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BRIMON: Wireless Sensor Network based Railway Bridge Monitoring

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Golden-gate bridge (UCB) Short-term monitoring ... as many as 200 sensors per bridge. Protocols and architecture needs to be ... 2km bridge with 200 sensors ... – PowerPoint PPT presentation

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Title: BRIMON: Wireless Sensor Network based Railway Bridge Monitoring


1
BRIMON Wireless Sensor Network based Railway
Bridge Monitoring
  • Kameswari Chebrolu
  • Assistant Professor
  • Department of Electrical Engineering
  • IIT Kanpur
  • http//home.iitk.ac.in/chebrolu

2
People
  • Kameswari Chebrolu
  • Bhaskaran Raman
  • Nilesh Mishra
  • Hemanth Haridas
  • Phani Kumar Valiveti
  • Raj Kumar

3
Motivation
  • Indian Railways consists of 1,20,000 bridges
    spread over a large geographical area
  • Many in weak and distressed conditions
  • 57 are over 80 years old
  • An automated system to track bridge's health is
    of utmost importance.
  • Short term monitoring
  • Long term monitoring

4
Existing Techniques
  • Mostly wired solutions
  • Equipment is bulky and very expensive
  • Large setup time (few days) for short-term
    monitoring
  • Few wireless solutions
  • WISDEN (UCLA)
  • Continuous monitoring
  • Golden-gate bridge (UCB)
  • Short-term monitoring

5
Problem Statement
  • Develop an easy to deploy, low maintenance and
    long-term structural health monitoring system for
    Railway bridges

Easy to deploy Huge number of bridges to
monitor Low maintenance Technical expertise is
difficult to get Long-term Useful to monitor a
structure's health over time
6
Application Requirements
30-125m
3-axis accelerometers
  • What to measure? Acceleration in 3-axis of motion
  • Frequency components of interest 0.25-20Hz
  • How long to measure?
  • Forced vibrations 20sec Free vibrations 20sec
  • Time Synchronization
  • Necessary only across node in a span
  • Need accuracy of 5ms

7
Implications of Requirements
  • 2km bridge can have as many as 200 sensors
  • 6 nodes per span 60m span
  • Data collection duration 40sec
  • Data generated by a node 3 channels 12 bits
    40 Hz 40 sec 57.6kbits
  • Maximum data from a data span (12 nodes)
    691.2kbits
  • Maximum data generated by the sensors on the
    bridge 1.44 MBytes

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

Key Goal Minimize energy consumption
9
Hardware Details
  • Sensor mote Tmote-Sky
  • 8 Mhz MSP430 processor
  • 250kbps 2.4Ghz radio complaint with 802.15.4
  • MEMS based ADXL 203 accelerometer
  • Dual axis
  • Range is /- 1.7g
  • Sensitivity 1000mv/g
  • 8dBi Omni Antenna

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
  • Protocols and architecture needs to be scalable

11
Outline
  • Motivation
  • Application Requirements
  • Challenges
  • Overview of Architecture
  • Event Detection
  • Data Transfer
  • Measurements on a Bridge
  • Conclusions

12
Architecture Overview
Channel 5
  • Data span as an independent network
  • Each cluster operates on a different
  • channel

Data Transport modules
Channel 3
Clusters
Channel 5
Event Signaling module (Channel 1)
Channel 3
Cluster heads
1
Piers
13
Topology Formation
3
6
1
2
3
4
5
6
1
2
Channel 3
4
5
Channel 5
14
Time Synchronization
3
6
1
2
3
4
5
6
1
2
Channel 3
4
5
Channel 5
15
Sleep-Wakeup
3
6
1
2
3
4
5
6
1
2
Channel 3
4
5
Channel 1
Channel 5
16
Command Control Wakeup
Train Arrival Detection
3
6
1
2
3
4
5
6
1
2
4
5
17
Vibration Sensing
3
6
1
2
3
4
5
6
1
2
4
5
18
Data Gathering by individual cluster heads
3
6
1
2
3
4
5
6
1
2
Channel 3
4
5
Channel 5
19
Sleep-Wakeup
3
6
1
2
3
4
5
6
1
2
Channel 3
4
5
Channel 1
Channel 5
20
Data Uploading
Train Detection
3
6
1
2
3
4
5
6
1
2
4
5
21
Sleep-Wakeup
3
6
1
2
3
4
5
6
1
2
4
5
22
Data Analysis Centre
Send Data to Repository
23
BriMon Architecture Event Detection
Span
P
Head node
24
BriMon Architecture Event Detection
Span
P
Head node
25
BriMon Architecture Event Detection
Span
P
Head node
26
BriMon Architecture Event Detection
Span
Head node
27
Event Detection Analysis
  • Question What should be the duration of sleep
    and wake up?
  • Tdc max time available between detection of
    oncoming train and data collection
  • Tcc sleep/wakeup cycle Tsl Tw
  • Tw Tdet Tcd Tpc (at head mote)
  • Tdet Time taken to detect the train
  • Tcd Maximum clock drift
  • Tpc Time taken for command propogation

28
Event Detection
  • Tw 2Tcd Tpc (at non-head mote)
  • Ans Tdc Tcc Tw Tsl 2Tw

29
Radio Range Measurements
  • Tdc D/V
  • D 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

30
Time Synchronization
  • Tw is function of Tdet Tcd Tpc
  • Tsl Tdc - 2 Tw
  • Tpc We use same protocol for synchronization as
    well as command issue
  • Flooding with multiple retransmissions (3)
  • Tpc turns out to be about 72ms
  • Error in synchronization is 0.18ms

31
Time Synchronization
  • Calculating Tcd
  • Worst case clock drift in 36 sec is 20ppm
  • Synchronization error is 0.31ms
  • Tcd 36s 20 10-6 (0.72) 0.18 0.9ms
  • Tcd
  • Tw 125ms Tsl 360.25 35.75
  • Duty Cycling 0.3

32
Data Transfer
  • Long distance wireless links infeasible
  • 2km bridge with 200 sensors generate 1.5MB data
  • Transfer to single hop over 10-20 hops presents
    scalability problems
  • Data transfer time for 14 node network is 5 min
  • Reference A Wireless Sensor Network for
    Structural Health Monitoring Performance and
    Experience, EmNetS-II, May 2005

33
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 channels
  • Transfer data of the span motes to the head mote
  • Transfer data from head mote to train

34
Data Transfer
C3
C5
C7
C9
Head Mote
35
Data Transfer within SpanRouting Issues
  • Links are very stable in our setting
  • Reference Implications of Link Range and
    (In)Stability on Sensor Network Architecture,
    WINTECH 2006
  • Any simple protocol can be used
  • Centralized 2 Phase routing
  • Average duration of routing for 6 nodes 567ms

36
Routing Protocol An Example
37
Data Transfer within Span Transport Protocol
  • Transport protocol
  • Transfers data from the motes to the head mote
  • NACK based block transfer

CMD Data TFR
CMD Data TFR
CMD Data TFR
CMD Data ACK
CMD Data ACK
CMD Data ACK
HEAD Mote
NODE-2
NODE-3
NODE-4
Block Data TFR
Block Data TFR
Block Data TFR
Block Data ACK
Block Data ACK
Block Data ACK
38
Single Hop Data Transfer
39
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
  • Contact Range required contact duration
    speed of train

Contact Range D
Head node
40
Throughput Considerations
  • Contact range required for data transfer is
  • 330m at train speed of 80kmph
  • 250m at train speed of 60kmph
  • Our measurements give a contact range of 400m
    (one-side)
  • 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)

41
Lifetime Estimate
  • Can achieve 1.5 year of operation using a 2500mAH
    battery

36s
131s
15s
33s
42
Measurements on a Bridge
Omni antenna
43
Measurements on a Bridge
Sink Mote
44
Data Analysis Tool
45
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 1/2 years
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