| Since the relative and differential positioning technology needs the support of the reference station network,the PPP technology that does not need the support of reference stations and can provide instantaneous centimeter level positioning is proposed and attracted wide attention.However,PPP technology also has its own bottleneck,that is,long convergence time and float ambiguity solution.The convergence of PPP usually takes 15 minutes or even longer,which greatly limits its application in real-time field.PPP ambiguity resolution can significantly improve the positioning accuracy,especially in the East,and greatly shorten the convergence time,and thereby improve the efficiency of operation,making ambiguity resolution a hot issue in the field of PPP research in recent years.This paper mainly focuses on how to quickly and effectively fix the undifferenced integer ambiguity..A lot of achievements have been made in the study of PPP undifferenced ambiguity resolution of CDMA signal system.The data processing strategy and algorithm are suitable for GPS,BeiDou and Galileo systems using CDMA signal system,but it cannot be applied to GLONASS system using FDMA signal system.There are many difficulties in the GLONASS PPP-AR of the FDMA signal system:1)different satellites use the signals with different wavelengths;2)unable to simplify the model of IFCBs;3)the precise correction of IFPBs when the mixed type of receiver is used.When resolving the undifferenced integer ambiguity of PPP,We need,firstly,to form a wide-lane ambiguity through the combination of Melboume-Wibbena,and IFCBs is bound to enter into the wide-lane ambiguity by this combination,but the influence of IFCBs cannot be eliminated through between-satellites differencing.Therefore,the idea of GLONASS PPP ambiguity resolution is centered on how to eliminate the influence of IFCBs.Unlike GPS,the ionospheric-free ambiguity of GLONASS just has integer characteristics,which is due to the ratio 9/7 of the two frequencies.The GLONASS PPP-AR algorithm based on ionospheric-free ambiguity is given.This method is not affected by IFCBs,and does not need to limit the same type of receiver,and the GLONASS PPP-AR data processing flow is simplified.The feasibility of the method is verified by the post processing experiment.Fixing the GLONASS ionospheric-free ambiguity on the GPS ambiguity resolution can effectively improve the positioning accuracy and shorten the PPP convergence time.Because the wavelength of the ionospheric-free ambiguity is only half of the narrow-lane ambiguity,it is more sensitive to the residual error in the ambiguity estimation.The dynamic filtering experiment of GLONASS PPP-AR is further carried out.When the narrow-lane ambiguity of GPS is fixed,the time of first ambiguity resolution is 1032s;if further fixed GLONASS ionospheric-free ambiguity,the time of first ambiguity resolution is 927s,making the time of first ambiguity resolution shortened by about 10%,and providing reference index for the wide application of the method in the operation.The method of GLONASS ionospheric-free ambiguity PPP-AR is sensitive to error,so it often requires long observation time to ensure the accuracy of ambiguity estimation,which seriously weakens the efficiency of PPP.Then we introduce the GLONASS PPP-AR based on.narrow-lane ambiguity,which-is differenlt from--both the GLONASS ionospheric-free ambiguity PPP-AR and the undifferenced and uncombined GLONASS PPP-AR.These two methods all bypass the Melbourne-Wubbena combination to avoid the influence of IFCBs,while the narrow-lane ambiguity PPP-AR uses the single station IFCBs that are stable over the time,thus eliminating the effect of IFCBs on Melbourne-Wubbena combination ambiguity by the correction IFWBs of every satellite and every station in order to realize narrow-lane ambiguity PPP-AR.In order to avoid making false decisions in the integer adjustment of IFWBs,especially in the data processing of large scale networks,this paper chooses to apply IFNBs correction to narrow-lane ambiguity to eliminate the influence of the hidden integer of IFWBs.IFWBs/IFNBs correction information is the prerequisite of GLONASS narrow-lane ambiguity PPP-AR,which has good temporal stability.The prediction accuracy can fully meet the needs of the real-time GLONASS narrow-lane ambiguity PPP-AR.For the same group of data,the GLONASS narrow-lane ambiguity PPP-AR and the ionospheric-free ambiguity PPP-AR experiment are carried out respectively.When the time of first ambiguity resolution is less than 10 minutes,the fixed solution percentage of the former is 20%higher than that of the latter.In addition,the GLONASS narrow-lane ambiguity is fixed on the basis of the GPS PPP-AR,and the time of first ambiguity resolution is 724s.For the ionospheric-free ambiguity,the time is 927s,reduced by more than 20%.The more ambiguities are used for AR,the higher the success rate of partial ambiguity resolution strategy will be.The inter-system PPP-AR needs only one reference satellite instead of the system to select their respective reference satellite when the intra-system PPP-AR,so that more ambiguities are involved in the ambiguity resolution.The algorithm of inter-system GPS/BeiDou PPP-AR is given in this paper.ISWBs/ISNBs is the precondition of realizing inter-system PPP-AR.In general,ISWBs/ISNBs have good time stability,and 85%of the variations between adjacent days are no more than 0.05 cycle;but there is also a jump situation,which is generally because the cold start of receiver or update of software version,so it is foreseeable;in addition,the ISWBs/ISNBs of a few receivers fluctuate with time and present a sub-daily signal,but the deviation of the ISWBs/ISNBs of the 2 hour update frequency and the day is generally not more than 0.1 cycle.The inter system GPS/BeiDou PPP-AR does not improve the positioning accuracy compared with intra-system AR,but it can shorten the time of first ambiguity resolution from 649s to 586s,i.e.an improvement of about 10%.Based on the research of the PPP-AR algorithm in this paper,the PPP-AR function of GLONASS,BeiDou and Galileo system can be further added in the PPP-RTK....odule that can only handle GPS.The GPS/GLONASS/BeiDou/Galileo four systems ionospheric-free combination PPP-AR software package and undifferenced and uncombined PPP-AR software package are implemented.The PPP-RTK module of PANDA software is further improved and extended.In addition,the ionospheric-free combination PPP-AR software package can also achieve inter system PPP-AR.Based on the two software packages developed in this paper,the GPS/GLONASS/BeiDou/Galileo four system ionospheric-free combination PPP-AR experiment and the GPS/GLONASS undifferenced and uncombined PPP-AR experiment are carried out respectively,which not only verify the data processing capability of the software package,but also prove the important role of the multi-system ambiguity resolution in the ionospheric-free combined PPP and the undifferenced and uncombined PPP. |
PDF Full Text Request