Transiently Powered Wireless Embedded Systems

KasımSinanYıldırımEmbeddedSo2wareGroup,Del2UniversityofTechnology

December 9, 20164TU Embedded Systems Student Event

TransientlyPoweredWirelessEmbeddedSystems

BaEery-lessComputers

Transiently Powered Wireless Embedded Systems

Przemysław Pawełczak Kasım Sinan Yıldırım Amjad Yousef Majid

Michel Jansen Koen Schaper

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IoT– WirelessEmbeddedSystems

Sensing Computation Communication

Power

MicrocontrollerSensor

Battery

Transceiver

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PoweringIoT•  Poweringcyber-physicalsystemsisachallenge– By2025:>100billionIoTdevices– sustainableoperaLon– large-scaledeployment

•  BaEeries– increaseweight,costofthehardware– replenishmentisgenerallyimpracLcal– ecologicalfootprint

•  TransferofelectromagneLcenergy– fromapowersourcetoreceiverdevicesovertheair– wirelesspowertransfer

Iris Mote

Transiently Powered Wireless Embedded Systems

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WirelessPowerTransfer(WPT)-I

•  Non-radiaLvetechniques– eitherinducLveormagneLcresonantcoupling• varyingmagneLcfluxinducescurrent

– transferpowerovershortdistances

N

S

Receiver

Source

InducLveCoupling

Transiently Powered Wireless Embedded Systems

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WirelessPowerTransfer(WPT)-II•  RadiaLvetechniques– usetheelectricfieldoftheelectromagneLcwaves•  radiofrequency(RF)wavesasanenergydeliverymedium

– transferpoweroverlongerdistances– provisionofenergytomanyreceiverssimultaneously• broadcastnature

– lowcomplexity,sizeandcostfortheenergyreceiverhardware– suitabilityformobility– chargelow-powerembeddeddevices• RFID(RadioFrequencyIdenLficaLon)tags

chip

antennaTransiently Powered Wireless Embedded

Systems6

RFIDSystemOverview

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Antenna

IC

Tiny memory

Energy Harvester

http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=4447347

BackscaEerCommunicaLon•  TransmiYngdatarequirestoomuchenergyforabaEery-freedevice•  ModulatethereflecLonsofanincidentRFsignal–  usethesignalsentbythereadertocommunicatedataback– notbygeneraLngradiowaves

Transiently Powered Wireless Embedded Systems

8http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=4447347

•  Anewclassoflow-powerbaEery-lessembeddedsystems– TransientlyPoweredComputers(TPCs)

•  CRFIDs(ComputaLonalRFIDs)– RFIDtechnologyasafoundaLon– Allowsensing,computaLonandcommunicaLonwithoutbaEeries•  Chargeasupercapacitorusingharvestedrfenergy

– EquippedwithabackscaEerradio•  simplecircuitryforthereceiver•  allowscommunicaLontocomealmostforfree

RF-PoweredCompuLng

A CRFID platform: WISP - Wireless Identification and Sensing Platform(University of Washington)

Transiently Powered Wireless Embedded Systems

Ultimate goal: replacing existing battery-powered wireless sensor networks

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WISPHardware-Overview

TI MPS430Microcontroller

Flash Memory

Temperature Sensor

Modulator

PowerHarvester

Impedance Matching Demodulator

Power Management

Sensors and Peripherals

AntennagetsRFsignal

RFsignalrecLfiedintoDCvoltage

ChargeSupercapacitor • Getenergyfrom

supercapacitor• Processesbits• Pollssensorstogatherdata

Processincomingsignaltodetect1san

0s

Transistorthatchangesantennaimpedancefor‘backscaEer’

MaximizepowertransfertoPower

Harvester

RFID readerAntenna

Sample, Alanson P., et al. "Design of an RFID-based battery-free programmable sensing platform." IEEE Transactions on Instrumentation and Measurement 57.11 (2008): 2608-2615.Transiently Powered Wireless Embedded

Systems10

WISPCam:BaEery-lessCamera

•  WISPCam-UniversityofWashington

WISPCam captures a 160x120 low resolution image for face detection

Naderiparizi, Saman, et al. "Wispcam: A battery-free rfid camera." 2015 IEEE International Conference on RFID (RFID). IEEE, 2015.

Transiently Powered Wireless Embedded Systems

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AmbientBackscaEer

•  TradiLonalbackscaEercommunicaLon,(e.g.inRFID)–  adevicecommunicatesbymodulaLngitsreflecLonsofanincidentRFsignal-notbygeneraLngradiowaves

•  AmbientbackscaEer– CommunicateusingambientRFsignalsastheonlysourceofpower•  AmbientRFfromTVandcellularcommunicaLons

Vincent Liu et al. “Ambient Backscatter: Wireless Communication Out of Thin Air “, lSIGCOMM, August 2013

Transiently Powered Wireless Embedded Systems

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Ac/ve Passive Ideal

PowerSource BaEery-powered RF-powered(baEery-free)

RF-powered(baEery-free)

PhysicalOpera/ngRange Unlimited Requiresproximityto

RFpowersource Unlimited

Lifespan Monthstoyears NofundamentallimitaLon NofundamentallimitaLon

Future…

Transiently Powered Wireless Embedded Systems

NotYet

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ProgrammingChallenges

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WISPtagsvsBaEery-poweredNodes-I

•  ConLnuouslyvaryingvoltagelevel– WSNs:stablevoltagelevelsintheshortterm(baEery-powered)– WISP:fluctuaLnginputvoltage1

1Benjamin Ransford et al., "Mementos: system support for long-running computation on RFID-scale devices." Acm Sigplan Notices 47.4 (2012): 159-170.

Different voltage levels at different distances to the reader

Transiently Powered Wireless Embedded Systems

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WISPtagsvsBaEery-poweredNodes-II

•  FrequentlossofcomputaLonstate–  frequently``die''duetopowerloss•  needtosavethecomputaLonstateintothenon-volaLlememory•  recoverwhentheyharvestedsufficientenergytostartup•  savingcomputaLonalstatetonon-volaLlememoryisalsoenergyconsuming

1Naderiparizi, Saman, et al. "Wispcam: A battery-free rfid camera." 2015 IEEE International Conference on RFID (RFID). IEEE, 2015.

Operating range

Pow

er o

n

Computation

Energy is available intermittently

Computation is intermittent

Transiently Powered Wireless Embedded Systems

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WISPtagsvsBaEery-poweredNodes-III

•  TheclassicalmoEo– ``computeinsteadofcommunicatewheneverpossible'’– NolongervalidfortheWISPpladorm•  backscaEercommunicaLoncomesalmostforfree

•  IntermiEentpower–  lightweightmethodsintermsofcomputaLonaredesirable

Transiently Powered Wireless Embedded Systems

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ASimpleProgram:Fibonacci

Transiently Powered Wireless Embedded Systems

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function fibonacci(n){ a= 1; b= 1; while(i<=n){ c = a + b; a = b; b = c; }

return b;}

main { i = 0; while(TRUE){ fibonacci(i++); }}

TPCs– How?•  HowtodesignprogramsundertheeffectoffrequentpowerinterrupLons?– Howtoensure•  Consistencyofthenon-volaLlememory?•  Correctnessoftheprogram?

•  Howtodeterminewhenandwhattosaveinnon-volaLlememory– Energyconsuming

Transiently Powered Wireless Embedded Systems

Operating range

Pow

er o

n

Computation

1Chain: Tasks and Channels for Reliable Intermittent ProgramsAlexei Colin, Brandon Lucia, OOPSLA 2016

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ExecuLonUnderIntermiEentPower

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function fibonacci(n){ a= 1; b= 1; while(i<=n){ c = a + b; a = b; b = c; }

return b;}

main { i = 0; while(TRUE){ fibonacci(i++); }}

1,1,2,3 1,1,2 1,1 1,1 1,1

Reboot

Reboot

RebootReboot

HowtoDesignPrograms

Transiently Powered Wireless Embedded Systems

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Non-volaLlememory

main { i = j; while(TRUE){ print fibonacci(i++); j++; }}

j = 0

Computational state

Save computational state into non-volatile memory.Recover state when there is sufficient energy and continue.

ExecuLonUnderIntermiEentPower

Transiently Powered Wireless Embedded Systems

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main { i = j; while(TRUE){ print fibonacci(i++); j++; }}

1,1,2,3j=4

Reboot 5,8,13

21,3434,55

j=7Reboot

Non-volaLlememory

j

Computational state

J=8Reboot

The program can be interrupted at any time!

Trade-offs

Transiently Powered Wireless Embedded Systems

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The more frequent you save the computational state, the more overhead you introduce!

The less frequent you save the computational state, the more redundant computations you need to do!

How to ensure consistency of the non-volatile memory?When and what to save?

Exercise:BubleSort

Transiently Powered Wireless Embedded Systems

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Implement Power-Aware Bubble Sort on array A in non-volatile memory

Which variables to store in non-volatile memory?

When to update the variables in non-volatile memory?

Conclusions

•  RF-BasedTPCsareemerging•  TherearelotsofresearchopportuniLesinthisdomain– CommunicaLonProtocols•  Physicallayer•  MAClayer•  RouLng,SynchronizaLon

– ProgrammingPladorms– OperaLngSystems– Safety,security– Manymore…

Transiently Powered Wireless Embedded Systems

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ThankYou!

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