How to insert pilot symbols in OFDM system?

[engineer_eda]

Hi,

Can anyone please help me in understanding pilot carriers in OFDM system? As far as I know pilot symbols are inserted before IFFT in OFDM system. Are they actually zero points added into the modulated data after constellation mapper (and before IFFT)?And what is the formula to add pilots in the data in parallel stream?

Thanks in Advance!

 

[engineer_eda]

I would appreciate if you provide me the explanation about my questions above. Thanks!