Is There Light at the Ends of the Tunnel_ Wireless Sensor Networks

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					  Is There Light at the Ends of the
              Tunnel?
Wireless Sensor Networks for Adaptive Lighting in
                 Road Tunnels
                     IPSN 2011

                       Sean
                   Outline
•   Goal
•   Challenge
•   Contribution
•   System Architecture
•   Hardware & Software
•   Testbed
•   Evaluation
•   Conclusion
                               Goal
• WSN-based Close-loop adaptive lighting in road tunnel
   – Improve tunnel safety
   – Reduce power consumption
• State-of-the-art solutions
   – Pre-set lighting based on date and time
   – Relying only on external sensor
• Testbed evaluation
• Real deployment
   – Project TRITon
   – 630m, two-way, two-lane tunnel
                             Challenge
• Peculiarities of Tunnels
   –   harsh environment, relatively studied on WSN
   –   Vehicular traffic            o. Interference with WSN radio
   –   dirt and dust accumulation o. Occlusion & noise to light sensor
   –   Periodic tunnel cleaning                              direct sunlight
   –   Limited deployment & debugging
   –   Light variation
        • Need filtering
   – Better connectivity
        • Robustness
        • Packet collision



                                                                         Variation caused
                                                                         by vehicle
                           Challenge
• Real-world constraints
   –   Extended lifetime : at least 1-year by tunnel operators
   –   WSN cannot fail due to continuous operation
   –   Sensed data must arrive timely
   –   Quality of sensing
   –   Integration with conventional, industrial-strength equipment
                   Contribution
• Verify WSN-based solution to adaptive lighting is feasible
• Understand what extent the mainstream WSN technology can
  achieve
• Real testbed implement
• Gaining practical insight into tunnel scenario
   – Real-world lesson asset
               System Architecture
• 3 components
  – An external sensor
     Measure the veil luminance        Determine the legislated curve
  – A grid of light sensor along the tunnel length
     Compute error between legislated curve and actual lighting
  – A control algorithm
     Drive above error to zero




                                     HPS in Testbed
                                     LED for project
Hardware & Software



          • Collection tree
             – Use LQI as path cost
             – Periodically reconstructed every 3min

          • Light Sensing
             – Average 4 sensor value into S(i)
             – Average all S(i) into S(all)
             – if |S(all) – S(i)| differs from S(all) by 50%,
               discard it
             – Recompute S(all)
                         Testbed
•   40 nodes, 260m-long, two-way, two-lane tunnel
•   PLC relies only on first 15 node
•   7-month experiments
•   More dense than TRITon
    – 44 nodes, 630m
• Light sensor sample every 5s, PLC collects data every 30s
                   Evaluation
•   Light adaptive effect
•   Loss rate
•   Timely delivery
•   Resilience to gateway failures
•   Retransmission cost
•   Expected lifetime
             Light adaptive effect
• Artificial step response               Still follow the reference trend




• Node position relative to lamps bears great influence
• Behavior of other node is closer to node 7 than node 4
                   Light adaptive effect
 • Real-world reference




Bound by the dynamic range of light actuator
Only 150 lx maximum
                        Loss rate
Time spent transmitting and waiting for receiver to wake up becomes significant
                         Timely delivery
> 60s:
PLC will loss more than one sample in its cycle
                                                  30~60s:
                                                  PLC may loss a sample in its cycle
Resilience to gateway failures
Retransmission cost
Expected lifetime
        • Battery discharge profile
           – Temperature
           – Voltage
           – Discharge current
        • Underestimate
           – Use average discharge current of
             100mA
           – LPL-like MAC only consume a few mA

        • 250ms LPL is better
           – Power consumed in channel check
           – Packet strobe time
                                    Trade-off
                 Conclusion
• Reach the goal of close-loop adaptive lighting
• Provide real-world insights and experience by
  using WSN in road tunnel
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posted:4/2/2013
language:English
pages:19