| PPP(Precise Point Positioning),as an important means of GNSS high-precision positioning(centimeter level,millimeter level,etc.),is widely used in the field of geoscience research such as geodesy.Among them,ambiguity resolution is an important part of PPP to achieve high-precision positioning,namely PPP-AR.Because PPP is affected by Uncalibrated Phase Delays(UPD),its ambiguity loses its integer nature.PPP users want to restore the integer nature of undifferenced ambiguity to achieve PPP-AR,they need the phase bias products provided by the server.In order to meet the needs of GNSS high-precision positioning users for PPP-AR positioning technology,how to provide phase bias product services has become one of the hot issues in the field of GNSS high-precision.The implementation method of PPP-AR is not unique,and its corresponding phase bias products are also different in expression form.In the face of different PPP-AR methods,how to achieve compatible interoperability between different phase bias products and at the same time to generate a more robust phase bias combination product is one of the core problems that IGS(International GNSS Service)/iGMAS(International GNSS Monitoring & Assessment System)need to solve.This dissertation systematically and deeply studies the theory and algorithm model of PPP-AR.Based on the advantages and disadvantages of the existing PPP-AR methods,an improved phase clock/bias method is proposed and applied to the phase bias product service in analysis center of Wuhan University.At the same time,based on the research of different PPPAR methods,phase bias product combination method is proposed,which provides one of the feasible schemes for the phase bias product combination.The specific work and main contributions of this article include:1.Introduced the basic model of PPP-AR and the different PPP-AR implementation methods in detail.On the premise of taking into account the advantages of the traditional UPD method and the IRC(Integer Recovery Clocks)method and discarding its shortcomings,an improved phase clock/phase was proposed.Compared with the UPD method,the phase clock/bias method abandons the idea of calculating the phase bias based on the float ambiguity,which makes the phase bias product get rid of the irregular characteristics that change with time due to the influence of the pseudorange reference.Therefore,the phase clock/bias method is more stringent and higher accuracy.The experiment confirmed that GPS daily solution improved about 20% in the east component compared with UPD method.Compared with IRC method,the satellite clock with the phase clock/bias method is consistent with the clock datum of IGS legacy clock,so it is compatible with the IGS pseudorange bias products(such as DCB,etc.),and will not introduce bias in observations to avoid extending the convergence time of real-time PPP users.Single frequency PPP experiments confirmed that IRC can increase the convergence time by approximately 20%.2.Implemented multi-GNSS PPP-AR.Based on the multi-GNSS PPP model,the advantages of the multi-GNSS PPP float solution over the single-system PPP are demonstrated.At the same time,based on the UPD method and the phase clock/bias method,the multi-GNSS PPP-AR is studied and discussed.Experiments confirmed that the multi-GNSS PPP-AR based on the phase clock/bias method is improved by about 17% in the east compared to the UPD method.Due to imperfect Galileo and BDS construction and inaccurate models,the positioning accuracy of the multi-GNSS PPP-AR based on the phase clock/bias method is comparable to the GPS PPP-AR.3.Through the research on the current satellite clock combination method adopted by IGS/iGMAS,a satellite clock combination method based on the double-difference clock method is proposed.Compared with the clock combination of IGS,its advantage is that it can detect the gross error of clock by epoch;compared with the clock combination method of iGMAS,this method does not require tedious and repeated clock fitting.Compared with the IGS clock combination product,the clock conbinaiton product obtained by our method has 97%of clock difference less than 10 ps,and the accuracy of the combined clock is equivalent to the accuracy of the IGS clock combination product.On days where the double-difference clock is relatively large(greater than 20 ps),the PPP positioning result of the clock combination product obtained by this method is improved by about 9% compared to the PPP positioning result of the IGS clock combination product.4.Based on the research on PPP-AR and the method of satellite clock combination,phase bias product combination method is proposed.This method first converts the phase bias products publicly released by various analysis centers into the unified expression form of widelane UPD and IRC;then adjusts the double-difference between each phase bias product in integer cycle steps and realizes wide-lane UPD and alignment of IRC.Finally obtain a combination product of phase bias by weighted average.The experiment confirmed that the combination residuals of the wide lanes of the phase bias products are all less than 0.04 weeks,and the combination residuals of IRC are about 98% between(-0.1～0.1)narrow lane wavelengths.Compared with other phase bias products participating in the combination,the average improvement in the three directions is about 10%.5.The open-source,PRIDE PPP-AR,software is introduced in detail,and the service performance of the software is analyzed through experiments.The software’s positioning algorithm model and error correction model are consistent with the server model that generates phase clock/ bias products.The PRIDE PPP-AR software is used in conjunction with the phase clock/bias products provided by the analysis center of Wuhan University to obtain more consistent positioning results with the server. |
