%
% FUNCTION 2.10 : "cp0203_qpsk_mod"
%
% This function receives a binary stream in input ('bits')
% and returns the corresponding sequence of QPSK symbols
%  ('S'),
% plus the two sequences 'Sc' and 'Ss' containing the real
% and the imaginary part of each symbol
%
% Programmed by Guerino Giancola
%


function [r_bits] = cp0203_qpsk_demod(S)


ns = length(S);         % number of bits
nb = ceil(2*ns);        % number of symbols

r_bits = zeros(1,nb);

for i = 1 : ns
    if (angle(S(i))>0 & angle(S(i))<pi/2)
        r_bits(2*(i-1)+1) = 1;
        r_bits(2*(i-1)+2) = 1;
    end
    if (angle(S(i))>pi/2 & angle(S(i))<pi)
        r_bits(2*(i-1)+1) = 0;
        r_bits(2*(i-1)+2) = 0;
    end
    if (angle(S(i))>-pi/2 & angle(S(i))<0)
        r_bits(2*(i-1)+1) = 1;
        r_bits(2*(i-1)+2) = 0;  
    end
    if (angle(S(i))>-pi & angle(S(i))<-pi/2)
        r_bits(2*(i-1)+1) = 0;
        r_bits(2*(i-1)+2) = 1;       
    end
end