st_trellis.m

通信中常用的卷积码信道译码源码程序

function [ST_NextState, ST_Output, Lut_InfBits, ModMap] = ...
    st_trellis(modulation_type, number_of_states);

%------------------------------------------------------------------------------
% Generate space-time trellis.
% 
% Format:
% -------
% [ST_NextState, ST_Output, Lut_InfBits, ModMap] = ...
%   st_trellis(modulation_type, number_of_states)
% 
% Author: MVe
% Date:   22.08.2002
%------------------------------------------------------------------------------

%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Initialisation -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%

j = sqrt(-1);
modulation_type = upper(modulation_type);

RootDir = pwd;
STTCFile = [RootDir '/dat/Tarokh_STTC.dat'];

% Check modulation 
if ~or(strmatch(modulation_type, '4-PSK'),...
       strmatch(modulation_type, '8-PSK'))
  error(sprintf('Unknown modulation type ''%s''', modulation_type));
end % if ~or(strmatch(modulation_type,'4-PSK'),...

% Check states
if sum(number_of_states==[4,8,16,32])~=1
  error(sprintf('Unknown number of states ''%d''',number_of_states));
end % if sum(states==[4,8,16,32])~=1

% Add paths
Path_list = [RootDir ' ' RootDir '/tls ' ...
                    RootDir '/st-decoder ' RootDir '/st-encoder'];
eval(['addpath ' Path_list]);


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Find correct trellis-structure -- %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Format of 'ST_Output'
%  row number = current state
%  column 1 = output when input is 00...00
%  column 2 = output when input is 00...01
%  column 3 = output when input is 00...10
%    etc..
%
% Format of 'ST_NextState':
%  row number = previous state
%  column 1 = next state when input is 00...00
%  column 2 = next state when input is 00...01
%  column 3 = next state when input is 00...10 
%    etc..
%
% Find correct trellis-structure
[ST_NextState, ST_Output] = ...
    find_sttc(STTCFile, modulation_type, number_of_states);

% Modulation mapping (no gray-encoding)
switch modulation_type
 case '4-PSK'
% $$$   % Tarokh: "Space-Time Codes for..."
% $$$   ModMap = sqrt(2)*exp(j*2*pi*[0:1/4:3/4]).';	  
  % Djordje
  ModMap = sqrt(2)*exp(j*2*pi*([0:1/4:3/4]-3/8)).'; 
 case '8-PSK'
  % Tarokh: "Space-Time Codes for..."
  ModMap = sqrt(2)*exp(j*2*pi*[0:1/8:7/8]).';	
end % switch modulation_type


%%%%%%%%%%%%%%%%%%%%%%%%%
%% -- Look-up tables --%%
%%%%%%%%%%%%%%%%%%%%%%%%%

k = log2(size(ModMap,1));
n = log2(size(ModMap,1));
m = ceil(log2(size(ST_NextState,1))/k);
inputs = double(dec2bin([0:2^k-1]))-48;

% Look-up tables for decoding data sequence ('sttc')
% Format:
%  row = current state
%  column = previous state
%
Lut_InfBits = cell(number_of_states);
for i1 = 1:2^k
  for i2 = 1:number_of_states
    Lut_InfBits{i2,ST_NextState(i2,i1)}=inputs(i1,:);
  end % for i2 = 1:number_of_states
end % for i1 = 2^k