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

1 Outline Goals Challenges Technical Approaches Real-world Deployments Future Technology Developments

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

3 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

4 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!”

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!” 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

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

7 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)

8 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?

9 Distance vs. Received Signal Strength RSSI and distance for Consolidated network RSSI [dBm] Distance [meters] 1/R 2 ? 1/R 4 ?

10 Distance vs. Received Signal Strength RSSI and distance for Consolidated network RSSI [dBm] Distance [meters] 1/R 2 ? 1/R 4 ?

11 Distance vs. Received Signal Strength RSSI and distance for Consolidated network RSSI [dBm] Distance [meters] 1/R 2 ? 1/R 4 ?

12 Be cautious of RSSI Chipcon CC 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

13 Scalability: 32 acre Test Network 1,100 m 600 m Motes - 32 Acres - ~3m accuracy?

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

15 Outdoor Measurement Results Steven Lanzisera, UC Berkeley