ldpcdecoderandencoder.m

这是国标数字电视地面传输标准里信道编解码器的MATLAB程序

%encode
load GAfinal
code=rand(1,3048)>0.5;%随机产生一个信号源码字，这个code还是逻辑结果，不是数
code=code+0;          %为了变成数，把code加零，对code无影响
coded=zeros(1,7493);%为coded分配空间
for n=1:4445
    k=zeros(1,3048)-1;
    gcolumn=GAfinal(1:3048,n);
    onescount=1;
        for m=1:3048
            if gcolumn(m)==1
                k(onescount)=code(m);
                onescount=onescount+1;
            end
        end
        for x=onescount-1:-1:2
            k(x-1)=xor(k(x),k(x-1));
        end
    coded(n)=k(1);
end
coded(1,4446:7493)=code;

%randomcoded=coded;
%for n=1:106
    %randomcoded(n*70)=~randomcoded(n*70)+0;
%end

receivecode=zeros(1,7493);
for k=1:7493
    if coded(k)==0
        receivecode(k)=1;
    else 
        receivecode(k)=-1;
    end
end

%decode
load HAmatrix
nzmax=nnz(H);
ir=zeros(1,nzmax);
jc=zeros(1,7494);
[i,j]=find(H);
for a=1:nzmax
    ir(a)=i(a);
end
 k=0;
for n=1:7493
    for m=1:4445
        if H(m,n)==1
            k=k+1;
        end
    end 
    jc(n+1)=k;
end

yi=coded;
LLR_intrinsic=-2.*yi;


    LLR_extrinsic = zeros(1,nzmax);
    check_LLR = zeros(1,nzmax);
    check_LLR_mag = zeros(1,nzmax);
    LLR_overall = zeros(1,n);
    decoded=zeros(1,n);
       
    
    %initialize variable-to-check messages
        for k=1:n
            if jc(k)==0
                jc(k)=jc(k)+1;
                for l=jc(k):jc(k+1)
                    LLR_extrinsic(l) = LLR_intrinsic(k);
                end
            else
                for l=jc(k)+1:jc(k+1)
                  LLR_extrinsic(l) = LLR_intrinsic(k);
                end
            end
        end
                
    for iteration=1:100
        %Step 1: compute check-to-variable messages
        for k=1:nzmax
            if LLR_extrinsic(k)<0
                check_LLR(k) = -1;
            else
                check_LLR(k) = 1;
            end
            if LLR_extrinsic(k)<0
                check_LLR_mag(k)= -LLR_extrinsic(k);
            else 
                check_LLR_mag(k)=LLR_extrinsic(k);
                
            end
        end
         
        
        rowTotal = ones(1,m);  
        for k=1: nzmax
            rowTotal(ir(k))=rowTotal(ir(k))* check_LLR(k);  
        end
        for k=1:nzmax
            check_LLR(k) = check_LLR(k) * rowTotal(ir(k));
        end
            %sign of check-to-variable messages
        
        for k=1:nzmax
            check_LLR_mag(k) = -log( tanh(max(check_LLR_mag(k),0.000000001)/2 ) );
        end
        for k=1:m
            rowTotal(k) =  0;
        end
        for k=1:nzmax
            rowTotal(ir(k))=rowTotal(ir(k)) + check_LLR_mag(k);
        end
        for k=1:nzmax
            check_LLR_mag(k) = -log( tanh(max( rowTotal(ir(k))- check_LLR_mag(k),0.000000001)/2 ) );
        end
            %magnitude of check-to-variable messages
            
        for k=1:nzmax
            check_LLR(k) = check_LLR(k) .* check_LLR_mag(k);
        end
            %check-to-variable messages
            
        %Step 2: compute variable-to-check messages
        
        for k=1:n
           LLR_overall(k) = LLR_intrinsic(k);
            if jc(k)==0
                jc(k)=jc(k)+1;
                for l=jc(k):jc(k+1)
                    LLR_overall(k)=LLR_overall(k) + check_LLR(l);
                end
            else
                for l=jc(k)+1:jc(k+1)
                  LLR_overall(k)=LLR_overall(k) + check_LLR(l);
                end
            end
        end
               
        
        for k=1:n
            if jc(k)==0
                jc(k)=jc(k)+1;
                for l=jc(k):jc(k+1)
                    LLR_extrinsic(l) = LLR_overall(k) - check_LLR(l);
                end
            else
                for l=jc(k)+1:jc(k+1)
                    LLR_extrinsic(l) = LLR_overall(k) - check_LLR(l);
                end
            end
        end
     %variable-to-check messages
            
                
                
            
        decoded=zeros(1,n);
        for k=1:n
            if LLR_overall(k)<0
                decoded(k)=1;
            else
                decoded(k)=0;
            end
        end
        
        checkrowtotal=zeros(1,4445);     
        for k=1:n
            if jc(k)==0
                jc(k)=jc(k)+1;
                for l=jc(k):jc(k+1)
                    checkrowtotal(ir(l))=checkrowtotal(ir(l))+decoded(k);
                end
            else
                for l=jc(k)+1:jc(k+1)
                    checkrowtotal(ir(l))=checkrowtotal(ir(l))+decoded(k);
                end
            end
        end
      
        for k=1:m
            if( mod(checkrowtotal(k),2)~=0)
               break;
            end
        end
   
        if k==m
           break;
        end
    end