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Spectrally efficient digital modulation method and apparatus

  • US 4,737,969 A
  • Filed: 01/28/1987
  • Issued: 04/12/1988
  • Est. Priority Date: 01/28/1987
  • Status: Expired due to Fees
First Claim
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1. A method of transmitting QAM signals on respective in-phase (I) and quadrature (Q) channels comprising the steps of:

  • retrieving an optimized pulse stored in a memory, wherein said pulse in generated by;

    selecting an autocorrelation function R(t) exhibiting the property of low intersymbol interference and corresponding to a first pulse;

    windowing said autocorrelation function R(t) with a function selected to attenuate the tails of said autocorrelation function R(t) while substantially preserving the low intersymbol interference property thereof, thus generating a windowed autocorrelation function Rw (t) corresponding to a second pulse;

    determining the power spectrum of said second pulse by taking the Fourier transform of said windowed autocorrelation function Rw (t);

    determining the voltage spectrum of said second pulse;

    truncating said voltage spectrum at upper and lower frequency bounds to generate a truncated voltage spectrum corresponding to a third pulse, said upper and lower frequency bounds being selected to minimize the occupied bandwidth of said third pulse while substantially preserving the low intersymbol interference property thereof;

    determining the inverse Fourier transform of said truncated voltage spectrum, andwindowing the inverse Fourier transform of said truncated voltage spectrum with an arbitrary function to generate said optimized pulse, said arbitrary function being selected to minize the length of said optimized pulse in the time domain while substantially preserving its low intersymbol interference property and substantially minimizing said occupied bandwidth;

    transmitting the optimized pulse thus formed on one of said I an Q channels when a 1 is desired to be transmitted, andtransmitting the negative of the optimized pulse thus formed on one of said I and Q channels when a 0 is desired to be transmitted.

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