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48 data carriers or 24 in 802.11 OFDM transmission?

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Antonio_Magma

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I understand to obtain a real output from IFFT, its input has to be conjugate symmetric. In 802.11a, 64-point IFFT is used with 48 data carriers and 4 pilot carriers.

If all the 48 data carriers are carrying data then where are its conjugate carriers?
 

hi,

To get a real signal after IFFT operation, you need to feed conjugate symmetric. This results in wastage of half the carriers.

If all the 48 data carriers are carrying data then where are its conjugate carriers?
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There are no conjugate carriers. In 802.11a they use the whole 48 data carriers for sending data, this will result in complex numbers in the time domain. These complex number are modulated using QAM (Quadrature Amplitude Modulation).

The catch is, If you are not willing to do QAM at the Tx before transmission you need to get a real signal as the output of the IFFT operation (which will result in wastage of half the data carriers) as in your case.

i hope this answers your doubt....
 

Sorry guys,

can anyone explain to me the difference between data and pilot ? I 'm quite new to this topic and I would need also material on this..

Thanks in advance.

Lupin
 

Helo lupin data is the actual data which u ar intending to send it to the receiver..while the pilot means some kind of accessory data used for the estimation of the channel.... so to estimate the channel pilot bits are used.... hope the answer is satisfactory....
 

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