% ofdm_fading.m
%
% Simulation program to realize OFDM transmission system
% (under one path fading)
%
function [ber]=ofdm_fading(ebn0)
%********************** preparation part ***************************

para=128;   % Number of parallel channel to transmit (points)
fftlen=128; % FFT length
noc=128;    % Number of carrier
nd=6;       % Number of information OFDM symbol for one loop
ml=1;       % Modulation level : BPSK
sr=250000;  % Symbol rate
br=sr.*ml;  % Bit rate per carrier
gilen=32;   % Length of guard interval (points)

%******************* Fading initialization ********************
% If you use fading function "sefade", you can initialize all of parameters.
% Otherwise you can comment out the following initialization.
% The detailed explanation of all of valiables are mentioned in Program 2-8.

% Time resolution

tstp=1/sr/(fftlen+gilen); 

% Arrival time for each multipath normalized by tstp
% If you would like to simulate under one path fading model, you have only to set 
% direct wave.

itau = [0];

% Mean power for each multipath normalized by direct wave.
% If you would like to simulate under one path fading model, you have only to set 
% direct wave.
dlvl = [0];

% Number of waves to generate fading for each multipath.
% In normal case, more than six waves are needed to generate Rayleigh fading
n0=[6];

% Initial Phase of delayed wave
% In this simulation four-path Rayleigh fading are considered.
th1=[0.0];

% Number of fading counter to skip 
itnd0=nd*(fftlen+gilen)*10;

% Initial value of fading counter
% In this simulation one-path Rayleigh fading are considered.
% Therefore one fading counter are needed.
  
itnd1=[1000];

% Number of directwave + Number of delayed wave
% In this simulation one-path Rayleigh fading are considered
now1=1;        

% Maximum Doppler frequency [Hz]
% You can insert your favorite value
fd=320;       

% You can decide two mode to simulate fading by changing the variable flat
% flat     : flat fading or not 
% (1->flat (only amplitude is fluctuated),0->nomal(phase and amplitude are fluctutated)
flat =1;
    
%************************** main loop part **************************

noe = 0;    % Number of error data
nod = 0;    % Number of transmitted data

berlim=1000;

while noe<berlim

nod=nod+1;
%************************** transmitter *********************************

%************************** Data generation **************************** 

seldata=rand(1,para*nd*ml)>0.5;  %  rand : built in function

%****************** Serial to parallel conversion ***********************

paradata=reshape(seldata,para,nd*ml); %  reshape : built in function

%************************** BPSK modulation ***************************** 

moddata=paradata.*2-1;

%******************* IFFT ************************

y=ifft(moddata);      %  ifft : built in function

%********* Gurad interval insertion **********

[ich3,qch3]= giins(y,zeros(size(y)),fftlen,gilen,nd);
fftlen2=fftlen+gilen;

%********* Attenuation Calculation *********

ebn0=0:2:20;
spow=sum(ich3.^2+qch3.^2)/nd./para;  %  sum : built in function
attn=0.5*spow*sr/br*10.^(-ebn0/10);
attn=sqrt(attn);

%********************** Fading channel **********************

% Generated data are fed into a fading simulator
[ifade,qfade]=sefade(ich3,zeros(size(ich3)),itau,dlvl,th1,n0,itnd1,now1,length(ich3),tstp,fd,flat);
  
% Updata fading counter
itnd1 = itnd1+ itnd0;

%***************************  Receiver  *****************************
%***************** AWGN addition ********* 

[ich4,qch4]=comb(ifade,zeros(size(ifade)),attn);

%****************** Guard interval removal *********

[ich5,qch5]= girem(ich4,zeros(size(ich4)),fftlen2,gilen,nd);

%******************  FFT  ******************

ry=fft(ich5);% fft : built in function

%***************** demoduration *******************

demodata=ry>0;   

%**************  Parallel to serial conversion  *****************

demodata1=reshape(demodata,1,para*nd*ml);

%************************** Bit Error Rate (BER) ****************************

% instantaneous number of error and data

noe2=sum(abs(demodata1-seldata));  %  sum : built in function

% cumulative the number of error and data in noe and nod

noe=noe+noe2;
   
end

ber=noe/(nod*para*nd*ml);