Active RFID

Selecting an optimal radio frequency for operation of an Active RFID system requires consideration of several factors, including technical performance, regulatory issues, and co-existence with other technologies. This paper assesses a broad range of radio frequencies against these parameters, and presents rationale for the selection of 433 megahertz (MHz) as the optimal frequency for global use of Active RFID.

Active RFID and Passive RFID are two fundamentally different technologies, each with unique advantages. While often considered competing technologies, they actually complement each other, balancing cost and capability. Active RFID and Passive RFID offer tremendous potential for combined use within many applications, including air cargo and intermodal cargo management. Along with technical performance and regulatory issues, this opportunity for combined use must also be considered when selecting a frequency for Active RFID.

Because of the need to power the tag from the reader, Passive RFID uses very high radio signal levels, on the order of 1000 times as great as an Active RFID system. For example, Passive RFID systems within the 862 to 928 MHz band require up to 4 watts (4000 mW) of power to achieve a few meters of read range (hence the 4 watt power levels sought by standards initiatives such as SC 31). On the other hand, several commercially available Active RFID systems transmit less than one milliwatt for 100 meter range.

Additionally, Passive RFID readers transmit continuously for best performance. This combination of high-power transmissions and continuous operation causes Passive RFID systems to substantially interfere with any low-power systems operating in the same vicinity at a similar frequency, including Active RFID. Therefore, for best performance, a frequency other than those in common use for Passive RFID systems should be selected for Active RFID. Given the widespread use and expected adoption of 862 MHz to 928 MHz for Passive RFID, this is not an ideal band for Active RFID.

In regulatory parlance, Active RFID typically falls under the category of “Short-Range Devices” – low-power devices with a communication range typically of a hundred meters or less. Other devices in this category include keyless entry systems for vehicles and garage door openers. While there are many of these devices in operation throughout the world, by regulation they are designed to “share” their frequency band. This sharing of a frequency band is accomplished by 1) using a limited duty cycle to ensure other devices get “air time”, and 2) using retransmissions to overcome any temporary interference from other devices. Because of these design considerations, Active RFID is able to co-exist with these other short-range devices and operate reliably.

The practical result of the data presented above is that Active RFID systems are in global operation today, and 433 MHz is the most widely used frequency. This includes the largest deployment of Active RFID to date – a global supply chain visibility network operating at several hundred sites across more than 20 countries, tracking thousands of ocean, air, rail, and truck-based shipments daily. Within this system, 433 MHz Active RFID has been used reliably and effectively within day-to-day operations at ports, transportation terminals, warehouses, and other industrial facilities for more than seven years. In addition to proving its operational effectiveness, these implementations have also shown that 433 MHz Active RFID can be used without interfering with other systems in the same band.

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