viterbi.m

卷积码的维特比译码仿真

function [decoder_output,survivor_state,cumulated_metric]=viterbi(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 outpt not of the right size')
end

L=size(G,2)/k;
number_of_states=2^((L-1)*k);

for j=0:2^k-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);

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
    
    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);