function y=mod_4PSK(x)

% 4PSK Modulator 
%
% x -- binary input bits.  The length  of x must be multiples of 4.
% y -- complex output. vector 

% cons   =exp(j*([ 1 4 2 3 8 5 7 6]*pi/4-pi/8));
cons   =exp(j*([ 8 2 6 4]*pi/4));
% cons   =exp(j*([ 1 8 2 3 7 6 5 4]*pi/4));
temp = reshape(x,2,length(x)/2);
y = cons(bi2de(temp')+1);