1. Overlapping BSS Proposed Solution – “OSQAP”
Nov 2008
doc.: IEEE /0xxx
Nov 2008
Overlapping BSS Proposed Solution – “OSQAP”
Date:
Authors:
Graham Smith, DSP Group
Graham Smith, DSP Group

2. “OSQAP” - OBSS Solution for QAPs
Nov 2008
doc.: IEEE /0xxx
Nov 2008
Abstract
The problem of OBSS is quantified and examined in 08/0457r4 where a solution for OBSS is presented, discussed in detail and a set of recommendations given.
This submission presents the Proposed solution
“OSQAP” - OBSS Solution for QAPs
Graham Smith, DSP Group
Graham Smith, DSP Group

3. OBSS and QoS A major assumption of this solution is:
Nov 2008
OBSS and QoS
A major assumption of this solution is:
OBSS is a significant problem ONLY when QoS is used AND when some ‘guaranteed performance’ is at stake
Graham Smith, DSP Group

4. OBSS – Existing Problem for QoS
Nov 2008
OBSS – Existing Problem for QoS
OBSS is a problem for 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 EDCA and Admission Control
Conclusions:
EDCA has an OBSS problem in all cases except when overlapping with non-QoS networks
HCCA does not have an OBSS problem except when overlapping with other HCCA networks
Graham Smith, DSP Group

5. OBSS Solution Objectives: Channel Selection is first important step
Nov 2008
OBSS Solution
Objectives:
HCCA and Admission Control QAPs co-operate
Admission Control QAPs co-operate
HCCA networks co-operate
Channel Selection is first important step
TPC not to be relied upon
TPC works in example of apartments, where the range is somewhat limited, but difficult when applied to other scenarios, e.g. Houses, where the ranges are more varied
Graham Smith, DSP Group

6. QAP = HCCA or EDCA Admission Control
Nov 2008
Basic Methodology
QAP = HCCA or EDCA Admission Control
QAP, “QLoad Element = Expected QoS load” (see note)
Channel selection to avoid another QAP if possible
If must share, selection based upon relative “QLoads”
QAPs negotiate bandwidth sharing
Sharing HCCA QAPs must coordinate TXOPs
Note: QSTAs can either inform QAP of their TSPEC requirement(s) in advance, or as required.
Graham Smith, DSP Group

7. Note that the QAP must remember the allocation required
Nov 2008
QLoad - TSPEC
QSTA can send a TSPEC with Inactivity Interval set to (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
TSPEC Element
Note that the QAP must remember the allocation required
Using these TSPECs and/or actual TSPECs QSTA can send at any time, preferably at Association
Graham Smith, DSP Group

8. QAP ‘Q Load Element’ - New
Nov 2008
QAP ‘Q Load Element’ - New
QBSS Load element Format
Not adequate for purpose
Propose to add or replace with new Element – “Q Load Element”
This is important
Scheduled Slot field
Base timing for the Scheduled Service Intervals that the HC is using (see later)
QLoad Self
Potential QoS traffic for this QAP
QLoad Total
Potential QoS traffic for sharing QAPs. If Total>Self, indicates sharing
Graham Smith, DSP Group

9. Channel Priority – Finding a Clear Channel
Nov 2008
Channel Priority – Finding a Clear Channel
When a QAP is searching for a channel, it should do so in the following order:
Set CHP (Channel Priority) to 0
Check no other AP present
Check no other QAP present
If another QAP present, then check QAP Q Load is small enough such that the two can share
If QAP finds no other QAP present, then set CHP = 1
CHP = 1 “Supervisor”. Only one Supervisor
Graham Smith, DSP Group

10. Ideal Channel Selection
Nov 2008
Ideal Channel Selection
CHP = 0
This may be out of scope, but could be used in informative text and used by WFA for certification
Graham Smith, DSP Group

11. Wireless DS QoS CF-Poll (Null Data) for AP to AP communication
Nov 2008
Propose use of
Wireless DS QoS CF-Poll (Null Data)
for AP to AP communication
Graham Smith, DSP Group

12. Wireless DS QoS CF-Poll (Null Data)
Nov 2008
Wireless DS QoS CF-Poll (Null Data)
AP to AP QoS CF-Poll Address Fields
Function To DS
From DS
Address 1 2 3 4
Wireless DS RA
= QAP B TA
= QAP A DA
=QAP B SA
=QAP A
AP to AP QoS CF-Poll Frame Type and Sub-type
Type value
b3 b2
Type Description
Subtype value b7 b6 b5 b4
Subtype Description 10
Data
1110
QoS CF-Poll (no data)
QoS Control Field
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
Use TID field as identifier
Graham Smith, DSP Group

13. Nov 2008 WDS QoS CF Polls To Supervisor from QAP with CHP=0 ACTION
Bits 0-3
Bit 4
Bits 5-6
Bit 7
Bits 8-15
Request for new (total) QLoad
1000 1 00
QLoad requested in units of 32us
Request for addition to QLoad
1010
Additional QLoad in units of 32us
CHP is set to 0
0001
Is Supervisor There?
0100
From Supervisor QAP with CHP=1
ACTION
Bits 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
Time to start of TXOP in units of 32us
New QLoad Accepted
1000 00
QLoad requested in units of 32us
New QLoad Denied
1001
Additional QLoad Accepted
1010
Additional QLoad in units of 32us
Additional QLoad Denied
1011
Supervisor Claim, CHP = 1
0000
Note: Bits 8 – 15 allows 8.192ms max for QLoad. Could consider using b7 as well.
Graham Smith, DSP Group

14. Use of AP to AP QoS CF Poll for Sharing
Nov 2008
Use of AP to AP QoS CF Poll for Sharing
QAP B sees QAP A has available bandwidth.
QAP B builds its QLoad, as STAs associate on this channel.
QAP B decides if wants to apply to share – if so
QAP B sends QoS CF Poll to QAP A
TID Field = 1000 NAV = 0, TXOP = QLoad
QAP A ACKs, then:
Approved: QAP A responds: TID Field = 1000 NAV = 0, TXOP = QLoad
Denied: QAP A responds TID Field = 1001 NAV = 0, TXOP = 0
If approved, both QAPs adjust the QLoads (self and total)
Could use this to formulate a “mandated” sharing rule
Graham Smith, DSP Group

15. QAP A or QAP B get additional QSTA/QLoad
Nov 2008
QAP A or QAP B get additional QSTA/QLoad
New QSTA on QAP A :
QAP A gets ADDTS request (zero Inactivity Time)
If available space, QAP A increases the QLoad values
QAP A sends QAP B a QoS CF Poll, with TID field set to 1010 and TXOP limit contains addition.
QAP B ACKs
QAPs adjust the Q Load values (self and total)
New QSTA on QAP B :
QAP B gets ADDTS request (zero Inactivity Time)
QAP B sends QoS CF Poll to QAP A
TID field = 1010 (special case “Request additional QLoad”)
NAV = 0, TXOP = duration of new TXOP request
QAP A responds with QoS CF Poll to QAP B
Approved TID Field = 1010 NAV = 0, TXOP = duration of new TXOP request
Denied TID Field = 1011 NAV = 0, TXOP = 0
QLoad values updated QAP A adjusts the time of start of QAP B TXOP period.
Graham Smith, DSP Group

16. Supervisor for EDCA-Admission Control?
Nov 2008
Supervisor for EDCA-Admission Control?
There is an argument that the CHP bit is not required for Admission Control.
Set to zero, unless QAP is HCCA and the Supervisor.
Changes to the set of WDS QoS CF Polls are required
Problems that need to be looked at are associated with conditions when more than two APs sharing.
Complicated when sharing APs cannot see every AP
Graham Smith, DSP Group

17. Nov 2008
Possible WDS QoS CF Polls if no Supervisor used for EDCA Admission Control
ACTION
Bits 0-3
Bit 4
Bits 5-6
Bit 7
Bits 8-15
Request to share OR
Request for new (total) QLoad
1000 1 00
QLoad requested in units of 32us
Agree to share OR
Agree to new (total) QLoad
1100
Request to share or new QLoad Denied
1001
Request for addition to QLoad
1010
Additional QLoad in units of 32us
Additional QLoad Accepted
1110
Additional QLoad Denied
1011
Is Supervisor There?
0100
WDS QoS Polls for HCCA
ACTION
Bits 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
Time to start of TXOP in units of 32us
Is Supervisor There?
0100 00
Supervisor Claim, CHP = 1
0000
CHP is set to 0
0001
Note: Bits 8 – 15 allows 8.192ms max for QLoad. Could consider using b7 as well.
Graham Smith, DSP Group

18. Supervisor QAP goes away
Nov 2008
Supervisor QAP goes away
RULE
If QAP with CHP = 0, does not hear Beacons (suggest a number) 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”
Graham Smith, DSP Group

19. This exchange could be used at other times to confirm OBSS sharing
Nov 2008
Two QAPs with CHP = 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 Poll
QAPs compare received TSF Timer in received Beacon to own TSF timer
QAP that has higher TSF timer sends “Supervisor Claim” WDS QoS Poll
This exchange could be used at other times to confirm OBSS sharing
Graham Smith, DSP Group

20. Nov 2008
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?
Alternatives/Options:
HCCA precedence over EDCA Admission Control
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?
Higher QLOAD
1 and 2 are proposed.
Graham Smith, DSP Group

21. What if a Third QAP comes along?
Nov 2008
What if a Third QAP comes along?
√ OK
X NO
X NO
Graham Smith, DSP Group

22. Could be extended for more QAPs but must all hear each other
Nov 2008
Third QAP
Sees one AP with CHP = 1 and one AP with CHP = 0
Looks at Total QLoad determines available space and decides if wants to consider to apply
QAP C builds its QLoad, as STAs associate on this channel.
QAP C decides if wants to apply to share – if so
QAP C sends QoS CF Poll to QAP A (as per Slide 22)
TID Field = 1000 NAV = 0, TXOP = QLoad
Approved: QAP A responds: TID Field = 1000 NAV = 0, TXOP = QLoad
Denied: QAP A responds: TID Field = 1001 NAV = 0, TXOP = 0
QAP A is now responsible for “Handoff” QoS Polls to both QAPs
Keeps B where it is and fits C in between.
Seems to work
Could be extended for more QAPs but must all hear each other
Is this restriction OK?
Graham Smith, DSP Group

23. Nov 2008
Hidden QAPs
If QAP stays after Beacon Report, set CHP to 0 and sends (OBSS) Beacon Request
QAP B now knows of QAP A and its Q Load
QAP ‘A’ and QAP ‘B’ calculate their maximum allocated bandwidth, based upon their Q Loads
If HCCA, QAP A and QAP B must harmonize their Scheduled Allocations
Graham Smith, DSP Group

24. Beacon Report Exchanges for Hidden QAP
Nov 2008
Beacon Report Exchanges for Hidden QAP
(OBSS) Beacon Request
Provides other QAP the Q Load element
Informs CHP
Graham Smith, DSP Group

25. Harmonizing HCCA Fixed Time Slot
Nov 2008
Harmonizing HCCA
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)
Graham Smith, DSP Group

26. Nov 2008
Fixed Slot time 10ms
Min 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
G711,G729,G723.1
30ms
G726-32
10ms
Video
SDTV, HDTV
0ms
16ms
10ms fixed Slot
Graham Smith, DSP Group

27. TXOP Scheduling QAP A Acts as “Supervisor” (CHP=1)
Nov 2008
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)
Graham Smith, DSP Group

28. Nov 2008
AP to AP Poll
Graham Smith, DSP Group

29. Nov 2008
AP to 2 APs
Graham Smith, DSP Group

30. Hidden APs Harmonizing SI for HCCA
Nov 2008
Hidden APs Harmonizing SI for HCCA
QAP A CHP = 0; QAP B CHP = 1
QAP A determines that a scheduled stream to a particular QSTA is blocked and suspects that it is due to scheduling from the QAP B. In this case, QAP A shifts its TSF timer, at DTIM, in the positive direction by 5% of the slot time, i.e. 500us.
Similarly, QAP B determines that a scheduled stream to a QSTA is blocked and suspects that it is due to scheduling from the QAP A. In this case, QAP B shifts its TSF timer, at DTIM, in the negative direction by 5% of the slot time, i.e. 500us.
Graham Smith, DSP Group

31. Proposal Nov 2008 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”
Use of RDS QoS CF Polls for sharing (See previous slide)
Rules and procedures for Channel Selection and setting of CHP
Rules and Procedures for Sharing
Graham Smith, DSP Group

32. OBSS Summary Nov 2008 Two (three) HCCA networks could share
Two EDCA Admission Control networks could share
An HCCA and one or more EDCA Admission Control Network(s) could share
Proposed additions to the Standard are :
“Q LOAD Element” for HCCA and EDCA Admission Control QAPs
Rules and procedures for sharing
Admission Control only
HCCA only
Mixed Admission Control and HCCA
Fixed 10ms Slot time for HCCA
Use of Wireless DS QoS CF Polls (null data) for inter-AP negotiation and HCCA TXOP scheduling
Possibly “OBSS” Beacon Request Report (hidden APs)
Graham Smith, DSP Group

33. OBSS Requirements Check
Nov 2008
OBSS Requirements Check
Graham Smith, DSP Group