Doc.: IEEE 802.11-09/0496-00-00aa Submission Apr 2009 Graham Smith, DSP GroupSlide 1 Considerations for Statistical Multiplexing Support in OBSS Proposal

Apr 2009

Graham Smith, DSP Group

Slide 1

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

Submission

Considerations for Statistical Multiplexing Support in OBSS Proposal - QLoad

Date: 2009, April 29

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

#100, Rancho Cordova, CA 95742

916 851 9191 X209

[email protected]

Authors:

Apr 2009


Slide 2

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

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

Apr 2009


Slide 3

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

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.

Apr 2009


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

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

Apr 2009


Slide 5

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

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

Apr 2009


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

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

Apr 2009


Slide 7

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

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

Apr 2009


Slide 8

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

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

Apr 2009


Slide 9

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Submission

Video StatisticsIf each video stream can be represented by a Normal Distribution,then the sum of the streams is also a Normal Distribution 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

Apr 2009


Slide 10

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

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

Apr 2009


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

Submission

Mean, Max and Min We have shown accurate representation of the composite videoby summation of the Normal Distributions for each stream:Sum of Normal Distributions:

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

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

Hence, we 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

Apr 2009


Slide 12

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

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

Apr 2009


Slide 13

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

Submission

SUMMARY SO FAR1. If TSPECs include MAX, MIN and MEAN information, the HC

can calculate the MAX , MIN and MEAN for the composite requirement for that AP

2. If this information included in QLoad, overlapping QAPs can calculate the total MAX, MIN and MEAN for total traffic

Could add MAX and MIN to QLoad but ALTERNATIVELY and BETTER

• Just include MEAN and STDEV in QLoad– QAP calculates STDEV from the MAX, MIN and MEAN given in the

TSPECs

Given this information, we know how to calculate the total requirement. Is it practical?

Apr 2009


Slide 14

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

Submission

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

Apr 2009


Slide 15

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

Submission

QLoad

Simple addition of the QLoad traffic is now not used, therefore:

Proposal QLoad Element is amended to include the MEAN and STDEV for the total traffic for that 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}

• Note: The original “rules” for simply adding the QLoads no longer apply

Apr 2009


Slide 16

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

Submission

Proposed Extended QLoad Element

ElementID

LengthOverlapVisiblePriority

QAP (Self)

ID

Qload(Self)MEAN

Qload(Self)

STDEV

QAP ID

QloadMEAN

QloadSTDEV

1 1 1 2 2 2 22 2 VAR

Channel Priority

Overlap, Visibility 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)

Visible bit = 1 if QAP is visibleVisible bit = 0 if QAP is not visible

CHP = 1 HigherCHP = 0 Lower

1

QAPPriority

Streams1

b0

b0

b7

b4

Number AC3 streams Number AC2 streams

QAP Priority Streams

QAPPriority

Streams

Qload STDEV

b0 b7 b14

Visiblebit


b8 b15

STDEV

b4

SEE LATER

Apr 2009


Slide 17

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

Submission

QLoad Element FieldsOverlapNumber 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

Visible BitIf the QAP that corresponds to ID, MEAN and STDEV values is directly visible to the QAP Self, then this is set to 1Visibility bit set to 1 for Self

Channel Priority Used only if QAP is operating with HCCA, indicates HCCA SupervisorQAP Priority StreamsNumber of streams on ACs 2 and 3 per QAP. Used so that the contention overhead can be estimated.

Apr 2009


Slide 18

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

Submission

Example

A

A

B

A

B

C

QAP A is by itselfQAP A Overlap = 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 Visibility Bit = 1

QAP B adds QAP A to its Qload ElementOverlap = 1QAP A ID + Amean + Astdev with Visibility Bit = 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 Visibility Bit = 1QAP C ID + Cmean + Cstdev with Visibility Bit = 1

QAP C adds QAP A Qload information to its Qload ElementOverlap = 1QAP A ID + Amean + Astdev with Visibility Bit = 1QAP B ID + Bmean + Bstdev with Visibility Bit = 0

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

Overlap = 1QAP A ID + Amean + Astdev with Visibility Bit = 1QAP C ID + Cmean + Cstdev with Visibility Bit = 0

Apr 2009


Slide 19

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

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 in the OBSS Graph– The sum of all the Visibility Bits = 0

• The individual QLoads of each QAP in the OBSS Graph

• The QLoads of those QAPs that are directly overlapping (visible) and therefore contend for the same air time– Important as EDCA efficiency reduces as traffic increases on same

Access Category

HOW ABOUT SHARING RULES?

Apr 2009


Slide 20

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

Submission

SharingGiven the MEAN and STDEV values for each QAP in the OBSS

Graph, every QAP can now calculate:• Total Peak traffic • Total Mean TrafficTotal Traffic Allocation based upon:

1. MAX traffic = µtot + 2 σtot

2. 90% Traffic = µtot + 1.3 σtot

3. 80% Traffic = µtot + 0.83σtot 4. Other?

Total Traffic Allocation limit is also affected by– EDCA Overhead

Contention overhead reduces the total traffic bandwidth. Important as number of streams increases

– HCCA Allocation LimitNeed to allow bandwidth for non-QoS traffic, say only 90% of total bandwidth should be reserved

Apr 2009


Slide 21

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

Submission

EDCA Overhead – Capacity drops with # streams

Maximum throughput on (shared) channel decreases as number of video streams increases

As number of video streams increases, the contention also increases. In order to keep latency low the capacity of the Channel is decreased.

1 stream @ 33Mbps

2 Streams @ 14Mbps = 28Mbps total

5 Streams @ 4.5Mbps = 22.5Mbps total

HENCE:Total Allocation MUST take account of the number of streamsNote: This is also for Admission Control on each QAP

Limits to ensure low loss:Total Throughput vs # VI Streams54Mbps (Simulated)

0

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35

1 2 3 4 5

# Video Streams

Max T

hro

ug

hp

ut,

Mb

ps

NOTE: Above graph is for independent streams. Downlink streams from QAP may be better due to queuing at the AP

Apr 2009


Slide 22

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

Submission

Basic Sharing Requirments ?

1. Ability to calculate the Total Traffic Requirement of all the sharing QAPs• Calculate Total Traffic

100%, 90%, 80%, Other?

2. Ability to adjust for EDCA contention• Note QLoads of QAPs that are “Visible” and the number of streams

• To enable this, add # of Streams per QAP to the QLoad Element

3. Adjust for HCCA limit• Do not allow allocation over 90% to allow for other traffic

Apr 2009


Slide 23

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

Submission

Extended QLoad Element

ElementID

LengthOverlapVisiblePriority

QAP (Self)

ID

Qload(Self)MEAN

Qload(Self)

STDEV

QAP ID

QloadMEAN

QloadSTDEV

1 1 1 2 2 2 22 2 VAR

Channel Priority

Overlap, Visibility 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

1

QAPPriority

Streams1

b0

b0

b7

b4

Number AC3 streams Number AC2 streams

QAP Priority Streams

QAPPriority

Streams

Qload STDEV

b0 b7

Visiblebit


b8 b15

STDEV

b4

Added # of EDCA streams

Apr 2009


Slide 24

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

Submission

Sharing Conclusion

Conclusion is that in order for the OBSS scheme to provide reliable service on a regular basis:

• Basic or Recommended Sharing Rules are required

• Especially true for HCCA– HCCA needs to have a common Sharing procedure so that QAP

with CHP = 1 has a known timing scheme for allocation of time within the fixed slot for TXOPs

A separate Presentation on Sharing will be prepared

Apr 2009


Slide 25

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

Submission

Conclusions

• New QLoad Element has significant advantages– Need to decide if extended version is preferred

• Information enables QAPs to make better decisions on individual allocations

Recommendations:

1. Use extended version of QLoad

• Prepare “Sharing” presentation

2. Revise main proposal accordingly

Documents

Doc.: IEEE 802.11-09/0496-00-00aa Submission Apr 2009 Graham Smith, DSP GroupSlide 1 Considerations for Statistical Multiplexing Support in OBSS Proposal