Time of arrival (TOA or ToA) is the absolute time instant when a radio signal emanating from a transmitter reaches a remote receiver.
The time span elapsed since the time of transmission (TOT or ToT) is the ''
time of flight'' (TOF or ToF).
Time difference of arrival (TDOA) is the difference between TOAs.
Usage
Many
radiolocation systems use TOA measurements to perform
geopositioning via
true-range multilateration. The true range or distance can be directly calculated from the TOA as
signals
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
travel with a known
velocity. TOA from two
base stations will narrow a position to a
position circle; data from a third base station is required to resolve the precise position to a single point.
TDOA techniques such as
pseudorange multilateration use the measured time difference between TOAs.
Ways of synchronization
As with TDOA,
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 speed.
Sound ranging
In land warfare, artillery sound ranging is a method of determining the coordinates of a hostile battery using data derived from the sound of its guns (or mortar or rockets) firing. The same methods can also be used to direct artillery fire at a ...
to a lightning strike works this way (
speed of light and
sound velocity
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as wel ...
).
* 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
transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
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
real-time locating system (RTLS) concept as defined in the
international standard ISO/IEC FCD 24730-5.
Literature
An introductory description of the concept is given with. In contrast to some faulty explanations, the concept may be applied as well with
IEEE 802.15.4aCSS as with IEEE 802.15.4aUWB modulation.
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See also
* Angle of arrival
The angle of arrival (AoA) of a signal is the direction from which the signal (e.g. radio, optical or acoustic) is received.
Measurement
Measurement of AoA can be done by determining the direction of propagation of a radio-frequency wave incident ...
* GSM localization
* Ranging
Length measurement, distance measurement, or range measurement (ranging) refers to the many ways in which length, distance, or range can be measured. The most commonly used approaches are the rulers, followed by transit-time methods and the in ...
* Triangulation
References
External links
Seminar "Security in mobile communication", which was held at the Communication Security (COSY) Group at the Ruhr-University Bochum, Germany
Radio
Wireless locating
Radio geopositioning