Selection Rationale for a New Civil Global Positioning System (GPS) Signal

Sally L. Frodge, Michael Biggs

Abstract:	The development of civil applications using two GPS frequencies experienced tremendous growth in the mid-to- late 1980's and early 1990s as it became clear that real-time centimeter (cm) accurate systems were indeed practical and could be expected to be robust. Much initial research and development was accomplished in such fields as surveying, where applications were either static or in a relatively low-dynamic environment. As it became apparent that highly accurate GPS-based systems could support platforms and applications within higher dynamic environments, more applications and areas explored GPS as a potential solution. Today it would be difficult to estimate the number of high-accuracy civil applications and areas into which GPS has grown. These systems use dual-frequency methods to achieve the necessary results. The quest to modernize GPS has taken these growing civil applications and requirements as well as other functions into account. The Standard Positioning Service (SPS), published by the Department of Defense (DoD), defines what is available for civil use and included only the GPS L1 signal at 1575.42 MHz. The L2 signal centered at 1227.60 MHz was authorized for military use only. Nonetheless, many civil applications were developed, dependent upon the availability of the L2 signal. To accommodate and reflect the requirements of the existing civil dual-frequency applications and to support the future and planned use of GPS by civil aviation safety-of-life services, work was accomplished to define a modernized GPS system. To date, the International Civil Aviation Organization (ICAO) has defined the constituent elements of its Global Navigation Satellite System (GNSS) as being the United States’ Global Positioning System (GPS), the Russian Federation GLONASS, and augmentation systems. The United States, as part of its GPS modernization initiative, has identified two new coded signals for civil use. One new signal was selected as being centered on 1176.45 MHz, designated as GPS L5. The L5 is the signal planned to support safety-of-life functions. The other, centered at 1227.6 MHz (L2), is planned to have C/A code placed on it. It is assumed that the applications utilizing the civil aspects of L2 will not have a safety-of-life requirement. The L2 frequency falls in a band utilized extensively by high power air traffic control and military surveillance radar, however it should be available in most locations for ground-based use. The purpose of this paper is to identify the rationale leading to the GPS L5 frequency decision.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	607 - 612
Cite this article:	Frodge, Sally L., Biggs, Michael, "Selection Rationale for a New Civil Global Positioning System (GPS) Signal," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 607-612.
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