Scientific Service Support based on GALILEO E5 Receivers
Background & Objectives
The scientific community has been actively and intensively making use of GPS since the very start of GNSS. GPS has undoubtedly revolutionised certain aspects, such as surveying techniques, and has enabled scientists to realise applications which had not been feasible before. The current paradigm in the scientific community, however, is that accurate results essentially require two-frequency receivers with a preferred use of carrier phase measurements for precise positioning applications. This way of thinking is primarily motivated by the fact that ionospheric delays can be eliminated by using at least two or more frequencies, and carrier phase measurements are less corrupted by multipath effects than range measurements.
However, Galileo will offer one dedicated signal that is superior to all other signals which will be available in space: the broadband signal E5. This signal will feature an ultimately low-range noise in the centimetre range, as well as the lowest multipath error impact ever observed in the history of satellite navigation, which can be as low as a couple of centimetres in benign environments (and smaller by far than the multipath errors on every signal in all other environments, too).
Phase 1: The definition of requirements will be accomplished with the help of scientists representing potential user groups from the areas of positioning and position change, LEO orbit determination, and ionosphere and troposphere monitoring.
Phase 2 will be devoted to the adaptation of the E5 receiver module. The software design of the SX5 application will be developed as a parallel process.
Phase 3 features the implementation of this application software and is followed by prototype testing, validation and performance analysis.
Finally, the results will be disseminated and user demonstrations will be carried out.
The SX5 prototype will be based on existing receiver developments in order to benefit from previous activities. Several technology approaches are available, namely FPGA-based and SW-defined receivers. A trade-off will be made regarding the technology best suiting SX5 needs.
A central effort of this project is devoted to the development of the SX5 application prototype delivering specified functionality to the scientific user community based on the analysis of the corresponding requirements. This work will be based on a scientific software package, which has been available for research purposes for many years, although substantial work is required within this project, for example with respect to the development of improved and specific E5 algorithms.
The drastically increased range precision of the Galileo E5 signal will allow for combined ‘code-and-carrier positioning’ with high accuracy – but only a single-frequency Galileo receiver will be needed in future rather than a (more expensive) multi-frequency device. Carrier phase and range measurements will almost become equitable types of observables in terms of accuracy (up to now, range measurements are very much of inferior quality when compared to the carrier phases). As for a dual-frequency GPS-receiver, such a single-frequency system will be able to eliminate the ionospheric propagation error.
The central objective of SX5 will be to develop a software application for precise positioning based on an E5 Galileo receiver primarily targeting scientific users. Consequently, a full exploitation of the Galileo E5 signal allowing the realisation of applications, which previously required dual-frequency receivers, can be achieved. Moreover, this project is intended to lead the way to full flexibility and receiver access for the scientific community, providing a basis for meeting the individual requirements of the various scientific applications by tailored configuration and access to receiver internals.
Work performed & results
The expected results are:
- The feasibility assessment of joint code-plus-carrier E5 positioning and data analysis versus conventional and established methods will provide a realistic view on the capabilities of this single-frequency approach. Whilst the SX5 approach is expected to be interesting for double-difference LEO orbit determination, it could be critical with respect to tropospheric water vapour estimation. Complementary to this, the use of tropospheric delay corrections from numerical weather models can be beneficial for precise positioning.
- The implementation of SX5 prototype software will be another important outcome of this project. It covers a selection of the applications (SX5 eScience) in a geospatial context including an assessment of the use of near real-time data processing using scientific networks.
- The tailored E5 receiver module will provide the full configuration flexibility of a receiver to scientists (SX5 eXpert) and could be part of further developments targeting at commercialisation.
SX5 will almost exclusively employ the Galileo E5 signal and has the potential to strengthen European GNSS industry competitiveness by having a significant advantage in adopting this new technology, which is superior to single-frequency GPS. Space weather monitoring (ionosphere) will benefit from the fact that the E5 single-frequency approach is ‘calibration-free’.