In a traditional path-loss approach a fixed power level is transmitted, and the tag reader must possess the capability to measure the absolute power received--so a lot of intelligence, such as WiFi is required, which is a more costly technology and burns up a lot of power.

"Our approach is less costly, more forgiving and does not require line-of-sight," said Dr. Kevin Chung, CEO of Avante.

In Avante's weighed zoning approach the tag carries both the ID of the tag and the levels of the successive levels of signal strength sent. Rather than asking the reader to measure the absolute power levels, the relative power levels are measured instead. The physical location can then be deduced. The weighed zoning approach is said to provide a one-meter to three-meter locating capability for assets in indoor and outdoor facilities.

"Say it is a rainy day," said Chung. "So that all the losses would be higher. But all the readings will exhibit the same loss. Because Avante uses a weighted zoning approach to calculate the distance--it doesn't depend on accurately measuring absolute power levels--it still is able to deliver accurate fixes, with much less power than more traditional approaches." The need for this new system stems from the inadequacy of earlier real time locating system (RTLS) techniques, according to Chung. Traditionally, there have been two basic methods to determine the position of an asset tagged with an active RFID: The first is the traditional-triangulation, time-lapsed method. It uses the times of arrival of the response signals from the responding tag to a set of readers to deduce the position of the asset.

However, it requires more costly tags and readers that must exhibit nanosecond, internal-time clock accuracy. A second RTLS approach uses a "free space signal loss." However, neither of these methods are effective at locating assets in environments in which the signal paths between the tag and the reader is obstructed.

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