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

2. 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.

3. Background A comparison of 802.11 technologies is listed in the table below Protocol ReleaseFrequency (GHz) Throughput (Mbps) Data Rate (Mbps) Modulation 802.11a 1999 52354 OFDM 802.11b 1999 2.44.311 DSSS 802.11g 2003 2.41954 OFDM 802.11n 2008 2.4, 5100300OFDM

4. 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

5. 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

6. 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

7. 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.

8. 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

9. Results Type of ImageRAWMLDL type 11051 type 21005010 type 31000500100 Size in Mb

10. Theoretical Values