Impact of DME/TACAN on GNSS L5/E5a Receivers at Low Altitude Considering Multipath

Nicolas Gault, Axel Garcia-Pena, Alexandre Chabory, Christophe Macabiau

Abstract:	In the context of civil aviation, GNSS L5/E5a Radio Frequency Interference (RFI) environment is dominated by pulsed interferences such as JTIDS/MIDS and DME/TACAN causing a degradation of the effective C/_0 observed by the receiver. The mitigation of the pulse RFI as well as its precise characterization is fundamental to guarantee the provision of the civil aviation Safety-of-Life service, as depicted in (Garcia-Pena, Macabiau, et al., 2020). In order to mitigate the pulsed RFI impact, in civil aviation standards, a temporal blanker is used as a counter measure. The effective C/_0 is thus computed accounting for the temporal blanker introduction through the derivation of the blanker duty cycle, bdc, and the equivalent noise level contribution of the non-blanked interference, R_I. However, none of the characterizations found in the scientific literature or in the standards considers any multipath effect. This effect is especially important at low altitude since the airborne GNSS receiver could be significantly affected by echoes created by low altitude obstacles, potentially increasing bdc and R_I. Therefore, in this work, it is proposed to update the mathematical model of the effective C/_0 with the introduction of multipath. The introduction of this new model is used to compare the impact of multipath at low and at high altitude flight levels (FL). The comparison is conducted in two parts in this work. First, an analysis shows that to increase the blanking duty cycle by 50%, the size of an obstacle should be four times larger when the aircraft is at high altitude FL in comparison with low altitude FL. Second, an analysis of a potential low altitude hot-spot located at JALTO, Philadelphia, shows that the impact of multipath must not be neglected; nevertheless, it is shown that the low altitude hot spot exceeding the existing worst-case scenario at FL400 is highly unlikely.
Published in:	Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022) September 19 - 23, 2022 Hyatt Regency Denver Denver, Colorado
Pages:	276 - 303
Cite this article:	Gault, Nicolas, Garcia-Pena, Axel, Chabory, Alexandre, Macabiau, Christophe, "Impact of DME/TACAN on GNSS L5/E5a Receivers at Low Altitude Considering Multipath," Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), Denver, Colorado, September 2022, pp. 276-303. https://doi.org/10.33012/2022.18361
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