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This paper deals with the Galileo 1 /GPS Tracking for GNSS stations. This study has been done under a European SpaceAgency contract: "Evolutionary Navigation Systems", for which EADS Astrium was prime. Francisco Amarillo Fernandez was the ESA project technical manager.To obtain a navigation solution of position (latitude, longitude, and altitude) and time (four unknowns), conventional satellite positioning techniques make use of simultaneous "one way range unambiguous" observables to all satellites in view. Four measurements are necessary to solve for the three unknown components of position (or velocity) and the unknown user clock (or frequency) bias.The pseudorange "one way range unambiguous" is the true distance between the satellite and the receiver plus an offset due to a miss-alignment between the transmitter's and the receiver's clocks, environmental propagations.In addition, the carrier phase "one way range ambiguous" observables are frequently processed in user professional applications to reduce the noise of the "one-way range unambiguous" observables. For example, the "CarrierSmoothing Method" is able to transform a set of "one-way range unambiguous" observables and another one of "one-way range ambiguous" observables into one single set of observables, which has all good properties of both observables and none of the bad. In order to have a maximum of satellites in view, the pseudorange is measured with a hemi-directional antenna. In this case,1 Galileo is a trademark of the European Commission and the space program Galileo is a joint initiative of the European Commission and the European Space Agency the pseudorange observables are affected by multipath and interference.To minimise the effects of multipath and interference, a new method "the Delta Tracking Method" is proposed. Instead of measuring the pseudoranges of all the satellites simultaneously which impose a hemi-directional antenna, the pseudoranges are measured sequentially using a directional antenna. Due to the much higher directivity of the antenna (while preserving the stability of the antenna phase response) the "sequential pseudorange" observables can be much less affected by multipath and interference.For a general user, a sequential "one-way range unambiguous" implies: Potentially different receiver positions Different satellite positions Different receiver clock errors Different satellite clock errors Different tropospheric errors Different ionospheric errorsThe "Delta Tracking Method" transforms a sequential "one-way range unambiguous" by means of "one-way range ambiguous" observables into a set of simultaneous "one way range unambiguous". 475978-1-4244-5037-4/10/$26.00

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