Improving Fixed-ambiguity Precise Point Positioning (PPP) Convergence Time and Accuracy by using GLONASS

Altti Jokinen, Shaojun Feng, Wolfgang Schuster, Washington Ochieng, Chris Hide, Terry Moore, Chris Hill, Carl Milner

Abstract:	The resolution of GPS carrier-phase ambiguities when carrying out Precise Point Positioning (PPP) has been a major research challenge in recent years. There are two main fixed-ambiguity PPP methods: Fractional Cycle Bias (FCB) estimation and Integer-Recovery Clock (IRC). Both methods should in theory provide a similar level of performance. The main challenge when using these existing fixed-ambiguity PPP methods is the long time period (up to 60 minutes) required to obtain the ambiguity fixed PPP solution. For a wide range of applications e.g. land surveying, this long convergence period is not acceptable. It has been shown that using GLONASS with GPS could facilitate accurate float PPP solution with a lower convergence time compared to GPS alone. Therefore, it is interesting to explore if using GPS/GLONASS float solution could improve fixed-ambiguity PPP. To date, not much work has been done related to the effect of using both GPS and GLONASS when performing fixed-ambiguity PPP. In this paper, GPS ambiguities only are attempted to be fixed to integers and GLONASS ambiguities are kept as float values (i.e. the paper is investigating the impact of using GLONASS float solutions on ambiguity fixed GPS PPP). Imperial College’s minimum constellation method which is based on testing ambiguity fixing for all possible combinations of satellites, is used in this paper when attempting to fix ambiguities. The main aim is to reduce the time required to the initial ambiguity resolution and make ambiguity resolution possible in a larger number of scenarios. Ambiguity validation is carried out by using the ratio test and variable threshold computation driven by the required confidence level. Furthermore, integrity monitoring of the solution is carried out using the state of the art Carrier-phase Autonomous Integrity Monitoring (CRAIM). The results show that inclusion of GLONASS can reduce the time required to obtain an initial GPS ambiguity resolution, by at least, 10% compared to employing GPS alone. In addition, using both GPS and GLONASS can reduce the 3D and vertical position error at the initial ambiguity resolution epoch.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3708 - 3727
Cite this article:	Jokinen, Altti, Feng, Shaojun, Schuster, Wolfgang, Ochieng, Washington, Hide, Chris, Moore, Terry, Hill, Chris, Milner, Carl, "Improving Fixed-ambiguity Precise Point Positioning (PPP) Convergence Time and Accuracy by using GLONASS," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 3708-3727.
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