Tomorrow: Uplink Video Transmission Today: Downlink Video
Broadcast Changing Landscape of Multimedia Applications
Slide 2
Motion-Compensated Predictive Coding (MPEG/H.26) High
compression efficiency Rigid complexity partition between encoder
(heavy) & decoder (light) High fragility to transmission losses
Image Coding (Motion JPEG) Low complexity High robustness to
transmission losses Low compression efficiency + Previous frame
Current frame DFD (Displaced Frame Difference) Motion search range
Motion Vector Contemporary Video Coding Standards
Slide 3
Challenges: Low bandwidths high compression efficiency Limited
handheld battery power low end-device complexity Lossy wireless
medium robustness to transmission losses Rethinking Video Over
Wireless High compression efficiency Flexible partition of
complexity between encoder & decoder Inbuilt robustness to
channel loss Backward compatibility with existing video standards
Puri & Ramchandran, Allerton 02 Light PRISM Uplink Encoder
Light PRISM Downlink Decoder Heavy PRISM Downlink Encoder Heavy
PRISM Uplink Decoder Trans-coding Proxy New Architecture: PRISM
(Power-efficient, Robust, hIgh-compression Syndrome-based
Multimedia coding)
Slide 4
DecoderEncoder X Y X ^ X and Y are correlated sources Y is
available only at decoder Source Coding with side-information
(SlepianWolf, Wyner-Ziv) Exploit side-information Y at the decoder
while encoding X No MSE performance loss over case when Y is
available at both encoder and decoder when innovations is Gaussian
For the video coding case, X is the block to be coded and the
side-information Y consists of the previously decoded blocks in the
frame memory Background: Distributed Source Coding
Slide 5
The encoder does not have access to Y1, Y2, etc Neither the
encoder nor the decoder knows the correct side- information Can
decoding work? Yes! A modified Wyner-Ziv paradigm is needed
(Ishwar, Prabhakaran, & Ramchandran ICIP 03.) Predictive
Decoder Predictive Encoder Quantized DFD X... Y1Y1 YMYM Y1Y1 YMYM
Motion Vector X PRISM Decoder PRISM Encoder X... Y1Y1 YMYM Y1Y1
YMYM X ? Motion-Free Encoding?
Slide 6
X Wyner-Ziv Encoder bin index Y1Y1 Wyner-Ziv Decoder X YTYT
Wyner-Ziv Decoder... YMYM Wyner-Ziv Decoder... Decoding failure
Decoding failure PRISM Robustness Comparisons: Predictive Coding:
channel errors lead to prediction mismatch and drift PRISM: drift
stopped if syndrome code is strong enough: Targeted noise
Correlation Noise + Induced Channel Noise + Quant. Noise Need
concept of motion compensation at decoder! Need mechanism to detect
decoding failure In theory: joint typicality (statistical
consistency) In practice: use CRC
Slide 7
Secondary description of video sent over auxiliary-channel.
Need to find statistics of correlation noise Z = X X main. Can
leverage algorithm of Zhang, Regunathan and Rose (Asilomar 99) to
develop recursive correlation estimation algorithm. (Wang,
Majumdar, Ramchandran, and Garudadri: PCS 04.) Auxiliary channel
allows drift correction without intra-refresh. Standards-Compliant
Auxiliary-Channel MPEG/H.26x Encoder X Auxiliary-Channel Encoder
MPEG/H.26X Decoder Auxiliary-Channel Decoder X main Final
reconstruction Coset Index Wireless Channel Auxiliary-Channel X ^
MPEG/H.26x bit-stream Wireless Channel
Slide 8
Results Channel simulator provided by Qualcomm Inc. conforming
to a CDMA 2000 1x standard. Performance comparison among 3 systems:
H.263+ bitstream with 20% extra rate for FEC (RS codes) H.263+
bitstream with 20% extra rate for standard-compliant auxiliary
channel PRISM Standard-compliant auxiliary channel version
outperforms H.263+FEC by 2.5-4 dB between error rates of 2-10%.
PRISM outperforms H.263+FEC by 6-8 dB between error rates of 2-10%.
H.263+ with FEC Stefan, 352x240, 15fps, 2200 kbps, 8% error rate
H.263+ with Auxiliary ChannelPRISM
Slide 9
PRISM for Wireless Video Broadcast Broadcast source coding
studied in information theory literature. (Heegard & Berger,
IT85, Steinberg & Merhav IT04) Lossy channel: need broadcast
source-channel coding view. Can use PRISM constructions. (Majumdar
& Ramchandran, ICIP 04) No need to deterministically track Y b
and Y g at encoder. No need for multiple prediction loops
complexity savings. Multiple side-informations at each decoder
motion search at each decoder. Standards-compliant implementations
possibly using the auxiliary channel setup. (Wang, Majumdar, &
Ramchandran, ICASSP 05) Decoder Bad Decoder Good Encoder X Y g
(good side-information) Y b (bad side-information) XgXg XbXb Rate =
R Rate = R
