Robust Navigation for Urban Air Mobility via Tight Coupling of GNSS with Terrestrial Radionavigation and Inertial Sensing

Robert Tenny, Todd E. Humphreys

Abstract:	This paper presents a method of tightly coupling carrier-phase-differential GNSS (CDGNSS) with terrestrial radionavigation system (TRNS) signals and data to build a robust positioning, velocity, and timing (PVT) solution for urban air mobility (UAM). UAM will require precise and robust PVT solutions that are resilient to interference and jamming. CDGNSS offers absolute positioning with high availability and sub-decimeter accuracy but cannot serve as the sole source of PVT for UAM because of its vulnerability to interference: a single potent GNSS jammer could deny UAM service across an entire city were GNSS the sole means UAM navigation. TRNS signals are stronger than those of GNSS and offer additional frequency diversity. Their multipath errors, although larger than for GNSS at street level due to the low elevation angles with which TRNS signals propagate from terrestrial transmitters, are manageably small at altitudes where UAM vehicles will operate. Thus, TRNS offers an attractive backup to GNSS for UAM. This paper explores two techniques for fusion of TRNS and CDGNSS: loosely- and tightly-coupled. The loosely-coupled technique fuses information from the two sensing modalities at the level of full PVT solutions. The tightly-coupled technique explored here fuses GNSS carrier phase and pseudorange measurements with TRNS pseudorange, Doppler, and calibrated pressure sensor measurements, together with inertial sensor measurements, to produce a unified PVT solution. Innovations-based measurement exclusion is applied to reduce the impact of GNSS and TRNS multipath errors and of pressure anomalies due, e.g., to ground effect at take-off and landing. Both loosely- and tightly-coupled techniques are tested on an aerial vehicle platform in an environment where both GNSS and TRNS signals are available. Error growth of the tightly-coupled technique during extended intervals of GNSS denial is studied to determine whether UAM service could continue uninterrupted when only inertial and TRNS measurements remain available.
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:	1599 - 1609
Cite this article:	Tenny, Robert, Humphreys, Todd E., "Robust Navigation for Urban Air Mobility via Tight Coupling of GNSS with Terrestrial Radionavigation and Inertial Sensing," Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), Denver, Colorado, September 2022, pp. 1599-1609. https://doi.org/10.33012/2022.18469
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