Real-time locating systems, (RTLS), use a variety of tags defined by the technlogy that reads them. Active or passive RFID Tags can also be used in a Real Time Location System.
1. Ultra-Wide-Band Location Tags (UWB): Ultra-wide-band (UWB) readers transmit a very wide pulse over a GHz of spectrum. The readers then listen for chirps from the ultra-wide-band tags. These tags have a spark-gap-style exciter that generates a little pulse within them, which creates a short, coded, very wide, nearly instantaneous burst. The readers then report very accurate time measurements from the tags back to a central server. UWB systems are most commonly used inside of barcode scanners for use in warehouses and other sophisticated supply chain applications. When someone goes to scan a box during inventory, pulling the trigger of the scanner both reads the barcode and sends out a UWB pulse. The system then localizes precisely where the item is—down to one centimeter of space—based on that pulse. If you are looking at an ultra-wide-band system, there are a few things to consider. First, while all of the frequency transmitted gives you tremendous accuracy, but has a weak signal, so the frequency doesn’t interfere with electronics in the area (i.e., cell phones, WiFi, etc.). This means the range of ultra-wide-band is pretty low. Second, it requires careful calibration, which makes installation complex. And finally, if you use a UWB system, you need a good data connection, because the system is passing a lot of real-time information around. Thus, you need to synchronize all the readers together with very stable and low-jitter IP networks.
2. WiFi Location Tags: A highly energy efficient protocol first introduced in 2010. It allows devices to run for several years on tiny coin-cell operated batteries. Due largely to the simplicity of the technology, Bluetooth-based beacons can be created quickly and for a lower cost than competitors.
3. Infrared Location Tags: There’s nothing very technical about infrared tags, as they’re simply transmitting codes with light, and that code is picked up from ceiling-mounted readers. While this requires extensive infrastructure, it’s very simple in a technological sense. The benefit to this is that infrared RTLS solutions are pretty foolproof. They use light instead of radio waves (is there really a difference?), so this solution can’t go through walls. This is a benefit when it comes to RTLS because if the system says an asset is in room 4B, it is in room 4B without a doubt. Radio-based systems have more trouble with false positives, as the radio waves can sometimes be picked up by other readers through walls. As an aside, it’s not common to see an infrared RTLS solution by itself; it’s often paired with either an active RFID or a WiFi system to cut down on those systems’ issues with inaccuracy.
4. Passive Location RFID Tags: Passive RFID tags are very short-range and require many high-power readers in order to function as a real-time location system. The benefit is that passive RFID tags are by far the least expensive of all real-time location systems. There is some hesitancy in the medical space to have so much RF energy in the vicinity, making passive RFID less common for some medical use cases and more common at airports (for luggage tracking), shipping facilities (for box and pallet tracking) or in stores and libraries (for anti-theft or point-of-sale metrics). KitCheck is an exemption and a great example of how to use passive RFID in the medical space. This company creates boxes that you put pharmaceutical trays (from a crash cart, for instance) inside of, and at the click of a button, it will tell you what is missing. Everything in the box has a passive tag on it, and this box acts as the high-power reader.
5. Active RFID Location Tags: Active RFID tags transmit a short-range radio signal. Readers pick up this signal and measure the received signal strength (through either a one-to-one match or a trilateration between multiple readers) to get a location for the asset. Some active RFID systems like AirFinder use iBeacon tags for a few reasons. First, they’re ubiquitous and can be found anywhere. Second, they are inexpensive and only cost between $2 and $10 apiece. Third, iBeacon tags aren’t proprietary. But with all that said, there’s nothing special about using a BLE (Bluetooth Low Energy) tag of any sort, as any low-power radio tag will do. One of the considerations for active RFID is that readers may pick up signals through walls or floors, making it more prone to false positives than, say, an infrared location system may be. A great deal of the hard work on our AirFinder system has gone into creating sophisticated algorithms to calm down the floor and room hopping.
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