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Jan M. RabaeyJan M. Rabaey

BWRCBWRC

University of California @ BerkeleyUniversity of California @ Berkeley

http://http://bwrcbwrc..eecseecs..berkeleyberkeley..eduedu

What is the relation between wirelessWhat is the relation between wirelessand and FibonacciFibonacci??

World Wireless Subscriber Growth (in tens of millions)World Wireless Subscriber Growth (in tens of millions)Source: Goldman-Sachs

The sky (or the air) is the limitThe sky (or the air) is the limit

Wireless subscribers (projected)

Source: Goldman-Sachs

Infrastructure

Mobile Terminals

Total wireless business: $ 98 bn

What is next?What is next?

The data wave gets unpluggedThe data wave gets unpluggedExample: More than 2 billion SMS messages in Europe monthlyExample: More than 2 billion SMS messages in Europe monthly

Third Generation Wireless NetworkThird Generation Wireless Network(UMTS-UTRA 2000)(UMTS-UTRA 2000)

●● Small, lightweight pocketSmall, lightweight pocketcommunicator , that will offercommunicator , that will offerservices “anywhere, anytime”services “anywhere, anytime”

●● Mobile Internet access, highMobile Internet access, highspeed data, videospeed data, videoconferencing, roaming, virtualconferencing, roaming, virtualhome environmenthome environment

●● Rates between 340 Kb/sec to 2Rates between 340 Kb/sec to 2MbitMbit/sec/sec

●● Unification of the many diverseUnification of the many diversesystems (paging, cordless,systems (paging, cordless,cellular, mobile satellite) into acellular, mobile satellite) into aseamless radio infrastructureseamless radio infrastructure

From Handsets to Mobile DevicesFrom Handsets to Mobile Devices

Internet access the most important driver(text, graphics, multimedia)

Berkeley Infopad,1990-1996

The Wire ReplacementThe Wire Replacement

●● Initiative by Intel, Initiative by Intel, EricssonEricsson, , NokiaNokia, IBM, and Toshiba, IBM, and Toshiba

●● Original Goal: provide wireless interface between PC andOriginal Goal: provide wireless interface between PC andperiphery based on periphery based on picocell picocell technologytechnology

• Small cells of 10 m• 10 picoNets/cell• Located in ISM band (2.45 GHz) (as do microwave ovens)• Point-to-point network configuration• FFH/DS spread-spectrum radio’s (1400 hops/sec)• 432 kbs full-duplex, 721/56 kbs asymmetric half-duplex• 0 dBm (1 mW) output power• 80 mW and 300 µW in send- and listening modes, respectively

Example: Example: BluetoothBluetooth

Other Approaches:Other Approaches: HomeRF HomeRF, , HomeRFHomeRF--litelite, 802.11, 802.11

The Smart HomeThe Smart Home

SecurityEnvironment monitoring and controlObject taggingIdentification

Dense network of Dense network of sensor and monitor nodessensor and monitor nodes

The Interactive MuseumThe Interactive Museum

Cafe

Offices

Exhibits

Wirelessnode

Entrance

Others: toys, medical, inventory, warehouse

The Distributed Approach to InformationThe Distributed Approach to InformationProcessingProcessing

Source: Richard Newton

4th Generation Challenges4th Generation ChallengesThe BWRC PerspectiveThe BWRC Perspective

●● Ubiquitous services put wireless spectrum at aUbiquitous services put wireless spectrum at apremiumpremium–– Effective use of ether hampered by standardizationEffective use of ether hampered by standardization

and fragmentationand fragmentation

–– Current spectral efficiency far below theoretical limitsCurrent spectral efficiency far below theoretical limits

●● Ubiquitous wireless networking requires steepUbiquitous wireless networking requires steepreduction in cost and energy dissipationreduction in cost and energy dissipation–– To be acceptable, radio cost has to be between 50To be acceptable, radio cost has to be between 50

cents and 5$cents and 5$

–– Frequent battery replacement on 100’s of devicesFrequent battery replacement on 100’s of devicesunacceptableunacceptable

Spectrum at a PremiumSpectrum at a Premium

The existing standards approach wastesThe existing standards approach wastesspectrum and can’t track the changes inspectrum and can’t track the changes inimplementation and usageimplementation and usage–– CMOS implementation results in radioCMOS implementation results in radio

computational capabilities expanding with Moore’scomputational capabilities expanding with Moore’slaw (or even faster …)law (or even faster …)

–– Future applications are moving from wellFuture applications are moving from wellunderstood voice to data with unknownunderstood voice to data with unknownrequirementsrequirements

–– Ad hoc, self organizing and inexpensiveAd hoc, self organizing and inexpensiveinfrastructure moves wireless systeminfrastructure moves wireless systemimplementation from providers to usersimplementation from providers to users

Universal Spectrum SharingUniversal Spectrum Sharing

Provides a strategy (etiquette) for Provides a strategy (etiquette) for peacefulpeacefuluncoordinated coexistenceuncoordinated coexistence in unlicensed RF bands in unlicensed RF bands

●● Allow a wide range of individual (local) system optimizationsAllow a wide range of individual (local) system optimizationsin a framework which yields fairness and globally maximalin a framework which yields fairness and globally maximalutilizationutilization

●● Have a minimum level of constraints to allow maximumHave a minimum level of constraints to allow maximumflexibility in implementationflexibility in implementation

●● Allow rapid exploitation of new technologiesAllow rapid exploitation of new technologies

●● Be extensible to new applicationsBe extensible to new applications

Example EtiquetteExample Etiquette

●● Use transmit power as a constraint whichUse transmit power as a constraint whichencourages “good behavior”encourages “good behavior”

●● Good behavior meansGood behavior means–– localizationlocalization in time-frequency-spatial signal space in time-frequency-spatial signal space

which allows other users to coexist withoutwhich allows other users to coexist withoutinterferenceinterference

–– stationarystationary or predictable behavior which facilitates or predictable behavior which facilitatesadaptation by other usersadaptation by other users

–– alignmentalignment to a time and frequency structure which to a time and frequency structure whichfacilitates co-existencefacilitates co-existence

Enabled by Progress in CommunicationEnabled by Progress in CommunicationTheory and AlgorithmsTheory and Algorithms

●● MultipathMultipath-Fading Mitigation-Fading Mitigation

●● MultipathMultipath-Fading Exploitation-Fading Exploitation

●● Interference SuppressionInterference Suppression

●● Interference AvoidanceInterference Avoidance

●● Channel Error-Control CodingChannel Error-Control Coding

●● Adaptive Transmission RateAdaptive Transmission Rate

MotivationsMotivations●● Increase system data rate without sacrificing any bandwidthIncrease system data rate without sacrificing any bandwidth

●● Relax requirements in speed and/or power of the analogRelax requirements in speed and/or power of the analogcircuitry of TX and RXcircuitry of TX and RX

●● Increase reliability through (spatial) diversityIncrease reliability through (spatial) diversity

ΣBaseband Signal

Despreading

X

Adaptive

ErrorSignal

●● Tracks changes in channel,Tracks changes in channel,environment, and interferingenvironment, and interferingusersusers

●● Uses common error metricsUses common error metricssuch as MSE, and commonsuch as MSE, and commonalgorithms such as LMS andalgorithms such as LMS andRMSRMS

Example 1: Example 1: Adaptive Multi-User Detection for CDMAAdaptive Multi-User Detection for CDMA

-10

0

10

20

30

40

0 1000 2000 3000

Sym bol Tim e s

Ou

tpu

t S

IR (

db

)

-10

0

10

20

30

40

0 1000 2000 3000

Sym bol Tim e s

Ou

tpu

t S

IR (

db

)

8 bit

10 bit

12 bit16 bit

Example 2: Spatial ChannelsExample 2: Spatial Channels

ArrayProcessing

Multiple Antennae SystemMultiple Antennae System

RF TX

ArrayProcessing

ArrayProcessing

RF TX

RF TX

RF TX

RF RX

RF RX

RF RX

RF RX

RF RX

RF RX

h11

hrt

hr1

h1t

TX data RX data

x1

x2

xt

y1

y2

yr

rich

sca

tter

ing

envi

ron

men

t

.

.

.

.

.

.

Capacity GainCapacity Gain

-10 -5 0 5 10 15 20 25 30 35 400

20

40

60

80

100

120

140

SNR (dB)

(1,1) Baseline with adaptation

Exp

ecte

d M

utu

al In

form

atio

n (

bit

s/s/

Hz)

(4,4) MMSE successive decoding(4,4) Optimum power allocation with adaptation

(12,12) MMSE successive decoding(12,12) Optimum power allocation with adaptation

Source: Ada Poon (UC Berkeley)

The Down side:The Down side:Algorithmic ComplexityAlgorithmic Complexity

Block RLS using Block RLS using GrammGramm--Schmitt Schmitt DecompositionDecomposition

1.375 Gmults/secfor 25 Mchip/sec rate

Source: Martin Benes (UC Berkeley)

Digital Baseband ProcessingDigital Baseband ProcessingRequirementsRequirements

W ide-band C D M A FD M AM ultipleA ntenna

M atchedFilter

B lindM M SE

ExactD ecorrelator

SV D

Perform anceBits/sec/H z

1 2 2 6

M ultiplications 124 496 230,000 736M em ory 248 1240 640,000 2120A LU 124 502 240,000 800W ord Length 8-bit 12-bit 16-bit 16-bit

De ns ity Ac c e s s Time

(Gbits /c m2) (ns )

DRAM 8.5 10

DRAM (Lo g ic ) 2.5 10

S RAM (Cac he ) 0.3 1.5

Density Max. Ave. Power Clock Rate(Mgates/cm2) (W/cm2) (GHz)

Custom 25 54 3Std. Cell 10 27 1.5

Gate Array 5 18 1Single-Mask GA 2.5 12.5 0.7

FPGA 0.4 4.5 0.25

Silicon technology tracking Silicon technology tracking Moore’s Moore’s LawLaw

Die Area: 2.5x2.5 cmVoltage: 0.6 - 0.9 VTechnology: 0.07 µm 15 times denser

than today2.5 times power

density5 times clock rate

Silicon in 2010Silicon in 2010

2010 Die: 2.5 x 2.5 cm2

NTRS Processor 2010NTRS Processor 2010

Pentium II @ 2010 Pentium II @ 2010 Devices: Devices:7,500,0007,500,000

Clock Speed: Clock Speed: 1 GHz for 200mW1 GHz for 200mW Chip Size: Chip Size:6 mm6 mm22

Devices:Devices: 900M900M Performance > 50 GOPS Performance > 50 GOPS Power Dissipation: Power Dissipation:175W175W

Shannon beats Shannon beats Moore’s Moore’s lawlaw

1

10

100

1000

10000

100000

1000000

10000000

1980

1984

1988

1992

1996

2000

2004

2008

2012

2016

2020

Algorithmic Complexity(Shannon’s Law)

Processor Performance (~Moore’s Law)

Source: Data compiled from multiple sources (avail on request)

1G

2G

3G

Courtesy: Ravi Subramanian, morphICs Tech. Inc

Energy to Play a Major RoleEnergy to Play a Major Role

1

10

100

1000

10000

100000

1000000

10000000

1980

1984

1988

1992

1996

2000

2004

2008

2012

2016

2020

Algorithmic Complexity(Shannon’s Law)

Processor Performance (~Moore’s Law)

Battery Capacity

Source: Data compiled from multiple sources (avail on request)

1G

2G

3G

Courtesy: Ravi Subramanian, morphICs Tech. Inc

Wireless System Design MetricsWireless System Design Metrics

Flexibility

Power

Cost

Performance as a Functionality ConstraintPerformance as a Functionality Constraint(“Just-in-Time Computing”)(“Just-in-Time Computing”)

The System-on-a-ChipThe System-on-a-Chip

RAM

500 k Gates FPGA+ 1 Gbit DRAMPreprocessing

Multi-

SpectralImager

µCsystem+2 GbitDRAMRecog-nition

Ana

log

64 SIMD ProcessorArray + SRAM

Image Conditioning100 GOPS

●● Embedded applications whereEmbedded applications wherecost, performance, and energycost, performance, and energyare the real issues!are the real issues!

●● DSP and control intensiveDSP and control intensive

●● Mixed-modeMixed-mode

●● Combines programmable andCombines programmable andapplication-specific modulesapplication-specific modules

●● Software plays crucial roleSoftware plays crucial role

SOC SOC anno anno 20102010

Picking the Correct ArchitecturePicking the Correct Architecture

µP

Prog Mem

MACUnit

AddrGenµP

Prog Mem

µP

Prog M em

Satellite

ProcessorDedicated

Logic

Satellite

Processor

Satellite

Processor

GeneralPurpose

µP

Software

DirectMapped

Hardware

HardwareReconfigurable

Processor

ProgrammableDSP

Fle

xibi

lity

1/Efficiency

Choosing the CorrectChoosing the CorrectImplementation ArchitectureImplementation Architecture

Signal Update BlockAcquisition andTiming Recovery Signal Update Block

AdaptivePilot

Correlator

AdaptiveData

Correlator

C0 CL-1

Digital Baseband

Sk

...

Data Out

Receiver

ChannelCoefficientEstimates

AdaptivePilot

Correlator

Dat

a In

300 million multiplications/sec357 million add-sub’s/sec

Adaptive Multi-User DetectionAdaptive Multi-User DetectionA Direct Mapping ApproachA Direct Mapping Approach

Correlator

Power and area are dominated by MACs and multipliesOnly 36% of power of DSP-processor solution going into arithmetic

The Energy-Flexibility GapThe Energy-Flexibility Gap

Embedded ProcessorsSA1100.4 MIPS/mW

ASIPsDSPs 2 V DSP: 3 MOPS/mW

DedicatedHW

Flexibility (Coverage)

Ene

rgy

Eff

icie

ncy

MO

PS/

mW

(or

MIP

S/m

W)

0.1

1

10

100

1000

ReconfigurableProcessor/Logic

Pleiades10-80 MOPS/mW

Future Wireless ModemFuture Wireless Modem

ReconfigurableDataPath

FPGA Embedded uP

Dedicated FSM

DedicatedDSP

“The software-defined Radio”

Embedded Processor

FPGA

Accelerators

Example: Berkeley Maia Processor

The Energy Problem RevisitedThe Energy Problem Revisited

SecurityEnvironment monitoring and controlObject taggingIdentification

Dense network of Dense network of sensor and monitor nodessensor and monitor nodes

Energy Minimization starts atEnergy Minimization starts atthe System Levelthe System Level

Cafe

Offices

Exhibits

Entrance

ReconfigurableDataPath

FPGA Embedded uP

Dedicated FSM

DedicatedDSP

( )γ10Totaloptimal distceilhops =

Energy Constraints

Use CasesEnvironment Analysis

Traffic Analysis

Positioning NetworkArchitecture

6

7

10

1112

13

14

15

16

17

1819

20

Tra

nsm

it P

ow

er

-70dBm

-30dBm

10dBm

100 Kbps

50dBm

90dBm

Distance1m 10m 100m 1Km 10Km

Tra

nsc

eive

r P

ow

er

50dBm

90dBm

10dBm

-30dBm

-70dBm

Assumes R-4 loss due to ground wave(@ 1 GHz)

Bluetooth goal • 700 Kbps• 10 m• 1 mW Tx

The Cost of CommunicationThe Cost of Communication1 megawattfor 100Kbps!

Tra

nsm

it P

ow

er

-70dBm

-30dBm

10dBm

100 Kbps

50dBm

90dBm

Distance1m 10m 100m 1Km 10Km

Tra

nsc

eive

r P

ow

er

50dBm

90dBm

10dBm

-30dBm

-70dBm

Assumes R-4 loss due to ground wave(@ 1 GHz)

PicoRadioPicoRadio Energy Optimization Energy OptimizationThe Varying Communication DistanceThe Varying Communication Distance

Communication versus ComputationCommunication versus Computation

●● Computation cost (2004): 60 Computation cost (2004): 60 pJpJ/operation/operation

●● Communication cost (thermal energy minimum):Communication cost (thermal energy minimum):–– 100 m distance: 20100 m distance: 20 nJ nJ/bit @ 1.5 /bit @ 1.5 GHzGHz

–– 10 m distance: 210 m distance: 2 pJ pJ/bit @ 1.5 /bit @ 1.5 GHzGHz

●● Computation versus CommunicationsComputation versus Communications–– 100 m distance: 300 operations == 1bit100 m distance: 300 operations == 1bit

–– 10 m distance: 0.03 operation == 1bit10 m distance: 0.03 operation == 1bit

Computation/Communication requirements varyComputation/Communication requirements varywith distance, data type, and environmentwith distance, data type, and environment

Requires Adaptive and Time-Varying Solution!

Communicating over Long DistancesCommunicating over Long DistancesMulti-hop NetworksMulti-hop Networks

Source

Dest

Example:● 1 hop over 50 m

1.25 nJ/bit

● 5 hops of 10 m each5 × 2 pJ/bit = 10 pJ/bit

● Multi-hop reducestransmission energy by 125!(ignoring overhead and cost ofretransmissions)

Joined Networking-PositioningJoined Networking-Positioning

2

1

3

4

5

6

7

8

9

10

1112

13

14

15

16

17

1819

20

0 0.5 10

0.2

0.4

0.6

0.8

1

Delaunay Mesh of 25 Networked Nodes

x

0 0.5 10

0.2

0.4

0.6

0.8

1

Solution on 25 Ranges and 50% Error

x

0 0.5 10

0.2

0.4

0.6

0.8

1

50 Solutions and Mean

x

0.4 0.45 0.5 0.55 0.60.4

0.45

0.5

0.55

0.6

Zoom on Error

x

dx 0.0054

dy 0.0058

1% error●● Ubiquitous radio networksUbiquitous radio networksoffer accurate localizationoffer accurate localizationwith minimal overheadwith minimal overhead

●● Potential to substantiallyPotential to substantiallyreduce networkingreduce networkingoverhead!overhead!

Maximizing Sleep ModeMaximizing Sleep Mode

Example: Collision-sense multiple access (CSMA)Example: Collision-sense multiple access (CSMA)with with overlayedoverlayed locally-synchronized TDMA framing locally-synchronized TDMA framing

RX/TX in sleep mode time

Sender 1

Sender 2

CSMA

Best addressed at the media-access (MAC) layer of the protocol stack

The Holy Grail: The Holy Grail: Energy ScavengingEnergy Scavenging

Integrated micro-vibratorprovides 10-100 µW of free power(equivalent to 2340 free DSPoperations/sec) [Amirtharajah &Chandrakasan, DISPS99]

Power (Energy) Density

Batteries (Zinc-Air) 1050 -1560 mWh/cm3

Batteries (rechargeable Lithium) 300 mWh/cm3 (3 - 4 V)

Solar

15 mW/cm2 - direct sun

1mW/cm2 - ave. over 24 hrs.

Vibrations 0.05 - 0.5 mW/cm3

Inertial Human Power

Acoustic Noise

3E-6 mW/cm2 at 75 Db

9.6E-4 mW/cm2 at 100 DbNon-Inertial Human Power 1.8 mW (Shoe inserts)

Nuclear Reaction

80 mW/cm3

1E6m Wh/cm3

One Time Chemical Reaction

Fluid Flow

Fuel Cells

300 - 500 mW/cm3

~4000 mWh/cm3

Energy SourcesEnergy Sources

SummarySummary

●● Wireless communications is in for aWireless communications is in for atremendous growth in the next decadetremendous growth in the next decade

●● The opportunity lies in the The opportunity lies in the “last meter”:“last meter”:providing access to ubiquitous distributedproviding access to ubiquitous distributedsensor, monitor and access devicessensor, monitor and access devices

●● Energy, cost, and spectrum limitationsEnergy, cost, and spectrum limitations open openthe door for novel and innovative systemthe door for novel and innovative systemconcepts and implementationsconcepts and implementations

●● The sky (air) is really the limitThe sky (air) is really the limit