The Performance of a Wireless Sensor Network for Structural

Health Monitoring

Jeongyeup Paek, Nupur Kothari, Krishna Chintalapudi, Sumit Rangwala, Ramesh

Govindan

Embedded Networks Laboratory, USCSep. 24. 2004

Overview of Wisden

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

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

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)

Four Seasons Building

Four Seasons Buildingand Eccentric mass shaker

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

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

Results

Results (cont’)

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

Seismic Test Structure

Full-scale realistic model of hospital ceilingLocated in the civil engineering building at USC

Results

Results (cont’)

Results (cont’)

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

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)