Theory and Practice of the Interference Mitigation Technology (AIM+) in Septentrio Receivers

T. Willems and W. De Wilde

Abstract:	Because GPS and other satellite navigation signals as received on ground are of very low power, they are vulnerable to radio-frequency interference. In addition, the radio-frequency spectrum is crowded, and getting more crowded every day. In some cases, the effect of interfering signals is becoming noticeable, particularly in the GLONASS L2 band and the L5 band. Accidental and intentional jamming is also on the rise. GNSS positioning accuracy ultimately depends on the availability and the accuracy of satellite measurements. When one individual measurement is adversely affected or becomes unavailable due to interference, the advanced positioning engine implemented in most high-end receivers is able to limit the effect on final positioning accuracy. However, a source of interference is likely to affect multiple signals in the same GNSS band and can block reception of a whole GNSS band. In such cases, the effect at the positioning level can be more severe. Although it depends on the user’s application and the employed GNSS receiver (single or multi-frequency, GPS-only or multi-constellation, etc.), it is clear that interference has become a real threat to positioning accuracy and availability. As a result, interference countermeasures form a crucial part of professional GNSS receivers. Septentrio has implemented unique receiver interference mitigation techniques. These countermeasures include: adaptive notch filtering, pulse blanking and GLONASS L2 band remapping. Working in concert, these countermeasures as well as other analog and digital countermeasures form what is known as Septentrio’s AIM+ (Advanced Interference Mitigation) technology. This paper discusses the different categories of interference sources which have been encountered in the field and the methods used by Septentrio in the design of their receivers to alleviate effects for the user. This includes dedicated hardware and software to mitigate continuous wave, narrowband, pulsed and other types of interference. In addition to a description of different mitigation techniques (adaptive notch filtering, pulse blanking and GLONASS L2 band remapping), we provide specific case studies of how each technique has worked in the field. This demonstrates the effectiveness of AIM+ in real world applications. We conclude that, in many cases, positioning accuracy and availability can be maintained by appropriate countermeasures in the analog and digital domain.
Published in:	Proceedings of the 2013 International Technical Meeting of The Institute of Navigation January 29 - 27, 2013 Catamaran Resort Hotel San Diego, California
Pages:	835 - 842
Cite this article:	Willems, T., De Wilde, W., "Theory and Practice of the Interference Mitigation Technology (AIM+) in Septentrio Receivers," Proceedings of the 2013 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2013, pp. 835-842.
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