SNR_DB=[0:1:12];
sum=1000000;
data= randsrc(sum,2,[0 1]);
[a1,b1]=find(data(:,1)==0&data(:,2)==0);
message(a1)=-1-j;
[a2,b2]=find(data(:,1)==0&data(:,2)==1);
message(a2)=-1+j;
[a3,b3]=find(data(:,1)==1&data(:,2)==0);
message(a3)=1-j;
[a4,b4]=find(data(:,1)==1&data(:,2)==1);
message(a4)=1+j;
scatterplot(message)
title('QPSK 星座图')
A=1;
Tb=1;
Eb=A*A*Tb;
P_signal=Eb/Tb;
NO=Eb./(10.^(SNR_DB/10));
P_noise=P_signal*NO;
sigma=sqrt(P_noise);
for Eb_NO_id=1:length(sigma)
noise1=sigma(Eb_NO_id)*randn(1,sum);
noise2=sigma(Eb_NO_id)*randn(1,sum);
receive=message+noise1+noise2*j;
resum=0;
total=0;
m1=find(angle(receive)<=pi/2&angle(receive)>0);
remessage(1,m1)=1+j;
redata(m1,1)=1;
redata(m1,2)=1;
m2= find( angle(receive)>pi/2&angle(receive)<=pi);
remessage(1,m2)=-1+j;
redata(m2,1)=0;
redata(m2,2)=1;
m3=find( angle(receive)>-pi&angle(receive)<=-pi/2);
remessage(1,m3)=-1-j;
redata(m3,1)=0;
redata(m3,2)=0;
m4=find( angle(receive)>-pi/2&angle(receive)<=0);
remessage(1,m4)=1-j;
redata(m4,1)=1;
redata(m4,2)=0;
[resum,ratio1]=symerr(data,redata);
pbit(Eb_NO_id)=resum/(sum*2);
