trellis_decoder.m

通信中常用的卷积码信道译码源码程序

function [outputs,varargout] = ...
    trellis_decoder(Data_received, Trellis, Lut, alpha_channel, dec_name, ...
                    varargin);

%------------------------------------------------------------------------------
% Decode codes with trellis.
%
% Format:
% -------
%
% Convolution codes (hard/soft): 
% [outputs [raw_ber]]= ...
%  trellis_decoder(Data_received, Trellis, Lut, alpha_channel, ...
%                  'convolution', SF, [fading_gains], [sigma_2], [Data], ...
%                  [TerminateF], [PunctureF], [ModMap])
%
% Trellis coded modulation:
% outputs = ...
%  trellis_decoder(Data_received, Trellis, Lut, alpha_channel, ...
%                  'tcm', SF, fading_gains, TerminateF, PunctureF)
%
% Turbo codes (BPSK):
% [outputs [raw_ber]] = ...
%  trellis_decoder(Data_received, Trellis, Lut, alpha_channel, 'turbo',...
%                  SF, fading_gains, sigma_2, Data, TerminateF, PunctureF, ...
%                  alpha_rsc, iterations)
% 
% Turbo coded modulation (QPSK):
% [outputs [raw_ber]] = ...
%  trellis_decoder(Data_received, Trellis, Lut, alpha_channel, 'turbocm',...
%                  SF, fading_gains, sigma_2, Data, TerminateF, PunctureF, ...
%                  alpha_rsc, iterations, alpha_bit, ModMap)
%
% 
% Author: MVe
% Date:   05.07.2002
%------------------------------------------------------------------------------

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

Data = NaN;

% Check if the function call format is correct and extract
% additional parameter(s) if necessary.
tmp1 = length(varargin);

% If additional arguments are given (for soft decoding)
if tmp1>0
  switch dec_name
   case 'convolution'
     if tmp1==6
       fading_gains = varargin{1};              % fading coefficients
       N0 = 2*varargin{2};                      % noise power
       Data = varargin{3};                      % original data bits
       TerminateF = varargin{4};                % terminated trellis or not
       PunctureF = varargin{5};                 % punctured code or not
       ModMap = varargin{6};			% constellation
       if length(fading_gains) ~= length(Data_received)
         error(['length(fading coefficients) == length(data received)' ...
                ' required']);
       end % if fading_gains ~= length(Data_received)
     end % if tmp1==6
    
   case 'tcm'
     if tmp1==3
       fading_gains = varargin{1};              % fading coefficients
       TerminateF = varargin{2};                % terminated trellis or not
       PunctureF = varargin{3};                 % punctured code or not
       if length(fading_gains) ~= length(Data_received)
         error(['length(fading coefficients) == length(data received)' ...
                ' required']);
       end % if fading_gains ~= length(Data_received)
     end % if tmp1==3

   case 'turbo'
    if tmp1==7 
      fading_gains = varargin{1};	         % fading coefficients
      N0 = 2*varargin{2};                    % noise power
      Data = varargin{3};		             % original data bits
      TerminateF = varargin{4};		         % terminated trellis or not
      PunctureF = varargin{5};               % punctured code or not
      alpha_rsc = varargin{6};		         % interleaver between RSC's
      iterations = varargin{7};              % number of MAP-iterations 
      if length(fading_gains) ~= length(Data_received)
        error('length(fading coefficients) == length(data received) required');
      end % if fading_gains ~= length(Data_received)
    end % if tmp1==7 

   case 'turbocm'
    if tmp1==9
      fading_gains = varargin{1};	         % fading coefficients
      N0 = 2*varargin{2};                    % noise power
      Data = varargin{3};		             % original data bits
      TerminateF = varargin{4};		         % terminated trellis or not
      PunctureF = varargin{5};               % punctured code or not
      alpha_rsc = varargin{6};		         % interleaver between RSC's
      iterations = varargin{7};              % number of MAP-iterations 
      alpha_bit = varargin{8};               % bit-level interleaving
      ModMap = varargin{9};                  % constellation points
      if length(fading_gains) ~= length(Data_received)
        error('length(fading coefficients) == length(data received) required');
      end % if fading_gains ~= length(Data_received)
    end % if tmp1==7 

    
  end % switch dec_name
  
end % if tmp1>0

% Works currently only for vectors of size 1xD
tmp1 = size(Data_received);
tmp2 = size(Data);
if sum([length(tmp1)>2, sum(tmp1(:)>1)>1, length(tmp2)>2, sum(tmp2(:)>1)>1])
  error('Decoder works only with vector inputs');
else
  tmp = bin2dec(char([tmp1(1)>tmp1(2), tmp2(1)>tmp2(2)]+48));
  switch tmp
   case 0
    reshape_flag = 0;
   case 1
    Data = Data.';
   case 2
    reshape_flag = 1;
    Data_received = reshape(Data_received,tmp1(2),tmp1(1));
   case 3 
    reshape_flag = 1;
    Data_received = reshape(Data_received,tmp1(2),tmp1(1));
    Data = Data.';
  end % switch tmp    
end % if sum([length(tmp1)>2, sum(tmp1(:)>1)>1, length(tmp2)>2,...

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Hard decision decoding (only for convolution codes) -- %% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if ~Trellis.SoftDecF

  outputs = convolution_dec(Data_received,Trellis,Lut,alpha_channel);

  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  %% -- Soft decision decoding  -- %%
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
else

  switch dec_name
   
   case 'tcm'
    % SIHO trellis
    outputs = ...
        tcm_dec(Data_received,Data,Trellis,Lut,alpha_channel,...
                fading_gains,TerminateF,PunctureF,SF);
    
   case 'convolution'

    % Trellis decoder with soft inputs
    [outputs, berrs, ferrs] = ...
	conv_dec_soft_C(Data_received,Data,Trellis,Lut,alpha_channel,...
			fading_gains,N0,TerminateF,PunctureF,ModMap);
    
% $$$     % MAP
% $$$     [outputs, Raw_BER] = ...
% $$$         map_siso1_bpsk(Data_received,Data,Trellis,alpha_channel,...
% $$$                        fading_gains,N0,TerminateF,PunctureF);

    
   case 'turbo'
    % Iterative MAP
    [outputs, Raw_BER] = ...    
        map_app_siso1_bpsk(Data_received,Data,Trellis,fading_gains,N0, ...
                           alpha_channel,alpha_rsc,TerminateF,PunctureF,...
                           iterations);
   case 'turbocm'
    % Iterative MAP
    [outputs, Raw_BER] = ...    
        map_app_siso1_bpsk(Data_received,Data,Trellis,fading_gains,N0, ...
                           alpha_channel,alpha_rsc,TerminateF,PunctureF,...
                           iterations, alpha_bit, ModMap);

  end % if strcmp(dec_name,'convolution')

end % if ~Trellis.SoftDecF

% Reshape the output vector if necessary
if reshape_flag
  outputs = outputs.';
end % if reshape_flag

% Output uncoded bit error rate, if required
if exist('Raw_BER','var')
  varargout{1} = Raw_BER;
end % if exist('Raw_BER','var')

% Output number of coded bit errors, if required
if exist('berrs','var')
  varargout{1} = berrs;
end % if exist('berrs',...


% Output number of coded frame errors, if required
if exist('ferrs','var')
  varargout{2} = ferrs;
end % if exist('ferrs',...