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


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WirelessPowerTransfer(WPT)-I

•  Non-radiaLvetechniques– eitherinducLveormagneLcresonantcoupling• varyingmagneLcfluxinducescurrent

– transferpowerovershortdistances

N

S

Receiver

Source

InducLveCoupling


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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


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)


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.


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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


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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…


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


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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


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WISPtagsvsBaEery-poweredNodes-III

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

•  IntermiEentpower–  lightweightmethodsintermsofcomputaLonaredesirable


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ASimpleProgram:Fibonacci


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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


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


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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


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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


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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


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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…


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ThankYou!


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Transiently Powered Wireless Embedded Systems