Source: Development and Positioning Accuracy Assessment of Single-Frequency Precise Point Positioning Algorithms by Combining GPS Code-Pseudorange Measurements with Real-Time SSR Corrections
Miso Kim 1 and Kwan-Dong Park 2,*
1 PPSoln Inc., 606 Seobusaet-gil #A-2409, Seoul 08504, Korea; mskim@ppsoln.com
2 WCSL (World Class Smart Lab) of intelligent vehicle Inha research Lab, Department of Geoinformatic
Engineering, Inha University, 100 Inha-ro, Incheon 22212, Korea
* Correspondence: kdpark@inha.ac.kr; Tel.: +82-32-860-7604
Received: 2 May 2017; Accepted: 8 June 2017; Published: 9 June 2017
Dual-frequency receivers are usually involved in PPP to remove the
ionospheric delay effect. However, in the PPP-Real Time Kinematic (RTK) mode of PPP, one can get tropospheric and ionospheric delays generated from a GNSS network.
One of the most prominent PPP services is the IGS-RTS, which is managed by the International GNSS Service (IGS). RTS stands for real-time service, and thus, real-time streams of satellite orbits
and clock-offset corrections can be obtained through the IGS-RTS service
When such corrections are applied to broadcast navigation messages, the accuracies of three-dimensional orbits for static positioning reached accuracy of ~10 cm in the horizontal direction compared to RTK when integer ambiguities are estimated as float numbers. For a mobile platform, the absolute accuracy was within the range of 20 to 30 cm.
For four days’ worth of data, the horizontal and vertical accuracies were in the range of 0.8–1.6 m and 1.6–2.2 m, respectively. When the same data were processed using Differential GPS (DGPS) positioning
mode, PPP outperformed DGPS by 20–70%.
In this paper, the authors developed PPP algorithms that consider real-time State Space Representation (SSR) corrections for GPS pseudorange processing. SSR corrections have been produced by Seoul Broadcasting System, who operates 20-site GNSS network and a GNSMART server.
Pseudorange measurements are the range or distance from the user antenna to each satellite, and are calculated based on the signal transmission time from the satellites to the user. Such observables,
however, contain clock offsets at both the satellite and the user receiver, and are thus not exactly “true” or “geometric” ranges. To make things worse, ionospheric and tropospheric delays, in addition to hardware effects and multipath, come into play
We have developed a suite of real-time precise point positioning programs to process GPS pseudorange observables, and validated their performance through static and kinematic positioning tests. To correct inaccurate broadcast orbits and clocks, and account for signal delays
occurring from the ionosphere and troposphere, we applied State Space Representation (SSR) error corrections provided by the Seoul Broadcasting System (SBS) in South Korea.
Site displacements due to solid earth tide loading are also considered for the purpose of improving the positioning accuracy, particularly in the height direction. When the developed algorithm was tested under static
positioning, Kalman-filtered solutions produced a root-mean-square error (RMSE) of 0.32 and 0.40 m in the horizontal and vertical directions, respectively. For the moving platform, the RMSE was found
to be 0.53 and 0.69 m in the horizontal and vertical directions