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Digital communication system using superposed transmission of high speed and low speed digital signals

  • US 5,280,537 A
  • Filed: 11/24/1992
  • Issued: 01/18/1994
  • Est. Priority Date: 11/26/1991
  • Status: Expired due to Term
First Claim
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1. A method of superposed transmission of high and low speed digital signals in a digital communication system, comprising the steps of:

  • (a1) forward error correction encoding high speed digital signals to be transmitted to obtain encoded high speed digital signals;

    (a2) modulating a first carrier in a first frequency with the encoded high speed digital signals obtained at the step (a1) to obtain modulated high speed signals;

    (b1) forward error correction encoding low speed digital signals to be transmitted to obtain encoded low speed digital signals;

    (b2) spreading a spectrum of the encoded low speed digital signals obtained at the step (b1) to obtain spread spectrum signals;

    (b3) modulating a second carrier in a second frequency with the spread spectrum signals obtained at the step (b2) to obtain modulated spread spectrum signals;

    (c) transmitting the modulated high speed signals obtained at the step (a2) and the modulated spread spectrum signals obtained at the step (b3) through an identical frequency band on a transmission path in a form of superposed transmission signals;

    (d1) demodulating the modulated high speed signals in the superposed transmission signals transmitted through the transmission path at the step (c) to reproduce the encoded high speed digital signals;

    (d2) forward error correction decoding the encoded high speed digital signals reproduced at the step (d1) to reproduce the high speed digital signals;

    (e1) obtaining a phase inverted replica of the modulated high speed signals in the superposed transmission signals transmitted through the transmission path at the step (c) according to the high speed digital signals reproduced at the step (d2);

    (e2) power combining the superposed transmission signals transmitted through the transmission path at the step (c) with the phase inverted replica obtained at the step (e1) to obtain modulated spread spectrum signals in the superposed transmission signals;

    (f1) despreading a spectrum of the modulated spread spectrum signals obtained at the step (e2) to obtain modulated low speed signals;

    (f2) demodulating the modulated low speed signals obtained at the step (f1) to reproduce the encoded low speed digital signals; and

    (f3) forward error correction decoding the encoded low speed digital signals reproduced at the step (f2) to reproduce the low speed digital signals.

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