find_codegenerator.m

通信中常用的卷积码信道译码源码程序

function [g,varargout] = ...
    find_codegenerator(CGFile, coderate, constraint_length, varargin);

%------------------------------------------------------------------------------
% Find maximum free distance non-systematic code generator polynomials 
% for convolutional codes, or recursive systematic code generator
% polynomials for turbo codes.
% 
% Format:
% -------
% 
% Convolution:
% [g, [gen_form]] = ...
%  find_codegenerator(CGFile, coderate, constraint_length, ['non-recursive'])
% 
% Turbo:
% [g, [gen_form]] = ...
%  find_codegenerator(CGFile, coderate, constraint_length, 'recursive')
%
% 
% Author: MVe
% Date:   26.07.2002
%------------------------------------------------------------------------------

% Check function call format
tmp = length(varargin);
if tmp>0
  if tmp == 1
    gen_type = varargin{1};
    if ~or(strmatch(gen_type, 'non-recursive'),strmatch(gen_type, 'recursive'))
      error(sprintf('Unknown encoder / decoder type ''%s''', gen_type));
    end % if ~or(strmatch(gen_type, 'non-recursive'), ...
  end % if tmp == 1
else
  if tmp==0
    gen_type = 'non-recursive';
  else
    error('Wrong number of arguments');
    end % if tmp==0    
end % if tmp~=0

% Coderate in string-format
[det div] = rat(coderate);
coderate_s = [num2str(det) '/' num2str(div)];

% Check if coderate is valid

switch gen_type
 case 'non-recursive'  
  if sum([det~=1, div>4, div<2])>0
    error('Only coderates 1/k, k = 2,3,4 for NSC supported');
  end % if sum([det~=1, div>4, div<2])>0
 case 'recursive'
  if sum([det~=1, div>3, div<2])>0
    error('Only coderates 1/k, k = 2,3 for RSC supported');
  end % if sum([det~=1, div>3, div<2])>0
end % switch gen_type

tmp = textread(CGFile,'%s','delimiter','\n','whitespace','',...
	       'commentstyle','c++');

MatchB = ['#define CodeRate ', coderate_s, ' begins'];
BCode = strmatch(MatchB,tmp);
MatchE = ['#define CodeRate ', coderate_s, ' ends'];
ECode = strmatch(MatchE,tmp);

switch gen_type
 case 'non-recursive'  
  CodeGens = tmp(BCode(1)+1:ECode(1)-1);
 case 'recursive'
  CodeGens = tmp(BCode(2)+1:ECode(2)-1);
end % switch gen_type
  
% Clean-up redundant information (empty lines, comments)
i = 1;
while i <= length(CodeGens)
  if isempty(double(CodeGens{i}))
    CodeGens(i) = [];
  else
    i = i+1;    
  end
end
CodeGens(strmatch('%',CodeGens)) = [];

% Insert correct generator polynomial to variable 'CodeGenerator'
eval(CodeGens{constraint_length-1});
if isempty(CodeGenerator)
  error(sprintf('Codegenerator for %s-rate, K=%d, %s encoder not found ', ...
		coderate_s,constraint_length,gen_type));
else
  g = CodeGenerator;
end % if isempty(Codegenerator)  

% Codegenerator is in octal-form
varargout{1} = 'octal';