A Low-Cost Atomic Clock: Impact on the National Airspace and GNSS Availability

John Murphy, Trent Skidmore

Abstract:	Availability is perhaps the most misunderstood and controversial of the Required Navigational Performance (RNP) parameters. The ability to meet a stringent availability requirement of 0.99999 could be a tremendous cost driver in the development, deployment, and operational costs of both the Wide Area Augmentation Systems (WAAS) and any future CAT II/III GNSS-based precision approach aids. This paper discusses the improved Global Navigation Satellite System (GNSS) availability obtainable using a GPS receiver integrated with a low-cost, flight-worthy atomic clock. Emphasized is the stability and improvement in dilution of precision (DOP), especially in the vertical plane, made possible by an atomic clock during times of degraded coverage due to planned or unplanned satellite outages. This improvement manifests itself in the ability to navigate using a minimum of three satellites (four if Receiver Autonomous Integrity Monitoring NAIM] is required) due to improved stability of an atomic clock over conventional crystal oscillators found in most GPS receivers. Compared are the availability improvements resulting from additional geostationary satellites (carrying a navigation payload) with those made possible using a properly integrated atomic clock.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	1329 - 1336
Cite this article:	Murphy, John, Skidmore, Trent, "A Low-Cost Atomic Clock: Impact on the National Airspace and GNSS Availability," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 1329-1336.
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