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P-code-aided global positioning system receiver

  • US 4,972,431 A
  • Filed: 09/25/1989
  • Issued: 11/20/1990
  • Est. Priority Date: 09/25/1989
  • Status: Expired due to Term
First Claim
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1. A method of processing received signals in a global positioning system (GPS), to recover an L2 carrier signal that has been modulated with an encrypted P-code signal, the method comprising the steps of:

  • receiving a signal transmitted from each of a plurality of satellites, the signal containing an encrypted version of a pseudorandom code sequence known as P code;

    independently generating a replica of the P-code pseudorandom code sequence without encryption;

    correlating the received encrypted P-code sequence with the locally generated replica of the P-code sequence, to obtain a frequency spectrum containing a peak indicative of the timing relationship between the received encrypted P code sequence and the locally generated P code sequence;

    bandpass filtering the result of the correlation step; and

    squaring the correlated and filtered signal to recover the L2 carrier signal with a favorable signal- to-noise ratio.

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