PPP Systems

Fundamentals
Title	PPP Systems
Author(s)	GMV
Level	Basic
Year of Publication	2011

Precise point positioning (PPP) stands out as an optimal approach for providing global augmentation services using current and coming GNSS constellations. PPP requires fewer reference stations globally distributed rather than classic differential approaches (e.g. RTK), also one set of precise orbit and clock data is valid for all users everywhere, and the solution is largely unaffected by individual reference-station failures. There are always many reference stations observing the same satellite because the precise orbits and clocks are calculated from a global network of reference stations. As a result, PPP gives a highly redundant and robust position solution.

Several software products implementing a PPP processing strategy have been developed recently by government agencies, universities, industries and individuals. Some online PPP services are also available.

PPP Services

Precise Point Positioning (PPP) is a global precise positioning service, since it requires the availability of precise reference satellite orbit and clock products in real-time using a network of GNSS reference stations distributed worldwide.

• GAPS: The University of New Brunswick (UNB) developed the GPS Analysis and Positioning Software (GAPS). According to Leandro et. al. (2007) the algorithms used in GAPS follow more or less standard PPP approaches. GAPS is available as an online processing engine via the web page http://gaps.gge.unb.ca/ppp/. Static as well as kinematic processing is possible. They accept an observation file in the RINEX 2.10 or 2.11 formats. IGS product files necessary for processing the observations are automatically retrieved from one of the IGS global data centers.

Regional PPP

Blog magicGNSS Precise Point Positioning (PPP) is normally understood as a global positioning service, since precise satellite orbit and clock products used as input in PPP are best calculated using a network of GNSS reference stations distributed worldwide.

However orbit and clock corrections for PPP can also be provided over a world region in a similar way to WAAS or EGNOS corrections. It is even possible to provide a national PPP service over a single country, using national GNSS stations exclusively.

Satellite orbits and clocks calculated using regional stations do not have of course a high overall accuracy, but they do have a higher accuracy over the service area and, most importantly, orbit and clock errors largely cancel out over the service area. For a static or kinematic PPP user located inside the region, positioning accuracy using global or regional products is very similar.

In magicGNSS version 3.1 it is possible to evaluate the performance of regional PPP in a very simple way. Just process an ODTS scenario to calculate orbits and clocks covering the time period of your interest. On the Stations tab, select stations over your region only. Click on the station icons to select/deselect, you can use core stations and/or your own stations.

In regional ODTS it is better to deselect “Refine Station Coordinates” in Settings. Core stations have already precise coordinates, and for your own stations you are supposed to have processed them beforehand in PPP using the “Update My Station Coordinates” option. Try also to use a longer ODTS scenario duration (3 to 4 days), in order to maximize satellite visibility. It is also important to select a good reference clock in ODTS. The reference clock time should be close enough to UTC (or GPS Time), with an offset of the order of the microsecond or less. You can see the offset of a station clock by processing it in PPP.