Study on Precise Point Positioning Based on Combined GPS and GLONASS

X. Li, X. Zhang, F. Guo

Abstract:	Mathematical models of GPS/GLONASS combined precise point positioning (Abbreviated as PPP) are introduced in this paper. GPS/GLONASS combined PPP models are developed based on the GPS-only PPP and numerical experiments are carried out to assess the performance of GPS/GLONASS combined PPP. The results show that: the positioning precision and convergence speed of GPS/GLONASS combined PPP are improved but not significantly compared with GPS-only PPP when the number of satellites reaches 8~9 or even more. Whereas, a few GLONASS satellites added to the combined PPP properly can improve the positioning results and convergence speed significantly when the number of satellites is less as only 4~5. Precise Point Positioning (Abbreviated as PPP) is a technique for absolute positioning. In this approach, the IGS precise orbit products and satellite clock products are adopted, all kinds of error sources are taken into account and corrected with precise models, and the un-differenced dual-frequency carrier phase observations of a standalone receiver are processed to compute the point position with high accuracy. Research on PPP is carried out widely and deeply by numerous experts in many universities and institutes home and abroad. Great achievement has been made in the aspect of algorithms,softwares, analysis of experiments results , practical applications and so on ( Kouba and Heroux, 2001[2]; Gao, 2001[3]; Shirong Ye, 2002[4]; Han Baoming, 2002[4]; Zhang 2005[6]; Hu Congwei, 2005[7]). Presently, PPP is mainly based on GPS single system and it can reach the precision level of mm~cm in static positioning and cm~dm in kinematic mode. With the restoration of GLONASS system of Russia, International GLONASS-Pilot Project began to operate at the beginning of new millennium, and GLONASS is added to IGS (International GNSS Services). At present, precise ephemeris of GLONASS satellites are provided by CODE(Center of Orbit Determination, Switzerland) , IAC(Information and Analytical navigation Center, Russia), BKG(Germany) and ESA/ESOC(European Space Operation Center, Germany). Simultaneously, precise satellite clock products are provided both by IAC and ESOC. Combination of multiple GNSS system has lots of advantages in many aspects such as continuity, reliability, precision and efficiency compared with any single system. GPS and GLONASS are two independent global satellite navigation positioning systems and their combination can improve the geometry significantly to assure full availability and improve the autonomous completeness and precision. Mathematical models of GPS/GLONASS combined PPP are introduced in this paper firstly, and then performance of single GPS PPP and GPS/GLONASS combined PPP are analyzed and compared with each other based on the practical cases.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	2449 - 2459
Cite this article:	Li, X., Zhang, X., Guo, F., "Study on Precise Point Positioning Based on Combined GPS and GLONASS," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2449-2459.
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