LOS (Line of Sight)
Line of sight (LOS) means the radio path between a tag and an anchor is clear. The first pulse that arrives is the direct pulse. Time of flight then maps to true distance, which is why UWB two-way ranging can look like 10 to 30 cm in an empty room.
Vendor slides almost always show LOS: empty box, roof anchors, tag in the middle, nothing in the way. That drawing is valid physics for that room. It is not a measurement of a brownfield warehouse. Pallet racking, mezzanines, dock doors, and the forklift itself remove LOS on the jobs that matter.
Use LOS as a site condition, not as a brand promise. If the proof was an empty hall or a booth, you still need a coverage map on your floor. The operational argument is in ask for a coverage map, not 30 cm on the slide.
Key Components
Direct path: Geometric clearance from transmitter to receiver, including antenna height and tag mount (cage, cabin, mast), not a surveyor standing in the aisle centerline.
First arriving path: The earliest pulse the engine can lock. Under LOS that peak is the direct path.
Anchor geometry: Enough visible anchors around the tag to solve position. One LOS ray is a range. Position needs several.
Changing clearance: A travel lane can be LOS at 10:00 and blocked at shift change when trucks park under the same steel.
Applications in Manufacturing and Logistics
LOS pockets are where centimeter RTLS is cheapest to prove: open receiving, some assembly halls, yards with sky (then you are on GPS, not indoor LOS). High-bay and steel mezzanines are NLOS jobs. Do not copy the LOS number across both.
Safety cells and bay picks need LOS or a dense enough grid that a blocked path still leaves other anchors. Zone-level forklift loops often do not. Mix radios by pocket instead of assuming the whole plant is the lab drawing.
Benefits and Challenges
LOS is the condition under which brochure accuracy is fair. It is also rare in loaded racking. Treating LOS as the plant baseline overbuys hardware and still fails in the canyon aisle.
The practical test is not a checkbox. Walk the aisle with stock in the faces and a tag on a real truck. If the pin stays in the aisle, LOS (or enough redundant paths) is adequate for that job. If it jumps a bay, you are in NLOS or multipath, whatever the slide said.
Related Terms
The blocked-path opposite is NLOS. Extra delayed copies of the pulse are multipath. Indoor ranging uses time of flight on UWB and other RTLS stacks. Outdoor open-sky positioning is GPS / GNSS.
Frequently Asked Questions
Does LOS mean I can see the anchor with my eyes? Almost. Radio LOS is geometric clearance at the antenna, including rack beams above eye height. A clear walkway with steel above the tag is still NLOS to a roof anchor.
Can I assume LOS if the ceiling is open? No. Open to the roof is not open to the tag. Loads, masts, and parked trucks sit in that volume.
Is LOS required for zone-level tracking? Not always. BLE zone presence can work without a clean first path. Bay-level UWB and tight no-go rules usually need it, or a denser grid.