Galileo ionospheric correction algorithm: an optimization study of NeQuick-G

At present most low-cost GNSS receivers operate one frequency in the L band. For themone of the largest error contributions is the delay of radio signals in the Ionosphere. NeQuick-Gisthe official ionospheric correction algorithm (ICA), which has been adopted for Galileo, the EuropeanGNSS Programme. The NeQuick-G implementation is complex when compared with other ICAs. Itis also demanding in terms of computational resources. The Joint Research Centre completed areference implementation of NeQuick-G based on the official document“Ionospheric CorrectionAlgorithm for Galileo Single Frequency Users”provided by the European Global Navigation SatelliteSystems Agency. The rationale behind the JRC implementation of NeQuick-G was the intent to write anindependent source code from scratch, without using the pseudo-codes from the reference documentand solely relying on the physics descriptions. Using such implementation as baseline, this paperdescribes an optimization attempt of the official pseudo-code from an algorithmic perspective. Theobjective was to reduce the computational load while not sacrificing the performance. The newproposed integration method is able to speed up calculations to 21% and 49% with respect the twoofficial integration algorithms. The overall computational burden depends on the number of operations,which is eventually closely correlated to the number of calls of the ionospheric model. This underlinesthe quest tofind an integration method reducing this number of calls. Moreover, based on thefindings of this study, the authors strongly recommend revisiting the convergence control of theintegration routines introduced in (European Commission, 2016, https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_Ionospheric_Model.pdf).Peer Reviewe