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

 

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