Mobile Networking for Smart Dust

1. Mobile Networking for Smart Dust J.M. Kahn, R.H. Katz and K.S.J. Pister Department of Electrical Engineering and Computer Sciences University of California, Berkeley Berkeley, CA 94720 Supported by DARPA MTO MEMS Program

2. Outline Smart Dust What is it? Applications Power Management Delivery and Interrogation Smart Dust Networking Radio-frequency communication Optical communication: passive dust mote transmitters Optical communication: active dust mote transmitters Summary

3. Smart Dust A dust mote is an autonomous node incorporating sensing, computing, communications and a power source in a mm3 volume A collection of dust motes is dispersed throughout an environment Dust motes use wireless communication to relay information to a base station over distances of 10s to 1000s of m

4. Smart Dust Mote

5. Applications of Smart Dust Civilian Surveillance Meteorological or geophysical monitoring Non-invasive measurement Measurement in hostile environments Military Stealthy monitoring of hostile environments Perimeter surveillance Chemical or biological monitoring Identification of friend or foe

6. Power Management Sources Solar cells Thermopiles Storage Batteries ~1 J/mm3 Capacitors ~1 mJ/mm3 Usage Digital control: nW Analog circuitry: nJ/sample Communication: nJ/bit

7. Delivery and Interrogation Delivery Systems Manual Micro air vehicle Projectile Wind-borne (�maple seeds�) Interrogation Hand-held �binoculars� Micro air vehicle

8. Radio-Frequency Communications Pros Long range Line-of-sight path not required Not severely affected by rain, fog or atmospheric turbulence Cons Antenna may be too large for dust motes Requires modulator, demodulator, filtering (power consumption) Requires complex multiplexing scheme (TDMA, FDMA, CDMA)

9. Corner-Cube Retroreflector Fabricate CCR using MEMS technology. Light striking within about �30� of body diagonal undergoes 3 bounces and returns to source in a narrow beam (<< 1�). Can deflect one mirror electrostatically, modulating return beam at up to ~10 kbps. Dust mote can transmit passively: without radiating energy and without aiming beam.

10. First-Generation Dust Mote

11. Optical Communication UsingPassive Dust Mote Transmitters

12. Optical Communication UsingPassive Dust Mote Transmitters (cont.) Requires each dust mote to have a line-of-sight path to the base station. Uplink transmissions are multiplexed using space-division multiplexing.

13. Optical Communication UsingPassive Dust Mote Transmitters (cont.) Protocol Dust motes are asleep. Base station broadcasts a wakeup/query, then a periodic interrogating signal synchronized to its camera. Dust motes wake up, transmit simultaneously to base station, synchronized to its camera. Reliability Dust mote positions and orientations are random, and some are not in field-of-view of base station. To insure coverage, use an excess of dust motes. Base station is only single point of failure.

14. Optical Communication UsingPassive Dust Mote Transmitters (cont.) Pros Dust motes need not radiate power, nor steer beam Exploits asymmetry: powerful base station, low-power dust motes Utilizes space-division multiplexing Only baseband electronics are required Cons Requires line-of-sight path to base station Short range (up to about 1 km) Bit rate limited to about 10 kbps Affected by rain, fog, atmospheric turbulence

15. Active Dust Mote Transmitter Beams should have divergence << 1� and be steerable over a hemisphere.

16. Optical Communication UsingActive Dust Mote Transmitters Base station uses CCD or CMOS camera (up to 1 Mbps) Using multi-hop routing, not all dust motes need to have a line-of-sight path to the base station.

17. Optical Communication UsingActive Dust Mote Transmitters (cont.) Minimizing transmitted energy/bit: Dust mote should transmit in short bursts at high bit rate Link Acquisition Need protocols for dust motes to aim their directional transmitters at other nodes Dust motes should execute raster scan using a narrow (not wide) beam

18. Optical Communication UsingActive Dust Mote Transmitters (cont.) Link Non-Reciprocity Arises because dust motes use directional transmitters but non-directional receivers May cause a dust mote to waste power transmitting to nodes unable to receive from it. A dust mote should transmit only to nodes that acknowledge its transmissions. May cause collisions at dust motes during mote-to-mote communications. Routing How to acquire, propagate and update routing information?

19. Optical Communication UsingActive Dust Mote Transmitters (cont.) Pros Longer range than passive links (up to about 10 km) Higher bit rates than passive links (up to about 1 Mbps) With multi-hop, avoids need for every dust mote to have line-of-sight path to base station Utilizes space-division multiplexing Only baseband electronics are required Cons Requires protocol to steer directional transmitters Requires higher power than passive transmitter Affected by rain, fog, atmospheric turbulence

20. Atmospheric Turbulence Enhancing signal detection reliability Adaptive optics on imaging receiver Spatial receiver diversity (multiple receivers) Temporal receiver diversity Maximum-likelihood sequence detection based on Markov model of scintillation process Interleaving and forward error correction

21. Summary Smart dust motes incorporate sensing, computation, communications and power in a mm3 volume. Free-space optical communication offers advantages in terms of size, power and network throughput. Passive dust mote optical transmitters: Use corner-cube retroreflector Consume very little power Require line-of-sight path to base station Active dust mote optical transmitters: Use laser and beam-steering mirror Enable higher bit rates, longer ranges, multi-hop routing