Galileo Initiative for Local Technologies
Background & Objectives
Local elements or augmentations are used to enhance the performance delivered by global navigation satellite systems (GNSS). Such enhancements include improved position accuracy, the verification of accuracy, interference detection, and improved signal coverage in difficult environments. Although described as local for historical reasons, these enhancements may cover geographical areas ranging from a single building up to the size of a continent. All users will see significantly improved satellite navigation performance with the new Galileo signals, especially when used in combination with GPS. Nevertheless, local elements will continue to be needed to provide yet higher levels of performance. Although the need for some local element functions is reduced or eliminated, new applications are emerging where local elements will be as important as ever. These new areas include safety critical transport applications, location-based services, accuracy optimisation for precision surveys, and tool positioning in agriculture, construction, and other segments.
The GILT project aimed to develop key parts of a technological base for Galileo-based local elements (augmentations). GILT focused on Galileo-specific technical opportunities for local integrity, tropospheric error correction, location-based services (LBS), pseudolites and interference.
The technological base was implemented using a “building block” approach that focussed on the innovative technical opportunities created by Galileo in seven application areas. The seven application areas are:
- Integrity solutions for local areas - High Integrity Spot Coverage (HISC) to serve aviation and other applications;
- Integrity solutions for regions - High Integrity Area Coverage (HIAC) to serve rail and road applications and potentially other land based activities;
- Integrity solutions for coastal regions - Medium Integrity (MI) to serve maritime and other applications;
- Troposphere corrections for accuracy optimisation;
- Location-based services (LBS);
- Pseudolites for improved availability in locations with poor satellite visibility;
- RF interference detection for signals that represent a threat to the performance of GNSS services.
The objective of the GILT project was to develop key parts of a technological base for Galileo-based local elements in advance of the implementation of local infrastructures. The project focused on Galileo-specific high performance features. GILT also aimed to prepare an overall planning framework for the introduction of Galileo-based local services, including prioritisation and interactions with external drivers (GPS modernisation etc.).
Work performed & results
The building blocks were tested by analysis or by simulation (in advance of the Galileo SIS), using tools that were available within the GILT team. For HISC, different approaches for raw data processing were investigated and service volume simulations were used to analyse the availability of the different performance levels for several frequency combinations of Galileo/GPS satellites. By using these signals, greater accuracy and advanced integrity determination will be achieved more efficiently. The feasibility of the HIAC architecture was tested using simulations. Integrity risk values were achieved, approaching those for safety critical applications. Methods for achieving further reductions in alert limits were proposed. Updates to the RTCM 3.0 standard were proposed for the broadcast of correction parameters. MI results included an architecture tested by simulation to (1) allow use of separate satellite constellations or a combined Galileo and GPS satellite constellation to be selected by the user of local element data, (2) use of Internet protocols to achieve a scalable infrastructure, and (3) provision of a solution where the performance trade-offs (accuracy/integrity) are user selected. Tropospheric corrections were prototyped and it was shown that the solution could provide a global accuracy of better than 2 cm residual RMS zenith delay error, which is a significantly improvement over a priori models using a "standard atmosphere", such as the EGNOS model. A protocol was defined for disseminating corrections. For LBS, techniques were demonstrated for reducing the volume of assistance data to be passed through mobile networks. Several techniques were used including computing long term ephemeris and broadcasting new navigation data. Time transfer accuracy of +/- 1ms was demonstrated and also a 50% reduction in time-to-fix. Pseudolite ranging, channel sounding, and truth recordings were gathered in some typical city centre environments. Analysis showed how the wide bandwidth signals to be employed by Galileo will provide improved pseudolite ranging. It was confirmed that reliable pseudolite pseudo-ranging is a practical proposition in these environments. Interference detection techniques and algorithms were defined and evaluated for the continuous and pulsed signals that pose a threat to user receivers and augmentations. These algorithms were tested using simulation.