sccc_decoding.m

用Matlab仿真turbocode的算法

function [hard,ext_de]=sccc_decoding(La_eq,L_transprob,n,mem1,mem2,ST1,ST2,interleaving)

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % to initialize alpha & beta(in form of log-probability)
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    m1=2^mem1;
    m2=2^mem2;    
    fstst1=-1e10*ones(m1,1);
    lstst1=fstst1;
    fstst2=-1e10*ones(m2,1);
    lstst2=fstst2;
    fstst1(1)=0;
    fstst2(1)=0;
    lstst1(1)=0;
    lstst2(1)=0;
    
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % to set the a priori value(in form of log-probability) for equalizer and decoder
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    La_u=-log(2)*ones(2,(n+mem1));   
  
    
        [L_eq,dummy]=log_MAP(La_eq,L_transprob,fstst2,lstst2,ST2);
           
        ext_eq=L_eq-La_eq;        
        ext_eq=ext_eq(:,1:2*(n+mem1));%remove the tail bits' information
        ext_eq(:,interleaving)=ext_eq(:,:); %deinterleaved
        ext_eq_sys=ext_eq(:,1:2:end);   % extrinsic infomation for systematic bit
        ext_eq_code=ext_eq(:,2:2:end);  % extrinsic infomation for parity bit  
        
        LLR_eq_ext=ext_eq(1,:)-ext_eq(2,:); %log-likelyhood ratio
        LLR_eq_ext_sys=LLR_eq_ext(1:2:end);
        LLR_eq_ext_code=LLR_eq_ext(2:2:end);
        
        L_transprob_de=zeros(4,n+mem1);
        L_de=L_transprob_de;
        L_de_sys=zeros(2,n+mem1);
        L_de_code=L_de_sys;
        L_transprob_de(1,:)=0.5*(LLR_eq_ext_sys+LLR_eq_ext_code)-log(2);
        L_transprob_de(2,:)=0.5*(LLR_eq_ext_sys-LLR_eq_ext_code)-log(2);
        L_transprob_de(3,:)=0.5*(-LLR_eq_ext_sys+LLR_eq_ext_code)-log(2);
        L_transprob_de(4,:)=0.5*(-LLR_eq_ext_sys-LLR_eq_ext_code)-log(2);  
        
    
        La_de_sys=La_u;
        La_de_code=zeros(size(La_u));
            
               
        [softout,L_de]=log_MAP(La_de_sys,L_transprob_de,fstst1,lstst1,ST1); 
        
        L_de_sys(1,:)=max(L_de(1,:),L_de(2,:))+log(1+exp(-abs(L_de(1,:)-L_de(2,:))));
        L_de_sys(2,:)=max(L_de(3,:),L_de(4,:))+log(1+exp(-abs(L_de(3,:)-L_de(4,:))));
        L_de_code(1,:)=max(L_de(1,:),L_de(3,:))+log(1+exp(-abs(L_de(1,:)-L_de(3,:))));
        L_de_code(2,:)=max(L_de(2,:),L_de(4,:))+log(1+exp(-abs(L_de(2,:)-L_de(4,:))));              
        ext_de=zeros(2,2*(n+mem1));       
        ext_de(:,1:2:end)=L_de_sys-La_de_sys-ext_eq_sys;    
        ext_de(:,2:2:end)=L_de_code-La_de_code-ext_eq_code;
        ext_de(:,:)=ext_de(:,interleaving);
        %La_eq=ext_de; 
        
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        % hard desicion
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        [dummy,hard]=max(softout);
        hard=hard-ones(1,length(softout));
        hard=hard(1:n);