Real Time Differential Positioning of Aircraft Using GPS and GLONASS

David Lowe, David Walsh, Stefano Capaccio, Peter Daly, Gill Richards and Sarah Sharkey

Abstract:	Differential GPS (DGPS) is successfully used world- wide to provide positioning accuracy at the metre level. However, there are a number of applications which would benefit from a greater satellite availability. These applications require a very high level of system performance, especially system integrity and availability. One of the most stringent is the precision approach and landing of aircraft. The most obvious way to improve the satellite availability is to increase the number of satellites by combining the GPS and GLONASS systems. In January 1996 GLONASS achieved a full constellation of 24 operating satellites plus one spare satellite in orbit. There are, therefore, a total of 48 operating satellites when GLONASS and GPS are combined. The Institute of Satellite Navigation (ISN) has developed a 20 channel GPS/GLONASS (GNSS) receiver capable of obtaining carrier phase and code phase observables from any combination of 20 GPS and GLONASS satellites. Each channel can track either GPS or GLONASS satellites. Software has been written to calculate a real time differential position solution using GPS and GLONASS satellites, just GPS, or just GLONASS. This paper describes the first real time differential GNSS (DGNSS) positioning of an aircraft carried out by the ISN for the UK Civil Aviation Authority (CAA). The purpose of these tests was to prove the real time system and to perform an initial assessment of the increased performance when using combined GPS and GLONASS.observables. This work forms an initial stage of a project to evaluate GNSS for aviation applications. Further tests are planned which will lead to a more advanced investigation of accuracy and integrity issues. The trials were performed using a BAC l-l 1 aircraft and UHF differential links provided by the UK Defence Research Agency (DRA). The positioning system which has been developed is described, including the determination, transmission and reception of GPS and GLONASS differential corrections in RTCM format. The GLONASS RTCM correction format was devised by the ISN in the absence of any accepted protocol. The results of the test show that the increased level of satellite availability greatly enhances the effectiveness of the satellite navigation system, and demonstrate real time differential positioning of an aircraft using GPS and GLONASS.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	49 - 56
Cite this article:	Lowe, David, Walsh, David, Capaccio, Stefano, Daly, Peter, Richards, Gill, Sharkey, Sarah, "Real Time Differential Positioning of Aircraft Using GPS and GLONASS," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 49-56.
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