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Detecting false-locking and coherent digital demodulation using the same

  • US 5,490,176 A
  • Filed: 10/20/1992
  • Issued: 02/06/1996
  • Est. Priority Date: 10/21/1991
  • Status: Expired due to Fees
First Claim
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1. A method of detecting false-locking of a reference signal onto a digitally quadrature modulated signal with multiple levels and phase offset and demodulated by coherent digital demodulation, said digitally quadrature modulated signal containing bit stream signals, said method comprising the steps of:

  • mixing said digitally quadrature modulated signal with a first reference signal and with a second reference signal which is in phase quadrature with the first reference signal, in order to obtain baseband analog signals corresponding to the bit stream signals,recovering, from said baseband analog signals, trains of clock signals which correspond to said bit stream signals;

    monitoring the phase offset between said trains of clock signals;

    detecting false-locking when the phase offset changes sign; and

    correcting the first and second reference signals, when false-locking is detected, to lock the first and second reference signals in frequency and phase with the digitally quadrature modulated signal.

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