global  dt  t  df  N
close all
N=2^10; %采樣點數(shù)
L=64;   %每碼元的采樣點數(shù)
M=N/L;   %碼元數(shù)
Rb=2;	%碼速率是2Mb/s , 碼速率單位是Mb/s
Ts=1/Rb;        %碼元間隔
dt=Ts/L;   %時域采樣間隔 , 時間單位是微秒
df=1/(N*dt)  %頻域采樣間隔 ,頻率單位為MHz
T=N*dt;          %截短時間
Bs=N*df/2;      %系統(tǒng)帶寬
Na=4;           %示波器掃描寬度為4個碼元
alpha=0.5;
db=input('眼圖的信噪比db=');
if db==[]|db>15|db<0
    db=15;
end;
b=0;
a=.5;
to=.5;
phi=0;
t=linspace(-T/2,T/2,N);
f=linspace(-Bs,Bs,N)+eps;
hr1=sin(pi*t/Ts)./(pi*t/Ts);
hr2=cos(alpha*pi*t/Ts)./(1-(2*alpha*t/Ts).^2);
hr=hr1.*hr2;
HR=abs(t2f(hr));
GT=sqrt(HR);
GR=GT;
C=1-a*exp(-j*(2*pi*f*to*Ts+phi));
H=C.*HR;
h=real(f2t(H));
for loop1=1:16
    Eb_N0(loop1)=(loop1-1);
    eb_n0(loop1)=10^(Eb_N0(loop1)/10);
    Eb=1;
    n0=Eb/eb_n0(loop1);
    sita=n0*Bs;
    n_err1=0;
    n_err2=0;
    for loop2=1:600
        a=abs(sign(randn(1,M)));
        imp=zeros(1,N);
        imp(L/2:L:N)=a/dt;
        IMP=t2f(imp);
        n_ch=sqrt(sita)*randn(size(t));
        nr=real(f2t(t2f(n_ch).*GR));
        sr1=real(f2t(IMP.*HR))+nr;
        sr2=real(f2t(IMP.*H))+nr;
        y1=sign(sr1(L*(.5+b):L:N));
        y2=sign(sr2(L*(.5+b):L:N));
        n_err1=n_err1+length(find(y1~=a));
        n_err2=n_err2+length(find(y2~=a));
    end
Pe2(loop1)=n_err2/(M*loop2);
Pe1(loop1)=n_err1/(M*loop2);
eb_n0=10.^(Eb_N0/10);
figure(1)
 semilogy(Eb_N0,0.5*erfc(sqrt(eb_n0)),'r');
hold on;
 semilogy(Eb_N0,Pe1+eps,'k');
hold on;
 semilogy(Eb_N0,Pe2+eps,'b');
 axis([0,13,1e-6,1]);
 legend('理想曲線','普通加性高斯白噪聲信道','多徑信道');
 title(['取樣時間偏差為0']);
    end 
 xlabel('Eb/N0')
 ylabel('Pe')