function y=qpsk_modul(x)
for k=1:length(x)./2
    temp1=x((1:2)+(k-1)*2);
     yy=temp1(1)*2+temp1(2);
     y_t=0;
     switch yy,
      case 0,
        y_t=1+i;
      case 1,
        y_t=-1+i;
      case 2,
        y_t=1-i;
      case 3,
        y_t=-1-i;
      otherwise,
          disp('error');   
     end
   y(k)=y_t;
end