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One frequency repeater for a digital microwave radio system with cancellation of transmitter-to-receiver interference

  • US 4,701,935 A
  • Filed: 01/09/1986
  • Issued: 10/20/1987
  • Est. Priority Date: 01/09/1985
  • Status: Expired due to Term
First Claim
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1. A one frequency repeater for a digital radio wave transmission system wherein a carrier is modulated by a digital baseband signal and is transmitted as a digital radio wave signal, said repeater comprising:

  • a first digital signal source for producing a first digital baseband signal;

    transmitter circuit means coupled to said first digital signal source for producing a first digital radio wave signal modulated by said first digital baseband signal, said first digital radio wave having a first carrier frequency;

    transmitting antenna means for radiating said first radio frequency signal supplied from said transmitter circuit means;

    receiving antenna means for receiving a second digital radio wave signal modulated by a second digital baseband signal, said second digital radio wave signal having a second carrier frequency substantially equal to said first carrier frequency, said receiving antenna means receiving said first digital radio wave signal as a transmitter-to-receiver interference signal due to coupling between said first transmitting antenna means and said first receiving antenna means;

    receiver circuit means for extracting said second digital baseband signal by demodulating said second radio wave signal received at said receiving antenna, said demodulated second digital baseband signal being accompanied by a baseband interference signal derived from said transmitter-to-receiver interference signal;

    means coupled to said first digital signal source for producing an estimated-interference signal corresponding to said baseband interference signal from said first digital baseband signal, said estimated-interference signal producing means comprising transversal filter means comprising a delay line with a predetermined number of tap gains; and

    interference cancelling means coupled to said receiver circuit means and said estimated-interference signal producing means for cancelling said baseband interference signal from an output signal of said receiver circuit means using said estimated-interference signal to thereby produce said demodulated second digital baseband signal without said baseband interference signal;

    decision circuit means for detecting said second digital baseband signal from an output of said interference cancelling means and regenerating said second digital baseband signal; and

    tap gain control means for controlling said tap gains, said tap gain control means comprising first subtracting means for subtracting said regenerated second digital baseband signal from said output signal of said interference cancelling means and providing a first error signal, first multiplier means for multiplying said first digital baseband signal by said first error signal and providing a multiplied signal, and low-pass filter means for smoothing said multiplied signal, said smoothed multiplied signal being supplied to said transversal filter means to control said tap gains so that said first error signal is zero.

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