Delay Bound Rich Image Delivery over WLANs

Shira S. KrishnanGeorgia Tech, ECE

Multimedia Communications Laboratory

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.

Background

A comparison of 802.11 technologies is listed inthe table below • ProtocolProtocol 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

802.11g2003 2.4 19 54

OFDM

802.11n 2008

2.4, 5 100 300 OFDM

802.11n802.11n 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

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 2:1 and Diagnostically lossless compressed form of 10:1

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

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.

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

ResultsType of Image RAW ML DL

type 1 10 5 1

type 2 100 50 10

type 3 1000 500 100

Size in Mb

Theoretical Values