Performance of the NeQuick G Iono Model for Single-Frequency GNSS Timing Applications

GNSS timing is currently used worldwide in critical real-time systems that require precise synchronisation or time-stamping at geographically dispersed sites, such as wireless telephone stations, electrical power grids and financial services. For applications where multiple timing equipment needs to be deployed, it is desirable to use low-cost, single-frequency receivers. Together with calibration issues, the ionospheric delay is the major limiting factor for accurate timing in single-frequency setups. Increasing demands in cost-saving and accuracy will make the availability of precise single-frequency solutions more and more interesting. In this paper we analyse single-frequency timing accuracy using the Galileo NeQuick G model, as compared with the standard GPS Klobuchar model, and taking the dual-frequency iono-free solution as reference. The analysis is done by post-processing RINEX files from two calibrated GNSS receivers, one located at mid-latitude and the other one close to the equator. Unlike Klobuchar, NeQuick G is based on a rather complex mathematical algorithm. For offline applications in post-processing this is not an issue, but for a real-time implementation it might be necessary to evaluate the model not too frequently, in order to improve execution speed. NeQuick G efficiency is analysed from this point of view also.