1. Clarification on Beacon Transmission Rules
May 2006
January 2013
doc.: IEEE /0102
doc.: IEEE /0528r0
March 2013
Clarification on Beacon Transmission Rules
Date:
Authors:
Slide 1
Daniel Cohn ,Yaron, Alpert, Lantiq
Page 1
Daniel Cohn, Lantiq; Matthew Fischer, Broadcom
Bruce Kraemer, Marvell

2. May 2006
January 2013
doc.: IEEE /0102
doc.: IEEE /0528r0
January 2013
Problem Statement
text on medium access rules for beacon transmission can lead to confusion
Clause states: “At each TBTT, the AP shall schedule a Beacon frame as the next frame for transmission according to the medium access rules specified in Clause 9”
But, when EDCA is the medium access procedure, “rules specified in clause 9” don’t appear to always allow this
This is because a different access function may choose a backoff value that will grant it access to the medium before the access function transmitting the beacon (AC_VO)
Slide 2
Daniel Cohn ,Yaron, Alpert, Lantiq
Page 2
Daniel Cohn, Lantiq; Matthew Fischer, Broadcom
Bruce Kraemer, Marvell

3. May 2006
January 2013
doc.: IEEE /0102
doc.: IEEE /0528r0
January 2013
Problem Statement
Clearly the intention of the standard is for beacons to be transmitted at the TBTT before frames mapped to other ACs
In addition, to decrease beacon transmission jitter, it can be beneficial to allow the use a different IFS and contention window for beacon transmission than for other frames in AC_VO
There is a precedent for this, e.g. Channel Switch Announcement is transmitted after PIFS and no backoff,
PIFS
The PIFS may be used as described in the following list and shall not be used otherwise:
<snip>
A STA transmitting a Channel Switch Announcement frame as described in 10.9
Slide 3
Daniel Cohn ,Yaron, Alpert, Lantiq
Page 3
Daniel Cohn, Lantiq; Matthew Fischer, Broadcom
Bruce Kraemer, Marvell

4. Proposed Solution Modify the text in 10.1.3.2 as follows:
May 2006
January 2013
doc.: IEEE /0102
doc.: IEEE /0528r0
January 2013
Proposed Solution
Modify the text in as follows:
At each TBTT, the AP shall schedule a Beacon frame as the next transmission. At each TBTT the AP should suspend the decrementing of the backoff timer for any pending non-beacon transmission and transmit the Beacon according to the medium access rules specified in Clause 9.
Modify the text in “ Beacon generation in an IBSS” as follows:
c) Wait for the period of the random delay, decrementing the random delay timer using the same algorithm as for backoff, except that AIFSN =1 should be used as the initial medium idle period within the backoff procedure.
Slide 4
Daniel Cohn ,Yaron, Alpert, Lantiq
Page 4
Daniel Cohn, Lantiq; Matthew Fischer, Broadcom
Bruce Kraemer, Marvell

5. Backward Compatibility
May 2006
January 2013
doc.: IEEE /0102
doc.: IEEE /0528r0
January 2013
Backward Compatibility
AP behavior per existing text (wait AIFS if idle free or AIFS + backoff is medium busy) is compliant with proposed text so the proposed solution is backward compatible
Slide 5
Daniel Cohn ,Yaron, Alpert, Lantiq
Page 5
Daniel Cohn, Lantiq; Matthew Fischer, Broadcom
Bruce Kraemer, Marvell