1.4.4. Positioning

In the previous section, which described the general information workflow, a positioning service has been introduced to obtain the user location. We will now give a short introduction to positioning methods. A more detailed discussion is done in the Unit Networks & Positioning of the Lesson Techniques for LBS Cartography.

If we do not consider the manual input of the position as a location method a general classification of positioning methods can be done into two groups: The first group is called network-based positioning. Here, a tracking and evaluation of the user location is done by using the base station network (see image A). Using this technique either the mobile device is sending a signal or the device is "sensed" by the network. The position is calculated by the control stations of the network.
The second positioning group is called terminal-based positioning. In this case the location is calculated by the user device itself from signals received from base stations. A well know example for a terminal-based system is the location determination by use of the Global Positioning System (GPS), and also Galileo in several years. The base stations for the GPS system are the GPS-satellites (see image B in the Figure). Finally a third group of positioning techniques emerges from combination of network and terminal positioning techniques.

The basic principle for the calculation of the user position, valid for all groups, is:

1. Base Stations have a known position.
2. Information from a signal is transformed into distances (N.B.: this is not valid for Angle Of Arrival (AOA) technique).
3. Using the obtained distances (device - base station x) as circle radius around the base station. Obtaining the position from the arc intersection (see image A)

Types of positioning and basic principle. The currently two most common position technologies are the already mentioned GPS and the position evaluation using the Cell-ID from the nearest base transceiver station, a network method. Whereas GPS delivers a very accurate position (accuracy up to 5m) does the Cell-ID deliver a very coarse position (accuracy between 100m to 30 km). Especially GPS is (currently) an outdoor positioning method. To obtain indoor positions with high accuracy, as needed for instance in museums or shopping malls, localisation methods based on WLAN, Bluetooth or infrared technologies should be applied. In general it is important to note that the position technology and its accuracy influences the application of different location based services (see also application examples in Unit 2).