turbo_sys_demo.zip_Turbo码 matlab_Turbo码的仿真_turbo codes_turbo码 性能

% 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 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 %while end %nEN diary off