www.pudn.com > mentos_fs.rar > viterbi_decoder.m

function [decoder_output,survivor_state,cumulated_metric]=viterbi_decoder(G,k,channel_output) 
 
n=size(G,1); 
 
if rem(size(G,2),k)~=0 
   error('Size of G and k do not agree') 
end 
if rem(size(channel_output,2),n)~=0 
   error('Channel out not of the right size') 
end 
 
L=size(G,2)/k; 
 
number_of_states=2^((L-1)*k); 
 
for j=0:number_of_states-1 
   for l=0:2^k-1 
      [next_state,memory_contents]=nxt_stat(j,l,L,k); 
      input(j+1,next_state+1)=l; 
      branch_output=rem(memory_contents*G',2); 
      nextstate(j+1,l+1)=next_state; 
      output(j+1,l+1)=bin2deci(branch_output); 
   end 
end 
 
state_metric=zeros(number_of_states,2); 
depth_of_trellis=length(channel_output)/n; 
channel_output_matrix=reshape(channel_output,n,depth_of_trellis); 
survivor_state=zeros(number_of_states,depth_of_trellis+1); 
 
%body encoder 
for i=1:depth_of_trellis-L+1 
   flag=zeros(1,number_of_states); 
   if i<=L 
      step=2^((L-i)*k); 
   else 
      step=1; 
   end 
   for j=0:step:number_of_states-1 
      for l=0:2^k-1 
         branch_metric=0; 
         binary_output=deci2bin(output(j+1,l+1),n); 
         for ll=1:n 
            branch_metric=branch_metric+metric(channel_output_matrix(ll,i),binary_output(ll)); 
         end 
          
         if((state_metric(nextstate(j+1,l+1)+1,2)>state_metric(j+1,1)+branch_metric)|flag(nextstate(j+1,l+1)+1)==0) 
            state_metric(nextstate(j+1,l+1)+1,2)=state_metric(j+1,1)+branch_metric; 
            survivor_state(nextstate(j+1,l+1)+1,i+1)=j; 
            flag(nextstate(j+1,l+1)+1)=1; 
         end 
      end 
   end 
   state_metric=state_metric(:,2:-1:1); 
end 
 
%tailer encoder 
for i=depth_of_trellis-L+2:depth_of_trellis 
   flag=zeros(1,number_of_states); 
   last_stop=number_of_states/(2^((i-depth_of_trellis+L-2)*k)); 
   for j=0:last_stop-1 
      branch_metric=0; 
      binary_output=deci2bin(output(j+1,1),n); 
      for ll=1:n 
         branch_metric=branch_metric+metric(channel_output_matrix(ll,i),binary_output(ll)); 
      end 
       
      if((state_metric(nextstate(j+1,1)+1,2)>state_metric(j+1,1)+branch_metric)|flag(nextstate(j+1,1)+1)==0) 
         state_metric(nextstate(j+1,1)+1,2)=state_metric(j+1,1)+branch_metric; 
         survivor_state(nextstate(j+1,1)+1,i+1)=j; 
         flag(nextstate(j+1,1)+1)=1; 
      end 
   end 
   state_metric=state_metric(:,2:-1:1); 
end 
 
state_sequence=zeros(1,depth_of_trellis+1); 
state_sequence(1,depth_of_trellis)=survivor_state(1,depth_of_trellis+1); 
for i=1:depth_of_trellis 
   state_sequence(1,depth_of_trellis-i+1)=survivor_state((state_sequence(1,depth_of_trellis+2-i)+1),depth_of_trellis-i+2); 
end 
decoder_output_matrix=zeros(k,depth_of_trellis-L+1); 
for i=1:depth_of_trellis-L+1 
   dec_output_deci=input(state_sequence(1,i)+1,state_sequence(1,i+1)+1); 
   dec_output_bin=deci2bin(dec_output_deci,k); 
   decoder_output_matrix(:,i)=dec_output_bin(k:-1:1)'; 
end 
decoder_output=reshape(decoder_output_matrix,1,k*(depth_of_trellis-L+1)); 
cumulated_metric=state_metric(1,1);