%BP迭代译码算法
function Outputdecode=LDPCDecode(Sign,row,col,block,H,sigma,IterNum)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%clear
%clc
%row=16;col=32;block=4;SNR=1;k=1; 行16，列32 块4
%H=GenH(row,col,block);
%InputM=randint(1,16*4);
%PerEncode=LDPCEncode(InputM,row,col,block,H);3
%[Sign,OutputCode,ErrCode,sigma]=BPSKAn(PerEncode,SNR)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% PerData用于误比特判断
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
rows=row*block;
cols=col*block;
LLRsigma=sigma;
IterNumLen=length(IterNum);
%%%%%%%%%%%%%%%%%%%%%%%%%%
ErrDecode=zeros(1,IterNumLen);
%Outputdecode=zeros(IterNumLen,cols);
%Outputdecode=zeros(2,cols);
%信道初始LLR值
LLRInitial=zeros(1,cols);
for i=1:cols
LLRInitial(1,i)=2*Sign(1,i)/(LLRsigma^2);
end
LLRQ=zeros(rows,cols); %变量点到校验点的LLR信息
LLRR=zeros(rows,cols); %校验点到变量点的LLR信息
%初始化LLRQ
for i=1:rows
for j=1:cols
if H(i,j)~=0
LLRQ(i,j)=LLRInitial(1,j);
end
end
end
%迭代过程
%maxiter=IterNum(IterNumLen);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%OutputdecodeNum=zeros(maxiter,cols);
Outputdecode=zeros(1,cols);
%m=1;
for iter=1:IterNum
%校验点到变量点的LLR计算
for i=1:rows
for j=1:cols
if H(i,j)~=0%判断H矩阵不为0的点进行迭代计算
LLRRPro=1;%计算LLRR中Beita的积
%计算变量节点传向校验节点的消息
for k=1:cols
if H(i,k)~=0&&k~=j%利用H矩阵对LLRQ值进行判断
LLRRPro=LLRRPro*tanh(LLRQ(i,k)/2);
end
end
%信息为0时的处理
if LLRRPro~=0
LLRR(i,j)=2*atanh(LLRRPro);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%if LLRR(i,j)==inf||LLRR(i,j)==-inf
% LLRR(i,j)=0;
%end
else
LLRR(i,j)=0;
end
end
end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%LLRR
%变量点到校验点的LLR计算
for i=1:cols
for j=1:rows
LLRMid=0;
if H(j,i)~=0
for k=1:rows
if k~=j&&H(k,i)~=0
LLRMid=LLRR(k,i)+LLRMid;%外信息加上除去本身的信道信息
end
end
LLRQ(j,i)=LLRMid+LLRInitial(1,i);%出过错
end
end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%LLRQ
%迭代后码字判断
LQ=zeros(1,cols);
%计算后验概率
for i=1:cols
LQMid=0;
for j=1:rows
LQMid=LLRR(j,i)+LQMid;
end
LQ(1,i)=LQMid+LLRInitial(1,i);
end
%估计码字
decode=zeros(1,cols);
%%%%%%%%%%%%%%%%%%
%LQ
for i=1:cols
if LQ(1,i)<0
decode(1,i)=1;
end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%decode
%SUM=sum(abs(PerData-decode(1:(length(PerData)))))
%迭代次数判断以及译码码字和误比特输出
%if IterNum(1,m)==iter
% ErrDecode(1,m)=sum(abs(PerData-decode(1:(length(PerData)))));
%if ErrDecode(1,m)>200&&m==maxiter
% Outputdecode=decode;
%(1,:)=decode;
%Outputdecode(2,:)=[PerData,ones(1,length(PerData))];
% end
% m=m+1;
%end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%if ErrDecode(1,IterNumLen)>200
% break
%end
%码字检测
check=[];
check=H*decode';
mark=0;%迭代译码结束标志
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%sumerr=sum(mod(check,2))
for i=1:rows
if mod(check(i,1),2)==1
mark=1;
break
end
end
if mark==0
break
end
end
Outputdecode=decode;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%DeNum=sum(abs(decode-PerEncode));
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%判断迭代译码后的码字是否正确
%if mod(sum(check),2)~=0
% ErrDecode=1;
% end
%end
