Wi-Fi positioning system

A Wi‑Fi positioning system (WPS, WiPS, or WFPS) is a way to find out where a device is using nearby Wi‑Fi access points. This helps when satellite navigation like GPS cannot be used, such as inside buildings.

Wi‑Fi positioning is useful in cities with many wireless access points. It works by measuring signal strength from these points and comparing it to a database of known locations. Each access point has a unique identifier to help find the device's position.

The accuracy of this system depends on the database and how many access points are nearby. The database is built using information from mobile devices with other location systems, like GPS, along with Wi‑Fi access point details. This system helps guide people where GPS does not work well, such as inside large buildings or underground areas.

Motivation and applications

Accurate indoor location tracking is becoming more important for Wi‑Fi devices. This is because more people use augmented reality, social networking, health care monitoring, personal tracking, inventory control, and other location-aware apps.

In wireless security, Wi‑Fi helps find and map unusual network points called rogue access points. Wi‑Fi cards are popular and cheap, making them a great choice for localization systems. Researchers have studied this for over 15 years.

Problem statement and basic concepts

Using Wi‑Fi to find where a device is inside a building can be tricky. There are a few ways to do this. These ways look at four main things: received signal strength indication (RSSI), fingerprinting, angle of arrival (AoA), and time of flight (ToF).

The first step is usually to learn how far the device is from some nearby access points. Knowing these distances, trilateration can help figure out where the device is, using the known spots of the access points. Looking at the angles where signals come into the device can also help find its spot using triangulation methods.

Using these methods together can make finding the location even more exact.

Techniques

Signal strength

RSSI localization measures the signal strength from several Wi-Fi access points to guess how far away a device is. This method is simple but not very exact, usually within 2 to 4 meters, because signal strength can change with the surroundings.

Cisco uses RSSI to find devices through its access points, updating locations on its cloud service called Cisco DNA Spaces.

Monte Carlo sampling

Monte Carlo sampling is a way to guess where devices are inside buildings. It makes maps of signal strength and uses special math to get better results, often within a single room using just one access point.

Fingerprinting

Fingerprinting records signal strengths from many access points and saves them with known spots. When tracking a device, its current signal strengths are checked against the saved data to guess its location. This can be very accurate but needs updates if the area changes.

Angle of arrival

With MIMO Wi-Fi, which uses many antennas, it is possible to guess the direction of signals to find device locations. Systems like SpotFi and ArrayTrack use this way.

Time of flight

Time of flight (ToF) uses times from wireless signals to work out distances. This method can be accurate within about 2 meters and helps track things in buildings.

Self-advertisement

Since 2019, French law says drones heavier than 800 grams must share their GPS location using Wi-Fi. This information can help find the position of nearby devices.

Privacy concerns

When using Wi-Fi to find out where someone is, there are some privacy worries. To help with this, Google suggested a way for owners of Wi-Fi access points to choose not to be part of finding locations. This can be done by adding "_nomap" to the name of the Wi-Fi network. The Mozilla Location Service also allows owners to choose not to take part by using the "_nomap" method.

Public Wi-Fi location databases

There are several public Wi-Fi location databases that you can use.