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Coded Wireless Video Broadcast / Multicast:A Cross-layer Framework With Protections To Harvest The True Potential of 4G Access Networks

James She, Ph.D.

Research Fellow, Computer Laboratory

Presentation @ The Chinese University of Hong Kong, Hong Kong – Jan 2011

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Outline1. Introduction & Background

2. A Preliminary Cross-layer Design

3. Coded Wireless Video Broadcast/Multicast

4. An Information-theoretical Bound of Expected

Distortion

5. Conclusion & Future Work

4G/Broadband Wireless Access and 1-to-many/all Video Applications

Wireless Broadcast/Multicast and Problems

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In a single-hop wireless network:

1. Multi-user channel diversity: Rate is limited to receiver with the worst channel low video quality

2. Error Control: Retransmission

Not efficient or scalable

• efficient use of spectrum• higher system scalability

Research Objectives

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Limitations of Existing Cross Layer Designs (CLDs):

1. Many for unicast are not applicable

2. Some for multicast/broadcast using erasure/network codings:

– Some statistical number of receivers within a multi/broadcast group

– Multi-hop wired/wireless infrastructure

Research Objectives:

1. Practical and generic cross-layer frameworks (advanced source + channel coding) for single-hop network

2. Fundamental understanding of the proposed frameworks, using information theory

3. Possible implementations

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Outline1. Introduction & Background

2. A Preliminary Cross-layer Design

3. Coded Wireless Video Broadcast/Multicast

4. An Information-theoretical Bound of Expected

Distortion

5. Conclusion & Future Work

A preliminary cross-layer design - Superposition Coded Multicast

Scalable Video Source (MPEG4/ H.264AVC):

Bitstream with successive refinable layers

…

… …

Layered Channel (Superposition coding): Multi-resolution modulated (layered) broadcast signals

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layered broadcast signal

layer 2 (QPSK)layer 1 (BPSK)

Encoding: superimpose two modulated signals (i.e., vector additions: x1 + x2 x )

Decoding, y: 1. decode the lower order signal (BPSK), y1,

from received signal, y 2. substract it from y for decoding y2.(QPSK)

(i.e., y - y1 y2.)

e.g., 2 layered video data (basic + enh. qualities)

… …

Superposition Coded Multicast (SCM)

2 quality layers (base & enhancement)

Novelty:Novelty: exploits the layered properties in scalable source and multi-resolution channel

BS only broadcasts/multicasts a single type of radio signals that contains all layers

decodable by receivers at various channel levels for multiple rate of video delivery.

Base station

Receiver(s)

Simulation Results

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Conclusion:Higher video quality regardless of the avg. channel SNR of a receiver!

poor receiver (low SNR avg.)good receiver (high SNR avg.)

Compare achievable video qualities (PSNR):• Normal Multicast vs. SCMPS: ‘Normal’ uses the rate everyone supports

SCM SummaryTwo critical components identified:

1. Scalable video (source)

2. Multi-resolution modulation (channel)

Resolved multi-user channel diversity + video quality improvement.

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An limitaiton:

• Video quality fluctuates with channel condition at a receiver regardless of the SNR avg.

Error control problem!

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Outline1. Introduction & Background

2. A Preliminary Cross-layer Design

3. Coded Wireless Video Broadcast/Multicast

4. An Information-theoretical Bound of Distortion

Bound

5. Conclusion & Future Works

Proposed - Coded Wireless Video Broadcast/Multicast

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Deal with error control & multi-user channel diversity: Introduced protections to each successive layer at the source Achievable by modifying the Multiple Description Coding based on Reed Solomon

RS(N, K) [18]

Each MDC/protected packet (with multiple layers of bitstreams) is sent through SCM as a multi-resolution modulated signal

[18] P. A. Chou, H. J. Wang, and V. N. Padmanabhan, “Layered multiple description coding,” Proc. PV 13th Int. Packet Video Workshop,Nantes, France, Apr. 2003.

Note:

For any layer l, a smaller Kl

value, the higher robustness to tolerate fading duration for that layer.

System Model And Error Control Advantages

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Scalable Video Encoder

WirelessChannel

Video Decoder

Superposition Modulation

PHY layerMAC layer

Video in

Video out

layer 2 buf fer

layer 1 buf fer

layer 1 buf fer

layer 2 buf fer

Coded WirelessVideo Broadcast/ Multicast signals

Coded WirelessVideo Broadcast/ Multicast signals

+

16QAM modulatedanalog forms

BPSK modulatedanalog forms

superposedanalog forms

Multicast addressed

Multicast addressed

Superposition Demodulation

+superposedanalog forms

Demodulatedbase layer data

Demodulatedenhancement layer data

Protection Codere.g. Reed-Solomon

Scalabe bitstream

App. layer

1

2

3

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Scalable Error Controls: Receiver recovers its own lost bitstreams of layer l when successfullyreceived any Kl “partial” MDC packets of layer l.

A Quick Video(00:00:51-00:02:05)

• Prob. of receiving/recovering a layer l by receiver m (i.e., receiving at least Kl partial packets of layer l by receiver m)

Formulations For AnalysisPerformance/video quality measurement:Total received/recovered bitstreams, Tm, of a GoF by a receiver m.

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, ,, 0 ( ( )) (1 ( ))l m l ml jNN K N j

l m j jloss SNR SNRP loss

, ( ) ,1 1l mlT b b Pi ml l i

1 ,l

Ll mmT T

•With the layers dependency, the amount of received/ recovered bitstreams of a layer l in a GoF:

Total received/recovered bitstream of a GoF:

layer l

Optimized & Experimental Results

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Compare layered broadcast w/o protection (e.g., SCM) and the proposed one:• 2 layers w/ optimized (searched) parameters • 2 different standard video sequences (Foreman and Paris)

SS-1

Coded Wireless Video Broadcast/Multicast• better video quality even in a poorer channel• smaller quality difference between receivers with highest and lowest SNR avg.

Note: SS-1: lowest SNR avg.SS-10: highest SNR avg.

(Foreman)

Layered source+channel (SCM)

Layered source+channel with protection

poor receiver good receiver

Summary

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Novelties:Novelties:

1. Introduced protections on successive layers over layered broadcast

2. Utilized partial MDC (protected) packets (never discussed in wired infrastructure)

3. Modified existing MDC for practical implementation

4. An analytical model for analysis and optimization.

Resolved both multi-user channel diversity and error control problems which are not possible in all previous and recent works [1-4]

[1] Chris T. K. Ng et al., “Recursive Power Allocation in Gaussian Layered Broadcast Coding with Successive Refinement,” IEEE Intl. Conf. on Comm. (ICC), Jun 24–27, 2007, Glasgow, Scotland, pp. 889–896.

[2] C. Tian et al., “Successive Refinement Via Broadcast: Optimizing Expected Distortion of a Gaussian Source Over a Gaussian Fading Channel”, IEEE Trans. on Information Theory, vol. 54, no 7, pp.2903-2918, Jul. 2008.

[3] Y. S. Chan et al., “An End-to-End Embedded Approach for Multicast/Broadcast of Scalable Video over Multiuser CDMA Wireless Networks”, IEEE Trans. on Multimedia, vol. 9, no. 3, pp. 655-667, Apr. 2007.

[4] Murali R. Chari et al., “FLO Physical Layer: An Overview”, IEEE Trans. on Broadcasting, vol. 53, no. 3, pp. 145-160, Mar. 2007

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Outline1. Introduction & Background

2. A Preliminary Cross-layer Design

3. Coded Wireless Video Broadcast/Multicast

4. An Information-theoretical Bound of Expected

Distortion

5. Conclusion & Future Works

Informaton-theoretical Bound of Expected DistortionDid you realize that we send less video data? Costs of protections

If / when the proposed framework is better than a similar layered broadcast WITHOUT protections?

The expected distortion without layers [3] :

where each source symbol is sent by a channel symbol under symbol error, perr.

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Apply a generic (n, kl) protection code in a layer l: i.e. A source symbol, S n protected layered source symbol, Vi , where i=1,..., n. Recall: smaller kl value for layer l, more robustness, but less effective data sent

[3] X. Yu and En-hui Yang, “Optimal quantization for noisy channels with random index assignment", Proc. of the 2008 IEEE Intern. Symp. Inform. Theory, Toronto, Canada, July 6-11, 2008.

Assume a successive refinable source with Gaussian distribution (i.e., L layers in each source symbol, S)

Bound of Expected Distortion

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Each Vi a layered channel symbol, x(i), for each coded broad/multicast transmission:

A receiver collects n channel symbols, x(1), ... ..., x(n) over n channel symbol durations.

Each x(i) is decoded into up to layer l with prob. upon the receiver`s instantaneous

channel condition.

x(i)

protected layered source symbols, Vi

~

lpiV

Bound of Expected Distortion

The Bound of Expected Distortion:

Applicable to a system without protection (i.e., kl =n)

The discreteness (i.e., binomial CDF terms) can be approximated by a normal CDF to determine optimal k values for optimization. 22

V1 ... ... Vn

1

1

1

, ,01

12

, ,01

2 1 1

1 1 1

L

l

l

l ij jj

i

klk R j n j

M i M iji

klj n j

l M i M iji

p

np p

jD

np p

j

After n channel symbol durations (or n transmissions),

kL

kl

k1

Numerical Anylysis -1

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(a) higher pM,1 (k1*=5, k2

*=2) (b) lower pM,1 (k1*=14, k2

*=2)

(a)higher pM,2 (k1*=18, k2

*=1) (b) lower pM,2 (k1

*=18, k2*=3)

Fixed symbol error at layer 2

Fixed symbol error at layer 1

Expected distortions of two systems (with and without protections) under various pM,1 in layer 1 and pM,2 in layer 2.

Numerical Anlysis - 2

Simulation Comparisons

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Fixed lower, pM,2, in layer 2

Layered broadcast without and with protections under optimized parameters:

Systems with their optimized configurations .

Fixed higher, pM,2, in layer 2

Summary of Expected Distortion

Novelties:Novelties:

A general closed-form formula for the bound of expected distortion

Generic to any (n, k) protection code and any number of layers (source/channel), useful for a new coding design

More accurate analysis/optimization, instead of using simply using throughput/bitstream amount.

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Outline1. Introduction & Background

2. A Preliminary Cross-layer Design

3. Coded Wireless Video Broadcast/Multicast

4. An Information-theoretical Bound of Expected

Distortion

5. Conclusion & Future Works

Contributions 1st framework using protections for tackling multi-user diversity and

error control.

1st realization through existing codings, as well as the associated analytical and optimization models.

1st information-theoretical distortion bound for comparisons, and optimization through a simple search.

Advanced the fields by introducing a new design dimension – protections, for cross-layer designs that was unapparent in the past literature.

LESS is MORE sometimes!

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Future Work Extend into cooperative communications under multi-BSs wireless networks (e.g.,

optical-wireless hybrid network) by considering space-time coding

Promising results from preliminary investigations in EPON-WiMAX access networks

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Final Remark: a cross-layer design with protections is shown to be useful in cooperative networks for better video broadcast/multicast

On-gogin Research and Industrial Collaborations

Electrical & Computer

Engineering

• WiFi platform (prototype)

• WiMAX/LTE BS system and cooperative broadcasting networks (prototype and research)

• New scalable source coding with protection (research)

Electrical & Computer Engineering

• SPC chipset and software-defined radio platform (research)

• Coded MIMO Broadcast/Multicast(research)

Electrical & Electronic Engineering

(Taiwan)

(Italy)

(Saudi Arabia)

(Ottawa)

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Acknowledgement

Sponsors:Sponsors:

IPMG

Collaborators:Collaborators:

Prof. Pin-Han Ho, University of WaterlooProf. En-hui Yang, University of WaterlooDr. Xiang Yu, Research-In-Motion

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Collaborations and students1. Looking for like-minded researchers and

organizations/industries for collaborations and funs!

2. Looking for smart, creative and entrepreneurial students to join me as my research interns.

Email: james.she@cl.cam.ac.uk

Web: http://www.cl.cam.ac.uk/~js864

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The End

THANK YOU

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SCM:

[1] J. She, et al., “IPTV over WiMAX: Key Success Factors, Challenges and Solutions”, IEEE Communications Magazine, vol. 45, no. 8, pp.87-93, Aug. 2007.

(Top 50 most accessed article in IEEE Xplore 2008, and cited in Wikipedia under MobileTV)

Coded Wireless Video Broadcast/Multicast:[2] J. She, et al., “A Cross-Layer Design Framework for Robust IPTV Services over IEEE 802.16 Networks”, IEEE Journal of Selected Areas on Communications (JSAC), vol. 27, no. 2, Feb. 2009, pp. 235-245.[3] J. She, et al., “A Framework of Cross-Layer Superposition Coded Multicast for Robust IPTV Services over WiMAX”, Proceedings of the IEEE Wireless Communication and Networking Conference, pp. 3139-3144, Mar. 2008, Las Vegas, Nevada, USA. (Nominated for the Best Student Paper Award)

Expected Distortion Comparison:[4] J. She, et al., “Distortion Comparisons For Protected Successive Refined Over Broadcast Channel ”, submitted to Trans. Multimedia, Jul. 2010.

L-SPC:[5] J. She, et al., “Logical Superposition Coded Modulation”, submitted to Trans. Wireless Communication, Nov. 2010.

Selected Publication From This Research