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An Improved Between-Satellite Single-Difference Precise Point Positioning Model for Combined GPS/Galileo Observations

  • Akram Afifi EMAIL logo and Ahmed El-Rabbany


This article introduces a new model for precise point positioning (PPP), which combines dual-frequency GPS and Galileo observations. Our model is based on the between-satellite single-difference (BSSD) linear combination, which cancels out some receiver-related biases, including receiver clock error and non-zero initial phase bias of the receiver’s oscillator. Two different scenarios are considered when forming BSSD linear combinations. In the first scenario, either a GPS or a Galileo satellite is selected as a reference for both GPS and Galileo observables. The second scenario, on the other hand, selects two reference satellites: a GPS reference satellite for the GPS observables and a Galileo satellite for the Galileo observables. Natural Resources Canada’s GPSPace PPP software is modified to enable a combined GPS/Galileo PPP solution and to handle the newly introduced biases. A total of 12 data sets representing two-day GPS/Galileo measurements at six IGS stations are processed to verify the developed PPP model. Precise satellite orbit and clock products from the IGS-MGEX network are used to correct both of the GPS and Galileo measurements. It is shown that using one reference satellite to form the BSSD linear combinations improves the precision of the estimated parameters by about 25 % compared with the GPS-only PPP solution. When two reference satellites are used, however, the precision of the estimated parameters improves by about 50 % compared with the GPS-only PPP solution. Additionally, the solution convergence time is reduced to 10 min for both BSSD scenarios, which represents about 50 % improvement in comparison with the GPS-only PPP solution.


This research was partially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Government of Ontario and Ryerson University. The GNSS data and the satellite precise products used in our analysis are downloaded from the International GNSS service (IGS) website.


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Received: 2014-12-24
Accepted: 2015-4-27
Published Online: 2015-5-1
Published in Print: 2015-6-1

© 2015 Walter de Gruyter GmbH, Berlin/Boston

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