An ionosphere broadcast model for next generation GNSS

Abstract

The ionosphere is a significant error source of the Global Navigation Satellite Systems (GNSS) error budget. Ionosphere induced range errors vary from a few to tens of meters at the zenith. Since the ionosphere is a dispersive medium, the most part of the ionospheric delay can be eliminated through linear combination of dual-frequency observables. However, single frequency operations require additional ionospheric information for the signal delay or range error corrections. To aid single frequency operations the Global Positioning System (GPS) broadcasts 8 coefficients in the navigation message to drive the Ionospheric Correction Algorithm (ICA). Similarly, for ionospheric correction the global navigation satellite system Galileo transmits 3 correction coefficients as driver parameters of the electron density NeQuick model. The GLONASS satellite navigation system does not broadcast ionospheric correction parameters and therefore a standalone GLONASS single frequency band receiver cannot correct the ionospheric delay. However, if the receiver includes a GPS/Galileo receiving unit, the ionospheric delay of the GLONASS signal can be corrected using broadcasted ionospheric parameters. In the present work, we present an ionospheric correction algorithm called Neustrelitz TEC broadcast model NTCM-BC which can be used as an alternative to the GPS-ICA or Galileo-NeQuick. Like the GPS-ICA or Galileo-NeQuick, to drive the NTCM-BC, 9 ionospheric correction coefficients need to be uploaded to the satellite vehicles (SVs) for broadcasting via the navigation message.

Our investigation using worldwide ground GPS data from a quiet and a perturbed ionospheric and geomagnetic activity period of 17 days each shows that the 24 hour prediction performance of the NTCM-BC is better than the GPS-ICA in a global average. During quiet ionospheric condition, the mean and standard deviation of the 3D position errors are found to be about 40 and 20 cm less for the NTCM-BC compared to the GPS-ICA, whereas during perturbed condition the estimates are found about 70 and 35 cm less for the NTCM-BC.