Ofmd modulator: IFFT

[Altera_Forum]

Hi All. 

 I am realizing an Ofmd modulator.  I have a problem with zero padding of the IFFT. :confused:  I decide to use the FFT MegaCore Function v9.0. I have 1536 samples and I choose a 2048 samples IFFT.  Now, how I have to do zero padding?  I think it depends from  1) the input data mode that I choose in FFT MegaCore (natural, bit reversed, DC centred) 2) my samples order. They are DC-centered because they corresponding to carriers from (-768 to 768) excluding 0, that is DC carrier.  In that case where have I to put zeros?   Moreover from FFT MegaCore User Guide: what does it mean that the signal is in "natural order", "bit-reversed" or "DC centred? And if I pass to the IFFT Ip core a signal DC-centred and the output is in natural order, have I to re-order samples in DC-centred order before transmission?  I hope someone can explain me, sorry if I was a bit confusing.

[Altera_Forum]

To keep the shape of the spectrum, u should pad ONE zero to the front to keep DC centred, and 2048-1536-1 zeros to the center of the 1536 samples. 

Scale factor should be considered.

[Altera_Forum]

Thank you hawke. I don't undestand two things. 1) Why have I to put a zero in front of my vector? 2) And why "Scale factor should be considered"? Thank you again.

[Altera_Forum]

Hello Dear, please i need the core of ofdm modulator if you can send it to me : tahkou_khaled@yahoo.fr