Berkeleys Mesh Network: Dust in the RFID Wind

UC/Berkeley scientists are perfecting a cloud of motes-tiny network sensors-to create reader-free RFID networks that can still find items.

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.

/zimages/6/28571.gifSymbol 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."

Next Page: RFID glitter falling from the sky.