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Session B5: Trends in Future Satellite Navigation Technology, System Design and Development

All-in-one High-Accuracy Service for Both PPP-AR and RTK Techniques
L. Martínez, L. Pinilla, A. Souto, E. Carbonell, A. Chamorro, G. Tobías, D. Calle, I. Rodríguez, GMV
Date/Time: Friday, Sep. 20, 10:40 a.m.

Everybody knows about the differences between the two main techniques that can be used as solution for precise user positioning: Precise Point Positioning (PPP) with Ambiguity Resolution (AR) or Real-Time Kinematic (RTK).
While both of them may achieve similar performances, there have always been several differences between these two solutions. While PPP-AR is an absolute positioning technique that uses global corrections to achieve a sub-decimeter level of accuracy, RTK needs for a base station with a well-known position, near to the rover station (user) in order to be able to have fast-convergence and sub-decimeter level accuracy. The larger the distance between base and rover stations is, the worse the positioning accuracy is. In the case of the PPP-AR, in order to improve the convergence time, either regional atmospheric corrections or multi-frequency phase biases are needed.
Thus, selecting the optimal user solution (either PPP-AR or RTK), considering the needs of the final application, is a must. This decision is not only linked to the user algorithm, but also on the nature of high-accuracy solution pursued. A high-accuracy correction generator is needed to provide a PPP-AR service, while a dense stations network in the service area is needed for a RTK solution.
If we talk about Real-Time processing, PPP-AR makes use of State-Space Representation (SSR) corrections, while RTK makes use of Observation Space Representation (OSR) corrections. Those two formats are defined in Radio Technical Commission for Maritime Services (RTCM) standard. Being that RTK is more common than PPP-AR in receivers COTS (Commercial off-the-shelf), the possibility of offering both SSR and OSR services seems to be the optimal one.
And with this, how about the possibility of having both PPP-AR and RTK services all-in-one? Within GMV GSharp® (Safe High-Accuracy Reliable Positioning Solution), both PPP-AR and RTK user algorithms can be used using different services from the same solution, since both SSR and OSR corrections can be provided.
This is possible thanks to the conversion of the SSR corrections to OSR ones. It is logical that if GNSS observables are used to compute SSR corrections, the other way around should also work, having as input the SSR corrections and computing the GNSS observables for what it is called a Virtual Reference Station (VRS).
With this possibility, having a high-accuracy service where the different GNSS products (satellites orbits, clocks, phase and code biases, together with the atmospheric delays) are computed, is enough to compute both SSR corrections and OSR corrections. This solution opens the possibility of having a grid of Virtual Reference Stations for RTK purposes, reducing the impact of what has always been the big disadvantage of the RTK solution: the highly dense base stations network needed. The service provision to the user is simplified by the fact of having an equally spaced grid of stations, what simplifies the selection of the station to be used as base station in RTK algorithm. And last but not least, the conversion from SSR to OSR opens the door to provide a high-accuracy service, based on SSR corrections, to the users that are forced to use RTK algorithm because of the legacy users’ equipment.
Since the VRS generation through the SSR to OSR conversion is already a reality, performances achievable in different service areas can be shown, being able to know not only that both services can be provided all-in-one, but also the performances achievable when using both PPP-AR and RTK solutions using the same High-Accuracy service provider.



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