c10ex12.m

连续与离散信号系统的Matlab仿真示例代码．

%	This program utilizes the psd function to plot the 
%	power spectral density of a cosine signal in Gaussian
%	noise for various combinations of FFT size and number of
%	segments averaged - Example 10-12
%
I_noise = input('Enter 1 for Gaussian noise of variance 5 added to signal ');
N_tot = 2048;
N_seg_0 = 8;
k = 1:N_tot;
f_0 = 20;
del_t = 0.005;
f_samp = 1/del_t;
t = del_t*(k-1);
max_t = max(t);
x = cos(2*pi*f_0*(k-1)*del_t);
n = sqrt(5)*randn(size(x));
if I_noise == 1
	x = x+n;
else
	x = x;
end
subplot(4,1,1),plot(t,x),axis([0 2 -5 5]),xlabel('t'),ylabel('x(t)')
for l = 1:3
N_seg = N_seg_0/2^(l-1);
NFFT = N_tot/N_seg;
[P, F] = PSD(x,NFFT,f_samp);
subplot(4,1,l+1),plot(F,P),axis([0 100 -5 80]),ylabel('PSD - dB'),...
	text(40, 50, ['FFT points = ',num2str(NFFT),'; no. segments = ',num2str(N_seg)])
	if l == 3
		xlabel('frequency - Hz')
	end
end