National Academies Press: OpenBook

The Global Positioning System: A Shared National Asset (1995)

Chapter: Resistance to Radio Frequency Interference

« Previous: Current and Future Applications and Requirements
Suggested Citation:"Resistance to Radio Frequency Interference." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
Page 30

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

GPS APPLICATIONS AND REQUIREMENTS 30 Challenges to Full Utilization of GPS Selective Availability and Anti-Spoofing When SA dithering of the GPS signals is employed, the DGPS corrections required to circumvent the resulting accuracy degradation must keep up with the dithering rate. This is not a problem for local-area DGPS, since the local correction broadcast usually has a sufficient data rate to provide timely corrections. The space- based WAAS, however, broadcasts its differential corrections as part of the navigation message data carried by a GPS-like L1 signal. SA has a negative effect on this signal format; the high correction data rate necessary to keep up with the SA dither rate constrains the flexibility of providing additional information on this navigation message. SA also decreases navigation availability and integrity monitoring availability for SPS users because the ranging errors it introduces require better satellite geometry for the specified 100-meter level of navigation accuracy. This sometimes rules out the operational use of GPS, especially when there are failed satellites present, and significantly reduces the effectiveness of RAIM.22 The employment of A-S, which overlays the Y-code on L2 rather than the P-code, denies the second frequency needed for real-time ionospheric correction to all but authorized PPS users. Without dual-frequency receivers on board aircraft, the WAAS needs to employ a large network of ground sites to collect ionospheric data, that will be interpolated by the user to estimate the ionospheric delay in the pseudorange measurements. The disadvantages of this constraint are a decrease in the vertical positioning accuracy of wide-area DGPS, and an increase in the size, complexity, and cost of the WAAS ground network. Resistance to Radio Frequency Interference A-S also limits an SPS receiver's ability to deal with RF interference from known sources such as the third harmonic of some UHF (ultra-high frequency) television channels and airborne VHF (very-high frequency) transmitters. Solutions to the potential problem of RF interference must be found if GPS is to become the primary navigation and surveillance system for aviation, and organizations such as the RTCA are actively studying the issue. Resistance to interference can be greatly improved through the use of dual-frequency receivers that can track the code on both L1 and L2 because it is unlikely that interference from a single source will simultaneously affect both frequencies. As discussed in Appendix G, access to the wider bandwidth of the P- code, which is approximately 20 MHz (versus 2 MHz for the C/A-code), also would increase resistance to interference and reduce vulnerability to multipath. 22 An analysis of the effects of SA on RAIM was conducted for this study by the MITRE Corporation. The results are presented in the next chapter, and the full analysis can be found in Appendix F.

Next: Operational Procedures »
The Global Positioning System: A Shared National Asset Get This Book
Buy Paperback | $61.00 Buy Ebook | $48.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

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.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook,'s online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!