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Coherent demodulator for .pi./4 shifted QPSK signal

  • US 5,179,578 A
  • Filed: 01/22/1991
  • Issued: 01/12/1993
  • Est. Priority Date: 01/26/1990
  • Status: Expired due to Fees
First Claim
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1. A demodulator for coherent demodulation of a π

  • /4 shifted QPSK signal in which signal constellation phases alternate between two sets of possible phase values for each successive symbol pair, comprising;

    reference means for generating a recovered carrier reference signal;

    means for demodulating an input π

    /4 shifted QPSK signal by using said recovered carrier reference signal; and

    means for controlling said reference means by using said demodulated π

    /4 shifted QPSK signal, includingmeans for compensating a π

    /4 shift characteristic of said demodulated π

    /4 shifted QPSK signal to develop a compensated signal, andmeans for applying said compensated signal as a control signal to said reference means to cause said recovered carrier reference signal to synchronize with said π

    /4 shifted QPSK signal.

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