Time of arrival

Time of Arrival (ToA), also named Time of Flight (ToF), which both means the travel time of a radio signal from a single transmitter to a remote single receiver. By the relation between light speed in vacuum and the carrier frequency of a signal the time is a measure for the distance between transmitter and receiver. However, in some publications the fact is ignored, that this relation is well defined for vacuum, but is different for all other material when radio waves pass through.

Similar to the TDOA technique, this TOA or Time of arrival called technology only differs in the fact that it uses the absolute time of arrival at a certain base station rather than the measured timedifference between departing from one and arriving at the other station. The distance can be directly calculated fromthe time of arrival as signals travel with a known velocity. Time of arrivaldata from two base stations will narrow a position to two circles and data froma third base station is required to resolve the precise position with the third circle when matching in a single point. There are many ToA-based localization systems, including GPS.

Ways of synchronization

As with TDOA,
synchronization of the network base stations is important. This synchronizationcan be done in different ways:

* With exact synchronous clock on both sides. Inaccuracy in the clock synchronization translates directly to an imprecise location.
* With two signals which have different spreading speed. Distance to a lightning strike can be measured in this way (speed of light and sound velocity).
* Via measurement to a third reference point.

See also

* GSM localization
* RTLS
* Triangulation
* Trilateration
* Multilateration

External links

* [http://www.crypto.rub.de/its_seminar_ss07.html Seminar „security in mobile communication“ which was held at the Communication Security (COSY) Group at the Ruhr-University Bochum, Germany]