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

function afwig = WignerDist(sig) 
% WignerDist -- Alias-Free Wigner-Ville Distribution 
%  Usage 
%    afwig = WignerDist(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 
%	Interpol2 
% 
%  References 
%   Mallat's book, sections 4.5.1 and 4.5.4 
% 
sig = sig(:); 
N   = length(sig); 
sig = Interpol2(sig); 
f = [zeros(2*N,1) sig zeros(2*N,1)]; 
afwig = zeros(N, N); 
q  = (0 : 2*N-1); 
p(1:N) = q(1:N); 
p(N+1:2*N) = q(N+1:2*N) - 2*N; 
for n=1:N, 
     nplus    = 2*n + p; 
     nminus   = 2*n - p; 
    x = f(2*N+nplus) .* conj(f(2*N+nminus)); 
    aux = fft(x); 
    afwig(:,n) = aux(1:2:2*N-1)'; 
end 
% this should be zero : 
max(max(abs(imag(afwig(1:N/2,:))))); 
abstf = real(afwig(1:N/2,:)).*(real(afwig(1:N/2,:))>=zeros(N/2,N)); 
tfmax = max(max(abstf)); 
tfmin = min(min(abstf)); 
colormap(1-gray(256)) 
image(linspace(0,N,N),linspace(0,N/2,N/2),256*(abstf-tfmin)/(tfmax-tfmin)); 
axis('xy') 
title(''); 
xlabel('Time') 
ylabel('Frequency') 
 
% Written by Maureen Clerc and Jerome Kalifa, 1997 
% clerc@cmapx.polytechnique.fr, kalifa@cmapx.polytechnique.fr 
     
     
     
%    
% 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 
%