May 2009

Graham Smith, DSP Group

Slide 1

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Considerations for Statistical Multiplexing Support in OBSS Proposal - QLoad

Date: 2009, May 3

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

#100, Rancho Cordova, CA 95742

916 851 9191 X209

Graham.smith@dspg.com

Authors:

May 2009

Graham Smith, DSP Group

Slide 2

doc.: IEEE 802.11-09/0496-02-00aa

Submission

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

May 2009

Graham Smith, DSP Group

Slide 3

doc.: IEEE 802.11-09/0496-02-00aa

Submission

IntroductionThe 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 TotalThe 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.

May 2009

Graham Smith, DSP Group

Slide 4

doc.: IEEE 802.11-09/0496-02-00aa

Submission

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

May 2009

Graham Smith, DSP Group

Slide 5

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Video Throughputs

Video Throughput

0

2

4

6

8

10

12

1 11 21 31 41 51 61 71

Time, seconds

Mb

ps

Samples of throughputs of three actual individual video clips is shown below.

Video 1 Video 2 Video 3

MAX Mbps 11.4 10.0 8.6

MIN Mbps 3.3 8.1 3.6

MEAN Mbps 7.9 9.2 5.8

Video 1

Video 2

Video 3

May 2009

Graham Smith, DSP Group

Slide 6

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Video Throughputs

Composite stream of all three videos

0

5

10

15

20

25

30

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73

Time, seconds

Mb

ps

The TOTAL throughput of all three videos, “composite video”, is shown below

MAX Mbps 27.6

MIN Mbps 16.6

MEAN Mbps 22.8

Composite Stream for all 3 Videos

May 2009

Graham Smith, DSP Group

Slide 7

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Simple Addition of the three does not result in the Composite

MAX Mbps 30.0

MIN Mbps 15.0

MEAN Mbps 22.8

Addition of statistics for all 3 Videos

MAX Mbps 27.6

MIN Mbps 16.6

MEAN Mbps 22.8

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 Mbps 17.7

MIN Mbps 7.6

MEAN Mbps 13.7

Composite Stream for Videos 1 and 2

MAX Mbps 20.0

MIN Mbps 6.9

MEAN Mbps 13.7

Addition of statistics for Videos 1 and 2

Based upon MAX Mbps, then simple addition produces 13% Over allocated

May 2009

Graham Smith, DSP Group

Slide 8

doc.: IEEE 802.11-09/0496-02-00aa

Submission

VIDEO STATISTICS

  Video 1 Video 2 Video 3 Composite

MEAN 7.92 9.16 5.76 22.84

MAX 11.40 10.01 8.55 27.65

MIN 3.31 8.14 3.57 16.62

STDEV 1.84 0.37 1.41 2.22

Video 1 Video 2 Video 3 Composite

MEAN 7.92 9.16 5.76 22.84

+2σ 11.59 9.91 8.57 27.27

-2σ 4.25 8.41 2.94 18.41

Statistics for the Video streams, including “standard deviation”, are:

Note that MAX and MIN can be estimated as MEAN +/- 2 STDEV

May 2009

Graham Smith, DSP Group

Slide 9

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Video Statistics

VIDEO 1 Statistics

0

5

10

15

20

25

2 3 4 5 6 7 8 9 10 11 12 13 14

Mbps bins

Pro

bab

ilit

y

VIDEO 2

01020304050607080

1 2 3 4 5 6 7 8 9 10 11 12 13

Mbps bins

Pro

bab

ilit

y

VIDEO 3

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

2 3 4 5 6 7 8 9 10 11 12 13 14

Mbps bins

Pro

bab

ilit

y

Composite Video (1, 2 and 3)

0.00

5.00

10.00

15.00

20.00

25.00

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Mbps bins

Pro

bab

ilit

y

HISTOGRAMS and NORMAL DISTRIBUTIONS

May 2009

Graham Smith, DSP Group

Slide 10

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Video StatisticsIf 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:

Mean µ = Σµi

Stddev σ = sqrt(Σσi2)

Very good correlation between Actual composite andSum of three videos

Normal Distribution of Video

0

5

10

15

20

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Mbps bins

Pro

babi

lity Composite Video

Sum of NormalDistributions

May 2009

Graham Smith, DSP Group

Slide 11

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Video StatisticsSo 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

May 2009

Graham Smith, DSP Group

Slide 12

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Mean, Max and Min Sum of Normal Distributions:

Mean µ = Σµi and Stddev σ = sqrt(Σσi2)

Also MAX = Mean + 2σ and MIN = Mean - 2σ

Hence, to estimate the total MEAN and STDEV from the individual streams:

MEAN µ = ΣMEANi

STDEV σ = 0.25 sqrt{Σ(MAXi – MINi)2} (see note)

Using resulting µ and σ, we can calculate total MAX and MIN

MAX Mbps 27.65

MIN Mbps 16.62

MEAN Mbps 22.84

Actual Composite Stream 3 Videos

MAX Mbps 27.68

MIN Mbps 17.99.

MEAN Mbps 22.84

Estimated Composite Stream 3 Videos

Very good!!

NOTE: Calculating STDEV from just MAX or just MIN does not give accurate resultMAX calculated based on square root of MAXi2 produces MAX tot = 31.55Mbps

May 2009

Graham Smith, DSP Group

Slide 13

doc.: IEEE 802.11-09/0496-02-00aa

Submission

CDFThe CDF then shows the probabilities of transmitting at a certain data rate.

Cumulative Density Function

0

20

40

60

80

100

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Mbps bins

Pro

bab

ility Composite Video

Sum of three videos

MAX90%

NOTE:90% = 1.3sigma80% = 0.83sigma

May 2009

Graham Smith, DSP Group

Slide 14

doc.: IEEE 802.11-09/0496-02-00aa

Submission

SUMMARY SO FAR1. 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 QAPAs this is information required to “Add” the streams

Given this information, we know how to calculate the total requirement.

May 2009

Graham Smith, DSP Group

Slide 15

doc.: IEEE 802.11-09/0496-02-00aa

Submission

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

May 2009

Graham Smith, DSP Group

Slide 16

doc.: IEEE 802.11-09/0496-02-00aa

Submission

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:– MEAN µ = ΣMEANi

– STDEV σ = 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

May 2009

Graham Smith, DSP Group

Slide 17

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Extended QLoad Element

ElementID

LengthOverlap

&Priority

QAP Self ID

QloadSelf

MEAN

QloadSelf

STDEV

QAP ID

QloadMEAN

QloadSTDEV

1 1 1 2 2 2 22 2 VAR

b0 b6 b7

Channel Priority

Overlap and Priority Octet

ReservedOverlap (4 bits)

Etc.For all QAPs

In OBSS Graph

QAP ID

Random Value

1

Octet 6 of MAC Address

1

QLOAD ELEMENT

MEAN and STDEV values are in units of 32 µsec periods per second (as per Medium Time)

CHP = 1 HigherCHP = 0 Lower

Add the following fields to QLoad Element:QAP ID QLoad MEAN QLoad STDEV

May 2009

Graham Smith, DSP Group

Slide 18

doc.: IEEE 802.11-09/0496-02-00aa

Submission

QLoad Element Fields

OverlapNumber of APs that are sharing this channel and are overlapping QLoad MEAN and STDEVThe 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 AddressOnce selected, QAP retains this IDChosen so that it is still possible to know which specific QAP this isQAPs need recognize their own QLoad

Channel Priority Used only if QAP is operating with HCCA, indicates HCCA Supervisor

May 2009

Graham Smith, DSP Group

Slide 19

doc.: IEEE 802.11-09/0496-02-00aa

Submission

“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

May 2009

Graham Smith, DSP Group

Slide 20

doc.: IEEE 802.11-09/0496-02-00aa

Submission

“Distance” Field in QLoad

Qload STDEV

b0 b13 b15

STDEV

b14

Distance

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

May 2009

Graham Smith, DSP Group

Slide 21

doc.: IEEE 802.11-09/0496-02-00aa

Submission

Example

A

A

B

A

B

C

QAP A is by itselfQAP A Overlap = 0 Distance = 0

MEAN Self = AmeanSTDEV Self = Astdev

QAP B decides to share with AQAP A Overlap = 1

Adds QAP B to Qload ElementQAP B ID + Bmean + Bstdev with Distance = 1

QAP B adds QAP A to its Qload ElementOverlap = 1QAP A ID + Amean + Astdev with Distance = 1

QAP C decides to share with A (hidden from B)QAP A Overlap = 2

Adds QAP C to Qload ElementQAP B ID + Bmean + Bstdev with Distance = 1QAP C ID + Cmean + Cstdev with Distance = 1

QAP C adds QAP A Qload information to its Qload ElementOverlap = 1QAP A ID + Amean + Astdev with Distance = 1QAP B ID + Bmean + Bstdev with Distance = 2

QAP B sees QAP C appear in QAP A Qloadadds QAP C to its Qload Element

Overlap = 1QAP A ID + Amean + Astdev with Distance = 1QAP C ID + Cmean + Cstdev with Distance = 2

May 2009

Graham Smith, DSP Group

Slide 22

doc.: IEEE 802.11-09/0496-02-00aa

Submission

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)

May 2009

Graham Smith, DSP Group

Slide 23

doc.: IEEE 802.11-09/0496-02-00aa

Submission

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