What is an Indoor Positioning System and how does it work?

Updated: Oct 17, 2019

You are no doubt familiar with the concept of using GPS to navigate around the road network using your SatNav.

A plethora of smartphone applications and outdoor navigation solutions now sit comfortably in dashboards and phone holders of consumers around the globe.

A network of satellites sitting above the Earth enables the precise location of an object to be known by latitude, longitude, and altitude.

Global Positioning Systems

The Global Positioning network depends on signals between the object receiving them on the ground, and the satellite. However, buildings get in the way of those signals.

Global Positioning Systems do not work, or have limited capabilities, when it comes to indoor locations. The roofs, walls, and other structures compromise the microwaves to such an extent that precise positioning is seriously compromised.

And, like the waves of the ocean, when they come crashing into the shoreline, signals are unable to get any further.

But as you may expect, technologists have found ways to solve the problem.

In a nutshell, an indoor positioning system (IPS), is GPS for spaces where those satellite signals either do not work or are corrupted by infrastructure, or people.

In essence in indoor scenarios the signals from the satellite have been replaced with another type of signalling system.

But there is, as they say, more than one way to crack a nut, and technology experts fit their solutions into four main categories. These are worth exploring in more depth, because they can be used alone or can be mixed up depending on the location solutions required.

Proximity Positioning

Near field communication (NFC) tags and QR Codes can communicate location information to smartphones. If the smart phone is close to the tag or the code, it will tell the phone where it is on the planet.

The location of a moving smartphone or similarly Bluetooth-enabled device can be determined by the use of beacons. Bluetooth Low Energy (BLE) beacons emit signals that can be received and interpreted by smartphones. The user’s position can then be worked out in relation to that beacon. But, as any mathematician, astronomer, or gunnery expert in triangulation might tell you, to be able to determine a more precise location, the more beacons there are, the better.

Wi-fi access points and ultrasound devices can be used in much the same way as Bluetooth Beacons to locate any enabled device.

Visible light communication (Li-Fi) devices have their own unique identification, which can allow receivers to determine accurate positions.

Trilateration Positioning

This style of location positioning involves the computation of a position from signals that have been received from emitters that have been placed in different locations. The more signal emitters there are, the more precise the positioning will be.

Signals can be measured in two ways to gauge location. These are by measurement of the relative signal strength, or the time it has taken for the signal to reach the receiving equipment.

Thinking about waves spreading out from a stone that has been thrown into a pond, they lose strength the further away they are from the impact point of the pebble. That’s the Relative received Signal Strength Indication (RSSI) method.

But rooms and dynamic environments give the signals more things to bounce off and interact with, including human beings. This means the accuracy of the RSSI method is poor.

On the other hand, Time of Flight (ToF), works like radar or sonar, by bouncing a signal off the receiver, and by measuring the difference between the time it was sent and time it was received.

Both RSSI and ToF are able to use Bluetooth Low Energy (BLE), Ultrasounds, and Wi-Fi. Ultra-Wide band also provides very accurate positioning by using Time of Flight to compute distances between receiver and emitters.

Fingerprinting Positioning

In this method, the technologies use signal measurements across buildings to compute the position of an object that is moving. It is particularly well suited for Bluetooth Low Energy (BLE) devices which emit signals that are stable over time.

There are different methods of fingerprinting, including using variations in the earth’s magnetic field. However, the magnetic field is unstable from one moment to the next so this is not a particularly reliable method.

Visual Positioning

Photo fingerprinting is based on the analysis of images of the inside of rooms, comparing one image to the other. But these environments can be dynamic, often changing, with objects added and taken away. To provide reliability and stability this method requires that the images are regularly refreshed.

Motion Positioning

This method utilises a sensor in a smartphone – the accelerometer – to determine its velocity (speed). When the speed of something is known, and there is a difference in time, the distance of an object – the smartphone sensor – can be mathematically worked out.

Accelerometers are little miracles buried deep in the workings of smartphones. They measure changes in orientation in three dimensions and allow the phone to “know” how it is being held in relation to the planet.

Smartphone users will be familiar with the way a screen view can change from a vertical display to a horizontal display, depending on how it is held. The accelerometer is the technology that tells the smartphone which way it is being held up.

Similarly, if you have one of those apps that displays where the stars are in the night sky, and it changes depending on how you hold up the