By Qian Deng MobiUS: Enable Together-Viewing Video Experience across Two Mobile Devices

A New Better-Together Mobile Application Bigger Screen, Higher Resolution, Real-Time Playback

Content Introduction Collaborative Half-frame Decoding Energy Efficiency Optimization System Architecture and Implementation Experimental Results and Evaluation Discussion and conclusion

Introduction Assumption The size of higher resolution video is about twice of device screen size Two devices can communicate via high-speed local wireless networks Two devices are homogeneous: same/similar software and hardware capabilities Challenge Real-time synchronous playback Resource-constrained environment: limited battery life, memory, etc. Dynamic adaption: expanding and shrinking video on two or one screen

Collaborative Half-frame Decoding schemeComput. complexity BW efficiency Impl. complexity Feasibility Thin/CHigh/LowWorstSimpleNo Thick/CHighBadSimpleNo WTHDLowBadComplexPossible PTHDLowGoodComplexPreferred Full-Frame Decoding-based Approaches Half-Frame Decoding-based Approaches Energy Efficiency and Bandwidth Saving

Collaborative Half-frame Decoding Property of Video Coding Temporal Correlation Motion Compensated Prediction --- Motion Vector (MV) Problem Cross-boundary reference Solution Cross-device collaboration (CDC), transmit the missing reference to each other

Collaborative Half-frame Decoding Two Fundamental Facts: Later frame only depends on a previous reference Highly skewed MV distribution Push-based CDC Record positions of blocks needing cross-device reference and associated motion vectors Perform a light-weight pre-scanning process and motion analysis Before decoding nth frame, look ahead by one frame

Energy Efficiency Optimization Situation: High bandwidth requirement for helping Streaming data should be low enough for multiple radio interfaces More than 90% MVs are smaller than 16 Solution: Guardband-based collaborative half-frame decoding scheme Only decode guardband blocks that will be referenced No guarantee the guardband to be correctly and completely decoded

Energy Efficiency Optimization Reduce 75% CDC traffic Worst case, increase 7% computation Multi-macroblock-wide guardband, reduce CDC traffic marginally

System Architecture and Implementation v automatically set up a network between two mobile devices Low Precision Requirement Detect arrival or departure of the other device Check capability of new added device Inform arrival and departure of other devices

System Architecture and Implementation RTT-based Synchronization Scheme Host Device Client Device Wait Half RTT Receive Notification Display this frame Next frame ready, Notify client

System Architecture and Implementation Frame: decoded frames Local: bitstream for itself Network: bitstream for other Help: CDC data Two decoder modules Parser: divide into two half stream and extract MVs

Experimental Results and Evaluation Decoding Speed

Experimental Results and Evaluation Synchronization

Experimental Results and Evaluation Energy Efficiency Half-frame lead to energy saving WiFi consumes more than half energy

Discussion and conclusion Discussion Further Optimization Opportunities Service Provisioning User Study Assumption on Homogeneity Conclusion Expansion to more than two screens Implementation on multiple radio interface Realize real-time play on any divices

Thank You Questions?