1. MAC improvement using random AIFSN
May 2006
doc.: IEEE /0657r0
May 2006
MAC improvement using random AIFSN
Date:
Authors:
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Todor Cooklev
Todor Cooklev

2. May 2006
doc.: IEEE /0657r0
May 2006
Abstract
We identify a use case for HD video over and establish relevant requirements. Next, we the use of random AIFSN and draft text.
Todor Cooklev
Todor Cooklev

3. Outline 11n scenario for digital home Current 11e backoff mechanism
May 2006
doc.: IEEE /0657r0
May 2006
Outline
11n scenario for digital home
Current 11e backoff mechanism
Benefits of random AIFSN scheme
Simulation results based on 11n
Proposed text
Implementation considerations
Conclusions
Todor Cooklev
Todor Cooklev

4. 11n scenario for digital home
May 2006
doc.: IEEE /0657r0
May 2006
11n scenario for digital home
Many traffic streams anticipated in CE dominated home…
Video
Support for 4-5 HD video streams is reasonable 120Mbps
Content: Premium, time-shifted, DVD, personal, Gaming
Voice
Up to 4 streams with tight delay constraints – low throughput
Best-effort
Web, file transfer, printing - 10Mbps
11n with 2x2 or 2x3 MIMO + channel bonding
May provide 130Mbps under best-case conditions
Contention among equal-priority traffic is an important issue
Can be reduced through new AIFSN scheme
Todor Cooklev
Todor Cooklev

5. 11n/11e scenario for Digital Home
May 2006
doc.: IEEE /0657r0
May 2006
11n/11e scenario for Digital Home
HDTV
HDTV V4
HDTV V3 V2 V1
Live or time-shifted
Premium HD content
Voice 3-4
Data 2-3
Cable, Satellite
STB / PVR
Media PC
over WLAN
Internet
Personal
content V5
Todor Cooklev
Todor Cooklev

6. 802.11e Channel Access Mechanism
May 2006
doc.: IEEE /0657r0
May 2006
802.11e Channel Access Mechanism
Fig.1 EDCA channel access mechanism
Arbitration inter-frame space (AIFS) is one of the EDCA parameters used to ensure traffic differentiation
Each AC has fixed AIFS duration associated with it. The smaller the AIFS the higher the medium access priority
Todor Cooklev
Todor Cooklev

7. Proposed Channel Access Mechanism
May 2006
doc.: IEEE /0657r0
May 2006
Proposed Channel Access Mechanism
Fig. 2 Proposed channel access mechanism
Proposed Mechanism
AIFSN is random with a certain probability density function
For example the distribution can be uniform
Advantages
Possible to assign the ACs a non-integer AIFSN value on an average
Less collisions within an AC; higher throughput
Fig. 3 Proposed medium access control logic
Todor Cooklev
Todor Cooklev

8. Simulation with Random AIFSN
May 2006
doc.: IEEE /0657r0
May 2006
Simulation with Random AIFSN
Simulation Parameters
54 Mbps PHY, 12 nodes – 4 BE, 4 Video and 4 Voice
Default EDCA parameters for all ACs except for random AIFSN for video
Global Throughput per AC
Global Delay per AC
Todor Cooklev
Todor Cooklev

9. Proposed Text : Section 9.2.3.4
May 2006
doc.: IEEE /0657r0
May 2006
Proposed Text : Section
OLD…
A Non-AP QSTA computes the time periods for each AIFS[AC] from the dot11EDCATableAIFSN attributes in the MIB. QSTAs update their dot11EDCATableAIFSN values using information in the most recent EDCA Parameter Set element of Beacons received from the QAP of the QBSS (see ). A QAP computes the time periods for each AIFS[AC] from the dot11QAPEDCATableAIFSN attributes in its MIB.
NEW…
Non-AP QSTA compute AIFSN[AC] using some probability density function over a finite interval. This interval is bounded on one side by the default values in Table The other limit of this interval is from the dot11EDCATableAIFSN attributes in the MIB. QSTAs update their dot11EDCATableAIFSN values using information in the most recent EDCA Parameter Set element of Beacons received from the QAP of the QBSS (see ).
Todor Cooklev
Todor Cooklev

10. Proposed Text : Section 9.9.1.3
May 2006
doc.: IEEE /0657r0
May 2006
Proposed Text : Section
OLD…
The value of AIFSN[AC] shall be greater than or equal to 2 for non-AP QSTAs and is advertised by the QAP in the EDCA Parameter Set Information Element in Beacons and Probe Response frames transmitted by the QAP. The value of AIFSN[AC] shall be greater than or equal to 1 for QAPs.
NEW…
QSTA choose the value of AIFSN according to some probability density function (PDF) over a finite interval. One of these limits (either the lower or the upper limit) is the default value specified in Table The other limit is in the dot11EDCATableAIFSN attribute in the MIB. Any PDF is acceptable, including a PDF where QSTA always select one number that belongs to this interval. The limit value AIFSN[AC] is advertised by the QAP in the EDCA Parameter Set Information Element in Beacons and Probe Response frames transmitted by the QAP. If this limit value is smaller than the default values in Table 20.2, then it becomes the lower bound of the interval. If this limit value is higher than the default values in Table 20.2, then it becomes the higher bound of the interval.
Todor Cooklev
Todor Cooklev

11. Implementation Issues
May 2006
doc.: IEEE /0657r0
May 2006
Implementation Issues
The suggested operation is mandatory, so that it will not get advertised in beacons and probe responses.
Since any probability density function is acceptable, all current implementations using fixed AIFSN comply with this proposal, i.e. no change is necessary.
Those that do want to change and implement, for example, uniform probability density function, will not only see an improvement in their throughput, but will improve overall network performance.
Fairness? The improvement according to the proposed scheme does not come at the expense of degradation somewhere else. The performance of the entire network is improved.
Todor Cooklev
Todor Cooklev

12. Conclusions Contention in wireless home scenarios is great
May 2006
doc.: IEEE /0657r0
May 2006
Conclusions
Contention in wireless home scenarios is great
Current AIFSN scheme is static
The proposed random-AIFSN has benefit to all traffic classes – throughput increases and delay decreases
While the proposal is to make the suggested scheme mandatory, in reality it is optional because all current implementations comply with it.
Todor Cooklev
Todor Cooklev