viterbi_decoder.m

matlab信道编码程序

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);