Elsevier

Advances in Space Research

Volume 51, Issue 6, 15 March 2013, Pages 1008-1018
Advances in Space Research

The GFZ real-time GNSS precise positioning service system and its adaption for COMPASS

https://doi.org/10.1016/j.asr.2012.06.025Get rights and content

Abstract

Motivated by the IGS real-time Pilot Project, GFZ has been developing its own real-time precise positioning service for various applications. An operational system at GFZ is now broadcasting real-time orbits, clocks, global ionospheric model, uncalibrated phase delays and regional atmospheric corrections for standard PPP, PPP with ambiguity fixing, single-frequency PPP and regional augmented PPP. To avoid developing various algorithms for different applications, we proposed a uniform algorithm and implemented it into our real-time software. In the new processing scheme, we employed un-differenced raw observations with atmospheric delays as parameters, which are properly constrained by real-time derived global ionospheric model or regional atmospheric corrections and by the empirical characteristics of the atmospheric delay variation in time and space. The positioning performance in terms of convergence time and ambiguity fixing depends mainly on the quality of the received atmospheric information and the spatial and temporal constraints. The un-differenced raw observation model can not only integrate PPP and NRTK into a seamless positioning service, but also syncretize these two techniques into a unique model and algorithm. Furthermore, it is suitable for both dual-frequency and sing-frequency receivers. Based on the real-time data streams from IGS, EUREF and SAPOS reference networks, we can provide services of global precise point positioning (PPP) with 5–10 cm accuracy, PPP with ambiguity-fixing of 2–5 cm accuracy, PPP using single-frequency receiver with accuracy of better than 50 cm and PPP with regional augmentation for instantaneous ambiguity resolution of 1–3 cm accuracy. We adapted the system for current COMPASS to provide PPP service. COMPASS observations from a regional network of nine stations are used for precise orbit determination and clock estimation in simulated real-time mode, the orbit and clock products are applied for real-time precise point positioning. The simulated real-time PPP service confirms that real-time positioning services of accuracy at dm-level and even cm-level is achievable with COMPASS only.

Section snippets

Introduction and motivation

Precise point positioning (PPP) (Zumberge et al., 1997) can provide mm-cm positioning accuracy with single GNSS receiver. The global real-time precise positioning service based on PPP is proved being very promising because of its cost-efficiency, global coverage and its accuracy meeting the requirements of most applications (Agrotis et al., 2010, Bar-Sever et al., 2003, Bar-Sever, 2010; Dixon, 2006; Mireault et al., 2008, Ge et al., 2009, Melgard et al., 2009). In the global real-time PPP

Uniform positioning scheme

A uniform positioning scheme is introduced in this section to satisfy the requirements of various applications including standard PPP, PPP with ambiguity fixing, single-frequency PPP and regional augmented PPP. In the new algorithm, un-differenced raw observations are employed, the ionospheric and tropospheric delays are estimated as parameters with proper spatial and temporal constraints and real-time derived atmospheric model or atmospheric corrections as well. The positioning performance in

Real-time service system

The EPOS-RT software (server-part) is running at the GFZ IGS real-time data analysis centre for providing orbits, clocks, UPD (uncalibrated phase delay), GIM (global ionospheric map), RAC (regional augmentation correction) in real-time. Recently, new software module “iPPP” (client-part) in C/C++ was developed to implement the proposed uniform positioning algorithm. Now the system is running operationally to provide standard float PPP, ambiguity-fixed PPP, single-frequency PPP (SF-PPP) and

Positioning performance

We process the stream data of about 80 IGS stations in real-time for providing orbits and clocks at 5 s sampling interval. From the IGS real-time combination, the user range accuracy of the orbits and clocks is about 0.1 ns or 3 cm. UPDs are also determined in real-time using the same network. About 150 streams are employed for GIMs generation. Orbits, clocks, GIMs and UPDs are broadcasted through the same caster via INTERNET.

For assessing the performance of the proposed algorithm, about 60

Adaption for COMPASS

We have adapted the service system to accept the COMPASS data for this study. As the COMPASS signal is very similar to GPS and GALLIEO’s, the adaption is very straight forward. The only difference is recently there are only GEOs and IGSOs in the COMPASS system instead of MEOs. The tracking network for GEOs and IGSOs can only be a regional one and the observation geometry for precise orbit determination and as well as positioning are somehow different from current GPS and special attention might

Conclusions and outlooks

A global real-time precise positioning service system is operational running at the GFZ IGS real-time data analysis centre. Based on the real-time data streams from IGS, EUREF and SAPOS reference networks, various products are generated in real-time by EPOS-RT software and broadcasted to users by NTRIP. The system structure and data flow at both server side and client side are carefully illustrated. The real-time processing at the server-end includes precise orbit determination, clock

References (39)

  • H. Bock et al.

    GPS single-frequency orbit determination for low Earth orbiting satellites

    Adv. Space Res.

    (2009)
  • C. Shi et al.

    An improved approach to model ionospheric delays for single-frequency Precise Point Positioning

    J. Adv. Space Res.

    (2012)
  • Agrotis, L., San, P.A., Dow, J., Zandbergen, R., Svehla, D., Ballereau, A. ESOC’s RETINA system and the generation of...
  • Banville, S., Langley, R. Improving real-time kinematic PPP with instantaneous cycle-slip correction. in: Proceedings...
  • Bar-Sever, Y., Bell, B., Dorsey, A., Srinivasan, J. Space applications of the NASA global differential GPS system....
  • Bar-Sever, Y. Complete real-time GLONASS product line from the Global Differential GPS (GDGPS) system. Institude of...
  • J. Boehm et al.

    Global Mapping Function (GMF): A new empirical mapping function based on numerical weather model data

    Geophys. Res. Lett.

    (2006)
  • Chen, K., Gao, Y. Real-Time Precise Point Positioning Using Single Frequency Data. Long Beach, CA: 2005, pp. 1514–1523,...
  • Collins, P., Lahaye, F., Hérous, P., Bisnath, S. Precise point positioning with AR using the decoupled clock model. in:...
  • Dixon, K. StarFire: a global sbas for sub-decimeter precise point positioning. in: Proceedings of ION GNSS 2006, Sept....
  • D. Dong et al.

    Global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in California

    J. Geophys. Res.

    (1989)
  • Y. Feng

    GNSS three carrier ambiguity resolution using ionosphere-reduced virtual signals

    J. Geod.

    (2008)
  • Gabor, M.J., Nerem, R.S. GPS carrier phase AR using satellite-satellite single difference. in: Proceedings of 12th Int...
  • M. Ge et al.

    Resolution of GPS carrier-phase ambiguities in precise point positioning (PPP) with daily observations

    J. Geod.

    (2008)
  • Ge, M., Chen, J., Gendt, G. EPOS-RT: Software for real-time GNSS data processing, Geophysical research abstracts....
  • Ge, M., Dousa, J., Li, X., Ramatschi, M., Wickert, J. A novel real-time precise positioning service system: global...
  • Ge, M., Zhang, H., Jia, X., Song, S. What is achievable with the current COMPASS constellations? In: Proceedings of ION...
  • J. Geng et al.

    Rapid re-convergences to ambiguity-fixed solutions in precise point positioning

    J. Geod.

    (2010)
  • Han, S., Rizos, C., GPS network design and error mitigation for real-time continuous array monitoring system. in:...
  • Cited by (49)

    • Analysis of GNSS clock prediction performance with different interrupt intervals and application to real-time kinematic precise point positioning

      2020, Advances in Space Research
      Citation Excerpt :

      Hence, many existing prediction models fail. To solve the above problems, this study firstly uses 7-day GFZ (GeoForschungsZentrum) final clock products (Li et al., 2013) sampled at 30 s to analyze the characteristics of GNSS clocks. It is found that the clock offset is consistent with the linear regression model.

    • Performance assessment of multi-GNSS real-time PPP over Iran

      2017, Advances in Space Research
      Citation Excerpt :

      In this contribution, we are to investigate the positioning accuracy and convergence time of real-time PPP solutions over Iran, while the current BeiDou constellation is contributed to the GPS or combined GPS + GLONASS observations. The BeiDou navigation satellites system is a Chinese project with different constellations (X. Li et al., 2013; W. Li et al., 2013; Cai et al., 2014). The first constellation of BeiDou, namely BeiDou-1 and including three satellites, has been operational since 2000, with limited coverage and applications over China and the neighboring areas.

    • Integrity Monitoring for Real-time Orbit Corrections based on Prior Statistic Parameters

      2023, Proceedings of the International Technical Meeting of The Institute of Navigation, ITM
    View all citing articles on Scopus
    View full text