transmitter.m

详细的OFDM设计过程

function m1 = transmitter(training_seq, pilot, pilots_ten, message, bn, en, size_frame, is_updated)

% This is simulation for the transmitter in the OFDM system.


% ------- transmitter.m ------------------------------------
% Black team
% April-08-05
% ----------------------------------------------------------


global nr_cyclic_bits
global nr_subcarriers
global encoder_order
global nr_pilots
global nr_frames
global nr_fft
global Ex

%initialization, just for transmitter
global start
global begin_flag               % to know when is the beginning of all
global train_flag               % to know when is the beginning of message


if(begin_flag==0)
    % transmit only10_pilots.
    
    % transmit one more frame to record the length of message   
    Len = length(message);
    len_bits = de2bi(Len,nr_subcarriers);
    % BPSK modulation for length frame
    len_symbols = modulation(len_bits,ones(1,nr_subcarriers),Ex*ones(1,nr_subcarriers));        
    len_frames = reshape(len_symbols,nr_subcarriers,1);
    
    frames = [pilots_ten len_frames];
    for nr = 1:nr_pilots + 1
        IFFTframes(:,nr) = symifft(frames(:,nr));
    end 
    % add 10_empty_pilots for Noise_var estimation
    IFFTframes = [IFFTframes zeros(nr_fft,nr_pilots)];   
    cyclic_frames = add_prefix(IFFTframes,nr_cyclic_bits);
    m1 = reshape(cyclic_frames,1,(nr_cyclic_bits + nr_fft) * (nr_pilots + nr_pilots + 1) );
  
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

                         
    begin_flag = 1;
    
else
    
    if(is_updated == 0)
     % wait
     wait = 1     
    else

             
      %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      
        % transmit message      
                  
             size_block = size_frame * nr_frames ;
             untransmit_bits = length(message) - start + 1;
            if (untransmit_bits > size_block)                  % if the remain message is larger than a block
                transmit_bits = message(start:size_block+start);
                start = start + size_block;
                flag = 0;
            else
            % if not, we add zeros to get one block
               flag = size_block - untransmit_bits;             %  flag: how many '0's are padded 
               transmit_bits = [message(start:end) zeros(1,flag)];
               start = 0;
             end
     
           % convolution coding
          coded_bits = conencoder(transmit_bits);                 %ouput of the encoder
 
          
          
            % interleaver
           inter_output = interleaving(coded_bits,5,5);             %output of the interleaver
    
           % modulation
          modulated_symbols=[];
           for i = 1:nr_frames
                modulated_symbols = [modulated_symbols ...
                  modulation(inter_output((i-1)*size_frame*encoder_order+1 : i*size_frame*encoder_order),bn,en)];
            
          end
          
          % serial to parallel : construct a matrix, each column is a frame.   
          frames = reshape(modulated_symbols,nr_subcarriers,nr_frames);
                                   
          % insert pilots before transmitted message
          frames = [pilot frames];     
          
          % compute the IFFT
          % In the references, the formula for ifft and fft was
          % IFFT : x(k) = 1/sqrt(N) * sum( X(n) * exp(2.pi.j.n.k/N) )
          % FFT : X(n) = 1/sqrt(N) * sum( x(k) * exp(-2.pi.j.n.k/N) )
          % symifft :obtain real value to transmit
          % symfft : pick up only half values to get back data
    
          for nr = 1:nr_frames+1
                IFFTframes(:,nr) = symifft(frames(:,nr));
          end 
          
          % add zero-pilot to estimate noise power
          IFFTframes = [IFFTframes(:,1) zeros(nr_fft,1) IFFTframes(:,2:end)];   
           
          % add the cyclic prefix 
          cyclic_frames = add_prefix(IFFTframes,nr_cyclic_bits);
                
           % parallel to serial
           m1 = reshape(cyclic_frames,1,(nr_cyclic_bits + nr_fft) * (nr_frames + 2) );

                     
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        if (train_flag == 0)
           
         % transmit message with syn. training sequence to know when to start processing message
        
         train_flag = 1;
        end
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
    end
end