% 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 onlyclear all% Write display messages to a text filediary 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 sizeL_total = input(' Please enter the frame size (= info + tail, default: 400)   ');if isempty(L_total)   L_total = 400;	 % infomation bits plus tail bitsend% Code generatorg = 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 puncturingpuncture = input(' Please choose punctured / unpunctured (0/1): default 0     ');if isempty(puncture)     puncture = 0;end% Code raterate = 1/(2+puncture);   % Fading amplitude; a=1 in AWGN channela = 1; % Number of iterationsniter = 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 criteriorferrlim = 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];endfprintf('\n\n----------------------------------------------------\n'); if dec_alg == 0   fprintf(' === Log-MAP decoder === \n');else   fprintf(' === SOVA decoder === \n');endfprintf(' 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');endfprintf(' 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));endfprintf('\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      % Scale the received bits            rec_s = 0.5*L_c*yk;% 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.          if dec_alg == 0            L_all = logmapo(rec_s(1,:), g, L_a, 1);  % complete info.         else               L_all = sova0(rec_s(1,:), g, L_a, 1);  % complete info.         end            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.         if dec_alg == 0            L_all = logmapo(rec_s(2,:), g, L_a, 2);  % complete info.           else            L_all = sova0(rec_s(2,:), g, L_a, 2);  % complete info.          end         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_sys_demo EbN0db ber fer      end         end		%whileend 		%nENdiary off