www.pudn.com > turboprog.rar > turbo_sys_demosecond.m

% This script simulates the classical turbo encoding-decoding system.  
% It simulates parallel concatenated convolutional codes. 
% Two component rate 1/2 RSC (Recursive Systematic Convolutional) component encoders are assumed. 
% First encoder is terminated with tails bits. (Info + tail) bits are scrambled and passed to  
% the second encoder, while second encoder is left open without tail bits of itself. 
% 
% Random information bits are modulated into +1/-1, and transmitted through a AWGN channel. 
% Interleavers are randomly generated for each frame. 
% 
% Log-MAP algorithm without quantization or approximation is used. 
% By making use of ln(e^x+e^y) = max(x,y) + ln(1+e^(-abs(x-y))), 
% the Log-MAP can be simplified with a look-up table for the correction function. 
% If use approximation ln(e^x+e^y) = max(x,y), it becomes MAX-Log-MAP. 
% 
% Copyright Nov 1998, Yufei Wu 
% MPRG lab, Virginia Tech. 
% for academic use only 
 
clear all 
 
% Write display messages to a text file 
diary turbo_logmap.txt 
 
% Choose decoding algorithm  
dec_alg = input(' Please enter the decoding algorithm. (0:Log-MAP, 1:SOVA)  default 0    '); 
if isempty(dec_alg) 
   dec_alg = 0; 
end 
 
% Frame size 
L_total = input(' Please enter the frame size (= info + tail, default: 400)   '); 
if isempty(L_total) 
   L_total = 400;	 % infomation bits plus tail bits 
end 
 
% Code generator 
g = input(' Please enter code generator: ( default: g = [1 1 1; 1 0 1 ] )      '); 
if isempty(g) 
   g = [ 1 1 1; 
         1 0 1 ]; 
end 
%g = [1 1 0 1; 1 1 1 1]; 
%g = [1 1 1 1 1; 1 0 0 0 1]; 
 
[n,K] = size(g);  
m = K - 1; 
nstates = 2^m; 
 
%puncture = 0, puncturing into rate 1/2;  
%puncture = 1, no puncturing 
puncture = input(' Please choose punctured / unpunctured (0/1): default 0     '); 
if isempty(puncture)  
    puncture = 0; 
end 
 
% Code rate 
rate = 1/(2+puncture);    
 
% Fading amplitude; a=1 in AWGN channel 
a = 1;  
 
% Number of iterations 
niter = input(' Please enter number of iterations for each frame: default 5       '); 
if isempty(niter)  
   niter = 5; 
end    
% Number of frame errors to count as a stop criterior 
ferrlim = input(' Please enter number of frame errors to terminate: default 15        '); 
if isempty(ferrlim) 
   ferrlim = 15; 
end    
 
EbN0db = input(' Please enter Eb/N0 in dB : default [2.0]    '); 
if isempty(EbN0db) 
   EbN0db = [2.0]; 
end 
 
fprintf('\n\n----------------------------------------------------\n');  
if dec_alg == 0 
   fprintf(' === Log-MAP decoder === \n'); 
else 
   fprintf(' === SOVA decoder === \n'); 
end 
fprintf(' Frame size = %6d\n',L_total); 
fprintf(' code generator: \n'); 
for i = 1:n 
    for j = 1:K 
        fprintf( '%6d', g(i,j)); 
    end 
    fprintf('\n'); 
end         
if puncture==0 
   fprintf(' Punctured, code rate = 1/2 \n'); 
else 
   fprintf(' Unpunctured, code rate = 1/3 \n'); 
end 
fprintf(' iteration number =  %6d\n', niter); 
fprintf(' terminate frame errors = %6d\n', ferrlim); 
fprintf(' Eb / N0 (dB) = '); 
for i = 1:length(EbN0db) 
    fprintf('%10.2f',EbN0db(i)); 
end 
fprintf('\n----------------------------------------------------\n\n'); 
     
fprintf('+ + + + Please be patient. Wait a while to get the result. + + + +\n'); 
 
for nEN = 1:length(EbN0db) 
   en = 10^(EbN0db(nEN)/10);      % convert Eb/N0 from unit db to normal numbers 
   L_c = 4*a*en*rate; 	% reliability value of the channel 
   sigma = 1/sqrt(2*rate*en); 	% standard deviation of AWGN noise 
 
% Clear bit error counter and frame error counter 
   errs(nEN,1:niter) = zeros(1,niter); 
   nferr(nEN,1:niter) = zeros(1,niter); 
 
   nframe = 0;    % clear counter of transmitted frames 
   while nferr(nEN, niter)0 
            nferr(nEN,iter) = nferr(nEN,iter)+1; 
         end    
      end	%iter 
       
% Total number of bit errors for all iterations 
      errs(nEN,1:niter) = errs(nEN,1:niter) + err(1:niter); 
 
      if rem(nframe,100)==0 | nferr(nEN, niter)==ferrlim 
% Bit error rate 
         ber(nEN,1:niter) = errs(nEN,1:niter)/nframe/(L_total-m); 
% Frame error rate 
         fer(nEN,1:niter) = nferr(nEN,1:niter)/nframe; 
 
% Display intermediate results in process   
         fprintf('************** Eb/N0 = %5.2f db **************\n', EbN0db(nEN)); 
         fprintf('Frame size = %d, rate 1/%d. \n', L_total, 2+puncture); 
         fprintf('%d frames transmitted, %d frames in error.\n', nframe, nferr(nEN, niter)); 
         fprintf('Bit Error Rate (from iteration 1 to iteration %d):\n', niter); 
         for i=1:niter 
            fprintf('%8.4e    ', ber(nEN,i)); 
         end 
         fprintf('\n'); 
         fprintf('Frame Error Rate (from iteration 1 to iteration %d):\n', niter); 
         for i=1:niter 
            fprintf('%8.4e    ', fer(nEN,i)); 
         end 
         fprintf('\n'); 
         fprintf('***********************************************\n\n'); 
 
% Save intermediate results  
         save turbo_sys_demo EbN0db ber fer 
      end 
       
   end		%while 
end 		%nEN 
 
diary off