fmodulate1.m

解调时考查频率偏移量的一种鉴频算法 采用了双滤波器结构

function diff_energy=fmodulate1(deltaf)
N=10240;                       %numbers of noise sample
fc=300;

fs=1000;
T=1/fs;
randn('state',0);

noise=randn(1,N);
B=fir2(60,[0,0.1,0.1,1],[1,1,0,0]);
A=1;
bandnoise=filter(B,A,noise);
n=1:N;
insignal=bandnoise.*cos(2*pi*(fc+deltaf)*n*T);
I=insignal.*cos(2*pi*fc*n*T);
Q=-insignal.*sin(2*pi*fc*n*T);


B2=fir2(60,[0,0.05,0.05,1],[1,1,0,0]);
IB1=B2.*cos(2*pi*0.1*fs/2*[1:length(B2)]*T);
QB1=B2.*sin(2*pi*0.1*fs/2*[1:length(B2)]*T);
I11=filter(IB1,A,I);
I12=filter(QB1,A,I);
Q11=filter(IB1,A,Q);
Q12=filter(QB1,A,Q);
I1=I11-Q12;
Q1=I12+Q11;
IB2=IB1;
QB2=-QB1;
I21=filter(IB2,A,I);
I22=filter(QB2,A,I);
Q21=filter(IB2,A,Q);
Q22=filter(QB2,A,Q);
I2=I21-Q22;
Q2=I22+Q21;

energy1=sum(abs(I1+i*Q1).^2);
energy2=sum(abs(I2+i*Q2).^2);
diff_energy=energy1-energy2;