Fixed Ambiguity Precise Point Positioning (PPP) with FDE RAIM

A. Jokinen, S. Feng, C. Milner, W. Ochieng, C. Milner, W. Schuster, C. Hide, T. Moore, C. Hill

Abstract:	Precise Point Positioning (PPP) has been one of the major research interests in the Global Navigation Satellite System (GNSS) research field in recent years. PPP is a promising method because it can provide centimeter level positioning accuracy by using only one GNSS receiver, without using local reference networks. It is clear that this can provide cost savings compared to the traditional Real Time Kinematic (RTK) method, particularly if high accuracy positioning is required in remote areas. The primary reasons why PPP is not currently widely used are: the long time period required to obtain a highly accurate (ambiguity fixed) initial position solution (i.e. convergence time) and a lack of integrity monitoring for mission critical applications. These issues are discussed in this paper. To reduce convergence time and improve accuracy, carrier-phase ambiguity resolution is attempted in this paper. Wide-lane ambiguities are first fixed to integers based on float values estimated by the Melbourne-Wubbena combination. Thereafter, narrow-lane ambiguity resolution is done by employing the LAMBDA method and validation using a confidence level based ratio test. There are no narrow-lane FCB errors because integer satellite clock corrections provided by French Space Agency (CNES) are used. Finally, the fixed ionosphere-free ambiguities are calculated based on the fixed wide-lane and narrow-lane ambiguities, and used to estimate the user antenna position. To monitor the integrity of PPP, the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring (ICRAIM) is used. Three separate test statistics are applied, one for all measurements, one for carrier-phase measurements and one for code-phase measurements. Horizontal and vertical protection levels are also calculated by using ICRAIM. Data recorded by the International GNSS Service (IGS) stations are used. For example, step or ramp type errors are added to the data to test integrity monitoring. In addition, multiple failure detection and exclusion is tested. The test results show that with most stations it is possible to obtain an initial ambiguity fixed position solution on average between 2000 and 4000s after stating the GNSS receiver. On integrity, it is shown that the ICRAIM method is capable of detecting and excluding significant errors.
Published in:	Proceedings of IEEE/ION PLANS 2012 April 24 - 26, 2012 Myrtle Beach Marriott Resort & Spa Myrtle Beach, South Carolina
Pages:	643 - 658
Cite this article:	Jokinen, A., Feng, S., Milner, C., Ochieng, W., Milner, C., Schuster, W., Hide, C., Moore, T., Hill, C., "Fixed Ambiguity Precise Point Positioning (PPP) with FDE RAIM," Proceedings of IEEE/ION PLANS 2012, Myrtle Beach, South Carolina , April 2012, pp. 643-658. https://doi.org/10.1109/PLANS.2012.6236939
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