CSI 5169 Winter 2006

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CSI 5169Winter 2006
Multimedia Wireless Transmissions and Wireless
Data Compression
Chuanfa Xi cxi079_at_uottawa.ca
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Outline

• Introduction

• Models for multimedia wireless transmissions

• Wireless data compression

• Conclusions

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Introduction
Multimedia

• Information coded as text, graphics, animation,
  audio, video, etc.

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Introduction
Multimedia vs. Data transmission
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Introduction
QoS for Multimedia transmissions

• Throughput Data rate (bits per second)

• Delay Delivery time from source to destination

• Jitter Short-time instability of a signal

• Error Rate Packet loss

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Introduction
Wireless vs. Wired Networking

• Bandwidth

• Signal strength

• Interference

• Mobility makes high error rate

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Introduction
Current Wireless Technologies
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Introduction
Multimedia Applications

• Streaming audio

• Streaming video

• Multimedia messaging

• Peer-to-peer (P2P) gaming

• Video and audio supported shopping

• Long-distance education

• Video and audio conferencing

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Models
DPSM
ARQ
FEC
Cross-Layer Approach
Path Diversity
Improved UDP
Parity Data Adjustment
Joint Source Channel Decoding
Game Theoretic Approach
Two-Stage FEC Scheme
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Two Basic Technologies for error control
ARQ (Automatic Repeat-reQuest)

• An Error control method for data transmission in
  which the receiver detects transmission errors in
  a message and automatically requests a
  retransmission from the transmitter.
• Usually, when the transmitter receives the ARQ,
  the transmitter retransmits the message until it
  is either correctly received or the error
  persists beyond a predetermined number of
  retransmissions.

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Two Basic Technologies for error control
FEC (Forward Error Correction)

• A system of error control for data transmission.
  It is specifically designed to allow the receiver
  to correct some errors without having to request
  a retransmission of data. The maximum fraction of
  errors that can be corrected is determined in
  advance by the design of the code, so different
  FEC codes are suitable for different conditions.
• FEC does not require handshaking between the
  transmitter and the receiver.

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DPSM (Dynamic Packet Size Mechanism)
Problems

• In wireless environments, packets transmitted may
  have bit errors introduced.

PER Packet Error Rate BER Bit Error Rate
Objective

• Control Packet Error Rate in wireless multimedia
  transmission

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DPSM (Dynamic Packet Size Mechanism)
DPSM Algorithms
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DPSM (Dynamic Packet Size Mechanism)
Implementation Model Structure
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DPSM (Dynamic Packet Size Mechanism)
QoS Watch Dog

• Bandwidth estimation

R min (R0, Rest)

• Bit error detection
• Decision making

RCAP Agent

• Interface between Application and UDP layer
• Sender's RCAP adds packet sequence numbers
• Receiver's RCAP sends back an ACK every
  round-trip-time (RTT)

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DPSM (Dynamic Packet Size Mechanism)
Implementation Qos Watch Dog Algorithm
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DPSM (Dynamic Packet Size Mechanism)
Summary

• Dynamically change packet sizes to control Packet
  Error Rate according to current packet error rate
  and bandwidth

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Parity Data Adjustment
Problems

• UDP has no function to recover error
• The longer the parity data, the more errors can
  be recovered
• Parity data introduces more traffic

Objective

• UDP Lite
• (Lightweight User
• Datagram Protocol
• , RFC3828)

• Increase bandwidth and error protection

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Parity Data Adjustment
Parity data adaptation

• After sender receives marked NACK from the
  receiver, it increase the parity data length
• RR02k
• R parity data length
• R0 Initial R
• k is increased by 1 for
  each following NACK
• If no marked NACK, then RR-Rstep
• Parity data length R is changed dynamically

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Parity Data Adjustment
Implementation Senders Algorithm

• Application layer add parity data
• Add UDP Lite header and checksum
• Add IP header and checksum
• RLP layer fragment the packet to small units
  with equal length, set timer for retransmission
• MAC/PHY Send the data

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Parity Data Adjustment
Implementation Receivers Algorithm

• RLP layer detect error, assemble units. If error
  is detected, send a NACK to the sender and set
  timer for retransmission
• IP layer calculate checksum of IP header.
  Discard the packet if checksum error
• UDP layer calculate checksum of UDP header.
  Discard the packet if checksum error
• Application layer Correct errors, assemble data,
  send back NACK for retransmission if error
  happens and time is out

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Parity Data Adjustment
Experimental Results UDP vs. UDP Lite
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Parity Data Adjustment
Experimental Results Parity data length
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Parity Data Adjustment
Summary

• Use Lightweight User Datagram Protocol (UDP Lite)
  to increase bandwidth
• Use an adaptive algorithm automatically adjust
  parity data length in error control

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Path Diversity
Problems

• Access point coverage can be spotty
• Contention among exposed and hidden nodes
• Shadowing due to obstacles and human traffic
• 802.11 ARQ error recovery can add large delays

Objective

• Achieve low-delay video communication over 802.11
  wireless networks.

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Path Diversity
Approach

• Use error resilient video compression
  (H.264/MPEG-4)
• Use multiple paths simultaneously or switch
  between them as a function of channel
  characteristics

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Path Diversity
System Structure
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Path Diversity
Experimental Setup
40m (max)
AP1
Wired 100Mbps Ethernet
802.11b 11Mbps WLAN
Sender
MobileReceiver
25m
AP2

• Data rate(CBR) 360kbps
• Packet length1500 bytes
• Time-stamp Sequence No.

• ARQ up to 16 retries
• Receiver moves at 1m/s

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Path Diversity
Experimental Cases

• Conventional single path case
• Balanced split stream (non-adaptive)
• Simple adaptive
• Oracle

AP1
Wired 100Mbps Ethernet
802.11b 11Mbps WLAN
Sender
MobileReceiver
AP2
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Path Diversity
Experimental Results
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Path Diversity
H.263 Video Performance
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Path Diversity
Summary

• The experimental results are highly location
  dependent
• Optimal path diversity drastically reduce loss
  rate and improves video quality

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Two-Stage FEC Scheme
Problems

• Any bit error can cause a whole packet being
  dropped
• No cooperation between layers
• 802.11 MAC ARQ is not efficient for packet bit
  error

Objective

• Increase data throughput and error protection

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Two-Stage FEC Scheme
Approach

• 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

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Two-Stage FEC Scheme
ImplementationSystem Diagram
Video Encoder
Stage1 FEC Encoder
Stage2 FEC Encoder
Application
UDP-lite
Enhanced Protocol Stack
IP
MAC
PHY
Video Decoder
Stage2 FEC Decoder
Stage1 FEC Decoder

• Stage 1 Packet level
• Stage 2 Bit level

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Two-Stage FEC Scheme
Enhanced MAC/PHY layer
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Two-Stage FEC Scheme
Two-stage FEC

• Stage 1, packet level FEC is added across
  application layer packets to correct packet drops
  due to congestion or route disruption.
• Stage 2, FEC is processed within each application
  packet, and a very small amount of bit-level FEC
  is added to recover any bit errors from the
  MAC/PHY layers.

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Two-Stage FEC Scheme
Experimental Results
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Two-Stage FEC Scheme
Experimental Results
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Two-Stage FEC Scheme
Summary

• Two-stage FEC with enhanced MAC/PHY layer using
  header CRC/FEC increases application layer
  throughput
• Make wireless multimedia error protection more
  efficient.
• Cooperation between layers can increase
  performance for multimedia over wireless networks.

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Wireless Data Compression
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Wireless networking

• Bandwidth varies

• Signal strength varies

• Interference from other equipment

• Mobility makes high error rate (Link loss)

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Wireless Data Compression
Advantages and disadvantages

• Advantages
• Significantly reduce the size of data

• Disadvantages
• Cause delay problem due to the compression and
  uncompression overheads
• Decrease the ability of fault tolerance

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Wireless Data Compression
Coding Categories

• Source coding
• DPCM (Differential Pulse-Code Modulation)
• Transformation
• Sub-Band

• Entropy coding
• Run-Length
• Huffman Coding

• Hybrid coding

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Wireless Data Compression
Multimedia Compression Technologies

• MPEG-1 Designed for up to 1.5 Mbit/sec
• MPEG-2 Designed for between 1.5 and 15 Mbit/sec
• MPEG-4 56Kbps, standard for multimedia
  compression
• .MPEG-7 Basis for search and retrieval
• MPEG-21 A multimedia framework
• H.261 64Kbit/s
• H.263 Based on H.261 with enhancements of video
  quality
• H.264 Technically identical to MPEG-4

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Wireless Data Compression
Summary

• MPEG-4/H.263 is the correct choice for Multimedia
  wireless transmissions

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Conclusions

• Each model addressed some aspects of improving
  the performance of multimedia wireless
  transmissions

• Cooperation is important

• Algorithms and models have to be tested in real
  environment

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References

• Aura Ganz, Zvi Ganz, Kitti Wongthavarawat.
  Multimedia Wireless Networks Technologies,
  Standards, and QoS. Prentice Hall, September 18,
  2003.
• T. Vu, D. Reschke, W. Horn, Tu Ilmenau Germany.
  "Dynamic Packet Size Mechanism (DPSM) for
  Multimedia in Wireless networks". August 2002.
• Gang Ding, Halima Ghafoor, Bharat Bhargava,
  "Error Resilient Video Transmission over Wireless
  Networks," wstfes, p. 31, IEEE Workshop on
  Software Technologies for Future Embedded
  Systems, 2003.
• Allen K. Miu, John Apostolopoulos, Wai-tian Tan,
  Mitchell Trott, Low-Latency Wireless Video Over
  802.11 Networks Using Path Diversity, IEEE ICME
  2003, Baltimore, MD, July 2003
• Yufeng Shan, Su Yi, Shivkumar Kalyanaraman, and
  John W. Woods, Two-stage FEC scheme for scalable
  video transmission over wireless networks, The
  International Society for Optical Engineering,
  October 2005.
• Guy E. Blelloch. Introduction to Data
  Compression. Carnegie Mellon University, October
  16, 2001.

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Questions
1. List two disadvantages of wireless
networking. Answer Variable bandwidth and
high bit error rate
2. How does UDP Lite act differently from UDP
in multimedia wireless transmission? Answer UDP
Lite lets partially damaged payloads be delivered
rather than discarded.
3. List four common QoS parameters for multimedia
data transmission. Answer Throughput,
Delay, Jitter and Error rate