function y=modulation(x)
n=length(x);
y=zeros(1,n);
dem=zeros(1,8);
for j=1:n/8
    for k=1:8
        if x((j-1)*8+k)==0
            dem(k)=1+i;
        elseif x((j-1)*8+k)==1
            dem(k)=-1+i;
        elseif x((j-1)*8+k)==2
            dem(k)=-1-i;
        else dem(k)=1-i;
        end
    end
    dem=ifft(dem,8);
    y((j-1)*8+1:j*8)=dem;
end