channel estimation in ofdm using preamble

Hi all,

In ofdma the preamble is of 2 symbol long first one consist of 4 shorth
and then long of some sequence.

how do we use second symbol preamble (or long preamble) to find the freq
response of channel to train equalizer? currently when i do a cross
correlation of a preamble received after channel with known sequence of
preamble i don't see the frequency response of the channel am i doing
something wrong??

On Wed, 03 Dec 2008 09:23:16 -0600, "adi_sharma1984"
<sharmaa@rohan.sdsu.edu> wrote:

>Hi all,
>
>In ofdma the preamble is of 2 symbol long first one consist of 4 shorth
>and then long of some sequence.
>
>how do we use second symbol preamble (or long preamble) to find the freq
>response of channel to train equalizer? currently when i do a cross
>correlation of a preamble received after channel with known sequence of
>preamble i don't see the frequency response of the channel am i doing
>something wrong??
>

Take the FFT of both symbols of the long portion of the preamble. Add
them together to suppress the noise.   You can use the same FFT that
would be used for the demodulation.

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php