null sub carriers in OFDM

Hi !
I would like to know the utility of null subcarriers at the edge of an
OFDM spectrum. For example in Hiperlan2 or 802.11g, there are 5 null sub
carriers at both edges of the spectrum. Is it useful for the receiver, in
the case of multi user, in order to choose as well as possible the
sub-band and so to relax the constraint on the analog filter ?
Thanks a lot
Sylvain

I believe it is just to provide a guard band with adjacent signals and to
provide enough room for the IF filter transition band. Without the nulls
adjacent signals would interfere.

-Clark

"6.20" <traverso@ensea.fr> wrote in message
news:HfidnYK7jItgVMXZRVn-gQ@giganews.com...
> Hi !
> I would like to know the utility of null subcarriers at the edge of an
> OFDM spectrum. For example in Hiperlan2 or 802.11g, there are 5 null sub
> carriers at both edges of the spectrum. Is it useful for the receiver, in
> the case of multi user, in order to choose as well as possible the
> sub-band and so to relax the constraint on the analog filter ?
> Thanks a lot
> Sylvain
>
>