After using the ionospheric weighting model,most of the TTFF are smaller than 2 hours;and the precision of the horizontal baseline components are better than 0.02m,the vertical baseline components are better than 0.06m.