Installation guide

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Wi-Fi Location-Based Services—Design and Deployment Considerations
OL-11612-01
RFID Tag Considerations
Figure 63 Transponder Active RFID Tag
These RFID tags are usually mounted on the windshield or other unobstructed area of the vehicle. On
approaching a tollbooth or choke point containing a tag exciter, the electromagnetic field of the exciter
activates the RFID tag transmitter. The transponder active tag responds by beaconing its unique ID to
the tag reader while the vehicle remains within range, as illustrated in Figure 64.
Figure 64 Active RFID Tag Toll Reporting
This technique provides for detection of the tag and conserves active tag battery life by having the tag
beacon its unique identifier only when it has been activated by an exciter. Typically the beacon duration
is set by a preprogrammed internal timer. After the transmission interval of the transponder active tag
has expired, it returns to the suspended mode unless once again activated by an exciter.
802.11 Active RFID Tags
802.11 (Wi-Fi) active RFID tags (shown in Figure 65) are designed to operate in the unlicensed ISM
bands of 2.4–2.4835 GHz or 5.8 – 5.825 GHz (802.11 active RFID tags currently manufactured and
available at publication are limited to 2.4 GHz).
These tags exhibit the features of active RFID tags as discussed previously but also comply with
applicable IEEE 802.11 standards and protocols. Wi-Fi RFID tags can readily communicate directly
with standard Wi-Fi infrastructure without any special hardware or firmware modifications and can
co-exist alongside Wi-Fi clients such as laptops, VoIP wireless phones, and so on. Although assets
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Reader
System
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Antenna