www.pudn.com > TimeFrequency.rar > WVDist_AF.m

function afwig = WVDist_AF(sig) 
% WVDist_AF -- Alias-Free Wigner-Ville Distribution 
%  Usage 
%    afwig = WVDist_AF(sig) 
%  Inputs 
%    sig     1-d signal 
%  Outputs 
%    afwig   complex-valued matrix representing the alias-free 
%            Wigner-Ville distribution of zero-extended signal with 
%            rows corresponding to frequencies and columns corresponding 
%            to times. 
% 
%  Side Effects 
%    Image Plot of the alias-free Wigner-Ville distribution 
% 
%  See Also 
%    WVDist, WVDist_AF, ImagePhasePlane 
% 
%  References 
%   Jechang Jeong and William J. Williams, 
%   "Alias-Free Generalized Discrete-Time Time-Frequency Distribution," 
%   IEEE Transactions on Signal Processing, vol. 40, pp. 2757-2765. 
% 
 
sig = sig(:); 
n   = length(sig); 
f   = [zeros(n,1); sig; zeros(n,1)]; 
afwig = zeros(n, n); 
ix  = 0:(n/2-1); 
zerosn = zeros(n,1); 
 
for t=1:n, 
  tplus    = n + t + ix; 
  tminus   = n + t - ix; 
  x = zerosn; 
  %even indices 
  x(1:2:(n)) = f(tplus) .* f(tminus); 
  %odd indices 
  x(2:2:(n)) = (f(tplus+1).*f(tminus) + f(tplus).*f(tminus-1))/2;   
  afwig(:, t) = 2* (fftshift(fft(x))); 
end 
 
abstf = real(afwig); 
tfmax = max(max(abstf)); 
tfmin = min(min(abstf)); 
colormap(1-gray(256)) 
image(linspace(0,1,n),linspace(0,1,n),256*(abstf-tfmin)/(tfmax-tfmin)); 
axis('xy') 
title('Alias Free Wigner Distribution'); 
xlabel('Time') 
ylabel('Frequency') 
 
% 
% Copyright (c) 1994-5, Shaobing Chen 
% 
     
     
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% Part of WaveLab Version 802 
% Built Sunday, October 3, 1999 8:52:27 AM 
% This is Copyrighted Material 
% For Copying permissions see COPYING.m 
% Comments? e-mail wavelab@stat.stanford.edu 
%