Ultra-low power wirelessThe changing landscape of WSN

Kris Pister

Prof. EECS, UC Berkeley(Founder & CTO, Dust Networks)

Outline

• Technology status

• Standards update

• Implications

Autonomous Microsensor Networks with Optical Communication Links

• PI: Kris Pister

• Source: Hughes (MICRO)

• Funding: $25k, $10k matching, 0% ovhd,

• Duration: 1 year

• Comments: Collaboration w/ Prof. Joe Kahn under separate MICRO

IAB 1997

COTS DustGOAL:

• Get our feet wet

RESULT:

• Cheap, easy, off-the-shelf RF systems

• Fantastic interest in cheap, easy, RF:– Industry

– Berkeley Wireless Research Center

– Center for the Built Environment (IUCRC)

– PC Enabled Toys (Intel)

• Fantastic RF problems

• Optical proof of concept

IAB Spring 2000

IAB Spring 2003 – Al Molnar87

5m

650mOscillator

Divider

Transmitter

Receiver (in fab)

Inductor Chip

900MHz Transmitter

UCB Hardware Results ~2003

• 2 chips fabbed in 0.25um CMOS– “Mote on a chip” worked, TX only

– 900 MHz transceiver worked

• Records set for low power CMOS– ADC, Mike Scott, M.S.

• 8 bits, 100kS/s

• 2uA@1V

– Microprocessor, Brett Warneke, PhD.• 8 bits, 1MIP

• 10uA@1V

– 900 MHz radio – Al Molnar M.S.• 100kbps, “bits in, bits out”

• 20 m indoors

• 0.4mA @ 3V

2.4 GHz Transceiver Front End

• Cook et al., ISSCC 2006

• Active Area: 0.8mm2 • Zero external RF

components

Noise Factor vs. Power Consumption

CC2420 NF, 55mW

~2 mm^2 ASIC

Mote on a Chip? (circa 2001)

• Goals:– Standard CMOS– Low power– Minimal external components

uP SRAM

RadioADC

Temp

Ampinductor

crystal

battery

antenna

~$1

Single-chip 802.15.4 motes

• Atmel

• Chipcon (TI)

• Ember

• Freescale

• Jennic

• Oki

• …

System Cost, 2005

• Single-chip mote– Processor, memory

– 2.4G radio (not 802.15.4)

– Software?

Single-chip $1.50

Passives $0.20

PCB Assembly & Test $0.20

Battery $0.10

Total $2

Radio Performance

200k Bit rate (bps)100k 300k

I RX (

mA

)

5

10

20

15

25

X cc1000

Molnar 04 (0.4mA)

X

X cc2420

XOtis 05 (0.4mA)

Cook 06 (300 W)

X

With software:10 years D cell

With software:10 years coin cell

~4 mm^2 ASIC

Mote on a Chip

• Goals:– Standard CMOS– Low power– Minimal external components

uP SRAM

RadioADC

Temp

Ampinductor

crystal

battery

antenna

Security

Location

Time

Zero

RF Geolocation Performance

• 1 m of measurement error = 3.3 ns

Ranging in a Coal Mine Adit (Tunnel)

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

60

70

Distance (m)

Tim

e of

Flig

ht (n

s)

1 m Error

2 m Error

Ideal

Measured Data

Each point uses channel information derived from frequency hopping data

Die area, power• ADC

– Zero area, zero power• Digital

– 32 bit uP 1mm2 0.25mm2– Crypto - ~ uP– Dedicated datapath?– 0.25mW/MHz 50uW/MHz

• Memory– ROM & Flash 128kB/mm2 0.5MB/mm2– RAM 16kB/mm2 64kB/mm2– ~mW/MHz ~ uW/MHz

• RF– 2mm2 1mm2– 10s of mW 100s of uW

• Leakage– 10s uA @ 85C? <1uA @ 85C (circuit solutions; processes get worse)

Conclusion

• Today’s motes have more computational horsepower than many/most(/all?) of the first machines on the internet.

• Today’s motes have radios that have comparable performance to 1G cell phones.

• Network protocols that take advantage of these revolutions will have roughly the same hardware cost as those that don’t.

Cost of Sensor Networks

Time

$

Computing Power

Sensors

Installation, Connection and Commissioning

Mesh Networking

Oil Refinery – Double Coker Unit

• Scope limited to Coker facility and support units spanning over 1200ft

• Expanded to 27 units, implemented 14 to start

• No repeaters were needed to ensure connectivity

• Gateway connected via Ethernet port in control room to process control network

• Electrical/Mechanical contractor installed per wired practices

GW

Chevron’s Richmond Refinery

1 km

Standards

• IEEE 802.15.4

• Zigbee

• ISA

• HART

Low Data Rate WPAN Applications (Zigbee)

RESIDENTIAL/LIGHT

COMMERCIAL CONTROL

CONSUMER ELECTRONICS

TVVCRDVD/CDremote

securityHVAClighting controlaccess controllawn & garden irrigation

PC & PERIPHERALS

BUILDING AUTOMATION

securityHVAC

AMRlighting controlaccess control

mousekeyboardjoystick

PERSONAL HEALTH CARE

patient monitoring

fitness monitoring

INDUSTRIALCONTROL

asset mgtprocess control

environmentalenergy mgt

Zigbee

• Zigbee 1.0 ratified in 2004 • Great marketing tool, but…

– Nothing interoperable yet– “Zigbee” products typically aren’t

• Everything shipped to date is IEEE 802.15.4 + proprietary MAC

• Lost industrial automation in 2005• Losing building automation in 2006?• Fighting Zensys in home automation• Latest: Zigbee Pro

– “The stack that works” – Hot debate on frequency hopping

ISA SP100

• http://www.ISA.org/community/SP100• SP100.11

– Safety critical– Feedback control

• SP100.14– Monitoring– Latency-tolerant alarming

• CFP Conference last week

– ~25 proposals

– 2 universities• both from PRC

ISA SP-100 Proposals

• Still too early to call, but…– Winners

• 802.15.4 • TDMA• Frequency hopping

– Losers• RF site surveys• Point-to-point communication• Narrow band, high power• Zigbee

– Walking dead• Single-hop to wired infrastructure• Star-connected networks

• Truth and light appears to be winning!– Truth: the guys running the plants– Light: time synchronized, TDMA, channel hopping, mesh routing

• Tough battles– “We are at war with Dust Networks in industrial automation”

Star-mesh or Star-LAN

Q: Star-connectivity is known to be death for reliability, so why do it?

A: Don’t trust the motes, don’t think that they have the power to be routers.

Star-mesh or Star-LAN

What if WiFi gets jammed (easier to do than freq-hopping 802.15.4)?What if you lose ethernet? (power failure, cable, …)

Mesh, with backbone

Use powered infrastructure when you have it.Lower latencyLower power

But, if it goes away…

Mesh, with backbone

Assume that the motes are smart, and that their radios are good.Use protocols that leverage those capabilities:

Time-synchronized, TDMA, Channel Hopping MACMesh routing

Wireless Cost Profiles

Time

Cost

Wired System Cost

Star Wireless + Service

Self-Organizing Wireless + Simple Radios

Reduced Wiring Costs

Service Curve: Site Surveys and Expert Tuning

Technology Curve: Self-Organizing and Self-Optimizing

New Automation

Opportunities

“There’s good money to be made in RF site surveys” - Name withheld to protect the guilty

Wireless HART

• Highway Addressable Remote Transducer• 20 years old• HART today:

– Wired industrial automation protocol– 1200 bps digital communication on top of 4-20mA

analog communication line– Shipping ~3Million/year– ASP ~$1k– Installation cost (wiring dominated): ~$10k?

• Wireless HART group formed in 2004– 802.15.4 based– Time synchronized, TDMA, channel hopping, mesh

routing

Wireless HART

• Again, still too early to tell, but…

Truth and light appear to have won

Implicatons for Industrial Automation

• Cost of installation:sensor was 10:1, going to 1:10

• Size of sensor market will increase

• “New” requirement on sensors to be low energy per sample

• New applications possible– Condition-based maintenance– Tracking

Implications

• “For several years I was a skeptic, but I now believe that wireless mesh sensor networks will have higher reliability than wired sensors.”– Refinery technologist

• “Yup.” - ksjp

Next generation capabilities• Coming soon:

– 32 bit ARM; 1MB flash; 64kB RAM– 2.4GHz RF, bps to Mbps, ~1nJ/bit– ~ s synchronization across network– ~ 1 meter location accuracy– < 10mm2

– 1A in-network average current consumption

• Baby version– 32 bit ARM; 128kB Flash; 8kB RAM– Same RF, same power– 2mm2?