Alternative Position Navigation & Timing (APNT) Based on Existing DME and UAT Ground Signals

Sherman C. Lo, Benjamin Peterson, Dennis Akos, Mitch Narins, Robert Loh, and Per Enge

Abstract:	The United States (US) Federal Aviation Administration (FAA) is developing alternative position navigation and timing (APNT) technologies to maintain efficient and safe operations even with a degradation of the Global Positioning System (GPS) and other Global Navigation Satellite Systems (GNSS). Several technologies are being studied and developed including terrestrial passive ranging system, upgraded distance measuring equipment (DME) and multilateration (MLAT) based navigation. Terrestrial ranging systems are attractive as they have little capacity constraints and a simpler architecture than the other alternatives. They can also provide additional capabilities such as signal security and precise time reference. Finally, it may be possible to utilize existing FAA infrastructure and signals thus reducing cost and mitigating spectrum concerns. These last two benefits motivate the study presented in this paper. This paper examines two of the passive ranging systems being studied for APNT. These are attractive as they leverage existing signals and ground infrastructure. The first design implements a ranging broadcast using existing DME ground transponders without the need for any changes. The second concept is to use the ranging functionality existing within universal access transceiver (UAT) ground broadcast. UAT is a protocol that has been implemented by the FAA to support automatic dependent surveillance – broadcast (ADS-B). This paper presents the signal and message structure of both systems. It covers their basic concept of operation. Of interest is whether the system has the capability of supporting APNT in the future airspace. To understand this capability the accuracy of both systems are assessed. Additional analysis includes developing the data capacity of the DME based system and examining the current signal in space performance of UAT ranging.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	3309 - 3317
Cite this article:	Lo, Sherman C., Peterson, Benjamin, Akos, Dennis, Narins, Mitch, Loh, Robert, Enge, Per, "Alternative Position Navigation & Timing (APNT) Based on Existing DME and UAT Ground Signals," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 3309-3317.
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