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Why we need Channel Estimation Sequence for OFDM system?

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cambyzhu

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Can anyone tell me why we need the Chhanel estimation sequence to form an OFDM frame? What exactly this sequence doing?
 

Channel estimation is implemented to obtain the transfer function of the real
channel, which is necessary for non-differential modulated OFDM systems, such
as IEEE 802.11a.
eg.

d is the transmitted data before IFFT and d' is the received data after
FFT. Then
d' = d * H, where H is the transfer function.

Therefore H should be estimated before estimation of the transmitted data d
from d'.\]
 

For the purpose of the channel estimation, the transmitted data should be known at the receiver, which are called the pilot data. The channel estimation is not only used in OFDM but also in CDMA.
 

RF channel introduces distortion to the signal causing intersymbol interference. Channel estimation allows to determine that distortion. Furthermore it is possible to remove the distortion by multiplying received signal by inverse of RF channel transfer function.
 

channel estimation is essential for coherent detection.coherent receivers must know the carrier phase information ,hence we must transmit pilot data and based on this data the detector estimates the channel impulse response and compensates it.


regards
 

Hi,

Any one could u please explain how we doing channel estimation using pilot symbols.

1)Pilots we are inserting in between data subcarriers and they are not modulated.
Whether we need to extract the pilots from data after FFT operation or is there any process ?

2)After extraction what we are doing for estimating the channel?

Thanks in advance
Goud
 

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