>Zeph80 said the following on 09/03/2006 18:53:
>> Maybe I'm not framing my question right.Everywhere I read, they mentio
how
>> the head of the symbol(first n samples) is affected due to previou
symbols
>> and so how discarding the CP solves that.(the distortion occurs onl
in
>> head).What about the tail of the OFDM symbol,wont that be affected b
the
>> future symbols as much as the head would be by prevoius symbols.
>
>Technically, no. By definition, any realisable channel response must b

>causal - something at time t = 1 can't possibly affect something that
>happened at t = 0.
>
>However, the question of whether so-called precursor rays are an issue
>depends on your frame of reference. If your timing algorithm is
>designed with t = 0 defined as the strongest incoming ray, rather than
>the first incoming ray, then it will appear that precursors are
>affecting previous symbols. But in actual fact, its the fact that
>you're windowing blocks too late that's causing the interference.
>
>If you design your timing recovery algorithm to sync to the first
>incoming ray, then there will be no "precursors".
>
>
>> Why no guard interval at the end too?
>
>There is nothing to stop you utilise a cyclic postfix as well, the math

>is identical.
>
>Be aware though, a lot of standard OFDM synchronisation algorithms in
>the literature rely on the correlation statistics of the standard cycli

>prefix structure. Adding a postfix will probably require quite a bit o

>re-working of these algorithms.
>
>
>
>--
>Oli
>

Thank you, that makes a lot of sense.Though the cause for my confusio
stems, from the fact that while studying equalization they always conside
future symbols (at least in Sc systems).I realize the system is causal, s
is establishing a timning reference more difficult in these cases, or i
that the delay spread happens to be longer that the symbol time,and henc
precursor considered in Sc systems.