1. The Performance of a Wireless Sensor Network for Structural Health Monitoring Jeongyeup Paek, Nupur Kothari, Krishna Chintalapudi, Sumit Rangwala, Ramesh Govindan Embedded Networks Laboratory, USC Sep. 24. 2004

2. Overview of Wisden

3. Wisden A wireless multi-hop sensor network based data acquisition system for structural health monitoring Features  Time-synchronized data delivery from multiple sensor nodes  Reliable data delivery over multiple hops with tolerable latencies  Ease and flexibility of deployment

4. Wisden (cont’) Hardware  Mica-2 mote  Vibration card : 4-channel, 16-bit ADCs  Accelerometer : tri-axis (-2.5g ~ 2.5g) Reliability  Application layer NACK mechanism  Hop-by-hop and end-to-end loss recovery over self-configured tree topology

5. Wisden (cont’) Data Compression  Lossy run-length encoding for silence suppression  Required to handle the large data volume Data Synchronization  Calculate residence time of a packet within each node  Time-stamp data at the base station (possibly with GPS)

6. Four Seasons Building

7. Four Seasons Building and Eccentric mass shaker

8. Wisden deployment Setup  10 motes in 90’ X 180’ area on the fourth floor of the building  Four nodes co-located with the wired instruments  Tri-axis, with 50Hz sampling rate for each channel  0.5 packets/sec transmission rate

9. Deployment experiences High packet loss rate  Delivery rate as low as 37.6% for some links Multi-hop network  Maximum of 4-hop paths Frequent route changes  Increased delay for packet loss recovery Ambient noise  Human movements, power generator  Interference with other wired/wireless devices

10. Results

11. Results (cont’)

12. Problems Lossy Run-length compression  Loss of high-frequency components of data Time-synchronization  Adjusting time takes time  …with GPS at the base station Software bug  Counter wrap-around problem

13. Seismic Test Structure Full-scale realistic model of hospital ceiling Located in the civil engineering building at USC

14. Results

15. Results (cont’)

17. Conclusion Our deployments indicate that Wisden can deliver time-synchronized data reliably across multiple hops with tolerable latencies. However, a number of improvements can be made.  Lossless compression  Time synchronization

18. Reference A Wireless Sensor Network for Structural Monitoring,  Ning Xu, Sumit Rangwala, Krishna Chintalapudi, Deepak Ganesan, Alan Broad, Ramesh Govindan, Deborah Estrin, In Proceedings of the ACM Conference on Embedded Networked Sensor Systems, November 2004 The Performance of a Wireless Sensor Network for Structural Health Monitoring,  Jeongyeup Paek, Nupur Kothari, Krishna Chintalapudi, Sumit Rangwala, Ning Xu, John Caffrey, Ramesh Govindan, Sami Masri, and Daniel Whang, submitted 2nd European Workshop on Wireless Sensor Networks (EWSN 2005)