An optimal packetization scheme for fine granularity scalable bitstream Hua Cai 1, Guobin Shen 2, Zixiang Xiong 3, Shipeng Li 2, and Bing Zeng 1 1 The Hong Kong University, 2 Microsoft Research Asia, 3 Texas A&M University ISCAS 2002 A degressive error protection algorithm for MPEG-4 FGS video streaming X.K. Yang, C. Zhu, Z. G. Li, G. N. Feng, S. Wu. N.Ling* Laboratories for Information Technology, Singapore *Santa Clara University ICIP 2002

FGS Concept (1)

FGS Concept (2)

An optimal packetization scheme Key idea –Relationship between FGS enhancement-layer bitplanes. Results –Build a performance metric –Put the bitplanes of the same block into a packet.

FGS performance metric of streaming FGS bit streams over packet erasure networks

P1P2 P3P4P5 P6P7P8P9 P10P11P12P13P14P15P16 P1P2 P1 P2 P3P4P5P6P7P8P9P10 P3 P4P5P6 P7 P8P9 P st 2nd 3rd 4th 5th 6th 1st 2nd 3rd 4th 1st 2nd 3rd 4th frame Macro Blocks bit plane Baseline Binary-tree packetization Optimal packetization

Results

Results (2)

Results (3) Undecodable data ratio for three packetization scheme

A Degressive Error Protection (DEP) algorithm Partition the data of the FGS Enhancement-layer bit-stream into L blocks with non-increasing length k l ( l =1,2,..., L ) Packetize the L partitioned blocks into N packets with added FEC codes.

Parameters B(l,n) denotes the n -th byte in block l or the l -th byte in the packet n. Target bit budget R for the enhancement-layer of a frame. N =floor( R / L ). Data in block l are interleaved over k l consecutive packets while the last N - k l bytes associated with block l carry FEC codes, which are generated by an ( N, k l ) Reed-Solomon code..

Reed-Solomon codes Reed-Solomon codes are block-based error correcting codes with a wide range of applications in digital communications and storage. Reed- Solomon codes are used to correct errors in many systems including: –Storage devices (including tape, Compact Disk, DVD, barcodes, etc) –Wireless or mobile communications (including cellular telephones, microwave links, etc) –Satellite communications –Digital television / DVB –High-speed modems such as ADSL, xDSL, etc.

Example: A popular Reed-Solomon code is RS(255,223) with 8-bit symbols. Each codeword contains 255 code word bytes, of which 223 bytes are data and 32 bytes are parity. For this code: n = 255, k = 223, s = 8 2t = 32, t = 16 The decoder can correct any 16 symbol errors in the code word: i.e. errors in up to 16 bytes anywhere in the codeword can be automatically corrected.

Problem formulation All the information data associated with block l can be reconstructed from any subset of at least k l correctly received packets of the enhancement-layer. k denote the length vector ( k 1, k 2, …, k L ) for bit- streaming partition, where k 1 ≤ k 2 ≤ … ≤ k L. R = FEC bytes + FGS data Find optimal length vector k * to maximize the R- D performance in the presence of packet loss.

R-D Optimization for DEP Distortion calculated in DCT domain. Incremental PSNR with block l : Q ( l ). subject to k 1 ≤ k 2 ≤ … ≤ k L ≤ N, l=1,2,…,L P Dec (l) denotes the probability that block l is decodable. The probability that n or fewer packets are lost:, P Dec (l) = c(N-k l ). Finding optimal k * by local search hill-climbing algorithm

Effect of packet loss on PSNR for DEP and EEP

Data fraction of blocks with degressive priorities k l / N

Conclusion Optimal packetization scheme –Only suitable for End-to-end transmission Degressive error protection algorithm –Good to applying to streaming system References Reed solomon code – Local Search Algorithms –