Re: [802.19] Possible 802.11n spectrum scanning requirements
Title: Re: [802.19] Possible 802.11n spectrum scanning requirements
Dave,
In 2003, IEEE 802.11 and 802.15 working groups jointly approved IEEE Std 802.15.2™-2003. This recommended practice defined AFH for FHSS devices that has been implemented in IEEE Std 802.15.1™-2005. It does not seem to be implemented by IEEE Std 802.11™-2007 in the FHSS PHY clause 14. I guess some 802.11 radios are more accepted than others.
IEEE 802.11 WG has also claimed that “listen before talk” as an excellent mechanism for sharing the ISM band. However, the definition of CCA for the various PHY modes in 802.11-2007 all seem to only detect modes that correspond to the type of transmit mode that it is ready to send. Never looks for anything, but current 802.11 PHYs.
So how can TGn claim they are ‘sharing the ISM band”? There is a lot of detection for legacy 802.11 BSS’s before enabling 40MHz channel usage. Why should this be done for legacy 802.11 and not legacy 802.15 devices? It would seem reasonable to provide a method for detecting other than just 802.11 users of the spectrum before camping on more than half of the ISM band. The AFH scanning method used in 802.15.1 devices seems to be working well, is implemented in devices designed for low power and low cost, and is continuously being improved. It will even reduce available spectrum down to less than 25% of the full ISM band to avoid interference with other radios sharing the band. However, this reduces the number of channels available for sharing with other FHSS devices.
Given that the 802.11 WG has never implemented mechanisms to avoid interference with other 802 devices, now that the 802.11 WG wants to use more than half of the available ISM band for one BSS it may be time for a reasonable non-802.11 radio scan be defined. This would demonstrate to the IEEE 802 EC that the 802.11 WG is serious about fair use of the ISM band.
Regards, John
On 10/22/08 6:16 PM, "David Bagby" <david.bagby@xxxxxxxx> wrote:
Steve,
I honestly do not think that .19 should go down that road.
If it does, I strongly suggest that requirements to scan for other 802 family wireless devices would have to apply to ALL 802 wireless devices.
Let's consider:
1) The ISM bands are what they are: ISM band devices are required by law to accept any interference received from other ISM devices.
2) Another factoid is that 802 devices constitute a small portion of the things found in ISM bands. (ref the tutorial given by the hospital guys re what they saw in ISM bands when they scanned).
3) Independent of if we like it or not, the mixture of signals in the ISM bands is not static - what one accounted for in yesterday's design may or may not be good enough tomorrow - the band signal content is dynamic.
4) The law has no analogy of a homestead act for spectrum in the ISM bands - Ownership of spectrum is not conveyed by sales of devices.
5) The source of what one's device perceives as "interference" is not really relevant (in that it does not matter if it is from another 802 device or a non-802 device).
6) Channel width used by a device is also not relevant (100 1MHZ adjacent channels fill the same amount of spectrum as 1 100MHz channel).
My pragmatic conclusion, developed over many years, is that if one wants to play in the ISM bands, one had better be able to operate in the ISM environment, including accepting the interference one is likely to receive. If one's device can't handle that, don't expect to have a successful product.
SO then I ask why scan for 802 devices?
Presumably because "someone" wants "something" to happen to make their operation "better" when the "other" devices are found....
Who is to say what use of the ISM band is more important that another?
The only consistent answer to those questions I would expect to hear is "mine is more important than yours"; a rat hole argument that can never be "won".
I've observed that people tend to react emotionally along the lines of "just don't interfere with me"....
ISM band reality is that if ISM product operation depends on assumptions that can not be guaranteed in the ISM band, one may not have made a good choice of spectrum for the product design.
When I consider these points, I wonder what is the benefit of having 802 devices looking for only other 802 devices?
What will they do when they find them?
Who gets out of the way of whom?
why?
based on what objective or criteria?
Having found 802 devices, does it matter given the full extent of devices operating in the ISM band?
Seems to me like a lot of work to address a rather small percentage of the ISM "interference sources".
Suppose 802 did eventually require that all 802 devices look for other 802 devices....
to what end?
how would 802 keep that updated as new devices are invented?
Cross coupling operational aspects of different 802 standards in that manner would seem to be an enormous complication; and one that I don't see a payback for. The pace of the 802 standards process pretty much tells me that by the time that "802 family scanning" were standardized, the assumed mixture of devices would be obsolete. And what would old 802 devices do wrt to new ones? they would have no way to know how to scan for them...
I think it very unwise for .19 to attempt to extend simple "coexistence" (which is not and has never been a synonym for "zero interference interaction") into "cross 802 wireless standard awareness" or (even more complicated) "dynamic spectrum management between 802 devices".
I suspect that anyone which sticks a toe in that tar pit is unlikely to ever see their toe (or foot or...) again...
Dave
____________
David Bagby
Calypso Ventures, Inc.
office: (650) 637-7741
email: Dave@xxxxxxxxxxxxxxxxxxx
-----Original Message-----
From: Shellhammer, Steve [mailto:sshellha@xxxxxxxxxxxx]
Sent: Wednesday, October 22, 2008 3:05 PM
To: STDS-802-19@xxxxxxxxxxxxxxxxx
Subject: [802.19] Possible 802.11n spectrum scanning requirements
All,
On the 40MHz 11n coexistence conference call it was suggested that the 802.19 TAG start to look at possible Spectrum Scanning Requirements. A proposal was made to add include an option for spectrum scanning in the standard. The proposal was made by John Barr and can be found at,
https://mentor.ieee.org/802.11/file/08/11-08-1101-04-000n-additional-40-mhz-scanning-proposal.ppt
While the 802.11 WG discusses the merits of this proposal, the 802.19 TAG is a good forum for having technical discussions on possible requirements and technical feasibility. This information may be useful to 802.11 in making its decision on how to address this proposal. The text on Slide 6 of John’s presentation beings to discuss possible requirements. That may be a good place to look at to stimulate thinking on this topic.
During the conference call it was suggested that the primary non-802.11 systems that are of concern are 802.15.1 (Bluetooth) and 802.15.4 (Zigbee) since they both operate in the 2.4 GHz band.
Anyone who would like to prepare a presentation on possible spectrum scanning requirements for these non-802.11 systems please notify me. We can discuss any such presentations on the next conference call on November 3 or at the Plenary meeting in Dallas.
Thanks,
Steve
--
John R. Barr (John.Barr@xxxxxxxxxxxx)
Director, Standards Realization - <http://www.motorola.com>
Vice Chairman of the Board, Bluetooth SIG - <http://www.bluetooth.org>
(847) 576-8706 (office) +1-847-962-5407 (mobile) (847) 576-6758 (FAX)