turbo_sys_demo.m

Turbo coding algorithm

% 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)<FERRLIM err(iter)="length(find(xhat(1:L_total-m)~=x));" if iteration current the for errors frame Count % in bit of Number xhat(alpha)="(sign(L_all)+1)/2;" bits info. Estimate extrinsic L_a; - 2*rec_s(2,1:2:2*L_total) L_e="L_all" end complete 2); L_a, g, L_all="logmapo(rec_s(1,:)," else 0 dec_alg="=" priori a L_a="L_e(alpha);" two Decoder 2*rec_s(1,1:2:2*L_total) 1); L_a(alpha)="L_e;" one iter="1:niter" L_e(1:L_total)="zeros(1,L_total);" information Initialize rec_s="0.5*L_c*yk;" received Scale 2 and 1 decoder input get to demultiplex yk="demultiplex(r,alpha,puncture);" r="en_output+sigma*randn(1,L_total*(2+puncture));" -1) (+1 output encoder ; ) puncture alpha, x, en_output="encoderm(" mapping interleaver random alpha]="sort(rand(1,L_total));" [temp, L_total-m)); x="round(rand(1," 1; + nframe="nframe">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,3)==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  


% 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,3)==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