Angle of arrival
Encyclopedia
Angle of arrival measurement is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna array
. AoA determines the direction by measuring the Time Difference of Arrival (TDOA) at individual elements of the array -- from these delays the AoA can be calculated.
Generally this TDOA measurement is made by measuring the difference in received phase at each element in the antenna array. This can be thought of as beamforming
in reverse. In beamforming, the signal from each element is delayed by some weight to "steer" the gain of the antenna array. In AoA, the delay of arrival at each element is measured directly and converted to an AoA measurement.
Consider, for example, a two element array spaced apart by one-half the wavelength of an incoming RF wave. If a wave is incident upon the array at boresight, it will arrive at each antenna simultaneously. This will yield 0° phase-difference measured between the two antenna elements, equivalent to a 0° AoA. If a wave is incident upon the array at broadside, then a 180° phase difference will be measured between the elements, corresponding to a 90° AoA.
A current application of AoA is in the geodesic
location or geolocation
of cell phones. The aim is either to comply with regulations that require cell systems to report the location of a cell phone placing an emergency (i.e., 911) call or to provide a special service to tell the bearer of the cell phone where he is. Multiple receivers on a base station would calculate the AoA of the cell phone's signal, and this information would be combined to determine the phone's location on the earth.
AoA is generally used to discover the location of pirate radio stations
or of any military
radio transmitter.
In submarine
acoustics
, AoA is the method to localize objects with active or passive ranging
.
In optics
, AoA is considered from the perspective of interferometry
.
Antenna array
Antenna array may refer to:*Antenna array a group of isotropic radiators such that the currents running through them are of different amplitudes and phases*Interferometric array of radio telescopes used in radio astronomy...
. AoA determines the direction by measuring the Time Difference of Arrival (TDOA) at individual elements of the array -- from these delays the AoA can be calculated.
Generally this TDOA measurement is made by measuring the difference in received phase at each element in the antenna array. This can be thought of as beamforming
Beamforming
Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
in reverse. In beamforming, the signal from each element is delayed by some weight to "steer" the gain of the antenna array. In AoA, the delay of arrival at each element is measured directly and converted to an AoA measurement.
Consider, for example, a two element array spaced apart by one-half the wavelength of an incoming RF wave. If a wave is incident upon the array at boresight, it will arrive at each antenna simultaneously. This will yield 0° phase-difference measured between the two antenna elements, equivalent to a 0° AoA. If a wave is incident upon the array at broadside, then a 180° phase difference will be measured between the elements, corresponding to a 90° AoA.
A current application of AoA is in the geodesic
Geodesic
In mathematics, a geodesic is a generalization of the notion of a "straight line" to "curved spaces". In the presence of a Riemannian metric, geodesics are defined to be the shortest path between points in the space...
location or geolocation
Geolocation
Geolocation is the identification of the real-world geographic location of an object, such as a radar, mobile phone or an Internet-connected computer terminal...
of cell phones. The aim is either to comply with regulations that require cell systems to report the location of a cell phone placing an emergency (i.e., 911) call or to provide a special service to tell the bearer of the cell phone where he is. Multiple receivers on a base station would calculate the AoA of the cell phone's signal, and this information would be combined to determine the phone's location on the earth.
AoA is generally used to discover the location of pirate radio stations
Pirate radio
Pirate radio is illegal or unregulated radio transmission. The term is most commonly used to describe illegal broadcasting for entertainment or political purposes, but is also sometimes used for illegal two-way radio operation...
or of any military
Military
A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...
radio transmitter.
In submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
acoustics
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
, AoA is the method to localize objects with active or passive ranging
Ranging
Ranging 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...
.
In optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, AoA is considered from the perspective of interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
.
See also
- GeolocationGeolocationGeolocation is the identification of the real-world geographic location of an object, such as a radar, mobile phone or an Internet-connected computer terminal...
- GNSS
- GSM localization
- 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...
- RadiolocationRadiolocationRadiolocating 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...
- Time of arrivalTime of arrivalTime of arrival , also called time of flight , 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...
- 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...
- Wideband Space Division Multiple AccessWsdmaWSDMA is a high bandwidth channel access method, developed for multi-transceiver systems such as active array antennas. WSDMA is a beamforming technique suitable for overlay on the latest air-interface protocols including WCDMA and OFDM...