Re: [STDS-802-11-TGM] Oh, *that* energy detect?!
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Mark,
That all sounds correct, yes. Note that the term "CS/CCA" is new as of OFDM (it was just called "CCA" before that, but was clearly a CS and/or ED mechanism then, per the "CCA Mode x" tables I showed you this week). And, yes, CCA-ED is a separate thing, optional and required per regulatory domain rules. If you think you can simplify it, I'll look forward to your proposal. Don’t forget that all this just feeds into the overall CS mechanism, by combining with NAV, TX status and PHY-CCA, so there is more mess within the MAC, too.
CCA-ED is discussed explicitly in DSSS, HR/DSSS and OFDM PHYs. PHYs after that do, in my opinion, talk about still requiring the earlier clause PHYs' CCA pretty clearly. So, yes, I think by implication, CCA-ED is expected for all PHYs.
I would have said that CCA-ED threshold is in a MIB variable for 'future/unforeseen' flexibility. Like, a new reg domain comes along that needs a different (lower power?) level, so an external entity can force this, while the Standard catches up. Since the hard-coded level is in Annex D, it seems clear that this is "subject to change" if the regulations change, also. (In fact, there was discussion a few months ago about moving all the operating class parameters into ANA, so they could change rapidly/frequently without needing to amend the Standard. I'm not sure what happened to that idea.) I have no idea about the other ones, except maybe someone decided all the above should apply to all the thresholds, but too late to really fix everything up cleanly. This all does sound ripe for a D1.0 comment (including the ANA part).
> - What's the difference between "CCA-ED", "CCA-EnergyDetect", "CCA-Energy Detect", "CCA energy detect" and "CCA-EDBehavior"?
> Are the second and fourth just typos for the third, and the first just an abbreviation of the third; the fourth being the behavio(u)r associated
> with regdoms which require CCA-ED?
I'd say yes to all the above, except I think you meant the _fifth_ being "the behavio(u)r ..." I would also clarify that the fifth is the keyword for use in the Annex D table, only, also - so it isn't the behavior generically (that is CCA-Energy Detect), it is the keyword that tells you which domains require that behavior.
Mark
-----Original Message-----
From: Mark Rison [mailto:m.rison@xxxxxxxxxxx]
Sent: Friday, November 16, 2012 1:48 PM
To: Hamilton, Mark
Cc: STDS-802-11-TGM@xxxxxxxx
Subject: Oh, *that* energy detect?!
Hello Mark,
So let me see if I've now grokked this:
- CS/CCA includes both a "sniff the PHY header" mode and a "do energy detect" mode. The latter asserts CCA if the power is at least -62 dBm (assuming 20 MHz). These modes are both mandatory
- There's a *separate* "do energy detect" mode called CCA-ED which is the same as the "do energy detect" mode of CS/CCA except the threshold is -72 dBm. This mode is only used in some regdoms, namely the 3 GHz band in the USA (a.k.a. 11y)
If so, this is a very confusing way to describe it for a simple MAC person like me and I will raise a comment on D1.0!
Bonus questions:
- Is CCA-ED only required of the OFDM (11a) PHY? Or is it also required for PHYs which incorporate the OFDM PHY by reference (using the San Antonio wording)? What about 11n in GF mode, should this ever be done in a regdom where CCA-ED is mandatory?
- Why is the CCA-ED threshold in a MIB variable (dot11OFDMEDThreshold)? The other energy detect mode's threshold is not in any variable (or is this dot11EDThreshold (but this is only for the DSSS PHY) or even dot11TIThreshold (deprecated and in the dot11PhyOFDMTable though its description seems generic enough)?)
- What's the difference between "CCA-ED", "CCA-EnergyDetect", "CCA-Energy Detect", "CCA energy detect" and "CCA-EDBehavior"?
Are the second and fourth just typos for the third, and the first just an abbreviation of the third; the fourth being the behavio(u)r associated with regdoms which require CCA-ED?
Mark
--
Mark RISON, Systems Architect, Wi-Fi English/Esperanto/Français
Samsung Cambridge Solution Centre Tel: +44 1223 434600
Innovation Park, Cambridge CB4 0ZT Fax: +44 1223 TBCTBC
ROYAUME UNI WWW: http://www.samsung.com/uk
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