Download k L

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
bitplanes.
• Results
– Build a performance metric
P1 
X

( f ,l ,i )
D( f , l , i)  (1  pe ( f , l , i)) 
Y

(1  pe (m))
m  ( f ,l ,i )
– Put the bitplanes of the same block into a packet.
FGS performance metric of streaming FGS
bit streams over packet erasure networks
P1 
X

( f ,l ,i )
P2 
X

( f ,l ,i )
D( f , l , i)  (1  pe ( f , l , i)) 
R( f , l , i)  B   RBL  RARQ  RFEC
X

( f ,l ,i )
D( f , l , i)  (1  pe ( f , l , i))
Y

m  ( f ,l ,i )
(1  pe (m))
bit plane
frame
P1
1st
P2
P3
2nd
3rd
P4
P6
4th P10
P7
P11
P12
P5
P8
P13
Baseline
P9
P14
P15
P16
frame
P1
bit plane
1st
P1
2nd
3rd
P2
P3
P1
P4
4th P3 P3
0
1
P5
P4
2
3
P2
P6
P7
P2
P8
P5 P6 P6 P7 P7 P8
4
Macro Blocks
5 6 7 8
9
Binary-tree
packetization
P9
P10
P9 P9
10
P10
11 12 13
bit plane
1st
2nd
3rd
4th
5th
6th
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 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. ReedSolomon 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
kl correctly received packets of the
enhancement-layer.
• k denote the length vector (k1, k2, …, kL) for bitstreaming partition, where k1≤ k2 ≤ … ≤ kL .
• R = FEC bytes + FGS data
• Find optimal length vector k* to maximize the RD performance in the presence of packet loss.
R-D Optimization for DEP
• Distortion calculated in DCT domain.
• Incremental PSNR with block l : Q(l).
PSNR  l 1 Q(l )  PDec (l )
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:
L
c(n)  l 0 P (i)
, PDec(l) = c(N-kl) .
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
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