function y=demodulate_sig(x1,x2)
xx1(find(x1>=2))=3;
xx1(find((x1<2)&(x1>=0)))=1;
xx1(find((x1>=-2)&(x1<0)))=-1;
xx1(find(x1<-2))=-3;
xx2(find(x2>=2))=3;
xx2(find((x2<2)&(x2>=0)))=1;
xx2(find((x2>=-2)&(x2<0)))=-1;
xx2(find(x2<-2))=-3;
temp1=zeros(1,length(xx1)*2);
temp1(find(xx1==-1)*2)=1;
temp1(find(xx1==1)*2-1)=1;
temp1(find(xx1==1)*2)=1;
temp1(find(xx1==3)*2-1)=1;