Realizing RFID Sensor Networks with the Intel WISP

Realizing RFID Sensor Networkswith the Intel WISPJoshua Smith, Alanson Sample, Dan Yeager,Michael Buettner, Ben Greenstein, Polly Powledge,Richa Prasad, and David WetherallIntel Research & University of WashingtonCommercial (EPC Gen2) RFID TagIntel (EPC Gen2) WISP

CreditsCore WISP:• Josh Smith, Alanson Sample, Dan Yeager, Polly PowledgeRFID sensor networks:• Michael Buettner, Ben Greenstein, Richa Prasad, David Wetherall2djw \\ RFID sensor networks \\ 1 Nov 2008

Intel Research SeattleAn exploratory research lab in the IntelResearch network of labs– Roughly 20 people + students/visitorsFocus on computing systems that arewoven into the fabric of everyday life– Interdisciplinary projects, prototypes ofdevices/systems, user-centered view– “Vertical” expertise from sensing tomobile systems to ML to HCIDeep ties to universities and Intel groups– Open Collaborative Research model3djw \\ RFID sensor networks \\ 1 Nov 2008

4University of WashingtonComputer Science & EngineeringConsistently ranked among the top 10 programs in the nationExcellent breadth and depth in the field• Embedded systems; systems & networking; security & privacy; animation & games;computing & biology; intelligent internet systems; computer graphics & vision; AI &robotics; technology in education; programming systems; data management;software engineering; computer architecture; theory …A terrific environment for students and faculty• UW is a premier research university• Seattle is a great place to live – and to docomputer science (UW, Microsoft Research,Intel Research, Adobe Research, Google,Amazon.com, RealNetworks, …)• Top academic programs and labs are filledwith UW CSE alumsCome join us!djw \\ RFID sensor networks \\ 1 Nov 2008

RFID Sensor Networks (RSNs)Argue they can combine the best of RFID and sensor networks :• Enable new applications of physically embedded sensing• Retain the simplicity of the RFID model and ride its deployment• Retain the sensing/computing potential of wireless sensor networksResearch challenges:• Feasibility• Applications• OS issues / Intermittent power• Network issues / Asymmetric protocols5djw \\ RFID sensor networks \\ 1 Nov 2008

Wireless Sensor Network (WSN) – Vision• Sensors on items in everyday life to monitor and enable smartenvironmentsHabitatsHospitalHome•Bird migration•Temperature changes•Patient movement•Vitals, medicine, etc.•Find lost objects•HVAC control, etc.6djw \\ RFID sensor networks \\ 1 Nov 2008

Radio Frequency IDentification (RFID) – Vision• Many kinds of RFID, mostly driven by business needs aroundinventory and supply chain managementActive RFID:100 ft, $10sPassive HF:10 cm, < 1¢Passive UHF:30 ft, < 5¢7djw \\ RFID sensor networks \\ 1 Nov 2008

Wireless Sensor Networks – Key FeaturesTelosB mote(sensing + code)richdata• Collection of small, battery-powered sensing devices (motes)• Peer-to-peer communication (multi-hop network)• But form-factor limits for embedding sensing, and tend to bepeople-intensive and complex8djw \\ RFID sensor networks \\ 1 Nov 2008

RFID + WSN = RFID Sensor NetworksEPC Gen2readerapplicationcoderich dataWISPs(sensing + code)• Combine the best of both:– Small / inexpensive passive tags that sense/compute (WISPs) andcommunicate directly with apps in infrastructure (via readers)– Go beyond efforts that are battery-assisted or sense “physically”• Key advantages:– Ubiquitous, long-lived instrumentation, business simplicity, flexibility10djw \\ RFID sensor networks \\ 1 Nov 2008

ChallengesFeasibility– Can WISP devices be built?Applications– Can RSNs do anything useful?OS issues– How do we program with intermittent power?Network issues– How do we communicate with asymmetric protocols?11djw \\ RFID sensor networks \\ 1 Nov 2008Focusto dateNot yetexplored!

Challenge: FeasibilityIntel prototype shows passive yet programmable WISPs can be built– [Sample et. al.], IEEE Trans. on Instrumentation & MeasurementIntel WISP ~2008WISP with standard reader12djw \\ RFID sensor networks \\ 1 Nov 2008

Evolution of the Intel WISP PlatformCapabilities willimprove withMoore’s law:• smaller devices• lower energy• longer range• more function13djw \\ RFID sensor networks \\ 1 Nov 2008

WISP features ~2008/9Features:• Ultra-low power microcontroller(MSP430)• Power harvesting circuitry with storagecapacitor (to run away from reader)• 32K program space + 8K storage• WISP to reader backscatter and readerto WISP data communication (ASK)• Sensors: 3D-accelerometer, light,temperature• Real-time clock• Works with EPC Gen 2 readers• Range of up to 10ft14djw \\ RFID sensor networks \\ 1 Nov 2008Mature discreteimplementation

Flexible RFID reader for applications• Can control commercial Gen2 readers to an increasing extent (LLRP)which supports some but not all applications• Software-defined radio (USRP) reader allows for low-levelprogrammability and complements the WISP– Also valuable for RFID measurementUSRPEPC Gen 2protocolCommercial tagGNU Radio + LinuxNew RFIDprotocolIntel WISP15djw \\ RFID sensor networks \\ 1 Nov 2008

Commercial readers – “tags per second”HS mode16 tags8 tags4 tags2 tags1 tagTags read per secondTag Reads/Sec0 50 100 150 2002 4 6 8 10 12 14Distance (ft)Distance (ft)• Common metric of gross tags/second is uninformative– Larger tag set amortizes overhead– Some tags may be read multiple times or no times16djw \\ RFID sensor networks \\ 1 Nov 2008

Commercial readers – Tag SetsCost of lower data ratesTag sets Tag read Sets/Sec per second0 2 4 6 8 102 4 6 8 10 12 14 16 18 20Distance (ft)Distance (ft)16 Tags• Physical layer effects matter• Encoding and bit errors, frequency-selective fading• [Buettner, Wetherall] in Mobicom 2008HSDR17djw \\ RFID sensor networks \\ 1 Nov 2008

Challenge: ApplicationsRSNs enable new applications that leverage WISP features:• Passive long-lived, can be installed in inaccessible locations forthe duration, “infrastructure without wires”• Small and inexpensive can be used ubiquitously/widelyExample applications that stretch WSNs follow …18djw \\ RFID sensor networks \\ 1 Nov 2008

“Milk”Cold chain monitoring:• Track many small items, e.g., bags ofblood, items in fridge, with cheapand/or disposable tag• Use proximity of readers to sensetemperature and vital statistics whenrefrigerated most of the time• Use stored energy (super-cap) tosense for brief periods when items areaway from reader and exposed19djw \\ RFID sensor networks \\ 1 Nov 2008Milk carton with WISP andtemp and fullness sensors[Yeager, Prasad, Powledge,Smith, Wetherall], RFID 2008

“Planes”Embedded sensing without wiresor access, e.g., for planes,temperature and pressure intires, other infrastructure.WISP with strain gageembedded in compositematerial20djw \\ RFID sensor networks \\ 1 Nov 2008

“Brains”For non-intrusive physiological sensing in implantable medical devices,e.g., neural prosthetics, pacemakersNeural WISP [Hollman,Yeager, Prasad, Smith,Otis], BioCAS 200821djw \\ RFID sensor networks \\ 1 Nov 2008

“Elders”Instrument environment to sense details of object use, e.g., to helpwith the long-term care of elders• Tags plus acceleration is fine-grained and beats identifiers aloneTLC project: wearable(HF) RFID reader[Philipose and others] TLC project: Tagged objects and home setting22djw \\ RFID sensor networks \\ 1 Nov 2008

Challenge: OS issues / Intermittent PowerHow do we run a range of programson WISPs with intermittent power?WISP power model:• Gathers energy from readers,when in range at unpredictablerate and times• Has limited on board storage(capacitor

Strategy for intermittent power (1)• Duty cycle WISP task:– Wait until sufficient power is collected (preset threshold)– Run WISP task to completion; repeat• Implications– Variable frequency of operation; WISP responds occasionallyvoltagecharge runtime24djw \\ RFID sensor networks \\ 1 Nov 2008

Other strategies• Divide large computation into multiple small stages– Store state in non-volatile memory or on readers• WISP API to expose power state to application code– “Enough power yet to complete this step?”• Coordinate to match reader power to WISP needs– Continue to provide for a sufficient interval• Looking to refine model of “power tolerant tasking”25djw \\ RFID sensor networks \\ 1 Nov 2008

Challenge: Network issues / AsymmetryEPC Gen2readerReader incontrolWISPs onlyhear readerrich data WISPsHow 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 reader26djw \\ RFID sensor networks \\ 1 Nov 2008

Strategy for collecting sensor data (1)• Embed sensor data in loworder bits of tag identifiers• OK for small and sparseamounts of datareader tagQueryRN16• What about richer data?ACKID+dataQueryAcktime27djw \\ RFID sensor networks \\ 1 Nov 2008

Strategies for collecting sensor data (2)• Overload semantics of READcommand to return (changing)sensor data at known indices• Allows larger blocks to be read,but requires singulationreader tagQueryRN16ACK• Still not a good fit to the sameset of tags returning updatesIDReq_RNRN16timeReadx NDataQueryAck28djw \\ RFID sensor networks \\ 1 Nov 2008

Other strategies• Extend to “RSN protocols” for reading sensor data– Use short handles to WISPs rather than restart identification• Select sensors by value– Let WISPs respond only if they have important data– Bias responses to favor WISPs with more important data• 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 readers29djw \\ RFID sensor networks \\ 1 Nov 2008

Conclusion / Call to actionRFID sensor networks:• Aim to combine the best of RFID and WSN• Ubiquitous, long-lived instrumentation,simplicity (reader/tag split), and flexibility(applications)WISP Research Challenge:• Give research community access to WISPs• Develop RSN systems & applications• Plus: RFID security, RFID measurement,educational projects30djw \\ RFID sensor networks \\ 1 Nov 2008

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, IEEETransactions 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 2008.• “Maximalist cryptography and computation on the WISP UHF RFID tag,” H.Chae, D. Yeager, J. Smith, and K. Fu, RFID Security, July 2007.• "Neural WISP: An Energy Harvesting Wireless Brain Interface with 1mRange", J. Holleman, D. Yeager, R. Prasad, J. Smith, and B. Otis, IEEEBiological Circuits and Systems 2008 (accepted).31djw \\ RFID sensor networks \\ 1 Nov 2008