The first generation of active radio frequency identification (RFID) was the conventional battery-powered active RFID. As Peter Harrop, chairman of research and analyst firm IDTechEx, explains, the power source enables the tag to initiate a signal, give longer range, manage a sensor or otherwise improve on the capability of a passive (non-battery-powered) RFID tag. Second generation active RFID is what's known as a real-time locating system (RTLS), Harrop continues, "where people or things are located almost continuously from 30-300 meters away, usually by using many emitters. These are in the very rapid takeoff phase after the usual slow start with new technologies."
Today, however, there is also a third generation of active RFID, Harrop explains -- the Ubiquitous Sensor Network (USN), which is sometimes referred to as the Wireless Sensor Network (WSN). "The USN is characterized by the tag doubling as a reader and a so-called mesh network being used with a choice of sensors on each tag. It may be limited to 30 meters range and the tag may be rather like active RFID tags from ten years ago, even using AAA batteries, but this capability is still notable because it can make systems scalable, self-healing, affordable and extraordinarily capable."