1. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 1 Signaling of intolerance for 40 MHz transmissions Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair stuart@ok-brit.com as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdf stuart@ok-brit.compatcom@ieee.org Date: 2006-12-08 Authors:

2. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 2 Abstract There are various opinions regarding the ability of 20 MHz-only capable devices to coexist with 40 MHz transmissions on overlapping channels. In order to accommodate the various possible solutions to the decision to allow or forbid 40 MHz transmissions, some signaling mechanism is needed. This presentation offers a signaling mechanism and proposes a set of rules to use in making the decision to allow or forbid 40 MHz transmissions.

3. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 3 Detection of 40 MHz intolerant devices 40 MHz Intolerant Devices must be detected –Measure amount of traffic? Traffic is dynamic Measurement is complex –Which parameters are measured? Busy medium? Noise vs signal. Frame receptions? Per AC? Capture of TSPECS? Who measures? Who digests the measured results? What is the proper threshold? –Reception of beacons Much simpler Lower threshold Will need to propagate discovered information

4. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 4 Detection of neighboring devices Detect 40 MHz intolerant devices –The detection can be performed by: AP only AP + STA –AP cannot detect all overlap cases “Marginal overlap” case is important Requires STA participation

5. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 5 “Full overlap” AP 40 can receive beacons from AP 20-only AP 20 only STA_A 40 or 20 AP 40 or 20 STA_B 40 or 20 STA_C 20 only

6. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 6 “Marginal overlap” AP 40 and STA_B cannot receive beacons from AP 20-only –But STA in the overlap area can hear beacons from both APs –STA_B and STA_C will interact with each other AP 20 only STA_A 40 or 20 AP 40 or 20 STA_B 40 or 20 STA_C 20 only Inform Restrict Effective communication range of AP 20 only Effective communication range of AP 40 or 20

7. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 7 Detecting devices Marginal overlap case is important –STA_B and STA_C will interfere, but STA_B does not detect beacons from AP 20-only –So both AP and STA will need to participate in detection of intolerant 40 MHz devices –STA need a mechanism for communicating discovery to the AP So that AP can inform other STA in the BSS of the overlap (e.g. STA_B)

8. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 8 Classification rules Devices that may be 40 MHz intolerant: –Legacy 802.11b Proposed protection mechanisms are viewed as insufficient –Legacy 802.11g Same answer –TGn devices May indicate intolerance for various reasons –Information to be used to classify: Absence of HT Capability element New bit in HT Capability element: Forty_MHZ_Intolerant

9. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 9 Behavior rules Assuming that intolerant devices are discovered –BSS must be switched to 20 MHz-only operation if: The AP detects intolerant BSS overlap –Only covers Full overlap case Any STA in the BSS detects intolerant BSS overlap –Takes care of marginal overlap case –Provided that STA can signal overlap to AP See new Forty_MHZ_Intolerant bit Another AP indicates “intolerance” –New Forty_MHZ_intolerance bit may be set by an HT-AP –Recovery period before BSS may switch back to 40 MHz operation

10. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 10 Legacy BSS prevents 40 MHz operation Detection –Look for presence/absence of HT Capability element –New bit in HT Capability element: Forty_MHZ_Intolerant New bit can be used by intolerant TGn APs to require neighbors to switch from 20/40 to 20 –also needs to detect at least one unicast, non-mgmt, non-null data frame transmission that is from the BSS for which the beacon was detected Classification rules –Intolerant devices HT Capability element is absent (e.g. 802.11b/g) OR HT Capability element is present with Forty_MHZ_Intolerant = 1 Behavior rules 40 MHz prohibited if: –Detect Intolerant BSS STA conveys detection of marginal overlap case to its AP: –Dissociate and re-associate with Forty_MHZ_Intolerant = 1 –OR Send MGMT action frame with Forty_MHZ_Intolerant = 1 No MGMT action frame fits – define new one

11. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 11 OBSS Scanning Only STA are required to scan –STAs scan according to requests from AP Beacon Request Measurement request mgmt action –APs may also scan One scan every 30 minutes –Minimum dwell time per channel –Communicated through scan request All channels in the 40mhz-affected-channel set –All channels within +/- 10 mhz of the primary and secondary

12. doc.: IEEE 802.11-07/0049r0 Submission January 2007 Matthew Fischer, BroadcomSlide 12 Important points Legacy association does NOT cause switch to 20 mhz operation Legacy BSS does cause switch to 20 mhz Switch to 20 mhz operation does NOT propagate endlessly –Can go one hop, then stops –Effected through Forty_MHZ_Intolerant bit NOT through BSS width setting