Doc.: IEEE 802.11-09/0230-00-00aa Submission Feb 2009 Graham Smith, DSP GroupSlide 1 Overlapping BSS Proposed Solution – “OSQAP” Date: 2009 -02-06 Authors:

Feb 2009

Graham Smith, DSP Group

Slide 1

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Overlapping BSS Proposed Solution – “OSQAP”Date: 2009 -02-06

Name Affiliations Address Phone email Graham Smith DSP Group 2491 Sunrise Blvd,

#100, Rancho Cordova, CA 95742

916 851 9191 X209

[email protected]

Dan Dillon DSP Group 2491 Sunrise Blvd, #100, Rancho Cordova, CA 95742

916 851 9191 X205

[email protected]

John Janecek DSP Group 2491 Sunrise Blvd, #100, Rancho Cordova, CA 95742

916 851 9191 X208

[email protected]

Authors:

Feb 2009


Slide 2

doc.: IEEE 802.11-09/0230-00-00aa

Submission

AbstractPresentation 08/0457r4 examined the OBSS problem and

outlined possible solutionsPresentation 08/1260r1 further expanded on a solution,

“OSQAP”Presentation 08/1470r3 looked at the OBSS scenarios,

estimated worse case overlaps and ran simulations using Channel Selection so as to size the problem.

This presentation uses the results from 08/1470r3 to propose a comprehensive solution

“OSQAP” - OBSS Solution for QAPs

Feb 2009


Slide 3

doc.: IEEE 802.11-09/0230-00-00aa

Submission

OBSS and QoS

A major assumption of this solution is: OBSS solution is required for QoS applications

• The following Table was first presented in 08/457 and explain why OBSS is a significant problem ONLY when QoS is used AND when some ‘guaranteed performance’ is at stake

Feb 2009


Slide 4

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Effects of OBSS - 1

# Network A OBSS Network B Effect Result

1 Legacy Legacy Traffic simply competes Reduced bandwidth in each network

No lost packets Not recommended for

streaming

2 EDCA Legacy Higher priority traffic in Network A will drive down traffic in Network B

AC_VO and AC_VI traffic dominates. Could be OK for streaming traffic but no admission policy

Network A “wins”

3 EDCA EDCA Traffic competes on a priority basis. Networks compete on an ‘equal’ basis

Reduced bandwidth in each network

No real protection for streaming traffic in either network

Feb 2009


Slide 5

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Effects of OBSS - 2

4 Admission Control

Legacy Higher priority traffic in Network A will drive down traffic in Network B

AC_VO and AC_VI traffic dominates. Could be OK for streaming traffic

Network B bandwidth can be drastically reduced

5 Admission Control

EDCA Traffic competes on a priority basis.

Admission Control in Network cannot control traffic in Network B

No protection for admitted traffic in Network A

6 Admission Control

Admission Control

Traffic competes on a priority basis.

Admission Control in either Network cannot control traffic in other Network

No protection for admitted traffic in either Network

# Network A OBSS Network B

Effect Result

These cases are cause for concern, Admission Control is intended to provide QoS ‘protection’, and it breaks down in OBSS!

Feb 2009


Slide 6

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Effects of OBSS - 3

7 HCCA Legacy Scheduled TXOPs in Network A also apply CFP to Network B.

Full protection for scheduled traffic in Network A

Network B bandwidth reduced

8 HCCA EDCA Scheduled TXOPs in Network A also apply CFP to Network B.



9 HCCA Admission Control

Scheduled TXOPs in Network A also apply CFP to Network B

Admitted traffic Network B is lower priority than scheduled traffic in Network A



Both Networks using TSPECS

10 HCCA HCCA Each HCCA AP will admit streams and allocate time to them BUT each AP and STA will obey the TXOP allocation of the other.

No guarantee that each Network can allocate time when it needs to.

,

Reduced protection for scheduled traffic in either network.

Feb 2009


Slide 7

doc.: IEEE 802.11-09/0230-00-00aa

Submission

OBSS – Existing Problem for QoS

• OBSS is a problem for 802.11 when it is intended to be used for applications that require QoS.

• EDCA does not address the OBSS problem • EDCA Admission Control only solves the bandwidth

allocation problem within its own network and does not address OBSS.

• HCCA does overcome OBSS problems in all but the case where two HCCA networks overlap BUT it steps on overlapping EDCA Admission Control networks

Feb 2009


Slide 8

doc.: IEEE 802.11-09/0230-00-00aa

Submission

OBSS Solution• Objectives:

1. Admission Control QAPs co-operate2. HCCA and Admission Control QAPs co-operate3. HCCA networks co-operate

• Channel Selection– Shown in 08/1470 to be extremely important

Following few slides are the Summary of 08/1470:08/1470 includes the results of a Channel Selection Simulation

Program that was applied to various overlapping scenarios

Feb 2009


Slide 9

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Probability of Zero or One overlap100% Assignment

00.10.20.30.40.50.60.70.80.9

1

24 22 19 17 11 9

Channels

Prob

ablil

ity

Detached Houses, 12 overlaps

Terrace Houses, 16 overlaps

Town Houses, 24 overlaps

Single Apartments, 28 overlaps

Double Apartments, 53 overlaps

Zero or One overlap is almost guaranteed for 20MHz channels

NOTE: If APs in apartments set their PHY rate to 54Mbps only (11a/g), the overlaps decrease toSingle Apartment Block – 18 (Less than Town Houses) Double apartment Block – 29 (Similar to Single Apartment blocks)

Feb 2009


Slide 10

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Identifying Hidden APsQAPs advertise their overlaps and use this information in the Channel

Selection• We see following overlap situations; QAP A:QAP B: QAP C• 0 No sharing• 1:1 QAP A sees QAP B who sees only QAP A• 1:2 QAP A knows that QAP B sees an AP that

is hidden from QAP A• 2:1:1 QAP A sees two APs who do not see each

other• 2:2:1 QAP A knows that QAP B sees an AP that

is hidden from QAP A• 2:2:2 Could be that all three QAPs see each other

but not sure. (Note: Can be sure by looking at the QLoads)

• 3:1:1:1 QAP A sees three other QAPs, but knows that they do not see each other

• *3* Any other combination with a 3 implies hidden APs

Can we use this in any meaningful way?

Feb 2009


Slide 11

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Submission

Channels Conclusions – 40/20MHz Channels

Use of 11 and 9 Channels• For “House” scenarios, 40MHz channels should be able

to operate OK.• For “Apartment” Scenarios, 40MHz channels can

cause concernCONCLUSION• 40MHz channels should drop back to 20MHz when the

overlapping situation becomes excessive.• We need a workable method for 11n APs to decide

when keeping to 40MHz channel is not the right thing to do (for their own sake as well as others)

Feb 2009


Slide 12

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Channel Search Conclusions – Overlap Indication

• Channel Search algorithm is slightly better if the overlaps are used (as against just number of APs on same channel)

• QAPs should indicate their overlap situation• QAPs know if “hidden” QAPs are on same channel, if

they know the overlap figures

Conclusion: Worthwhile that a QAP indicates its overlap situation

Feb 2009


Slide 13

doc.: IEEE 802.11-09/0230-00-00aa

Submission

“OSQAP”

• Based upon 08/1470 and upon other work in the task group,

• The original “OSQAP” proposal as per 08/0457 and 08/1260 has been modified

Feb 2009


Slide 14

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Basic MethodologyQAP = HCCA or EDCA Admission Control

1. QAP, proposed addition of “QLoad Element”– Overlap information– QoS loads

2. Channel selection• If sharing, selection can be based upon:

• Number of other APs on same channel• Overlap situation • Relative “QLoads”

3. QAPs sort out bandwidth sharing

Furthermore5. Sharing HCCA QAPs must coordinate TXOPs

Feb 2009


Slide 15

doc.: IEEE 802.11-09/0230-00-00aa

Submission

QLoad Element

• Propose new Element “QLoad” for an QAP

Indicates the following:• “QLoad Self”

– Total potential QoS traffic for this QAP• “QLoad Total”

– Total potential QoS traffic for this QAP AND the other QAPs with which it is sharing the channel

• “Overlap Count”– Number of QAPs that are within range of this QAP and that are

sharing this channel

Feb 2009


Slide 16

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Potential QoS Requirements – “QLoad Self” - TSPEC

TSPEC Element

QSTA can send a TSPEC with Inactivity Interval set to 0 (or 1 if 0 is ‘reserved/ignore’)

Causes the TSPEC to expire instantly, once accepted:• QAP recognizes this as a special case and knows that the intention

is for the QSTA to inform the QAP of its expected load• QSTA knows if its TSPEC will be accepted later

Note that the QAP must remember the allocation requiredUsing these TSPECs and/or actual TSPECs

QSTA can send at any time, preferably at Association

Feb 2009


Slide 17

doc.: IEEE 802.11-09/0230-00-00aa

Submission

QAP ‘Q Load Element’ - New

QLoad SelfPotential QoS traffic for this QAP in units of 32 µsec periods per second (as per Medium Time)QLoad TotalPotential QoS traffic for sharing QAPs, in units of 32 µsec periods per secondNOTE: If QLoad Total>Q Load Self, indicates sharingOverlapNumber of APs that are sharing this channel and are overlapping Channel Priority Used only if QAP is operating with HCCA, indicates HCCA Supervisor.

2

Overlap and Priority

1

Q LoadSelf

2

b0 b6 b7

Channel Priority

Overlap and Priority Octet

Q LOAD Element

CHP = 1 HigherCHP = 0 Lower

Q LoadTotal

Reserved

2

Overlap (4 bits)

The Q Load Element is used to • Aid in Channel Selection• Determine the ‘sharing’ between overlapping QAPs

Feb 2009


Slide 18

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Suggested General Scheme

• Monitor the QLoad Element(s) in the Beacon(s) overheard from each overlapping QAP

• Intended for EDCA Admission Control and HCCA overlaps with EDCA Admission Control

• (Overlapping HCCA requires further addition)

Feb 2009


Slide 19

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Using the QLoad ElementQLoad Rules:QAPs keep a note of the QLoad Elements of their overlapping QAPs1. For QAPs that are directly overlapping, “QLoad Total” MUST be the SAME

for each QAPa) If sharing with only one other, then “QLoad Total” is sum of the two “QLoad Self”b) If QAP is not sharing, then “QLoad Self” = “QLoad Total”

2. If a QAP increases or decreases its QLoad Self it must adjust its QLoad Total accordingly

3. If any overlapping QAP increases or decreases its “QLoad Total”, then the other QAPs follow and set their “QLoad Totals” to be the same

4. If a QAP sees that an overlapping QAP is no longer overlapping, then it reduces its own “QLoad Total” by the “QLoad Self” of the QAP that has disappeared

Hopefully these become clearer from the following examples

Feb 2009


Slide 20

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Example #1A QAP A finds a clear channel

A Overlap =0 QLoad Self = 30% QLoad Total = 30% (Rule 1b)

A

B

QAP B joins AInitially QAP B has no Qload SelfA Overlap 1 QLoad Self = 30% QLoad Total = 30%B Overlap 1 QLoad Self = 0% QLoad Total = 30% (Rule #1a)

QAP B adds to its QLoad SelfB Overlap 1 QLoad Self = 10% QLoad Total = 40% (Rule #2)QAP A must adjust Qload TotalA Overlap 1 QLoad Self = 30% QLoad Total = 40% (Rule #1a)

QAP B adds some more to Qload SelfB Overlap 1 QLoad Self = 25% QLoad Total = 55% (Rule #2)A Overlap 1 QLoad Self = 30% QLoad Total = 55% (Rule #1a)

QAP C joins AInitially QAP C has no Qload SelfC Overlap 1 QLoad Self = 0% QLoad Total = 55% (Rule #1)A Overlap 2 QLoad Self = 30% QLoad Total = 55% B Overlap 1 QLoad Self = 25% QLoad Total = 55%

QAP C adds to its QLoad SelfC Overlap 1 QLoad Self = 35% QLoad Total = 90% (Rule #2)QAP A must adjust QLoad TotalA Overlap 2 QLoad Self = 30% QLoad Total = 90% (Rule #1)QAP B must then adjust Qload TotalB Overlap 1 QLoad Self = 25% QLoad Total = 90% (Rule #1)

A

B

C

Feb 2009


Slide 21

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Example #1 Extended

Adding new QAPs is straightforward using Rules #1 and #2Adding to QLoad Self is straightforward using Rules #1 and #2

Also note that each QAP is aware of the hidden QAPsOverlaps are: A = 2:2:1; B = 2:2:1; C = 1:2; D = 1:2

110%? More later

QAP D joins BInitially QAP D has no Qload SelfD Overlap 1 QLoad Self = 0% QLoad Total = 90% (Rule #1)A Overlap 2 QLoad Self = 30% QLoad Total = 90% B Overlap 2 QLoad Self = 25% QLoad Total = 90%C Overlap 1 QLoad Self = 35% QLoad Total = 90%

QAP D adds to its QLoad SelfD Overlap 1 QLoad Self = 20% QLoad Total = 110% (Rule #2)QAP B must adjust QLoad TotalB Overlap 2 QLoad Self = 25% QLoad Total = 110% (Rule #1)QAP A must then adjust Qload TotalA Overlap 2 QLoad Self = 30% QLoad Total = 110% (Rule #1)QAP C must then adjust Qload TotalC Overlap 1 QLoad Self = 35% QLoad Total = 110% (Rule #1)

A

B

C

D

Feb 2009


Slide 22

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Example #2 – Reduction in QLoad Self(e.g. A QSTA disassociates)

Any QAP can decrease its QLoad Self and the corresponding reduction in ALL the QLoad Totals will follow

This means that a QAP must keep a note of the QLoad Elements of its overlapping QAPs

QAP B reduces its QLoad SelfB Overlap 2 QLoad Self = 15% QLoad Total = 95% (Rule #2)QAP A sees QAP B at 95% and QAP C at 110%QAP A can see that QAP B QLoad Self has reduced, and Qload Self for QAP C is the same. Hence QAP A knows it is a reduction A Overlap 2 QLoad Self = 30% QLoad Total = 95% (Rule #3)QAP D only sees B, must follow but also can see the reduction in QLoad SelfD Overlap 1 QLoad Self = 20% QLoad Total = 95% (Rule #3)QAP C only sees QAP A sees the reduction and therefore followsC Overlap 1 QLoad Self = 35% QLoad Total = 95% (Rule #3)

A

B

C

D

Feb 2009


Slide 23

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Example #3 – QAP D Disappears

Note: Although the Overlap information is not directly used, it can be used to confirm the required action. The main purpose, however, is to aid Channel Selection.

QAP D Disappears (or moves)QAP B Overlap reduces to 1:2 (it was 2:2:1)i.e. QAP B knows that QAP D has gone. QAP B reduces Qload Total by Qload Self of QAP DB Overlap 1 QLoad Self = 15% QLoad Total = 95-20% = 75% (Rule #4)

QAP A sees QAP B at 75% and QAP C at 95%QAP A Overlap was 2:2:1, now is 2:1:1, i.e. it knows that a QAP has gone.Therefore, Rule #3 appliesA Overlap 2 QLoad Self = 30% QLoad Total = 75% (Rule #3)QAP C only sees QAP A sees the reduction and therefore followsC Overlap 1 QLoad Self = 35% QLoad Total = 95% (Rule #3)

A

B

C

Feb 2009


Slide 24

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Example #4 – QAP A DisappearsQAP A Disappears (or moves)QAP B Overlap reduces to 1:1 (it was 2:2:1)i.e. QAP B knows that QAP A has gone. QAP B now in 1:1 overlap, hence simply add the QLoad Self B and DB Overlap 1 QLoad Self = 15% QLoad Total = 15+20 = 35% (Rule #1a)

Similarly QAP D now is 1:1 overlapD Overlap 1 QLoad Self = 20% QLoad Total = 35% (Rule #1a)

QAP C overlap now 0C Overlap 1 QLoad Self = 35% QLoad Total = 35% (Rule #1b)

B

C

D

Feb 2009


Slide 25

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Probability of Using 40MHz ChannelProbability of Zero Overlaps with 40MHz Channels

0

0.2

0.4

0.6

0.8

1

11 9

Number of Channels

Prob

abili

ty

Detached Houses, 12 overlaps

Terrace Houses, 16 overlaps

Town Houses, 24 overlaps

Single apartment, 28 overlaps

Double apartment, 53 overlaps

• Sharing a 40MHz channel is not as efficient as two independent 20MHz channels (assumption)

• Graph above shows universal use of 40MHz channels is not always possible or a good thing

• Need a scheme that causes APs to scale back to 20MHz channels when overlapping occurs.

Feb 2009


Slide 26

doc.: IEEE 802.11-09/0230-00-00aa

Submission

20/40MHz Operation20/40 BSS Operation*Co-Existence with neighboring BSSs is managed through a number of

mechanisms, including:– Overlapping BSS scanning and careful channel selection on initial BSS setup to

avoid channels already in use by other BSSs.– Changing channels or operating width after BSS setup if a new BSS is detected

operating on the secondary channelAlso

– 40MHz Intolerance bit can be set by any STA, (7.3.2.61) but only for 2.4GHz– 20/40 Intolerant Channel Report Element (7.3.2.59)– Overlapping BSS Scan Parameters element (7.3.2.60)

In high OBSS conditions, networks should fall back to 20MHz operationNEED TO MAKE SOME RULES?

* Reference: “Next Generation Wireless LANS: Throughput, Robustness and Reliability in 802.11n”, Eldad Perahia and Robert Stacey, Cambridge University Press 2008.

Feb 2009


Slide 27

doc.: IEEE 802.11-09/0230-00-00aa

Submission

40/20MHz Channels – when to switchAssuming that an independent 20MHz channel is better than a shared

40MHz channel, then:Proposed Rules (these agree with the “Co-Existence with neighbors”)1. If an 11n QAP cannot find a free channel using 40MHz, then it

must switch to using 20MHz. • If it still cannot find a clear channel, then it can settle on a 40MHz

channel (secondary?)• Rule #2 then comes into play

2. If an 11n QAP, using 40MHz, finds itself overlapping with more than one other QAP (20 or 40MHz) then it must switch to using 20MHz (• It may decide to search again using 40MHz, and then rule 1 applies

Note: The 11n AP could simply switch to using the primary channel, and the new AP settles on the secondary channel.

Feb 2009


Slide 28

doc.: IEEE 802.11-09/0230-00-00aa

Submission

QLoad Total > 100% If QLoad Total >100% then simple rule is:Rule #5• “If QLoad Total = X, where X > 100%, then

each QAP effectively reduces its QLoad Self by 100/Xi.e. Each QAP should not allocate above (QLoad Self x 100/X)”

• Note: The advertised value of “QLoad Self” does not change in the QLoad Element

Feb 2009


Slide 29

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Beacons or Direct Communication?

• The preceding slides show a scheme based upon simple monitoring of Beacons of the overlapping QAPs, for EDCA Admission Control and mixed EDCA Admission Control and (single) HCCA

• An alternative is to have the QAP s communicate directly to each other using the Wireless DS QoS CF-Poll (Null Data) as proposed in 08/0457 and 08/1260

• It is now suggested that simple Beacon monitoring should be sufficient

(Note: This is a natural break, could stop here and seek views.Next part deals with HCCA)

• Note: QAP communication using Wireless DS QoS CF-Poll (Null Data) is proposed for HCCA QAPs that are sharing. This is next part of presentation

Feb 2009


Slide 30

doc.: IEEE 802.11-09/0230-00-00aa

Submission

HCCA Considerations

• HCCA QAPs have to co-operate more tightly as the TXOP allocation schedules need to be aligned

• Propose use of CHP bit (Channel Priority) in the QLoad Element

Feb 2009


Slide 31

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Channel Priority HCCA – Finding a Channel When a HCCA QAP is searching for a channel, it should do so in the following

order:1. Set CHP (Channel Priority) to 02. If finds a clear Channel, set CHP to 13. If no clear channel, then may share with

a) Any legacy AP: Set CHP to 1b) An Admission Control QAP, overlap 0 or 1:

Resulting HCCA QAP overlap being 1:1, or 1:2 Set CHP to 1 (see Note 1)c) An HCCA QAP with CHP = 1 CHP stays at 0 (see Notes 1 & 2)

4. If an HCCA QAP cannot find a channel that meets the rules, it must fall back to Admission Control

NOTES:1. If 3b) or 3c), check that “QLoad Total” is such that the two can share2. An HCCA QAP may not share with an HCCA QAP which has CHP = 0, unless

it also is sharing directly with the corresponding HCCA QAP that has CHP = 1

Feb 2009


Slide 32

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Harmonizing HCCA

• When sharing use Fixed Time Slot– Each AP (HC) knows how much of the Time Slot it can use. – AP to AP Schedule control– Supervisor AP (CHP=1) hands off to the other QAP(s)

Feb 2009


Slide 33

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Wireless DS QoS CF-Poll (Null Data) for AP to AP Communication

AP to AP QoS CF-Poll Address Fields

FunctionTo DS

From DS

Address 1

Address 2

Address 3

Address 4

Wireless DS 1 1 RA= QAP B

TA= QAP A

DA=QAP B

SA=QAP A

AP to AP QoS CF-Poll Frame Type and Sub-type

Type valueb3 b2

Type Description

Subtype value b7 b6 b5 b4

Subtype Description

10 Data 1110 QoS CF-Poll (no data)

Applicable Data Frame

Bits 0-3 Bit 4 Bits 5-6 Bit 7 Bits 8-15

QoS CF Poll TID EOSP= 1

ACK Policy Agg (11n) TXOP Limit

QoS Control Field

Use TID field as identifier

Feb 2009


Slide 34

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Fixed Slot time 10msMin and Max Service Intervals for Voice and Video

Category Minimum Service Interval Maximum Service Interval

Voice G711, G729, AMR-NB, AMR-WB, iLBC, EVRC, VMR-WB

20ms 20ms

VoiceG711,G729,G723.1

30ms 30ms

VoiceG726-32

10ms 10ms

VideoSDTV, HDTV

0ms 16ms

10ms fixed Slot

Video Video Video Video Video

Slot = 10ms Slot = 10ms Slot = 10ms Slot = 10ms Slot = 10ms

Voice 20ms Voice 30ms

Scheduled 20ms and 30ms Voice with Video streams

SI = 10ms

SI = 20ms

SI = 30ms

Feb 2009


Slide 35

doc.: IEEE 802.11-09/0230-00-00aa

Submission

TXOP Scheduling

QAP A Acts as “Supervisor” (CHP=1)• QAP A controls the 10ms slot timing• QAP A sends message to QAP B indicating end of TXOPs for this

Time Slot, and time to start of QAP B TXOP periods. • Uses Wireless DS (AP to AP), QoS CF-Poll (null data)

Feb 2009


Slide 36

doc.: IEEE 802.11-09/0230-00-00aa

Submission

AP to AP Poll

A QLOAD B QLOAD A B

Slot Slot

A Actual B Actual A Actual B Actual

QAP A is the “Supervisor” and effectively in charge of the 10 ms slot and handing off the slot to QAP B

QAP A knows the 10ms slot timing

QAP A sends QoS CF Poll to QAP BTID = 1111 NAV=0

TXOP Limit = T2

T1

QAP A sends QoS CF Poll to QAP BTID= 1111 NAV=0

TXOP Limit = T1

T2

Feb 2009


Slide 37

doc.: IEEE 802.11-09/0230-00-00aa

Submission

AP to 2 APs

A QLOAD B QLOAD

Slot Slot

A Actual B Actual A Actual B Actual

QAP A is the “Supervisor” and effectively in charge of the 10ms Slot and handing off to QAPs B and C

QAP A knows the 10 ms slot timing

QAP A sends QoS CF Polls to QAPs B and CQAP A sends QoS CF Polls to QAPs B and CTID= 1111 NAV=0

TXOP Limit = Tb and Tc

Tb

C QLoad A BC

Tc

TbTc

C Actual C Actual

Feb 2009


Slide 38

doc.: IEEE 802.11-09/0230-00-00aa

Submission

WDS QoS CF Polls To Supervisor from QAP with CHP=0

From Supervisor QAP with CHP=1

ACTIONBits 0-3 Bit 4 Bits 5-6 Bit 7 Bits 8-15

Indication from Supervisor to another QAP of Time to start TXOP (HCCA sharing)

1111 1 10 0 Time to start of TXOP in units of 32us

Supervisor Claim, CHP = 1 0001 1 00 0 0

ACTION Bits 0-3 Bit 4 Bits 5-6 Bit 7 Bits 8-15

CHP is set to 0 0000 1 00 0 0

Is Supervisor There? 0010 1 00 0 0

* May not be required unless a more strict control of QLoad is needed

Feb 2009


Slide 39

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Supervisor QAP goes away

RULE• If QAP with CHP = 0, does not hear 3? Beacons from Supervisor,

then following:– QAP with CHP = 0 sends WDS QoS Poll “Is Supervisor There?”– Retry limit of 3?– IF Supervisor is there, responds with “Supervisor Claim”

• If no response– If no other QAP on this channel then

• QAP sets CHP = 1– If another QAP (CHP = 0) on this channel

• Carry out procedure for higher claim• Sends “Supervisor Claim”

Feb 2009


Slide 40

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Two QAPs with CHP = 1

1. HCCA QAP checks if other is also HCCA– If other is not, then sends “Supervisor Claim” WDS QoS Poll– Other QAP should ACK and then send “CHP set to 0” WDS QoS

Poll2. QAPs compare received TSF Timer in received

Beacon to own TSF timer– QAP that has higher TSF timer sends “Supervisor Claim” WDS

QoS Poll– Other QAP should ACK and then send “CHP set to 0” WDS QoS

PollThis exchange could be used at other times to confirm

OBSS sharing

Feb 2009


Slide 41

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Can Two APs have CHP = 1?• Although unlikely, we shall assume that a QAP with

CHP = 1, picks up Beacons from another QAP, on the same channel, with CHP = 1. How do the QAPs sort this out?

• Proposal:• Higher TSF timer

• When QAP establishes its BSS it sets TSF timer to zero • QAP with higher TSF value is the “Supervisor”

(One could have faster clock, but seems fair)• Use WDS QoS Poll interchange to confirm

Feb 2009


Slide 42

doc.: IEEE 802.11-09/0230-00-00aa

Submission

What if a Third HCCA QAP comes along?

√ OK

X NO

X NO

ACHP=1

B

C

CONDITION 1 - Overlap 1:2:1C sees QAP A with CHP = 1OK to join (or request to join?)

ACHP=1

B

C

CONDITION 2 - Overlap 1:2C sees QAP B with CHP = 0NOT allowed to join as HCCAMay join as Admission Control

ACHP=1

C

BCHP=1

CONDITION 3 - Overlap 2:1;1C sees 2 QAPs with CHP = 1NOT allowed to join as HCCAMay join as Admission Control

Not seen as restrictiveas probability of zero orone overlap is very highin practice

Feb 2009


Slide 43

doc.: IEEE 802.11-09/0230-00-00aa

Submission

Proposal• Add new QLOAD Element

– Channel Priority CHP– Slot time concept for HCCA

• Use of TSPEC with Inactivity Interval set to 0 or 1 to build “QLoad”

• Monitoring of QLoad Element of overlapping QAPs to determine sharing loads

For HCCA QAPs• Rules and procedures for Channel

Selection and setting of CHP• Rules and Procedures for Sharing

2

Overlap and Priority

1

Q LoadSelf

2

b0 b6 b7

Channel Priority

Overlap and Priority Octet

Q LOAD Element

CHP = 1 HigherCHP = 0 Lower

Q LoadTotal

Reserved

2

Overlap (4 bits)

Feb 2009


Slide 44

doc.: IEEE 802.11-09/0230-00-00aa

Submission

OBSS Summary

• EDCA Admission Control networks can share • An HCCA and one or more EDCA Admission Control Networks

can share • Two (three) HCCA networks can share• HCCA networks will drop back to Admission Control when

sharing not possible with other HCCA networks

Proposed additions to the Standard are :• “Q LOAD Element” • Rules for indicating overlap and QLoad sharing• Description of Channel Selection • Rules for 20/40MHz channels• Fixed 10ms Slot time for HCCA QAPs that share• Use of Wireless DS QoS CF Polls (null data) for HCCA TXOP

scheduling

Documents

Doc.: IEEE 802.11-09/0230-00-00aa Submission Feb 2009 Graham Smith, DSP GroupSlide 1 Overlapping BSS Proposed Solution – “OSQAP” Date: 2009 -02-06 Authors: