function [x1 x2 bin] = stTrellis(G)
% Create space time trellis structure 
% G    : generator matrix
% 
% x1   : matrix of current states trellis
% x2   : matrix of next states trellis
% bin  : matrix of binary bits order: 0,1,2,... 2^col 
%  
%
% Copyright Bagawan S. Nugroho, 2006

[row col] = size(G);

% M-ary, QPSK
m = 4;   

% Initialize the trellis
N = 2^col;
bin = zeros(1, col);
x = zeros(N, 2);

% Generate the trellis 
for i = 1:N
   % Get the binary vector with type of char and convert into numeric
   b = int8(dec2bin(i - 1)) - 48;  
   % Fill-in into size(1, col) vector
   bin(i, col - length(b) + 1:col) = b;
   % Get the trellis output
   x(i,:) = mod((bin(i,:) * G'), 4);
end

% States trellis
x1 = (reshape((x(:,1))', m, N/m))';
x2 = (reshape((x(:,2))', m, N/m))';