An Overview of PicoRadio and Smart Dust KD Kang

PicoRadio  Sensor networks collect and disseminate wide ranges of environmental data  Size, weight, cost & power consumption matter < 1cm 3, < 100mg, < $1, < 1uw Bluetooth > $10 & 100mw Range of a Pico node < 2m Self-configuring ad hoc networking is a must  Multihop routing

Main Properties of Sensor Networks – PicoRadio View  Low sensor data rates  Active duty cycle < 1%  Location info make things simple  Content- and location-based addressing

Protocol Support  Physical Layer Mudulation Coding & decoding  MAC Layer Avoid message intereference  Network Layer Determines the path for packet delivery

Multihop networks  Energy consumption proportion to r 4  Use several short intermediate hops  Communication cost dominates Communication-computation trade-off

Energy trade-offs  Network discovery & maintenance may consume more energy than actual data transmissions Proactive routing Reactive routing Hybrid, e.g., directed diffusion

Energy trade-offs  Standby power Send & receive consume a lot of power, but Low data rate Careful medium access control  Separate potentially conflicting transmissions in time and frequency/code domain More complex radio???

Dynamic voltage scheduling  Power consumption proportional to V 2  Aggressively reduce the voltage  Careful!  Turn-on takes time & power More efficient physical layer  Application semantics

Radio power saving  Frequency Broadband  Frequency hopping  Time Spreading Time synchronization required  Spatial Multiple antennas More expensive HW More antenna power consumption

Energy Harvesting

Smart Dust KD Kang

Objective  A few cubic “milimeter” size  No more than 10 uw power consumption  Float in the air  Swallow to examine your body  RF not viable Limited space for antenna High frequency Excessive power consumption  Optical transmission Requires much less power than RF when a LOS is available Space-division multiplexing necessary

Key ideas  Passive optical transmission techniques  Dust modes do not emit light  Use CCR (corner-cube retroreflector)  Requires an uninterrupted LOS  Inherently directional

Active transmitters  Enable peer-to-peer communication between dust motes  High power consumption Used for short duration burst-mode communication How to aim the beam toward the receiving part?

Collision problems  Uplink collisions May not be serious if  Dust motes are sufficiently separated  Transmissions are detected by different pixels  Collisions due to peer-to-peer communications can be more serious