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Demodulation system having adaptive matched filter and decision feedback equalizer

  • US 5,394,110 A
  • Filed: 02/02/1994
  • Issued: 02/28/1995
  • Est. Priority Date: 02/02/1993
  • Status: Expired due to Term
First Claim
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1. A demodulation system comprising:

  • a demodulator for demodulating to an analog-baseband signal an intermediate frequency band modulated signal having intersymbol interference due to fading in propagation paths;

    an analog-digital converter for sampling-quantizing said analog-baseband signal and outputting it as a digital-baseband signal;

    an adaptive matched filter that includes a transversal filter for inputting said digital-baseband signal and a control signal generating circuit for supplying tap coefficients to the transversal filter, and which, according to control over the transversal filter by the control signal generating circuit using tap coefficients generated through correlation and time-average processing of a polarity signal indicating polarity of the digital-baseband signal and a polarity signal indicating polarity of the output signal of the transversal filter, makes symmetric an asymmetric impulse response within said inputted digital-baseband signal due to said fading in said propagation paths and outputs a matched signal;

    a decision feedback equalizer that includes a decision feedback transversal filter for inputting said matched signal from the adaptive matched filter and a control signal generating circuit for supplying tap coefficients to the decision feedback transversal filter, and which, according to control over the decision feedback transversal filter by the control signal generating circuit using tap coefficients generated through correlation and time-average processing of a polarity signal included in the inputted matched signal and an error signal within the signal outputted after equalizing, eliminates from the inputted signal intersymbol interference due to said fading and outputs a signal after equalizing; and

    a reset circuit for fixing to predetermined values said tap coefficients of the adaptive matched filter when fading is judged to occur in the range 0<

    ρ

    <

    1(ρ

    being the ratio of the amplitude of a reflected wave to the amplitude of a principal wave) based on the tap coefficients of the decision feedback equalizer.

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