And is GPS considered a type of RTLS technology?
RTLS stands for real-time location system. An RTLS is any solution that can tell you where an asset, individual, vehicle or other object is located, in real time. RFID stands for radio frequency identification. Many real-time location systems employ active RFID technology. The active tags are set to send out a signal every few seconds or minutes (depending on how near to real time you want the information to be) and antennas pick up those signals. Software then uses triangulation or other methods to calculate each tagged object's position.
There are also real-time location systems that utilize other technologies. Sonitor offers a solution that uses active tags that transmit ultrasound signals instead of RF signals. One difference between ultrasound and RFID is that sound waves do not penetrate walls the way electromagnetic energy does. So if you wanted to know whether an object was located within a specific room, ultrasound systems could tell you that. With an RFID system, it can sometimes be difficult to determine if an asset is on one side of a wall or another.
There are also RTLS solutions that use infrared, a line-of-sight technology that can tell you where an object is located—but if that item is in a drawer or under a blanket, the system will not function. In many cases, infrared and active RFID are combined, in order to provide the benefits of being able to read through walls, as well as more precise location information when needed.
GPS technology, when integrated in a tag that includes some sort of transmitter (such as a cellular radio) to communicate a tagged object's identity and GPS coordinates, could be considered an RTLS technology, though most people do not refer to it as such.
—Mark Roberti, Founder and Editor, RFID Journal
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