Making sense of UWB RFID

Ubisense uses ultra-wideband sensors and existing wireless infrastructure to provide precise real-time location tracking.

By Bob Trebilcock, Editor at Large -- Modern Materials Handling, 10/15/2007

Each month, I write an e-mail newsletter focused on best practices in the factory and distribution center with John Hill, a principal at ESYNC. If you’ve been lucky enough to hear John speak at Georgia Tech, ProMat, or the North American material handling show, you know that he is a true innovator, one of the first proponents of bar codes, warehouse management systems and RFID in the supply chain.

A couple of weeks ago, John told me he was getting excited about real time location systems. RTLS systems use active and passive RFID technology to track the location of assets in a warehouse, factory, yard, port or even up and down a highway.

While Modern and John have been writing about RTLS for some time, what had captured John’s attention recently was ultra-wideband technology, or UWB, a technology that “provides users with the ability to locate an asset (or find a wandering patient in a hospital) with a simple push of a button,” according to John.

After his column came out, I got a call from Charles Sturman, vice president of marketing for Ubisense, an early provider of RTLS solutions using UWB technology out of Cambridge, England. Sturman offered to tell me more about UWB RTLS systems.

Learning about UWB 
One of the drawbacks of RTLS systems using active RFID tags is that they often require a separate infrastructure to track assets. If you buy that argument, then UWB may be an attractive alternative, since the solutions operate over an existing WiFi infrastructure to locate a tagged asset to within 3 inches of its actual location while providing a three-dimensional graphical representation of that asset on a computer screen.

The technology works, says Sturman, by placing sensors at strategic locations throughout a facility. Meanwhile, the assets being tracked—which can range from totes to work-in-process to lift trucks to patients in a hospital—are tagged with a small, compact low power tag that emits a pulse or broadband spectrum signal.

“Through ultra-wideband technology, the tags are transmitting across a range of frequencies in the spectrum. And since it’s a wide signal, we can transmit a very small amount of power,” says Sturman. What’s more, the sensors can connect to the software system that analyzes the signals through a standard Ethernet network. No separate infrastructure is required.

The signal is picked up by the sensors, which not only measures the time of arrival, but also an angle of arrival. “The combination of the two data points means that UWB is more accurate than other solutions and very, very robust,” says Sturman. “By mounting two or three tags on a lift truck, and adding an RFID tag to a pallet, we can tell you not only where the lift truck is located in a facility, but what’s on it and which way it’s pointing.”

Since UWB tags can update their location as often as 40 to 100 times a second, the system can provide a real-time graphical representation of assets moving through a facility in real-time: You can actually watch a representation of your lift trucks moving through your facility. The trade-off: the more frequently you update the image, the faster the tag battery loses power.

How is UWB being used today? 
One European logistics company uses the technology in conjunction with bar codes camera-based imaging systems to track the location of shipments as they move through its facilities.

The drawback? 
As John Hill pointed out, UWB tags are still relatively expensive, which may limit its use for now to high value assets. But it illustrates how RFID in the supply chain continues to evolve in interesting and surprising ways.