基于MATLAB的LDPC编译码仿真程序

function [H]=genH(rows,cols,bits_per_col) row_flag(1:rows)=0; parity_check=zeros(rows,cols); %add bits_per_col 1's to each column with the only constraint being that the 1's should be %placed in distinct rows %%%%%%%%使每列随机产生3个1即列重为3%%%%%%%%%%%%% % bits_per_col=3; for i=1:cols a=randperm(rows); for j=1:bits_per_col parity_check(a(j),i)=1; row_flag(a(j))=row_flag(a(j))+1; end end %计算每行1的最多个数 max_ones_per_row=ceil(cols*bits_per_col/rows); %add 1's to rows having no 1(a redundant row) or only one 1(that bit in the codeword becomes %zero irrespective of the input) for i=1:rows if row_flag(i)==0 %如果该行没有1，则随机添加两个1 for k=1:2 j=unidrnd(cols);%在指定的整数范围内产生一个随机数 while parity_check(i,j)==1 j=unidrnd(cols); end parity_check(i,j)=1; %在找到的新位置上置1 row_flag(i)=row_flag(i)+1; %行重加1 end end if row_flag(i)==1 %如果该行只有1个1，则随机再添加1个1 j=unidrnd(cols); while parity_check(i,j)==1 j=unidrnd(cols); end parity_check(i,j)=1; row_flag(i)=row_flag(i)+1; end end %try to distribute the ones so that the number of ones per row is as uniform as possible %尝试在列上分散1的位置，使得每行1的个数均衡（相近或相一致） for i=1:rows j=1; a=randperm(cols); while row_flag(i)>max_ones_per_row; %如果该行行重大于允许的最大行重，则进行处理 if parity_check(i,a(j))==1 %随机选择某一该行上为1的列来处理，将该列该行上的1分散到其他的行 %随机查找该列上适合放置1（行重小于允许的最大行重，且该位置上为0）的行 newrow=unidrnd(rows); k=0; while (row_flag(newrow)>=max_ones_per_row | parity_check(newrow,a(j))==1) & k<rows newrow=unidrnd(rows); k=k+1; end if parity_check(newrow,a(j))==0 %将待处理行上的1转放到找到的行上 parity_check(newrow,a(j))=1; row_flag(newrow)=row_flag(newrow)+1; parity_check(i,a(j))=0; row_flag(i)=row_flag(i)-1; end end%if test j=j+1; end%while loop end%for loop %try to eliminate cycles of length 4 in the factor graph %尝试删除4环 for loop=1:1000 chkfinish=1;%是否还寻找四环的标志位 for r=1:rows ones_position=find(parity_check(r,:)==1);%找出r行中的1的位置 ones_count=length(ones_position);%r行中1的数量 for i=[1:r-1 r+1:rows]%相当于行坐标 common=0; for j=1:ones_count%相当于列坐标 if parity_check(i,ones_position(j))==1%相同位置上存在1 common=common+1 ; if common==1 thecol=ones_position(j);%把该位置赋给thecol end end if common==2 chkfinish=0; %如果还存在4环，则不结束循环，还进入下一次循环 common=common-1; if (round(rand)==0) % 随机决定是保留前面的列还是后面的列 coltoberearranged=thecol; %保留后面的列，交换前面的列 thecol=ones_position(j); else coltoberearranged=ones_position(j); %保留前面的列，交换后面的列 end parity_check(i,coltoberearranged)=3; %make this entry 3 so that we dont use %of this entry again while getting rid %of other cylces newrow=unidrnd(rows);%在指定的整数范围内产生一个随机数 iteration=0; %尝试5次在待交换的列中随机查找0 while parity_check(newrow,coltoberearranged)~=0 & iteration<5 newrow=unidrnd(rows); iteration=iteration+1; end if iteration>=5 %超过5次后则扩大范围随机查找非1的0或3，直到找到为止 while parity_check(newrow,coltoberearranged)==1 newrow=unidrnd(rows); end end %把该列中找到的0或3置为1 parity_check(newrow,coltoberearranged)=1; end%if common==2 end%for j=1:ones_count end%for i=[1:r-1 r+1:rows] end%for r=1:rows %如果本次循环已不存在4环，则结束循环，不进入下一次循环 if chkfinish break end end%for loop=1:10 %replace the 3's with 0's parity_check=parity_check==1; %Get the Parity Checks H=parity_check; %%%%%下面的求方差仅用作评估%%%% %%计算列重 %col_flag(1:cols)=0; %for j=1:cols % ind=find(H(:,j)==1); % col_flag(j)=length(ind); %end %%计算行重 %row_flag(1:rows)=0; %for i=1:rows % ind=find(H(i,:)==1); % row_flag(i)=length(ind); %end %%每行1的个数的方差 %variance=var(row_flag);