Code

Power Spectrum of Discrete PAM signals

Senthilkumar March 28, 2012 Coded in Scilab

This function is used to plot and compare the power spectra of different discrete PAM signlas such as: NRZ polar, NRZ Bipolar, NRZ Unipolar, Manchester format etc.

function [Sxxf_NRZ_P,Sxxf_NRZ_BP,Sxxf_NRZ_UP,Sxxf_Manch]=PowerSpectra_PAM()
a = input('Enter the Amplitude value:');
fb = input('Enter the bit rate:');
Tb = 1/fb;  //bit duration
f = 0:1/(100*Tb):2/Tb;
for i = 1:length(f)
  Sxxf_NRZ_P(i) = (a^2)*Tb*(sinc_new(f(i)*Tb)^2);
  Sxxf_NRZ_BP(i) = (a^2)*Tb*((sinc_new(f(i)*Tb))^2)*((sin(%pi*f(i)*Tb))^2);
  if (i==1)
    Sxxf_NRZ_UP(i) = (a^2)*(Tb/4)*((sinc_new(f(i)*Tb))^2)+(a^2)/4;
  else
    Sxxf_NRZ_UP(i) = (a^2)*(Tb/4)*((sinc_new(f(i)*Tb))^2);
  end
  Sxxf_Manch(i) = (a^2)*Tb*(sinc_new(f(i)*Tb/2)^2)*(sin(%pi*f(i)*Tb/2)^2);
end
//Plotting
a = gca();
plot2d(f,Sxxf_NRZ_P)
poly1= a.children(1).children(1);  
poly1.thickness = 2;  // the tickness of a curve.
plot2d(f,Sxxf_NRZ_BP,2)
poly1= a.children(1).children(1);  
poly1.thickness = 2;  // the tickness of a curve.
plot2d(f,Sxxf_NRZ_UP,5)
poly1= a.children(1).children(1);  
poly1.thickness = 2;  // the tickness of a curve.
plot2d(f,Sxxf_Manch,9)
poly1= a.children(1).children(1);  
poly1.thickness = 2;  // the tickness of a curve.
xlabel('f*Tb------->')
ylabel('Sxx(f)------->')
title('Power Spectral Densities of Different Line Codinig Techniques')
xgrid(1)
legend(['NRZ Polar Format','NRZ Bipolar format','NRZ Unipolar format','Manchester format']);
endfunction
//Result
//Enter the Amplitude value:1
//Enter the bit rate:1

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