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PERFORMANCE IMPROVEMENTS TO THE EXISTING GPS CONFIGURATION 78 The NRC committee strongly believes that preservation of our military advantage with regard to radionavigation systems should focus on electronic denial of all useful signals to an opponent, for example, by jamming and spoofing, while improving the ability of civil and friendly military users to employ GPS in a jamming and spoofing environment. Continued effort to deny the accuracy of GPS to all users except the U.S. military via SA appears to be a strategy that ultimately will fail. Thus, the NRC committee recommends that the military employ jamming techniques in a theater of conflict to fully deny an enemy the use of GPS or other radionavigation systems. The NRC committee believes that the principal shortcoming in a jamming strategy, regardless of the level of SA, is the difficulty military GPS receivers currently have acquiring the Y-code during periods when the C/A- code is unavailable due to jamming of the L1 signal.6 The implementation of direct Y-code acquisition capability, as recommended later in this chapter, would provide the optimal solution to this problem. In the interim, various operating disciplines, also discussed in this chapter, can minimize the impact of L1 C/A-code jamming on the ability to acquire the Y-code. The committee believes that a focused, high-priority effort by the DOD to develop and deploy direct Y-code user equipment, backed by forceful political will from both the legislative and executive branches, can bring about the desired result in a relatively short period of time. The technology for developing direct Y-code receivers is available today. Impact of SA on GPS User Equipment Manufacturers and U.S. Competitiveness It has been argued that SA provides a competitive advantage to U.S. manufacturers of GPS and DGPS user equipment, and DGPS service providers. This has apparently been true in the past and to some extent currently. However, the advantage is at best temporary, as indicated by growing foreign competition, especially from Japan. Foreign manufacturers already possess the technology to achieve results equivalent to those of U.S. manufacturers. Within 1 to 2 years, any competitive advantage for U.S. manufacturers will disappear. One market analysis has shown that if SA is eliminated, the number of GPS and DGPS users in North America is expected to increase substantially. The market for GPS receivers and systems is estimated to be around $64 billion by the year 2004, as compared to $42 billion with SA at its current level.7 There is considerable concern within the U.S. civil user community, and even more concern among the international community, regarding the reliability of a navigation system under the control of the U.S. military. Removal of the SA signal degradation is likely to be viewed as a good faith gesture by the civil community and could substantially improve international acceptance and potentially forestall the development of rival satellite navigation systems. 6 The C/A-code is normally used initially to acquire the Y-code. 7 The analysis by Michael Dyment, Booz·Allen & Hamilton, 1 May 1995, is shown in Appendix E.
