% 二進制輸入AWGN信道的容量 2007-6-4
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echo on
a_db=[-20:0.2:20];
a=10.^(a_db/10);
for i=1:201
    f(i)=quad('keep_fun',a(i)-5,a(i)+5,1e-3,[2],a(i));
    g(i)=quad('keep_fun',-a(i)-5,-a(i)+5,1e-3,[2],-a(i));
    c(i)=0.5*f(i)+0.5*g(i);
    echo off;
end
echo on;
pause
semilogx(a,c)
title('二進制輸入AWGN信道的容量')
xlabel('SNR')
ylabel('Capacity (bits/transmission)')