IoT Interfaces, Location and Privacy · Study deck

Indoor Positioning: BLE Beacons and Ranging

This first route explains why indoor positioning differs from GPS, the satellite-based location system.

UX Uma is your guide for this deck.

locationawarenessindoor
iotclass.org

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
Angle-of-arrival triangulation: two fixed receivers each measure the bearing to a transmitter, and the crossing bearings locate it.
Angle-of-arrival triangulation: two fixed receivers each measure the bearing to a transmitter, and the crossing bearings locate it.
iotclass.org

Major section

Overview · Start Simple

This first route explains why indoor positioning differs from GPS, the satellite-based location system.

  • It then uses Bluetooth Low Energy (BLE) beacons, short-range radio transmitters, to estimate distance.
  • That estimate is called ranging.
  • The calibrated case uses measurements at known site points to tune and check the estimate.
  • Each needs installed points and a measured site model.
Hyperbolic lateration: a constant time-difference-of-arrival between two reference points restricts the device to one branch of a hyperbola, not a circle.
Hyperbolic lateration: a constant time-difference-of-arrival between two reference points restricts the device to one branch of a hyperbola, not a circle.
iotclass.org

Major section

In 60 Seconds · Indoor Positioning Basics

Satellite positioning is often unreliable indoors, so test alternatives at the site.

  • BLE beacons and existing Wi-Fi can support room or zone estimates; UWB and ultrasonic systems may support tighter ranging with suitable anchors and geometry.
  • GPS does not work indoors -- building walls attenuate satellite signals by 20-40 dB, making them too weak to use.
  • Real-world systems combine multiple technologies with sensor fusion to provide seamless positioning as you walk from outdoors to indoors.
Two half-wavelength-spaced antennas estimate angle of arrival from phase difference while a reflected path creates a false bearing.
Two half-wavelength-spaced antennas estimate angle of arrival from phase difference while a reflected path creates a false bearing.
iotclass.org

Major section

Indoor Place in Building Models · Checkpoint: Indoor Place Model

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.
Comparison of indoor positioning technologies by accuracy and infrastructure requirements.
Comparison of indoor positioning technologies by accuracy and infrastructure requirements.
iotclass.org

Major section

Match Tech to Indoor Jobs · Indoor Accuracy Needs Infrastructure

Wi-Fi fingerprinting can reuse access points but drifts when the building changes.

  • 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.
  • Different estimators fail for different mathematical reasons.
  • Triangulation uses angles.

Key terms

BLE advertising
BLE advertising is inexpensive but RSSI changes with bodies, shelves, doors, and phone orientation.

Why it matters

Motion capture, robot docking, and AR alignment may justify UWB, vision, LiDAR, or tighter fusion because the cost of a wrong position is much higher.

iotclass.org

Major section

Why Indoor Positioning is Different · Indoor Positioning Technologies

UWB needs anchors for tighter position estimates, while ultrasonic systems need their own sensors.

  • Satellite signals are extremely weak (~10^-16 watts received).
  • This requires alternative technologies designed for indoor environments.
  • Walls, device placement, and update interval can change whether the estimate is useful for the product action.

Why it matters

iotclass.org

Major section

BLE Beacon Positioning · Phoebe's Field Notes: Why RSSI Ranging Needs Calibration

The simple exchange in Figure: BLE iBeacons for Indoor Positioning shows what a BLE beacon broadcasts and what a receiver observes.

  • That observation establishes proximity evidence, not a precise position by itself.
  • The application still has to compare signals, know where beacons are installed, and decide what action the estimate can support.
  • A weak or missing broadcast should lead to an uncertain state rather than a silently confident location.
Visible-light positioning: ceiling LEDs flicker a distinct binary ID faster than the eye perceives, and a phone camera decodes the nearest fixture's pattern to fix its location.
Visible-light positioning: ceiling LEDs flicker a distinct binary ID faster than the eye perceives, and a phone camera decodes the nearest fixture's pattern to fix its location.
iotclass.org

Major section

BLE Beacon Retail Trilateration · Checkpoint: BLE Ranging

The positioning system uses trilateration from RSSI measurements to estimate shopper location.

  • Solving these approximate circles gives a position near (1.5, 0.8) m.
  • RSSI uncertainty changes each estimated range; quantify position error with calibrated site measurements before reporting a confidence bound or room assignment.
  • Key Insight: BLE trilateration depends on path-loss calibration.
Active Badge infrared proximity location: two worn badges each flash a unique infrared ID that a fixed ceiling sensor uses to route a call to whichever room the badge is in.
Active Badge infrared proximity location: two worn badges each flash a unique infrared ID that a fixed ceiling sensor uses to route a call to whichever room the badge is in.
iotclass.org

Deck summary

Key takeaways

This first route explains why indoor positioning differs from GPS, the satellite-based location system.

  • Satellite positioning is often unreliable indoors, so test alternatives at the site.
  • Indoor positioning is rarely about latitude and longitude.
  • Wi-Fi fingerprinting can reuse access points but drifts when the building changes.
  • UWB needs anchors for tighter position estimates, while ultrasonic systems need their own sensors.
iotclass.org

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?

AThe most recent room label without its timestamp
BA promised accuracy copied from another building
CAn exact room pin without the confidence estimate
DThe system shows area, uncertainty and freshness.
Show answer

Answer: D The example prefers an honest bounded estimate to a precise-looking wrong room.

iotclass.org

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?

ACombine suitable technologies through sensor fusion
BTreat lower infrastructure cost as equal positioning precision
CTreat outdoor satellite reception as unchanged indoors
DChoose ultrasonic ranging because sound reflections identify the target across this site.
Show answer

Answer: A The chapter describes mixed systems to bridge the indoor and outdoor paths.

Q3Three beacons sit at A (0, 0) m, B (8, 0) m, and C (0, 6) m. A calibrated range estimate is 5 m from each. Which position fits all three ranges?

A(0, 0) m.
B(5, 0) m.
C(8, 6) m.
D(4, 3) m.
Show answer

Answer: D (4, 3) m.

iotclass.org

Print reference

Answers

Answer key.

  1. D · The example prefers an honest bounded estimate to a precise-looking wrong room.
  2. A · The chapter describes mixed systems to bridge the indoor and outdoor paths.
  3. D · (4, 3) m.
iotclass.org