PowerConsumptionbyWirelessCommunication

LinZhongELEC518,Spring2011

2

Powerconsumption(SMT5600)

Lighting: Keyboard, 73, 3%

Lighting: Display I, 148, 5%

Lighting: Display II, 61, 2%

LCD, 13, 0%

Speaker, 45, 2%

Bluetooth, 440, 16%

GPRS, 1600, 58%

Compute, 370, 13%

Cellular network, 17, 1%

Flight mode: Sleep, 3, 0%

3

Powerconsumption(T-Mobile)

1

10

100

1000

10000

IDLE-Flight m

ode

Com

puting

LCD

LCD

lighting

Keyboard lighting

Speaker

Discoverable

Paging

Connected

Transmission

Connected

Transmission

Connected

Transmission

Pow

er (m

W)

Bluetooth Wi-Fi Cellular

4

Powerconsumption(Contd.)

• Theoreticallimits– Receivingenergyperbit>N*10-0.159

• N:Noisespectralpowerlevel• Widebandcommunication

Distance:d

Propagationconstant:a(1.81-5.22)

PRXPTX∝ PRX*da

5

Powerconsumption(Contd.)

• Whatincreasespowerconsumption– Governmentregulation(FCC)

• Availablespectrumband(Higherband,higherpower)• Limitedbandwidth• Limitedtransmissionpower

– Noiseandreliability– Highercapacity

• Multipleaccess(CDMA,TDMAetc.)– Security– Addressability(TCP/IP)– More……

6

Wirelesssystemarchitecture

Application

Transport

Network

Datalink

Hostcomputer

RFfrontends

BasebandNetworkinterface

Networkprotocolstack Hardwareimplementation

Physical

7

Powerconsumption(Contd.)

BasebandprocessorAntenna

interface

LNA

Low-noiseamplifier

PA

Poweramplifier

IntermediateFrequency (IF)signalprocessing

LocalOscillator(LO)

PhysicalLayer

IF/Baseband

Conversio

n

MACLayer&above

>60%non-displaypowerconsumed inRF

RFtechnologies improvemuchslowerthanIC

8

Powerconsumption(Contd.)

67%

18%

8%

6%1%

PA

FS

Mixer

Source:Lietal,2005

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1579876

Components Power (mW)

Power amplifier (PA) 246

Frequency synthesizer (VCO/FS)

67.5

Mixer 30.3

LNA 20

Baseband Amplifier 5

Low-noiseamplifier(LNA)

• Bandwidth(sameasthesignal)• Gain(~20dB)• Linearity(IP3)• Noisefigure(1dB)• Powerconsumption

10

Circuitpoweroptimization

• Majorpowerconsumers

BasebandprocessorAntenna

interface

LNA

Low-noiseamplifier

Highdutycycle

PA

Poweramplifier

Highpowerconsumption

IntermediateFrequency (IF)signalprocessing

LocalOscillator(LO)

Almostalwayson

PhysicalLayer

IF/Baseband

Conversio

n

MACLayer&above

Hugedynamicrange105

11

Circuitpoweroptimization(Contd.)

• Reducesupplyvoltage– Negativelyimpactamplifierlinearity

• Higherintegration– CMOSRF– SoCandSiPintegration

• Power-savingmodes

12

Circuitpoweroptimization(Contd.)

• Power-savingmodes– Completepoweroff

• (Circuitwake-uplatency+networkassociationlatency)ontheorderofseconds

– Differentpower-savingmodes• Lesspowersavingbutshortwake-uplatency

13

Power-savingmodes

BasebandprocessorAntenna

interface

LNA

Low-noiseamplifier

PA

Poweramplifier

IntermediateFrequency (IF)signalprocessing

LocalOscillator(LO)

PhysicalLayer

IF/Baseband

Conversio

n

MACLayer&above

RadioDeepSleep Wake-uplatencyontheorderofmicroseconds

14

Power-savingmodes(Contd.)

BasebandprocessorAntenna

interface

LNA

Low-noiseamplifier

PA

Poweramplifier

IntermediateFrequency (IF)signalprocessing

LocalOscillator(LO)

PhysicalLayer

IF/Baseband

Conversio

n

MACLayer&above

SleepMode Wake-uplatencyontheorderofmilliseconds

Low-rateclockwithsavednetworkassociationinformation

15

Networkpoweroptimization

• Usepower-savingmodes– Example:802.11wirelessLAN(WiFi)

• Infrastructuremode:Accesspointsandmobilenodes

– Example:Cellularnetworks

16

802.11infrastructuremode• Mobilenodesniffsbasedona“ListenInterval”

– ListenIntervalismultipleofthe“beaconperiod”• Beaconperiod:typically100ms

• DuringaListenInterval– Accesspoint

• buffersdataformobilenode• sendsoutatrafficindicationmap(TIM),announcingbuffereddata,everybeaconperiod

– Mobilenodestaysinpower-savingmode• AfteraListenInterval

– MobilenodechecksTIMtoseewhetheritgetsbuffereddata

– Ifso,send“PS-Poll”askingfordata

17

Buffering/sniffingin802.11

Gast,802.11WirelessNetwork:TheDefinitiveGuide

802.15.1/Bluetoothusessimilarpower-savingprotocols:HoldandSniffmodes

Cellularnetworks

• Discontinuoustransmission(DTX)• Discontinuousreception(DRX)

Wirelessenergycost

• Connection– Establishment– Maintenance

• Transferdata– Transmitvs.receive

19

Energyperbittransfer

Oppermannetal.,IEEEComm.Mag.200420

Wastefulwirelesscommunication

21

TimeMicropowermanagement

SpaceDirectionalcommunication

SpectrumEfficiency-drivencognitiveradio

Spacewaste

• Omnitransmissionèhugepowerbypoweramplifier(PA)

22

Timewaste• NetworkBandwidthUnder-Utilization

– Modestdataraterequiredbyapplications• IE~1Mbps,MSNvideocall~3Mbps

– Bandwidthlimitofwiredlink• 6MbpsDSLathome

23230 0.2 0.4 0.6 0.8 1

0

200

400

600

800

1000

1200

1400

Time (s)

Dat

a Si

ze (B

yte)

0

20

40

60

80

100

Time EnergyIdleintervalsinbusytime(%)

User1 User2 User3 User4

Spectrumwaste

24

Observedfroman802.11guser

25

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07Throughout(bps)

EnergyperbitDistribution ofobserved802.11gthroughput

Temporalwaste

26

0 0.2 0.4 0.6 0.8 10

1

Time(s)

Radio

Acti

vity

90%oftime&80%ofenergyspentinidlelisteningFour802.11glaptopusers,oneweek

FundamentalproblemwithCSMA

• CSMA:CarrierSenseMultipleAccess– Clientscompeteforairtime

• Incomingpacketsareunpredictable

27

FundamentalproblemwithCSMA

28

Micropowermanagement(µPM)• Sleepduringidlelistening• Wakeupintimetocatchretransmission• Monitorthetrafficnottoabuseit

• ~30%powerreduction• Noobservedqualitydegradation

29J.LiuandL.Zhong,"Micropowermanagementofactive802.11interfaces,"inProc.MobiSys’08.

Directionalwaste

OngoingprojectwithAshutosh Sabharwal

Directionalwaste

Twowaystorealizedirectionality

• Passivedirectionalantennas– Lowcost– fixedbeampatterns

• Digitalbeamforming– Flexiblebeampatterns– Highcost

32Phased-arrayantennasystemfromFidelityComtech

Desclos,Mahe,Reed,2001

ChallengeI:Rotation!!!

33

Solution:Don’tgetridoftheomni directionalantennasUsemultipledirectionalantennas

Butcanweselecttherightantennaintime?

ChallengeII:Multipathfading

34

ChallengeIII

• Canwedoitwithoutchangingtheinfrastructure?

35

Characterizingsmartphonerotation

• Howmuchdotheyrotate?• Howfastdotheyrotate?

• 11HTCG1users,eachoneweek• Logaccelerometerandcompassreadings

– 100Hzwhenwirelessinuse

36

DeviceorientationdescribedbythreeEulerangles

• θ andφ basedontri-axisaccelerometer• ψ basedontri-axiscompassandθ andφ

37

Rotationisnotthatmuch

• <120° persecond

10-4 10-3 10-2 10-1 100 101 102 1030

0.1

0.2

0.3

0.4θ

Rotational speed(°/s)

PD

F

100ms1s10s

10-4 10-3 10-2 10-1 100 101 102 1030

0.1

0.2

0.3

0.4φ

Rotational speed(°/s)

PD

F

100ms1s10s

10-4 10-3 10-2 10-1 100 101 102 1030

0.1

0.2

0.3

0.4ψ

Rotational speed(°/s)

PD

F

100ms1s10s

38

Directionalityindoor

39

5dBi

8dBi

8dBiantenna 5dBiantenna

Measurementsetup• RSSImeasuredatbothends

41

Datapackets

ACKpackets

Directional channel still reciprocal

42

0 60 120 180 240 300 360-60

-50

-40

-30

-20NLOS ind. / 5dBi antenna

Direction(°)

RSS

(dB

m)

Dir-ClientDir-APOmni-ClientOmni-AP

Directional beats omni close to half of the time

[0,0.1) [0.1,1) [1,10) [10,inf)0

5

10

15

20

25

30

tota

l tim

e(%

)

superiority intervals(s)

5dBi

43

Fieldcollectedrotationtracesreplayed

RSSispredictable(toabout100ms)

44

10ms 100ms 1s 10s

0.01

1

100

Prediction Intervals(s)

Erro

r(dB

)

5dBi

Zero order First order

Multi-directionalantennadesign(MiDAS)

• OneRFchain,oneomniantenna,multipledirectionalantennas

• Directionalant.onlyusedfordatatransmitandACKReception– Standardcompliance– Tradeoffbetweenriskandbenefit

45

Packet-based antenna selection• Assessanantennabyreceivingapacketwithit

– Leveragingchannelreciprocity• Continuouslyassesstheselectedantenna• Findoutthebestantennabyassessingthemonebyone– Potentialriskofmissingpackets

• Staywithomni antennawhenRSSchangesrapidly

• Nochangein802.11networkinfrastructure

46

Symbol-basedantennaselection

• AssessallantennasthroughaseriesofPHYsymbols– SimilartoMIMOantennaselection

• NeedshelpfromPHYlayer

47

Antenna training packet

SEL

Regular packet

ACK

Tracebasedevaluation

• Rotationtracesreplayedonthemotor• RSSItracescollectedforallantennas• Algorithmsevaluatedontracesoffline

0 5 10 15 20-60

-55

-50

-45

RSS(dB)

time(second)

Dir1 Dir

3

Dir 3

Omni

48

Anearlyprototype

49

Controllable motor

3 directional antennas1 omni antenna

WARP

Laptop

FinalistofMobiCom’08BestStudentDemo

Thebusierthetraffic,thebetter

10ms 100ms 1s 10s0

1

2

3

4

5

6

Average Packet Interval

Gai

n(dB

)

Upper bound Symbol-based Packet-based

50

Two 5dBiantennasenough

51

three two-opp two-adj one0

1

2

3

4

5

6

Antenna Configuration

Gai

n(dB

)

Upper bound Symbol-based Packet-based

Two5dBi antennasenough

52

5dBi 8dBi0

1

2

3

4

5

6

Antenna Gain

Gai

n(dB

)

Upper bound Symbol-based Packet-based

0 60 120 180 240 300 360-60

-50

-40

-30

-20NLOS ind. / 5dBi antenna

Direction(°)

RSS

(dB

m)

Dir-ClientDir-APOmni-ClientOmni-AP

0 60 120 180 240 300 360-60

-50

-40

-30

-20NLOS ind. / 8dBi antenna

Direction(°)

RSS

(dB

m)

Dir-ClientDir-APOmni-ClientOmni-AP

Real-timeexperiments:3dBgain

• Packet-basedantennaselection• Three5dBiantennas• Continuoustraffic(1400bytepackets)• Fieldcollectedrotationtrace

NLOS ind. LOS ind.-75

-60

-45

Environment

Avg

. RSS

(dB

)

Omni Multi antenna

53

Throughputimprovement

54

NLOS ind. LOS ind.0

1

2

3

4

Environment

Throughput(Mbps)

Omni Multi antenna

SNRvs.transmissionrate(802.11a)

55

(D.Qiao,S.Choi,andK.Shin,2002)

0 10 20 300

5

10

15

20

25

30

35

SNR (dB)

Goo

dput

(Mbp

s)

6Mbps9Mbps 12Mbps 18Mbps 24Mbps 36Mbps48Mbps54Mbps

MiDAS+rate adaptation+power control

• RecallthatRSSisquitepredictableupto100ms

56

0

50

100

150

200

0 10 20 30 40

%

OmniSNR(dB)

Goodput Gain-UpperboundGoodput Gain-MiDASTXpowerreduction-UpperboundTXpowerreduction-MiDAS

Protocolwaste

Cellularnetwork WLAN(Wi-Fi)

Connection

Transmissionefficiency

Availability

58

HowtocombinethestrengthofbothWi-FiandCellularnetwork?

EstimateWi-FinetworkconditionWITHOUTpoweringonWi-Fiinterface

UsecontexttopredictWiFi availability

• Visiblecellularnetworktowers• Motion• Timeoftheday,dayoftheweek

59

Context Wi-FiConditions

Statisticallearning

AhmadRahmatiandLinZhong,"ContextforWireless:Context-sensitiveenergy-efficientwirelessdatatransfer," inProc.MobiSys’07.JournalversionwithnewresultstoappearinIEEETMC

P(WiFi|Context)

Cellularnetworkoffersclues

Cellularnetworkoffersclues

Wedon’tmovethatmuch

62

0%

10%

20%

30%

40%

50%

moving (1,5] (5,10] (10,30] (30,60] (60,120] (120,inf)

Lengthofmotionlessperiod(minute)

Shoehornedsmartphonewithaccelerometer

Datacollectedfrom2smartphone users2006

Ourlifeisrepetitive

63

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

Prob

abilityofsam

eWi-Fiavailability

(normalize

dau

tocorreletaion

)

Time(days)

Datacollectedfrom11smartphone users

WiFi availabilityisHIGHLYpredictable

64

• Application– MobileEKGmonitoring– 35%batterylifeimprovement(12to17hours)

0.5

0.6

0.7

0.8

0.9

1

0 120 240 360 480 600

Pred

ictio

naccuracyofW

i-Fi

availability

Time(minutes)