function ZFL(b,h,n)
%Zero_forcing linear Equalizer co nhieu kenh truyen
% b:input       -nhap gia tri ngoai                               
% b=sign(rand(1,5)-.5)          %ma hoa BPSK 
% h:channel     -nhap gia tri ngoai                               
% n:noise       -nhap gia tri ngoai                               
% d:output
% eq_tap:bac cua bo can bang
%------------------
subplot(7,1,1); plot(abs(fft(h))); 
title('channel impulse respond');

eq_tap = length(h);
pulse=zeros(1, eq_tap); pulse(1)=1;

% --ZFL equalizer--
%fft(h) .* fft(eq) = fft(pulse)
eq = ifft(fft(pulse) ./ fft(h));
                            
ho = conv(b, h);              % channel output
No = .2;
n = No * n;
y = ho+n;                     % input Equalizer
d = conv(y, eq);              % equalizer output
subplot(7,1,7); stem(d); title('d chua ma hoa')
grid;
d = sign(d);

l=length(b);
e1 = abs(b - d(1:l))/2 ;  %error
BE1 = sum(e1)

e2 = abs(b - d(eq_tap +1 :eq_tap +l))/2 ;  %error
BE2 = sum(e2)

BE = min (BE1, BE2);
BER = BE / l

if BE1 <= BE2
     do = d(1:l);
     subplot(7,1,6); stem(e1,'x'); title('error')
else 
     do = d(eq_tap +1 :eq_tap +l);
     subplot(7,1,6); stem(e2,'x'); title('error')
end

subplot(7,1,2); stem(h(1:5),'filled'); title('channel')
grid;  
subplot(7,1,3); stem(eq,'b.'); title('equalizer')
grid;   
subplot(7,1,4); stem(b,'b.'); title('input')
grid;   
subplot(7,1,5); stem(do,'b.'); title('ZFL Equalizer output voi N_0=0.2')
grid;

return