SMART DUST

SMART DUSTHardware Limits to Wireless Sensor Networks

Kris PisterBerkeley Sensor & Actuator Center

Electrical Engineering & Computer Sciences UC Berkeley – pister@eecs.berkeley.edu

(on leave to start Dust Inc – kpister@dust-inc.com)

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Ken Wise, U. Michigan

• http://www.eecs.umich.edu/~wise/Research/Overview/wise_research.pdf

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Bill Kaiser, UCLA

• http://www.janet.ucla.edu/WINS

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Wireless dawn sensor

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Computation

Difference EngineCharles Babbage, 1822

Steve Smith, UCB

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Multi-hop message passing

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Lots of exponentials

• Digital circuits• Speed, memory• Size, power, cost

• Communication circuits• Range, data rate• Size, power, cost

• MEMS Sensors• Measurands, sensitivity• Size, power, cost

CommunicationComputation

Sensing

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Smart Dust Goal

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COTS Dust - RF Motes

• Simple computer• Cordless phone radio• Up to 2 year battery life

N

S

EW 2 Axis Magnetic Sensor

2 Axis Accelerometer

Light Intensity Sensor

Humidity Sensor

Pressure Sensor

Temperature Sensor

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Open Experimental Platform to Catalyze a Community

Small microcontroller

- 8 kb code, 512 B data

Simple, low-power radio

- 10 kb

EEPROM storage (32 KB)

Simple sensors

WeC 99“Smart Rock” Mica 02

NEST open exp. platform

128 KB code, 4 KB data

50 KB radio

512 KB Flash

comm accelerators

Dot 01

Demonstrate scale

Rene 00

Designed for experimentation

-sensor boards

-power boards

TinyOS

Networking

Services

David Culler, UCB

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800 node demo at Intel Developers Forum

4 sensors$70,000 / 1000Concept to demo in 30 days!

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Structural performance due to multi-directional ground motions (Glaser & CalTech)

.

Wiring for traditional structural instrumentation+ truckload of equipment

Mote infrastructure15

13

14

6 

5` 

15

118 

Mote Layou

t 129 

Comparison of Results

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Cory Energy Monitoring/Mgmt System

• 50 nodes on 4th floor• 5 level ad hoc net• 30 sec sampling• 250K samples to database over 6 weeks

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29 Palms Sensorweb Experiment

• Goals• Deploy a sensor network onto a road from an unmanned

aerial vehicle (UAV)• Detect and track vehicles passing through the network• Transfer vehicle track information from the ground network

to the UAV• Transfer vehicle track information from the UAV to an

observer at the base camp.

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Last 2 of 6 motes are dropped from UAV

• 8 packaged motes loaded on plane

Last 2 of six being dropped

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Available Sensors

• Demonstrated w/ COTS Dust• Temperature, light, humidity, pressure, air flow• Acceleration, vibration, tilt, rotation• Sound• GPS• Gases (CO, CO2)• Passive Infra-red• Contact/touch

• Available• Images, low-res video • Gases (VOCs, Organophosphates, NOx…)• Neutrons

Demonstrated Actuators• Motor controllers• 110 VAC relays• Audio speaker• RS232: LCD, …

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Blue Mote Hardware

• Chipcon cc1000 radio• RX Power: 9.6-14 mA (-102 -> -105 dBm)• TX Power: 12-25 mA, (-5 to 4 dBm) range

~50m indoors• Bit rate up to 76,800 kbps

• TI MSP430 Processor• ~1mA @ 4MHz

• Operating Voltage 2.1-3.3 V

• Sleep mode = 3 A

• Same damn 51 pin connector

• $50-$100

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Basic Operations

• Sleep

• Listen for activity on radio

• Sample sensors

• Synchronize clocks

• Scheduled chat with neighbor

• Message via multihop• Data• “Warning!”• “We’re all fine down here”

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Cost of Basic Operations

Operation Current[A]

Time[s]

Charge[A*s]

Sleep 3u

Sample 1m 20u 20nTalk to neighbor15 byte payload

25m 5m 125

Listen to neighbor15 byte payload

10m 8m 80

Sound an alarm 25m 1s?

Listen for alarm 2m 2m 4

QAAbattery = 2000mAh = 7,200,000,000 A*s

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Typical Topologies

Linear

Star

Tree

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Application Energy Breakdown

• Collect Data from 3 Children every 15 seconds (RX cost include synchronization)

• Send 4 data packets every 15 seconds

• Alarm check once per second

• Send 10 alarms per day

• Expected Lifetime: 4.1 Years

Cost Each (mJ) Number Per Day mJ per Day % of TotalRX 0.24 17280 4147.2 28%TX 0.375 23040 8640 59%Alarm Check 0.012 86400 1036.8 7%Alarm Send 75 10 750 5%

Total: 14574Battery Life (years): 4.1

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Alarm Msg

!

HDK Implementation

Collect data from children Send to parent

Periodic Alarm Message Checks

Sensor Sampling

Alarm Msg Forward

Report Interval (user controlled, 0 to 256 seconds)

Reporting Slots 32 ms

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Time period definitions

Periodic Alarm Message Checks

Sensor Sampling

Report Interval (user controlled, 0 to 256 seconds)

Reporting Slots 32 ms

Tepoch

talarm

tsample

tslot

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HDK Extrema

• Max data rate through a single mote: 1kB/s

• Max data rate via linear multihop: 300B/s

• Latency in multihop communication: n*tslot

• Alarm lifetime = talarm*Qbat/Qcheck

• Alarm latency < n*talarm

• E.g. talarm = 0.1s; n=20; N=1,000,000Lifetime = 6 yearsLatency < 2 s

• “We’re all fine” lifetime = (Qbat / (Qmsg )* (Tepoch /(1+nkids))• E.g. Tepoch = 20 min; nkids = 1000

Lifetime = 3 years

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Application Energy Breakdown

• Collect Data from 3 Children every 15 seconds (RX cost include synchronization)

• Send 4 data packets every 15 seconds

• Alarm check once per second

• Send 10 alarms per day

• Expected Lifetime: 4.1 Years

Cost Each (mJ) Number Per Day mJ per Day % of TotalRX 0.24 17280 4147.2 28%TX 0.375 23040 8640 59%Alarm Check 0.012 86400 1036.8 7%Alarm Send 75 10 750 5%

Total: 14574Battery Life (years): 4.1

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~2 mm^2 ASIC

One Chip, Four Dissertations

• CMOS ASIC• 8 bit microcontroller• Custom interface circuits

• External components

uP SRAM

RadioADC

Temp

Ampinductor

crystal

battery

antenna

~$1

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Working silicon

• 8 bit uP

• 3k RAM

• OS accelerators

• World record low power 8 bit ADC (100kS/s, 2uA)

• HW Encryption support

• 900 MHz transmitter

Functional, running TinyOS, sending packets to Blue

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Working mote, happy grad student

Jason Hill

Jason’s mote

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Power and Energy

• Sources• Solar cells ~0.1mW/mm2, ~1J/day/mm2

• Combustion/Thermopiles

• Storage• Batteries ~1 J/mm3

• Capacitors ~0.01 J/mm3

• Usage• Digital computation: nJ/instruction• Analog circuitry: nJ/sample• Communication: nJ/bit

10 pJ20 pJ/sample

11 pJ RX, 2pJ TX (optical)

10 nJ/bit RF

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Energy and Lifetime

• 1 mAh ~= 1 micro*Amp*month (Am)• Lithium coin cell: 220 Am (CR2032, $0.16) • AA alkaline ~ 2000 Am

• 100kS/s sensor acquisition: 2A• 1 MIPS custom processor: 10A• 100 kbps, 10-50 m radio: 300A

• 1 month to 1 year at 100% duty• 10 year lifetime w/ coin cell 1% duty

• Sample, think, listen, talk, forward…2 times/second!

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Energy Considerations

• Storage• Batteries today: 700 Wh/kg (Tadiran)• Battery limits: 8,000 Wh/kg (Aluminum/air)• Gasoline: 12,700 Wh/kg (upper heating value)• H2: 50,000 Wh/kg (upper heating value)

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Energy Considerations

• Sensing• 1pJ/S @ 10 bits (re: 20pJ/S @ 8 bits)• Power ~ 22N f

Scott, Boser, Pister, An Ultra-Low Power ADC for Distributed Sensor Networks, ESSCIRC 2002.

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Energy Considerations

• Computation• Power ~ CV2 f• C = NgC0 • C0 = r 0 A/d ~ 5fF/m2

• For 8 bit ops, Ng ~100• A ~ Ld

2

• A = 0.020m2 today (Ld =0.13) 10pJ• A = 0.001m2 2010 (Ld =50nm) 0.5pJ

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RF Sensitivity

• Pn = kBT f Nf

• Sensitivity = Pn * SNRmin

• e.g. GSM (European cell phone standard), 115kbps

kBT 200kHz ~8x SNRS = -174dBm + 53 dB + 9 dB + 10 dB = -102 dBm

RX power = ~200mWTX power = ~4W 50 uJ/bit

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RF Path Loss

• Isotropic radiator, /4 dipole• Pr=Pt / (4 (d/)n)

• Free space n=2

• Ground level n=2—7, average 4

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N=4

From Mobile Cellular

Telecommunications,

W.C.Y. Lee

Pt = 10-50W

-102dBm

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Path Loss

• Like to choose longer wavelength• Loss ~(d)n

• 916MHz, 30m, 92dB power loss need –92dBm receiver for 1mW xmitter power!

• Penetration of structures, foliage, …

• But…• Antenna efficiency • Size – /4 @ 1GHz = 7.5cm

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Output Power Efficiency

• RF• Slope Efficiency

• Linear mod. ~10%• GMSK ~50%

• Poverhead = 1-100mW

• Optical• Slope Efficiency

• lasers ~25%• LEDs ~50%

• Poverhead = 1uW-100mW

Slope Efficiency

TrueEfficiency

Pin

Pout

Poverhead

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Cassini

Limits to RF Communication

• 8 GHz (3.5cm)• 20 W• 1.5x109 km• 115 kbps• -130dBm Rx• 10-21 J/bit

• kT=4x 10-21 J @300K• ~5000 3.5cm photons/bit

Canberra• 4m, 70m antennas

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Integrated Microwatt Transceiver, Howe/Rabaey, UCB

fclock

Rejects non-linear LNA components Shapes LNA thermal noise Selects System Frequency Bands

Prefilter: micro-machined LC passive

RF Filter (Low Q)

A

D LNA

NM Filter

NM Filter

NM Filter

•Radios need filters•The best filters are electromechanical•Power is related to size

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Mike Sailor’s Smart Dust

M. SailorUCSD Chemistry

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CMOS Cameras

• Today• 5mm scale• 1mJ/image• 110,000 pixels

• Tomorrow• 1mm scale• 50pJ * #pixels / image ~ 1uJ• 16k pixels

• Soon• 1mm scale• 1pJ * # pixels /image ~ 1uJ• 1M pixel

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Single Nanotube Inverter - IBM

Atomic Force Microscope image showing the design of an intra-molecular logic gate. A single carbon nanotube (shaded in blue) is positioned over gold electrodes to produce two p-type carbon nanotube field-effect transistors in series. The device is covered by an insulated layer (called PMMA) and a window is opened by e-beam lithography to expose part of the nanotube. Potassium is then evaporated through this window to convert the exposed p-type nanotube transistor into an n-type nanotube transistor, while the other nanotube transistor remains p-type.

Derycke, Martel, Appenzeller, Avouris; Carbon nanotube inter- and intra-molecular logic gates; Nano Letters, August 26, 2001

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Carbon Nanotube Circuits - Delft

A. Bachtold, P. Hadley, T. Nakanishi, C. Dekker; Logic circuits with carbon

nanotube transistors Science, 294, 1317-1320 (2001).

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Nano Dust?

• Nanotube sensors

• Nanotube computation

• Nanotube hydrogen storage

• Nanomechanical filters for communication!

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Mobility

• Walking

• Hopping

• Flying

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Mobility

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Milli-Millennium Falcon

Increase the thrust and Increase the thrust and decrease the mass, decrease the mass, while controlling while controlling thermal lossesthermal losses

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Thrust Measurements vs. Theory

0

5

10

15

20

25

0 0.5 1 1.5 2 2.5

Time (sec)

Thru

st (m

illin

ewto

ns)

Predicted altitude: 50 m

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Rocket in Action

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Synthetic Insects(Smart Dust with Legs)

Goal: Make silicon walk.

•Autonomous•Articulated•Size ~ 1-10 mm•Speed ~ 1mm/s

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2 Degree of Freedom Legs

1st LinkMotor

2nd LinkMotor

1mm

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Silicon Inchworm Motors

1mm

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Current Layout for Motor and Legs

Legs

7.6 mm

Sola

r Cel

lsMotor

Motor

CMO

S

Linkages

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Solar Powered Robot Pushups

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Big Products from Small Workers

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The Dark Side

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Conclusion

• Tremendous promise

• More new questions than answers