How indoor positioning systems work

There are many types of indoor positioning systems (IPS). Some people refer to them as indoor navigation system (INS). The systems are also called Realtime Locating Systems (RTLS), which is a broader term than just indoor systems – RTLS can be outdoor – but RTLS typically refers to IPS and INS.

Why do people need indoor positioning system? GPS does not work indoor, because intentionally weak GPS radio signals simply cannot penetrate building made of metal, concrete or bricks, and accuracy of typical GPS (5-10m) is not enough for indoor applications. Thus, indoor positioning systems are required. They work indoor and they are typically more precise than GPS.

The vast majority of really working indoor positioning systems rely on stationary beacons (anchors) that act as satellites in GPS and mobile beacons (tags) measuring their position against the stationary beacons. It shall be very clear that mobile beacons position themselves or the IMS position them against the stationary beacons distributed in the building – not against the building itself.

There are systems, for example, based on the Earth magnetic field. They don’t need beacons. But such system didn’t prove themselves robust enough and precise enough for practical industrial applications. Thus, the majority of working today indoor positioning and navigation systems use stationary beacons. The underlying technologies and architectures may differ drastically (for example, time-of-flight vs. RSSI (radio signal strength)), but still the majority of those systems are beacon-based.

GPS is a Global Positioning System from the US. Like its siblings GLONASS (Russia), Galileo (EU),  BeiDou (China) and other less known systems from Japan and India, it is a Global Navigation Satellite System (GNSS) that relies on satellites. Satellites knows their own position very precisely based on the data from the ground stations. The satellites have atomic clocks. Based on the translated position of the satellites, and precise clock stamps from the satellites, the mobile beacons are capable to calculate their own position using trilateration. But key for the technology for the system – direct visibility to the satellites, which is usually not the case indoor.

A few quick words about technologies. Among the most popular today are the following:

  • UWB
  • BLE
  • WiFi
  • Ultrasound
  • etc.

Since we are focusing on industrial applications (robotics, drones, forklifts, vehicles, humans, cranes, other machines) where accuracy does matter, far less accurate solutions, for example, BLE or WiFi, are touched only briefly and left for retail, airports, museums and similar applications, where it is sufficient to reach a particular gate or a room but not much more than that.

Terminology

  • AoA – Angle of Arrival (BLE)
  • AoD – Angle of Departure (BLE)
  • AR – Augmented Reality
  • BLE – Bluetooth Low Energy
  • GNSS – Global Navigation Satellite System
  • GPS – Global Positioning System
  • IA – Inverse Architecture (Marvelmind)
  • IP67 – Ingress Protection
  • IPS – Indoor Positioning System
  • IMU – Inertial Measurement Unit
  • LIDAR – Light Detection and Ranging
  • LoRa – proprietary radio modulation
  • LoS – Line-of-sight
  • MEMS – Micro-Electro-Mechanical Systems
  • NIA – Non-Inverse Architecture (Marvelmind)
  • Non-LoS – Non-line-of-sight
  • RSSI – Received Signal Strength Indicator
  • RTLS – Real-time Locating Systems
  • TDoA – Time Difference of Arrival
  • TDMA – Time Division Multiple Access
  • ToA – Time of Arrival
  • UWB – Ultra Wideband
  • VR – Virtual Reality
  • ZigBee – Wireless mesh network standard

Types of indoor positioning methods

Trilateration – time of flight

  • GPS (radio)
  • UWB (wideband radio)
  • Marvelmind Robotics’ Indoor “GPS” (ultrasound)

RSSI-based

  • BLE (Bluetooth Low Energy)
  • WiFi
  • ZigBee
  • LoRa

Triangulation

  • LIDARs

Mixed

  • BLE + angle of arrival (AoA)
  • BLE + angle of departure (AoD)

Odometry

Inertial

  • Inexpensive MEMS IMU vs. laser-based IMU

Optical

  • QR codes
  • Stargazers
  • Optical flow
  • Motion capture

Sensor fusion

  • IMU+ultrasonic
  • Drift vs. jumps
  • Location update rate

Other types and exotic

  • Li-Fi
  • RFID
  • Magnetic

No method or indoor positioning system is good for all

Too many contradicting requirements. Users must choose:

  • Accuracy
  • Update on request vs. 100-400Hz for VR/AR
  • IP67 and Ex requirements
  • Price and total cost of ownership
  • Power consumption and battery lifetime of stationary beacons
  • Power consumption and battery lifetime of mobile beacons
  • Weight
  • Size
  • Tolerance to particular types of interference (radio, light, sound)
  • Location only vs. Location+Direction
  • Embedded IMU
  • Data communication to and from mobile beacons
  • Capacity
  • Flexibility

Detailed review and comparison of indoor positioning systems, technologies and methods with focus on industrial applications

If anything is unclear, contact us via info@marvelmind.com