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?
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