Multipath — why RTLS accuracy degrades in real environments.
Multipath is the single most common cause of RTLS accuracy regression.
Metal racking, glass, HVAC, conveyor cages and concrete-aggregate floors create radio reflections that arrive after the direct path — and the RF system cannot tell them apart. The fix is geometric, not algorithmic.
What multipath actually is.
A radio signal from a tag travels by line-of-sight to the anchor. It also bounces off any nearby metal or hard surface and arrives a few nanoseconds later.
The anchor receives both; the timing math assumes line-of-sight; the position estimate is wrong by the path length of the reflection.
UWB is more multipath-tolerant than BLE-AoA, which is more tolerant than RAIN RFID phase-based location, which is more tolerant than GPS indoors (which simply does not work).
No RTLS solves multipath in algorithm alone. Every production-grade RTLS solves it in placement geometry — anchor positions chosen so the strongest reflected path is geometrically distinguishable from the direct path.
The five most common multipath environments.
Metal racking warehouses: parallel vertical metal creates predictable reflection corridors. UWB and BLE-AoA need geometric offset.
Hospital corridors with glass partitions: glass is RF-translucent at BLE but reflects at higher UWB frequencies.
Pharma cleanrooms with stainless panels: stainless walls and ceiling create resonant cavities.
Automotive body shops: large flat metal surfaces plus moving metal create dynamic multipath that varies with production cycle.
HVAC-dense ceilings: ducting and trays at anchor mount height create line-of-sight gaps and reflective surfaces.
How a properly-designed survey identifies multipath risk.
Predictive RF modelling against the as-built environment, not the architectural drawing.
Material reflection map: every dominant flat metal or glass surface within 10 m of any proposed anchor is identified.
Anchor geometric offset calculation: anchors positioned so the strongest reflection is distinguishable from the direct path.
Multi-time-of-day validation: designs that work at 09:00 may fail at 14:00.
Frequently asked questions
Is multipath the same as RF interference?
No. Interference is unwanted signals from other transmitters. Multipath is reflected versions of your own signal arriving after the direct path. Different problems, different fixes.
Does UWB really tolerate multipath better than BLE-AoA?
Yes — UWB’s wide bandwidth (500 MHz vs BLE’s 2 MHz) gives much finer time-of-arrival resolution. UWB still degrades; it degrades less.
Can multipath be solved with software filtering?
Partially. RTLS platforms apply Kalman filters and ML-based outlier rejection. These help with random noise but do not solve systematic multipath — that requires correct placement geometry.
What is the worst multipath environment you have audited?
A stamped-metal automotive press shop. Large dynamic metal surfaces (parts moving through 12-tonne presses) combined with stainless guarding and concrete-aggregate floor.
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