Scalable Video Coding and Transport Over Broad-band wireless networks Authors: D. Wu, Y. Hou, and Y.-Q. Zhang Source: Proceedings of the IEEE, Volume:

Scalable Video Coding and Transport Over Broad-band wireless networks

Authors: D. Wu, Y. Hou, and Y.-Q. Zhang

Source: Proceedings of the IEEE , Volume: 89, Issue: 1 , Jan 2001, pp. 6 -20.

Presented by: Yu Hen Hu

Presentation of Research Paper

© 2002-2005 by Yu Hen Hu 2

Overview

• Issues of wireless transmission of video

• Scalable video coding• Network-aware end system• Adaptive Service

© 2002-2005 by Yu Hen Hu 3

Wireless Video Communication System

Source Coding

Packetize, FEC

Pre-processing

Source Decoding

Post-processing

Time varying wireless channel

Network queue

Wireless transmitter

error resilience

Network layer

Physical layer

Packet recovery

Network protocol

Wireless receiver

Network layer

Physical layer

error concealment

© 2002-2005 by Yu Hen Hu 4

Application: Video Communication

• Encoded video – Consists of many

segments of bit streams.

– Bits highly dependent within each segment

– Rate vary dramatically with type of frames, motion, etc.

– Not all bits need to be transmitted – lossy compression

– Deadline exists for each segment.

• QoS– Subjective perceptual

visual quality– Objective visual quality

measures: PSNR, etc.

• Control parameters– SNR scalability:

• Quantization levels

– Spatial, temporal scalability:

• Frame rate, • frame size

– Data partitioning– Entropy coding method– Type of frames, macro-

blocks, etc.

© 2002-2005 by Yu Hen Hu 5

Characteristics of Wireless Video Links

• High BER (bit error rate)– Due to fading channels (multi-path, shadowing)

• Bandwidth variations– Movement of mobile unit– Hand-off between basestations– Noisy channel causes retransmission

• Heterogeneity of end terminals– For multi-cast, and broadcast wireless system,

one video stream serves multiple destinations with terminals of different capabilities.

© 2002-2005 by Yu Hen Hu 6

Physical: Wireless Channels

• Time varying channel characteristics (physical layer)– Fading– Interferences– Mobile clients– Noise– Channel estimation

required.

• Shared spectrum– Limited bandwidth– Sharing in both local

spatial and local temporal domains

• Resource constrained– Low power– Small form factor display

• QoS measures– BER (bit error rate)

• Control parameters– Transmission power– Modulation methods (soft-

radio)

• Impacts on network packet delivery – Delay– Transmission Error– Mis-match between

bandwidth demand and available effective BW.

© 2002-2005 by Yu Hen Hu 7

Uni-cast VS Multi-Cast

• Uni-cast • One stream serves one

receiver• Can not scale up

• Multi-cast • One stream serves multiple

receivers • Packets need to be duplicated

and transcoded• scalable

© 2002-2005 by Yu Hen Hu 8

Adaptive Service Framework

© 2002-2005 by Yu Hen Hu 9

Scalable Video Coding

• Partition of video into layers• SNR scalability: Different quantization levels• Spatial scalability: Different resolutions• Temporal scalability: Different frame rate

© 2002-2005 by Yu Hen Hu 10

SNR Scalability

SNR Scalable Encoder

Quantizer Q at enhancement layer has smaller quantization steps

Example:

DCT coefficient: 0.1234

Base layer quantized output: 0.12

Enhancement layer input: 0.0034

Enhancement layer output: 0.0034

0.1234 0.12

0.12

0.0034 0.0034

0.0034

0.12

0.1234

© 2002-2005 by Yu Hen Hu 11

Spatial and Temporal Scalability

• Lower layer bit streams are obtained from down-sampled raw video. x = yn + upsample (yn-1 + upsample (yn-2 + upsample (yn-3 + … + upsample(y0) …))

• Down-sampling and up-sampling are performed in both spatial and temporal domain.

• Spatial domain: frame size

• Temporal domain: frame rate

© 2002-2005 by Yu Hen Hu 12

Applications of Scalable Video Coding to Wireless Channels

• Adapt to multiple terminal characteristics– Each terminal (receiver) subscribes to different

amount of video layers according to its own capability.

• Adapt to variable band-width– Send appropriate amount of video layers for the

currently available band-width

• Network supports are needed to achieve above goals

© 2002-2005 by Yu Hen Hu 13

Network aware rate scaling

• If network condition (available rate) is known, – encoder can optimize

the encoding decision to maximize the perceptual quality subject to rate constraint.

– Rate control buffer size may be adjusted to avoid buffer overrun

• Encoding decisions that affect rate include: – Quantization level– Coding mode (Intra,

inter) selection.– Frame rate– Sending or dropping

enhancement layer

© 2002-2005 by Yu Hen Hu 14

Network Monitoring

Criteria Type of monitoring

Method Passive Active

Frequency On-demand Continuous

Replication Centralized distributed

© 2002-2005 by Yu Hen Hu 15

Architecture of scalable videotransportation from mobile to wired terminal

Network monitoring and adaptation

© 2002-2005 by Yu Hen Hu 16

Adaptive Services

• Goal:– Rearrange network

resources to meet the demand of wireless video transport

• Strategy– Reserve minimum

bandwidth for base-layer video stream

– Adapt resources for enhance layer stream via traffic shaping

• Method– Service contract:

• specify traffic characteristics and QoS requirement

– Call admission control and resource reservation

• Ensure enough resources are available for individual services

– Mobile multicast• Guarantee QoS during

handoff

– Sub-stream shaping

© 2002-2005 by Yu Hen Hu 17

Transporting from Wired to Mobile Terminals

© 2002-2005 by Yu Hen Hu 18

Sub-stream Traffic Shaping

© 2002-2005 by Yu Hen Hu 19

Link Layer Error Control:ARQ and RCPC

• ARQ (automatic repeat request) is a link layer error control method.

• Resend only upon request from receiving end.

• Advantage: – efficient usage of BW

• Disadvantage:– Delay unbound

• RCPC: rate-compatible punctured convolution:– If too late, don’t send

© 2002-2005 by Yu Hen Hu 20

Service Comparison

Services Guaranteed Adaptive-baseAdaptive – enhanced

Best-effort

Path setup Y Y Y N

Traffic characteristics

Y Y N N

End-to-end QoS guarantee

Y If needed N N

Network feedback N N If needed N

Resource reservation

Y Y N N

QoSBounded delay,

zero lossSmall delay, low

lossBetter than best

effortN

Target Applications

Non-adaptive CBR/VBR

Adaptive CBR/VBR

Adaptive CBR/VBR

None-real time