Scalable Video Coding and Transport Over Broad-band wireless networksOverviewWireless Video Communication SystemApplication: Video CommunicationCharacteristics of Wireless Video LinksPhysical: Wireless ChannelsUni-cast VS Multi-CastAdaptive Service FrameworkScalable Video CodingSNR ScalabilitySpatial and Temporal ScalabilityApplications of Scalable Video Coding to Wireless ChannelsNetwork aware rate scalingNetwork MonitoringArchitecture of scalable video transportation from mobile to wired terminalAdaptive ServicesTransporting from Wired to Mobile TerminalsSub-stream Traffic ShapingLink Layer Error Control: ARQ and RCPCService ComparisonScalable Video Coding and Transport Over Broad-band wireless networksAuthors: D. Wu, Y. Hou, and Y.-Q. ZhangSource: Proceedings of the IEEE , Volume: 89, Issue: 1 , Jan 2001, pp. 6 -20. Presented by: Yu Hen HuPresentation of Research Paper© 2002-2005 by Yu Hen Hu 2Overview•Issues of wireless transmission of video•Scalable video coding•Network-aware end system•Adaptive Service© 2002-2005 by Yu Hen Hu 3Wireless Video Communication SystemSource CodingPacketize, FECPre-processingSource DecodingPost-processingTime varying wireless channelNetwork queueWireless transmittererror resilienceNetwork layerPhysical layerPacket recoveryNetwork protocolWireless receiverNetwork layerPhysical layererror concealment© 2002-2005 by Yu Hen Hu 4Application: 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 5Characteristics 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 6Physical: 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 7Uni-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 8Adaptive Service Framework© 2002-2005 by Yu Hen Hu 9Scalable 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 10SNR ScalabilitySNR Scalable EncoderQuantizer Q at enhancement layer has smaller quantization stepsExample: DCT coefficient: 0.1234Base layer quantized output: 0.12Enhancement layer input: 0.0034Enhancement layer output: 0.00340.1234 0.120.120.00340.00340.00340.120.1234© 2002-2005 by Yu Hen Hu 11Spatial 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 12Applications 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 13Network 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 14Network MonitoringCriteria Type of monitoringMethod Passive ActiveFrequency On-demand ContinuousReplication Centralized distributed© 2002-2005 by Yu Hen Hu 15Architecture of scalable videotransportation from mobile to wired terminalNetwork monitoring and adaptation© 2002-2005 by Yu Hen Hu 16Adaptive 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 17Transporting from Wired to Mobile Terminals© 2002-2005 by Yu Hen Hu 18Sub-stream Traffic Shaping© 2002-2005 by Yu Hen Hu 19Link 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 20Service ComparisonServices Guaranteed Adaptive-baseAdaptive – enhancedBest-effortPath setup Y Y Y NTraffic characteristicsY Y N NEnd-to-end QoS guaranteeY If needed N NNetwork feedback