The Performance of a Wireless Sensor Network for Structural Health Monitoring

1. Center for Embedded Networked Sensing The Performance of a Wireless Sensor Network for Structural Health Monitoring Jeongyeup Paek, Nupur Kothari, Krishna Chintalapudi, SumitRangwala, Ramesh Govindan Embedded Networks Laboratory, USC – http://enl.usc.edu Introduction: Wisden, A Multi-hop Wireless Data Acquisition System for SHM Overview of Wisden Techniques and Software Goal • Features Time-synchronized data delivery from multiple sensor nodes Reliable data delivery over multiple hops with tolerable latencies Ease and flexibility of deployment • Hardware Mica2 motes as sensor nodes Tri-axis accelerometers with sensing range of ±2.5g Vibration card for high quality sensing (16bit ADC) • Reliable Transmission Application layer NACK mechanism Hop-by-hop and end-to-end loss recovery over self-configured tree topology • Data Compression Run-length encoding for silence suppression • Data Synchronization Light-weighted approach Synchronize data at the base station • Evaluation of a sensor network data acquisition system for SHM Based on actual deployment of Wisden in the Four Seasons Building forced vibration test. Deployment of Wisden: In a real environment - Four Seasons Building Deployment Setup • 10 motes in 90’x180’ area on the fourth floor of Four Seasons Building • Four nodes co-located with the wired instruments • Tri-axis, with 50Hz sampling rate for each channel • 0.5 packets/second transmission rate Deployment Experiences • High packet loss rate – delivery rate as low as 37.6% for some links • Multi-hop network –path lengths up to 4 hops • Frequent route changes – increased delay for packet loss recovery • Ambient noise – including human movements and interferences with other wired/wireless devices • Ease of deployment –half an hour of deployment time Results from Deployment:Wisden can deliver Time-synchronized data Reliably Results • Wisden can deliver time-synchronized vibration data over multi-hop network Captured correct time and magnitude of the vibrations • Wisden can capture the dominant frequency response of the structure With some loss of high frequency components • Insufficient reliability and occasional high-latency observed This was due to a software bug in Wisden Problems found from the test • Lossy Run-length Encoding Loss of high-frequency components of data • Time synchronization Adjusting time may introduce delay itself • Software bug in Wisden Counter wrap-around problem caused slow retrieval of data Test at Seismic Test Structure • Reliability of 99.3% achieved with tolerable latencies • Correctly captured the dominant modes of the structure • Software bug was fixed References 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, J. Wallace and Daniel Whang, submitted to 2nd European Workshop on Wireless Sensor Networks (EWSN 2005) UCLA – UCR – Caltech – USC – CSU – JPL – UC Merced