Revisiting Smart Dust with RFID Sensor Networks

Transcription

1 Revisiting Smart Dust with RFID Sensor Networks Michael Buettner, Ben Greenstein, Alanson Sample, Joshua Smith and David Wetherall Intel Research & University of Washington Commercial (EPC Gen2) RFID Tag Intel (EPC Gen2) WISP

2 RFID Sensor Networks (RSNs) Argue they can combine the best of RFID and sensor networks : Enable new applications closer to the smart dust vision Retain the simplicity of the RFID model and ride its deployment Retain the sensing/computing potential of wireless sensor networks Research challenges: Feasibility Applications Intermittent power Asymmetric protocols 2

3 Wireless Sensor Networks Key Features TelosB mote (sensing + code) rich data Collection of small, battery-powered sensing devices (motes) Peer-to-peer communication (multi-hop network) Range of monitoring applications: habitat monitoring, structural integrity of bridges volcanic activity, forest fires, etc. 3

4 UHF RFID (EPC Class1 Gen2) Key Features EPC Gen2 reader identifiers inventory application (backscatter) RFID tags (fixed function) Powered reader infrastructure plus simple passive tags Direct reader to tag communication 4W EIRP from readers, tags backscatter, range of up to ~30ft Applications around inventory / supply chain management 4

5 RFID + WSN = RFID Sensor Networks EPC Gen2 reader application code rich data WISPs (sensing + code) Combine the best of both: Small / inexpensive passive tags that sense/compute (WISPs) and communicate directly with apps in infrastructure (via readers) Key advantages: Ubiquitous, long-lived instrumentation, business simplicity, flexibility Go beyond efforts that are battery assisted or sense physically 5

6 Challenges Feasibility: can WISP devices be built? Applications: can RSNs do anything useful? Focus to date Intermittent power: how do we program for this model? Asymmetric protocols: how do we communicate in this model? Not yet explored! 6

7 Challenge: Feasibility Intel prototype shows that passive yet programmable WISPs can be built: [Sample, Yeager, Powledge, Smith] Features: Power harvesting circuitry with energy storage Microcontroller + 32K of Flash Backscatter communication Sensors: accelerometer, light, strain gage, temperature 7 Intel WISP ~2008 WISP with standard reader

8 Evolution of the Intel WISP Platform Mature discrete implementation Capabilities will improve with Moore s law: smaller devices lower energy longer range more function 8

9 Challenge: Applications RSNs enable new applications that leverage WISP features: Passive long-lived, can be installed in inaccessible locations for the duration, infrastructure without wires Small and inexpensive can be used ubiquitously/widely Example applications that stretch WSNs follow 9

10 Milk Cold chain monitoring: Track many small items, e.g., bags of blood, items in fridge, with cheap and/or disposable tag Use proximity of readers to sense temperature and vital statistics when refrigerated most of the time Use stored energy (super-cap) to sense for brief periods when items are away from reader and exposed 10 Milk carton with WISP and temp and fullness sensors [Yeager, Prasad, Powledge, Smith, Wetherall]

11 Planes Embedded sensing without wires or access, e.g., for planes, temperature and pressure in tires, other infrastructure. WISP with strain gage embedded in composite material 11

12 Brains For non-intrusive physiological sensing in implantable medical devices, e.g., neural prosthetics, pacemakers Neural WISP [Hollman, Yeager, Prasad, Smith, Otis] 12

13 Elders Instrument environment to sense details of object use, e.g., to help with the long-term care of elders Tags plus acceleration is fine-grained and beats identifiers alone TLC project: wearable (HF) RFID reader [Philipose and others] TLC project: Tagged objects and home setting 13

14 Challenge: Intermittent Power How do we run programs on WISPs with intermittent power? WISP power model: Gathers energy from readers, when in range (~15ft) at unpredictable times Has limited on board storage (capacitor << battery) Expends energy to sense/compute and communicate Slowly loses stored energy 14 WISP voltage over time WISP activity Reader activity

15 Strategies for intermittent power WISP API to expose power state to application code Enough power yet to complete this step? Divide large computation into multiple small stages Store state in non-volatile memory or on readers Coordinate to match reader power to WISP needs Continue to provide for a sufficient interval Implications Lower reliability due to unpredictable contacts, power durations Variable frequency of operation due to pre-charge period 15

16 Challenge: Asymmetric Protocols EPC Gen2 reader Reader in control WISPs only hear reader rich data WISPs How do WISPs efficiently communicate data in an RFID setting? WISP communication model differs from RFID and WSN: RFID protocol optimized for reading identifiers (slotted Aloha) Readers control each step and WISPs only hear reader 16

17 Strategies for asymmetric protocols Extended RSN protocols for reading sensor data Typically same set of tags with different values Use short handles to WISPs rather than restart Select sensors by value and efficiently compare across tags Bias responses to send most important sensor values first Reader can help search for min / max Yield reader control Let WISPs drive interaction depending on their needs May be able to approximate within EPC Gen2 Coexist well with vanilla RFID tags and readers 17

18 Conclusion / Call to action RFID sensor networks: Use RFID reader/tag structure to simplify operation Extend application space for sensor networks WISP Research Challenge: Starting to make WISPs available to the research community To promote experimentation and application development 18

19 Thank you. Questions? Some WISP papers: Design of an RFID-Based Battery-Free Programmable Sensing Platform, A. Sample, D. Yeager, P. Powledge, A. Mamishev, and J. Smith, IEEE Transactions on Instrumentation and Measurement (accepted). Wirelessly-Charged UHF Tags for Sensor Data Collection, D. Yeager, R. Prasad, D. Wetherall, P. Powledge, and J. Smith, IEEE RFID Maximalist cryptography and computation on the WISP UHF RFID tag, H. Chae, D. Yeager, J. Smith, and K. Fu, RFID Security, July "Neural WISP: An Energy Harvesting Wireless Brain Interface with 1m Range", J. Holleman, D. Yeager, R. Prasad, J. Smith, and B. Otis, IEEE Biological Circuits and Systems 2008 (accepted). 19