sumproduct_example.m

density evolution for LDPC codes design and some related documents

% =================================================================
% sumproduct_example.m
% (C) Tadashi Wadayama, 2002
% =================================================================
function sumproduct_example()
% -----------------------------------
% 晞崋僷儔儊乕僞丄専嵏峴楍偺撉傒崬傒
% -----------------------------------
filename = '6.3.spmat';			% 専嵏峴楍僼傽僀儖(spmat宍幃)
fp = fopen(filename,'r');
n = fscanf(fp,'%d',1);			% 晞崋挿
m = fscanf(fp,'%d',1);			% 専嵏婰崋悢
kmax = fscanf(fp,'%d',1);		% 峴廳傒偺嵟戝抣
jmax = fscanf(fp,'%d',1);		% 楍廳傒偺嵟戝抣
for j = 1:m
  row_weight(j) = fscanf(fp,'%d',1);	% 奺峴偺峴廳傒
end;
for j = 1:n
  column_weight(j) = fscanf(fp,'%d',1);% 奺楍偺楍廳傒
end;
counter = zeros(1,n);
row_list = zeros(m,kmax);
for i = 1:m
  for j = 1:row_weight(i);
    a = fscanf(fp,'%d',1);
    row_list(i,j) = a;
    counter(a) = counter(a) + 1;
    column_list(a,counter(a)) = i;
  end
end;
fprintf('n = %d, m = %d\n',n,m);
fprintf('kmax = %d, jmax = %d\n',kmax,jmax);
fprintf('row_list\n');disp(row_list);
fprintf('column_list\n');disp(column_list);
% -----------------------------------
% 暘嶶偺弶婜愝掕偲懳悢栟搙斾偺寁嶼
% -----------------------------------
%捠怣楬偼AWGN捠怣楬傪壖掕
rword = [1.620803,0.264281,-0.031637,-0.127654,0.746347,1.003543]; % 庴怣岅
var = 0.794328;				% 暘嶶
lambda = 2.0/var * rword;		% 懳悢栟搙斾
% -----------------------------------
% 懳悢椞堟sum-product暅崋朄
% -----------------------------------
alpha = zeros(m,n);beta = zeros(m,n);
loop_max = 5;				% 嵟戝斀暅夞悢
for loop_counter = 1: loop_max;
% 峴張棟
  for i = 1:m
    for j = 1:row_weight(i);
      sum = 0.0; prod = 1.0;
      for k = 1:row_weight(i);
	if k ~= j
	  tmp = lambda(row_list(i,k)) + beta(i,row_list(i,k));
	  sum = sum + gallager_f(abs(tmp));
	  prod = prod * sign(tmp);
	end;
      end;
      alpha(i,row_list(i,j)) = prod * gallager_f(sum);
    end;
  end;
% 楍張棟
  for i = 1:n
    sum2 = 0.0;
    for j = 1:column_weight(i);
      sum = 0.0;
      for k = 1:column_weight(i);
	if k ~= j
	  sum = sum +  alpha(column_list(i,k),i);
	end;
      end;
      beta(column_list(i,j),i) = sum;
      sum2 = sum2 + alpha(column_list(i,j),i);
    end;
    posterior(i) = lambda(i) + sum2;
  end;
  fprintf('----------------------------- 儖乕僾 = %d\n',loop_counter);
  fprintf('奺價僢僩偺懳悢帠屻妋棪斾:\n');
  disp(posterior);
end;