Video 80211 Path Diversity ICME03

8/14/2019 Video 80211 Path Diversity ICME03

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Low Latency Wireless Video Over 802.11Networks Using Path Diversity

John Apostolopolous

Wai-tian Tan

Mitchell Trott

Hewlett-Packard Laboratories

Allen MiuMIT Laboratory for

Computer Science


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Motivation

Prevalent 802.11

infrastructure provides

inexpensive connectivity

Emergent mobile devices

integrated with cameras and

802.11 interfaces

High quality (low-latency)

conversational

communication over 802.11

networks (e.g. VoIP, Videoconferencing)


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Challenges

802.11 operates in ISM band Interference from other electronic devices (e.g. BT,

microwaves)

Lossy Environment

Access point coverage can be spotty Quality changes over time

Signal fading due to multi-path

Shadowing due to obstacles and human traffic

Contention among exposed and hidden nodes

Low Latency requirement 802.11 ARQ error recovery can add large delays


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Our Approach

Use error resilient video compression H.264/MPEG-4 AVC

Best-effort error recovery (standard 802.11 ARQ)

Distributed AP infrastructure to stream video via

multiple access points (exploit path diversity) Use multiple paths simultaneously or switch between

them (site selection) as a function of channelcharacteristics

AP1

Microwave

(Interferer)

Sender MobileReceiver

Wired Wireless

AP2


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Preliminary investigation

In a 802.11 path diversity network with

mobile clients,

How does path diversity affect packet loss

characteristics?

What is the resulting performance gain forconversational video communication?


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Test-bed Setup

Sender MobileReceiver

Wired

100Mbps

Ethernet

802.11b

11Mbps

WLAN

AP1

AP2

~25m

Ad hoc mode ARQ up to 16 retries Open cubicle area

Receiver moves @1m/s

~40m (max)

Two 360kbps cbr streams 1500 byte UDP packets time-stamped


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Diversity Scenarios

Conventional single path case

SenderMobile

Receiver

Wired

100Mbps

Ethernet

802.11b

11Mbps

WLAN

AP1

AP2

AP1 only

AP2 only


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Diversity Scenarios


SenderMobile

Receiver

Wired

100Mbps

Ethernet

802.11b

11Mbps

WLAN

AP1

AP2

AP1 only

AP2 only

Balanced split stream (non-adaptive)


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Diversity Scenarios


SenderMobile

Receiver

Wired

100Mbps

Ethernet

802.11b

11Mbps

WLAN

AP1

AP2

AP1 only

AP2 only


Adaptive, fine-grain site selection (based on loss rate)


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Diversity Scenarios


SenderMobile

Receiver

Wired

100Mbps

Ethernet

802.11b

11Mbps

WLAN

AP1

AP2

AP1 only

AP2 only


Adaptive, fine-grain site selection (based on loss rate)

Oracle (optimal adaptive, can be realized by repetition coding)


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Path Diversity Reduces Packet Loss

20 40 60 80 100 Infinite0

5

10

15

20

25

30

Avg

PacketLos

sRa

te(%)

Delay cutoff (ms)

AP1AP2BalancedSite SelectionOracle


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Path Diversity Reduces Burst Loss

20 40 60 80 100 Infinite

0

500

1000

1500

2000

Numb

erof

BurstEven

ts

Burst event = 2 or more consecutive losses

Delay cutoff (ms)

AP1AP2BalancedSite Selection

Oracle


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H.263 Video Performance

20 40 60 80 100 Infinite24

26

28

30

32

34

Mother and Daughter Sequence

Delay Cutoff (ms)

PSNR

(dB

)

AP1

AP2Balanced

Site Selection

PSNR gain = 1.6 3.0 dB

1/3 delay reduction


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Conclusion

All path diversity schemes help reduce burstlosses

Optimal path diversity drastically reduce loss

rate and improves video quality A simple site selection algorithm can

effectively increase video quality without

increasing bandwidth usage


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Complete Trace

0 0 1 1 2 2 3 3 4 4 5 5 66 7 7


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Single Stream from AP1

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

Discarded


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Single Stream from AP2

0 1 2 3 4 5 6 7


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Split stream from AP1 & AP2

0 0 1 1 2 2 3 3 4 4 5 5 66 7 7


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0 0

1 1

2 2

3 3

4 4

5 5

66

7 7

Discarded


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0 0

1 1

2 2

3 3

4 4

5 5

66

7 7

Discarded


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0 1

1 1

2 3

3 3

4 5

5 5

76

7 7

Discarded

Re-numbered


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0 1 2 3 4 5 76


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Fine-grained Site Selection

0 0 1 1 2 2 3 3 4 4 5 5 66 7 7


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Fine-grained Site Selection

0 1 2 3 4 5 6 7

Selected site transmits 95% packet Other site transmits 5% packet for probing Site selection based on error rate of last 300 packets


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Oracle

0 0 1 1 2 2 3 3 4 4 5 5 66 7 7

Equivalent to repetition coding


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Oracle

0 0 1 1 2 2 3 3 4 4 5 5 66 7 7

Equivalent to repetition coding

0 1 2 3 4 5 6 7


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Existing Solutions

Robust video communication in lossy channel: Error resilient video compression

ARQDelay can be intolerable

Head of line blocking

FEC codingCan be inefficient

Receiver diversity antennaDoes not exploit path diversity


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Methodology

Walking with receiver in open cubicle area Analyzed packet loss from a 15 minute trace

Experiment repeated once after 3 months, showing

similar performance results

Analyzed the performance of 5 different

diversity scenarios from sampling thesame trace Difficulty in finding meaningful comparisons

between different scenarios


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20 40 60 80 100 Infinite0

5

10

15

20

25

30Average Packet Loss Rate

Percent

20 40 60 80 100 Infinite0

500

1000

1500

2000Number of Burst Events

Count

AP1AP2BalancedSite SelectionOracle

20 40 60 80 100 Infinite18

20

22

24

26

28PSNR (Foreman)

Delay Threshold (msec)

PS

NR(

dB)

20 40 60 80 100 Infinite24

26

28

30

32

34PSNR (Moth&Dthr)

Delay Threshold (msec)

PS

NR(

dB)

AP1AP2BalancedSite Selection


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0 5000 10000 15000 20000 25000-80

-60

-40

-20Received Signal Strength

Power(dBm

)

AP1AP2

0 5000 10000 15000 20000 250000

10

20

30Average Packet Loss Rate (5 sec window)

Percent

0 5000 10000 15000 20000 250000

5

10Number of Burst Losses (5 sec window)

Count

0 10 20 30 40 50 60 70 80 90

20

25

30

35

Video Quality

AveragePSNR

(dB)

Sequence Number

Oracle

AP1

AP2

Video 80211 Path Diversity ICME03

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