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

Introduction Wireless LANs are being used extensively across homes, offices and campuses. The b/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 technologies like n are being considered. Compatibility of n with existing b/g or a installations is also of great interest.

Background A comparison of technologies is listed in the table below Protocol ReleaseFrequency (GHz) Throughput (Mbps) Data Rate (Mbps) Modulation a OFDM b DSSS g OFDM n , OFDM

802.11n n 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 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 n draft 2.0 specs used to model systems Ns2 models modified suitably to reflect the scenario of interest

Results Type of ImageRAWMLDL type type type Size in Mb

Theoretical Values