www.gusucode.com > 构造围长8列重4的准循环的LDPC码的MATLAB源码 > 构造围长8列重4的准循环的LDPC码的MATLAB源码/girth84rr.m
% This program constructs coumn-weight four girth 8 quasi-cyclic LDPC codes given
% k( row weight, j(column weight) is fixed at 4) and m (size of each sub-matrix). The
% program constructs a distance graph first then converts it into a matrix.
% For details of the algorithm see PhD thesis by G.Malema, LDPC codes: Construction and Implementation
%(University of Adelaide 2007) and other publications.
% Author : Dr. Gabofetswe Alafang Malema,University of Botswana
% Department of Computer science. e-mail: malemag@mopipi.ub.bw
j=4; % column-weight should be fixed at 4.
k=8; % row-weight is variable.
m=130; % size of each sub-matrix.is variable.
M=j*m; % total number of rows.
shift=zeros(k,j); % stores shift values for each sub-matrix.
rows = struct('connect',0,'counter',0,'con',0); % structure used for storing connections.
emptyset = [];
for y = 1:M % connections and number of connections for rows and columns are initialized.
rows(y).counter = 0;
rows(y).con = intersect(emptyset,rows(y).con);
rows(y).connect = intersect(emptyset,rows(y).connect);
%rows(y).mem = intersect(emptyset,rows(y).mem);
end
group1 = [1:m]; %row group one
group2 = [m+1:2*m]; % row group two,
group3 = [2*m+1:3*m]; % row group three, these groups are connected to group one.
group4 = [3*m+1:4*m];
g= 1; % determines the girth of the code, in these case 8.
found_code = 1; % true if algorithm does not fail.
% the for loop finds a rows(from groups 1,2,3) that are apart at atleast a distance
% of 8. They are then connected. The rest of the groups are connected
% according to this first connection. The process is repeated k times which
% is the number of connections for each row.
for kk = 1:k
r1 = ceil(rand*length(group1)); % randomly choose a row from group1
i = group1(r1);
%while rows(i).counter < k
mem=[]; mem1 = rows(i).con;
mem2 = [];
for y = 1:g
%mem2 = [];
for x = 1:length(mem1)
x1 = mem1(x);
mem2 = union(mem2,rows(x1).con);
end
mem = union(mem1,mem2);
mem1=mem;
end
% find row not in mem in the given range.
A = intersect(mem,group2);
A = setxor(A,group2);
if (isempty(A)~=1)
r1 = ceil(rand*length(A));
row1 = A(r1);
else
disp('Row two not found');
found_code = 0;
break;
end
% create list of neighbors at a distance of 6 or less for row1.
mem3 = []; mem1=rows(row1).con;
mem2 = [];
for b = 1:g
%mem2 = [];
for x = 1:length(mem1)
x1 = mem1(x);
mem2 = union(mem2,rows(x1).con);
end
mem3 = union(mem1,mem2);
mem1 = mem3;
end
mem3 = union(mem3,row1);
% Find row 2 not in mem or mem3 at a distance of atleast 7.
check1 = intersect(mem,group3);
check1 = setxor(check1,group3);
check2 = intersect(mem3,group3);
check2 = setxor(check2,group3);
check3 = intersect(check1,check2);
if isempty(check3)~=1
r2 = ceil(rand*length(check3));
row2 = check3(r2);
else
disp('Row three not found');
found_code = 0;
break;
end
% create list of neighbors at a distance of 6 or less for row1.
mem4 = []; mem1=rows(row2).con;
mem2 = [];
for b = 1:g
%mem2 = [];
for x = 1:length(mem1)
x1 = mem1(x);
mem2 = union(mem2,rows(x1).con);
end
mem4 = union(mem1,mem2);
mem1 = mem4;
end
mem4 = union(mem4,row2);
% Find last 4th row.
check1 = intersect(mem,group4);
check1 = setxor(check1,group4);
check2 = intersect(mem3,group4);
check2 = setxor(check2,group4);
check3 = intersect(mem4,group4);
check3 = setxor(check3,group4);
check4 = intersect(check1,check2);
check4 = intersect(check4,check3);
if (isempty(check4)~=1)
r3 = ceil(rand*length(check4));
row3 = check4(r3);
else
disp('Row four not found');
found_code = 0;
break;
end
% connect all the rows by using a shift.
u = find(group1 == i);
y = find(group2 == row1);
x = find(group3 == row2);
z = find(group4 == row3);
p1 =circshift(group1,[1 -u+1]);
p2 =circshift(group2,[1 -y+1]);
p3 =circshift(group3,[1 -x+1]);
p4 =circshift(group4,[1 -z+1]);
shift(kk,1)=u; % stores shift values of the sub-matrices.
shift(kk,2)=y;
shift(kk,3)=x;
shift(kk,4)=z;
a = kk;
for b=1:m
g1=p1(b);g2=p2(b);g3=p3(b);g4=p4(b);
rows(g1).connect(a,1)=g2;
rows(g1).connect(a,2)=g3;
rows(g1).connect(a,3)=g4;
rows(g2).connect(a,1) = g1;
rows(g2).connect(a,2) = g3;
rows(g2).connect(a,3) = g4;
rows(g3).connect(a,1) = g1;
rows(g3).connect(a,2) = g2;
rows(g3).connect(a,3) = g4;
rows(g4).connect(a,1) = g1;
rows(g4).connect(a,2) = g2;
rows(g4).connect(a,3) = g3;
set1 = [g1 g2 g3];
set2 = [g1 g2 g4];
set3 = [g1 g3 g4];
set4 = [g2 g3 g4];
rows(g1).con = union(rows(g1).con, set4);
rows(g2).con = union(rows(g2).con, set3);
rows(g3).con = union(rows(g3).con, set2);
rows(g4).con = union(rows(g4).con, set1);
end
%end % while loop.
end % for kk =1:k
count = zeros(1,M);
for z = 1:M
count(z)= rows(z).counter;
end
%create a sparse matrix H from the row connections above.
counter = 1;
H = zeros(M,5);
if found_code == 1
for i = 1:k
for z = 1:m
x1 = rows(z).connect(i,1);
x2 = rows(z).connect(i,2);
x3 = rows(z).connect(i,3);
H(z,counter)=1;
H(x1,counter)=1;
H(x2,counter)=1;
H(x3,counter)=1;
counter = counter + 1;
end
end
else
disp('Algorithm failed to find code. Try again or increase group size m.');
end