Getting a tiny wireless sensor to work is hard enough. But the real challenge may be in pulling thousands of smart-dust motes-each with extremely constrained processing, memory and communications resources-into a distributed network that actually does something useful.
Motes thus far deployed by the Center for Information Technology Research in the Interest of Society (Citris) are based on Mica, a two-board system built from off-the-shelf components. One board contains sensors and power for a given application. It's married to a generic, wireless controller board that includes the processor, radio and memory. While there are many variants, a Mica system typically has an 8-bit processor that runs at 4 or 8 MHz, a few kbytes of program memory and a radio that receives and transmits information. A recent Mica variant, constructed by Intel Corp., uses an ARM core and the Bluetooth protocol.
Because the radios have extremely limited range, the motes communicate primarily with their neighbors. That's where TinyOS comes in.
The operating system is "really oriented around networking, which is inherently asynchronous," said David Culler, professor of electrical engineering and computer science at UC Berkeley. "It allows you to treat [motes] as a distributed system where computation is done across the whole network."
The next generation of motes will be based on custom chips. One design, dating to February 2002, is a complete sensor system on four tiny chips. It uses bidirectional optical communications and thus can't use TinyOS, which requires a radio. More recently, in February 2003, Citris researchers announced Spec, a 5-mm2 chip with an 8-bit microprocessor, 900-MHz radio transmitter, 8-bit A/D converter, 3 kbytes of RAM and custom silicon to accelerate TinyOS. But it still needs a battery, antenna, inductor and sensors.
Next up, says EE and computer science professor Kristofer Pister, are motes that will use "energy scavenging" from solar energy or vibrations and thus won't need batteries. The motes should only need about 10 microwatts, he said. Pister is CEO of motes startup Dust Inc.
"There's nothing new about mesh networking," Pister said; what's "magical" is doing it with incredibly constrained-resource devices."