Study On Combined GPS/Galileo Precise Point Positioning With Ambiguity Resolution

Since 2008,the issue of Ambiguity Resolution(AR)in Precise Point Positioning(PPP)technology has been a very popular research point among the Global Navigation Satellite System(GNSS)community.Many studies in home and abroad show that fixing the ambiguous phase biases in PPP solutions can significantly shorten the convergence time and improve the positioning accuracy.Based on the software platform provided by my tutor,we implemented the PPP AR test.The fact that the Uncalibrated Phase Delays(UPD)exist in both satellite and receiver end makes the ambiguity biases fractional.These delays are all instrumentally dependent.Implementation of PPP AR is essentially to separate the fractional part of UPD from phase biases parameter and to recover its integer property.Hence,AR strategies proposed by many researchers are different in the way of separation.For example,one of them fixes the between-satellite single differenced ambiguity by correcting the related single differenced UPD,in which UPD from receiver has been cancelled duo to the operation of difference.Another one fixes the un-differenced ambiguity directly by estimating the instrumental UPDs with so called"decoupled clock model".In this effort,our approach is similar to the latter one,but we still use common clock error parameters in the code and phase measurement equation,and explicitly estimate the UPD both from satellite and receiver end epoch by epoch.It should be noted that the UPD parameter in our approach also contains the code instrumental biases.Therefore,it is necessary to make sure the mathematic-model consistency between server and user end.In the experimental stage,we firstly tested a combined cycle slip detection strategy to handle the active ionospheric phenomenon.Then we investigated a proposed partial AR strategy,which was also used in the following PPP AR tests.Next,GPS PPP AR was mainly tested.According to the statistical results of five days,static PPP AR showed a small improvement since the float PPP already has satisfying accuracy and convergence time;while kinematic PPP AR demonstrated a significant improvement both in accuracy and convergence time.For instance,the horizontal error component is about 1cm compared with 2cm,and the vertical component is better than 4cm compared with 5cm,and the convergence time has been shortened at least 50%.Besides,we also used the observation data from MGEX(Muti-GNSSEXperiment)to test the PPP AR results of GPS and Galileo systems.The GPS results still show an improvement in convergence time,but the kinematic fixed solutions are not as stable as the related float solutions,which may be caused by the low accuracy of calculated satellite UPDs.Since the number of observed satellites of Galileo system is relatively small,the kinematic solutions are quite noisy.We only tested its static PPP AR.But the results were not satisfactory.We investigated the reasons and found lower accuracy of calculated narrow lane UPDs.Hence,it is necessary to improve the accuracy of estimated narrow lane UPD.Further more,PPP AR of combined satellite system also needs to be investigated.