National Academies Press: OpenBook

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


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Suggested Citation:"OLD TECHNOLOGY (100,000 GATE ASIC)." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
Page 253

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APPENDIX K 253 Appendix K Direct Y-Code Acquisition Below are calculations showing the time for direct Y-code acquisition with older application specific integrated circuit (ASIC) technology and current ASIC technology. In the analysis, the following assumptions were made: (1) Receivers have limited knowledge of their current position. (2) Receivers are using the latest satellite ephemerides. (3) Time is known to ± 1 second. OLD TECHNOLOGY (100,000 GATE ASIC) The Y-code has 107 chips to search, given a 1-second uncertainty in clock offset (10.23 million chips per second). A well-designed receiver can obtain a signal-to-noise ratio of 12.6 dB in 0.001 seconds, based on the following derivation: Noise power = kTB, where k is Boltzman's constant, k = -198.6 dBm/Hz/Kelvin or 10-19.86 milliwatts/Hz/K. Assume the system temperature, T, is 100 Kelvin, then B, the noise bandwidth, is taken to be 1/0.001 seconds, or 1,000 Hz. Thus: Noise power = (10.-19.86 milliwatts/Hz/K)(1,000 Hz)(100 K) = 10-14.86 milliwatts or -148.6 dBm Given the minimum received power level for the L2 signal, which is -136 dBm, the ratio of signal-to-noise can be calculated: Signal-to-noise = received power - noise power = -136 dBm -(-148.6 dBm) = 12.6 dB.

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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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