matched_filter.m

对ASK调制解调进行了仿真,包括程序仿真和模型仿真

function [y]=matched_filter(nt,taup,f0,b,rmin,rrec,tr,trcs,winid)
eps=1.0e-16;

htau=taup / 2.;
c=3.e8; 
n=fix(2.*taup*b);
m=power_integer_2(n);
nfft=2.^m; 
x(nt,1:nfft)=0.;
y(1:nfft)=0.;
replica(1:nfft)=0.;  
winid=2;
if (winid==0.)
    win(1:nfft)=1.;
    win=win';
else
    if (winid==1.)
        win=hamming(nfft);
    else 
        if (winid ==2.)
            win =kaiser(nfft,pi);
        else
            if (winid ==3.)
                win =chebwin(nfft,60);
            end 
        
        end
    
    end

end
deltar= c/2./b;
max_rrec=deltar*nfft/2.;  
maxr=(max(tr)-rmin)*10^3;  
if (rrec>max_rrec | maxr>=rrec)
 'Error. Receive window is too large ; or scatterers fall outside window'

end
trec=2.*rrec/c;
deltat=taup/nfft;
t=0:deltat:taup-eps;
uplimit=max(size(t));
replica(1:uplimit)=exp(i*2.*pi*(.5*(b/taup).* t.^2));
figure(3)
subplot(2,1,1)
plot(real(replica))
title('Matched filter frequency domain response')
subplot(2,1,2)
plot(fftshift(abs(fft(replica))));
title('Matched filter frequency domain response')
for j=1:nt
    t_tgt=2.*(tr(j)-rmin)*10^3/c+htau;
    x(j,uplimit)=trcs(j).*exp(i*2.*pi* ...
        (.5*(b/taup).*(t+t_tgt).^2));
    y=y+x(j,:);
end
figure(1)
plot(t,real(y),'k')
xlabl('Relative delay-seconds')
ylabel('Uncompressed echo')
title('Zero delay coinde with minimum range')
rfft=fft(replica,nfft);
yfft=fft(y,nfft);
out=abs(ifft((rfft.*conj(yfft).* win')) ./ (nfft));
figure(2)
time=-htau:deltat:htau-eps;
plot(time,out,'k')
xlabel('Relative delay-second')
title('Zero delay coincide with minimum range')
grid on 
function n=power_integer_2(x)
m=0.;
for j=1:30
    m=m+1.;
    delta=x-2.^m;
    if (delta<0.)
    n=m;
    return 
    else     
    end
end