Cross-layer Two-stage FEC Scheme for Scalable Video Transmission over Wireless

Networks

Yufeng Shan, Su Yi, Shivkumar Kalyanaraman and John W. Woods

Rensselaer Polytechnic Institute

Google “Shiv RPI”

Outline

Problems Our proposed schemes

Enhanced wireless MAC/PHY layer Two-stage FEC

Simulations Conclusions

Problems – 802.11 LANs

Any bit error can cause a whole packet being dropped

802.11 MAC ARQ is not efficient for packet bit error

No cooperation between layers

Our proposed two schemes

Enhanced MAC/PHY layer using Header CRC/FEC helps to pass packet with errors to application

and to forward more packets to next node Two-stage FEC scheme at application layer

to cooperative with enhanced MAC/PHY layer for error recovery, both packet drop and bit error.

System Diagram

Video Encode

r

Stage1 FEC

Encoder

Stage2 FEC

Encoder

Enhanced Protocol Stack

Stage2 FEC

Decoder

Stage1 FEC

Decoder

Video Decoder

Application

UDP-lite

IP

MAC

PHY

Enhanced MAC/PHY layer using header CRC/FEC increases application layer throughput

Stage 1: Packet level

Stage 2: Bit level

Enhanced MAC/PHY layer

Enhance MAC/PHY layer for multimedia:

Header CRC: only CRC the header part Header FEC: add small bit level FEC to

protect header part from bit errors

FEC Packet payload

APP UDP IP MAC

HeadersOnly header CRC/FEC

Header

FEC

Enhanced MAC/PHY layer

802.11 physical bandwidth 2 MbpsPacket payload 1000 bytes

Packet CRC checks whole packet

Header CRC checks only headers

Header FEC protect headers with BCH(511,502,1)

Packet may have errors inside

Single hop application throughput

Two-stage FEC

FECs are processed only at application layer

Can recover both packet losses and bit errors inside packet

Cooperate with enhanced MAC/PHY layer to improve the application layer throughput.

Two-stage FEC

Protections FEC codes Code Rate

802.11 SW-ARQ Retransmit one time

RS only RS(255,239) 239/255

Two-stage FEC + HCRC

RS(255,245) +

Header CRC239/245

Two-stage FEC + HFEC

RS(255,245) +

BCH(511,502,1)

239/255Two-stage FEC: payload is protected by BCH(8191,8000,14)

Effective application throughput increased

Err

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hro

ug

hp

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ns-2 simulations

ns-2 802.11b wireless module, PHY layer bandwidth is set to 2Mbps;

MAC layer retransmission 2; Channel model: Gilbert (burst length: 2)

Two-stage FEC: RS code + BCH code

Two scenarios:

Single hop: from sender to receiver1, CBR traffic is set to 2Mbps

Multi-hop: from sender to recever2, receiver 1 is relay node, CBR traffic is set to 1.2Mbps

node1 node2 node3

Video sender Receiver 1 Receiver 2

ns-2 simulations - throughput

Packet CRC: 802.11b

Header CRC: BCH(8191,9000,14) for payload

Header FEC: BCH(8191,8000,14) for payload, BCH(510,480,3) for header

Single hop Multi-hop

ns-2 simulations – video

Monochrome Foreman, CIF, 30fps, 16 frame/GOP, source coder: MC-EZBC

Bitstream is pre-encoded with MD-FEC at 1 Mbps, 10% loss rate

Two kinds of simulations: Single hop fixed FEC, CBR 1Mbps Multi-hop w/ adaptive FEC, bitstream and

FEC protection adapts based on network conditions

ns-2 simulations - video

Single hop Multi-hop

Video PSNR of the first 7 GOPs

PSNR = 0

if no enough bandwidth for base layer

Conclusions

Two-stage FEC with enhanced MAC/PHY layer using header CRC/FEC increases application layer throughput

Efficient in wireless multimedia error protection.

Cooperation between layers can increase performance for multimedia over wireless networks.

Thanks