turbo_sys_demo.m

迭代多用户检测的MATLAB详细实现,非常全面,主要基于Vincent Poor和王晓东提出的算法实现,绝对的好东西.

% 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: 128)   ');
if isempty(L_total)
   L_total = 128;	 % 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 0 0 1 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];

%g = [ 1 1 1 0 1 ;   1 0 0 1 1];
% g = [1 1 0 0 1; 1 0 1 1 1 ];
g = [1 1 1 ;    1 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');

%**************************** Preparation part *****************************

sr   = 256000.0;                                                    % symbol rate
ml   = 1;                                                           % number of modulation levels
br   = sr * ml;                                                     % bit rate
%nd   = 100;                                                         % number of symbol
%************************** Filter initialization **************************

irfn   = 21;                                                        % number of filter taps
IPOINT =  8;                                                        % number of oversample
alfs   =  0.5;                                                      % roll off factor
[xh]   = hrollfcoef(irfn,IPOINT,sr,alfs,1);                         % T FILTER FUNCTION
[xh2]  = hrollfcoef(irfn,IPOINT,sr,alfs,0);                         % R FILTER FUNCTION

%********************** Spreading code initialization **********************

user  = 2;                                                          % number of users
seq   = 2;                                                          % 1:M-sequence  2:Gold  3:Orthogonal Gold
stage = 3;                                                          % number of stages
ptap1 = [1 3];                                                      % position of taps for 1st
ptap2 = [2 3];                                                      % position of taps for 2nd
regi1 = [1 1 1];                                                    % initial value of register for 1st
regi2 = [1 1 1];                                                    % initial value of register for 2nd

%******************** Generation of the spreading code *********************

%switch seq
%case 1                                                              % M-sequence
%    code = mseq(stage,ptap1,regi1,user);
%case 2                                                              % Gold sequence
%    m1   = mseq(stage,ptap1,regi1);
%    m2   = mseq(stage,ptap2,regi2);
%    code = goldseq(m1,m2,user);
%case 3                                                              % Orthogonal Gold sequence
%    m1   = mseq(stage,ptap1,regi1);
%    m2   = mseq(stage,ptap2,regi2);
%    code = [goldseq(m1,m2,user),zeros(user,1)];
%end
%code = code * 2 - 1;

%**************************************************************************

code=ones(user,10);
%code(:,13:2:40)=-1;
code(2,1:9:10)=-1;


%code=code/40.0;




clen = length(code);


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*a*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(user, L_total-m));    % info. bits
           
      for i=1:user
      [temp, alpha(i,:)] = sort(1:2*L_total);        % random interleaver mapping
      en_output(i,:) = encoderm( x(i,:), g, alpha, puncture ) ; % encoder output (+1/-1)
      interleave_output(i,:)=en_output(i,alpha(i,:));
      end
      nd=L_total*(2+puncture);
      
     % code=mseq(stage,ptap1,regi1,user);
      ich1=spread(interleave_output,code);
      ich2=compoversamp2(ich1,IPOINT);%over sample
      ich3=compconv2(ich2,xh); %filter
      
      if user==1
          ich4=ich3;
      else
          ich4=sum(ich3);
      end
      spow=sum(rot90(ich3.^2 ))/nd;
      attn=sqrt(0.5*spow*sr/(br)*10^(-EbN0db(nEN)/10));
      ich6=comb2(ich4,attn); %add gaussian AWGN
      ich7=compconv2(ich6,xh2);
      sampl=irfn*IPOINT+1;
      ich8=ich7(:,sampl:IPOINT:IPOINT*nd*clen+sampl-1);
      r=despread(ich8,code);

      % Initialize extrinsic information      
      L_e = zeros(user,L_total*2);     
      L_a = zeros(user,L_total*2);
      L_check=zeros(user,L_total*2);
      rec_s = zeros(user,L_total*(2+puncture));
      L_k = zeros(user,L_total*(2+puncture));
      L_all = zeros(user,L_total*2);
      
      rec_s = r/10;


  
 for iter = 1:niter   
  L_check=multi_dete(rec_s,L_e,sigma);
  
  %xhat=sign(L_check+L_e);

% Number of bit errors in current iteration
    %     err(2*iter-1) = length(find(xhat(1,1:1:2*(L_total-m))~=interleave_output(1,1:1:2*(L_total-m))));


  for i=1:user   %Decoder one 
     
         L_a(i,alpha(i,:)) = L_check(i,:);%-L_e(i,:);  % a priori info. 
%         if dec_alg == 0
            L_all(i,:) = logmapo(L_a(i,:), g, L_a(i,:), 1);  % complete info.
            %         else   
%            L_all(i,:) = sova0(rec_s(2*i-1,:), g, L_a(i,beta(i,:)), 1);  % complete info.   
            L_k(i,:) = L_all(i,:)- L_a(i,:); 
            
           L_e(i,:) = L_k(i,alpha(i,:));
           
 end        % extrinsic info.
      
        %   L_all = L_all+L_a;
% Decoder two         
%         L_a(i,:) = L_e(i,alpha);  % a priori info.
%         if dec_alg == 0
%            [L_all(i,:),L_check(i,:)] = logmapo(rec_s(2*i,:), g, L_a(i,:), 2);  % complete info.  
%         else
%            L_all(i,:) = sova0(rec_s(2*i,:), g, L_a(i,:), 2);  % complete info. 
%         end
%         L_e(i,beta(i,:)) = L_all(i,:) - 2*rec_s(2*i,1:2:2*L_total) - L_a(i,:);  % extrinsic info.
         
      %end i     
% Estimate the info. bits        
        % xhat = (sign(L_all)+1)/2;
        xhat=sign(L_all);

% Number of bit errors in current iteration
         err(iter) = length(find(xhat(1,1:2:2*(L_total-m))~=en_output(1,1:2:2*(L_total-m))));
% 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,1)==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