View source for Wide Area RTK (WARTK)

{{Article Infobox2
|Category=Fundamentals
|Authors=GMV
|Level=Basic
|YearOfPublication=2011
|Logo=GMV
|Title={{PAGENAME}}
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In [[Real Time Kinematics|Real Time Kinematics (RTK)]], the compensation of the ionospheric delay between the base station and each of the roving users works for baselines up to 10-20 kilometers. When using a network of base stations, [[RTK Systems|Network RTK]] (NRTK), to mitigate atmospheric dependent effects over distance, the allowed distance between baselines and rovers increases up to 50-70 kms. In the late 1990s, the '''Wide Area RTK''' concept was introduced by the [http://www.gage.es/ Research Group of Astronomy and Geomatics (gAGE)] from the Technical University of Catalonia (UPC) to address these problems.

==Wide-Area Real-Time Kinematics (WARTK)==

During the last few years, the group [http://www.gage.es/ gAGE/UPC] has developed the so-called Wide-Area Real-Time Kinematics (WARTK) technique, which allows the extension of local services based on the real-time carrier phase ambiguity resolution to wide-area scale (i.e. baselines between the rover and reference stations greater than 100 km), for both dual-frequency (only GPS) and 3-frequency systems (also with Galileo and modernized GPS). The Wide-Area Real-Time Kinematics (WARTK) technique for dual and 3-frequency systems are based on an optimal combination of accurate ionospheric and geodetic models in a permanent reference stations network. The main factor limiting the range extension of the RTK technique beyond a few tens of kilometers is the differential ionospheric correction between the roving and the nearest reference GNSS station. Such ionospheric correction prevents the real-time ambiguity fixing, and therefore the corresponding accurate navigation at sub-decimeter level. The ionosphere produces ambiguity biases and correlations whose mitigation becomes the main problem to sort out. Even with the aid of multi-reference-station techniques, due to the baseline limitation (<20 km), several thousands would be required to cover such a service to the whole European region, obviously unaffordable from a logistic and economic point of view.

The main techniques supporting WARTK are related to an accurate real-time computation of ionospheric corrections, combined with an optimal processing of GNSS observables (carrier phases in particular) in both 2 and 3-frequency systems. The method increases the RTK/NRTK service area, with permanent stations separated by up to 500–900 kilometers — all while requiring 100 to 1,000 times fewer receivers covering a given region.<ref> Hernández-Pajares et al, ''Feasibility Study of a European Wide Area Real Time Kinematic System,'' invited talk in 4th ESA Workshop on Satellite Navigation User Equipment Technologies (Navitec), ESTEC, Noordwijk, The Netherlands, December 2008</ref><ref>[http://www.gsa.europa.eu/index.cfm?objectid=42B6F1B2-A906-2D88-C40D0B75612EDD2D WARTK-EGAL Project]</ref>

Although its feasibility has been demonstrated with real data, no WARTK operational system has been deployed so far.

==WARTK Related Articles==

The following articles include further information about different important topics related to a WARTK:

* [[WARTK Fundamentals|WARTK Fundamentals]] introduces the recently-developed WARTK technique.

* The [[WARTK Standards|WARTK Standards]] article summarizes some conventions, models and formats commonly used by WARTK. 

* [[WARTK Systems|WARTK Systems]] sections provide an overview of the potential WARTK systems and applications.

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[[Category:Fundamentals]]