Signaling of intolerance for 40 MHz transmissions January 2007 doc.: IEEE 802.11-07/0049r2 January 2007 Signaling of intolerance for 40 MHz transmissions Date: 2006-12-08 Authors: 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 <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, 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 <patcom@ieee.org>. Matthew Fischer, Broadcom Matthew Fischer, Broadcom

January 2007 doc.: IEEE 802.11-07/0049r2 January 2007 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. Matthew Fischer, Broadcom Matthew Fischer, Broadcom

Detection of neighboring devices January 2007 Detection of neighboring devices Detect 40 MHz intolerant devices AP cannot detect all overlap cases “Marginal overlap” case is important Requires STA participation Therefore the detection is performed by: STA and AP Matthew Fischer, Broadcom

STA in 40MHz BSS detects Legacy BSS (Intolerant of 40MHz) January 2007 STA in 40MHz BSS detects Legacy BSS (Intolerant of 40MHz) STA_B 40 or 20 AP 20 only Inform AP 40 or 20 STA informs AP40 of neighboring intolerant BSS STA asserts its intolerant bit AP40 falls back to 20MHz mode but does not declare intolerance Matthew Fischer, Broadcom

40MHz AP detects Non-Overlapping Legacy BSS January 2007 40MHz AP detects Non-Overlapping Legacy BSS AP 20 only AP 40 or 20 AP 40 sees beacons from neighboring legacy AP20 Shows case where AP scans non-primary channel for beacons AP40 falls back to 20MHz mode but does not declare intolerance Matthew Fischer, Broadcom

40MHz AP detects Non-Overlapping Legacy BSS through traffic January 2007 40MHz AP detects Non-Overlapping Legacy BSS through traffic AP 20 only STA_C 20 only AP 40 or 20 AP 40 sees traffic from neighboring legacy AP20 AP40 falls back to 20MHz mode but does not declare intolerance Matthew Fischer, Broadcom

40MHz STA detects Non-Overlapping Legacy BSS through traffic January 2007 40MHz STA detects Non-Overlapping Legacy BSS through traffic AP 20 only STA_C 20 only AP 40 or 20 Inform STA_A 40 or 20 STA 40 sees traffic from neighboring legacy AP20 STA 40 signals to AP 40 to fall back to 20 MHz mode AP40 falls back to 20MHz mode but does not declare intolerance Matthew Fischer, Broadcom

Classification rules Devices that may be 40 MHz intolerant: January 2007 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 Matthew Fischer, Broadcom

Behavior rules Assuming that intolerant devices are discovered January 2007 doc.: IEEE 802.11-07/0049r2 January 2007 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 Matthew Fischer, Broadcom Matthew Fischer, Broadcom

January 2007 Finite propagation AP that switches to 20 MHz does NOT set the Forty_MHZ_Intolerant bit This prevents a chain of propagation of the fall to 20 MHz operation Matthew Fischer, Broadcom

40 MHz -> 20 MHz fallback January 2007 Detection Look for presence/absence of HT Capability element Any channel 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 Look for traffic from any overlapping BSS on channels Channels that overlap the secondary 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 New HT Information Exchange MGMT Action frame Matthew Fischer, Broadcom

Recovery to 40 MHz operation January 2007 Recovery to 40 MHz operation BSS must wait for thirty minutes with NO “intolerant” detection before reverting to 40 MHz operation Matthew Fischer, Broadcom

OBSS Scanning Only STA are required to scan One scan every 30 minutes January 2007 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 Matthew Fischer, Broadcom

January 2007 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 AP could deny association based on Forty_MHZ_Intolerant = 1 But still must respect the bit in any received frame Matthew Fischer, Broadcom

January 2007 doc.: IEEE 802.11-07/0049r2 January 2007 motion Move to adopt the changes proposed in doc 11-07-1940-06-000n-40mhz-operation-in-24ghz-40mhz-intolerant-bit.doc. Matthew Fischer, Broadcom Matthew Fischer, Broadcom