awgn_decoding.m

用Matlab仿真turbocode的算法

function output_AWGN=AWGN_decoding(AWGN_in,Noise,interleaving,sigmaq,st_t1,mem1,ST1)
%(output1_bin,Noise,interleaving,sigmaq,st_t1)



signal_AWGN=AWGN_in+Noise;
n=(length(signal_AWGN)-2*mem1)/2;%length of info
rep_AWGN=[1 -1];

 for symbol=1:length(rep_AWGN)
     L_transprob(symbol,:)=-(1/(2*sigmaq))*(abs(signal_AWGN-rep_AWGN(symbol))).^2;
 end
 
    
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    
     La_u=-log(2)*ones(2,n+mem1);    %a priori;
    La_e=-log(2)*ones(2,2*(n+mem1)); %a priori; 
    ext_de=zeros(2,2*(n+mem1));
    L_de=zeros(2,2*(n+mem1));
    La_eq=La_e;
   
     L_eq=L_transprob;
          
        ext_eq=L_eq-La_eq;
        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));
           
        
    fstst1=-1e10*ones(size(st_t1,1),1);
    lstst1=fstst1;
    fstst1(1)=0;
    lstst1(1)=0;
           
        [softout,L_de]=log_MAP(La_de_sys,L_transprob_de,fstst1,lstst1,ST1); 
      
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        % hard desicion
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        [dummy,hard]=max(softout);
        output_AWGN=hard-ones(1,length(softout));
        output_AWGN=output_AWGN(1:n);