The benefits: Higher data rates
The physics: If more information is encoded (at the same bandwidth of 20
MHz), more energy is needed. That is, you will see an increase from -82 dB
receiver sensitivity @ 11 Mbps to -68 dB for 54 Mbps (of which you get 25
Mbps net data rate).
The drawbacks: If your typical link lives well at -70 to -75 dB signal
level, you will need higher gain antennas or more TX power for the same
distance (if you want to take advantage of full speed). Or, in practice, you
will have to live with a significantly reduced cell radius. And in no way
will it help you with trees. This is more "good line of sight needed" (i.e.
including the fresnel zone) than ever before.
Of course, if you don't need the full 54 Mbps, lower OFDM rates are
available which require less signal at the receiver. My guess it that we
will see many links which do not arrive at full speed because we can't make
the -68 dB happen in all cases.
In 802.11g (or .a) BSS mode, some CPEs could be at full speed, some at lower
speed. With Turbocell, which uses multicasts, ALL CPEs use the same speed.
So you will have to pick the lowest OFDM modulation scheme that works with
the most far away CPE. This is not different now, but in order to select 54
Mbps, all your customers would have to have a signal level better than -68
(not only some).
Kind regards,
--
true global communications GmbH
Thomas Giger
In der Au 27, 61440 Oberursel, Germany.
fon +49.6171.63810 fax +49.6171.638119
X-NCC-RegID: de.tgc
> -----Original Message-----
> From: Brett Hays [mailto:bretth@htonline.net]
> Sent: Thursday, July 31, 2003 3:44 PM
> To: Karlnet Mailing List
> Subject: Re: [Karlnet] ofdm in 2.4ghz?
>
>
> So, in practice what benefits are people seeing?
>
> Will a marginal link due to trees improve with ofdm?
>
>
> ----- Original Message -----
> From: "Roger Boggs" <rogerboggs@att.net>
> To: "Brett Hays" <bretth@htonline.net>; "Karlnet Mailing List"
> <karlnet@WISPNotes.com>
> Sent: Thursday, July 31, 2003 8:27 AM
> Subject: Re: [Karlnet] ofdm in 2.4ghz?
>
>
> > http://www.wave-report.com/tutorials/OFDM.htm
> > http://www.wi-lan.com/library/whitepaper_wofdm_general.pdf
> >
> > At 08:07 AM 7/31/03 -0500, you wrote:
> > >Is there a one paragraph explanation of OFDM that someone
> could post. I
> am
> > >not sure I understand it. Is it a 'near line of sight' technology?
> > >
> >
> > Roger Boggs
> >
> >
> >
>
>
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>
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