function [output_mod_data]=OFDM_modulator(input_mod_data,guard_length)
% Function OFDM_modulator +++++++++++++++++++++++++++++++++++++++++++++++++
% realize OFDM modulation

% Input data:  input_mod_data - input data vector of modulator 
%              guard_length- the length of guard interval
% Output data: output_mod_data - output data vector of modulator

% Begin:  Feb, 2005
% Last edited: Feb.1, 2005
%   Feng Wan   

output_mod_data=zeros(size(input_mod_data,1),size(input_mod_data,2)+guard_length,size(input_mod_data,3));
ifft_length=length(input_mod_data);
temp_data=sqrt(ifft_length)*ifft(input_mod_data);     %IFFT
%Add the cyclic prefix
for n1=1:guard_length
    output_mod_data(n1)=temp_data(ifft_length-guard_length+n1);
end
for n1=1:ifft_length
    output_mod_data(n1+guard_length)=temp_data(n1);
end