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 Radiolocation, also known as radiolocating or radiopositioning, is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar—as well as detecting buried cables, w ...

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 travel with a known velocity. TOA from two

base station Base station (or base radio station) is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a "land station in the land mobile service." The term is used in the context of mobile telephony, wireless com ...

s will narrow a position to a

position circle A position circle is a circle that can be measured both from a chart and from the surface of the earth for the purpose of position fixing. For the purposes of land or coastal navigation, a position circle can be generated by making a horizontal ang ...

; data from a third base station is required to resolve the precise position to a single point. TDOA techniques such as

pseudorange multilateration Trilateration is the use of distances (or "ranges") for determining the unknown position coordinates of a point of interest, often around Earth (geopositioning). When more than three distances are involved, it may be called multilateration, for emph ...

use the measured time difference between TOAs.

Ways of synchronization

As with TDOA,

synchronization Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...

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 to a lightning strike works this way ( 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

oscillator Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

s of the involved transmitters 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 Real-time locating systems (RTLS), also known as real-time tracking systems, are used to automatically identify and track the location of objects or people in real time, usually within a building or other contained area. Wireless RTLS tags are ...

(RTLS) concept as defined in the

international standard international standard is a technical standard developed by one or more international standards organizations. International standards are available for consideration and use worldwide. The most prominent such organization is the International Or ...

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 802.15.4a IEEE 802.15.4a (formally called IEEE 802.15.4a-2007) was an amendment to IEEE 802.15.4-2006 specifying that additional physical layers (PHYs) be added to the original standard. It has been merged into and is superseded by IEEE 802.15.4-2011. Overv ...

CSS as with IEEE 802.15.4aUWB modulation.Funknetzwerke daheim
/ref>

References

External links