Spectrum Implications for the Use of L2C for Aviation

D. J. Chadwick

Abstract:	A survey of the spectrum allocations and radio frequency assignments for the band between 960 Megahertz (MHz) and 1400 MHz was conducted in 1997. That work was used to support a decision on a choice for additional navigation frequencies for the Global Positioning System (GPS). Two frequencies emerged from this process: (a) 1227.6 MHz, the existing L2 used by the Department of Defense (DoD), and (b) 1176.45 MHz (called L5). L5 was selected to fall within a band that is internationally protected for safety-of-life services. The L2 frequency is in a band that does not have that protected status, but there is uncertainty about the effect that might have on the use of L2 for civil applications. As part of the GPS modernization, L2 will carry a civilian code known as L2C, a time-multiplexed combination of the L2 moderate code (CM) and the L2 long code (CL). Non-safety applications could begin using this capability before L5 is on-orbit. Whether or not there are applications for L2 in safety services is an ongoing debate. This paper seeks to provide updated information on the spectrum environment in the 1215-1240 MHz band to provide a technical basis for that discussion. GPS has become a major source of navigation signals in the National Airspace System (NAS) and throughout the world. It is used as a primary means of navigation in many areas. WAAS was commissioned in July, 2003 for use in the National Airspace System (NAS) for en route, terminal area, non-precision and vertically guided approaches through LPV. Harmful radio frequency interference to GPS signals can have a catastrophic impact on safety-of-flight and concern has been raised over the use of the L2 frequency because it is not in an Aeronautical Radionavigation Service (ARNS) band. The Federal Aviation Administration (FAA), International Civil Aviation Organization (ICAO) and RTCA, among many others, have taken positions to the effect that ARNS protection is required for any safety-of-life aeronautical function. Changes have occurred in the spectrum environment in the band between 1215 and 1240 MHz since the 1997 analysis. Not only have there been changes in frequency assignments, but also there have been two World Radiocommunication Conferences (WRCs) since then. The WRC in 2000 did not make any changes that directly affected the 1215-1240 MHz band. However, the recent 2003 World Radiocommunication Conference (WRC 2003) did make some allocation table changes that affect the band. In addition, some Administrations have chosen to adopt allocations by footnote for additional radio services other than those contained in the Spectrum Allocation Table (the “Table”) issued by the International Telecommunications Union (ITU). Some of these new allocations could limit the utility of L2 for safety services. A discussion of these allocations and their impact on future use of L2C for aviation is included.
Published in:	Proceedings of the 2004 National Technical Meeting of The Institute of Navigation January 26 - 28, 2004 The Catamaran Resort Hotel San Diego, CA
Pages:	1037 - 1048
Cite this article:	Chadwick, D. J., "Spectrum Implications for the Use of L2C for Aviation," Proceedings of the 2004 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2004, pp. 1037-1048.
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