Berkeleys Mesh Network: Dust in the RFID Wind

By Renee Boucher Ferguson  |  Posted 2006-11-03

Berkeleys Mesh Network: Dust in the RFID Wind

UC/Berkeley researchers have created tiny wireless "motes"—aka network sensors—that use radio signals to communicate where they are located in physical space.

The end 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 UC/Berkeley who made a name for himself with his 1997 development of technology called Smart Dust—a self-organizing network of tiny wireless "motes."

"There was a lot of industry demand, so we started a company and now were shipping products that let you network [sensors]," Pister said. "The next thing is that these sensors can figure out where they are in 3-D and measure their location."

In January 2003 Smart Dust was commercialized when Pister co-founded Dust Networks.

Now Pister is back at Berkeley full time, working with graduate student Steven Lanzisera on this next phase of sensor network innovation, dubbed RF Time of Flight.

It could have a huge impact on the ubiquitous use of RFID—a technology that has struggled to gain widespread adoption despite backing by Wal-Mart—the worlds largest retailer—and the U.S. Department of Defense.

Pister believes that 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 at 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 broadcasted 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 and find one another, form a network, 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.

Symbol to bridge Wi-Fi and RFID. Click here to read more.

Then a dozen (or 100,000) motes come into the network, set up a multi-hub 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.

"If you know a range to a bunch of different points then you know where you are," said Pister. "Even if that range is moving you can still do the math and figure out where you are at that point."

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, bi-directional wireless technology, and an antenna and 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."

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Pister said Dust Networks has an advantage over its competitors—Cross Bow, Millennial, Ember—in that its components burn less power, providing a decade of life for a D-cell battery, for example.

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 ever-smaller size.

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

"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, in Scottsdale, Ariz.

"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."

Though its taken a while for the Smart Dust concept to prove out, Emerson Electric Co. announced in October that it would use Dust Networks 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 Emersons Rosemount division.

"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 sees asset tracking as 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 Department of Defense). 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.

RFID vendors raise the stakes with new products. Click here to read more.

"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 capability on a square millimeter silicon chip by the summer of 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."

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