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TriopusNet: Automating Wireless Sensor Network
Deployment and Replacement in Pipeline
MonitoringIPSN 2012
Ted Tsung-Te Lai, Wei-Ju Chen, Kuei-Han Li, Polly Huang, Hao-Hua Chu
NSLab study group 2012/03/26Reporter: Yuting
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PipeProbe: A Mobile Sensor Droplet for Mapping Hidden Pipeline
Jeffery reported it at study group last year◦ http://nslab.ee.ntu.edu.tw/NetworkSeminar/index.
php?action=schedule&year=2010_Fall&pattern=
http://mll.csie.ntu.edu.tw/papers/PipeProbe_Sensys10.pdf
http://mll.csie.ntu.edu.tw/papers/PipeProbe_Sensys10.pptx (Best Presentation Award)
Previously…
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Sensor network data is wirelessly transmitted to nearby gateway nodes The gateway is a (laptop) computer wired to a Kmote node
The overview of TriopusNet
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Autonomous sensor deployment◦ For pipeline monitoring
Centralized repository at pipeline’s source◦ Automatically releasing nodes
Placement:◦ Nodes will latch itself in pipeline
Replacement:◦ Source will send new nodes to replace failed one,
ex: low battery level; experiences a fault
Abstract
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Evaluated on testbed
Advantage:◦ Less sensor nodes to cover a sensing area◦ High data collection rate◦ Recover from the network disconnection
Abstract
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Flow assurance◦ A major safety concern◦ Ex: clean and uncontaminated water
Traditional method:◦ Manually placing, but it’s hard and waste time
TriopusNet◦ Automated◦ Scalable◦ Human effort strictly needed only at the start to
deposit mobile sensors
Motivation
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Sensor deployment algorithm depends on:◦ Sensing coverage◦ Network connectivity ◦ Deployment location
Upon arrival at its deployment location, a traveling sensor activates its latching mechanism
Sensor Deployment
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Upon detection of low battery level (or a fault), the sensor node retracts its mechanical arms to detach itself◦ Flow in the pipes carries it out◦ System releases a fresh sensor node and runs the
sensor replacement algorithm ◦ And adjust the locations of existing ones
Sensor Replacement
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Automates sensor deployment and replacement by leveraging natural water propulsion to carry sensor nodes throughout pipes
Real prototype and pipeline testbed show that this quality deployment using no more sensor nodes
Successfully replaced a battery-depleted sensor node with a fresh sensor node while recovering data collection rate from the departure of a battery-depleted sensor node
Main Contributions
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Pipelines interconnect a set of vertical and horizontal pipes, starting with a single water inlet and ending at multiple water outlets
Pipelines form a virtual tree! The inlet also serves as
the storage point wheresensor nodes are depositedinto a dispatch queueat the start of deployment
System Overview
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A significant size reduction in 2nd type - 6 cm in diameter◦ May still get stuck in some pipes
(a~d): gyro, water pressure sensors, relays, Kmote(TelosB-like w/o USB)◦ In water, sonar and light are better than radio -> they leave the choice in future
One customized motor drives three arms in 2nd type
TriopusNet node
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Preparation Step Sensor Deployment Step Sensor Latching Step Sensor Replacement Step
Four Steps
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Pipeline spatial topology must be measured a-priori as an input for automated sensor deployment◦ PipeProbe system (their previous work)
Inlet must be filled with sensor nodes Faucets in the pipeline are turned on
◦ Manually or automatically (by installing a remote-control actuation device)
One-time manual effort
1. Preparation Step
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Runs the sensor deployment algorithm prior to releasing
Then sends the “release” message including the deployment position, to the head sensor node
2. Sensor Deployment Step
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Sensor node continuously computes its current location as it travels
When the node approaches its deployment position:◦ Latch itself◦ Report the completion◦ Triopusnet releases the next (repeat step2)
3. Sensor Latching Step
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Some sensor node may report low-battery to the system◦ Detach itself, carried out by the water◦ Triopusnet releases fresh one
4. Sensor Replacement Step
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Must be installed prior to any sensor node deployment inside the pipelines
Must have wireless communication with at least one in-pipe sensor node
Must also have a network connection to a computer for:◦ Remote control◦ Data logging◦ Automated sensor deployment and replacement
algorithms
Gateway Nodes
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Linear actuator controls a mechanical arm◦ Push: SW1&4, pull: SW2&3
Motor calibration was achieved by adding a spiral gear that connects and pushes three separate gears
Some Information (Not All Here)
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Placing nodes close to the releasing point early may result in blockage◦ Transforms the layout of the pipelines into a tree◦ Subsequently runs a post-order traversal of the tree◦ Deploying nodes in the above sequence will:
assure covering all pipes without blocking others
1. Sensor Deployment Order
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Before sensor nodes can be released, the sensor deployment algorithm computes first the coarse-grain positions:◦ The pipe segment◦ The approximate latching point
Assume a simple coverage function (but not limited)◦ Circle with radius R◦ “Subtracting 2*R distance from the most recently
deployed sensor node in segment S gives the position of the new one”
◦ “If segment S is not long enough to accommodate the new sensor node, the new sensor node is placed in the next segment”
2. Sensor Deployment (Position)
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The sensor movement algorithm computes first the flow paths from the inlet to each outlet
Then selects a path intersecting the pipe segment the node is positioned to
3. Sensor Movement (Faucet Turn-On Order)
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There are both vertical and horizontal pipes Adopts the pipeline localization technique
from the PipeProbe system [4] Sensor node tracks its location by:
◦ Counting the number of turns with: pressure and gyroscope sensors
◦ Segment offset distance from the last run: Vertical: the change in water pressure Horizontal: multiplying velocity by traveled time
Buoyancy? -> the sensor node was designed with its weight density equal to the water density
4. Sensor Localization
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Turning on radio after latching and measures the packet received rate for the link quality
Upon detecting a low packet received rate, the sensor node moves one increment closer to its downstream sensor node
Until a pre-defined link quality threshold is met, sends a “latching completion” packet◦ May be tricky to ensure the first sensor node of an
intermediate segment is connected to the sensor nodes of all downstream segments May moves into one of the unreachable downstream
segment Repeats until full sensing and network coverage
5. Sensor Latching
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Collection tree protocol (CTP) implemented in TinyOS 2.1
Use anycast (provided by CTP) to multiple sinks(gateway nodes) in order to balance traffic load
6. Data Collection
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Battery-depleted node (determined simply by voltage)
◦ Informs the downstream gateway◦ Faucet can be turned on◦ Downstream nodes are also flushed out◦ Fishing net is inserted at the ends of pipelines
Good nodes◦ Each upstream node repeats:
detachment, movement, localization, reattachment◦ Until the uncovered area reaches the root location◦ System then releases fresh nodes
With a smaller prototype in the future, it will be easier and save more energy!
7. Sensor Replacement
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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6 “transparent” pipe tubes (10 cm in diameter)
2 water valves control the volumetric flow rate on each flow path
Experimental Testbed
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And:time to replacementenergy consumption (2 cases)
Performance Metrics
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System parameter:◦ PRR threshold = 95%◦ Water flow velocity = 12.5 cm/sec◦ Each node’s sensing range R >= radio range
4 scenarios * 5 runs/scenario = 20 test runs Data was logged during both:
◦ node deployment and data collection Replacement performance is measured
in scenario #4◦ 20 test runs of node replacement
Experimental Procedure
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Static deployment: a good baseline for performance comparison◦ Nodes are 90 cm apart ( average radio range
between two sensor nodes in a straight pipe )◦ Might have better DCR, but more redundant
nodes(DCR: Dada Collection Rate)
Deployment - Node Locations
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The radio range can reach up to 170 cm for nodes placed in different tubes
Benefits of using online deployment
Deployment - Node Locations
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Indicate whether a network is well connected
80% of the sensor nodes show a data collection rate exceeding 99%◦ And all are above 86.5%
Each sensor node sent 1000 data packets to a gateway node
Deployment - Data Collection Rate (DCR)
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18,20,20,30 location estimates for scenario 1~4, respectively
Overall median: 7.14cm 90% of the errors are less than 20.45 cm Sufficient for most pipeline applications,
ex: pinpointing the location of pipe leakage
Deployment - Positional Accuracy
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Time to manually turn on/off faucets is not included here
If the flow velocity is set at 12.5 cm/sec, the average time to deploy nodes is less than 2.5 minutes
Deployment - Time to Deployment
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Primary energy consumer in the sensor node is in the motor and relays that drive the three mechanical arms◦ (Note: energy consumption: motors > radio >
MCU) A single act of latching:
◦ 1.01W * 2 sec < 1% * 600mAh = 2.16J # of latching:
◦ average is: 2.35; 90% of nodes required less than 5
Deployment - Energy Consumption
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DCR before a node reported low-battery level and after the node was replaced:◦ 0.989 and 0.984 respectively◦ Small difference, effective!◦ [YT] But which node are they use? ( last or 2nd last
) DCR without automated replacement: 0.81
Replacement – Data Collection Rate(DCR)
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Depends on the location of the node and the size of the network
Replacement - Time to Replacement
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Several assumptions and limitations require extensions before practical deployment◦ Node is too big to be flushed out independently
[YT] If the size is reduced, there may be extra works on gryo measurement
◦ Node placement requires controlling or obtaining the direction of the water flow in the pipes Automatical method:
attaching a sensor-trigger node to activate/deactivate the infrared sensor in each automatic faucet
Before Practical Deployment
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Nodes are equipped with a water flow sensor
Can infer the current flow path May Releases new nodes whose
destinations must match the current water flow path
An Opportunistic Node Placement Scheme
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Abstract Introduction System Overview, Assumptions and
Limitations Hardware Design System Design Experiment Discussion Conclusion
Outline
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Pipeline monitoring Autonomous sensor deployment Scales down human effort Real pipeline testbed No more nodes than non-automated static
sensor deployment Restore sensing and network coverage from
the departure of a battery-depleted node
Conclusion
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Strength◦ Save lots of nodes using online deployment method◦ Successfully replaced a battery-depleted sensor node
with a fresh one Weakness
◦ Not adaptive with varying water flow rate now◦ No automatically water faucet now◦ Will the mechanical arms be reliable under strong
water flow?◦ For high traffic load, the deployment performance may
not be as good as now◦ Evaluation for DCR in replacement is not clearly
enough
Comments
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Thanks for your listening!