GNSS Local Augmentation Integrity Standards … Future Communications Links to Users

Charles S. Dixon and Russell G. Morrison

Abstract:	A number of standards exist today for GPS local communications data links for various Integrity “market segments” and user groups. These standards support provision of a combination of differential, integrity and other data to users in real time and with high reliability. Today they relate only to GPS, and specifically to today’s incarnation of GPS, which provides services based on a single civilian carrier frequency. This paper describes the current main standards for aviation and maritime users, and examines the potential for inclusion of Galileo Operation of stand-alone Galileo navigation, and Galileo augmented by local components is a feasible operational mode for some future systems, however the dominant market potential is envisaged for augmentations addressing combined Galileo and GPS. This would significantly increase the quantity of data carried; a system dealing with Galileo as well as GPS will have of the order of twice as many satellites visible as one using only GPS. Whether differential corrections are derived and transmitted by the Local Augmentation system, or whether it deals only with Integrity status of the satellites, dealing with twice as many satellites results in twice the data volume. The situation is actually more complex than this since both Galileo and modernised GPS will include multiple frequencies, and it is envisaged that many instances of Local Augmentation will include services based on use of more than one carrier signal. The quantity of data that may be transmitted to users over the local augmentation systems data link could potentially increase to seven or more times the present volume. The paper identifies several mechanisms to deal with the anticipated increase in data volume without compromising the time to alert the user (TTA) in case of a system malfunction. TTA is a critical parameter for Safety-of-Life service users. The options include increasing the communications link capacities, reducing the rate of update of some of the parameters carried on the link, and optimising the transmission protocols and correction mechanisms. Specific Integrity Alert messages are highlighted as a serious contender that could satisfy the identified integrity needs.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1636 - 1644
Cite this article:	Dixon, Charles S., Morrison, Russell G., "GNSS Local Augmentation Integrity Standards … Future Communications Links to Users," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1636-1644.
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