Enhanced Observed Time Difference
Enhanced Observed Time Difference (EOTD or E-OTD) describes a method for locating mobile radio terminals in GSM networks. It is often more precise than the Cell-ID method , but requires complex additional installations in the network, and a certain minimum density of base stations is also required. The position determination can achieve an accuracy of up to 25 m.
The position is determined in three steps:
- First, the terminal determines the differences in the signal propagation times between its own location and at least two neighboring base stations. This is done by observing the arrival times of normal bursts ; special signals are not necessary for this
- In parallel, special hardware within the network, the LMU (Location Measurement Unit), measures the differences in the signal transit times of the same signals
- then the transit time differences determined by the mobile station are transmitted to the LMU, which can calculate an approximate position based on the measurements of the mobile station and its own measurements
In UMTS- based systems the corresponding system is called Observed Time Difference of Arrival (OTDOA). With the Uplink Time Difference of Arrival (U-TDOA) procedure, the location accuracy increases to better than 100 m. As the name uplink suggests, it is the UMTS base stations that record and evaluate the location signal from the cell phone. U-TDOA is one possible method in America for emergency position reporting .
See also
literature
- Dan K. Jonsson, J. Olavesen: Estimated accuracy of location in mobile networks using E-OTD (pdf) , Agder University College, Diploma thesis Grimstad 2002
- MA. Dru, S. Saada: Location-based mobile services: the essentials (pdf) , Alcatel-Lucent Telecommunications Review, 2001