UX Design · Study deck
Indoor Positioning: BLE Beacons and Ranging
This first route explains why indoor positioning differs from GPS and develops BLE beacon ranging through a complete calibrated case.
UX Uma is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Compare Indoor Positioning Technologies: Evaluate Wi-Fi, BLE, UWB, and ultrasonic systems for accuracy and cost
- Apply Trilateration Calculations: Compute position estimates from beacon distance measurements
- Design Sensor Fusion Systems: Combine GPS, Wi-Fi, BLE, and IMU for seamless indoor-outdoor transitions
- Troubleshoot Multipath Effects: Identify and mitigate RF interference in indoor environments
Major section
Start Simple
A dot in the wrong room wastes time, while a system that admits uncertainty can guide a useful search.
- Bluetooth Low Energy, or BLE, is a short-range radio system for small exchanges.
- Ultra wideband, or UWB, uses very short radio pulses for precise ranging.
- Each needs installed points and a measured site model.
Major section
Indoor Place in Building Models
Indoor positioning is rarely about latitude and longitude.
- The useful answer is usually a building, floor, room, aisle, doorway, dock, bed bay, exhibit, or safe walking route.
- A simple application taxonomy keeps the old localization vocabulary connected to product decisions.
- Represent the answer at the level the application can defend.
- Indoor systems also need explicit degradation states.
Major section
Match Tech to Indoor Jobs
BLE proximity, Wi-Fi fingerprinting, Wi-Fi RTT, UWB ranging, ultrasonic beacons, QR/NFC check-in, camera/vision, powerline fingerprinting, active floors, barometers, and IMU dead reckoning each fail differently.
- BLE advertising is inexpensive but RSSI changes with bodies, shelves, doors, and phone orientation.
- Wi-Fi fingerprinting can reuse access points but drifts when the building changes.
- Wi-Fi RTT using IEEE 802.11mc can improve range estimates when compatible access points and devices are available.
Major section
Match Tech to Indoor Jobs (continued)
Powerline positioning reuses electrical infrastructure but still needs a room-by-room signature map.
- UWB systems based on IEEE 802.15.4z can support precise ranging but need planned anchor geometry and site commissioning.
- Room-level asset tracking can often tolerate BLE plus map constraints.
- Robot docking, augmented reality alignment, or high-value tool tracking may justify UWB anchors, calibration tags, tighter time synchronization, and alerts when anchor health degrades.
Major section
Match Tech to Indoor Jobs (continued)
Commissioning should be treated as part of the product, not as a one-time installation chore.
- A classroom-style BLE localisation prototype is a useful minimum evidence path.
- The embedded device scans known beacons, records the beacon identifier, encounter time, and RSSI, then uploads the scan through a phone or Bluetooth gateway to a cloud service.
- An operations dashboard may need battery health, stale anchors, survey age, and the percentage of events corrected by map matching.
Major section
Indoor Accuracy Needs Infrastructure
An indoor location event should include more than x/y coordinates.
- BLE beacons may use iBeacon, AltBeacon, or ordinary Bluetooth LE advertising payloads.
- UWB anchors need known coordinates, clock behavior, channel configuration, and non-line-of-sight detection.
- Wi-Fi fingerprints need survey-device metadata and re-survey dates.
- Different estimators fail for different mathematical reasons.
Major section
Indoor Accuracy Needs Infrastructure (continued)
Classic indoor-location systems make those choices concrete.
- Sensor-fusion code should preserve source weights and rejection reasons so a support team can tell whether the issue is a missing beacon, a moved access point, a bad floor plan, or a phone sensor problem.
- Triangulation uses angles.
- Access control may need conservative geofence margins.
Major section
Indoor Accuracy Needs Infrastructure (continued)
BLE RSSI ranging depends on a log-distance path-loss exponent, so a concrete corridor, a human body, or a metal cabinet can turn a small RSSI change into metres of distance error.
- Wi-Fi fingerprinting is a nearest-neighbour or probabilistic match against a surveyed signal database, so it fails when the database no longer represents the building.
- UWB two-way ranging and time-difference-of-arrival systems depend on timestamp precision, anchor geometry, clock handling, and non-line-of-sight rejection.
- One receiver pair does not yield a unique point; a second independent curve is needed to create the crossing.
Major section
Indoor Accuracy Needs Infrastructure (continued)
That leads to a simpler historical design in Figure: Active Badge infrared proximity location: a system that reports room-level proximity instead of solving continuous coordinates.
- Lateration estimates position from distances to known anchors; trilateration is the familiar two- or three-dimensional case, while hyperbolic lateration uses time-difference-of-arrival curves.
- This makes the infrastructure requirement visible before the chapter compares installed systems.
- Project Tango-style phone localization is a useful camera/IMU boundary case.
Major section
Indoor Accuracy Needs Infrastructure (continued)
Distance estimates can come from time of flight, round-trip time, time difference of arrival, or signal-strength attenuation, and each method needs its own calibration and line-of-sight assumptions.
- Poor geometry or clock disagreement widens the plausible region even when every receiver reports a value.
- Active Bat used ultrasonic time-of-flight pings to reach roughly 3-10 cm resolution.
- Higher accuracy usually costs more anchors, calibration, power, maintenance, and deployment effort.
Major section
Indoor Accuracy Needs Infrastructure (continued)
Nearly parallel bearings make that intersection unstable, so placement geometry remains part of the accuracy promise.
- Figure: Active Badge infrared proximity location shows each badge's unique infrared pulse reaching the fixed room sensor and then informing the call-routing decision.
- Infrared line of sight and receiver placement bound the result, but the coarse answer fits the service.
- The result is only as reliable as fixture visibility, camera orientation, lighting conditions, and the current lamp-location map.
Major section
Indoor Accuracy Needs Infrastructure (continued)
For tasks that require a point rather than a room, Figure: Angle-of-arrival triangulation shows the extra directional evidence that triangulation consumes.
- Figure: Angle-of-arrival triangulation shows each receiver contributing a bearing rather than a distance, with the bearing lines intersecting at the transmitter estimate.
- Together these three views show why “more infrastructure” means maintaining reference coordinates, clocks or bearings, line of sight, and a tested service boundary—not merely installing more radios.
- Figure: Visible-light positioning shows three luminaires emitting distinct binary identities faster than a person notices, while the camera decodes the nearest usable pattern.
Major section
Indoor Accuracy Needs Infrastructure (continued)
This final example connects the estimator survey back to operations: every accuracy claim carries a physical installation and recalibration obligation.
- Moving computation onto the client avoids a central vision server, but the device still has to fuse motion tracking, depth perception, and area learning into a map it can relocalize against.
- A headcount dashboard may only need zone-level Wi-Fi or camera evidence.
- A Kalman filter, particle filter, or hidden Markov model can carry uncertainty through time, reject impossible wall crossings, prefer corridor paths, and smooth handoffs between GPS, Wi-Fi, BLE, UWB, IMU, and barometer signals.
Major section
Indoor Accuracy Needs Infrastructure (continued)
The important engineering output is not just the best estimate; it is the covariance, source weights, rejected observations, and freshness metadata that decide whether the UI should show a dot, a zone, or a warning.
- Privacy risk: collect room-level or zone-level events when exact paths are unnecessary, and make retention match the operational need.
- With the place model and maintenance plan established, the next question is why outdoor GPS is the wrong starting point indoors.
- Panel: B adds the echo from a reflector; the same array now has two plausible phase differences, so geometry alone cannot decide which bearing is real.
Major section
BLE Beacon Positioning
Changing n from 2.0 to 3.0 can change estimated distance by 40-60%.
- In a concrete hospital (n=3.2), a beacon showing -72 dBm is only 2.5 meters away, but the same reading in an open office (n=2.5) suggests 3.3 meters — a 30% error.
Major section
BLE Beacon Retail Trilateration
The positioning system uses trilateration from RSSI measurements to estimate shopper location.
- With RSSI variance of +/-3 dBm, distance error is +/-30%.
- Key Insight: BLE trilateration accuracy depends heavily on path loss exponent calibration.
- A path loss exponent error of 0.3 (using n=2.2 instead of n=2.5) would shift the position estimate by 0.8 meters.
Deck summary
Key takeaways
A dot in the wrong room wastes time, while a system that admits uncertainty can guide a useful search.
- Indoor positioning is rarely about latitude and longitude.
- BLE proximity, Wi-Fi fingerprinting, Wi-Fi RTT, UWB ranging, ultrasonic beacons, QR/NFC check-in, camera/vision, powerline fingerprinting, active floors, barometers, and IMU dead reckoning each fail differently.
- Powerline positioning reuses electrical infrastructure but still needs a room-by-room signature map.
- Commissioning should be treated as part of the product, not as a one-time installation chore.
Retrieval practice
Recall check 1 of 2
UX Uma says: answer from memory, then check your reasoning.
Q1A nurse searches for a cart and the location estimate spans more than one room. What should the system communicate?
Show answer
Answer: C The example prefers an honest bounded estimate to a precise-looking wrong room.
Retrieval practice
Recall check 2 of 2
UX Uma says: answer from memory, then check your reasoning.
Q2A hospital needs positioning as users move from outdoors to indoors. Which approach matches the chapter’s account?
Show answer
Answer: B The chapter describes mixed systems to bridge the indoor and outdoor paths.
Print reference
Answers
Answer key.
- C · The example prefers an honest bounded estimate to a precise-looking wrong room.
- B · The chapter describes mixed systems to bridge the indoor and outdoor paths.