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'''Time of arrival''' ('''TOA''' or '''ToA'''), sometimes called [[Physics:Time of flight|time of flight]] (ToF), is the travel time of a radio signal from a single transmitter to a remote single receiver.
Compared to the TDOA technique, ''time of arrival'' uses the absolute time of arrival at a certain [[Engineering:Base station|base station]] rather than the measured time difference between departing from one and arriving at the other station. The distance can be directly calculated from the time of arrival as signals travel with a known [[Physics:Group velocity|velocity]]. Time of arrival data from two base stations will narrow a position to a [[Position circle|position circle]]; data from a third base station is required to resolve the precise position to a single point. Many [[Engineering:Radiolocation|radiolocation]] systems, including [[Engineering:GPS|GPS]], use ToA.

==Ways of synchronization==
As with TDOA, [[Synchronization|synchronization]] of the network base station with the locating reference stations is important. This synchronization can 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 frequency, hence [[Physics:Dispersion (optics)|different speed]]. Sound ranging to a lightning strike works this way ([[Physics:Speed of light|speed of light]] and sound velocity).
* Via measurement to or triggering from a common reference point.
* Without direct synchronisation, but with compensation of clock phase differences,

==Two-way ranging==
Two way ranging is a cooperative method for determining the range between two radio transceiver units.  When synchronisation of the oscillators of the involved [[Engineering:Transmitter|transmitter]]s is not viable, hence the clocks differ, then applying the measurement as a two ways travel to the receiver and mirrored back to the transmitter compensates for some of the phase differences between the oscillators involved. This concept is applied with the [[Engineering:Real-time locating system|Real-time locating system]] (RTLS) concept as defined in the [[International standard|international standard]] ISO/IEC FCD 24730-5.<ref>[http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=46534 Information technology -- Real Time Locating Systems (RTLS) -- Part 5: Chirp Spread Spectrum (CSS) at 2,4 GHz air interface]</ref>

==Literature==

An introductory description of the concept is given with.<ref>[https://www.wiley.com/RTLS+For+Dummies-p-9780470533222 RTLS For Dummies by Ajay Malik, Wiley New York 2009]</ref> In contrast to some faulty explanations, the concept may be applied as well with [[IEEE 802.15.4a]]CSS as with IEEE 802.15.4aUWB modulation.<ref>[http://www.channelpartner.de/archivsuche/643120/ Funknetzwerke daheim]</ref>

==See also==
* [[Angle of arrival]]
* GSM localization
* [[Multilateration]]
* Ranging
* [[Triangulation]]
* [[Trilateration]]

==References==
<references />

==External links==
* [https://web.archive.org/web/20070510132834/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]

[[Category:Geolocation]]
[[Category:Wireless locating]]

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