turbo_main.m

一个turbo码的仿真程序

clear all

% Write display messages to a text file
diary turbo_record.txt

L_total = 400;	 % frame size = info + tail

% 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

[n,K] = size(g); 
m = K - 1;
nstates = 2^m;

puncture = 0;      %puncturing into rate 1/2; 

rate = 1/(2+puncture);   % Code rate

a = 1;               % Fading amplitude; a=1 in AWGN channel
niter = 5;           % Number of iterations
ferrlim = 15;        % Number of frame errors to count as a stop criterior

EbN0db = input(' Please enter Eb/N0 in dB : default [2.0]    ');
if isempty(EbN0db)
   EbN0db = [2.0];
end


fprintf('\n\n----------------------------------------------------\n'); 
fprintf(' === Log-MAP decoder === \n');
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        

fprintf(' Punctured, code rate = 1/2 \n');
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
      nframe = nframe + 1;    
      x = round(rand(1, L_total-m));    % info. bits
      [temp, alpha] = sort(rand(1,L_total));        % random interleaver mapping
      en_output = encoderm( x, g, alpha, puncture ) ; % encoder output (+1/-1)
          
      r = en_output+sigma*randn(1,L_total*(2+puncture)); % received bits
      yk = demultiplex(r,alpha,puncture); % demultiplex to get input for decoder 1 and 2
      
      rec_s = 0.5*L_c*yk;        % Scale the received bits   

% Initialize extrinsic information      
      L_e(1:L_total) = zeros(1,L_total);
      
      for iter = 1:niter
% Decoder one
         L_a(alpha) = L_e;  % a priori info. 
         L_all = logmapo(rec_s(1,:), g, L_a, 1);  % complete info.
         L_e = L_all - 2*rec_s(1,1:2:2*L_total) - L_a;  % extrinsic info.

% Decoder two         
         L_a = L_e(alpha);  % a priori info.
         L_all = logmapo(rec_s(2,:), g, L_a, 2);  % complete info.  
         L_e = L_all - 2*rec_s(2,1:2:2*L_total) - L_a;  % extrinsic info.
         
% Estimate the info. bits        
         xhat(alpha) = (sign(L_all)+1)/2;

% Number of bit errors in current iteration
         err(iter) = length(find(xhat(1:L_total-m)~=x));
% Count frame errors for the current iteration
         if err(iter)>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_main EbN0db ber fer
      end
      
   end		
end 		

diary off