DME Multipath Simulations as a Critical enabler to Support DME/DME RNP Reversion

Victor M. Gordo, Gema A. Paz, Javier San-Juan

Peer Reviewed

Abstract:	DME has become the main alternative (A-PNT) system to GNSS in the short/mid term, but most aircraft avionics do not include On Board Performance Monitoring and Alerting (OPMA) for DME, limiting the use of DME/DME for RNAV applications and not RNP ones. However, SESAR2020 Pj14.3.4 and EUROCAE WG-107 are trying to demonstrate the capability of DME/DME RNP Reversion based on the integrity monitoring systems of ground transponders; but to reach an equivalent level of integrity without OPMA, it is essential to detect and mitigate multipath affections as they could have an important impact in the navigation service provided, both in term of accuracy and continuity of service. To this end, it is necessary to use simulation models to predict potential areas where DME signals would be rejected due to multipath or even false locks could occur This paper presents a DME multipath assessment model, as well as validation results. The major sources of multipath errors for DME are reflection on the terrain and physical structures (such as buildings), as well as diffraction on these structures. The proposed methodology evaluates, following a physical optics approach, the three first order signals that interfere in the receiver: direct signal, terrain reflected and reflected in the existing structures. To confirm the applicability of the proposed model, it has been validated against two real cases of detected DME multipath problems. The first one a DME associated to ILS in Valencia International Airport (LEVC) and the second one in Dulles International Airport on the DME AML associated to a VORTAC. In both cases, flight calibration registers obtained using an oscilloscope in the areas were DME unlocks were detected, have been simulated using the described model and obtaining a narrow correlation with the real signals.
Published in:	Proceedings of the 2019 International Technical Meeting of The Institute of Navigation January 28 - 31, 2019 Hyatt Regency Reston Reston, Virginia
Pages:	508 - 521
Cite this article:	Gordo, Victor M., Paz, Gema A., San-Juan, Javier, "DME Multipath Simulations as a Critical enabler to Support DME/DME RNP Reversion," Proceedings of the 2019 International Technical Meeting of The Institute of Navigation, Reston, Virginia, January 2019, pp. 508-521. https://doi.org/10.33012/2019.16707
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