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Suggested Citation:"INTRODUCTION." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
Page 67

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PERFORMANCE IMPROVEMENTS TO THE EXISTING GPS CONFIGURATION 67 3 Performance Improvements to the Existing GPS Configuration INTRODUCTION As pointed out in the previous section, civil users of the GPS have accommodated themselves to the currently available SPS (Standard Positioning Service) in attempting to meet their individual performance requirements, and a number of innovative uses of GPS have been demonstrated with the existing system. An even more capable system would likely result in a larger number of applications. Improved accuracy, integrity, availability, and reliability of the signal could provide improved results at significantly lower cost. For example, if the stand-alone GPS could provide an accuracy approaching 5 meters (2 drms), the need for many of the existing or planned differential systems could be avoided. In accordance with the committee's statement of task, this chapter will recommend a sequence of enhancements to the GPS that will serve to improve the accuracy of the system for civilian, commercial, and military users. After a discussion of the current performance achievable from the basic GPS, the subsequent sections address specific accuracy improvements focused on enhancing civilian, commercial, and military use of the system. Many of the suggested improvements also will have benefits other than better accuracy, such as increased integrity, improved availability, and enhanced resistance to RF (radio frequency) interference. These improved characteristics are discussed where appropriate. The final section of this chapter presents an overall strategy for implementing the recommended improvements. As noted throughout the text, some of the improvements are meant to be applied to the current GPS satellite constellation and others to the Block IIR and Block IIF constellations. When available, the approximate cost of each improvement also is given. Example with SA turned to zero: In this case, the error in the differential correction due to the satellite clock does not include any clock dithering, and so is dominated by the satellite oscillator stability, which is ∆f/f = 5 x 10-13. Using the formula: 0.2 m = t(c)( ∆f)/f to calculate the range error, where c is the speed of light = 3x 108 m/sec, gives a required update period of t = 1,333 seconds (22.2 minutes).

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The Global Positioning System (GPS) is a satellite-based navigation system that was originally designed for the U.S. military. However, the number of civilian GPS users now exceeds the military users, and many commercial markets have emerged. This book identifies technical improvements that would enhance military, civilian, and commercial use of the GPS. Several technical improvements are recommended that could be made to enhance the overall system performance.

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