Transcript Document

Presentation of Research Paper
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
Overview
• Issues of wireless transmission of
video
• Scalable video coding
• Network-aware end system
• Adaptive Service
© 2002-2005 by Yu Hen Hu
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Wireless Video Communication System
Preprocessing
Source
Coding
Packetize,
FEC
Network
queue
Wireless
transmitter
error
resilience
Network
layer
Physical
layer
Time varying
wireless
channel
© 2002-2005 by Yu Hen Hu
Wireless
receiver
Network
protocol
Physical
layer
Network
layer
Packet
recovery
Source
Decoding
Postprocessing
error
concealment
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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.
© 2002-2005 by Yu Hen Hu
• 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, macroblocks, etc.
4
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
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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
© 2002-2005 by Yu Hen Hu
• Resource constrained
– Low power
– Small form factor display
• QoS measures
– BER (bit error rate)
• Control parameters
– Transmission power
– Modulation methods (softradio)
• Impacts on network packet
delivery
– Delay
– Transmission Error
– Mis-match between
bandwidth demand and
available effective BW.
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Uni-cast VS Multi-Cast
•
•
•
Uni-cast
One stream serves one
receiver
Can not scale up
•
•
•
•
© 2002-2005 by Yu Hen Hu
Multi-cast
One stream serves multiple
receivers
Packets need to be duplicated
and transcoded
scalable
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Adaptive Service Framework
© 2002-2005 by Yu Hen Hu
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Scalable Video Coding
•
•
•
•
© 2002-2005 by Yu Hen Hu
Partition of video into layers
SNR scalability: Different quantization levels
Spatial scalability: Different resolutions
Temporal scalability: Different frame rate
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SNR Scalability
0.1234
0.12
0.12
0.0034
0.0034
0.12
0.0034
© 2002-2005 by Yu Hen Hu
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
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Spatial and Temporal Scalability
• Lower layer bit streams
are obtained from downsampled raw video.
x = yn + upsample (yn-1 +
upsample (yn-2 +
upsample (yn-3 + … +
upsample(y0) …))
• Down-sampling and upsampling are performed
in both spatial and
temporal domain.
• Spatial domain: frame
size
• Temporal domain: frame
rate
© 2002-2005 by Yu Hen Hu
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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
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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
© 2002-2005 by Yu Hen Hu
• Encoding decisions
that affect rate include:
– Quantization level
– Coding mode (Intra,
inter) selection.
– Frame rate
– Sending or dropping
enhancement layer
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Network Monitoring
Criteria
Method
© 2002-2005 by Yu Hen Hu
Type of monitoring
Passive
Active
Frequency
On-demand
Continuous
Replication
Centralized
distributed
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Architecture of scalable video
transportation from mobile to wired terminal
Network monitoring and adaptation
© 2002-2005 by Yu Hen Hu
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Adaptive Services
• Goal:
– Rearrange network
resources to meet the
demand of wireless
video transport
• Strategy
– Reserve minimum
bandwidth for baselayer 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
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Transporting from Wired to Mobile Terminals
© 2002-2005 by Yu Hen Hu
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Sub-stream Traffic Shaping
© 2002-2005 by Yu Hen Hu
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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:
• RCPC: ratecompatible punctured
convolution:
– If too late, don’t send
– efficient usage of BW
• Disadvantage:
– Delay unbound
© 2002-2005 by Yu Hen Hu
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Service Comparison
Guaranteed
Adaptive-base
Adaptive –
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
Bounded delay,
zero loss
Small delay, low
loss
Better than best
effort
N
Non-adaptive
CBR/VBR
Adaptive
CBR/VBR
Adaptive
CBR/VBR
None-real time
Services
QoS
Target
Applications
© 2002-2005 by Yu Hen Hu
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