Abstract
Mitigation of man-made radio frequency interference (RFI) is a problem of increasing importance for radio astronomy. Indeed, numerous terrestrial and satellite services of all kinds create lots of electromagnetic signals in a large part of the radio spectrum that are likely to disturb radio astronomical observations. Moreover, the advent of large, highly sensitive radio telescopes such as SKA, LOFAR, etc., will permit the observation of extremely faint and distant radio sources which exhibit large amounts of red shift, hence overlapping with unprotected bands in the radio spectrum. Among various possible causes of RFI, GNSSs have specific characteristics which can be handled appropriately to design efficient mitigation techniques. GNSS signals are generally well documented and the ephemerides of satellites are well known. Therefore, various partially or fully informed methods can be used, which exploit knowledge of the characteristics of the modulations. Adaptive cancellation techniques can also be used that use auxiliary observations coming from additional antennas. Besides, knowing the spatial direction of the disturbing source, spatial filtering and related techniques that can be implemented in antenna arrays are likely to mitigate RFI with minimum knowledge of the GNSS. After recalling some radio astronomy basics, the paper presents a few examples of RFI caused by satellite systems on radio-astronomical observations. Then, we give a brief overview of state-of-the-art RFI mitigation techniques for radio astronomy and we present in some details the principles and results pertaining to some methods that seem particularly appropriate to mitigate RFI arising from GNSS signals. The importance of cooperation between GNSS designers and astronomers is finally pointed out.
Résumé
La lutte contre les interférences radioélectriques (RFI) d’origine humaine est un problème d’importance croissante pour la radioastronomie. En effet, de nombreux services de télécommunication terrestres et par satellites produisent des signaux électromagnétiques dans une grande partie du spectre radio, qui peuvent perturber les observations radioastronomiques. De plus, l’avènement de grands radiotélescopes très sensibles comme le SKA, LOFAR, etc. permettra l’observation de sources très faibles et éloignées présentant un taux important de « red shift » et par conséquent situées dans des parties non protégées du spectre radio. Parmi les diverses sources de RFI, les systèmes globaux de navigation par satellites (GNSS) possèdent des caractéristiques spécifiques qui peuvent être prises en compte de façon appropriée dans la conception de techniques efficaces de lutte contre les interférences. Les caractéristiques des signaux GNSS ainsi que les éphémérides des satellites sont en général bien connues et accessibles. Par conséquent, des méthodes partiellement ou totalement informées, exploitant les caractéristiques connues des modulations, peuvent être utilisées. Des techniques d’annulation adaptative utilisant des observations fournies par des antennes auxiliaires peuvent aussi être employées. D’un autre côté, connaissant la direction des sources perturbatrices, le filtrage spatial et des techniques assimilées pouvant être mises en œuvre dans des réseaux d’antennes, sont potentiellement capables de lutter contre les interférences avec une connaissance réduite des caractéristiques des GNSS. Après quelques rappels de base sur la radioastronomie et ses objets d’étude, l’article présente quelques exemples de perturbations d’observations radioastronomiques par des émissions satellites. Un bref état de l’art des techniques de lutte contre les interférences radioélectriques en radioastronomie est ensuite exposé ; les principes de certaines méthodes apparaissant bien adaptées à la lutte contre les interférences provenant de GNSS sont détaillés et des résultats de ces méthodes présentés. L’importance de la coopération entre concepteurs de GNSS et radioastronomes est finalement soulignée.
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The authors wish to acknowledge the reviewers for their careful review of the paper and for their remarks and suggestions which helped to improve it significantly.
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This work was first presented at the 3rd CNES-ESA Workshop on GNSS Signals and Signal Processing, Toulouse, 21–22 April 2008.
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Gilloire, A., Sizun, H. RFI mitigation of GNSS signals for radio astronomy: problems and current techniques. Ann. Telecommun. 64, 625 (2009). https://doi.org/10.1007/s12243-009-0112-3
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DOI: https://doi.org/10.1007/s12243-009-0112-3
Keywords
- Radio frequency interference mitigation
- Radio astronomy
- Global Navigation Satellite Systems
- Informed mitigation techniques
- Adaptive cancellation
- Antenna arrays