constellation_qam.m

This m file shows constellation for MQAM.

function [vect] = constellation_qam(k)
% function [vect] = constellation_qam(k)
%
% Rectangular signal-space constellations for MQAM
%
% Copyright (C) Olena Mingaliova, Alexander Konovalenko
%
% This program is free software; you can redistribute it and/or
% modify it under the terms of the GNU General Public License
% as published by the Free Software Foundation; either version 2
% of the License, or (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program; if not, write to the Free Software
% Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
%
% http://www.gnu.org/licenses/gpl.html
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% where:
%  M = 2^k, k is number of bits per symbol
% The output vect is Mx2 matrix
%
% test:
% v=constellation_qam(9);grid on; plot(v(:,1),v(:,2),'x');
%
%
% this function was tested with both MatLab & Octave
%


step = 2;

if k <= 1
   disp('ERROR: Incorrect input parameters, k<=1');
   return
end

M = 2^k;
%vect = zeros(M,2);

i = 1;
if mod(k,2) == 0
   vect = zeros(M,2);
   sqrtM = 2^(k/2);
   xmin = -sqrtM + 1;
   xmax = sqrtM - 1;
   ymin = -sqrtM + 1;
   ymax = sqrtM - 1;
   for x = xmin:2:xmax
      for y = ymin:2:ymax
         vect(i,1) = x;
         vect(i,2) = y;
         i = i + 1;
      end
   end
elseif k ~= 3
   % odd k
   square = constellation_qam(k-1); % vector
   square_side = 2^((k-1)/2) - 1;
   side2 = 2^(k-3)/(square_side + 1);
   xmin_sq = min(square(:,1));
   ymin_sq = min(square(:,2));
   % left rectangular:
   xmin = xmin_sq - step*side2;
   xmax = xmin + step*(side2 - 1);
   ymin = ymin_sq;
   ymax = ymin + step*square_side;
   
   left = zeros(square_side,2);
   right = left;
   down = left;
   up = left;
   j = 1;
   offset = (square_side + side2 + 1)*step;
   for x = xmin:step:xmax
      for y = ymin:step:ymax
         left(j,1) = x;
         left(j,2) = y;
	 right(j,1) = x + offset;
         right(j,2) = y;
         up(j,1) = y;
	 up(j,2) = x + offset;
         down(j,1) = y;
         down(j,2) = x;
         j = j + 1;
      end
   end
   vect = [left; square; right; up; down];
else
   vect = [-3 1; -3 -1; -1 1; -1 -1; 1 1; 1 -1; 3 1; 3 -1];
end

vect = sortrows(vect,2);