7-5.m

matlab数字信号与应用源代码7

%例程7－5  基于LMS算法的系统辨识

clear
clc
ee=0;
fs=800;
det=1/fs;
f1=100;
f2=200;
t=0:det:2-det;
x=randn(size(t))+cos(2*pi*f1*t)+cos(2*pi*f2*t);
%未知系统
[b,a]=butter(5,150*2/fs);
d=filter(b,a,x);
%自适应FIR滤波器
N=5;
delta=0.06;
M=length(x);
y=zeros(1,M);
h=zeros(1,N);
for  n=N:M
         x1=x(n:-1:n-N+1);
         y(n)=h*x1';
         e(n)=d(n)-y(n);
         h=h+delta.*e(n).*x1;
end
X=abs(fft(x,2048));
Nx=length(x);
kx=0:800/Nx:(Nx/2-1)*(800/Nx);
D=abs(fft(d,2048));
Nd=length(D);
kd=0:800/Nd:(Nd/2-1)*(800/Nd);
Y=abs(fft(y,2048));
Ny=length(Y);
ky=0:800/Ny:(Ny/2-1)*(800/Ny);
figure(1);
subplot(3,1,1)
plot(kx,X(1:Nx/2));xlabel('Hz')
title('原始信号频谱')
subplot(3,1,2)
plot(kd,D(1:Nd/2))
title('经未知系统后信号频谱');xlabel('Hz')
subplot(3,1,3)
plot(ky,Y(1:Ny/2))
title('经自适应FIR滤波器后信号频谱');xlabel('Hz')