Definition
RTLS (Real-Time Location System) achieves indoor meter-level positioning through technologies such as active RFID and BLE AoA, used for managing assets like medical equipment, warehouse materials, and tooling fixtures, supporting geofencing, entry/exit statistics, and tamper alarms.
Technical Solutions
RTLS positioning technologies include: active RFID triangulation; BLE 5.1 AoA/AoD angle-of-arrival positioning (centimeter-level); UWB ultra-wideband (high precision); Wi-Fi fingerprinting (using existing APs). Tags/beacons are attached to assets or personnel, and base stations/gateways receive signals and calculate positions, reporting to the platform. Complementary to outdoor GNSS positioning, forming an integrated indoor and outdoor solution.
Use Cases
Healthcare: equipment, medication, and personnel tracking to prevent loss and mix-ups; Warehousing: tracking materials, forklifts, and pallets; Manufacturing: positioning of tooling fixtures and work-in-progress; Retail: product and shopping cart analysis. Combined with Geofencing, entry/exit statistics and boundary alarms can be implemented. The IoT platform can provide RTLS data access, trajectory analysis, reports, and other functions.
Anchor Layout and the Position Solution
Position comes from angle of arrival or time of flight
Real-time location does not read a coordinate already written on the tag. Anchors measure a radio feature and the position is inferred from that. An angle-of-arrival design uses an antenna array to judge which direction the wave came from, and it needs enough angles to intersect. A time-of-flight design measures how long the signal took, multiplies by speed to get a distance, and intersects several distances into a point. Received signal strength can only give a coarse near-or-far. One metal reflection makes it jump. It is not a basis for a meter-level fix. On the tag side the signal may be a beacon transmitted on a cycle, or a reply woken by an anchor. The update rate is set jointly by the transmit period and by what the anchors can process.
The solution needs the anchors' own coordinates surveyed first. An anchor coordinate that is a meter off skews the whole tag track, and that error does not disappear when the tag is replaced. The map has to share the anchor coordinate system. Floor height has to take part as well, or tags on two floors are flattened onto one plane and appear to pass through walls.
Anchors have to be able to see the tag
The condition for use is that every place in the active area can be "seen" at the same time by at least the minimum number of anchors the algorithm requires. Angle methods fail when the tag and the array lie nearly on one line. Time methods fail when only two anchors are available and the intersection angle is too small. Racks, people, and metal cabinets block the direct path. If the algorithm treats a reflected path as the direct one, the coordinate is pulled outside the wall. A demonstration that passes in an empty hall does not mean the rack aisles still work. Measure again with the racks full and with people walking. Do not accept the system in an empty room on the day construction finishes.
It suits assets or people that need a continuous track, a geofence, and dwell time. It does not suit a site that only needs one in-or-out record at a door. A portal identification is simpler for that. Tag orientation affects which way the antenna faces. A tag on metal has to use the matching tag construction. The update rate has to match speed of movement. A forklift that is moving quickly cannot be turned into a reliable track from one point per second.
Multipath, clocks, and a region that drifts
Multipath is the main source of indoor error. The same tag sitting still draws a circle as reflected paths change. Watch the jitter radius of a stationary tag, then decide how wide a fence must be. If the fence is narrower than the jitter, a stationary asset alarms in and out continuously. The clock is the second source. Time of flight is extremely sensitive to synchronization between anchors. When a sync wire or wireless sync drops, distances stretch as a whole and the track is dragged outside the area.
The third error is to treat a signal-strength threshold as a position. A drop in strength may only mean a person stood in front of the tag, while the system reports "left the shop." Require the minimum number of anchors before outputting a coordinate. When there are not enough, mark the fix as lost. Do not keep using the last point and pretend the tag is still there. If a map is updated and the anchor coordinates are not updated with it, old and new walls do not agree and a fence is drawn across an aisle. When battery voltage falls, transmit power falls and the edge of the area is lost first. Put that on the maintenance list before the tag's low-battery alarm, rather than searching only after the track has broken.
Floor changes and elevators are another kind of distortion. When a tag in a shaft is seen by anchors on two floors at once, the solution jumps back and forth between the floors, and fence statistics turn one ride into several entries and exits. Give the shaft its own anchors, or constrain vertical speed in the algorithm, and keep a floor confidence with the output. A coordinate with no confidence should not directly trigger an action such as closing a door or charging a fee.
Acceptance should also record what happens when an anchor fails. Switch off one critical anchor. The system should mark the fix as lost, rather than pulling the tag onto the line between the remaining anchors and continuing to output a coordinate that looks normal. That fault drill says more about whether the location can enter a business process than one walk around an empty room.