1. A High-Accuracy, Low-Cost Localization System for Wireless Sensor Networks Radu Stoleru, Tian He, John A. Stankovic, David Luebke University of Virginia Department of Computer Science

2. Overview Problem Statement State of Art Spotlight: THE System System Implementation Performance Evaluation Conclusions UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

3. Problem Statement Localization: –Find the position of sensor nodes –Research Challenge: Current limitations: –Sophisticated Hardware: timesynch with satellites (GPS) –Short Range, Highly Directional (ultrasound) –Reduced Cost Effectiveness: hefty price for a 1-time event –Large Form Factor (any solution that requires additional hardware) UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. High Location Accuracy ≡ High Cost How to solve this, practically?

4. State of Art Many algorithmic solutions, few evaluated in realistic environments Solutions that use ranging: –MIT Cricket (Priyantha et at., 2000) –UCLA AHLoS (Savvides et al., 2000) –Microsoft RADAR (Bahl et al., 2000) –UWashington SpotON (Hightower et al., 2000) –GPS Range-free solutions: –USC Centroid (Bulusu et al., 2000) –MIT Amorphous Computing (Nagpal et al., 2003) –Virginia APIT (He et al., 2003) –Rutgers DV-Hop (Niculescu et al., 2003) UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

5. System Design UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Main Idea: –Generate well-controlled (spatial/temporal) events in the sensor field –A node generates a timestamp when it detects an event –Using the above, obtain spatial information (i.e., location) for a node Scenario: –Nodes deployed from UAV (Spotlight device) –Nodes self-organize, time- synchronize –The UAV generates light events –Sensor nodes detect the events and report the timestamps –The Spotlight device computes the location of the sensor nodes

6. System Design UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Assumptions: –Line of Sight –Position and orientation for the Spotlight device GPS/INS (Inertial Navigation System) – cm positioning, arcsec attitude –Map of deployment area: LIDAR (Light Detection and Ranging) 10s centimeter accuracy SAR (Synthetic Aperture Radar) 10s centimeter accuracy. –Powerful Spotlight device >1000meters

7. System Design UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Generates Events Timestamp Events Report Timestamps Compute Location Report Location Spotlight System Architecture Event Distribution Function: the core of SpotlightWe propose 3 Functions

8. System Design UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Event Distribution Functions: –Point Scan –Area Cover –Line Scan 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111

9. System Design UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Execution Cost assuming: –All nodes in a square area, with length D –N events / unit time generated by the Spotlight device –r is tolerable localization error Event Overhead / Unit Time  Spotlight Device Power D 2 log r D/22D 2 D2D2 Event Overhead log r D 2 1# Time Stamps log r D21# Detections Localization Time Area CoverLine ScanPoint ScanCriterion

10. System Implementation UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.  Spotlight System Spotlight Device: –Projector –Laptop Mica2 motes Short range (10-20m) Versatile, it generates: –Point Scan –Line Scan –Area Cover Purpose: Investigate Capabilities

11. System Implementation UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Spotlight System Spotlight Device: –Telescope Mount –Diode Laser –Laptop XSM motes Long range (>1000m) It generates: –Point Scan –Line Scan (recently) Demo: later today

12. Performance Evaluation Performance metric: –Localization Error –Localization Time –Localization Range –Bias in Location Estimation UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Parameters Investigated –EDF (Point & Line Scan, Area Cover) –Event Size –Scanning Speed –Laser Power –Distance: Spotlight Device, Nodes

13. Performance Evaluation Localization Error vs. Event Size  Spotlight - Point Scan EDF Localization Duration vs. Event Size UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

14. Performance Evaluation Localization Error vs. Event Size  Spotlight - Line Scan EDF Localization Duration vs. Event Size UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

15. Performance Evaluation Position Estimation Bias  Spotlight - Line Scan EDF Position Estimation w/o Bias (ideal) UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

16. Performance Evaluation Localization Error vs. Event Size  Spotlight - Area Scan EDF Localization Duration vs. Event Size UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

17. Performance Evaluation Localization Error vs. Event Size Spotlight - Line Scan EDF Localization Duration vs. Event Size UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

18. Performance Evaluation Localization Range Spotlight - Line Scan EDF Detectable Event Sizes UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005.

19. Future Work UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Distributed Spotlight System Localization Overhead Reduction Dynamic Event Distribution Function Stealthiness Deployment in Unknown Terrain Self-Calibration Event Distribution Detection and Reporting

20. Conclusions UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Contributions: designed, implemented, evaluated the Spotlight Localization System Main ideas: – –Well-controlled (spatio-temporal) events in the network. Infer spatial information from temporal knowledge Long Effective Range (1000s meters) High Accuracy (10s centimeter) No hardware changes to existing motes Reusable localization system (amortized cost) Complexity

21. UNIVERSITY of VIRGINIA ACM SenSys November 2-4, 2005. Thank you!