turbo_enc.m

turbo码的MATLAB编程

function [outputs,inf_bits,varargout] = ...
    turbo_enc(Data,Trellis,alpha_rsc,TerminateF,PunctureF,NEncoders, varargin);

%------------------------------------------------------------------------------
% Encode binary 1-D data vector with turbo codes.
%
% Format:
% -------
% Binary outputs:
% [outputs,inf_bits] = turbo_enc(Data,Trellis,alpha_rsc,TerminateF,...
%                                PunctureF,NEncoders)
%
% Turbo coded modulation, QPSK outputs:
% [outputs,inf_bits,alpha_bit,ModMap] = turbo_enc(Data,Trellis,alpha_rsc,...
%                                        TerminateF, PunctureF, NEncoders, ...
%					'QPSK')
%
% 
% Author: MVe
% Date:   05.07.2002
%------------------------------------------------------------------------------

if length(varargin)==1
  cm_flag = 1;
  cm_type = varargin{1};
else
  cm_flag = 0;
end % if length(varargin)==1
  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Initialise few parameters -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

DLength = size(Data,2);

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

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

% Initialise state of the trellis.
state = 1;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- First encoder (possible termination of trellis) -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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) -- %
%
%% Drive trellis to zero state:           %%
%%   Tail bits == output of the feedback. %%
%
if TerminateF
  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 % if TerminateF

% Separate parity and information (+tail) bits
inf_bits(1,:) = outputs(1,1:1/Trellis.Rate:end);
tmp = reshape(outputs,1/Trellis.Rate, length(outputs)*Trellis.Rate);
tmp = tmp(2:end,:);
out_parity(1,:) = tmp(:).';

%%%%%%%%%%%%%%%%%%%%%%%%%%%
% -- Rest of the RCS's -- %
%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Initialise state of the trellis.
state = 1;

for i1 = 1:NEncoders-1
  
  % Interleaving between RSC's
  rsc_input(1,:) = inf_bits(1,alpha_rsc(i1,:));
  % -- Bin -> pointer -- %
  tmp_size = size(rsc_input);
  
  % "Pointer" presentation of the input data.
  tmp = zeros(tmp_size(2)/k,tmp_size(1));
  rsc_input_ptr = zeros(tmp_size(1),tmp_size(2)/k);
  tmp(:,1) = bin2dec(reshape(char(rsc_input(1,:)+48), k,tmp_size(2)/k).')+1;
  rsc_input_ptr = tmp.';
  
  % -- Outputs (only parity bits are of interest) -- %
  state = 1;
  for i2 = 1:length(rsc_input_ptr)
    % Output caused by transition (parity bits only)
    index_ptr = [(i2-1)*(n-k)+1:i2*(n-k)];
    out_parity(i1+1,index_ptr) = output_parity{state,rsc_input_ptr(i2)};
    % New state after the transition
    state = nextstate(state,rsc_input_ptr(i2));
  end % for 1:length(rsc_input)
  
end % for i1 = 2:NEncoders

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Puncturing (only for turbo-codes)-- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

d_size = length(inf_bits);

%% MODIFY !!!!!!!! %%
%% -- Puncture to 1/2-rate code -- %%

if PunctureF
  
  %% NOTE!! Do better!! WORKS ONLY FOR 1/2-rate RSC's !!!
  outputs = zeros(1,d_size*(1/Trellis.Rate));
  
  % Information (+tail) bits
  outputs(1:1/Trellis.Rate:end) = inf_bits;
  % Parity bits
  p_size = size(out_parity,1);
  tmp = zeros(1,d_size*(1/Trellis.Rate)-length(inf_bits));
  for i1 = 1:p_size
    tmp(i1:p_size:end) = out_parity(i1,i1:p_size:end);
  end % for i1 = 1:p_size
  
  outputs(2:1/Trellis.Rate:end) = tmp;
  
else
  
  outputs = zeros(1,d_size*(NEncoders+1));
  % Information (+tail) bits
  outputs(1:NEncoders+1:end) = inf_bits;
  % Parity bits
  p_size = size(out_parity,1);
  for i1 = 1:p_size
    outputs(i1+1:p_size+1:end) = out_parity(i1,:);
  end % for i1 = 1:p_size
    
end % if PunctureF

if cm_flag
  switch cm_type
   case 'QPSK'
    L_out=length(outputs);
    
    % Gray mapping
    ModMap = [1+j, -1+j, 1-j, -1-j].';
    M_bits = log2(length(ModMap));

    % Bit level interleaving
    [dummy,alpha_bit] = sort(rand(1,length(outputs)));
    outputs = outputs(alpha_bit);
    
    % "Pointer" presentation of the input data.
    tmp = zeros(L_out/M_bits,1);
    tmp(:,1) = ...
        bin2dec(reshape(char(outputs(1,:)+48),M_bits,L_out/M_bits).')+1;

    % Modulate output
    outputs = ModMap(tmp).';

    varargout{1} = alpha_bit;
    varargout{2} = ModMap;

   otherwise
    error(sprintf('Coded modulation type %s for turbo-codes not supported', ...
                  cm_type));
    
  end % switch cm_type
    
end % if cm_flag