资源简介
主要是基于删除信道下的LDPC码的编译码的实现 在MATLAB环境中运行实现
代码片段和文件信息
% function [degreesrholambdastats]=CompLeftExp(Ra);
%
% Computes degree distributions from the exponential
% family
%
% f(x;a) =(exp(a*x)-1)/(exp(a)-1)
%
% (“Tornado sequences“). Uses explicit formulas for the Taylor
% coefficients of f and g.
%
% Input: Rate 00
%
% Output:
% degrees=[a_r a_l N M] average and maximal degrees
% of right and left degree distributions
% rho 1xN array of right degrees
% lambda 1xM array of left degrees
% stats [deltaepsilonmuDeltaLambda2]
% distances to capacity 1-R comparison to
% lower bounds and fraction of degree 2 variable
% nodes Lambda2=lambda2*a_l/2
%
% Author: P. Oswald
% Last changed: 10/4/2002
function [degreesrholambdastats]=CompLeftExp(Ra);
%
% Safety bounds for degrees
Nmax=20000;Mmax=20000;
% Computation of a_r N and rho
% by taking a long enough piece of the Taylor series of f
b=exp(a)-1;Ir0=(b-a)/(a*b); % Ir0 = int_[01] f(x) dx
rho=[];c=a/b;Ir=0;n=2;
while Ir0-Ir>0.0000000001&n<=Nmax
rho=[rho c];c=c/n;Ir=Ir+c;c=c*a;n=n+1;
end
c1=sum(rho);rho=rho/c1;N=n-1;ar=c1/Ir;
%
% Computation of a_l M lambda and delta
% by implementing Step (2) and (3) of Algorithm 1.
% This is based on hand-derived recursions for the Taylor coefficients
% g_k of g which lead to recursions for s_k and sigma_k and finally
% to finding t such that hat(I)(t)=1/a_l where a_l=a_r*(1-R)
% is the average degree of the left (variable) nodes.
al=ar*(1-R);b=b/exp(a);
c=b/a;sk=c;c1=c/2;sigmak=c1;lambda=[];
if al<2
disp(‘Average degree of left nodes too small (decrease R or increase a)‘);
M=0;lambda=[];stats=[];
else
if al==2
lambda=1;M=2;delta=c;
else
m=2;q=sigmak/sk;
while q*al>1&m lambda=[lambda c];c=c1*b*(m-1);sk=sk+c;
m=m+1;c1=c/m;sigmak=sigmak+c1;q0=q;q=sigmak/sk;
end
if q*al>1&m==Mmax
disp(‘M too big (reduce a or increase R or change Mmax)‘);
M=m;lambda=[];stats=[];
else
M=m;t1=(al*sigmak-sk)/(al*c1-c);
delta=(sk-t1*c);lambda=[lambda (1-t1)*c]/delta;
end
end
%
% Computation of output
epsilon=1-delta/(1-R);
b=ar*log(R);mu=b/log(epsilon);Delta=epsilon/exp(b);
Lambda2=lambda(1)*al/2;stats=[delta epsilon mu Delta Lambda2];
end
degrees=[ar al N M];
% End CompLeftExp.m
属性 大小 日期 时间 名称
----------- --------- ---------- ----- ----
目录 0 2011-05-16 13:32 chandhuLDPC\
文件 2383 2009-01-05 21:02 chandhuLDPC\CompLeftExp.m
文件 2154 2011-05-12 18:32 chandhuLDPC\CompLeftPoly.m
文件 2273 2009-01-05 21:03 chandhuLDPC\CompLeftPoly2c.m
文件 2782 2009-01-05 21:05 chandhuLDPC\CompLeftSelf.m
文件 1570 2009-01-05 21:08 chandhuLDPC\main.m
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