GNSS Offline Signal Quality Assessment

M. Soellner, C. Kurzhals, G. Hechenblaikner, M. Rapisarda, T. Burger, S. Erker, J. Furthner, U. Grunert, M. Meurer, S. Tholert

Abstract:	This paper deals with the offline measurement of instantaneous frequency transfer distortions and its impact to navigation performance. Distortions on the frequency transfer-characteristics are relevant for users mainly via reductions of usable signal power and due to biases which are difficult to be removed. For characterisation of distortion effects for real satellites and navigation receivers, several evaluation parameters are introduced, which are based on the offline processing of recorded base-band samples. Typical communication system related parameters are considered (like PSD, scatter-plot and eye-diagram) but also parameters which are derived from the correlation function shape and thus show directly the distortion-impact on navigation performance. The latter class of parameters comply correlation-loss, S-curve-bias, code-code-coherency and the frequency transfer characteristic itself. Accurate measurements of frequency transfer distortions require careful consideration of measurement distortions. This complies at least measurement noise, sampling constraints and as most critical the calibration/equalisation of the measurement frequency transfer characteristics. For measurements with the satellite in orbit addionally care needs to be taken on multipath and interference, whereas the ionospheric dispersion reveals to be more harmless. These topics are discussed and some quantitative assessment results are given. As coarse conclusion, the reliable characterisation of satellites in orbit requires the use of high-gain-antennas (>20m diameter). Corresponding measurement setups with BaySEF connected to the DLR measurement setup using the 30 m - Weilheim antenna of DLR GSOC in Weilheim/Lichtenau, and with the 25-m dish in Chilbolton are shown, which were used for example measurements on the GIOVE-B satellite. Example offline signal quality assessment results for the various parameters and for the different signal transmissions in L1 from the early GIOVE-B in orbit tests (with BOC(1,1), with CBOC and with TMBOC) are presented, with the intention to test the evaluation methods rather than to assess the satellite. The results demonstrate the absolute qualification of applied evalation methods and will animate curious people to further assessments and analysis. For instance this concerns the conclusions, that can be drawn from certain evaluation parameter distortions. Future improvements derived from this activity for signal quality assessment are related to small refinements on evaluation parameters and mainly on the full control over accurate measurement system characterisation and calibration
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	909 - 920
Cite this article:	Soellner, M., Kurzhals, C., Hechenblaikner, G., Rapisarda, M., Burger, T., Erker, S., Furthner, J., Grunert, U., Meurer, M., Tholert, S., "GNSS Offline Signal Quality Assessment," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 909-920.
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