SMART DUST Hardware Limits to Wireless Sensor Networks

1. SMART DUSTHardware 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)

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

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

4. Wireless dawn sensor

5. Steve Smith, UCB Computation Difference Engine Charles Babbage, 1822

6. Multi-hop message passing

7. Communication Computation Sensing 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

8. Smart Dust Goal

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

10. Services Networking TinyOS Rene 00 Mica 02 Dot 01 Demonstrate scale • 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 Open Experimental Platform to Catalyze a Community David Culler, UCB WeC 99 “Smart Rock” Small microcontroller - 8 kb code, 512 B data Simple, low-power radio - 10 kb EEPROM storage (32 KB) Simple sensors

11. 800 node demo at Intel Developers Forum 4 sensors $70,000 / 1000 Concept to demo in 30 days!

12. Structural performance due to multi-directional ground motions (Glaser & CalTech) . Mote infrastructure Mote Layout 14 5 ` 15 15 13 6 12 9 11 8 Comparison of Results Wiring for traditional structural instrumentation + truckload of equipment

13. 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

14. 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.

15. Last 2 of 6 motes are dropped from UAV • 8 packaged motes loaded on plane • Last 2 of six being dropped

16. 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, …

17. 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 mA • Same damn 51 pin connector • $50-$100

18. 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”

19. Cost of Basic Operations QAAbattery = 2000mAh = 7,200,000,000 mA*s

20. Typical Topologies Star Tree Linear

21. Cost Each (mJ) Number Per Day mJ per Day % of Total RX 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: 14574 Battery Life (years): 4.1 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

22. 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 Alarm Msg HDK Implementation

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

24. 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=1,000,000 • Lifetime = 6 years • Latency < 2 s • “We’re all fine” lifetime = (Qbat / (Qmsg )* (Tepoch /(1+nkids)) • E.g. Tepoch = 20 min; nkids = 1000  Lifetime = 3 years

25. Cost Each (mJ) Number Per Day mJ per Day % of Total RX 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: 14574 Battery Life (years): 4.1 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

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

27. 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

28. Working mote, happy grad student Jason Hill Jason’s mote

29. 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 pJ 20 pJ/sample 11 pJ RX, 2pJ TX (optical) 10 nJ/bit RF

30. Energy and Lifetime • 1 mAh ~= 1 micro*Amp*month (mAm) • Lithium coin cell: 220 mAm (CR2032, $0.16) • AA alkaline ~ 2000 mAm • 100kS/s sensor acquisition: 2mA • 1 MIPS custom processor: 10mA • 100 kbps, 10-50 m radio: 300mA • 1 month to 1 year at 100% duty • 10 year lifetime w/ coin cell  1% duty • Sample, think, listen, talk, forward… 2 times/second!

31. 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)

32. 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.

33. Energy Considerations • Computation • Power ~ CV2 f • C = NgC0 • C0 = ere0 A/d ~ 5fF/mm2 • For 8 bit ops, Ng ~100 • A ~ Ld2 • A = 0.020mm2 today (Ld =0.13)  10pJ • A = 0.001mm2 2010 (Ld =50nm)  0.5pJ

34. RF Sensitivity • Pn = kBT Df Nf • Sensitivity = Pn * SNRmin • e.g. GSM (European cell phone standard), 115kbps kBT 200kHz ~8x SNR S = -174dBm + 53 dB + 9 dB + 10 dB = -102 dBm RX power = ~200mW TX power = ~4W  50 uJ/bit

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

36. -102dBm N=4 From Mobile Cellular Telecommunications, W.C.Y. Lee Pt = 10-50W

37. Path Loss • Like to choose longer wavelength • Loss ~(l/d)n • 916MHz, 30m,  92dB power loss •  need –92dBm receiver for 1mW xmitter •  power! • Penetration of structures, foliage, … • But… • Antenna efficiency • Size – l/4 @ 1GHz = 7.5cm

38. Output Power Efficiency Pout • RF • Slope Efficiency • Linear mod. ~10% • GMSK ~50% • Poverhead = 1-100mW • Optical • Slope Efficiency • lasers ~25% • LEDs ~50% • Poverhead = 1uW-100mW True Efficiency Slope Efficiency Pin Poverhead

39. Cassini • Canberra • 4m, 70m antennas 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

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

41. Mike Sailor’s Smart Dust M. Sailor UCSD Chemistry

42. 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

43. 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

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

45. Nano Dust? • Nanotube sensors • Nanotube computation • Nanotube hydrogen storage • Nanomechanical filters for communication!

46. Mobility • Walking • Hopping • Flying

47. Mobility

48. Milli-Millennium Falcon Increase the thrust and decrease the mass, while controlling thermal losses

49. Thrust Measurements vs. Theory Predicted altitude: 50 m

50. Rocket in Action