function x=det_QPSK(I,Q)

% x=det_QPSK(I,Q,modulation)
%
% QPSK detection
% I,Q :  input symbols
% x : output bit stream
% I,Q,x are column vectors.

i=sqrt(-1);
[m,n]=size(I);
if n~=1
    error('Input vector I should be a column.');
end
[m,n]=size(Q);
if n~=1
    error('Input vector Q should be a column.');
end

x= kron(I<0,[1 0].') + kron(Q<0,[0 1].');