function [vhat,iteration]=decode_ldpc(rx_waveform,No,amp,h,scale) %[vhat]=decode_ldpc(rx_waveform,No,amp,h,scale) %For examples and more details, please refer to the LDPC toolkit tutorial at %http://arun-10.tripod.com/ldpc/ldpc.htm dim=size(h); rows=dim(1); cols=dim(2); vhat(1,1:cols)=0; zero(1,1:rows)=0; prevhat(1:cols)=1; s=struct('alpha_mn',0,'beta_mn',0,'gamma_mn',0); %associate this structure with all non zero elements of h %Initialization : set gamma_n to log-likelyhood ratios for every code bit and then initialize the alpha_mns for % all non -zero elements of the parity_check matrix for j=1:cols gamma_n(j)=(4/No)*rx_waveform(j); temp=exp(-abs(gamma_n(j))); for i=1:rows if (h(i,j)==1) newh(i,j)=s; newh(i,j).alpha_mn=sign(gamma_n(j))*log((1+temp)/(1-temp)); end end end for iteration=1:100 %%%%%%%%%%%begin horizontal step%%%%%%%%%%%%%%%%%%%%%%5 for i=1:rows prod_of_alpha_mn=1; sum_of_alpha_mn=0; for j=1:cols if h(i,j)==1 for k=1:cols if ((h(i,j)==1)&(j~=k)) prod_of_alpha_mn=prod_of_alpha_mn*newh(i,j).alpha_mn; sum_of_alpha_mn=sum_of_alpha_mn+abs(newh(i,j).alpha_mn); end end temp=exp(-sum_of_alpha_mn); newh(i,j).beta_mn=sign(prod_of_alpha_mn)*log((1+temp)/(1-temp)); end end end %%%%%%%%%%%%%%end horizontal step%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%begin vertical step%%%%%%%%%%%%%%%%% for j=1:cols sum_of_beta_mn=0; for i=1:rows if (h(i,j)==1) sum_of_beta_mn=sum_of_beta_mn+newh(i,j).beta_mn; end end for i=1:rows newh(i,j).gamma_mn=gamma_n(j)+sum_of_beta_mn-newh(i,j).beta_mn; temp=exp(-abs(newh(i,j).gamma_mn)); newh(i,j).alpha_mn=sign(newh(i,j).gamma_mn)*log((1+temp)/(1-temp)); end %%%%%%calculate pseudo log APP ratios lambda_n(j)=gamma_n(j)+sum_of_beta_mn; if lambda_n(j)>=0 vhat(j)=0; else vhat(j)=1; end end %%%%%%%%%%%%%%%%%%%end vertical step%%%%%%%%% %%%%%%%%%%stop if v.hat'=0 or if u get the same codeword 20 consequtive times iteration; if prevhat==vhat converge=converge+1; else converge=0; prevhat=vhat; end if mul_GF2(vhat,h.')==zero break; end if converge==20 break end end %decoding
Make your own free website on Tripod.com