siso_app_c.m

通信中常用的卷积码信道译码源码程序

function [LuO,LcO] = siso_app_C(LuI, LcI, Trellis, BitsLut, dec, LcOFlag,...
				MaxFlag);

%------------------------------------------------------------------------------
% Maximum a posteriori decoder with soft-inputs and soft-outputs. 
%
% $RCSfile: siso_app_C.m,v $
% $Revision: 2.5 $
% $Date: 2003/11/19 16:00:54 $
% $Author: coffin $
%
% Calculates Log-likelihood ratios of received bits. A priori information 
% of information and coded bits from the other decoder and soft democulator 
% accepted. Soft inputs, soft outputs. Log-domain calculations for numerical 
% stability. No approximations used in the calculation of logarithm
% of sum of exponents.
%
% NOTE!: 
% -----
% The log-likelihood ratios for coded bits are *not* suitable to be
% passed to another component decoder and their purpose is solely
% for soft interference cancellation. Further, PCCCs should not use LLR
% information of coded bits in any case, see references.
% 
% Algorithm reference:
%   Benedetto, S., Divsalar, D., Montorsi, G. and Pollara, F.,
%   "A Soft-Input Soft-Output APP Module for Iterative Decoding of 
%    Concatenated Codes". IEEE Communications Letters, Vol.1, No.1, 1997.
%   Benedetto, S., Divsalar, D., Montorsi, G. and Pollara, F.,
%   "A Soft-Input Soft-Output Maximum A Posterioiri (MAP) Module to Decode
%    Parallel and Serial Concatenated Codes". TDA Progress Report 42-127.
% 
% Restrictions: Two 1/2-rate RSCs as CCs assumed.
%
% 
% Format:
% -------
% 
% [LuO,LcO] = siso_app(LuI, LcI, Trellis, BitsLut, dec, LcOFlag);
%
% Inputs:
% -------
%  LuI - log(P(u;I)), a priori log-likelihoods of the information bits 
%                     from other component decoder
%  LcI - log(P(c;I)), a priori log-likelihoods of the coded bits
%                     from demodulator (PCCC) or other component decoder(SCCC)
%  Trellis - Structure containing necessary information of CC trellises
%  BitsLut - Bit look-up table for edge output symbols
%  dec - Decoder 1 or 2
%  LcOFlag - Calculate likelihoods log(P(c;O)) or not
%
% Outputs:
% --------
%  LuO - log(P(u;O)), extrinsic bit information of the information bits
%  LcO - log(P(c;O)), extrinsic bit information of the coded bits
% 
% Author: MVe, [e-mail]
% Date:   14.10.2002
%------------------------------------------------------------------------------


% Format of 'edge' (transition connecting two states) for 1/2-rate CCs:
%  row = edge number
%                e_S         e_E          e_U           e_C1, e_C2
%  column = | start edge | end edge | input bit | output binary sequence |
%
[e_S, e_E, e_U, e_C1, e_C2] = deal(1,2,3,4,5);
edge(:,e_S:e_E) = Trellis.Edge(:,1:2);
edge(:,e_U) = Trellis.Edge(:,3)-1;		% binary input
edge(:,e_C1:e_C2) = BitsLut(Trellis.Edge(:,4),:);

if (MaxFlag)
  [LuO, LcO]=siso_app_MAX_CC(LuI, LcI, edge, BitsLut, Trellis.k, dec, ...
			     LcOFlag, Trellis.flag_3gpp);
else  
  [LuO, LcO]=siso_app_CC(LuI, LcI, edge, BitsLut, Trellis.k, dec, LcOFlag,...
			 Trellis.flag_3gpp);
end % if (MaxFlag)