trellis_init.m

通信中常用的卷积码信道译码源码程序

function Trellis = trellis_init(Trellis, Lut);

%------------------------------------------------------------------------------
% Calculate the transitions during time instants 1,2,...,m in trellis.
% 
% Format:
% -------
% 
% Trellis = trellis_init(Trellis, Lut)
% 
% Author: MVe
% Date:   03.07.2002
%------------------------------------------------------------------------------

% Format of 'init_state_ptr':
%  Row = previous state
%  Column = current state with inputs 1,2,...,2^Trellis.k
%
init_state_ptr = 1;

% All possible input sequences
init_state_input = [1:2^Trellis.k].';

% Binary presentation of the paths
% Format: 
%  row = state
%  Column 1 = path at previous time instant
%  Column 2 = path now
% 
Trellis.Init_path_bin = cell(Trellis.StNr,2);

% "Symbol" presentation of the paths
% Format: 
%  row = state
%  Column 1 = path at previous time instant
%  Column 2 = path now
% 
Trellis.Init_path = cell(Trellis.StNr,2);

% State presentation of the paths
% Format: 
%  row = state
%  Column 1 = state at previous time instant
%  Column 2 = state now
%
Trellis.Init_state_path = cell(Trellis.StNr,2);
[Trellis.Init_state_path{:}] = deal(1);

% Format of 'trellis_state_new':
%  Row = previous state
%  Column = new state with inputs 1,2,...,2^Trellis.k
%
trellis_state_new = zeros(Trellis.StNr,2^Trellis.k);

% Aux pointer for distance-metrics calculation.
state_prev_ptr = 0;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- "Fill" the states occured during time instances 1,2,...,m -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

for i1 = 1:Trellis.m
  
  % States of the trellis after current transitions.
  trellis_state_new(init_state_ptr,:) = ...
      Trellis.NextState(init_state_ptr, init_state_input);

  % CHECK IS THIS CORRECT!!!
  % Aux pointer of previous states. For calculating the distance-metrics.
  state_prev_ptr = kron(ones(1,2^Trellis.k),init_state_ptr);

  % Points to the values to be read from look-up tables. 
  %  Column 1 corresponds to transitions caused by 00...00 
  %  Column 2 corresponds to transitions caused by 00...01 
  %  Column 3 corresponds to transitions caused by 00...11 
  %    etc..
  %
  index_ptr = reshape(find(trellis_state_new), ...
		      length(find(trellis_state_new))/2^Trellis.k, ...
		      2^Trellis.k);
  weigths_ptr = Trellis.Output(index_ptr(:,:));

  % New state pointer
  init_state_ptr = trellis_state_new(index_ptr);
  
  % Path outputs in binary and "symbol" format.
  weigths_bin = Lut.Outputs_bin(weigths_ptr,:);
  weigths = Lut.Outputs(weigths_ptr,1);
  
  %% -- METRICS dependant begins -- %%

  % Calculate all paths during this time instant.
  for i2=1:size(weigths_bin,1)
    Trellis.Init_path_bin{init_state_ptr(i2),2} = ...
        [Trellis.Init_path_bin{(state_prev_ptr(i2)),1}, weigths_bin(i2,:)];
    Trellis.Init_path{init_state_ptr(i2),2} = ...
        [Trellis.Init_path{(state_prev_ptr(i2)),1}, weigths(i2)];
    Trellis.Init_state_path{init_state_ptr(i2),2} = ...
        [Trellis.Init_state_path{(state_prev_ptr(i2)),1}, ...
         init_state_ptr(i2)];
  end % for i2=1:size(index_ptr,1)

  %% -- METRICS dependant ends -- %%

  % Rotate buffers
  Trellis.Init_state_path = [Trellis.Init_state_path(:,2), ...
		    cell(Trellis.StNr,1)];
  Trellis.Init_path_bin = [Trellis.Init_path_bin(:,2), ...
		    cell(Trellis.StNr,1)];
  Trellis.Init_path = [Trellis.Init_path(:,2), ...
		    cell(Trellis.StNr,1)];

end % for i1 = 1:Trellis.m


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Create necessary pointers and variables for steady-state trellis  -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Some pre-calculated variables
state_ptr = init_state_ptr;
state_input = init_state_input;

% Format of 'state_new':
% Row = previous state
% Column = new state with inputs 1,2,...,2^Trellis.k
%
state_new = zeros(Trellis.StNr,2^Trellis.k);

% States of the trellis after transitions.
state_new(state_ptr,:) = Trellis.NextState(state_ptr, state_input);

% Points to the values to be read from look-up tables.
% Format: 
% Rows = states
%  Column 1 corresponds to transitions caused by 00...00 
%  Column 2 corresponds to transitions caused by 00...01 
%    etc.
%
index_ptr = reshape(find(state_new), ...
		    length(find(state_new))/2^Trellis.k, 2^Trellis.k);

% Pointer for path outputs
weigths_ptr = Trellis.Output(index_ptr(:,:));

% Path outputs in binary format.
Trellis.Steady_weigths_bin = Lut.Outputs_bin(weigths_ptr,:);
Trellis.Steady_weigths = Lut.Outputs(weigths_ptr,1);

% New state pointer
Trellis.Steady_state_ptr = state_new(index_ptr);

% Pointer to previous states. For calculating the metrics.
Trellis.Steady_state_prev_ptr = kron(ones(1,2^Trellis.k),(1:Trellis.StNr));