1. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 1 Considerations for Statistical Multiplexing Support in OBSS Proposal - QLoad Date: 2009, May 3 Authors:

2. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 2 Abstract This presentation first looks at the statistics of video streams and then how fields in the QLoad Element, proposed in OBSS solution “OSQAP”, could be added in order to support statistical multiplexing of the video loads. This presentation recommends a new version of the QLoad Element

3. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 3 Introduction The original OBSS Proposal “OSQAP” suggested a new QLoad Element for the sharing of overlapping QAPs – 08/457r4, 08/1260r1, 09/230r0 This QLoad element included fields for: Overlap QLoad Self QLoad Total The QLoad Total represents the aggregate of “QLoad self” from all the QAPs in the OBSS graph. The use of simple addition of the QLoad Totals by overlapping QAPs was suggested and basically using total Peak Load as basis for Sharing. Ed Reuss (Plantronics) and Brian Hart (Cisco) suggested that the QLoad should support statistical multiplexing so to be more efficient. In this presentation, this is investigated.

4. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 4 Mean, Max and Min in TSPEC The TSPEC has fields for –Mean Data Rate –Peak Data Rate –Minimum Data Rate Hence, a QSTA can specify the Max, Min and Mean of a video stream (or audio stream) and the QAP can calculate the Max, Min and Mean allocation time requirements

5. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 5 Video Throughputs Samples of throughputs of three actual individual video clips is shown below. Video 1Video 2Video 3 MAX Mbps11.410.08.6 MIN Mbps3.38.13.6 MEAN Mbps7.99.25.8 Video 1 Video 2 Video 3

6. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 6 Video Throughputs The TOTAL throughput of all three videos, “composite video”, is shown below MAX Mbps27.6 MIN Mbps16.6 MEAN Mbps22.8 Composite Stream for all 3 Videos

7. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 7 Simple Addition of the three does not result in the Composite MAX Mbps30.0 MIN Mbps15.0 MEAN Mbps22.8 Addition of statistics for all 3 Videos MAX Mbps27.6 MIN Mbps16.6 MEAN Mbps22.8 Composite Stream for all 3 Videos Video 2 is relatively constant, so based upon Videos 1 and 3, we get: Based upon MAX Mbps, then simple addition produces 8.7% Over allocated MAX Mbps17.7 MIN Mbps7.6 MEAN Mbps13.7 Composite Stream for Videos 1 and 2 MAX Mbps20.0 MIN Mbps6.9 MEAN Mbps13.7 Addition of statistics for Videos 1 and 2 Based upon MAX Mbps, then simple addition produces 13% Over allocated

8. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 8 VIDEO STATISTICS Video 1Video 2Video 3Composite MEAN7.929.165.7622.84 MAX11.4010.018.5527.65 MIN3.318.143.5716.62 STDEV1.840.371.412.22 Video 1Video 2Video 3Composite MEAN7.929.165.7622.84 +2σ11.599.918.5727.27 -2σ4.258.412.9418.41 Statistics for the Video streams, including “standard deviation”, are: Note that MAX and MIN can be estimated as MEAN +/- 2 STDEV

9. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 9 Video Statistics HISTOGRAMS and NORMAL DISTRIBUTIONS

10. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 10 Video Statistics If each video stream can be represented by a Normal Distribution, then the sum of the streams is also a Normal Distribution (becomes more “normal distribution” as the number of streams increases). Note: Summation of Normal Distributions: Meanµ = Σµ i Stddevσ = sqrt(Σσ i 2 ) Very good correlation between Actual composite and Sum of three videos

11. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 11 Video Statistics So far we can conclude the following: Based upon the three sample videos: Individual Video stream statistics can be reasonably modeled by a Normal Distribution Composite video can be modeled by a Normal Distribution Summation of the individual normal distributions for each video stream produces distribution that is close to the actual composite video normal distribution Max and Min can be estimated as –MAX = Mean + (2 x Standard Deviation) –MIN = Mean – (2 x Standard Deviation) HENCE: We now know how to sum the individual streams

12. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 12 Mean, Max and Min Sum of Normal Distributions: Meanµ = Σµ i and Stddevσ = sqrt(Σσ i 2 ) AlsoMAX = Mean + 2σ andMIN = Mean - 2σ Hence, to estimate the total MEAN and STDEV from the individual streams: MEAN µ = Σ MEAN i STDEV σ = 0.25 sqrt {Σ (MAXi – MINi) 2 } (see note) Using resulting µ and σ, we can calculate total MAX and MIN MAX Mbps27.65 MIN Mbps16.62 MEAN Mbps22.84 Actual Composite Stream 3 Videos MAX Mbps27.68 MIN Mbps17.99. MEAN Mbps22.84 Estimated Composite Stream 3 Videos Very good!! NOTE: Calculating STDEV from just MAX or just MIN does not give accurate result MAX calculated based on square root of MAXi 2 produces MAX tot = 31.55Mbps

13. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 13 CDF The CDF then shows the probabilities of transmitting at a certain data rate. MAX 90% NOTE: 90% = 1.3sigma 80% = 0.83sigma

14. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 14 SUMMARY SO FAR 1.As TSPECs include MAX, MIN and MEAN information, the HC can calculate the MAX, MIN and MEAN for the composite requirement for that QAP by assuming a “normal distribution” 2.If this information is included in QLoad, overlapping QAPs can also calculate the total traffic requirements, assuming “normal distribution” Could add MAX and MIN to QLoad but ALTERNATIVELY and BETTER Include MEAN and STDEV in QLoad for each QAP As this is information required to “Add” the streams Given this information, we know how to calculate the total requirement.

15. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 15 Aside -TSPECs and MAX, MIN, MEAN What if TSPEC does not include MAX, MIN and MEAN? e.g. Admission Control TSPEC only mandates MEAN In case of voice or CBR traffic: MEAN=MAX=MIN In case of Audio/Video: Unknown and variable (VBR traffic) OPTIONS Assume ‘standard’ STDEVs for Audio and Video –1.84, 1.41 and 0.87 were values for videos used in this presentation –Could look at many samples, audio and video, and determine “standard” values for Video and Audio (related to codec?) Assume MEAN=MAX=MIN –If STA did not generate full information, it does so at its own peril. IF only MAX and MEAN provided, then STDEV can still be calculated

16. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 16 QLoad Element Amended Proposed QLoad Element is amended to include the MEAN and STDEV for the total traffic for each QAP: Note that each QAP must calculated the Self MEAN and STDEV using: –MEANµ = Σ MEANi –STDEVσ = 0.25 sqrt{ Σ (MAXi – MINi) 2 } Mean and STDEV are expressed in 32us/sec  Maximum Mean value is 31250, requires 15 bits (max=mean and stdev=0))  Worse case STDEV is for a stream that varies from zero to maximum,  Worse case STDEV = (MAX – MEAN)/2 and MEAN = MAX/2  Maximum STDEV = MAX/4 = 13 bits

17. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 17 Extended QLoad Element Add the following fields to QLoad Element: QAP IDQLoad MEANQLoad STDEV

18. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 18 QLoad Element Fields Overlap Number of APs that are sharing this channel and are overlapping QLoad MEAN and STDEV The mean and standard deviation of the total traffic presented to the QAP by TSPECs from STAs associated to that QAP QAP ID First octet = random number (0 to 255) Second octet = octet 6 of MAC Address Once selected, QAP retains this ID Chosen so that it is still possible to know which specific QAP this is QAPs need recognize their own QLoad Channel Priority Used only if QAP is operating with HCCA, indicates HCCA Supervisor

19. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 19 “Distance” Field In 09/0496r1, a “Visibility” bit was proposed –If the QAP that corresponds to ID, MEAN and STDEV values is directly visible to the QAP Self, then this is set to 1 –Visibility bit set to 1 for Self Brian Hart and Ed Reuss have suggested that in place of the Visibility bit, it would be better to indicate how far away the QAP is, i.e. the number of ‘hops’. This allows the QAP to assess the effect of the QLoads of distant QAPs and allocate/share accordingly A “Distance” field is therefore added to QLoad

20. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 20 “Distance” Field in QLoad As maximum STDEV is 13 bits, 3 bits are used for “Distance” DISTANCE Distance is set to 0 for Self If the QAP that corresponds to ID, MEAN and STDEV values is directly visible to the QAP Self, then “Distance” is set to 1 If the QAP that corresponds to ID, MEAN and STDEV values is not directly visible to the QAP Self, then “Distance” is set to 1 plus the value reported for that QAP ID in the QAP that is directly visible If Distance >7, then Distance = 7 (see note) Note: It has been suggested that the practical, useful limit for Distance is 2

21. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 21 Example

22. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 22 Benefits of changes to QLoad Element Each QAP in the OBSS Graph now knows the following information: OBSS size –The sum of all the QAP IDs in its QLoad Element How many hidden QAPs (for a particular QAP) –The sum of all the “Distance” > 1 OBSS length (from a particular QAP) –Highest value of “Distance” The individual QLoads of each QAP in the OBSS Graph The QLoads of all those QAPs that are directly overlapping (Distance = 1) and therefore contending for the same air time The Qloads of QAPs that are not visible and the distances of those QAPs (Distance > 1)

23. doc.: IEEE 802.11-09/0496-02-00aa Submission May 2009 Graham Smith, DSP GroupSlide 23 Conclusion To assess the benefits of the proposed QLoad Element, it is necessary to consider how it can be used. Please see latest version of 09/0497, “Considerations for OBSS Sharing using QLoad Element”, which builds upon the QLoad Element proposed in this presentation