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Train sense
- 1. Fakultät Informatik – Institut für Systemarchitektur – Professur Rechnernetze TrainSense: A Novel Infrastructure to Support Mobility in Wireless Sensor Networks Presenter: Martin Rataj Supervisor: Dr.-Ing. habil. Waltenegus Dargie Chair of Computer Networks TU Dresden H. Smeets, Ch. I. Shih, M. Zuniga, T. Hagemeier, P. J. Marrón
- 2. Outline 1. Motivation for Mobility 2. Core Idea of TrainSense 3. Interesting Features 4. Practical Applications 5. Related Work Folie 1
- 3. Mobility in WSN Motivation • To increase the communication capacity • To enhance sensing coverage • To facilitate network deployment Challenges • Specification of the speed and direction of each node • Node tracking / positioning • Reliable source of energy • Automatic reprogramming • Path scheduling • Energy budgets Folie 2
- 4. Concept of TrainSense • Designed as a testing environment • Wireless nodes are integrated with model trains • Model train infrastructure provides many advantages • The existing infrastructure needs adjustments to provide: • Real-time train control • Precise positioning • Energy management • Automatic train-mote operations • Back-channel information Folie 3
- 5. Model Train Components • Host computer – user friendly interface to communicate with the controller • Controller – controls speed and direction of trains, control of turnouts • Detector – detects when a train reaches a certain point and informs the controller of this fact • Tracks – carry power and data • Locomotives with their decoders Folie 4
- 6. Contribution of Trainsense • Adjustments to HW and SW of the controller • New software for the host computer • Locomotives equipped with TrainSense motes • Host mote – communication to other motes • USB docking station Folie 5 Fig. 1:TrainSense mote Fig. 2: TrainSense architecture
- 7. Modified controller • As opposed to the commercial standard, it provides real-time guarantees – Change train speed commands – Switch turnouts – Trigger fired upon position detection • Based on the Maerklin/Motorola standard – Can address up to 80 trains and 256 turnouts – Packets contain speed information or direction commands for trains and switch commands for turnouts Folie 6
- 8. Positioning techniques • Position detection is based on a short circuit between the two rails, created by the wheels of the train • Detectors store the position in a register, which is periodically polled by the controller • Two techniques – Dead reckoning and Dead start • The train is expected to move at a constant speed 1) Dead reckoning • Introduces cumulative errors – needs calibration Folie 7 Node crosses a detector on position x Wait for x’/s seconds Send a “stop” packet to the train The position of the node is x+x’
- 9. Positioning techniques 2) Dead start • The train starts from a still position • Used if the train can not reach the nominal speed before encountering the first detector Folie 8 Fig. 3: Dead reckoning Fig. 4: Dead reckoning vs. Dead start
- 10. Energy management • For long can the power supply provide power on an outage? • First, the golden capacitors are charged for one minute • RSSI of packets sent at min. and max. power levels (- 20dBm and 0dBm) • Distance between motes: 2 m • Need to convert ±18V to 5V DC – an AC/DC converter is embedded in the on-board power supply unit • The motes are powered through their USB interface • Dirty tracks can cause short power outages – the power supply needs to be robust Folie 9 Fig. 5: Power disconnection experiment
- 11. USB Docking station • For re-programming and data download • The trains are not powerful enough to dock into regular USB ports – custom USB docking station • 97% of effectiveness of the regular USB port (based on an experiment) Folie 10 Fig. 6: USB Docking Station
- 12. Electromagnetic interference • Moving trains or turnout changes can cause an interference to the radio communication • 4 modes, noise floor is measured at 2 kHz 1) Baseline mode – Tracks are powered with 18V DC, no interference 2) Heavy traffic – The controller sends a continuous stream of packets 3) Frequent turnout changes – Turnouts switched back and forth as fast as possible 4) Dirty tracks – Power on/off every second Folie 11
- 13. Interference - results • Measurement at 2 kHz may not capture all noise • For example, the coils of the turnouts generate pulses in the order of milliseconds • Theory: Instead of increasing the sampling rate, measure PRR Folie 12 Fig. 7: Noise floor for the various modes Fig. 8: Packet Reception Rates
- 14. Practical Application Self-deployment • Goal: let the nodes move autonomously to create a distribution that maximizes a network metric • In this case, the nodes should move autonomously to repair a route • Two nodes, a sink and a source are placed 3 meters from each other • Nodes move from the sink to the source, one after another to establish a multi-hop route • TDMA-MAC is used to avoid collisions Folie 13
- 15. Practical Application Folie 14 Fig. 9: a) Self-deployment in a controlled environment, b) Self-deployment in an uncontrolled environment
- 16. Practical Application Data Muling • Goal: collect data from several static nodes along the track and upload the data via the docking station • Static nodes at 50, 150 and 200 cm from the dock, 20 cm away from the tracks • The data is broadcast with power level 1 of TelosB motes (transmission range about 30 cm) • Test the number of delivered packets for 7 different speeds Folie 15
- 17. Practical Application • Result: All packets were correctly delivered • Trade-off between speed and the number of packets Folie 16
- 18. Related Work Core technology Energy management $ Setup Positioning TrainSense (Smeets et al.) Model trains Unlimited energy from the tracks $ Quite difficult Detectors + dead- reckoning Sensei-UU (Rensfelt et al.) Robot following a line N/A $$$ Easy Travelled distance estimation MiNT-m (De et al.) Robotic vacuum cleaner (Roomba) Batteries, auto recharging mechanism $$ Very easy Video cameras Folie 17
- 19. Thank you for your attention Folie 18