Asset tracking uses tags on equipment, inventory or people and a network of readers or receivers to record where those tags are. The right technology depends on what you need to know: that an item passed through a doorway, which room it is in, or where it sits to within a metre. Start with that question, because the answer drives the tag type, the infrastructure and the cost.
Three questions to answer first
- What are you tracking? Pallets, tools, medical pumps, laptops, vehicles and people all have different sizes, values and surfaces to mount tags on.
- What level of location do you need? Presence at a checkpoint, zone or room-level location, or precise position.
- How often do you need an update? Once when an item leaves a building, every few minutes, or continuously in real time.
A warehouse that needs to know which dock door a pallet left through has very different needs from a hospital that wants to find the nearest available infusion pump.
The main technologies
Passive RFID
Passive tags have no battery. A reader sends out a radio signal, the tag uses that energy to reply with its identifier. Tags are cheap and thin enough to go on labels.
- Low frequency (LF) and high frequency (HF, including NFC) read at short range, from touching to a short distance. Common in access cards, library systems and tap-to-check-out tools.
- Ultra-high frequency (UHF) reads from several metres away and can read many tags at once. Common for inventory, pallets and portal readers at doorways.
Passive RFID tells you where a tag was last read. It does not track items between readers. It works best at chokepoints such as doors, dock bays and conveyor lines, or with handheld readers for cycle counts.
Active RFID and BLE tags
Active tags have a battery and transmit on their own. Bluetooth Low Energy (BLE) tags are now the most common form. Receivers, or access points with built-in BLE radios, pick up the signal and estimate location from signal strength. This typically gives zone or room-level location and works well for finding mobile equipment across a building. Battery life is a planning item: tags need to be checked and replaced on a schedule.
WiFi-based location
Some systems locate WiFi devices or WiFi tags using the existing access points. Accuracy depends heavily on access point density and placement, and is generally zone-level. It is attractive when the WiFi network is already designed with location in mind.
Ultra-wideband (UWB)
UWB measures precise timing between tags and anchors and can locate tags to well under a metre in good conditions. It needs its own anchor network and careful installation, and is used where precise position matters, such as tool tracking on production lines or vehicle and forklift tracking.
| Technology | Typical location | Tag power | Good fit |
|---|---|---|---|
| Passive HF / NFC | Touch or very close | None | Check-out, access, identification |
| Passive UHF | Checkpoint or read zone | None | Inventory, pallets, doorways |
| BLE / active RFID | Zone or room | Battery | Mobile equipment, staff duress |
| UWB | Sub-metre | Battery | Precise tracking, vehicles, tools |
What gets in the way
Radio-based tracking is affected by the building and the items themselves:
- Metal and liquids reflect and absorb radio energy. UHF tags on metal assets need special on-metal tags, and tags on fluid containers may read poorly.
- Structure. Concrete, steel racking and metal shelving create reflections and shadows that affect accuracy.
- Tag placement. A tag on the wrong side of an asset, or covered by a hand, may not be seen.
- Interference. BLE shares the 2.4 GHz band with WiFi and other devices. See common sources of WiFi interference.
These are reasons to pilot in a representative area before rolling out across a site.
The parts of a tracking system
- Tags suited to the asset, its surface and its environment
- Readers, receivers or anchors, with mounting locations and power (often PoE)
- Network connectivity for every reader, with its own VLAN if needed
- Location engine or middleware that turns reads into locations
- Integration with the system that uses the data, such as an asset register, ERP, maintenance or nurse call system
- A process for tagging new assets, retiring old tags and replacing batteries
Readers and receivers usually draw power from the network; see Power over Ethernet (PoE) for power budget planning.
Plan the process, not just the hardware. Most tracking projects that disappoint fail on process: assets that never get tagged, tags that fall off, batteries nobody replaces and data nobody looks at. Decide who owns the system before you buy it.
Combining tracking with WiFi
Many enterprise access points include BLE radios that can act as receivers, which saves a separate network. This works if the WiFi design accounts for location as well as coverage: location usually needs access points spread around the perimeter of an area, not just placed where coverage is easiest. If tracking is in your plans, raise it before the WiFi design is finalized. Our WiFi for healthcare and WiFi for warehouses guides touch on this for those settings.
How ehZee can help
RFID and asset tracking are part of the "extras" section of our WiFi survey checklist, so we ask about them early. Through our WiFi design and build service we can plan the wireless network, cabling and reader locations together, and verify coverage for both data and tracking.
Common questions
Can passive RFID tell me where something is right now?
Only where it was last read. If you need continuous location between checkpoints, you need an active technology such as BLE or UWB, or many more readers.
Can our existing WiFi do asset tracking?
Sometimes, if the access points support BLE or location services and are placed in a pattern that suits location. A survey will show whether the current layout is good enough for the accuracy you need.