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SHEAU-RU TONG Management Information System Dept., National Pingtung University of Science and Technology, Taiwan (R.O.C.) srtong@mail.npust.edu.tw YUAN-TSE YU Dept. of Software Engineering National Kaohsiung Normal University, Taiwan (R.O.C.) yuyt@nknucc.nknu.edu.tw 1

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Background Replicate Multiple Descriptor (RMD) Coding Simulation and Performance Evaluation Conclusions 2

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Multi-path fading and fast interference in wireless networks causes heavy packet loss burst and poor video broadcast quality. Low-layer forward error coding (FEC) is suitable for fixing short-term loss burst, but not for long- term loss burst. 3

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A HSDPA traffic trace (with link-layer FEC) of a moving vehicle where multiple-packet-loss events frequently occur. 4

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Multiple descriptor coding (MDC): Split a video stream into several sub-streams (descriptors) Encode each sub-stream independently and transmit them over different data paths. Exploiting path diversity. Protecting key-frame is more efficient! 5 Application-layer error resilience is desirable!

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Basic idea: logically applying MDC in the application layer with two new features. Replicate key-frames Interleave multiple descriptors over an IP multicast channel. Advantages: Distributing long loss burst over multiple descriptors to mitigate the damage impact. Exploiting time diversity of key frame transmission. 6

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The system architecture of RMD 7

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Frame replication/insertion b: the number of replicas. s: the number of the frame slots shifted. 8

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Analysis of RMD Frame slot time (I sub-stream ) where k is number of sub-streams, r video data rate and p GOP size. Delay (D) and buffer space (B) where S I and S O are the maximum frame size of I frames and the other frames, respectively. 9

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Key frame error probability (P kf_err ) where is the packet slot error rate, g is the number of packets for an I frame. 10 P kf_err with respect to various bs when k=4 and g=4.

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Simulation configurations 400 frames MPEG-4 with a QCIF format. 30 fps with GOP pattern of IPPPPPP. Packet size of 1024 bytes Comparing RMD with Single Descriptor (SD) Multiple Descriptors (MD) SD/FEC(255, 159) MD/FEC(255, 159) 11

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12 When the packet loss rate increases beyond 15%, RMD starts to outperform SD/FEC or MD/FEC (PSNR>21dB).

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13 The instances of PSNR with respect to various schemes when packet loss rate = 20%. RMD protects the key frame better!

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14 Average PSNR of RMD with respect to various ses when b=3. Average PSNR of RMD with respect to various ses when b=2. Impact of b and s in RMD The PSNR curve is improved (leveraged) as s and b increases. The improvement is magnified under a heavy packet loss condition (15%-35%)

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Redundancy cost ( =20%) RMD (b=3) has a redundancy ratio slightly higher than that of MD/FEC, but can gain a PSNR about 5 dB. 15

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RMD is an ideal application layer approach for combating excessive burst errors and protecting key frames. RMD (b=3) has a redundancy ratio slightly higher than that of MD/FEC, but can gain a PSNR about 5 dB subject to =20%. How to co-work RMD with other adaptive FEC to offer a full spectrum of protection against various burst errors is worthy of further study. 16