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Expanded partial response processing for analog signal enciphering and the like

  • US 4,754,481 A
  • Filed: 06/24/1985
  • Issued: 06/28/1988
  • Est. Priority Date: 06/24/1985
  • Status: Expired due to Term
First Claim
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1. In a communication system having channels with a prescribed bandpass B,a transmitting terminal comprisingmeans for receiving analog speech signal samples for transmission in a channel subject to transmission noise of up to a predetermined amplitude x,means for quantizing the speech signal samples in a prescribed amplitude range to a set of Q>

  • =64 quantizing levels sufficient to substantially approximate a continuously varying speech signal in which the span between each adjacent pair of levels is less than said predetermined transmission noise amplitude,means for limiting the range of quantizing levels of said speech signal samples over said prescribed amplitude range to be less than Q-x,means for sample masking said limited range speech signal samples to form encrypted speech signal samples having a bandwidth>

    Bmeans for partial response processing said encrypted limited range speech signal samples to reduce the bandwidth of the encrypted speech signal samples to less than B,means for passing said partial response processed encrypted limited range speech signal samples through a low pass filter having a square root cosine response characteristic with a cutoff frequency less than B andmeans for producing an analog signal responsive to said low pass filtered encrypted limited range speech signal samples.

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