GPS World, March 2016

10 0 10 0 10 0 10 Up generation of the PPP AR products the user can instantly switch streams to a different provider We looked at the PPP AR products provided by three organizations and examined position solutions for a set of stations in the SOPAC network with respect to convergence time to the pre defined threshold and position stability Using the decoupled clock products we found that the fixed solutions performed as expected After a few minutes a solution attains the correct ambiguity candidate and a fixed state is maintained Unlike the fixed solutions using the decoupled clock products instantaneous convergence was not attained in the horizontal and vertical components when the transformed IRC and FCB products were used The ambiguity resolved solutions were sensitive to changes in the satellite geometry As the number of satellites change the fixed ambiguities change causing datum shifts in the user solution The unstable solutions from both transformed products are attributed to the magnitude of the relative satellite code and widelane clock errors Additional refinement of the transformation model is required as the satellite hardware delay has not been completely mitigated Mismodeling of the hardware delay was absorbed by the ambiguity terms causing incorrect fixed solutions FUTURE RESEARCH Future prospective research includes refinement of the proposed transformation models to include the mismodeled effects thus providing the user with a more reliable solution The functional model needs to be further examined to ensure that the corrections were applied consistently Further analysis 56 GPS WORLD WWW GPSWORLD COM MARCH 2016 a b Sun of the instability of the user solution is required as solution jumps typically occur when there are changes in the number of satellites tracked Also to be analyzed are the post fit residuals to examine the effects of mismodeling The temporal and spatial behavior of the estimated terms will be examined for the different products used to understand the unmodeled effects that introduce incorrect solution fixes We would also consider increasing the number of reference stations to further test the reliability of the transformed products under varying user conditions ACKNOWLEDGMENTS We acknowledge Paul Collins Jianghui Geng and Denis Laurichesse for our valuable discussions and their suggestions The research was funded by the Natural Sciences and Engineering Research Council of Canada The results we have presented were derived from data and products provided by Natural Resources Canada Scripps Institution of Oceanography Centre National dEtudes Spatiales and the International GNSS Service This article is based on the paper Examining the Interoperability of PPP AR Products presented at ION GNSS 2015 the 28th International Technical Meeting of The Satellite Division of the Institute of Navigation held in Tampa Fla Sept 14 18 2015 GARRETT SEEPERSAD is a Ph D candidate at York University Toronto Canada in the Department of Earth and Space Science and Engineering He completed his B Sc in geomatics at the University of the West Indies and his M Sc in geomatics engineering at York University His area of research currently focuses on the development and testing of PPP functional stochastic and error mitigation models SUNIL BISNATH is an associate professor in the Department of Earth and Space Science and Engineering at York University His research interests include geodesy and precise GNSS positioning and navigation 0 05 10 15 20 25 30 10 Northing 0 05 10 15 20 25 30 10 Easting 0 05 10 15 20 25 30 Time hours Position error centimeters Float Fixed Y IGS Z IGS X IGS Z Y X Sun FIGURE 8 Position errors for site BRAN located in Burbank Calif for day of year 30 of 2015 illustrating the difference between the float and fixed solutions using the FCB products FIGURE 9 Orientation of the spacecraft body frame for GPS Block IIR IIR M satellites as a adopted within the International GNSS Service axis convention and b those provided in the manufacturer specifications MORE ONLINE Further Reading For references related to this article go to gpsworld com and click on More in the navigation bar then on Innovation