Cellular Communication Based Positioning
In cellular communication networks base stations are distributed throughout the covered area. There is a variety of ways in which a position can be determined in cellular communication networks such as GSM and UMTS. The most important techniques for positioning in cellular communication networks are cell of origin (COO), propagation time, time difference of arrival (TDOA), and angle of arrival (AOA).
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Cell of origin (COO)
The simplest but also most inaccurate way is to approximate the vehicle's position by the position of the COO, i.e. the cell which is used for communication. The COO only gives an approximation of the vehicle's position and it is not guaranteed that the base station associated to the COO represents the closest base station to the vehicle. In the GSM network COO can give an accuracy of less than 100 metres in urban areas and up to 35 kilometres in rural areas.
Propagation time
This involves measuring the time it takes for a signal to travel between a base station and a mobile telephone or vice versa. Alternatively, this approach might involve the measurement of the round-trip time of a signal transmitted from a source to a destination which is then echoed back to the source, giving a result twice that of the one-way measurement. The former requires that the receiving base station(s)/mobile telephone know the exact time(s) at which the transmitting mobile telephone/base station(s) will transmit, and that the receiver(s) have a very stable and accurate clock. The latter does not rely on such synchronisation between the mobile telephone and the base station(s) and thus, is the more common means of measuring propagation time. Three base stations are required to give unambiguous positioning.
Time difference of arrival (TDOA)
A mobile telephone can listen to signals transmitted simultaneously by several base stations and measure the time difference between each pair of arrivals.
Each TDOA measurement defines a curve on which the mobile telephone must be located.
Let 
and 
denote the known positions of the base stations 
and 
and let 
denote the TDOA.
The position 
can be determined by
Two or three TDOA measurements are required for unambiguous positioning. An important issue for TDOA systems is the need to have some means of establishing the synchronicity of the base stations. For self-positioning the base station must transmit the signal at the same time (or with a known time offset), for remote positioning the signal transmitted from the mobile telephone is received by several base stations and there must be a known time relationship between the receiver clocks.
Angle of arrival (AOA)
This involves measuring the AOA of a signal from a base station at a mobile telephone or the AOA of a signal from the mobile telephone at a base station. In either case a single measurement produces a straight line. If the mobile telephone is not on the direct line through two different base stations, both lines intersect at the vehicle's position.
