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What is PPP ?

What is PPP ?

What is PPP ?

What is PPP ?

What is PPP ?

What is PPP ?

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PPP, “Precise Point Positioning”?

In the world of GNSS, ” PPP ” stands for Precise Point Positioning.

What are the characteristics of this positioning method? In which cases can we recommend this technology? What are its limitations and alternatives?

…In the world of GNSS, ” PPP ” stands for Precise Point Positioning. Developed in the 2000s, it defines a GNSS positioning method that involves precise correction of orbits and clocks

Thelocal augmentation system: LBAS

PPP technology uses raw data retrieved from a global terrestrial network of reference stations to calculate highly accurate orbito-synchro corrections.

These corrections are transmitted to a receiver or software to improve positioning or timing accuracy. The PPP service can provide worldwide coverage, but is less accurate than NRTK.

Global corrections

The PPP consists of calculating global corrections to the raw GNSS signals, without resorting to the principle of the differential effect with another nearby station.

This method requires in-depth knowledge of all the parameters that affect the measurements (clocks, orbits, altitude of each satellite, propagation in the atmosphere, earth tides, etc.). A whole range of corrections is therefore available, in particular:

clock corrections
orbit corrections,
satellite electronic biases on code and phase (the latter being necessary to fix ambiguities).

In addition, there are public real-time PPP services that can be used for research and testing purposes, available via the IGS website: http: //www.igs.org/rts

PPP: Centimetric precision with global coverage

Finally, PPP is the only technology that can correct all GNSS-related errors with the utmost precision, providing a global service. It is therefore possible to position yourself centimetrically using PPP with a single real-time GNSS receiver.

The real advantage of PPP is that it is operational throughout the world. You don’t need to work close to a reference station, so you can cover the oceans, for example.

This is the case for TERIA, which in 2019 will enter into a partnership with France Brevet to exploit certain CNES ( Centre National des Études Spatiales) patents to set up a PPP-World service. Combined with the know-how of its experts and its network, this algorithm will extend the coverage of its services. TERIA will then be able to offer complementary solutions to its customers and partners wishing to work beyond the TERIA network coverage area using a PPP-only service.

Thanks to the different TERIAsat service levels, TERIA can offer a PPP-RTK service locally and a PPP-only service globally (already available since 2018)

To this end, work is being finalised to integrate new algorithms into the receiver market.

PPP limitations and recommended uses

However, PPP technology has a major drawback when used on its own. Currently, the atmospheric correction models used only converge on an accurate estimate after 20 to 30 minutes. This time corresponds to the initialisation time that users will have to wait before taking measurements if they want centimetric positioning.

Despite the centimetric accuracy and worldwide coverage, this long convergence time reduces its usefulness.

Today, 20 to 30 minutes of convergence time creates a waiting time that is far too long in areas of application that require real-time with a high level of responsiveness.

It should also be noted that this convergence time is repeated in the event of signal loss (masks, plant cover, tunnels, etc.). Under certain conditions it could be reduced, but it will remain significantly longer than convergence times in NRTK or PPP-RTK, where it is a few seconds, for example.

This precise positioning technology is therefore only used in very specific cases. This is particularly the case in geographical areas where it is not economically or technically possible to provide an RTK or NRTK service:

Isolated one-off projects

Arable farming areas

Maritime domains

Aerial applications

etc.

Precise Point Positioning alternatives and developments

PPP has a major limitation, but this can be overcome by combining other technologies.

TERIA has taken this step by capitalising on the best of both PPP and RTK techniques to deliver optimum results.

The PPP-RTK combination consists of transmitting PPP corrections and simultaneously broadcasting corrections based on tropospheric and ionospheric error modelling. These highly accurate corrections come from a dense network of GNSS stations (NRTK). This is the SSR concept(http://www.geopp.com/pdf/ion2005_fw.pdf )

As a result, it is possible to work with centimetre-level accuracy over the entire coverage area of atmospheric models, while maintaining a convergence time equivalent to NRTK ( Network Real Time Kinematic).

Compared with NRTK technology alone, this combination offers several advantages:

Errors are broken down by error item,
The service is global and locally enhanced,
Corrections depend on models and not on the nearest station(s)
The distribution of corrections does not depend on the position of the mobile,
The bandwidth required does not depend on the number of users

PPP-RTK is not yet standardised in terms of format; only the PPP part has its own RTCM messages.

TERIA has responded to this problem by creating the TERIAsat service, based on a proprietary format. This solution is based on existing RTCM messages and provides ionosphere and troposphere corrections via proprietary messages.

Current receivers are not compatible with RTCM messages for PPP. All commercial PPP solutions (such as Omnistar, Starfire, Atlas, etc.) work with proprietary formats.

The TERIAsat service offers European coverage with centimetre accuracy and a convergence time of around 10 seconds.
TERIAsat is compatible with and natively integrated into a number of devices, including :

SP60-Spectra
SP90m-Spectra
SP85-Spectra
and other brands to come ..

What’s more, it can be configured in all the equipment on the market via the new GNSS receiver: the TERIAsat Terminal or on-board the PYX or the TERIA DELTO .