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

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 – wireless radio All-terrain, GPS navigation

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

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

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

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)

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

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

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

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

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

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

PEG Consequences Some 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”

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

Thanks!