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Tian He @ Honeywell ACS Fellows Symposium Event-Driven Localization Techniques Tian He Department of Computer Science and Engineering University of Minnesota www.cs.umn.edu/~tianhe Slide 2 Tian He @ Honeywell ACS Fellows Symposium Motivation Location is everything Interactive Gaming WII (center meters) Location-aware services Location-aware Services (10 meters) Military Surveillance (meters) Slide 3 Tian He @ Honeywell ACS Fellows Symposium Existing Solutions Outdoor GPSPositioning with Wifi Hotspots Range-Based use absolute distance estimates or angle estimates Expensive, Precise Range-Free use only connectivity and proximity Cheap, Inaccurate Slide 4 Tian He @ Honeywell ACS Fellows Symposium The limitations of existing solutions The main issue: High Location Accuracy High Cost Current limitations: Sophisticated hardware: time-synch with satellites (GPS) Short Range, highly directional (ultrasound) Hefty price for a 1-time event Larger Form Factor (requires additional hardware) In-Situ Impact on the Accuracy. Slide 5 Tian He @ Honeywell ACS Fellows Symposium Event-Driven Localization A new localization paradigm for low-cost sensor nodes Achieving High Location Accuracy without High Cost Main idea Localize sensor nodes by externally disseminating controlled events Slide 6 Tian He @ Honeywell ACS Fellows Symposium Overview of the talk Event-Based Spotlight System [SenSys 05] Image-Based Passive Stardust System [SenSys 06] Sequence-based MSP System [SenSys 07] Slide 7 Tian He @ Honeywell ACS Fellows Symposium Spotlight @ 2005 Main Idea: Generate controlled events in the field according to known spatiotemporal (time/location) mapping. A node timestamps when it detects a controlled event Obtain spatial information (i.e., location) for a node Slide 8 Tian He @ Honeywell ACS Fellows Symposium Generates Events Timestamp Events Report Timestamps Compute Location Report Location Spotlight System Architecture Event Distribution Function: the core of SpotlightWe propose 3 Functions System Design (3) Slide 9 Tian He @ Honeywell ACS Fellows Symposium 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 System Design (4) Slide 10 Tian He @ Honeywell ACS Fellows Symposium Spotlight System Spotlight Device: Projector Laptop Mica2 motes Short range (10-20m) Versatile, it generates: Point Scan Line Scan Area Cover Purpose: Investigate Capabilities System Implementation (1) Slide 11 Tian He @ Honeywell ACS Fellows Symposium Spotlight System Spotlight Device: Telescope Mount Diode Laser Laptop XSM motes Long range (>1000m) It generates: Point Scan Line Scan (recently) System Implementation (2) Slide 12 Tian He @ Honeywell ACS Fellows Symposium Highlight of Spotlight Performance Indoor accuracy is as low as 0.5 centimeter! Outdoor localization accuracy is about a few feet (over a range of football court). Require no cost at sensor node A 900$ spotlight device (amortizable ) Slide 13 Tian He @ Honeywell ACS Fellows Symposium Star-Dust System @ 2006 Localization based on the Position of the light-Spot Slide 14 Tian He @ Honeywell ACS Fellows Symposium StarDust Design 0.01$ Corner-Cube Retroreflector Self-righting enclosure design Multiple color filtering Below 0.1$ Slide 15 Tian He @ Honeywell ACS Fellows Symposium ID ? Concept of Operation ID ? Slide 16 Tian He @ Honeywell ACS Fellows Symposium A football stadium where we deploy 6 sensor nodes in a 3x2 grid. The distance between the lighting device and the sensor nodes is approximately 500ft. Without illuminationWith illumination How it works Deployment area Slide 17 Tian He @ Honeywell ACS Fellows Symposium Each pixel P is described by an RGB Value The light reflected back by CCR has highest intensity. Edge Detection is applied to identify the location of light spot DifferenceEdge Detection How it works Slide 18 Tian He @ Honeywell ACS Fellows Symposium Mapping: Positions Nodes It is necessary to associate spots with sensor IDs. Solution: apply Label relaxation algorithm on a set of different constraints Color constraints Connectivity constraints Spatial Deployment constraints Temporal constraints ID matching turns out to be a very difficult problem! Slide 19 Tian He @ Honeywell ACS Fellows Symposium Highlight of StarDust Performance Accuracy Error is mainly caused by the error in mapping. 5 feet error under 12 colors with 91% correctness in mapping Range The effective range is 1500 ~4500 ft, depending on clearness of the atmosphere Time Milliseconds with unique colors. Cost less than 0.01$ per node if buy in a large quantity Slide 20 Tian He @ Honeywell ACS Fellows Symposium MSP: Multi-Sequence Positioning @ 2007 The issue Event-driven localization (such as spotlight) needs externally disseminating precisely controlled events, which would be hard to realized The idea MSP: A new event driven solution that requires no precise control of event generation. Slide 21 Tian He @ Honeywell ACS Fellows Symposium MSP: Multi-Sequence Positioning Slide 22 Tian He @ Honeywell ACS Fellows Symposium Indoor Implementation Laser line dissemination over a 360-node sensor network testbed Slide 23 Tian He @ Honeywell ACS Fellows Symposium Outdoor Implementation Sound Wave Dissemination Slide 24 Tian He @ Honeywell ACS Fellows Symposium Highlight of MSP Performance Sub-foot accuracy indoor A few feet accuracy outdoor. Require no cost at sensor nodes Require no precise control at event dissemination devices Work with different event dissemination methods Laser Sound . Slide 25 Tian He @ Honeywell ACS Fellows Symposium Comparison Chart Hardware Cost Ad HocRangePowerAccuracyFast Soft Cost Ideal +++++++ Spotlight ++++++/-- StarDust +++++/-++ MSP +++++/-++ Range Free +++/-+-+ UltraS -+--+++/- WiFi --+/---+ GPS -++-+++/- High Cost High accuracy ; Low cost Low Accuracy Even Driven Localization: Low cost and High Accuracy Slide 26 Tian He @ Honeywell ACS Fellows Symposium Conclusion Existing localization paradigms (range-free and range- based) suffer the conflict between cost and accuracy Event-Based Localization is a novel and effective paradigm which can achieve high accuracy and low cost simultaneously as shown in Spotlight [Sensys 2005], Stardust [SenSys 2006] and MSP [SenSys 2007]. High accurate, low cost localization without LOS requirement is yet an open problem to solve. Slide 27 Tian He @ Honeywell ACS Fellows Symposium http://mess.cs.umn.edu