>As long as the channel impulse response is less than the duration of
>the cyclical prefix, there should be no inter-symbol interference. In
>this case the receiver need only remove the cyclical prefix samples and
>conduct an FFT for demodulation of the symbol.
>
>Should this not be the case as is usually expected, the receiver needs
>to compensate by creating a time-domain equalizer (TEQ) at the front
>end. In truth, the purpose of the TEQ is to create an overall shortened
>impulse response when placed in series with the actual channel that
>ordinarily has a impuse response longer than the CP.
>
>There are any number of methods of computing the TEQ, all with various
>tradeoffs.
>
>Good luck.
>
>-V
>
>

Hi,

Thank you for your replies. I don't think I made myself clear in m
earlier posting.

1) What I want to understand through simulation is the effect of cycli
prefix length on performance in a multipath channel.

For example consider that the channel impulse response is [0.7071 0 0 0
0 0 0 0 0.7071], which is a channel with impulse response length 10
static paths with no fading component).
Now if we consider four cases
1)cp=0,
2)cp=5,
3) cp=11
4) cp =15

The first two cases, based on theory should result in ISI. My question is
when i perform the simulations i do not see much of a difference. Will th
difference be seen only at high SNR's ?


2) Presently, I transmit a known OFDM symbol at the beginning of th
simulation, At the receiver after FFT operation I divide the output wit
the known OFDM symbol values and store them as channel state informatio
for the remaining simulation.
For all subsequent transmissions after the FFT operation i divide th
output with the stored channel state information ( Zero forcing i
frequency domain).
My question is even for cyclic prefix lengths greater than the impuls
response, don't we still need to do equalization operation at the receive
( something trivial as i am doing now).
Also can anyone suggest me a reference to other frequency domai
equalization approaches.

Thanks