OFDM question - RF Cafe Forums

 Post subject: OFDM question

Posted: Tue Sep 27, 2005 8:24 am 

Hello Everybody ,

I have question about OFDM system architecture. Why does it block IFFT in the transmiter and block FFT in the receiver? Can somebody you please show me the formulas and give a quick explanation?

Thank you very much - Lurce Tenneman

 Post subject:

Posted: Mon Jul 09, 2007 4:29 pm 

Hi Lurce,

To the best of my knowledge, when looking at a system level block diagram of an OFDM transceiver, the IFFT is contained on the transmitter side just before the mixer and the FFT block is on the receiver side just after the mixer.

Really, there is a DAC and LPF (perhaps other blocks) after the IFFT in the TX and there is probably some type of AGC plus filters and an ADC after the mixer on the RX side.

The names of these blocks stand for Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT). They are supposed to represent the signal processing which is done to convert a time domain signal into a frequency domain signal and back again (which is what must be done to encode and decode the digital information into an analog signal).

I'm not 100% sure what they do, but I do know that they are part of a DSP algorithm and to find out more information you can visit a signal processing or modulation theory book to get a little more information.

I hope this helps a little bit.

-J