Research On Theories And Methods Of Precise Point Positioning

Precise Point Positioning integrated with advantages of both standard single-point positioning and differential positioning,can achieve centimeter-level positioning accuracy using code and phase measurements on a single receiver combined with precise ephemeris and precision clock determined from a number of global tracking station.Currently,the main challenge of the precise point positioning is its relatively long initialization time,usually takes 20 minutes or longer to make the float solution converges to centimeter-level accuracy,limiting its real-time applications.Quickly determing the un-differenced integer ambiguity,accelerateing precise point positioning's convergence speed,can greatly improve the performance of precise point positioning and lead to a more widely application area.In this context,this paper carried out the following studies:(1)The formation mechanism and characteristics of FCB are investigated based on the receiver's carrier phase measurement principle.Theoretical analysis and experimental data indicate that,FCB has long-term stability and has nothing to do with the signal loss of lock and local time adjustment,while its boot features correspond to the initial phase of the RF local oscillator.In receiver design,interger frequency multiplier,phase re-sync,RF sampling could be used to avoid FCB's boot variation.(2)A improved method for satellites and receivers fractional cycle bias(FCB)estimation using the reference station network is proposed.Firstly,the wide-lane ambiguity is obtained by the use of PPP estimation,compared with conventional Melbourne-Wubbena method,the estimation accuracy of the widelane FCB increased by 10%.Secondly,vertical total electron content(VTEC)is treated as parameter in un-combined PPP estimation instead of slant total electron content(STEC),and the estimation accuracy of the widelane FCB increased by 6%.After removing FCB and ambiguity resolution,fixed solution has significantly improved positioning accuracy compared with the float solution,especially the east part(about 41%).(3)Improved precision ionospheric delay extraction method using PPP.With respect to modeling error of ionosphere thin model,single-difference between satellites is used to eliminate reciver differential code bias.Furthmore,with FCB corrections and ambiguity fixing,the extracted dual-frequency PPP ionospheric delay's accuracy is improved from 3.84cm(float)to 1.46cm(fix).(4)A method of single-difference-betwe`en-satellite ionospheric delay extraction by the use of a single frequency receiver is proposed.With troposphere delay and satellite FCB corrections generated by reference network,as well as pseudorange multipath elimination by sidereal filtering,the single-difference carrier phase ambiguity can be sussessfully fixed.After ambiguity fixing,single frequency ionospheric delay accuracy can achieve 1.74 cm,which is close to dual frequency PPP's.Thus single frequency receivers can be used to densify a regional ionosphere auxiliary reference network to reduce network construction costs.(5)For the difference of satellite orbit repeat period,this paper presents a sidereal filtering method based on satellite elevation and azimuth,the filter offsets for each satellite and each epoch are determined according to the elevation and azimuth objective function.Finally sidereal filtering is applied to improve real-time ionospheric delay extraction and dynamic positioning accuracy,and realtime ionosphere delay precision is improved from 0.185 m to 0.028 m,postion accuracy is improved by 69.2%,72.3% and 27.6%(esat,north,vertical).