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Why Zone-Based Real-time Location Systems Are Superior

For indoor applications, zone-based approaches provide far more reliable results than triangulation-based methods, and at a cheaper cost.
By Abraham Blonder
In order to compensate for the differences between the electronics of two readers, some companies use complex tuning procedures as part of their project implementation, while others employ patented double-pass measurements that make the system even more expensive. Some systems use ultra-wideband (UWB) technology in order to improve detection range, by utilizing short pulses over a broader spectral range, generally using higher frequencies (3.1 GHz to 10 GHz). All of these technologies suffer from multi-pass beams that reduce their localization accuracy.

TDOA-based systems are definitely more accurate than those based on RSSI. Their accuracy varies between 5 percent and 10 percent of the distance between the readers, depending on the respective systems and environments involved. In practical terms, in an indoor environment with partitions (such as offices or hospitals), four synchronized readers are required to cover approximately 15 rooms. The location accuracy with such systems, for indoor applications with partitions, varies between +/-2 meters (6.6 feet) and +/-3 meters (9.8 feet).

Since the triangulation results are expressed in x,y coordinates, ignoring the partitions, a localization accuracy of +/-2 meters or +/-3 meters can easily lead to localizing a person or object in the incorrect room.

Zoning Methods
Zoning methods can be used when the localization requirement is for a zone (room-level accuracy). Initially, zoning methods utilized a reader within each zone (room). Each reader's gain is tuned to receive only signals from tags within said zone. When used in open space, however, this method is not very accurate, as it is impossible to delimit the RF zones by virtual lines. Reflection and tag orientation can easily lead to locating the tag in an adjacent zone. Such errors, however, can be reduced by comparing the respective RSSI levels, though they can not be completely eliminated.

USER COMMENTS

Glenn Tamir 2011-08-25 01:44:20 PM
The important question however is , does the accuracy meet t It may be possible to achieve incredible levels of accuracy with certain active RFID systems. However, the question that often does NOT get asked is, what is the need of the customer and the application? Does it really matter if one system can show which floor tile an IV pump is sitting on if all the customer needs to know id where it is located in a general area??? It's not about hitting the bullseye but meeting the needs of the customer and the application.
Glenn Tamir 2011-08-26 12:58:08 AM
I Completely agree with this article In this very well-researched article, it is clear that the Second-Generation Zoning method is the least expensive and most reliable system for healthcare applications and other indoor environments. LogiTag Systems, Inc., which has been specializing in RFID technology since 2004, has designed it RTLS system called "LogiTrack" based on this very technology. Thank you for validating that the direction LogiTag has been pursuing is the right course to take. It is reassuring to know this and bodes well for our future as we enter the US Market.
Jack Vandenberghe 2011-10-05 11:12:34 AM
What about for a warehouse? I like this artilce and am just wondering how RTLS could be applied not to single rooms, but to a large warehouse area that is not partioned into rooms?

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