FIG Peer Review Journal


An Improved GPS-Based Precise Point Positioning Model (5569)

Mohamed Elsobeiey and Ahmed El-Rabbany (Canada)
Mr. Elsobeiey Mohamed
Ryerson University
8 Schmirler Terrace
Corresponding author Mr. Elsobeiey Mohamed (email: mohamed.elsobeiey[at], tel.: +1 647-708-5605)

[ abstract ] [ paper ] [ handouts ]

Published on the web 2012-02-02
Received 2011-11-03 / Accepted 2012-02-02
This paper is one of selection of papers published for the FIG Working Week 2012 in Rome, Italy and has undergone the FIG Peer Review Process.

FIG Working Week 2012
ISBN 97887-90907-98-3 ISSN 2307-4086


In this paper we introduce an improved Precise Point Positioning (PPP) model, which rigorously accounts for all GPS errors and biases. We use between-satellite single-difference (BSSD), which cancels out the receiver hardware delay, receiver clock error, and the non-zero initial phase of the receiver’s oscillator. The decoupled satellite clock corrections, which are provided by Natural Resources Canada (NRCan), are applied to account for the GPS satellite hardware delay bias between code and carrier-phase measurements as well as the satellite initial phase bias. Tropospheric delay is accounted for using the NOAA-based numerical weather prediction (NWP) tropospheric signal delay model (NOAATrop). The NOAATrop model was extensively tested and found superior to standard tropospheric models such as the Saastamoinen and Hopfield models. All remaining errors, including carrier-phase windup, relativity, sagnac, Earth tides, and ocean loading can be accounted for with sufficient accuracy using existing models. It is shown that the PPP solution convergence is improved by up to 50% when using our BSSD-based model in comparison with traditional undifferenced PPP model. This is considered significant and can lead to the development of high-accuracy real-time PPP.
Keywords: GNSS/GPS; Positioning; Engineering survey