Availability of GNSS Performance to Support ADS-B

Matt Harris, Tim Murphy

Abstract:	Countries around the world are beginning to set positioning accuracy and integrity requirements to support Automatic Dependent Surveillance - Broadcast (ADS-B) applications. The requirements and applications that will be supported by ADS-B widely vary from one country to another, and are still being defined in most cases; however, mandates for ADS-B equipage and performance of the position solution will be in effect as early as late 2008 for some specific locations. Several parameters have been defined by the standards community that define discrete positioning performance levels, including Navigation Accuracy Category for Position (NACp) and Navigation Integrity Category (NIC), each with eleven categories, and Surveillance Integrity Level (SIL), which is the probability of containment associated with NIC. These performance categories were intended to provide a common set of metrics that will characterize ADS-B quality for the users who receive the ADS-B reports. Consequently, required levels of performance from ADSB needed to support specific operations may be expressed in terms of NACp, NIC and SIL. Aircraft position determination used in ADS-B reports will typically be derived from satellite navigation. The most common navigation sensor fielded on air transport airplanes that can support more stringent accuracy and integrity requirements is GPS combined with receiver autonomous integrity monitoring (RAIM). This paper presents results from trade studies to determine the availability of various GPS RAIM implementations to meet the range of future ADS-B requirements. The most influential system parameters that were traded in this study include the following: user location, GPS receiver awareness of selective availability, inertial integration, GPS satellite constellation, satellite failure probability assumptions, and satellite masking angle assumptions. The performance of combinations of these parameters are compared with the latest version of planned ADS-B requirements to determine what, if any, changes to current airplane designs may be necessary to meet such requirements.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	1116 - 1123
Cite this article:	Harris, Matt, Murphy, Tim, "Availability of GNSS Performance to Support ADS-B," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 1116-1123.
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