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% exa010201a.m,  for  example 1.2.2 
% 说明信号的子带分解； 
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clear 
n=256; w=pi/5; pow=0.08; 
u=randn(1,n); 
umean=mean(u); 
u=u-umean; 
u_p=dot(u,u)/n; 
u=u.*sqrt(pow/u_p); 
 
   for j=1:n 
      signal(j)=cos(0.8*w*j)+cos(1.5*w*j); 
   end; 
   signal=2*signal+u; 
%   figure(2) 
subplot(211) 
plot(signal);grid on; 
ylabel(' signal x(t)'); 
 
subplot(212) 
pf=fft(signal,n); 
for i=1:128 
   t(i)=(i-1)/256; 
   p(i)=abs(pf(i))^2; 
   p(i)=10*log10(p(i)); 
end 
plot(t,p);grid on; 
ylabel(' Spectrum of x (dB)');