st_trellis_enc.m

通信中常用的卷积码信道译码源码程序

function [outputs,alpha_channel] = ...
    st_trellis_enc(Data,ST_NextState,ST_Output,ModMap,TerminateF,NTx);

%------------------------------------------------------------------------------
% Encode binary 1-D data vector with space-time trellis codes.
%
% Format:
% -------
%
% [outputs,alpha_channel] = ...
%   st_trellis_enc(Data,ST_NextState,ST_Output,ModMap,TerminateF,NTx)
% 
% Author: MVe
% Date:   22.08.2002
%------------------------------------------------------------------------------

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

% Works currently only for 1-D input vectors
tmp = size(Data);
if or(length(tmp) > 2,sum(tmp(:)>1)>1)
  error('Encoder works only with vector inputs');
else
  if tmp(1)>tmp(2)
    Data = Data.';
  end % if or(length(tmp) > 2,sum(tmp(:)>1)>1)
end % if or(length(tmp) > 2,sum(tmp(:)>1)>1)

% Check is selected st-code valid
if size(ST_Output{1,1},1)~=NTx
  error('Number of output symbols ~= number of tx antennas');
end % if size(ST_Output{1,1},1)~=NTx

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Initialise few parameters -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

k = log2(size(ST_NextState,2));         % # of input bits
n = 1;                                  % output is one modulated symbol
m_bits = log2(size(ST_NextState,1));    % encoder memory (in bits)
m = ceil(m_bits/k);                     % encoder memory (in "symbols")
DLength = size(Data,2);
DLength_ptr = DLength/k;

% "Pointer" presentation of the input data.
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;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Space-time encoding and modulation -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Format of 'outputs':
%  Column #i = modulated symbols for antenna #i
%
outputs = zeros(NTx,n*DLength_ptr);
outputs_tmp = zeros(NTx,n*DLength_ptr);

for i1 = 1:length(Data_ptr)  
  
  % Output caused by transition (encoded symbols)
  outputs_tmp(:,(i1-1)*n+1:i1*n) = ST_Output{state,Data_ptr(i1)};
  % New state after the transition
  state =  ST_NextState(state,Data_ptr(i1));
  
end % for 1:length(Data)

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

if TerminateF

  %% Drive trellis to zero state (non-recursive encoder):             %%
  %%   Pad data with m zeros (tail bits are m zeros).                 %%
  %    
  for i1 = [1:m] + i1
    % Output caused by transition (encoded bits)
    outputs_tmp(:,(i1-1)*n+1:i1*n) = ST_Output{state,1};
    % New state after the transition
    state = ST_NextState(state,1);
  end % for i1 = [1:m] + i1

end % if TerminateF

% Modulate
outputs = ModMap(outputs_tmp);

% Interleave
[dummy,alpha_channel] = sort(rand(1,length(outputs)));
outputs = outputs(:,alpha_channel);