By Mary Catherine O'Connor

Jan. 23, 2006—Radio frequency identification is no longer just about identifying things and people. It's also about locating them, monitoring their environment and making sure they're safe. As wireless devices get more sophisticated and wireless networks grow larger and more nimble, RFID tags are being used with a range of other sensors, enabling end users to know not only what things are, but also where and how they are. As they converge with other technologies, RFID devices are being used to communicate not only ID numbers or other static data, but also dynamic, changing data supplied by sensors. And RFID devices aren't always using air-interface protocols created specifically for RFID. Instead, they may be using other air-interface protocols designed for wireless networks, such as Wi-Fi and ZigBee.

Wireless sensor networks (WSNs) are made up of groups of small devices, called nodes or motes (basically, very small nodes), that have three jobs: sense, compute and communicate. To achieve these functions, each device contains a battery, a radio transceiver (for communication), one or more sensors (to measure such things as temperature, humidity or light) and a microprocessor (to store data and control the sensor or sensors attached to the apparatus). The nodes in a WSN communicate with each other over peer-to-peer communication scheme by sending and receiving data to any nodes within their communication range. This enables the nodes to form mesh, or ad hoc, networks that can self-organize. Typical RFID networks, by contrast, include RFID tags, or sensors, that communicate directly to a single interrogator.



The convergence of RFID with ZigBee and Wi-Fi networks is changing the basic notions of what makes an RFID device. All devices in a wireless sensor network, whether ZigBee-compliant sensors, Wi-Fi location tags or sensor pods linked by a nonstandard wireless protocol, have some type of identification number, such as a media access control (MAC) address—the unique identifier built in to computer Ethernet cards and other types of networking equipment. This number can be used to identify and locate the object to which the sensor is associated, making it a de-facto RFID device. Cisco Systems offers a Wireless Location Appliance utilizing MAC numbers to locate assets within defined areas in which Cisco Wi-Fi access points are installed.