gen_h.m

gen_H:利用随机pi矩阵排列而成的LDPC稀疏校验矩阵产生； girthlenth：计算产生的矩阵H的围长

function H=gen_H(pi_matrix_dim)
clc
% need to call search_queen;rotMatrix;
m=pi_matrix_dim;
dv=3;% column weight
dc=4;% row weight
N=dc*m;% input random bit stream length

A=search_queen(m);  % use queen search algorithm to get a pi matrix;
B=rotMatrix(A);     
C=rotMatrix(B);
D=rotMatrix(C);
% B=search_queen(m); 
% C=search_queen(m); 
% D=search_queen(m); 

HD=[A B C D;B C D A;C D A B];  
HP=eye(dv*m);
HP_temp=eye(dv*m-1);
HP_temp1=[zeros(1,dv*m);HP_temp zeros(dv*m-1,1)];
HP=HP+HP_temp1;
H=[HP HD];

InputCode=(randn(1,N)>0.15),       % Information codeword;
sp=zeros(1,dv*m);                  % calculate checkbits value;
sptemp=dot(HD(1,:),InputCode);     
sp(1)=mod(sptemp,2);
for i=2:dv*m
    sptemp=dot(HD(i,:),InputCode);
    sp(i)=mod(sptemp+sp(i-1),2);
end

OutputCode=[sp InputCode],

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

save Hdata.mat H;
%
disp('H matrix has been saved to Hdata.mat file!');

S_figure=mod(H*OutputCode',2);

if sum(S_figure)==0
    disp('Generate H matrix correctly!');
else
    disp('Fail to generate H matrix !');
end