1. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 1 Overlapping BSS Proposed Solution Date: 2007-10-29 Authors:

2. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 2 Abstract The problem of OBSS is quantified and examined A solution for OBSS is presented and discussed A set of recommendations is given.

3. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 3 OBSS – Estimation of Size of Problem Floor Plan of Apartments Each Apartment 26 x 40 feet, about 1000 square feet Imagine similar floors above and below this one. Indoor propagation loss formula used: Lp = – 69 + 20 log F + 40 log d + WAF (p) + FAF (q)F in MHz, d in feet At shorter distances, the Free Space formula dominates, Lp =– 38 + 20 log F + 20 log d + WAF (p) + FAF (q) The predicted propagation loss is the higher of the two. Each wall (WAF) and floor (FAF) between apartments is assumed to be 10dB penetration loss (fireproof). Ceiling height is assumed to be 10 feet.

4. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 4 Received Signal Strengths 1Inside same apartment 2Next door (one each side) x2 3Two away (one each side) x2 4Three away (one each side) x2 5Opposite 6Opposite, across one (one each side) x2 7Opposite, across two (one each side) x2 8Opposite, across three (one each side) x2 9Directly up and down x2 10Up or down, neighbor (one each side) x4 11Up or down, two away (one each side) x4 12Up or down, three away (one each side) x4 13Opposite, up and down x2 14Opposite, up and down, two across x4 15Opposite, up and down, one across x4 16Opposite, up and down, three across x4 17Two floors directly up and down x2 30dB power control

5. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 5 Number of OBSS – DFS and TPC Table 1 – Theoretical OBSS for Apartments - 1000 sq. ft. Ideal DFS reduces problem significantly! Table 2 – Theoretical OBSS with 30dB Power Reduction Received signal strength within each apartment is high, better than -40dBm. Theoretically, therefore, the power could be reduced by 30dB with no deterioration in the throughput. Solves OBSS! Frequency BandNumber of Interfering Networks Interfering Networks per 20MHz Channel Interfering Networks per 40MHz Channel 2.4GHz311031 5GHz270-13 Frequency BandNumber of Interfering Networks with 30dB power reduction Interfering Networks per 20MHz Channel with 30dB power reduction Interfering Networks per 40MHz Channel with 30dB power reduction 2.4GHz833 5GHz400 5GHz for Home!

6. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 6 Effects of OBSS - 1 #Network AOBSS Network BEffectResult 1Legacy Traffic simply competes  Reduced bandwidth in each network  No lost packets  Not recommended for streaming 2EDCALegacyHigher 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” 3EDCA 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

7. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 7 Effects of OBSS - 2 4Admission Control LegacyHigher 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 5Admission Control EDCATraffic competes on a priority basis. Admission Control in Network cannot control traffic in Network B  No protection for admitted traffic in Network A 6Admission 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 AOBSS Network B EffectResult These cases are cause for concern, Admission Control is the highest QoS presently certified and it breaks down in OBSS!

8. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 8 Effects of OBSS - 3 7HCCALegacyScheduled TXOPs in Network A also apply CFP to Network B.  Full protection for scheduled traffic in Network A  Network B bandwidth reduced 8HCCAEDCAScheduled TXOPs in Network A also apply CFP to Network B.  Full protection for scheduled traffic in Network A  Network B bandwidth reduced 9HCCAAdmission 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  Full protection for scheduled traffic in Network A  Network B bandwidth reduced  Both Networks using TSPECS 10HCCA 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.

9. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 9 OBSS – EDCA on EDCA Table clearly shows that OBSS is a problem for 802.11 when it is intended to be used for applications that require QoS. EDCA does not address the problem at all. 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. Conclusions: 1.EDCA is not providing QoS in OBSS situation and any higher bandwidth streaming application is not protected 2.If we wish to solve OBSS problem then the use of HCCA would seem to be mandatory and we need to look into solving the OBSS situation for two HCCA networks (at the same time solving it for Admission Control)

10. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 10 Solving OBSS One clear recommendation would be to initiate mandatory certifications for DCF and TPC If so, it could be assumed that the OBSS situation could be eliminated or limited to a maximum of two QAPs Investigation carried out that shows how: –Two HCCA networks could co-operate –HCCA and Admission Control QAPs could co-operate –Two Admission Control QAPs co-operate Note: Still not protected against EDCA OBSS

11. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 11 OBSS – Basic Starting Point 1.When QSTAs associate, they send their TSPEC(s) corresponding to their expected requirements 2.Using the TSPECs, QAP ‘A’ builds knowledge of the QoS demands of its network, we shall call this the “Q Load” 3.Another QAP ‘B’, looking for a spare channel or whether to share, would interrogate QAP ‘A’ to establish the Q Load ‘A’. Based on this QAP ‘B’ can make a decision on whether to stay or not 4.Assuming that QAP ‘B’ does stay, then it determines its own Q Load ‘B’ 5.QAP ‘A’ and QAP ‘B’ now negotiate the bandwidth, based upon their Q Loads EDCA Admission Control only QAPs are now co-operating. Note, however, that they still do not have protection against legacy EDCA networks. 6.If a successful outcome then HCCA networks proceed to step 7. If not, then QAP B must leave to seek another Channel. 7.QAP ‘A’ and QAP ‘B’ harmonize such that they schedule TXOPs correctly with respect to both networks Each step will now be examined in more detail.

12. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 12 OBSS - TSPEC Exchange Figure 10 – TSPEC Element On association, a QSTA sends its TSPEC, QAP knows the STA’s requirement (s). The TSPEC has Inactivity Interval set to 0 (needs to be added for Admission Control) Causes the TSPEC to expire instantly, once accepted. QAP could recognize this as a special case and know that the intention is for the QSTA to inform the QAP of its expected load Note that the QAP must remember the allocation required for all the ‘sign on’ TSPECs and respond accordingly

13. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 13 QAP Q Load Reporting QBSS Load element Format Not adequate for purpose Propose to add or replace similar new Element – “Q Load Element” Scheduled Slot field Base timing for the Scheduled Service Intervals that the HC is using Allocated Admitted field Amount of medium time that has been approved for EDCA Admission Control Allocated Scheduled Total of Scheduled TXOPs that has been approved for HCCA STAs Also could be used in 11r Fast Handoff avoiding need to pre-register

14. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 14 Channel Priority – Finding a Clear Channel When a QAP is searching for a channel, it should do so in the following order: 1.Set its CHP to 1 2.Check no other AP present 3.Check no other QAP present 4.If another QAP present, then check QAP Q Load is small enough such that the two can share If QAP selects its channel based upon 1 or 2, then 5.Check that no other QAP is within range of its network QSTAs using Beacon Request Report 6.If positive, and decides to stay, set CHP to 0 If 4, and QAP chooses to share, sets CHP to 0

15. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 15 QAPs Negotiate Basic options for sharing ‘rules’ are: –First Come, First served (FCFS). TSPECs are accepted, HCCA and EDCA, in the order they appear. Both QAPs must know the prevailing total Q Load so as not to over-allocate. –Negotiated Bandwidth Simple Proportion (SPNB) Based upon the potential Q-Load of each QAP, the bandwidth is proportioned up between them accordingly. This way, each QAP knows its modified maximum bandwidth allocation On-Demand Negotiated Bandwidth (ODNB) Basically, when a QAP receives an ADDTS request, that, if accepted, would take the QAP over the SPNB allocation, it must get permission from the other QAP to accept it. Preferred Method This is enough for WMM-Admission Control QAPs, HCCA QAPS need to Harmonize

16. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 16 Harmonizing HCCA QAPs Explanation of Scheduling of TXOPs Schedule for QSTAs Desirable that the start times of the TXOPs are maintained at the same interval. This enables the QSTA use efficient S-APSD, Maintain the minimum service interval (SI) requirement as per the TSPEC

17. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 17 Fixed Slot time 10ms Min and Max Service Intervals for Voice and Video CategoryMinimum Service IntervalMaximum Service Interval Voice G711, G729, AMR-NB, AMR-WB, iLBC, EVRC, VMR-WB 20ms Voice G711,G729,G723.1 30ms Voice G726-32 10ms Video SDTV, HDTV 0ms16ms 10ms fixed Slot

18. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 18 Harmonize Slot times QoS (+) CF Poll Frame sent by HC At the beginning of the Slot, QAP sets bit 7 The suggested procedure (see next slide) 1.At the beginning of the Slot, the QAP A sets bit 7. This could be included in the first TXOP or, if there is no TXOP at that time then the QAP simply sends a QoS Poll to itself. 2.QAP B waits the maximum duration of the TXOPs sequence Period indicated in the Allocated Scheduled field in the Q LOAD element for QAP A 3.QAP B starts its Slot time and TXOPs Simple and straightforward

19. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 19 Service Interval Harmonization

20. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 20 OBSS Proposed Procedure Summary 1.Before seeking a channel, a QAP sets its CHP to 1 in the Q LOAD element. 2.QSTAs send their expected TSPECs as they associate, with Inactivity Period set to 0, and the QAP calculates its values for the Q LOAD Element 3.A QAP should try to find a channel that has no other QAP present, by first listening for another Beacon, and then issuing a standard Beacon Request (see figure). An extension to this is that the Beacon Request and resulting Probe Request is tailored to seek out the Q Load Element. 4.If no other QAP is reported, then the QAP may choose that channel. 5.If another QAP is reported, then the respective Q LOADs are examined and a decision made as to share or not. 6.If the decision is to share, then the CHP is set to 0. 7.If the QAPs are not hidden then the condition of sharing is recognized (CHP 0 and 1) and each QAP calculates its available schedule time based on Simple Proportion. 8.If the QAPs are hidden then the OBSS Beacon Request /Report is used such that each QAP knows the Q LOAD of the other and of the decision to share (CHP 0 and 1) EDCA Admission Control QAPs can now proceed

21. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 21 OBSS Proposed Procedure Summary HCCA QAPs need to harmonize their SIs. 9.Each HCCA QAP indicates its start of the Slot Time by setting bit 7 in the QoS CF Poll. 10.If QAPs are not hidden, the Slot Times are harmonized using the Start of Slot Time indication and the Allocated Scheduled information in the Q LOAD. Proposal for Hidden APs (to be discussed) If QAPs are hidden, if they experience scheduling problems to specific QSTAs, they adjust their respective Slot Times (TSF Timer), at DTIM intervals, by 0.5ms in a positive or negative direction as per the CHP setting.

22. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 22 Beacon Report Exchanges OBSS Beacon Request Provides other QAP the Q Load element Informs CHP

23. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 23 OBSS Summary Two HCCA networks could share Two EDCA Admission Control networks could share An HCCA and an EDCA Admission Control Network could share An EDCA Admission Control and an EDCA network would still not share. Additions to the Standard are proposed: “Q LOAD Element” for HCCA and EDCA Admission Control QAPs “OBSS” Beacon Request Report Fixed 10ms Slot time Use of bit 7 in QoS CF Poll to indicate start of Slot Time We now consider “Hidden –AP”

24. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 24 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 and the SPNB method. QAP A and QAP B must now harmonize their Scheduled Allocations

25. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 25 Harmonizing SI – Direct Method Direct Method (as per non-hidden QAPs) Could be possible using a common STA BUT The QSTA may be in power save mode If the first TXOP has been granted then the QSTA is prevented from transmitting, so sending the timer onto the other QAP is not possible The only legitimate transmission from a STA to an AP outside its network, is the Probe Request It is not advisable, or even allowed to change a scheduled time by too much.

26. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 26 Harmonizing SI – Indirect Method 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.

27. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 27 802.11n - 40MHz OBSS 40MHz Channels –Easy/intuitive to see how two 40MHz overlapping networks will be less efficient than separate, independent 20MHz channels. MUST use the OBSS proposals to: –Try to find clear channel –If not clear, look for 20MHz channel MUST introduce procedures for preventing or controlling OBSS and usage of 40MHz channels The same procedures as previously described can be used

28. doc.: IEEE 802.11-07/2684r0 Submission November 2007October 2007 Graham Smith, DSP GroupSlide 28 Recommendations Recommendations: –“Q LOAD Element” for HCCA and EDCA Admission Control QAPs –“OBSS” Beacon Request Report –Fixed 10ms Slot time for HCCA –Use of bit 7 in QoS CF Poll to indicate start of Slot Time –Addition of recommended practices for OBSS Note: Wi-Fi Alliance could then devise tests to certify the behavior (this is important) –What to do about TPC? Treat as a separate subject? Support for this approach? –Should we go ahead to write normative text based on this approach?