SMART DUST Hardware Limits to Wireless Sensor Networks

SMART DUST Hardware Limits to Wireless Sensor Networks Kris Pister Berkeley Sensor & Actuator Center Electrical Engineering & Computer Sciences UC Berkeley – pister@eecs. berkeley. edu (on leave to start Dust Inc – kpister@dust-inc. com) SMART DUST

• Ken Wise, U. Michigan SMART DUST http: //www. eecs. umich. edu/~wise/Research/Overview/wise_research. pdf

Bill Kaiser, UCLA • http: //www. janet. ucla. edu/WINS SMART DUST

Wireless dawn sensor SMART DUST

Computation Difference Engine Charles Babbage, 1822 Steve Smith, UCB SMART DUST

Multi-hop message passing SMART DUST

Lots of exponentials • • • Digital circuits • Speed, memory • Size, power, cost Communication circuits • Range, data rate • Size, power, cost Computation Communication MEMS Sensors • Measurands, sensitivity • Size, power, cost Sensing SMART DUST

Smart Dust Goal SMART DUST

COTS Dust - RF Motes • Simple computer • Cordless phone radio • Up to 2 year battery life N W E S 2 Axis Magnetic Sensor 2 Axis Accelerometer Light Intensity Sensor Humidity Sensor Pressure Sensor Temperature Sensor SMART DUST

Open Experimental Platform to Catalyze a Community Services David Culler, UCB Networking Tiny. OS We. C 99 “Smart Rock” Rene 00 Small microcontroller - 10 kb EEPROM storage (32 KB) Simple sensors Mica 02 Demonstrate scale - 8 kb code, 512 B data Simple, low-power radio Dot 01 Designed for experimentation -sensor boards -power boards NEST open exp. platform 128 KB code, 4 KB data 50 KB radio 512 KB Flash comm accelerators SMART DUST

800 node demo at Intel Developers Forum 4 sensors $70, 000 / 1000 Concept to demo in 30 days! SMART DUST

Structural performance due to multi-directional ground motions (Glaser & Cal. Tech). Mote Layout 1 3 1 54 6` 1 8 1 1 Mote infrastructure 1 5 29 Comparison of Results Wiring for traditional structural instrumentation + truckload of equipment SMART DUST

Cory Energy Monitoring/Mgmt System • 50 nodes on 4 th floor • 5 level ad hoc net • 30 sec sampling • 250 K samples to database over 6 weeks SMART DUST

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. SMART DUST

Last 2 of 6 motes are dropped from UAV • 8 packaged motes loaded on plane n Last 2 of six being dropped SMART DUST

Available Sensors • Demonstrated w/ COTS Dust • • Temperature, light, humidity, pressure, air flow Acceleration, vibration, tilt, rotation Sound Demonstrated Actuators GPS • Motor controllers Gases (CO, CO 2) • 110 VAC relays Passive Infra-red • Audio speaker Contact/touch • RS 232: LCD, … • Available • Images, low-res video • Gases (VOCs, Organophosphates, NOx…) • Neutrons SMART DUST

Blue Mote Hardware • • • Chipcon cc 1000 radio • RX Power: 9. 6 -14 m. A (-102 -> -105 d. Bm) • TX Power: 12 -25 m. A, (-5 to 4 d. Bm) range ~50 m indoors • Bit rate up to 76, 800 kbps TI MSP 430 Processor • ~1 m. A @ 4 MHz Operating Voltage 2. 1 -3. 3 V Sleep mode = 3 m. A Same damn 51 pin connector $50 -$100 SMART DUST

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” SMART DUST

Cost of Basic Operations Operation Current [A] 3 u 1 m 25 m Time Charge [s] [A*s] 20 u 5 m 20 n 125 m 10 m 8 m 80 m Sound an alarm 25 m 1 s? 25, 000 m? Listen for alarm 2 m 2 m 4 m Sleep Sample Talk to neighbor 15 byte payload Listen to neighbor 15 byte payload QAAbattery = 2000 m. Ah = 7, 200, 000 m. A*s SMART DUST

Typical Topologies Star Linear Tree SMART DUST

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 (m. J) RX 0. 24 TX 0. 375 Alarm Check 0. 012 Alarm Send 75 Number Per Day m. J per Day % of Total 17280 4147. 2 28% 23040 8640 59% 86400 1036. 8 7% 10 750 5% Total: 14574 Battery Life (years): 4. 1 SMART DUST

HDK Implementation Report Interval (user controlled, 0 to 256 seconds) Reporting Slots 32 ms Collect data from children Send to parent Periodic Alarm Message Checks Sensor Sampling ! Alarm Msg Forward SMART DUST

Time period definitions Report Interval (user controlled, 0 to 256 seconds) Reporting Slots 32 ms Tepoch tslot Periodic Alarm Message Checks talarm Sensor Sampling tsample SMART DUST

HDK Extrema • Max data rate through a single mote: 1 k. B/s • • Max data rate via linear multihop: 300 B/s Latency in multihop communication: n*tslot • • Alarm lifetime = talarm*Qbat/Qcheck Alarm latency < n*talarm • E. g. talarm = 0. 1 s; n=20; N=1, 000 àLifetime = 6 years àLatency < 2 s • “We’re all fine” lifetime = (Qbat / (Qmsg )* (Tepoch /(1+nkids)) • E. g. Tepoch = 20 min; nkids = 1000 Lifetime = 3 years SMART DUST

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 (m. J) RX 0. 24 TX 0. 375 Alarm Check 0. 012 Alarm Send 75 Number Per Day m. J per Day % of Total 17280 4147. 2 28% 23040 8640 59% 86400 1036. 8 7% 10 750 5% Total: 14574 Battery Life (years): 4. 1 SMART DUST

One Chip, Four Dissertations • CMOS ASIC • 8 bit microcontroller • Custom interface circuits • External components Temp ~$1 u. P SRAM Amp ADC Radio ~2 mm^2 ASIC battery antenna inductor crystal SMART DUST

Working silicon • • • 8 bit u. P 3 k RAM OS accelerators World record low power 8 bit ADC (100 k. S/s, 2 u. A) HW Encryption support 900 MHz transmitter Functional, running Tiny. OS, sending packets to Blue SMART DUST

Working mote, happy grad student Jason Hill Jason’s mote SMART DUST

Power and Energy • Sources • Solar cells ~0. 1 m. W/mm 2, ~1 J/day/mm 2 • Combustion/Thermopiles • Storage • Batteries ~1 J/mm 3 • Capacitors ~0. 01 J/mm 3 • Usage • Digital computation: n. J/instruction 10 p. J • Analog circuitry: n. J/sample 20 p. J/sample • Communication: n. J/bit 11 p. J RX, 2 p. J TX (optical) 10 n. J/bit RF SMART DUST

Energy and Lifetime • 1 m. Ah ~= 1 micro*Amp*month (m. Am) • Lithium coin cell: 220 m. Am • AA alkaline ~ 2000 m. Am (CR 2032, $0. 16) • 100 k. S/s sensor acquisition: 2 m. A • 1 MIPS custom processor: 10 m. A • 100 kbps, 10 -50 m radio: 300 m. A • 1 month to 1 year at 100% duty • 10 year lifetime w/ coin cell 1% duty • Sample, think, listen, talk, forward… 2 times/second! SMART DUST

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) H 2: 50, 000 Wh/kg (upper heating value) SMART DUST

Energy Considerations • Sensing • 1 p. J/S @ 10 bits • Power ~ 22 N f (re: 20 p. J/S @ 8 bits) Scott, Boser, Pister, An Ultra-Low Power ADC for Distributed Sensor Networks, ESSCIRC 2002. SMART DUST

Energy Considerations • Computation • Power ~ CV 2 f • C = N g C 0 • C 0 = er e 0 A/d ~ 5 f. F/mm 2 • For 8 bit ops, Ng ~100 • A ~ L d 2 • A = 0. 020 mm 2 today (Ld =0. 13) 10 p. J • A = 0. 001 mm 2 2010 (Ld =50 nm) 0. 5 p. J SMART DUST

RF Sensitivity • Pn = k. BT Df Nf • Sensitivity = Pn * SNRmin • e. g. GSM (European cell phone standard), 115 kbps k BT 200 k. Hz ~8 x SNR S = -174 d. Bm + 53 d. B + 9 d. B + 10 d. B = -102 d. Bm RX power = ~200 m. W TX power = ~4 W 50 u. J/bit SMART DUST

RF Path Loss • Isotropic radiator, l/4 dipole • Pr=Pt / (4 p (d/l)n) • Free space n=2 • Ground level n=2— 7, average 4 SMART DUST

N=4 From Mobile Cellular Telecommunications, W. C. Y. Lee Pt = 10 -50 W -102 d. Bm SMART DUST

Path Loss • Like to choose longer wavelength • Loss ~(l/d)n • 916 MHz, 30 m, 92 d. B power loss • need – 92 d. Bm receiver for 1 m. W xmitter • power! • Penetration of structures, foliage, … • But… • Antenna efficiency • Size – l/4 @ 1 GHz = 7. 5 cm SMART DUST

Output Power Efficiency • RF • Slope Efficiency • Linear mod. ~10% • GMSK ~50% • Poverhead = 1 -100 m. W Pout True Efficiency Slope Efficiency • Optical • Slope Efficiency • lasers ~25% • LEDs ~50% • Poverhead = 1 u. W-100 m. W Poverhead Pin SMART DUST

Limits to RF Communication Cassini • 8 GHz (3. 5 cm) • 20 W • 1. 5 x 109 km • 115 kbps • -130 d. Bm Rx • 10 -21 J/bit • k. T=4 x 10 -21 J @300 K • ~5000 3. 5 cm photons/bit Canberra • 4 m, 70 m antennas SMART DUST

Integrated Microwatt Transceiver, Howe/Rabaey, UCB • Radios need filters • The best filters are electromechanical • Power is related to size SMART DUST

Mike Sailor’s Smart Dust M. Sailor UCSD Chemistry SMART DUST

CMOS Cameras • Today • 5 mm scale • 1 m. J/image • 110, 000 pixels • Tomorrow • 1 mm scale • 50 p. J * #pixels / image ~ 1 u. J • 16 k pixels • Soon • 1 mm scale • 1 p. J * # pixels /image ~ 1 u. J • 1 M pixel SMART DUST

Single Nanotube Inverter - IBM Derycke, Martel, Appenzeller, Avouris; Carbon nanotube inter- and intra-molecular logic gates; Nano Letters, August 26, 2001 Atomic Force Microscope image showing the design of an intramolecular 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 ebeam lithography to expose part of the nanotube. Potassium is then evaporated through this window to convert the exposed ptype nanotube transistor into an n-type nanotube transistor, while the other nanotube transistor remains p-type. SMART DUST

Carbon Nanotube Circuits - Delft A. Bachtold, P. Hadley, T. Nakanishi, C. Dekker; Logic circuits with carbon nanotube transistors Science, 294, 1317 -1320 (2001). SMART DUST

Nano Dust? • Nanotube sensors • Nanotube computation • Nanotube hydrogen storage • Nanomechanical filters for communication! SMART DUST

Mobility • Walking • Hopping • Flying SMART DUST

Mobility SMART DUST

Milli-Millennium Falcon Increase thrust and decrease the mass, while controlling thermal losses SMART DUST

Thrust Measurements vs. Theory Predicted altitude: 50 m SMART DUST

Rocket in Action SMART DUST

Synthetic Insects (Smart Dust with Legs) Goal: Make silicon walk. • Autonomous • Articulated • Size ~ 1 -10 mm • Speed ~ 1 mm/s SMART DUST

2 Degree of Freedom Legs 1 st Link Motor 2 nd Link Motor 1 mm SMART DUST

Silicon Inchworm Motors 1 mm SMART DUST

Legs Linkages CMOS Motor Solar Cells Current Layout for Motor and Legs Motor 7. 6 mm SMART DUST

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Solar Powered Robot Pushups SMART DUST

Big Products from Small Workers SMART DUST

The Dark Side SMART DUST

Conclusion • Tremendous promise • More new questions than answers SMART DUST