EGNOS SDK Development process - EGNOS Portal

EGNOS-SDK EnhancementsR&D Algorithms: Best Satellite ConstellationPurpose: Relate the quality of the GPS satellite geometry to the accuracy of positionobtained.Dilution of Precision (DOP) is the ratio of the standard deviation of errors in the leastsquaressolution to the standard deviation of the measurement errors.The idea of Geometric DOP is to state how errors in the measurement will affect the finalstate estimation. The DOP parameters are defined as geometry factors that relateparameters of the user position and time bias errors to those of the pseudorange errors.The Geometry Dilution of Precision (GDOP) can be defined as: GDOP = ∆OutputLocation∆MeasuredDataNeglecting ionospheric and tropospheric effects, the signal from GPS satellites has afixed precision. Therefore, the relative satellite-receiver geometry plays a major role indetermining the precision of estimated positions and times.The computations can be done using a selection of the satellites that provides the bestDOP. Therefore the aim is to choose the satellite set that minimizes the DOP.Multiplying the User Equivalent Range Error (UERE) – the root-sum-square of thevarious errors and biases involved - by the DOP produces the expected precision of theGPS position at 1-sigma (1-σ) level.June 2012 - EGNOS Software Development Kitpag. 24