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The results show what can happen if there
is an overlapp, so they are valid for the overlap case, as well as for the
non-overlap 20 MHz operations. If you compare the two, then the
conclusion is that the BSSs shall operate in 20 MHz non-overlapping regions,
which 11n draft states now (and this is one of the conclusions drawn in the
earlier email by Bill). For the second reason, do you mean only 11n
devices? If so, then “may” does not guarantee that they will set 40
MHz Intolerant bit. How can it be guaranteed that this bit will be set (by
these devices) for other radios operating in 2.4 GHz then? - Ariton From: The results are not valid for 2.4 GHz for
at least two reasons: 1) no partial overlap is allowed in 2.4
GHz 2) any device may transmit the 40 MHz Intolerant
bit for any reason Regards, Eldad From: The latest draft on 802.11n enables CCA in
secondary channel (earlier called extension channel) and also allows for
transmission in 20 MHz primary channel (earlier called control channel) if the
secondary channel is busy; thus it allows switching as well. If one wants to
compare it with the latest draft then the results that use CCA and switching
should be considered. The only other (major) difference is 40 MHz Intolerant
bit, which would restrict the 20/40 MHz operating BSS in either 20 MHz only or
20/40 MHz. However, 40 MHz Intolerant bit does not apply to legacy BSSs
(802.11a/g/b). Hence, the results are still valid when legacy BSSs are
operating in the secondary channel, even for draft 5.0. - Ariton From: Please keep in mind that this paper is
based on 802.11n draft 1.0. The coexistence mechanisms for 40 MHz in 2.4
GHz in draft 5.0 are much different. Regards, Eldad From: Bill Shvodian
[mailto:bill.shvodian@IEEE.ORG] Ariton, Thanks for posting the coexistence
paper. It has some very interesting results. Here are my
conclusions: 1) Clearly without the Ext. CCA it would
be much better to keep the two networks on separate 20 MHz channels. 2) If the Ext. CCA is used without switching,
the throughput for the 802.11n network using 40 MHz is roughly the same as the
throughput for the 11n network in 20 MHz, while the throughput for the legacy
BSS drops from 28.3 Mbps for an unshared channel to 12 Mbps. So the
802.11n network sees no gain, while the legacy network sees a drastic 58% drop
in throughput. So again, it looks like it would be better to keep
the the two networks on separate 20 MHz channels. 3) In the case with Switching and CCA (and
reduced TXOP for 40 MHz transmissions), the 802.11n network sees a 10%
throughput increase from 60 mbps to 66 Mbps, while the legacy network sees a
14.5% decrease, from 28.3 Mbps to 24.2 Mbps. This seems like a case
of robbing Peter to pay Paul. I think that it is important to note how
poor the performance is without Ext. CCA and how with Ext. CCA but without
switching, there is no increased throughput for the 11n network, while the
legacy network throughput is badly degraded. The only option that appears
to have any merit is the one with Switching and Ext. CCA,
but even in that case the gain for the 802.11n network comes at the price of a
larger relative (percentage) decrease in the throughput for the
legacy network. So even then it can be argued that it is better, or at
least more fair, to keep the two networks on separate 20 MHz
channels. My conclusion from this paper is that the
802.11n network should use 20 MHz mode in a clear 20 MHz channel rather
than using 40 MHz mode where 20 MHz is shared with a legacy network.
I would be interested to hear if others come to the same conclusion.
Thanks again. Regards, Bill From: Ivan, Attached is some earlier work that I did
with a couple of colleagues at TI (Anuj Batra and Artur Zaks) on the 20/40 MHz
coexistence of overlapping BSSs in WLANs. I do not plan to make a presentation
on it; however, I just wanted to provide 802.19 members with some information
on 40 MHz operation impact on WLAN networks, and more specifically, overlapping
BSSs. Regards, - Ariton From: All,
We will be having a conference call on 40 MHz 802.11n Coexistence. The
call is on Monday June 9 at 1 PM EDT (10 AM PDT).
I will be traveling so Ivan Reede, the 802.19 vice chair, will chair the call.
At this point we have not had any volunteers to present any material. It
would be good if we could have a few volunteers to prepare some material to
lead focus the discussion. If anyone wants to volunteer please notify
Ivan Reede I_reede@amerisys.com
I would ask that the 802.11 liaison (Eldad) and 802.15 (Sheung) make those
working groups aware of this meeting. Agenda
TO ATTEND THE AUDIO CONFERENCE: 1. Call +1
858-845-5000 2. After the greeting press 1 to attend meeting. 3. Enter Meeting ID 80219 4. Enter Meeting Password 80219
followed by the # sign. 5. Follow the remaining prompts for recording the callers
name and joining the meeting. For assistance, dial #0 at any time. Steve |