Research On Multi-constellation And Multi-frequency Combined High-precision Baseline Resolution And Software Development

With the development and improvement of the four global navigation satellite systems including GPS,BDS,GLONASS and Galileo,global navigation satellite systems have been in the stage of multi-constellation and multi-frequency combined positioning.Multi-constellation can benefit the positioning precision,reliability and availability in highly-occluded and complex environments,thus the effective infusion of data is one of keys to multi-constellation combined baseline positioning resolution.Multi-frequency observations have the characteristic of fast ambiguity resolution,and BDS is the only navigation satellite system which can broadcast triple-frequency signals on the whole constellation till now.Therefore,it's significant for the promotion of BDS application in China to make the most of BDS triple-frequency observations,build the GNSS baseline resolution model with BDS triple-frequency constraint and realize the fast fixing of GPS/GLONASS/Galileo combined ambiguities.Thus,this paper researches these problems mentioned above,and the major contents and achievements are as follows:1.The fundamental theory of multi-constellation and multi-frequency combined positioning is clarified in detail.The coordinate and time systems of GPS,BDS,GLONASS and Galileo are compared and analyzed.Meanwhile,the temporal-spatial unification of four systems is achieved;Taking BDS as example,the linear combination of multi-frequency and common dual-frequency observations including their observation noise are illustrated.2.The key technology of multi-constellation GNSS combined baseline resolution is researched.Based on the introduction of modelling ill-posedness,the ill-posedness of baseline resolution model and its effects on ambiguity resolution are analyzed based on the method of condition number.The introduction of pseudorange observation equation can reduce the ill-posedness of baseline resolution model and speed up the convergence of ambiguity resolution;Aiming to the difference in characteristic among the short,medium,and long baselines,as well as the difference between CDMA and FDMA signal,the GPS/BDS/GLONASS/Galileo quad-system combined baseline resolution model that can be adapted to baselines with different distances is established;The experimental results show that the precisions of dual-system and multi-system combined positioning are higher than it of single system;Compared with the GPS-only positioning,the precisions of quad-system positioning of short and medium long baseline are improved by 53.3%,60.0%,42.8%and 47.2%,38.2%,42.8%in north,east and up directions respectively.The horizontal and vertical precisions of GPS/BDS/GLONASS combined positioning with two medium long baselines of 42km and 61km are better than 2cm.The horizontal and vertical precisions of two baselines with distances of 119km and 174km are better than 2cm and 4cm respectively.3.Baseline resolution model with BDS triple-frequency constraint is researched.With respect to BDS extra-widelane ambiguity resolution,the method of extra-widelane ambiguity search is proposed and with that,the success rate of extra-widelane ambiguity resolution is increased.GPS/GLONASS/Galileo combined baseline resolution model with BDS triple-frequency constraint is established in the use of fixed BDS ambiguities.The experimental results show that for short baselines,the ratios larger than 50 reach at 87.6%with constraint model while they are fewer than 10%with traditional model.Compared with traditional model,the condition numbers of normal equation with constraint model are 2 to 4 order of magnitudes fewer,which can weaken the ill-posedness of model and enhance the reliability of ambiguity resolution.4.The software of GNSS multi-constellation and multi-frequency combined baseline resolution(GBSS)is developed and tested.Making use of results mentioned above,a software of GPS/BDS/GLONASS/Galileo quad-system combined baseline resolution is developed.Multiple sets of data are used for empirical experiments and the results show that for baselines with different distances,the mutual differences of baseline vectors between resolutions of GBSS and GAMIT are all less than 1cm.The positioning precisions of 14901 baselines processed by GBSS software in north and east directions that are better than 1cm can make up 99.7%and 96.9%respectively,which can demonstrate the reliability and robustness of software.