viterbi.m

此程序经本人调试,完全能实现编码的仿真功能,而且在程序中有必要的说明,增加了程序的可读性.

% This is the viterbi() function. It is used for decoding 
% the trellis code which generated by cnv_encd()
% 采用Viterbi译码算法!
function [decoder_output,survivor_state,cumulates_metric]=viterbi(G,k,channel_output)
% 检查G的大小，并确定G是否与k匹配，若是，给出约束长度L,
n=size(G,1);
if rem(size(G,2),k)~=0
   error('size of G and k do not agree')
end
L=size(G,2)/k;
% 确定状态数：2^((L-1)*k)
number_of_states=2^((L-1)*k);

% 生成状态转移矩阵、输出矩阵和输入矩阵
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;           % 状态转移矩阵
        output(j+1,l+1)=bin2deci(branch_output); % 输出矩阵
    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);  % 输入矩阵
survivor_state=zeros(number_of_states,depth_of_trellis+1);

% 开始无尾信道输出编码
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);
            % 调用函数metric()计算Hamming距离
            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

% 开始尾部信道输出编码
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);
        % 调用函数metric()计算Hamming距离
        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

% 从最佳路径中得到解码输出
state_sequence=zeros(1,depth_of_trellis+1);
state_sequence(1,depth_of_trellis)=survivor_state(1,depth_of_trellis+1);
% 从幸存的状态矩阵中找出幸存路径
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);
% 依幸存路径计算译码输出
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));
cumulates_metric=state_metric(1,1);


% 参考输入验证：
% g=[1 0 1;1 1 1];
% k0=1;
% msg_in=[0 1 1 0 1 1 1 1 0 1 0 0 0 1];
% viterbi(g,k0,msg_in)
% de_out=[1 1 0 0 0]