TriopusNet : Automating Wireless Sensor Network Deployment and Replacement in Pipeline Monitoring

TriopusNet: Automating Wireless Sensor Network Deployment and Replacement in Pipeline Monitoring IPSN 2012 Ted Tsung-Te Lai, Wei-Ju Chen, Kuei-Han Li, Polly Huang, Hao-HuaChu NSLab study group 2012/03/26 Reporter: Yuting

Previously… • 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)

The overview of TriopusNet • Sensor network data is wirelessly transmitted to nearby gateway nodes • The gateway is a (laptop) computer wired to a Kmote node

Outline • Abstract • Introduction • System Overview, Assumptions and Limitations • Hardware Design • System Design • Experiment • Discussion • Conclusion

Abstract • 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 • Evaluated on testbed • Advantage: • Less sensor nodes to cover a sensing area • High data collection rate • Recover from the network disconnection

Motivation • 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

Sensor Deployment • 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 Replacement • 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

Main Contributions • 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

System Overview • 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 asthe storage point wheresensor nodes are depositedinto a dispatch queueat the start of deployment

TriopusNet node • 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

Four Steps • Preparation Step • Sensor Deployment Step • Sensor Latching Step • Sensor Replacement Step

1. Preparation Step • 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

2. Sensor Deployment Step • Runs the sensor deployment algorithm prior to releasing • Then sends the “release” message including the deployment position, to the head sensor node

3. Sensor Latching Step • 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)

4. Sensor Replacement Step • Some sensor node may report low-battery to the system • Detach itself, carried out by the water • Triopusnet releases fresh one

Gateway Nodes • 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

Some Information (Not All Here) • 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

1. Sensor Deployment Order • 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

2. Sensor Deployment (Position) • 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”

3. Sensor Movement (Faucet Turn-On Order) • 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

4. Sensor Localization • There are both vertical and horizontal pipes • Adopts the pipeline localization technique from the PipeProbesystem [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 velocityby traveled time • Buoyancy? -> the sensor node was designed with its weight density equal to the water density

5. Sensor Latching • 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

6. Data Collection • Collection tree protocol (CTP) implemented in TinyOS2.1 • Use anycast (provided by CTP) to multiple sinks(gateway nodes) in order to balance traffic load

7. Sensor Replacement • 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!

Experimental Testbed • 6 “transparent” pipe tubes (10 cm in diameter) • 2 water valves control the volumetric flow rate on each flow path

Performance Metrics • And:time to replacementenergy consumption (2 cases)

Experimental Procedure • 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 measuredin scenario #4 • 20 test runs of node replacement

Deployment - Node Locations • 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 • The radio range can reach up to 170 cm for nodes placed in different tubes • Benefits of using online deployment

Deployment - Data Collection Rate (DCR) • 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 - Positional Accuracy • 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 - Time to Deployment • 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 - Energy Consumption • 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

Replacement – Data Collection Rate(DCR) • 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 - Time to Replacement • Depends on the location of the node and the size of the network

Before Practical Deployment • 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

An Opportunistic Node Placement Scheme • 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

Conclusion • 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

Comments • 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

Thanks for your listening!

TriopusNet : Automating Wireless Sensor Network Deployment and Replacement in Pipeline Monitoring