lmf.m

线性调频信号的短时傅立叶变换

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 线性调频信号%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
k=20;                                      
fs=250;                                     
SNR=10;
n=0:1000-1;                                
x=exp(j*pi*k*(n/fs).^2);
x=awgn(x,SNR);
subplot(221);
plot(n/fs,real(x));
title('线性调频信号');
xlabel('时间');
ylabel('振幅');
%%%%%%%%%%%%%%%%%%%%%%%%%% 线性调频信号频谱 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
P=fft(x);
subplot(222);
plot(n/length(n)*fs,abs(P));
title('线性调频信号频谱');
xlabel('频率');
ylabel('振幅');
%%%%%%%%%%%%%%%%%%%%%%%%%%%% 短时傅立叶变换 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
N=40;
NFFT=512;
N1=round((1000-N)*2/N+1);
w=gausswin(N);
w=rot90(w);
STFT=zeros(N1,NFFT);
for i=1:N1;
    xt=x((i-1)*N/2+1:(i-1)*N/2+N);
    xt=xt.*w;                     %加高斯窗
    STFT(i,:)=fft(xt,NFFT);
end
fn=(1:NFFT)*fs/NFFT;
tn=(1:N1)*N/2/fs;
[F,T]=meshgrid(fn,tn);
subplot(223);
mesh(F,T,abs(STFT));
title('STFT');
xlabel('频率');
ylabel('时间');

subplot(224);
contour(T,F,abs(STFT));
title('T-F等高图');
xlabel('时间');
ylabel('频率');