Delay Bound Rich Image Delivery over WLANs

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Delay Bound Rich Image Delivery over WLANs
Shira S. Krishnan Georgia Tech, ECE Multimedia
Communications Laboratory
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Introduction

• Wireless LANs are being used extensively across
  homes, offices and campuses.
• The 802.11b/g technology, popular today is used
  for low bandwidth requirements like voice, data
  and low density image applications.
• For high density image and hi-def video
  transmission, next generation 802.11 technologies
  like 802.11n are being considered.
• Compatibility of 802.11n with existing 802.11b/g
  or 802.11a installations is also of great
  interest.

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Background

• A comparison of 802.11 technologies is listed in
• the table below
• Protocol

Protocol Release Frequency (GHz) Throughput (Mbps) Data Rate (Mbps) Modulation
802.11a 1999 5 23 54 OFDM
802.11b 1999 2.4 4.3 11 DSSS
802.11g 2003 2.4 19 54 OFDM
802.11n 2008 2.4, 5 100 300 OFDM
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802.11n

• 802.11n provides great advantages in terms of
  higher bandwidth and range
• Reliability - Greater SNR
• Predictable Coverage Use of multiple spatial
  streams means fewer dead spots in a coverage area
• Throughput Higher data rates
• It achieves this through a variety of MAC
  enhancements like
• Frame Aggregation Mac Service Data Unit (MSDU)
  and Message Protocol Data Unit (MPDU) aggregation
  single radio preamble for each transmission
  Maximum frame size increased to 64 KB
• MSDU More efficient Aggregation of Ethernet
  frames MPDU Aggregation of 802.11 frames
• Block Acknowledgements Ack for aggregated
  frames
• Reduced Inter-frame Spacing Lower overheads
  can be used only in greenfield deployments

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Traffic of Interest

• Traffic of Interest is High Density Images that
  have a delay bound of 5 seconds.
• Three different sizes of images are considered
  for analysis -- 10, 100 and 1000 Mb images
• Analysis of these images is done in the raw
  format, Mathematically lossless compressed form
  of 21 and Diagnostically lossless compressed
  form of 101

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Interactive time as a parameter

• For certain applications like image conferencing,
  reliable transmission is necessary over the
  network within specified time know as the
  interactive time
• For such application TCP will have to be used to
  ensure reliability and high speed network used as
  a transmission medium to ensure satisfaction of
  delay bound requirements

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Problem Definition

• Identify a wireless system that is most suited
  for rich media delivery within a set interactive
  timeframe using a network designed to handle
  other forms of traffic.

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Assumptions

• Packet losses not considered
• Wireless link failures not considered
• 802.11n draft 2.0 specs used to model systems
• Ns2 models modified suitably to reflect the
  scenario of interest

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Results
Type of Image RAW ML DL

type 1 10 5 1
type 2 100 50 10
type 3 1000 500 100
Size in Mb
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Theoretical Values