systems.m

802.16 physical layer simulation through diferent SUI Channel.

function n_ber = systems (SNR,n_mod_type,G,N_SUI,encode,samples,BW,channel);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%       
%%                                                                       %
%%      Name: systems.m                                                  %
%%                                                                       %
%%      Description: All the different stages of the system are          %
%%       called from this function. These stages are the encoder,        %
%%       the transmitter, the channel, the receiver and the decoder.     %
%%       The channel, through which the information and noise travel,    %
%%       is also simulated here.                                         %
%%                                                                       %
%%      Parameters: Each simulation depends on the signal to noise       %
%%       ratio of the system, type of modulation, size of the cyclic     %
%%       prefix, the channel that we are simulating, if the data is      %
%%       encoded or not and the number of bits sent; not to forget       %
%%       the bandwidth that we have available.                           %
%%                                                                       %
%%      Result: When the whole simulation is finished, the value of      %
%%       the BER is returned, with which a graph is shown that is of     %
%%       interest.                                                       %
%%                                                                       %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if n_mod_type == 1              % As the rate is not one of the things that interfere at first, I define it here.
    rate = 1/2;                 % It might be treated as a parameter and the value might be set manually.
end                             
rate = 3/4;                     

Nfft = 256;

data_total_rx = [];
data_total = [];
data_out = [];
data_in = [];

n_symbols = samples;          % Total symbols to transmit


% Depending on the input data (modulation, rate, number of symbols and if i encode or not)
% i generate the necessary data to carry out the simulation


















switch n_mod_type
    case 1
        amount = 11;
        amount_coded = 192;
        template = [1];
        codeRS=[12 12];
    case 2
        if rate == (1/2)
            amount = 23;
            template = [1 0 1 1];          % These templates are those that are used in the  
            codeRS=[32 24];                % Convolutional encoding and later in the Virerbi algorithm. 
        elseif rate == (3/4)                
            amount = 35;                   
            template = [1 0 1 0 1];        
            codeRS=[40 36];
        end
        amount_coded = 384;
    case 4
        if rate == (1/2)
            amount = 47;
            template = [1 0 1 1];
            codeRS=[64 48];                % The variable codeRS indicates the form in which 
        elseif rate == (3/4)               % data must be encoded in the Reed-Solomon encoding.
            amount = 71;                  
            template = [1 0 1 0 1];        
            codeRS=[80 72];
        end
        amount_coded = 768;
    case 6
        if rate == (2/3)
            amount = 95;                   % Logically, "amount" marks how many bytes i must generate in each case.
            template = [1 1 0];             
            codeRS=[108 96];              
        elseif rate == (3/4)                
            amount = 107;                
            template = [1 0 1 0 1];
            codeRS=[120 108];
        end
        amount_coded = 1152;
end

% Once the bytes needed to generate are found, they are generated for each case
 data_total = randint (1,amount*8*n_symbols);
 n_symbols = n_symbols;
 
 rate = amount_coded/(amount*8);

if encode==0
    
    % If encoding is not employed, the necessary bits are generated.
    n_symbols = floor(length(data_total)/amount_coded);
    amount = amount_coded/8;
    
    % Again, once the bytes needed to generate are found, they are generated.
    data_total = randint (1,amount*8*n_symbols);     
 
end

































bits_ofdm = amount * 8;


 for i=1:n_symbols
    % We combine only the groups of bits necessary to form an OFDM symbol.
     data_in = data_total( 1+(i-1)*bits_ofdm : i*bits_ofdm );
          
    % When the bits of the symbol to transmit are ready,the transmitter is called so that it forms the complete OFDM symbol
    
     [pilot_mapping,data_mapping] = encoder(data_in,codeRS,template,n_mod_type,encode);
     
     
     
     
     
     
     

pilots=pilot_mapping;
data=data_mapping;
guard1 = complex (0,0) * ones (1,28);
DC = complex (0,0);
guard2 = complex (0,0) * ones (1,27);

% The pilot and guard subcarriers are placed according to the standard.

symbol= [guard1 data(1:12) pilots(1) data(13:36)...
    pilots(2) data(37:60) pilots(3) data(61:84) pilots(4)...
    data(85:96) DC data(97:108) pilots(5) data(109:132) pilots(6)...
    data(133:156) pilots(7) data(157:180) pilots(8) data(181:192) guard2];
symbol_ofdm = sqrt(Nfft) .* ifft(symbol,Nfft);
margin = length(symbol_ofdm)*G;
symbolTx = [symbol_ofdm((end-margin+1):end) symbol_ofdm];
   
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
    % The channel is simulated:
     if N_SUI == 0                       % AWGN channel 
         symbol_channel = symbolTx;
     elseif N_SUI~=0                     % Channel with fading
         
         NextSymbol = 8 .* sqrt(Nfft) .* ifft(randint(1,Nfft));
         symbolTx = [NextSymbol NextSymbol symbolTx];
         symbol_channel = filter(channel,1,symbolTx);
         symbol_channel = symbol_channel(end-(256*(1+G))+1:end);
     end
     
    % The receiver is simulated:
     
    
    
    
    
    
    
    
    
    

margin = length(symbol_channel)*G;
margin = margin/(1+G);
symbol_ofdm_rx = symbol_channel(margin+1:end);
symbol_channel_rx = fft(symbol_ofdm_rx,Nfft) ./ sqrt(Nfft);
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

if encode == 1
    Eb = 1;
elseif encode == 0
    Eb = rate;
end

% Calculation of the variance of the noise.
sigma = (Eb*10^(-SNR/10)) / n_mod_type / 2;

% Finally, the noise to be added is calculated.
noise_channel = sqrt(sigma)*(randn(1,length(symbol_channel_rx)) + j*randn(1,length(symbol_channel_rx)));
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     symbol_channel_rx = symbol_channel_rx + noise_channel;
   
     
    % Decode the received bits:
     data_out = decoder (pilot_mapping,data_mapping,symbol_channel_rx,n_mod_type,codeRS,template,SNR,encode,bits_ofdm,channel,N_SUI);

    % The results are accumulated to finally verify the error.
     data_total_rx = [data_total_rx data_out];
 
 end

% Now the rate of error of the transmission is verified.

  n_ber = mean( data_total_rx(:) ~= data_total(:));