Technology for tracking location in real time with RFID and Wi-Fi has matured, and offers new opportunities for asset management and safety systems. The indoor environment blocks GPS signals and makes location management within a large building problematic. An alternative is to leverage the indoor Wi-Fi infrastructure by adding RFID tags and middleware to develop a real-time location system.
Users realise improved asset utilisation and safety and reduced MRO (maintenance, repair, operations) spend.
Real-time locating systems (RTLS) track the location of assets in real time. The systems are used to track both assets and people. Systems use this location information to improve asset utilisation and efficiency. When tracking people, location information improves safety and event response.
RFID tags are attached to mobile equipment. RFID readers receive radio signals from the tags and use them to determine tag location. Depending on the technology, location accuracy varies from about a meter to twenty meters.
The systems are configured to update location information as often as the end-use application requires – ranging from seconds to hours. For supply chain and transportation applications, RTLS commonly uses GPS to identify asset location.
The location information is combined with RFID data and used in an application. This is effective outdoors, where GPS is available. Unfortunately, GPS signals do not penetrate into building interiors. Here, we focus on technologies for RTLS for onsite and indoor applications.
The components of an indoor RTLS include:
– RFID tags
– RFID readers
– A location engine that interprets the tag and reader data streams
– Application software that adds other value to the location information
Dedicated RFID readers read RFID tags. Also, Wi-Fi network access points (AP) can read Wi-Fi tags.
This results in different classes of technology deployment and location accuracy.
Choke Points. For room-level location, dedicated RFID readers are placed in the doorways where items enter or leave a room. Passive RFID tags respond to reader signals and the reader identifies tags (items) entering a room. The RTLS engine keeps track of what is in the room. When the reader reads the same tag again, the engine assumes the item left the room. This approach works with passive RFID tags. The other approach uses active tags. An issue with choke points is misinterpretation of events in which a tag approaches a door, but returns into the room.
Closest Access Point. Here, Wi-Fi RFID tags with increased range periodically broadcast. The Wi-Fi access points (AP) read the tags. As each AP forwards the tag information, the RTLS software tracks the closest AP to the asset and the associated location range. This area can be large and include multiple rooms. For an access point with a range of 70 feet and omnidirectional coverage, the location area is roughly 15,000 square feet. This approach does not provide sufficient accuracy for many applications.
Triangulation. With more APs and overlapping coverage, triangulation can be employed to refine location estimates. Here, the distance from the tag to the AP is calculated by measuring either signal strength or arrival times. The RTLS software uses the known locations of the APs and draws a circle of possible locations mathematically around the AP. Two APs have two circles and provide estimates that are more refined. A third AP narrows this further. Location accuracy improves as the density of APs increases. The physical properties of the asset and the building’s interior affects the signals and can reduce accuracy. Reflection, interference caused by multiple paths, and signal attenuation (the effect of the assets physical properties like size and material) degrade the location accuracy.
RF Fingerprinting. This adds information about the physical properties of the asset and building. A virtual grid map is created of the floor plan with all the APs. The APs gather real-world data regarding physical objects and building properties within a given area. This database becomes an RF fingerprint that predicts how the RFID signals will interact with the building. The fingerprint accounts for attenuation, reflection, and multiple paths. By compensating for the structure’s interference, RF fingerprinting is a more accurate location tracking technology. This proprietary technology requires vendor-specific Wi-Fi access points. For example, the Cisco Wireless Location Appliance uses RF fingerprinting technology for Wi-Fi clients and Wi-Fi-enabled RFID tags. Cisco claims it tracks mobile devices to within 3m – about the size of a typical office cube.
Mine Logistics. Mincom has applied RTLS technology to manage the traffic flow of haulers moving materials in the 3D labyrinth of tunnels within large, established underground mines. From a safety viewpoint, this technology helps avoid collisions. From a business viewpoint, it can improve the mine’s production capacity and revenue when the production constraint is hauler logistics.
Mine Safety. Tata Consultancy Services designed a device for mine safety that is now being deployed in partnership with Coal India in the Jhanjra coal mine in Eastern India. Using a combination of RFID and Wi-Fi technologies, the system tracks the location of each miner. The miner’s communication device has essentials, such as a battery and helmet lamp, but also contains an RFID tag with redundant communication via both Wi-Fi and medium wave radio.
The system’s aboveground component tracks miners throughout the entire underground network and can detect unusual situations. For example, if a miner has not moved within a specified time, the miner and location are flagged on a display.
RTLS has matured with suppliers of middleware and sensors specifically designed for location identification and tracking across a variety of different industrial applications. Users should consider these systems for improving safety, asset management, and MRO spend.
[Ralph Rio is Research Director Enterprise Software, ARC Advisory Group.]
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