encoder.m

802.16 physical layer simulation through diferent SUI Channel.

function [pilot_mapping,data_mapping] = encoder (data_in,codeRS,template,n_mod_type,encode)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%                                                                       %
%%         Name: encoder.m                                               %
%%                                                                       %
%%         Description: In this file, all the different stages of        %
%%          the transmitter is called, which are defined in the  r       %
%%          IEEE802.16-2004 standard.                                    %
%%                                                                       %
%%         Result: It returns the chain of bits, already modulated       %
%%          in frequency domain, thanks to the IFFT, prepared to be      %
%%          through the channel.                                         %
%%                                                                       %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 BSID = 1;            % These three values are for the algorithm of randomization of the data. 
 DIUC = 7;            % They are used to calculate the seed.
 Frame = 1;           
 n_symbol = 1;         % At the time of generating the pilots, I need to know what symbol i am simulating 
                       % because the seed to do it depends on it. 
 Tx = 1;               % For some functions, it is necessary to indicate that i am transmitting and not receiving.
  
if encode
    % According to the scheme, i mus introduce the data to transmit by
    % diverse phases of encoding. We begin the randomization.


    seed = zeros (1,15);
    seed=[de2bi(BSID,4,'left-msb') 1 1 de2bi(DIUC,4,'left-msb') 1 de2bi(Frame,4,'left-msb')];
    data_random =zeros(1,length(data_in));
    for i=1:length(data_in)
        next = xor(seed(14),seed(15));
        data_random(i) = xor( data_in(i),next);
        seed = [next seed(1,1:14)];
    end

     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
 

% Now i encode with Reed-Solomon coding:
 m = 8;                          % Number of bits per symbol
 n = codeRS(1);                  % Length of the codeword
 k = codeRS(2);                  % Number of information symbols
 
 % To realize the Reed-Solomon code, the information is needed in decimal.

  data_random = reshape(data_random,8,length(data_random)/8)';
  data_random = bi2de(data_random,'left-msb');
 
% 36 bytes are needed with a stuffed zero at the end of the vector:
yk=[data_random' 0];
% The Galois vector is generated, the generating polynomial of the
% code. Then the symbols are encoded with Reed-Solomon.
msg = gf([yk],m); 
if n==k                      % bypass for BPSK
   codeRS = msg;   
elseif n~=k
   codeRS = rsenc(msg,n,k);
end
data_RS= codeRS.x;
% The binary data to continue working:
data_RS= double (data_RS);
data_RS= de2bi (data_RS,8,'left-msb');
% Serial the data for the next step.
data_RS = reshape (data_RS', 1, length(data_RS)*8);
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

% Afterwards, the data is sent to th convolutional encoder.
t=poly2trellis(7, [171 133]);
block = length (template);               % Length of the template
code_final=[];
% Transmitting --> encode.
code = convenc(data_RS,t);
code_punctured = code;
repeat = length(code)/block;         % When the template needs to be applied.
% Depending on the mapping, more or less bits will remain.
% Puncturing is realized.
for i=0:repeat-1
    sample = code_punctured (i*block+1:(i+1)*block);
    for j=1:block
        if template(j)==1
           code_final = [code_final sample(j)];
         end
     end
end
data_convolutional = code_final;
    



     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

% Finally, we interleave the block:
% The size of the block to use to interleave the sequence is needed.
% This value is taken from table 223 of the standard.
% The value of the used block depends on the mapping that we want.

switch n_mod_type
    case 1                          % for BPSK
        Ncbps=192; 
    case 2                          % for QPSK
        Ncbps=384; 
    case 4                          % for 16-QAM
        Ncbps=768; 
    case 6                          % for 64-QAM
        Ncbps=1152; 
end

s=ceil(n_mod_type/2);
  % In the following operations, it is necessary to consider the following values:
  % k-->index of the bit encoded BEFORE the first permutation
  % mk-->index of this bit BEFORE the second permutation and AFTER the first one
  % jk-->index after the SECOND permutation, just before the mapping of the sign.

    k = 0:Ncbps-1;
    mk = ((Ncbps/12)*mod(k,12))+floor(k/12);                     % First permutation
    jk = s*floor(mk/s)+mod(mk+Ncbps-floor(12*mk/Ncbps),s);       % Second permutation

    % Now I must arrange the indices to know in what order I must take the bits of the entering sequence. 
    [a c] = sort(jk);

 i = 1:Ncbps-1;
data_interleaved = zeros(1,Ncbps);
data_interleaved(i) = data_convolutional(c(i));     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
else 
   
    data_interleaved = data_in;
    
end

% Once the encoding is done, the data is mapped following the constellation
% in which we are working.

 data_mapping = mappingTX (data_interleaved, n_mod_type);
 
% Before the OFDM symbol is created, the pilot carriers must be inserted,
% which help with channel estimation.










% The values of the pilots are to be modulated on to the carriers. These
% are defined in the standard as such(pp 443) :

% Before beginning, it is necessary to consider that the value to calculate
% depends on 2 factors : the number of symbols and whether we are in the
% uplink or dwnlink. We will consider that we are in the downlink and we
% are transmitting the symbol "1". If we want to consider the other
% connection, the seed would be "10101010101".

seed = [1 1 1 1 1 1 1 1 1 1 1];

for i=1:n_symbol+2                         
    wk(i) = seed (11);                   
    next = xor(seed(9),seed(11));
    seed = [next seed(1,1:10)];
end

% Once the value of wk is found(that depends on the number of symbol with
% wihich it is working), the values of the subcarriers must be found and of
% the mapping of them with BPSK constellation.

wk = wk(n_symbol+2);

A = 1 - wk;                                 % Values defined in the standard.
B = 1 - (~wk);
value_carrier = [A B A B B B A A];

% For uplink, the values should be [A B A B A A A A]

pilot_mapping = 2*mappingTX(value_carrier,1);      

% The factor of "2" is due to the fact that the pilots are transmitted to a
% double power of the information bits.
 
 
 
return;