Many of today’s applications for satellite navigation systems demand positioning accuracies barely considered possible a few years ago. Systems offering real-time, worldwide, decimetre-level positioning are now possible.
This level of performance cannot be achieved using GNSS alone. Nor is it economic to achieve global coverage with this accuracy using standard differential GNSS techniques as the number of reference stations will be inhibiting.
The approach to this problem is to remove the spatial dependence by separating the error components for each satellite so that they can be applied as corrections anywhere. The question of estimating corrections to the broadcast satellite orbit and clock parameters is not an easy one.
Under the European Geostationary Navigation Overlay Service (EGNOS) programme, we were responsible for:
The definition of algorithms to synchronise a network of reference stations and to estimate satellite clock corrections.
The definition of a model to estimate the ionospheric delay over a region.
With the support of British National Space Centre (BNSC), we have developed this capability further to include the estimation of precise satellite orbits. The very latest advances in geodesy and satellite orbitography have been utilised to ensure optimum performance is achieved.
We have developed a suite of experimental software capable of estimating high-precision GNSS orbit and clock corrections in real-time. The software can be used either to estimate a high-precision navigation message (as in a GNSS Ground Segment) or to estimate high-accuracy corrections to the broadcast navigation messages (as required for a global augmentation system). Under the continued support of BNSC, we are continuing to extend the capability of this software and to improve its performance.