Distance Measuring Equipment Accuracy Performance Today and for Future Alternative Position Navigation and Timing (APNT)

S. Lo, Y.H. Chen, P. Enge, B. Peterson, R. Erikson, R. Lilley

Abstract:	Distance Measuring Equipment (DME) is seeing renewed interest for its ability to support future aviation navigation and surveillance needs. It is one of the major technologies being examined by the FAA Alternative Position Navigation and Timing (APNT) program to support needs to provide an alternative to GNSS in a NextGen airspace. As part of the APNT study of DME, we have been examining means to improve DME published accuracy. Some improvement is gained with little or no change to today‚s system. The field system may perform much better than specifications. However, meeting the most stringent APNT goals may require changes to the system. This paper looks at both aspects. As we care about actual performance, examination of the actual accuracy performance is based on measurements from several data collection efforts. A top-level examination of range accuracy is done using data from FAA flight inspection data. The results show the measured DME ranging accuracy is generally much better than that listed in the current specifications. Looking towards the future and improved performance, we used a bottom-up approach considering the components of range error, particularly the precision with which the signal can be measured, and multipath. Breaking down the components allows us to determine what most limits accuracy and where improvements may be gained. Key components examined are the precision of the DME transmitter and airborne interrogator signals, and multipath. DME signal precision derived from five different transmitters is presented. DME accuracy also depends on the airborne interrogator waveform and we will investigate the differences in transmitted waveform from several commercial DME avionics. We also take an initial look at DME multipath performance based on actual transmitted signal. Facility data-base resolution and fidelity, and precision of DME ground system location surveys are a function of today's 0.2 nm system error limit. These errors become noticeable when viewing flight data that is processed to the tighter tolerances required by APNT. Their contribution to system error will likely require reduction.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	711 - 721
Cite this article:	Lo, S., Chen, Y.H., Enge, P., Peterson, B., Erikson, R., Lilley, R., "Distance Measuring Equipment Accuracy Performance Today and for Future Alternative Position Navigation and Timing (APNT)," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 711-721.
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