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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.
The zoning method is mostly used for passageways (doors) or indoor environments, such as office spaces, hospitals and so forth. Tuning the reader for each room at the installation allows for precise and stable room-level accuracy. Even if a tag located close to a wall could be detected by the reader covering the adjacent room, the signal's intensity—after passing through the wall—would be significantly lower than that of the signal received by the reader within the same zone. The software application will thus consider that the tag is in the correct area.
Dynamic filtering is also used to further increase localization reliability. Such algorithms take into account the localization of the previous tag signals, in case of complex situations. Practically speaking, readers deployed using the zoning method, along with RSSI and sophisticated software, can warrant approximately 99 percent accuracy in tag localization, whether situated on a person or on an asset.
The communication protocols used by active tags for first-generation zoning systems are normally unidirectional—that is, they talk to the reader, but the reader can not call the tag ("tag talks first"). Such tags have the advantage of being rather inexpensive compared with other types of active tags. A zoning system's installation is simple and stable, which is also a cost-savings factor. The big disadvantage for this type of system is that it requires a single reader per room, which implies the device's cost, plus the expense of a network point and an electricity point.
The active tags employed in second-generation zoning systems are bidirectional—that is, they can both emit and receive signals. A single interrogator is installed and tuned to cover a large area—typically, a circle with a radius of 15 meters to 20 meters (49 feet to 66 feet), passing through several walls.
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