Lecture 9: Case Study -- Video streaming over Hung-Yu Wei National Taiwan University

Transcription

1 Lecture 9: Case Study -- Video streaming over Hung-Yu Wei National Taiwan University

2 QoS for Video transmission Perceived Quality How does network QoS translate to multimedia quality? Define your application Max. delay Video/buffer feedback Feedback from video decoder/decoder buffer Transport feedback Encoding Online/offline 2

3 H.264 Overview of H.264/AVC ITU-T standard MPEG-4 Part 10 ISO standard AVC (Advanced Video Coding ) 3

4 H.264 AVC Video Coding Layer (VCL) Video coding bitstream Video Frame (one or more slices) Slices (continuous group of macroblocks) I-slices P-slices B-slices Macro-blocks 4

5 H.264 AVC (continued) Network Abstraction Level (NAL) To provide network-ready service Video syntax to be used in various networking environments NAL unit could be readily encapsulated to a transport system RTP (real-time transfer protocol) MPEG-4 file format MPEG-2 transport stream IDR (instantaneous decoding refresh) picture 5

6 Parameter Set H.264 AVC (continued) SPS(sequence parameter set) Parameter for a coded video sequence PPS (picture parameter set) Parameter for a coded picture Information in NAL 6

7 H.264: Data partitioning (DP) Data partitioning (DP) Separate important and less important data into different packets Unequal error protection (UEP) Error resilience design 7

8 Coding Parameter Selection Encoder control Macroblock mode (e.g slice group pattern) Reference frames Motion vectors Rate control Satisfy rate and timing constraint For example: constant-bit-rate encoding rate for transmission over CBR channels Global parameter selection Temporal/spatial resolution Packetization modes (e.g. slice size) 8

9 Video Encoding/Decoding 9

10 Video transmission: Protocol Layers 10

11 Example: 3GPP protocol stacks Layer 2: RLC and MAC layer RLC (radio link control protocol) AM (acknowledged mode) mode ARQ for re-transmission UM (unacknowledged mode) mode No re-transmission 11

12 RoHC Robust Header Compression header compression protocols that compress RTP TCP UDP More IETF WG Could be applied to EDGE, WCDMA, cdma

13 Optimized video streaming over by cross-layer signaling Reference: I. Haratcherev, J. Taal, K. Langendoen, R. Lagendijk, and H. Sips, "Optimized video streaming over by cross-layer signaling," IEEE Communications Magazine, vol. 44, pp , 2006.

14 Link adaptation Main Idea supports multiple rates Cross-layer signaling Exchange cross-layer information Adaptation techniques Video rate control Radio rate control Channel state predictor Medium sharing predictor 14

15 Adaptive Coding and Modulation Shannon Capacity Transmission rate V.S. SNR SNR condition (channel condition) varies Adaptive Coding and Modulation Choose modulation scheme and coding scheme based on receiving SNR BER, FER Support multiple data rates Example: 1, 2, 5.5, 6, 9, 11, 12, 18, 24, 36, 48, 54 Mbps 15

16 DSSS b/g Differential Binary Phase Shift Keying 1 Mbps Differential Quadrature Phase Shift Keying 2 Mbps Complementary Code Keying 5.5 and 11 Mbps OFDM 6 and 9 Mbps 12 and 18 Mbps 16-Quadrature Amplitude Modulation 24 and 36 Mbps 48 and 54 Mbps 16

17 SNR V.S. data rate 17

18 Scenarios Wireless channel model Static Dynamic Spectrum sharing Share wireless medium No sharing 18

19 Architecture 19

20 Statistics-Based Throughput-based MAC Rate Control Apply 3 sets of rate. Then evaluate the performance Need longer time to obtain meaningful statistics FER-based ACK in provides FER info Parameter tuning is tricky Retry-based Short response time (need to be implemented in hardware) Sensitive to downscaling but insensitive to upscaling 20

21 MAC Rate Control (2) SNR-based rate control SNR is directly related to BER FER Challenges Difficult to get accurate SNR measurement Channel condition varies Feedback needed We need SNR at Rx but control MAC Hardware constraint Many radio interface cards only provide signal strength (not SNR) 21

22 Proposed MAC Rate Control Hybrid rate control SNR-based + statistics-based Measure signal strength indication of ACK message Throughput-based 2 control loops Evaluation Average PSNR Human perceptual score (0~5) 22

23 Results 23

24 Cross-layer signaling (CSI) Video rate control H.263 VRCA (video rate control algorithm) CSI predictor Cross-layer signaling No cross-layer signaling 24

25 Cross-layer signaling (Medium sharing) Medium sharing prediction 25

26 More design issues

27 Multimedia Application Mixed traffic Video VoIP Data Video server support Location of server Adaptive encoding V.S. transcoding Scalable for multi-subscriber scenario Broadcast, multicast, or unicast? Tradeoff: loss V.S. delay 27

28 Mobility Wireless mobile networks Doppler effect channel fading Handoff Handoff design issues Handoff initiation Seamless handoff techniques Reduce handoff latency Buffering Simultaneous binding Issues across several protocol layers 28

29 More MAC/PHY Enhanced MAC layer design to support multimedia Power-efficiency considerations Limited battery energy FEC/ARQ/H-ARQ joint design Optimized scheme selection Adaptation Optimized for future MAC/PHY n WiMAX 29

30 Cross-layer design and optimization How much cross-layer? Signaling only? Design (with cross-layer philosophy)? Optimization Optimal parameter selection Adaptive parameter tuning Which layers? 30