function [data_out]=ofdmsymbol_fft_cp(data_in,G,TxRx)
% We can make Nfft as a parameter as well
Nfft = 256;
if TxRx==10
data=data_in'; %this makes the input column vector to a array
% %% making odfm symbol and taking IFFT
% function symbol_ofdm = createsymbol (pilots,data)
%% now first generate the pilot
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
A=complex(-1,0);
B=complex(1,0);
pilots = [A B A B B B A A]; %%% here we direct making the pilot,detail procedure given below
% 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.
% % The values of the pilots are to be modulated 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 uplink 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 - 2*wk % Values defined in the standard.
% B = 1 - 2*(~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*mapping(value_carrier,1,Tx);
%
% % The factor of "2" is due to the fact that the pilots are transmitted to a
% % double power of the information bits.
% NOW The guard bands are prepared.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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_ofdm = [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];
% here the ofdm symbol is completed
%Now taking IFFT
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
symbol_ofdm = sqrt(Nfft).*ifft(symbol_ofdm,Nfft);
%Now adding cyclic prefix%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% we generate the cyclic prefix so that the multipaths do not affect our data so much.
margin = length(symbol_ofdm)*G;
data_tx = [symbol_ofdm((end-margin+1):end) symbol_ofdm];
data_out=data_tx;
% At receiving end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
elseif TxRx==01
data_rx=data_in;
% First, we must remove the CP.
margin = length(data_rx)*G;
margin = margin/(1+G);
symbol_ofdm_rx= data_rx(margin+1:end);
% After removing the CP, we have to inverse the IFFT, logcally by FFT.
symbol_rx = fft(symbol_ofdm_rx,Nfft) ./ sqrt(Nfft);
% Here the pilots are indicated, since i need to know where they are.
% now we will be able to estimate the channel.
pilots = [symbol_rx(41) symbol_rx(66) symbol_rx(91) symbol_rx(116) symbol_rx(142) symbol_rx(167) symbol_rx(192) symbol_rx(217)];
% After getting the received symbol, the channel is to be estimated using
% the pilot carriers. This is bypassed for an AWGN channel.
% Next, the values of the data and pilot carriers are extracted
data_total = [symbol_rx(29:40) symbol_rx(42:65) symbol_rx(67:90) symbol_rx(92:115) symbol_rx(117:128)...
symbol_rx(130:141) symbol_rx(143:166) symbol_rx(168:191) symbol_rx(193:216) symbol_rx(218:229)];
data_out=data_total'; %this makes it a column vector
else
disp('error in ofdmsymbol_fft_cp.m function');
end
