convolution_enc.m

通信中常用的卷积码信道译码源码程序

function [outputs,varargout] = convolution_enc(Data,Trellis,TerminateF,...
                                               enc_type,varargin);

%------------------------------------------------------------------------------
% Encode binary 1-D data vector with convolution codes.
%
% Format:
% -------
%
% [outputs,[ModMap]] = ...
%   convolution_enc(Data, Trellis, TerminateF, enc_type, ['tcm'])
% 
% Author: MVe
% Date:   05.07.2002
%------------------------------------------------------------------------------

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Initial parameter checking etc.. -- %% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

tmp1 = length(varargin);
tcm_flag = 0;
if tmp1>0
  if tmp1 == 1 & strcmp(varargin{1},'tcm')
    tcm_flag = 1;
  end % if tmp1 == 1 & strcmp(varargin{1},'tcm')
end % if tmp1>0
  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Initialise few parameters -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Extract most used variables from struct 'Trellis'
output_tot = Trellis.Output_bin;
nextstate = Trellis.NextState;
n = Trellis.n;
k = Trellis.k;

% "Pointer" presentation of the input data.
DLength = size(Data,2);
DLength_ptr = DLength/k;
tmp = zeros(DLength_ptr,1);
Data_ptr = zeros(1,DLength_ptr);
tmp(:,1) = ...
    bin2dec(reshape(char(Data(1,:)+48),k,DLength_ptr).')+1;
Data_ptr = tmp.';

% Initialise state of the trellis.
state = 1;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Encode input stream (doesn't include tail bits) -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

outputs = zeros(1,n*DLength_ptr);

for i1 = 1:length(Data_ptr) 
  % Output caused by transition (encoded bits)
  outputs(1,(i1-1)*n+1:i1*n) = output_tot{state,Data_ptr(i1)};
  % New state after the transition
  state =  nextstate(state,Data_ptr(i1));  
end % for 1:length(Data)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Terminate trellis with tail bits (if required) -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if TerminateF
  
  switch enc_type
    
    %% Drive trellis to zero state:                                     %%
    %%   Pad data with Trellis.m zeros (tail bits are Trellis.m zeros). %%
    %    
   case 'non-recursive'
    for i1 = [1:Trellis.m] + i1
      % Output caused by transition (encoded bits)
      outputs(1,(i1-1)*n+1:i1*n) = output_tot{state,1};
      % New state after the transition
      state = nextstate(state,1);
    end % for i1 = [1:Trellis.m] + i1
      
   case 'recursive'
    
    %% Drive trellis to zero state:           %%
    %%   Tail bits == output of the feedback. %%
    %
    for i1 = [1:Trellis.m] + i1
      % Output caused by transition (encoded bits)
      outputs(1,(i1-1)*n+1:i1*n) = Trellis.Tail_Output_bin{state};
      % New state after the transition
      state =  Trellis.Tail_NextState(state);
    end % i1 = [1:Trellis.m] + i1
    
  end % switch enc_type
end % if TerminateF

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Trellis coded modulation (only QPSK supported currently) -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if tcm_flag
  
  ModMap = [1+j, -1+j, 1-j, -1-j].';
  k = log2(length(ModMap));
  OLength_ptr = length(outputs)/k;
  tmp = zeros(OLength_ptr,1);
  Outputs_ptr = zeros(1,OLength_ptr);
  tmp(:,1) = ...
      bin2dec(reshape(char(outputs(1,:)+48),k,OLength_ptr).')+1;
  Outputs_ptr = tmp.';
  outputs = ModMap(Outputs_ptr).';
  varargout{1} = ModMap;

end % if tcm_flag