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Carrier frequency error detector capable of accurately detecting a carrier frequency error

  • US 5,276,710 A
  • Filed: 07/30/1992
  • Issued: 01/04/1994
  • Est. Priority Date: 07/30/1991
  • Status: Expired due to Fees
First Claim
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1. A carrier frequency error detector for use in a coherent demodulator for coherently demodulating a received signal to produce a demodulated signal, said received signal being incoherently detected in an N-phase phase-shift keying (PSK) modulated signal which is obtained by carrying out N-phase PSK modulation on a transmission carrier signal having a transmission carrier frequency by a transmission digital data signal where N represents a predetermined integer which is not less than two, said transmission digital data signal comprising a plurality of frames each of which includes a transmission unique word signal indicative of a transmission unique word, said carrier frequency error detector being for detecting a carrier frequency error in said received signal, said carrier frequency error detector comprising:

  • a local unique word generator for generating a local unique word signal indicative of a local unique word which is identical with said transmission unique word;

    correlation means for differentially detecting said received signal and said local unique word signal to produce a first differential detected signal and a second differential detected signal, respectively, and for correlating said first differential detected signal and said second differential detected signal to produce a correlated signal;

    a frame timing generator for generating a frame timing signal indicative of a start time of each of said frames;

    frequency fine detection means connected to said correlation means and said frame timing generator for detecting a fine frequency error related to said carrier frequency error in accordance with said correlated signal and said frame timing signal and to produce a frequency fine error detected signal indicative of said fine frequency error;

    a data buffer supplied with said received signal for buffering said received signal to produce a buffered signal;

    frequency coarse detection means connected to said data buffer, said local unique word generator, and said frame timing generator for detecting a coarse frequency error related to said carrier frequency error in accordance with said buffered signal, said local unique word signal, and said frame timing signal to produce a frequency coarse error detected signal indicative of said coarse frequency error;

    a first adder connected to said frequency fine detection means and said frequency coarse detection means for adding said frequency fine error detected signal to said frequency coarse error detected signal to produce a first added signal indicative of a result of addition by said first adder;

    a frequency shifter connected to said data buffer and said first adder for frequency shifting said buffered signal on the basis of said first added signal into a frequency shifted signal;

    maximum power frequency detection means connected to said frequency shifter for detecting a frequency having a maximum power in said frequency shifted signal to produce a maximum power frequency detected signal indicative of the frequency having said maximum power; and

    a second adder connected to said maximum power frequency detection means and said first adder for adding said first added signal to said maximum power frequency detected signal, and said second adder producing a second added signal indicative of a result of addition by said second adder as a carrier frequency error detected signal indicative of said carrier frequency error.

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