ge_cap.m

该文件包括几篇比较关于LDPC编码核心的基础读物

function y = ge_cap(b,g,pb,pg,iter)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% This function calculates the capacity of a Gilbert-Elliott
% channel according to the method of Mushkin and Bar-David (1989).
%
% This implementation is Copyright (C) 2003 by A. W. Eckford,
% and is released into the public domain as long as this
% entire comment is preserved in the source.
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


% The function takes five parameters:
% b - is the transition probability from the good to bad state
% g - is the transition probability from the bad to good state
% pb - is the inversion probability in the bad state
% pg - is the inversion probability in the good state
% iter - the number of iterations to use in the calculation
% (the exact capacity is calculated in the limit as iter -> infinity,
% so make this as large as is practical)

q = zeros(1,1001);
inc = (pb-pg)/1000;
tq = pg:inc:pb;
avg_coord = round((((b*pb + g*pg)/(b+g)) - pg)/inc) + 1;
q(avg_coord) = 1/inc;

mu = 1-g-b;

for c = 1:iter

	q1 = zeros(1,1001);
	for beta = pg:inc:pb

		beta_coord = round((beta-pg)/inc) + 1;
		alpha0 = pg + b*(pb-pg) + mu*(beta - pg)*(1-pb)/(1-beta);
		alpha0_coord = round((alpha0 - pg)/inc) + 1;
		alpha1 = pg + b*(pb-pg) + mu*(beta - pg)*pb/beta;
		alpha1_coord = round((alpha1 - pg)/inc) + 1;
		q1(alpha0_coord) = q1(alpha0_coord) + (1-beta)*q(beta_coord);
		q1(alpha1_coord) = q1(alpha1_coord) + beta*q(beta_coord);

	end

	
	q = q1;

end



trapz(tq,q);
H = -1*tq.*log2(tq) - (1-tq).*log2(1-tq);
EH = trapz(tq,H.*q);
y = 1-EH;