Real time location systems (RTLS) may be the fastest-growing RFID application most people have never heard of.

The market for these systems, which use active RFID or WiFi-enabled tags to track the location of assets in real time, reached $200 million in 2004. The market is expected to grow to $1.26 billion by 2011, according to Sathya Durga, a research analyst for Frost & Sullivan (877-463-7678).

Visibility and efficiency are driving the market. "If you look across manufacturing, logistics and transportation, there's a huge need for real-time information," says Durga. "The ability to more accurately track inventory with real-time information creates operational efficiency."

It helps, she adds, that "RTLS tags are getting cheaper by the day," which means the solutions are becoming more affordable.

While many RTLS use active RFID technology, not all active RFID tags are capable of providing real-time location information. Indeed, an RTLS tag is capable of doing more than a typical RFID tag.

"An active or passive RFID tag is only identified when it passes by a reader," explains Matt Armanino, senior vice president of corporate development for WhereNet (408-845-8500). "An RTLS tag, however, has the unique ability of being located in a real-time basis. An active RFID tag can't do that on its own."

That's because an RTLS tag is programmed to broadcast a signal identifying its location at regular intervals. That signal passes through software that sits on top of a network of RFID readers to calculate a location.

RTLS tags are applied to assets like lift trucks, parts bins and parts containers, work-in-process, trailers, shipping containers and rail cars. They are also being used to track the location of people in a facility.

"Any time you have important assets that are hard to find after you've moved them, there's an opportunity to use RTLS," says Michael Smith, business development manager at LXE. "As long as you have the ability to receive a ping from a reference tag at regular intervals, you can keep track of an asset."

How accurate is an RTLS? Depending on the technology, it can identify the location of a tagged asset to within as few as five feet. But not all applications require that degree of accuracy (See "Five types of location tracking," below).

In addition to identifying the location of the different types of assets, RTLS can perform other functions. For instance, sensors have been added to RTLS tags on refrigerated trailers in the yard of a wholesale grocer. The tags track the location of trailers; the sensors monitor the temperature inside the trailer and transmit a signal if the temperature inside goes out of an acceptable range.

Automakers have put buttons on the tags they install on parts bins in a lean manufacturing system. Press the button, and it sends a signal to have a lift truck driver bring another bin to that location to replenish the line.

The solutions can not only track the location of assets, but notify a supervisor if those assets are in the wrong place. "If a specific lift truck is in aisle 12 in the northwest corner of a building, and it's supposed to be in aisle four, the tag can page a person to redirect the forklift operator," explains Joshua Slobin, director of marketing for AeroScout (650-571-0800).

Finally, RTLS can be used for security purposes. "You may want to know if an expensive piece of test equipment or inventory is leaving the floor," says Mike Braatz, vice president of marketing for Pango (508-626-8900).

There are two types of RTLS technology in the market today, according to Mike Dempsey, general manager of Navis (510-267-5000). "One type involves proprietary active RFID tags and a software engine to determine where the asset sits," says Dempsey. "The other involves WiFi-enabled tags that can communicate over an existing 802.11 wireless network."

Both technologies have their pluses and minuses, as well as their supporters and detractors.

Active RFID tags, while more expensive to implement, provide a higher degree of location accuracy. They can also be employed over wider areas because of their broadcast range, like ports and trailer yards. "The key for our customers is that an active tag can locate an asset within 10 feet or less," says WhereNet's Armanino. "That accuracy allows them to automate processes that used to be done manually."

The advantage to WiFi RTLS solutions is that they may work over an existing wireless infrastructure—reducing the cost of implementation. It also enables two-way communication between the chip and system.

"A WiFi-enabled tag can hop onto an existing WiFi network and send a signal to the network that can be forwarded to an RTLS server," explains Tuomo Rutanen, vice president of business development for Ekahau (866-435-2428). "And be-cause WiFi is a two-way system, we can talk to the tag and tell it to do things."

For example, the system can tell the tag to blink lights or play a ring tone if it's been on the dock for too long or if it's in a zone it shouldn't be.

Inside a DC or plant, RTLS track pallets, containers and work-in-progress.

For instance, I.D. Systems (201-996-9000) installs solutions to track lift trucks and powered materials handling equipment in real time. The next step, says Greg Smith, vice president of marketing, is to integrate that solution with a lift truck-mounted RFID reader to read passive tags on cartons and pallets. The RTLS tag can keep track of the lift truck moving an asset, while the reader on the lift truck reads the tags on the pallet. "The interface exists to do that today," says Smith. "What hasn't been done yet is to sit down with a customer and work out the complex business rules that would apply to that type of scenario."

Likewise, RF Trax (281-276-5900) has installed GPS devices to track of rail cars in real time; RFID readers inside the cars can identify the contents being shipped. "If a locomotive driver slams two cars together, the system can not only identify the location of the cars in the middle of Montana, but also which pallets are inside those cars," says Fred Barrett, vice president of product development.

Similarly, Argo Tracker (502-202-2700) has implemented GPS tracking devices that include a USB port for expansion. "A user can expand the application by plugging an RFID reader or Zigbee device into the GPS device and get complete asset accountability down to the item level," says CEO Mike Hammons.

While some of these expanded solutions are here today, and others are still being developed, they may deliver on the promise of RFID to deliver real-time visibility across the supply chain.