Indoor Positioning Systems (IPS) are used to determine the position of mobile devices (smartphones) inside a closed space (a building), where GPS cannot be used. IPSs normally use wi-fi and GSM antennas as reference points instead of GPS satellites. They are also known as Indoor Navigation Systems.
This tag should be used to categorize questions regarding the techniques and tools used to determine the position of a mobile device inside a building, the libraries and tools used to perform such positioning, the techniques used to reach the required accuracy and so on.
Nowadays, most existing smartphones and mobile devices have a built-in GPS antenna and can determine their own geographic position with a quite good accuracy (usually less than 100 m).
Unfortunately, GPS systems require a clean view of the sky to contact GPS satellites and cannot be used in a closed space (a building).
For this reason, many others techniques have been developed to determine the position (location) os a mobile device inside a building. Almost all of these systems use some kind of beacons as reference points and calculate the mobile device position using a multilateration algorithm or a fingerprint one. The main difference is represented by the kind of reference beacon that is used.
Most used reference points (beacons) are:
- wi-fi access points (wi-fi ADSL routers/modems)
- GSM/3G cell phone antennas (BTS or Node-b)
- Bluetooth dongles
These systems are mainly used to guide the user through the map of the building to a specific room or even to a specific shelf ("indoor navigation").
Since 2011 (Google Maps 6.0), a first kind of IPS is available with Google Maps. It is a hybrid system that uses both cell phone antennas and wi-fi access points as reference points. Microsoft (Bing) and other companies are following.
Other IPSs exist that use magnetometer (compass), accelerometer (inertial navigation) and other sensor or techniques to perform such indoor positioning and navigation.
Usually, precision (accuracy) is in these ranges:
- phone-cells-based systems: 1 to 2 Km
- wi-fi-based systems: 10 to 150 m (most often 40 to 150 m)
- Bluetooth-based: 4 to 10 m (room-level)
A few techniques can be used to improve accuracy, like map pathfinding (the same kind of pathfinding used in many 2D and 3D games) and inertial navigation (based on accelerometers).
Many existing systems use more than one sensor and more than one algorithm to perform positioning and should be classified as "hybrid IPS systems". A few of them use what it is known as "sensor fusion" technique. This term is used to refer to IPSs that integrate signals (and location-related information) that comes from different sensors (accelerometers plus wi-fi antenna plus others).
Google Maps 6.0 API can be used both on the web (via javascript) and on Android devices (via Java/Dalvik). Indoor positioning is supplied transparently wherever a "floor map" is available. No specific code is required and indoor navigation merge smoothly with the outdoor one.
