Tomorrow: Uplink Video Transmission Today: Downlink Video Broadcast Changing Landscape of Multimedia Applications

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

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)

DecoderEncoder X Y X ^ X and Y are correlated sources Y is available only at decoder Source Coding with side-information (Slepian–Wolf, 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

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 Y1’Y1’ YM’YM’ … Motion Vector … X PRISM Decoder PRISM Encoder X... Y1Y1 YMYM Y1’Y1’ YM’YM’ X ? Motion-Free Encoding?

X Wyner-Ziv Encoder bin index Y1’Y1’ Wyner-Ziv Decoder X YT’YT’ Wyner-Ziv Decoder... YM’YM’ 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

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

Results Channel simulator provided by Qualcomm Inc. conforming to a CDMA x 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 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

PRISM for Wireless Video Broadcast Broadcast source coding studied in information theory literature. (Heegard & Berger, IT’85, Steinberg & Merhav IT’04) 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