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Method and apparatus for synthesizing a modulated carrier to reduced interchannel interference in a digital communication system

  • US 4,307,464 A
  • Filed: 12/26/1979
  • Issued: 12/22/1981
  • Est. Priority Date: 12/26/1979
  • Status: Expired due to Term
First Claim
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1. Apparatus for use in a digital communication system for synthesizing a digital-data-modulated carrier waveform for transmission via a selected medium, said digital data being a sequence of binary data bits each having one of first and second binary data values, and said carrier waveform is phase-shift-keyed by said binary data, comprising:

  • read-only memory means for storing at each of a multiplicity of individually addressable memory locations a data word defining each of a sequential plurality of carrier amplitudes;

    counter means having an input enabled at a clock frequency for providing an output signal sequentially and cyclically counting the input clock frequency, said count output signal coupled to said memory means to sequentially and cyclically read the carrier-amplitude-defining data words stored therein from the memory locations of said memory means;

    means receiving the sequential data words cyclically read out of said read-only memory means for converting each data word to an associated amplitude of an analog voltage, said analog voltage being a step-wise representation of said carrier waveform having a desired carrier frequency and a desired envelope shape;

    means for low-pass filtering said analog voltage to provide a substantially sinusoidal representation of said carrier waveform;

    means for modulating the substantially sinusoidal carrier waveform in accordance with each bit of digital data to be transmitted, and including means receiving the carrier waveform from said low-pass-filtering means for inverting the phase thereof;

    means receiving said binary data for selecting the output of said low-pass-filtering means for transmission of said modulated carrier waveform having said first binary data value and for selecting the output of said phase inverting means for transmission of said modulated carrier waveform having said second binary data; and

    means for coupling the data modulated carrier waveform to said selected medium.

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