Time of arrival
Encyclopedia
Time of arrival also called time of flight (ToF), is 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.
Compared to the TDOA technique, time of arrival uses the absolute time of arrival at a certain 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 velocity
. Time of arrival
data from two base stations will narrow a position to a circle; data from a third base station is required to resolve the precise position to a single point. Many radiolocation
systems, including GPS, use ToA.
of the network base station with the locating reference stations is important. This synchronization can be done in different ways:
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 .
Travel time
Travel time may refer to* Travel, movement of people between locations* Travel journal, record made by a voyager* Propagation speed, term in physics to measure things such as the speed of light or radio waves...
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.
Compared to the TDOA technique, time of arrival uses the absolute time of arrival at a certain base station
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...
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 velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
. Time of arrival
data from two base stations will narrow a position to a circle; data from a third base station is required to resolve the precise position to a single point. Many radiolocation
Radiolocation
Radiolocating 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, water mains, and other public utilities. It is similar to radionavigation, but radiolocation usually...
systems, including GPS, use ToA.
Ways of synchronization
As with TDOA, synchronizationSynchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
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 frequencies and hence spreading speed. Distance to a lightning strike can be measured in this way (speed of lightSpeed of lightThe speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
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 transmitterTransmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
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
Real-time locating system
Real-time locating systems are a type of local positioning system that allow to track and identify the location of objects in real time. Using simple, inexpensive badges or tags attached to the objects, readers receive wireless signals from these tags to determine their locations...
(RTLS) concept as defined in the international standard
International standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
ISO/IEC FCD 24730-5 .
Literature
A first 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 .See also
- Angle of arrivalAngle of arrivalAngle of arrival measurement is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna array...
- GSM localization
- RangingRangingRanging is a process or method to determine the distance from one location or position to another location or position. Another term for this method is lateration, see unilateration...
- RTLSRTLSRTLS may refer to:* Real-time locating system - general techniques for asset and staff tracking using wireless hardware and real-time software* Ravenna Training and Logistics Site - an Ohio Army National Guard base....
- TriangulationTriangulationIn trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...
- TrilaterationTrilaterationIn geometry, trilateration is the process of determinating absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. In addition to its interest as a geometric problem, trilateration does have practical applications in surveying and...
- MultilaterationMultilaterationMultilateration is a navigation technique based on the measurement of the difference in distance to two or more stations at known locations that broadcast signals at known times. Unlike measurements of absolute distance or angle, measuring the difference in distance results in an infinite number of...