| With the development of the Global Navigation Satllite System(GNSS),the applications of GNSS are also expanding,and the users are concentrating on the higher requirements for precision and reliability of GNSS products.Chinese BeiDou navigation satellite system(BDS)officially provides services in the Asia-Pacific region,which makes the triple-frequency GNSS positioning technology to be truly verified and used.The BDS constellation combines geostationary earth orbit(GEO),inclined geosynchronous satellite orbits(IGSO)and medium earth orbit(MEO)satellites.The constellation distribution,satellite orbit accuracy,signal characteristics,the number of visible satellites,and the observation accuracy are different from global positioning dystem(GPS).The studying of BDS high precision positioning technology can improve the precision,usability and reliability of BDS,expand the industry scope of BDS application,increase the market of BDS navigation products,and enhance the modernization defense level of our country.The paper focuses on data processing technology of the high precision positioning for BDS,and the main innovations and achievements are as follows:(1)The normal triple-freqeucny cycle-slip detection and repair methods are in poor performance and low reliability under high ionospheric activity,in order to solve this problem,based on real time estimating the ionospheric delay variation between epochs,a novel approach for cycle slip detection and repairment without the influence of epoch ionospheric delay variation using BeiDou triple-freqency observations is proposed.This algorithm can be easily actualized,and achieve high cycle-slip detection precision.The results indicate that the three line-independent cycle-slip detectors can effeetively detect and repair half-cycle-slip,and this approach can 100% detect and repair different types(small cycle-slip,big cycle-slip and special cycle-slip combination)existing in triple-freqency observations,even with larger sample interval data and under high ionospheric activity conditions.(2)Traditional geometry-free model three carrier ambiguity resolution(GF-TCAR)algorithm is susceptible to pseudorange measurement noise and ionospheric delay,which limits the ambiguity resolution(AR)success probability,in order to solve this problem,this paper propose a modified GF-TCAR method based on the weighted minimum the weighted total noise level.Based on analyzing the influences of different types on error extra-wide-lane(EWL)and wide-lane(WL)AR performance,this paper introduces the definition of the weighted total noise level to decrease ionospheric delay,and gives the method of calculating the optimum pseudorange combination coefficients to improve the EWL/WL AR success rate.By the real-time estimation of the ionospheric delay,a novel geometry-free and ionosphere-eliminated(GFIE)narrow-lane(NL)AR method is proposed to improve the estimation accuracy of NL ambiguity.The experimental results show that the algorithm can increases the single epoch EWL/WL AR success probability by up to 90% even in long baseline condition,which is 8% higher than that of the traditional code combination.The GFIE method single epoch NL AR success probability can reach more than 50%,which is 38~72% higher than the traditional geometry-free and ionosphere-Free(GIF)method.(3)The traditional geometry-based model three carrier ambiguity resolution(GB-TCAR)algorithm has system error in long baseline application,which will deteriorate the NL AR success probability and the reliability,and requires a large number of computations.This paper.introduces a long-baseline BeiDou triple-frequency real time kinematic(RTK)strategy based on ionosphere and troposphere estimation,which improves the AR success probability and the single epoch positioning accuracy.Examples show that,the single epoch NL AR success probability of this strategy can achieve up to 90% in the 181 km baseline application,which is 20% higher than that of the traditional GB-TCAR algorithm.At the same time,in 181 km baseline condition,the single epoch BeiDou triple-frequency RTK positioning precision can achieve 3 cm in east and north components,and about 10 cm in up component,compared with the traditional GB-TCAR method,the improvements are 40.0,14.8 and 39.8%,respectively.(4)In the case of hybrid constellation,the time domain,frequency domain and periodicity characteristics of multipath effects on the different types of satellite are different.The recursive filter will lead to the misalignment of the extracted multipath correction sequence and the original GEO and IGSO satellites observation,which jeopardize the sidereal filtering performance,and the average orbital repeat periods for MEO satellites is about seven days,which will fade the time-correlation of multipath errors.The paper introduces a BDS multi-frequency multipath migtigation method based on zero-phase filter and the elevation-angle model correction.A modified sidereal filtering introduce zero-phase filter to effectively ensure the the extracted multipath correction sequence and the original observation epoch-matched,and improve the multipath migtigation performance of sidereal filtering algorithm.And the multipath correction method based on the elevation angle is also given for mitigating the BDS MEO satellites code measurments multipath effects,which correction model is simple,parameters are little,performance is good,and the application is wide.The experimental results show that the modified sidereal filtering improves the standard deviations of GEO satellites B1,B2 and B3 frequencies code observertions by 27.3,22.8 and 30.2%,respectively,improves the accuracies of IGSO satellites B1,B2 and B3 frequencies code measurments by 21.2,26.0 and 27.1%,respectively.The multipath correction method based on the elevation angle can reduce the standard deviations of MEO satellite B1,B2 and B3 frequencies code measurments by 8,7,and 5%,respectively.Finally,the main work of this thesis is summarized,its engineering application is introduced,and the future work is presented. |
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