1. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Increased QoS through a Degraded Channel using a Diverse, Cross-Layered Protocol Elliot Ranger Brad Gaynor

2. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Topics Previous Questions Review Exploration –Background –Simulation Approach –Theory –Protocol Initial Conclusions Future Work

3. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Previous Comments How would you compare the features of your protocol with other protocols? –Rather then waiting for a problem to cut off communications, our algorithm continuously monitors and maintains connectivity through interference and topology variations. What do you compare your results to? –The performance of traditional routing schemes under harsh network conditions. Do you care about performance? –Of course. Our algorithm is designed to only add overhead when the additional robustness is required. Do you have any stats yet? –No, however, we have developed a statistical model to approximate the potential gain.

4. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Review: Initial Problem Statement Disconnected Network –Noisy Channel –Mobility Nodes Noise Sources Node D receives corrupted messages from Node C Some WSN applications require increased (QoS)

5. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Review: Initial Algorithm Cross-layer –Data must be shared between the network and data-link layers –Each layer must adapt to information from the other Steps: 1.Bad link is identified on the data-link layer 2.Link information is passed to the network layer 3.Network layer forms a cluster of nodes Cluster now responsible for maintaining link integrity Link protocol adapts to take advantage of the cluster 4.If a reliable link is later found Cluster dissolves Routing table is updated

6. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Exploration Background –HARQ, FEC (Turbo Codes), channel characteristics, multipath interference, mobility, bandwidth, fading, noise Simulation –Basic Opnet simulation –ACK/NACK simulation – lessons learned Need a realistic model of channel characteristics –Multipath –Obstructions –Mobility How to describe the routing algorithm How to mathematically quantify the pros/cons of the algorithm Developing a complete network implementation requires a significant amount of work!

7. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Theory - Multipath Multipath interference –Will affect nodes at certain spatial locations based on the geometry of the environment –Causes significant information loss Diversity –Multiple nodes –Unique links to the receiver –Independent multipath effects on a single receiver Diversity provides a more robust solution to multipath interference

8. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Theory - Obstructions Obstruction interference –Blocks an otherwise good link for some window of time –The time-span of this effect is related to the cause: Multipath Obstruction Node moves out of range Diversity provides a more robust solution to obstruction interference –Better than a single node, retransmitting –Difficult to analyze real-time what the cause of the interference is Algorithm must have hooks for adapting to various rates of change based on: –additional information about the environment –required throughput

9. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Protocol

10. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Initial Conclusions Framework for a diverse, cross-layered protocol Improved resistance to multi-path and obstruction-caused interference Graceful, proximity-based handoff of communications –Faster routing updates –Less dropped communications –Highly tolerant of node mobility A robust, adaptive, distributed routing algorithm

11. Tufts University. EE194-WIR Wireless Sensor Networks. April 21, 2005 Future Work Implementation –Determine a potential application which requires additional robustness –Design an actual protocol based on HARQ –Include a Turbo Code FEC for increased coding gains Quantify results –Comparison to HARQ, other MANET protocols overhead, energy, throughput –Measure increase in robustness