An optimal packetization scheme for fine granularity scalable bitstream

Hua Cai1, Guobin Shen2, Zixiang Xiong3, Shipeng Li2, and Bing Zeng1

1The Hong Kong University, 2Microsoft Research Asia, 3Texas 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 bitplan

es.

• Results– Build a performance metric

– Put the bitplanes of the same block into a packet.

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

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P1 P2

P3 P4 P5

P6 P7 P8 P9

P10 P11 P12 P13 P14 P15 P16

P1 P2

P1 P1 P2 P2

P3 P4 P5 P6 P7 P8 P9 P10

P3 P3 P4 P5 P6 P6 P7 P7 P8 P9 P9 P10

0 1 2 3 4 5 6 7 8 9 10 11 12 13

1st

2nd

3rd

4th

5th

6th

1st

2nd

3rd

4th

1st

2nd

3rd

4th

frame

frame

Macro Blocks

bit p

lane

bit p

lane

bit p

lane

Baseline

Binary-tree packetization

Optimalpacketization

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 kl (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 kl consecutive packets while the last N-kl bytes associated with block l carry FEC codes, which are generated by an (N, kl) 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, barco

des, etc) – Wireless or mobile communications (including cellular teleph

ones, 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 = 82t = 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 (k1, k2, …, kL) for bit-streaming partition, where k1≤ k2 ≤ … ≤ kL .

• 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 k1≤ k2 ≤ … ≤ kL ≤ N , l=1,2,…,L

PDec(l) denotes the probability that block l is decodable.

The probability that n or fewer packets are lost:

, PDec(l) = c(N-kl) .

Finding optimal k* by local search hill-climbing algorithm

L

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Effect of packet loss on PSNR for DEP and EEP

Data fraction of blocks with degressive priorities

kl / 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

– http://www.4i2i.com/reed_solomon_codes.htm

• Local Search Algorithms– http://www.owlnet.rice.edu/~comp440/handouts/lec4-6sl.pdf