%generates the 4PSK Gray encoded symbols
%inputs/outputs
%input -- binary (0,1) vector 
%num_bits -- length of input (make it even)
%out_vec -- 4PSK output of length num_bits/2
% 00 -- 1; 01 -- j; 11 -- -1; 10 -- -j

function [out_vec] = QPSK_Gray(in_vec, num_syms)

    for ii=1:num_syms
        if((in_vec(2*ii-1)==0)&(in_vec(2*ii)==0))
            out_vec(ii)=1;
        elseif((in_vec(2*ii-1)==0)&(in_vec(2*ii)==1))
            out_vec(ii)=i;
        elseif((in_vec(2*ii-1)==1)&(in_vec(2*ii)==1))
             out_vec(ii)=-1;
        else
             out_vec(ii)=-i;
        end
    end