Scalable Video over 3G Wireless Network using Unequal Error Protection (UEP)

PresenterAllan J. Lee

Electrical Engineering DepartmentFlorida Atlantic University

TopicsMotivationApproachMPEG-4 FGSWireless Channel CharacteristicsUnequal Error Protection FrameworkAlgorithmOpen Issues

Motivation 3G wireless networks offer higher

maximum throughput than previous networks Up to 2Mbps throughput under ideal

conditions under the proposed IMT-2000 framework.

Attracts the streaming of media-rich services to mobile clients.

Clients demand access to on-the-go services and entertainment.

Motivation

a picture of an Ericsson terminal, running Microsoft’s NetMeeting

Motivation

PacketVideo Player (PVPlayer™).

Motivation The air interface on wireless networks is

very hostile and unpredictable Characterized by high bit error rate, block of

bits erasure (burst errors) resulting in losses

Varying bandwidth

MotivationVideo degraded with various bit error rates

10-4 10-5 10-6

Motivation

Video quality for various burst error with length set to 1msec

10-4 10-5

Approach Use a progressive video bitstream

encoder such as an MPEG-4 FGS encoder. MPEG-4 FGS enhancement layer, when bit

plane coded form a progressive bitstream. Bits contribute differently to reconstructed video

quality

The base layer is a regular non-progressive stream.

Approach Protect the BL for guaranteed delivery

and the EL layer according to the channel characteristics. Use equal forward error protection (EFEP) on

the BL bitstream and unequal forward error protection (UFEP) for the EL

Develop an algorithm to derive a packet loss-protection solution for the EL based on the channel characteristics

Approach Use a product code as the protection

mechanism. Reed-Solomon (RS) coding to protect

against packet loss and a rate-compatible punctured convolutional (RCPC) code to protect against bit errors.

Wireless channel characteristics

Much more noisier and have much higher bit error rates than wired networks Multipath and shadow fading occur quite

often as a mobile client moves through and across cell coverage area.

Fading results in random and burst errors. Co-channel and adjacent channel

interference also causes errors and reduced throughput.

MPEG-4 FGS

Bitstream definition

MPEG-4 Fine Granularity Scalability (FGS)

Possible encoder structure

DCT Bitplane shit

Q

Frame memory

FGS enhancement layer encoding

BitplaneVLC

VLC

Enhancementbitstream

Base layer bitstream

DCT

Q-1

IDCT

Motion Estimation

Motioncompensation Motion vectors

Input Video -

-

Note!!No quantization in the EL processing

Bit-plane coding of the enhancement layer

7 0 3 0 0 0 0 0

5 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

1 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

7 0 5 0 0 3 0 0 0 1

1 0 1 0 0 0 0 0 0 0

1 0 0 0 0 1 0 0 0 0

1 0 1 0 0 1 0 0 0 1

0

0

0

0

Bit-plane coding

Zig-zagscanning

MSB

MSB-1

Block of 8 X 8 DCTCoefficient differences

….

….

(Run,EOP) coding

MSB -2

Row by row transmission results in aprogressive bitstream.

UEP Framework

+ + 0 0 0

X X + + 0 0 0

X X + + 0 0 0

X X X X + + 0 0 0

X X X X X X + + 0 0 0

Data + RS code CRC code RCPC code

12345

Packet

number

Packet length (bytes)

Sourcedata

The product code conceptRow code

Column code

Reed-Solomon codes

For Systematic codes

-the first k bits of N are source symbols

-the remaining N – k are redundancy symbols

k source symbols

N – k redundancy symbols

N (block length)

RS (7, 3) coding stream

1 2 3 6 9 13 17 + + 0 0 0

? ? ? ? ? ? ? ? ? ? ? ?

X X 5 8 11 15 19 + + 0 0 0

X X X X 12 16 20 + + 0 0 0

X X X X X X 21 + + 0 0 0

Packet Loss Protection Block of Packets (BOP)

RS Coding streams

1

2

3

4

5

Packet #2lost

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

Streams 1 to 6 can be decoded

UEP Algorithm for the enhancement layer

Assume we have a sequence of data bytes M to be transmitted-say the total number of bit-planes of the enhancement layer

We send a prefix (graceful degradation) of M instead and some FEC-maintain the overall bitrate

Prefix of M

FEC….

Stream i = 1 2 3 4 5 6 ….. L

UEP Algorithm for the enhancement layer

Prefix of M

FEC

Stream i = 1 2 3 4 5 6 …. L

….

….

123

N

Packet num

ber

.

.

.

.

.

.

Let mi be the data bytes for stream iThe FEC for stream i will be N – mi designated as fi

The FEC assignment across the block of packet will bef = (f1, f2, …, fL)

Mi(f) - data bytes in the ith stream

M(j, f) - a prefix of M with j bytes of M protected with FEC f

UEP algorithm for enhancement layer

Stream i = 1 2 3 4 5 6 …. L

123

N

Packet num

ber

Prefix of M

FEC

The incremental PSNR of stream i is gi(f) = PSNR[M(i, f)] – PSNR[M(i-1, f)]

fi fi+1 – earlier bytes protected better than later bytes because thedata is progressive

UEP algorithm for the enhancement layer

Stream i = 1 2 3 4 5 6 …. L

Packet num

ber

123

N

To find FEC vector f – use the channel loss profilePMF pn : n = 1, 2,….N : pn the probability that n packets are lostwith cdf c(k)-the probability that k or fewer packets are lostand c(fi) – the probability that stream i can be decoded.

Expected PSNR of Received message asa function of f is G(f) = c(fi)gi(f).

Seek f to maximize G(f) given a pn

FEC

Prefix of M

Simulation using NS-2

BW 2 MbpsWith varying degree of packet loss

EL bit sequencewith UEP

BL bit sequencewith EEP

DecoderEL + BL

Dropped EL packets

Varying picture qualitydue to varying EL

Open Issues Optimal BOP size need to be

determined L X N – affects both row and column

protection as well as the throughput. Also affects decoding time at the receiver.

Open Issues UEP algorithm should not be

computationally intensive Has implications on video decoding time Need to limit the processing power

requirement in the mobile device

Open issues Optimize the number of quality levels

offered by the UEP solution. This will limit the amount of side information

necessary for RS decoding.

Questions???