issues of FFT and zero padding in OFDM

[usab]

can any tell me that what is the effect of no of points of FFT/IFFT on the ofdm modulated data?
if the no of points is equal to, less/greater than the no of data samples what would happen?

also i need to know about the zero padding in FFT/IFFT?

 

[David83]

The number of points is the number of subcarriers, so you need the number of points greater than or equal to the number of symbols.

 

[usab]

Thankyou David83!

But I need to know the difference b/w the use of zero padding and cyclic prefix and guard band intervals , are they all same thing or not?
please explain!

 

[Mityan]

I think not the same.
Zero padding before fft means adding subcarriers without any signal, prodicung a frequency gap that is a margin for filter transition interval.
Cyclic prefix is extending the output fft vector by copying its end part to the beginning. In time domain this produces a guard interval for preventing inter-symbol interference (for the previous symbol delayed due to multipath may finish before next symbol comes).