Modern smartphones have multiple sensors, which can be combined to get a more precise indoor positioning result. Using vertical sensor fusion has one big advantage: combining various sensors results in a more homogenous and more reliable outcome than using just one type.
Most smartphones have the following sensors installed:
- Barometer: measures barometric pressure and thus can provide information about the current height – for example the floor level the smartphone is on.
- Acceleration sensor: measures force shift on the axes X, Y and Z when the phone is being moved. Helps saving energy.
- Bluetooth: Bluetooth is a radio standard for data transfer at short range. It can for example be used for connecting the smartphone to external devices such as speaker phones (Bluetooth 2.0) or for positioning (Bluetooth 4.0). The signal can be impaired by shielding objects, for example the human body.
- GPS: If there is visual contact with GPS satellites, the smartphone can determine its position. Inside buildings there are alternatives.
- Gyroscope: The gyroscope detects if the orientation of the smartphone is vertical or horizontal.
- Magnetometer: This sensor measures the strength of the earth’s magnetic field and its direction according to 3 axes. This sensor is not always suitable for indoor positioning, because it is being impaired by magnetic fields caused by electric cables etc.
- Mobile phone antenna: Via GSM, 3G/4G the position of a smartphone can be detected – however the positioning is not very precise.
- NFC: NFC is a radio standard with a maximum range of 10 centimeters. It is used for access control and contact-free payment. Apple uses it only for this purpose.
- Camera: Most smartphones have a camera on the front and one on the back. They can receive VLC (visible light communication) signals and can be used for virtual reality applications.
- Wi-Fi: Wi-Fi can be used for positioning with an accuracy of 5-15 meters. iOS devices are not able to determine their position client-based with the help of Wi-Fi. Since the introduction of iOS 7, Apple has been using the iBeacons technology for this purpose. Wi-Fi signals can be impaired by objects, such as the human body.