| The real-time differential technique of Global Navigation Satellite System(GNSS)has the advantages of all weather,all time,full automation,and no intervisibility required between stations.It has wide application prospects in building(structure)deformation monitoring,monitoring of geological disasters such as landslide and debris flow,development of unmanned technique,kinematic-to-kinematic positioning,etc.All of the above applications need the high-precision,high-success-rate,and reliable realtime fast positioning and the key lies in the fast and correct determination of integer ambiguity vector.As ambiguity dilution of precision(ADOP)is a scalar measure of the success rate of ambiguity resolution,this paper focused on the research of fast,reliable,and precise positioning method with multiple GNSSs(multi-GNSS)based on the theory of ADOP.The main research contents include the theoretical analysis of fixed success rate of ambiguity,the fast and precise positioning with controllable success rate under complex sky conditions,the theoretical analysis of reliability of multi-GNSS ambiguity resolution,and the fast,reliable,and precise positioning under open sky conditions.The main works and contributions are summarized as follows:(1)In view of the disadvantages of single-epoch ADOP expression that it is complicated and not conducive to theoretical analysis,based on the ADOP theory,the extended ADOP(E-ADOP)theory was developed by defining the SummationMultiplication Ratio of Weight(SMRW): the properties of the SMRW were analyzed and the E-ADOP expression,the mean E-ADOP expression of multiple epochs,and the lower-limit expression of the mean E-ADOP after adding satellites were deduced.Based on the E-ADOP theory,the main factors affecting the fixed success rate of ambiguity under different conditions were analyzed.In terms of fixed success rate of ambiguity of single-frequency single-epoch positioning based on GNSS,the main factor making the multiple systems superior to the single system is the large number of visible satellites in the former and the main reason why the BeiDou Navigation Satellite System(BDS)is better than the Global Positioning System(GPS)is that there are many high-elevation-angle visible satellites in BDS.(2)Considering that the current satellite selection(SS)algorithm can not achieve a stable and high success rate and is more time-consuming with the increase of the number of satellites,the ADOP factor was introduced into SS algorithm and a fast SS algorithm with an adaptive cutoff elevation angle based on the E-ADOP was proposed.The proposed SS algorithm has a high ADOP controllable success rate and is suitable for different complex observation conditions.In this proposed algorithm,the effect of removing low-or high-elevation-angle satellites on ADOP was studied,and it was proved that a small number of high-elevation-angle satellites can achieve a high success rate;the threshold factor and its theoretical and practical calculation formulas for fast selecting satellites were determined,and the steps of fast selecting satellites according to a given ADOP were given.The results indicated the proposed method can realize the fast positioning with a stable and high success rate and achieve the high-precision horizontal positioning.(3)Although both the single-frequency single-GNSS positioning and the SS or the partial ambiguity resolution(PAR)algorithm based on the multi-GNSS can achieve the fast positioning,the reliabilities of the above algorithms still need sufficient theoretical analyses and experimental verifications due to their different theoretical foundations.The strict variation formulas of accuracies of the float baseline vector and original ambiguity vector(OAV)before and after satellite-based observations added were derived;the relationships between the ADOPs of OAV before and after observations added and the whole ambiguity vector after observations added were deduced;the changing laws of the probability density functions,the integer least squares pull-in regions,and the R-ratio test-based integer aperture pull-in regions of OAV before and after observations added were analyzed.The theoretical analysis and experimental results indicated that the PAR algorithm based on the multi-GNSS is an optimal algorithm in terms of precision,fixed success rate,and fixed reliability of the float ambiguity solution;the experimental results showed that both the single-epoch singlefrequency positioning and PAR algorithms based on the BDS are better than those based on the GPS in the above three aspects.(4)For the single-epoch multi-GNSS positioning,due to the current PAR algorithms faced with the problem of how to quickly select the optimal ambiguity subset to achieve the high-success-rate,high-precision,and fast positioning,the PAR algorithm based on the E-ADOP and convex hull-based SS was proposed,in which both the positioning accuracy and success rate were considered.In this proposed method,the feasibility of the ADOP as a threshold to select a subset of ambiguities before ambiguity decorrelation was analyzed;the ambiguity selection method based on the convex hull-based SS was put forward,i.e.,the equipartition rotation method based on the convex hull and the method of minimal inscribed circle of polygon with the largest radius,to fast select the needed ambiguities corresponding to the evenly distributed low-elevation-angle satellites;the ambiguity selection method based on the E-ADOP-based SS with an adaptive cutoff elevation angle was proposed to fast select the ambiguities corresponding to the high-elevation-angle satellites according to the selected ambiguities relevant to the low-elevation-angle satellites and a given ADOP.The results indicated the proposed algorithm can achieve the high-precision,highsuccess-rate,and reliable fast positioning,and also can remedy the shortcoming of the algorithm in(2)that the vertical positioning accuracy is not high because its selected satellites are all high-elevation-angle satellites.There are 80 figures,25 tables,and 193 references in this paper. |
PDF Full Text Request