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PEG 2003 Design and Implementation

PEG 2003 Design and Implementation. Cory Sharp UC Berkeley NEST Retreat, June 2004, Santa Cruz, CA. PEG Goals. Use a lot of sensors 100 nodes In as large field as possible 20m x 20m To help a pursuer autonomous robot Intercept an evader human controlled robot Demoed in July 2003.

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PEG 2003 Design and Implementation

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  1. PEG 2003Design and Implementation Cory Sharp UC Berkeley NEST Retreat, June 2004, Santa Cruz, CA

  2. PEG Goals • Use a lot of sensors • 100 nodes • In as large field as possible • 20m x 20m • To help a pursuer • autonomous robot • Intercept an evader • human controlled robot • Demoed in July 2003

  3. Platform • Mica2Dot • 8-bit 4 MHz CPU, 128k program, 4k RAM • CC1000 Radio, abput 2 kB/s appl bw • Magnetometer • Ultrasonic transceiver • Robust enclosure • Pursuer • 266 MHz CPU, 20GB HD, 128MB RAM • 802.11 wireless radio • All-terrain, GPS navigation

  4. Software Design • Self-localization • Ultrasonic ToF • Vehicle detection • Calibrate, sense • Leader, position estimate • Route to pursuer • Pursuer • Filter estimates • Intercept planning • Navigate • Management services

  5. PEG Approach Approach of simplicity • Simple Sensor Network • Intelligent Processing on Pursuer • Core Services • Vehicle Detection • Routing • Navigation and Control

  6. Vehicle Detection • Bandwidth driven design (most precious resrc) • 40 packets per second • Half for local detection reports • Half for system wide behaviors • Assume (design) that one object excites at most 9 nodes • Calibration and Sensing • Use 8-bit digital pot with 10-bit ADC to recover a 16-bit magnetic signal • Sample at 20 Hz • Moving average to calibrate static environment • Determines a minimum detectible vehicle speed • Physical proximity of radio and magnetometer caused interactions; invalidate readings while TX/RX

  7. Vehicle Detection (2) • Local Detection Reports • 1-norm magnetometer axes, threshold readings • Individual nodes report at 2 Hz • Put readings into a neighborhood • Drove design of Hood • Leader Election, Position Estimation • Leader election requires no additional communication • Leader if a node has the max in its neighborhood • A node can report as leader at most 2 Hz, weak epoch of 0.5s • Leader reports immediately in its epoch • Maximum detecticle vehicle speed only a fcn of the sensor • Disambiguation is deffered to outside the SN • Position report is 8.8 fixed point (x,y)

  8. Routing • Route from many sources to few mobile pursuers • Not many-to-one (base station) routing • Not any-to-any • Landmark routing • Split problem into many-to-one and one-to-few • No geographic assumptions • Landmark is a rendezvous point • Spanning tree with crumb trails • Many-to-one • Focus on building good trees

  9. Routing (2) • Building good trees • Flooding from a beacon node • Select good routes • Consider both link quality and hop count • Precalibrate RSSI threshold for environment • Filter then select lowest hop count parent • Avoid broadcast storm (excess collisions) • Adaptive time-delayed backoff

  10. Routing (3) • Pursuers build “crumb-trails” • Selects a node in its proximity • By overhearing detection events • Landmark relays msgs down crumb trail • No coupling of pursuer to landmark • Allows for fail-over

  11. Navigation and Control • Classic control systems assume periodic readings with zero latency • Cleanly separate control system from sensor network • Assume reports from SN every few seconds • Low-level navigate with GPS • Pursuer use of evader position updates is robust to noise and latency

  12. Some Results • In the demo, the pursuer caught the evader every time • A few noisy nodes • Quelled nodes at (4,10) and (4,12)

  13. Deployment Experiences • Breakage, “Every touch breaks” • Disassembly, recharge, reprogram, reassembly • Packaging • Requirements for deployment versus development • Wish we had external recharge and reprogram • Magnetometer interference • Piano wire antenna, battery, metallic base spring • Debugging • No logging services, used a big antenna • Ping-like tools to identify failed nodes • Reprogram and Reconfig • Wireless reprogramming necessary • Minimize its use with liberal reparameterization

  14. PEG ConsequencesSome Next Steps • Extreme Scaling (ExScal) • 10,000 nodes monitoring a 10km long field • NEST Final Demo (Capstone) • Berkeley’s baby for next summer • Baseline system (Dialtone) • Everything that “proves to be pretty useful”

  15. Dialtone • Everything that any deployed application needs, a wish list: • Layered Application Retargetting • Config, VMLib, Reprogram • Reset, on/off (sleep), ident/ping, scream • File system / log to flash • Bootloader • Service control • Self-test (flash, battery, profiling, duty cycle, event log, error log) • Health monitoring, watchdog • RAM/ROM query (jhill) • Multihop Routing • Epidemic dissemination (smart flood) • TimeSync • RAM buffers, message buffers • Security

  16. Thanks!

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