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Bri Mon : A Sensor Network System for Railway Bri dge Mon itoring

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  1. Mon Bri BriMon: A Sensor Network System for Railway Bridge Monitoring Kameswari Chebrolu(IIT-Bombay) Bhaskaran Raman(IIT-Bombay) NileshMishra(USC) Phani Kumar Valiveti(Cisco Systems) Raj Kumar(Indian Army) Acknowledgment: Prof. C.V.R. Murty, Dr. K. K. Bajpai (Structural Engineering Lab, IIT-Kanpur) http://www.cse.iitb.ac.in/silmaril/br/doku.php?id=proj:brimon

  2. Motivation • Aging civil infrastructure • Indian Railways consists of 120,000 bridges spread over a large geographical area • Many in weak and distressed conditions • 57% are over 80 years old • 26.7% of 577,000 US bridges rated deficient • An automated system to track bridge's health is of utmost importance. • Short term monitoring • Long term monitoring Motivation Design Architecture Evaluation Conclusion

  3. Problem Statement • Develop an easy to deploy, low maintenanceandlong-term structural health monitoring system for Railway bridges Easy to deploy:Cost effective and faster deployment Low maintenance: Technical expertise is difficult to get Long-term: Useful to monitor a structure's health over time Motivation Design Architecture Evaluation Conclusion

  4. Data Analysis Centre

  5. Application Requirements • What to measure? Acceleration in 3-axis of motion • Frequency components of interest 0.25-20Hz • How long to measure? • 40 sec of total vibration during and after train’s passage • Time Synchronization • Need accuracy of 5ms 30-125m 3-axis accelerometers Motivation Design Architecture Evaluation Conclusion

  6. Implications of Requirements • 2km bridge can have as many as 200 sensors • 6 nodes per span; 60m span Motivation Design Architecture Evaluation Conclusion

  7. Existing Techniques • Visual inspection • Mostly wired solutions • Equipment is bulky and very expensive • Large setup time (few days) for short-term monitoring • Few wireless solutions • Proprietary non scalable solutions • Wisden (USC) • Golden-gate bridge (UCB) Image source: www.brimos.com Motivation Design Architecture Evaluation Conclusion

  8. Solution Approach • Battery operated wireless sensor motes • Cheap alternative • Easy to deploy and maintain • Eliminates hassle of laying cable to route data/power • No solar panels • Expensive and prone to theft • Sensors maybe placed under deck in shade Tmote-sky/Telosb motes Dual axis ADXL 203 Accelerometer Motivation Design Architecture Evaluation Conclusion

  9. Solution Approach • Battery operated wireless sensor motes • Cheap alternative • Easy to deploy and maintain • Eliminates hassle of laying cable to route data/power • No solar panels • Expensive and prone to theft • Sensors maybe placed under deck in shade Key Goal: Minimize energy consumption Tmote-sky/Telosb motes Dual axis ADXL 203 Accelerometer Motivation Design Architecture Evaluation Conclusion

  10. Challenges • Event Detection • Cannot predict train arrival • To conserve power, sensor nodes have to duty-cycle (sleep + wake cycle) • Remote Access • Bridges may not have network coverage to transfer data to central server • Scalability • Can have as many as 200 sensors per bridge • Architecture needs to be scalable Motivation Design Architecture Evaluation Conclusion

  11. Mon Bri C 3 C 5 C 7 C 9 Head Node 3 4 5 1 2 Accelerometer 6 Mote

  12. Mon Bri Event Detection(for data collection) Multi Channel Data Transfer(to moving train) C 3 C 5 C 7 C 9 Head Node Interaction amongst functionalities(time synch, routing, event detection and data transfer) 3 4 5 1 2 6

  13. Motivation Design Architecture Evaluation Conclusion

  14. Topology Formation 3 6 1 2 3 4 5 6 1 2 Channel 3 4 5 Channel 5 Motivation Design Architecture Evaluation Conclusion

  15. Time Synchronization 3 6 1 2 3 4 5 6 1 2 Channel 3 4 5 Channel 5 Motivation Design Architecture Evaluation Conclusion

  16. Sleep-Wakeup 3 6 1 2 3 4 5 6 1 2 Channel 3 4 5 Channel 1 Channel 5 Motivation Design Architecture Evaluation Conclusion

  17. Command Control: Wakeup Train Arrival Detection 3 6 1 2 3 4 5 6 1 2 4 5 Motivation Design Architecture Evaluation Conclusion

  18. VibrationSensing 3 6 1 2 3 4 5 6 1 2 4 5 Motivation Design Architecture Evaluation Conclusion

  19. Data Gathering by individual cluster heads 3 6 1 2 3 4 5 6 1 2 Channel 3 4 5 Channel 5 Motivation Design Architecture Evaluation Conclusion

  20. Sleep-Wakeup 3 6 1 2 3 4 5 6 1 2 Channel 3 4 5 Channel 1 Channel 5 Motivation Design Architecture Evaluation Conclusion

  21. Data Uploading Train Detection 3 6 1 2 3 4 5 6 1 2 4 5 Motivation Design Architecture Evaluation Conclusion

  22. Sleep-Wakeup 3 6 1 2 3 4 5 6 1 2 4 5 Motivation Design Architecture Evaluation Conclusion

  23. Data Analysis Centre Send Data to Repository Motivation Design Architecture Evaluation Conclusion

  24. BriMon Architecture: Event Detection Span P Head node Motivation Design Architecture Evaluation Conclusion

  25. BriMon Architecture: Event Detection Span P Head node • Tdc = max time available between detection of oncoming train and data collection Motivation Design Architecture Evaluation Conclusion

  26. Radio Range Measurements • Tdc = Dd/V • Dd is found to be about 400m with 8dBi omni-antenna for various speeds Omni antenna Motivation Design Architecture Evaluation Conclusion

  27. Error rate vs. distance between sender and receiver Motivation Design Architecture Evaluation Conclusion

  28. Radio Range Measurements • Tdc = Dd/V • Dd is found to be about 400m with 8dBi omni-antenna for various speeds • At 80kmph, Tdc = 36s • Use of 802.11 extends range to 800m* • Frontier Nodes Omni antenna * WWW’06 Motivation Design Architecture Evaluation Conclusion

  29. Event Detection • Tsl = sleep time • Tw = wake-up time Tdc = Tsl + 2Tw Tdc Tdc Tdc Tsl Tw Tw Motivation Design Architecture Evaluation Conclusion

  30. BriMon Architecture: Event Detection Span Head node • Wake-up time (head) = Beacon detection time + clock drift time + command propagation time • Wake-up time (non - head) = 2 * clock drift time + command propagation time Motivation Design Architecture Evaluation Conclusion

  31. Event Detection: Analysis Motivation Design Architecture Evaluation Conclusion

  32. Event Detection: Analysis Motivation Design Architecture Evaluation Conclusion

  33. Event Detection: Analysis Motivation Design Architecture Evaluation Conclusion

  34. Event Detection: Analysis Motivation Design Architecture Evaluation Conclusion

  35. Time Synchronization • Time synchronization required only within a span • Each span is an independent data-span • We use same protocol for synchronization as well as command issue • Flooding with multiple (3) retransmissions on each wake up cycle. • Error in synchronization is 0.18ms • 1-2 clock ticks per hop Motivation Design Architecture Evaluation Conclusion

  36. Data Transfer • Long distance wide area wireless links infeasible • Many bridges in remote locations • Transfer over single hop for 10-20 hops complete bridge data presents scalability problems • Bridge with 200 sensors generate 1.5MB data • 1.5 MB data transferred on single hop 802.15.4 radio with 80 Kbps takes 2.5 minutes. • Contact duration only 72 sec (1.2 min) at 80 Kmph Motivation Design Architecture Evaluation Conclusion

  37. Data Transfer: Our Approach • Use multiple channels; one for each data span • Data across spans independent • At most 12 nodes per span; very scalable • Adjacent channels are 7 spans apart with 16 available channels11, 13, 15, 17, 19, 21, 23, 25, 12 • Gather data of the span motes to the head mote • Transfer data from head mote to train 7 spans Motivation Design Architecture Evaluation Conclusion

  38. Mon Bri C 3 C 5 C 7 C 9 Head Node 3 4 5 1 2 6 Motivation Design Architecture Evaluation Conclusion

  39. Data Transfer within Span: Routing Issues • Outdoor 802.15.4 links can be made to operate in stable settings * • Any simple protocol can be used • Centralized 2 Phase routing • Neighbour-discovery phase • Tree construction phase • Average duration of routing tree formation for 6 nodes : 567ms • Routing runs infrequently once in few hours or on node failure/join *Reference: “Implications of Link Range and (In)Stability on Sensor Network Architecture”, WINTECH 2006 Motivation Design Architecture Evaluation Conclusion

  40. Mobile Data Transfer • Achievable data transfer rate using block transfer transport protocol on hardware is 46Kbps (tested on field) • Max data per data span is 693Kbits (12 nodes) • Contact duration required is 15sec Motivation Design Architecture Evaluation Conclusion

  41. Throughput Considerations Contact Range required = contact duration * speed of train • Contact range required for data transfer (in 15 sec) is • 330m at train speed of 80kmph • 250m at train speed of 60kmph • Our measurements give a contact range of 400m (one-side) Contact Range = D Head node Motivation Design Architecture Evaluation Conclusion

  42. Throughput Considerations • Transfer is possible with enough leeway. • Throughput can be further increased via • Compression • Multiple receivers at head and rear of train • Better Hardware • Simultaneous operation of flash and radio • Bluetooth Radio (1Mbps) Motivation Design Architecture Evaluation Conclusion

  43. Lifetime Estimate • Assuming one data collection operation per day BriMon can achieve 1.5 years of operation using 2500mAH batteries 36s 15s 131s 33s Motivation Design Architecture Evaluation Conclusion

  44. Measurements on a Road Bridge Omni antenna Motivation Design Architecture Evaluation Conclusion

  45. Measurements on a Road Bridge Sink Mote Motivation Design Architecture Evaluation Conclusion

  46. Measurements on a Road Bridge • Dominant free vibration frequency of 5.5Hz • Amplitude of vibration as high as 100 milli g (30 milli g for healthy bridges) Motivation Design Architecture Evaluation Conclusion

  47. Future Work • Deployment on a Railway bridge • Extending BriMon to other bridge architectures • Current approach focuses on span bridges Motivation Design Architecture Evaluation Conclusion

  48. Conclusions • Application specific design • Extensive measurement study • Novelty of our contributions • Event detection mechanism • Mobile data transfer • Integration with time-synchronization/routing • Estimates indicate network can operate without intervention for 1.5 years http://www.cse.iitb.ac.in/silmaril/br/doku.php?id=proj:brimon Motivation Design Architecture Evaluation Conclusion