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An Effective Architecture for Interactive Wireless Video Communication

An Effective Architecture for Interactive Wireless Video Communication. Hong-Bin Yu, Songyu Yu and Ci Wang Inst. of Image Commun. & Inf. Process., Shanghai Jiao Tong Univ., China;. Outline. Introduction Architecture Interaction Memory Requirement Simulation Conclusion. 1. Introduction.

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An Effective Architecture for Interactive Wireless Video Communication

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  1. An Effective Architecture for Interactive Wireless Video Communication Hong-Bin Yu, Songyu Yu and Ci Wang Inst. of Image Commun. & Inf. Process., Shanghai Jiao Tong Univ., China;

  2. Outline • Introduction • Architecture • Interaction • Memory Requirement • Simulation • Conclusion

  3. 1. Introduction

  4. Introduction • Compressed video • DCT, motion compensated prediction • is vulnerable to transmission errors (wireless channel)

  5. Introduction – H.264 • Save decoded frame in reference frame buffer • if error-free: • INTER coding  multiple reference frames  high coding efficiency • When error occur: • Encoder select one perfectly receive frame as reference  suppress temporal error propagation

  6. Introduction • Feedback channel: • rapid adjust transmission condition • ACK、NACK • Using ACK: • Encoder has to use a reference frame further back in time • Using NACK • Feedback is unavailable • Encoder doesn’t know whether frame is correct • Relatively long time to recover error

  7. Introduction • Because of • constrained latency • Error sensitivity of hybrid coded video stream •  • Error recovery algorithm • Video proxy server

  8. 2. Architecture

  9. Architecture

  10. Architecture Decoder Encoder

  11. Architecture Decoder Encoder Proxy Proxy

  12. Architecture • Consider 3G, enough bandwidth for multimedia communication • Video proxy sever: • At base station (boundary of wired and wireless) • MT1: • Encode real-time video • Encapsulates into RTP/UDP/IP packet

  13. Architecture • 2 wireless segment + 1 wired segment • Treat wired network is error free

  14. 3. Interaction

  15. Interaction Decoder Encoder Decoder Proxy Encoder Proxy

  16. Interaction Encoder side Decoder side

  17. Interaction • Feedback: • ACK • NACKep • NACKdp

  18. Interaction

  19. Architecture – Interaction • Simple packetization strategy: • A frame  3 slices  3 packets • For QCIF (176 x 144) • MB: 16 x 16 • A frame include 9 x 11 MBs

  20. Interaction • Simple packetization strategy: • A frame  3 slices  3 packets • For QCIF (176 x 144) • MB: 16 x 16 • A frame include 9 x 11 MBs

  21. Interaction • Simple packetization strategy: • A frame  3 slices  3 packets • For QCIF (176 x 144) • MB: 16 x 16 • A frame include 9 x 11 MBs

  22. Interaction Encoder side

  23. Interaction – Encoder side 1)

  24. Interaction – Encoder side 1) OK forward ACK

  25. Interaction – Encoder side 1) Fail NACKep

  26. Interaction – Encoder side 2) NACKdp NACKdp

  27. Interaction – Encoder side • When send perfectly: • G, U frame can be used as reference frame in motion prediction •  coding efficiency, no additional delay • G frame: send perfectly (with ACK) • U frame: unknown • B frame: bad frame (with NACK)

  28. Interaction – Encoder side ACK

  29. Interaction – Encoder side

  30. Interaction Decoder side

  31. Interaction – Decoder side

  32. Interaction – Decoder side • If packet error (NACK) • 來得及  retransmit • 來不及  unrecoverable error • Wireless link fading  unrecoverable error • Unrecoverable error • 改變reference frame，避開MT2沒收到的frame • 收到新frame  重新decoder  encoder send

  33. Memory Requirement • Related to decoder proxy, Encoder proxy need low memory. • Decoder proxy: • Related to frame buffer, packet buffer is low • Frame buffer in Decoder proxy • 3 x (176x144 + 2x88x72)= 114KB

  34. Simulation

  35. Simulation

  36. Simulation

  37. Conclusion • Proxy server with error recovery algorithm certainty can increase quality of video • But high power consumption

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