exe0410_01.m

Matlab程序为清华大学胡广书版信号处理的上机习题答案

clear all；

% 构造三个不同频率的正弦信号的叠加作为试验信号
N=512;
f1=5;f2=5.5;fs=80;
stepf=fs/N;
n=0:N-1;
t=2*pi*n/fs;
n1=0:stepf:fs/2-stepf;
x=exp(-2*pi*f1*0.1*t).*cos(f1*t)+exp(-2*pi*f2*0.1*t).*cos(f2*t);
M=N;
W=exp(-j*2*pi/M);

% A=1时的czt变换
A=1;
Y1=czt(x,M,W,A);
plot(n1,abs(Y1(1:N/2)));grid on;

x3n0=[x,zeros(1,3*N)];
M3n0=M+3*N;
deltf=fs/M3n0;
n1=0:deltf:fs/2-deltf;
W=exp(-j*2*pi/M3n0);
Y3n0=czt(x3n0,M3n0,W,A);
figure
stem(n1,abs(Y3n0(1:M3n0/2)));grid on;

x7n0=[x,zeros(1,7*N)];
M7n0=M+7*N;
deltf=fs/M7n0;
n1=0:deltf:fs/2-deltf;
W=exp(-j*2*pi/M7n0);
Y7n0=czt(x7n0,M7n0,W,A);
figure
stem(n1,abs(Y7n0(1:M7n0/2)));grid on;

x15n0=[x,zeros(1,15*N)];
M15n0=M+15*N;
deltf=fs/M15n0;
n1=0:deltf:fs/2-deltf;
W=exp(-j*2*pi/M15n0);
Y15n0=czt(x15n0,M15n0,W,A);
figure
stem(n1,abs(Y15n0(1:M15n0/2)));grid on;

% DTFT
%Y2=abs(fft(x));
%subplot(312)
%plot(n1,abs(Y2(1:N/2)));grid on;

% 详细构造A后的czt 
%M=60;
%f0=7.2;
%DELf=0.05;
%A=exp(j*2*pi*f0/fs);
%W=exp(-j*2*pi*DELf/fs);
%Y3=czt(x,M,W,A);
%n2=f0:DELf:f0+(M-1)*DELf;
%subplot(313);plot(n2,abs(Y3));grid on;