2011 International Technical Meeting
Session B2: Urban and Indoor Navigation Technology 1

Title: An Efficient Precise Point Positioning Model for Near Real-Time Applications
Author(s): M. Elsobeiey & A. El-Rabbany, Ryerson University, Canada
Date/Time: Tuesday, January 29, 2013, 9:05 a.m.

Recent developments in GPS positioning show that a user with a standalone GPS receiver can obtain positioning accuracy comparable to that of carrier-phase-based differential positioning. Such a technique is commonly known as precise point positioning (PPP). A significant challenge of PPP, however, is that it typically requires a minimum of 30 minutes to achieve centimeter- to decimeter-level accuracy. This relatively long convergence time is the result of un-modeled GPS residual errors. This paper addresses error mitigation techniques to achieve near real-time PPP at sub-decimeter-level accuracy.In this research, we developed between-satellite single-difference PPP algorithms to cancel out the receiver clock error, receiver initial phase bias, and receiver hardware delay. The decoupled clock corrections, provided by Natural Resources Canada (NRCan), were also applied to account for satellite hardware delay and satellite initial phase bias.To test the developed models, GPS data collected from several IGS stations were processed using different processing models, namely, un-differenced model, un-differenced decoupled clock model, between-satellite single-difference (BSSD) model, and between-satellite single-difference using the decoupled clock (BSSD-DC) model. The input data were the first-order ionosphere-free linear combination of code and carrier phase. IGS precise orbit was used in all cases. IGS precise clock corrections were applied to the un-differenced and BSSD models. However, decoupled clock corrections, obtained from NRCan, were applied to the Un-differenced-DC and BSSD-DC models to correct for code and carrier-phase satellite clock error. Tropospheric corrections were accounted for using the global numerical weather model developed by the European Centre for Medium-Range Weather Forecasts ECMWF. ECMWF Vienna mapping function 1 was used for mapping the zenith tropospheric delays (wet and dry) to each satellite-specific elevation angle. All remaining errors, including carrier-phase windup, relativity, sagnac, Earth tides, and ocean loading are accounted for with sufficient accuracy using existing models.The results showed that the improvement obtained through the implementation of the decoupled clock correction in the BSSD model is only about 10%, which reflects the stability of the satellite hardware delays in comparison with that of the receiver hardware delays. The same conclusion can be drawn when comparing the un-differenced model with the BSSD model. In addition, it was found that between-satellite single-difference using the decoupled clock corrections improves the standard deviation of the estimated coordinates by more than 60% and improves the convergence time of the estimated coordinates by about 50%.

Previous Abstract Return to Session B2 Next Abstract