Study On Data Processing Technology Of Accuracy And Availability Augmenting For Global Navigation Satellite System

Accuracy and availability are both the important performance of navigation satellite system.The coarse-free positioning algorithm can determine user positioning with sub-millisecond pseudoranges in some challenging environment such as urban canyon,foliage-covered area and indoor which is hard to get the full pseudoranges.It will greatly improve the availability.Unfortunately,the algorithm will fail if there is no a priror position.In addition,the Bei Dou navigation satellite system(BDS)is the first navigation satellite system which adopts hybrid navigation constellation.The GEO satellite of BDS has high navigation data rate and broadcast ionospheric grid information.The high navigation data rate makes feasibility of fast positioning.The retional use of regional ionospheric grid information can effectively improve the accuracy of the standard single point positioning.Herein,four aspects are studied in this thesis in order to improve the accuracy and availability of service.(1)The normal Global Positioning System(GPS)almanac can not effectively describe the motion of the Medium Earth Orbit(MEO)satellite without considering the long-term change.It can?t obtain a good effect directly via least squares curve fit with the normal GPS almanac.An improved almanac calculation method with semi-major axis compensation was proposed.The mean motion difference was considered in least squares curve fit.Then the effect of mean motion difference was compensating to semi-major axis for obtaining the broadcast almanac.The precision of user range error(URE)of almanac generated by the proposed method doubles than directly fit with normal GPS almanac,from about 2000 meters to better than 900 meters.An extended almanac set including mean motion difference was further proposed.The URE will further reduce by more than 50% on average.(2)For finding the rough position,an improved coarse-free positioning method with millisecond integer ambiguity search and a rapid positioning method with auxiliary clock were proposed.Additionally,the relationship between inter-satellite distance and maximum pseudorange difference is analyzed,which can be used to compress the search space.For sub-millisecond measurements,the success rates of the improved coarse-free positioning method can achieve 99.96%,99.86% and 99.79% for time offsets of 1,3 and 5 s respectively,and the average number of search candidates is about 672 with the data file of mars station of the International GNSS Service(IGS),.In addition,the success rates can reach 100% by using measurements of other 10 stations.In addition,with measurements of eleven stations,high success rates of 100% and 99% were achieved if the auxiliary time is better than 15 and 25 microseconds,respectively.(3)According the high data rate of GEO satellite in BDS,rapid positioning methods with altitude hypothesis aiding and Doppler-aided were proposed.They can determine user position without the frame synchronization of MEO/IGSO and can handle the ill-conditioned problem of the pseudorange observation equations of GEO satellites.Examples show that,we can determine user position with altitude aiding even if there are only 3 GEO pseudoranges.In addition,we can determine user position with enough Doppler information even if the number of GEO full pseudoranges is less than 3.(4)It is hard to confirm that which method has higher positioning accuracy between ionospheric grid and Klobuchar model if the receiver is located in the boundary of the valid grid.In this condition,part of pseudorange measurements can corrected with ionospheric grid while part of that cannot.Then it will has better correction accuracy if we use ionospheric grid correction,while more available pseudoranges with Klobuchar model.To handle this problem,a selection method was employed according the position dilution of precision(PDOP)of constellations.Examples show that,the positioning result with proposed method is close to or even better than the better result of model and grid correction.Compare with the worst result when the selection is not carried out,the position accuracy increased by 18.1%,16.5% and 19.9% in kun1,chu1,and lha1,respectively.Finally,the main work of this thesis and its engineering application are summarized and reviewed,the future work is also presented.The research results have been applied to develop various types of receivers and simulators.