Wireless Mesh Networks for Localization

1. Wireless Mesh Networks for Localization Dr. Kristofer Pister Prof. EECS, UC Berkeley Founder & CTO, Dust Networks

2. Outline • Goals • Challenges • Technical Approaches • Real-world Deployments • Future Technology Developments

3. First RFID myth • “Now I’ll know where all of my stuff is, all of the time!”

4. First RFID myth • “Now I’ll know where all of my stuff is, all of the time!” • The reality: • RFID systems tell you where your stuff was the last time it went by a reader. • Very useful if: • You have chokepoints in your supply chain • You can put a reader on ALL possible entries/exits • You can serialize your material flow

5. Second RFID myth • “Now I’ll know where all of my stuff is, all of the time!” • “And it will only cost ten cents per tag!”

6. Second RFID myth • “Now I’ll know where all of my stuff is, all of the time!” • “And it will only cost ten cents per tag!” • The Reality: • Tags may get to $0.10 or lower (probably $0.25 today) and… • Readers may get to $100 but… • Installing power and comm to all of the readers will dominate the cost of tags for most deployments

7. Mesh to the rescue? • Good news, bad news + Low cost of “reader” installation • Completely wireless • Self-configuring • 5-10 year battery life for infrastructure + Sense state of items as well as location - Increased tag cost • Dollars, not pennies - Constraints on measurement accuracy

8. RSSI-based localization • Received Signal Strength Indication • Used as a surrogate for range • Use range to known locations to estimate position • Tri-lateration or • Multi-lateration • (not Triangulation)

9. Other localization approaches • Acoustic • Sub-cm accuracy in unobstructed environments • GPS • Need clear line of sight to satellites • Pseudolites • Still doesn’t work well indoors • Rosum?

10. Distance vs. Received Signal Strength RSSI and distance for Consolidated network 60 40 1/R2? 1/R4? Distance [meters] 20 0 -100 -90 -80 -70 -60 -50 -40 RSSI [dBm]

11. Distance vs. Received Signal Strength RSSI and distance for Consolidated network 60 40 1/R2? 1/R4? Distance [meters] 20 0 -100 -90 -80 -70 -60 -50 -40 RSSI [dBm]

12. Distance vs. Received Signal Strength RSSI and distance for Consolidated network 60 40 1/R2? 1/R4? Distance [meters] 20 0 -100 -90 -80 -70 -60 -50 -40 RSSI [dBm]

13. Be cautious of RSSI • Chipcon CC2341 802.15.4 datasheet: • 0.5 m resolution • “Location error can be less than 3 m, depending on factors described below…” • Requires calibrated base stations • 10 m accuracy reasonable, 1m no way • Maybe it’s perfect for you, but… • Get a demonstration in your environment • Run it for a while and move stuff around

14. Scalability: 32 acre Test Network 1,100 m • 1400 Motes - 32 Acres • ~3m accuracy? 600 m

15. Technology to the rescue • Accurate RF distance measurement • UWB • 10cm? • RF Round-Trip Time of Flight • < 1m

16. Outdoor Measurement Results • Steven Lanzisera, UC Berkeley • slanzise@eecs.berkeley.edu • pister@eecs.berkeley.edu