Good performance, less computation: A new ionospheric model for the Galileo Open Service

A new ionospheric model (NTCM G), which can be used to correct single-frequency Galileo signals for ionospheric delay, is now available on the European GNSS Service Centre (GSC) website.

The model provides good performance to single-frequency Galileo users, whilst requiring less computing resources than the reference Nequick G model. It does not replace Nequick G, but offers an alternative for certain use cases where computational load is a driver.

The NTCM G model was developed by the German Aerospace Centre (DLR) and validated by the Joint Research Centre (JRC) of the European Commission, with the support of the European Space Agency (ESA). The description of the source code and its implementation were carried out jointly between DLR and JRC, with the European Union Agency for the Space Programme (EUSPA) supporting the review and the publication of the model description.

Radio signals used in GNSS applications have to pass through the ionosphere on their way to Earth. When propagating through this medium, their speed (and to a lesser extent, their direction) may be altered through refraction and diffraction, inducing position errors at user level. This propagation delay can be compensated for by dual-frequency receivers, but single-frequency users need to apply a correction model in order to get an accurate fix. The Nequick G code was published in 2014 in order to offer single-frequency Galileo users a solution for precisely estimating and correcting the ionospheric delay. However, this model is computationally intensive and may constitute a challenge for receivers used in some applications.

In this context, the German Aerospace Centre (DLR) developed the Neustrelitz Total Electron Content Model for Galileo (NTCM G), an empirical model that provides a practical and cost-effective solution for the determination of the global ionosphere total electron content. A complete definition of the model is explained in the published document.

This new algorithm provides an alternative to the reference Nequick G algorithm, not a replacement. It could be valuable for applications in which computational resources are limited (e.g. the initialisation of PPP algorithms to improve convergence or in IoT or embedded applications).

 

[Figure 1: The NTCM-G iono model description document]
 

NTCM G source code available in several programming languages

The implementation of the NTCM G algorithm in various programming languages (Matlab, Simulink, and C/C++) was carried out collaboratively by DLR and JRC.  The source code of the algorithm is available on the European GNSS Service Center (GSC) website.

The Galileo programme is publishing this algorithm in order to support receiver manufacturers and downstream market players who use Galileo in their applications.

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