Using Pilot tones to estimate carrier frequency offset in ofdm I have been studying carrier frequency offset estimation techniques in OFDM systems. I have understood several of them. when using Pilot tones, as stated in paper (1), the process involves two methods namely: acquisition and tracking modes. a large range CFO is estimated in the acquisition mode while in  the tracking mode, only fine CFO is estimated. 
I have confusion, What are the nature of those Pilot tones? how are they being generated?
the authors of the paper wrote equation (18) without any derivation? can I get the system model for this technique?
the questions may sound easy, but I really need it. Thanks in advance.

Reference:
(1) Praween Kumar Nishad,  P. Singh, "Carrier Frequency Offset Estimation in OFDM Systems", National Institute of technology
http://dspace.nitrkl.ac.in/dspace/bitstream/2080/1928/1/ID-451_praween.pdf
I am familiar with 802.11a, so I'll answer your questions with regard to how 802.11a does it.

What are the nature of those Pilot tones?


There are 64 sub-carriers in 802.11a.  Four of them are used as the pilot channels.  The pilots themselves are simply known data- if I remember correctly they are either (1 + i) or -(1 + i).

how are they being generated?


The transmitter just puts the appropriate data into the pilot sub-channels and then ifft's the entire symbol (i.e. with all of the other sub-channels).

the authors of the paper wrote equation (18) without any derivation?


This isn't really a question.

can I get the system model for this technique?


What do you mean by a system model?  We don't normally provide code.