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Modem for use in multipath communication systems

  • US 4,694,467 A
  • Filed: 07/03/1986
  • Issued: 09/15/1987
  • Est. Priority Date: 07/03/1986
  • Status: Expired due to Term
First Claim
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1. A modem for use in communication systems used for transmitting and receiving information bits, said modem comprisinga transmitter includingspectrum spreading means responsive to a plurality of sequentially supplied input information bits for providing a plurality of spread spectrum information bits, a first group thereof having spread spectrum characteristics in accordance with a first spread spectrum sequence and a second group thereof having spread spectrum characteristics in accordance with a second spread spectrum sequence which differs from said first spread spectrum sequence;

  • modulation means for modulating said plurality of spread spectrum information bits to provide a modulated transmitter signal;

    means for generating a preamble signal;

    means for sequentially transmitting said preamble signal and said modulated transmitter signal;

    a receiver includingmeans for receiving said preamble signal and said modulated transmitter signal;

    processing means includingmeans responsive to said preamble signal for processing said preamble signal to provide estimates of the frequency offsets of said received preamble signal;

    means responsive to said modulated receiver signal for generating complex baseband signal samples; and

    means responsive to said frequency offset estimates and to said complex baseband signal samples for shifting the frequencies of said baseband signal samples by said frequency offset estimates to reduce the frequency offsets of said baseband signal samples to a minimum;

    detector means comprisingmeans responsive to sid frequency shifted complex baseband signal samples for providing a plurality of signal samples which are time delayed relative to each other;

    means responsive to a selected number of said time delayed signal samples for de-spreading and for demodulating each of said selected signal samples to provide a selected number of de-spread and demodulated signal samples; and

    means for combining said selected number of de-spread and demodulated signal samples to provide a demodulated received output signal.

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