National Academies Press: OpenBook

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

Chapter: Option 2: Narrow-Band L4 Signal

« Previous: New Signal Structure Options
Suggested Citation:"Option 2: Narrow-Band L4 Signal." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
Page 89

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.

PERFORMANCE IMPROVEMENTS TO THE EXISTING GPS CONFIGURATION 89 discussed guidelines, the NRC committee determined that 2 of the 10 options should be seriously considered. These two options are discussed below in order of preference. Option 1: Wide-Band L4 Signal The optimal scenario for an enhanced civilian GPS signal would entail the provision of a new wide-band frequency, termed L4, that would be broadcast unencrypted to allow for universal access. The wide bandwidth sufficiently offset from the current L1 signal would allow for ionospheric delay correction, wide-lane ambiguity resolution, improved interference rejection, and faster accuracy recovery in multipath environments. The pseudorandom noise chosen for the L4 wide-band signal should have a bandwidth similar to the present P-code, but with a sequence length chosen for rapid acquisition by low-cost civilian receivers. 22 Although not needed for acquisition purposes, the signal could have C/A-code in phase quadrature, which would allow manufacturers to get the most benefit from the new signal without significant changes to their investment in application-specific integrated circuit (ASIC) correlators.23 Based on the previously mentioned frequency allocation analysis, it appears that several options may exist for a wide-band L4 signal. The first option would be to place the center of the wide-band L4 signal at 1258.29 MHz. If the Russian Federation follows through on plans to move GLONASS L2 transmissions to the lower portion of their frequency allocation (1242.9-1251.7 MHz by 1998 and 1242.9-1248.6 by 2005), even a wide- band signal placed at 1258.29 MHz would cause little frequency overlap. Therefore, the possibility of interference with GLONASS would be low. The second option would be to place the wideband L4 signal at 1841.40 MHz. Again, the feasibility of receiving a frequency allocation in this area of the spectrum would require further investigation. Option 2: Narrow-Band L4 Signal If a wide-band frequency allocation proves impossible to obtain for L4, a narrow-band signal should be considered as the second best option. Several potential frequencies have been identified that have sufficient spacing from L1 to allow for the correction of ionospheric delay. These include 1237.83 MHz (which is the upper null of the existing L2 frequency); 1258.29 MHz; and 1841.40 MHz. A narrow-band signal placed at any of these frequencies would carry a C/A-type code. 22 The code sequence length for the current P-code is 1 week. 23 A dual-frequency L1/L4 receiver would still need an additional RF/IF (intermediate frequency) section and synthesizers. For current dual-frequency receiver manufacturers, hardware changes would not be difficult.

Next: Increased Accuracy »
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!