Cutting Out the Middleman

Scientists are perfecting tiny network sensors for reader-free RFID networks.

UC Berkeley researchers have created tiny wireless "motes"—or network sensors—that use radio signals to communicate where theyre at in physical space. The goal: an RFID network that could revolutionize the industry with its ability to locate tagged items without the aid of readers.

"What we showed in the university was that you could network together a lot of sensors," said Kristofer Pister, a professor of electrical engineering and computer science at the University of California, Berkeley, who made a name for himself with his 1997 development of technology called Smart Dust—a self-organizing network of tiny wireless motes.

"The next thing is that these sensors can figure out where they are in 3-D and measure their location," Pister said.

Smart Dust was commercialized in January 2003, when Pister co-founded Dust Networks. Now, Pister is back at UC Berkeley full-time, working with graduate student Steven Lanzisera on this next phase of sensor network innovation, dubbed RF Time of Flight. The technology could have a huge impact on the ubiquitous use of radio-frequency identification, which has struggled to gain widespread adoption despite strenuous backing by Wal-Mart—the worlds largest retailer—and the Department of Defense.

Pister said he believes location estimation using RF Time of Flight will finally enable RFID to live up to its promise of tracking items in real time.

"The sound bite on RFID is that most people think its going to tell them where their stuff is all the time. In fact, what RFID does is tell you where your stuff was the last time it went through a reader successfully," said Pister. "Contrast having to put in readers everywhere you want [information] to just having the tags know where they are and having that broadcast every few feet."

To understand RF Time of Flight, one has to go back to the basics of Smart Dust. Smart Dust refers to motes laid out in a mesh network that search for and find one another, form a network, and then communicate information back and forth.

To set up a mesh network in a hospital or warehouse, for example, three access points are placed at random points and connected wirelessly to an interrogator, "like a little USB thing that you plug into your computer," said Pister. Then a dozen (or 100,000) motes come into the network, set up a multihub mesh, and start to communicate and report their nearest range. Measuring the distance from one mote to the next provides a reading of where tagged items are.

RF Time of Flight adds radio communication and ranging capability.

Intended to be about the size of a grain of sand or a piece of dust—the motes from Dust Networks are currently about the size of a quarter—the motes contain sensors, computing circuits, bidirectional wireless technology, and an antenna and a very low-battery power supply that are external to the chip. The motes can detect light, temperature or vibrations.

"About an inch on the side is the size of most commercial motes out there today," said Pister. "We all use the same antenna, so thats not a differentiator. The key question is who can use the smallest battery, and that has to do with how much power you burn."

Pister said Dust Networks has an advantage over its competitors—Cross Bow Technology, Millennial Net and Ember—in that its components burn less power, providing a decade of life for a D-cell battery, for example. Pister said he hopes to develop a "truly single-chip mote" within the next three years that will put a solar cell into the silicon chip itself, obviating the need for an external battery and shrinking the mote down to an even-smaller size.

Adding a power source directly to a mote would "really be a breakthrough," said Marlene Bourne, president and principal analyst at Bourne Research, in Scottsdale, Ariz.

"I dont think we are ready to take a handful of sensors—like a handful of glitter—and drop them out of an airplane and they read information," said Bourne. "Right now, theyre limited by the size of the battery. There are some solar-based approaches and some completely different approaches that could feasibly allow Smart Dust to be just that."

Although its taken a while for the Smart Dust concept to prove itself, Emerson Process Management announced in October that it would use Dust Networks TSMP (Time Synchronized Mesh Protocol)—the underlying system for the motes—as the communications technology used in its Smart Wireless field networks and software.

"Self-organizing mesh networking is one of the most exciting innovations to come along in the process industry in over 30 years," said Steve Sonnenberg, president of Emerson Process Managements Rosemount Division, in Chanhassen, Minn. "We have tested a number of wireless sensor networking technologies in real-world industrial environments over the last three years and have found that Dust Networks TSMP technology best meets the reliability, security, long battery life and ease-of-use requirements demanded by our end users."

Pister said asset tracking is the biggest application area for RF Time of Flight, from tracking patients and doctors in a hospital to tracking assets in a theater of war (particularly since early Smart Dust funding came from the DOD). But he also sees many other potential areas of use.

"Imagine if we put this capability into cell phones or Palm Pilots and kids start using it to find each other at the mall or on campus," said Pister. "In addition, they can leave little notes that are triggered by proximity to a restaurant or make-out spot. Somebody with a good consumer application could turn the corner in a matter of a year."

The time frame for an actual product could be relatively soon. Pister expects to have RF (radio frequency) capability on a square millimeter silicon chip by summer 2007.

"We will show that even little chips running on not very much power can measure their distance with three points of reference," said Pister. "[Whats needed] is someone finding an application for that technology. I do think RF Time of Flight is going to be a big deal and [will] give people the localization capability that delivers on the promise of RFID. But it will take creative people getting the applications right. The technologys almost ready."