Location Based Services
Location by mobile networks

The mobile networks enable to estimate user’s position based on knowledge of the base stations positions. Several approaches to location exploiting mobile communication networks can be distinguished. The approaches differ in parameters used for the derivation of the position.

First way is known as Cell Of Origin (COO). It exploits an identification of the base stations (Cell ID) to derivation of user position. The user position corresponds to the coordinates of its serving base station. Of course, an error in derived position is equal to the cell radius.

Higher accuracy is reached by Time of Arrival (TOA), which utilizes not only Cell ID but also ability to measure a delay between transmission of a signal by a mobile station and its reception by a base station. Since the signal is propagated with the speed of light, the distance of the user from the base station is calculated easily in the same way like in the satellite systems.

If signal is received from more than one base station, the TOA can be extended to Time Difference of Arrival (TDOA). In this case, the signal propagation time from all neighbouring base stations is confronted and the user position is derived as an intersection of estimated distances from each base station. In TDOA, the time of arrivals are processed by the network. If a mobile station is in charge of the data processing, the algorithm is denoted as Enhanced Observed Time Difference (E-OTD). The E-OTD requires special equipment, Location Measurement Unit (LMU), in the network. The LMU ensures accurate timing and accuracy of the data.

If directional antennas are used in either base station or mobile station, a direction from which the signal is received can be triangulated in the similar manner as in the TDOA. This method is denoted as Angle of Arrival (AOA).