Radiolocation, also known as radiolocating or radiopositioning, is the process of finding the location of something through the use of

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...

s. It generally refers to passive uses, particularly

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...

—as well as detecting buried cables, water mains, and other

public utilities A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and ...

. It is similar to radionavigation, but radiolocation usually refers to passively finding a distant object rather than actively one's own position. Both are types of radiodetermination. Radiolocation is also used in

real-time locating systems 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) for tracking valuable assets.

Basic principles

An object can be located by measuring the characteristics of received radio waves. The radio waves may be transmitted by the object to be located, or they may be backscattered waves (as in radar or passive

RFID Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder, a radio receiver and transmitter. When triggered by an electromag ...

). A

stud finder A stud finder (also stud detector or stud sensor) is a handheld device used with wood buildings to locate framing studs located behind the final walling surface, usually drywall. While there are many different stud finders available, most fall ...

uses radiolocation when it uses radio waves rather than

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...

. One technique measures a distance by using the difference in the power of the received signal strength (RSSI) as compared to the originating signal strength. Another technique uses the time of arrival (TOA), when the time of transmission and speed of propagation are known. Combining TOA data from several receivers at different known locations (time difference of arrival, TDOA) can provide an estimate of position even in the absence of knowledge of the time of transmission. The angle of arrival (AOA) at a receiving station can be determined by the use of a directional antenna, or by differential time of arrival at an array of antennas with known location. AOA information may be combined with distance estimates from the techniques previously described to establish the location of a transmitter or backscatterer. Alternatively, the AOA at two receiving stations of known location establishes the position of the transmitter. The use of multiple receivers to locate a transmitter is known as multilateration. Estimates are improved when the transmission characteristics of the medium is factored into the calculations. For RSSI this means electromagnetic permeability; for TOA it may mean

non-line-of-sight Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections. Near-line-of-sight (also NLOS) conditions refer to partial obstruction by a physica ...

receptions. Use of RSSI to locate a transmitter from a single receiver requires that both the transmitted (or backscattered) power from the object to be located are known, and that the propagation characteristics of the intervening region are known. In empty space, signal strength decreases as the inverse square of the distance for distances large compared to a wavelength and compared to the object to be located, but in most real environments, a number of impairments can occur: absorption, refraction, shadowing, and reflection. Absorption is negligible for radio propagation in air at frequencies less than about 10 GHz, but becomes important at multi-GHz frequencies where rotational molecular states can be excited. Refraction is important at long ranges (tens to hundreds of kilometers) due to gradients in moisture content and temperature in the atmosphere. In urban, mountainous, or indoor environments, obstruction by intervening obstacles and reflection from nearby surfaces are very common, and contribute to multipath distortion: that is, reflected and delayed replicates of the transmitted signal are combined at the receiver. Signals from different paths can add constructively or destructively: such variations in amplitude are known as

fading In wireless communications, fading is variation of the attenuation of a signal with various variables. These variables include time, geographical position, and radio frequency. Fading is often modeled as a random process. A fading channel is ...

. The dependence of signal strength on position of transmitter and receiver becomes complex and often non-monotonic, making single-receiver estimates of position inaccurate and unreliable. Multilateration using many receivers is often combined with calibration measurements ("fingerprinting") to improve accuracy. TOA and AOA measurements are also subject to multipath errors, particularly when the direct path from the transmitter to receiver is blocked by an obstacle. Time of arrival measurements are also most accurate when the signal has distinct time-dependent features on the scale of interest—for example, when it is composed of short pulses of known duration—but

Fourier transform A Fourier transform (FT) is a mathematical transform that decomposes functions into frequency components, which are represented by the output of the transform as a function of frequency. Most commonly functions of time or space are transformed ...

theory shows that in order to change amplitude or phase on a short time scale, a signal must use a broad bandwidth. For example, to create a pulse of about 1 ns duration, roughly sufficient to identify location to within 0.3 m (1 foot), a bandwidth of roughly 1 GHz is required. In many regions of the radio spectrum, emission over such a broad bandwidth is not allowed by the relevant regulatory authorities, in order to avoid interference with other narrowband users of the spectrum. In the United States, unlicensed transmission is allowed in several bands, such as the 902-928 MHz and 2.4-2.483 GHz Industrial, Scientific, and Medical ISM bands, but high-power transmission cannot extend outside of these bands. However, several jurisdictions now allow ultrawideband transmission over GHz or multi-GHz bandwidths, with constraints on transmitted power to minimize interference with other spectrum users. UWB pulses can be very narrow in time, and often provide accurate estimates of TOA in urban or indoor environments. Radiolocation is employed in a wide variety of industrial and military activities. Radar systems often use a combination of TOA and AOA to determine a backscattering object's position using a single receiver. In Doppler radar, the

Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who ...

is also taken into account, determining

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

rather than location (though it helps determine future location). Real Time Location Systems RTLS using calibrated RTLS, and TDOA, are commercially available. The widely used Global Positioning System ( GPS) is based on TOA of signals from satellites at known positions.

Mobile phones

Radiolocation is also used in cellular telephony via

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 c ...

s. Most often, this is done through trilateration between radio towers. The location of the Caller or handset can be determined several ways: * angle of arrival (AOA) requires at least two towers, locating the caller at the point where the lines along the angles from each tower intersect * time difference of arrival (TDOA) resp. time of arrival (TOA) works using multilateration, except that it is the networks that determine the time difference and therefore distance from each tower (as with seismometers) * location signature uses "

fingerprint A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...

ing" to store and recall patterns (such as multipath) which mobile phone signals are known to exhibit at different locations in each cell The first two depend on a line-of-sight, which can be difficult or impossible in

mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher ...

ous

terrain Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin word ...

or around

skyscraper A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ri ...

s. Location signatures actually work ''better'' in these conditions however. TDMA and GSM networks such as Cingular and T-Mobile use TDOA. CDMA networks such as

Verizon Wireless Verizon is an American wireless network operator that previously operated as a separate division of Verizon Communications under the name Verizon Wireless. In a 2019 reorganization, Verizon moved the wireless products and services into the div ...

and

Sprint PCS Sprint Corporation was an American telecommunications company. Before it merged with T-Mobile US on April 1, 2020, it was the fourth-largest mobile network operator in the United States, serving 54.3 million customers as of June 30, 2019. The co ...

tend to use handset-based radiolocation technologies, which are technically more similar to radionavigation. GPS is one of those technologies. Composite solutions, needing both the handset and the network include: * assisted GPS (

wireless Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...

or TV) allows use of GPS even indoors * Advanced Forward Link Trilateration ( A-FLT) * Timing Advance/Network Measurement Report ( TA/NMR) *

Enhanced Observed Time Difference Enhanced Observed Time Difference (E-OTD) is a standard for the location of mobile telephones. The location method works by multilateration. The standardisation was first carried out for GSM by the GSM standard committees (T1P1.5 and ETIS) in LCS ...

(

E-OTD Enhanced Observed Time Difference (E-OTD) is a standard for the location of mobile telephones. The location method works by multilateration. The standardisation was first carried out for GSM by the GSM standard committees (T1P1.5 and ETIS) in LCS ...

) Initially, the purpose of any of these in mobile phones is so that the public safety answering point (PSAP) which answers calls to an

emergency telephone number Most public switched telephone networks have a single emergency telephone number (sometimes known as the universal emergency telephone number or the emergency services number) that allows a caller to contact local emergency services for assis ...

can know where the caller is and exactly where to send

emergency services Emergency services and rescue services are organizations that ensure public safety and health by addressing and resolving different emergencies. Some of these agencies exist solely for addressing certain types of emergencies, while others deal w ...

. This ability is known within the NANP (

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

) as wireless enhanced 911. Mobile phone users may have the option to permit the location information gathered to be sent to other

phone number A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...

s or

data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...

networks, so that it can help people who are simply lost or want other location-based services. By default, this selection is usually turned off, to protect

privacy Privacy (, ) is the ability of an individual or group to seclude themselves or information about themselves, and thereby express themselves selectively. The domain of privacy partially overlaps with security, which can include the concepts of ...

International regulation

Radiolocation service (short: RLS) is – according to ''Article 1.48'' of the International Telecommunication Union's (ITU)

Radio Regulations Radio regulation refers to the regulation and licensing of radio in international law, by individual governments, and by municipalities. International regulation The International Telecommunication Union (ITU) is a specialized agency of the Unit ...

(RR) – defined as "A radiodetermination service for the purpose of radiolocation", where radiolocation is defined as: "radiodetermination used for purposes other than those of radionavigation."

Classification

This '' radiocommunication service'' is classified in accordance with ''ITU Radio Regulations'' (article 1) as follows:
Radiodetermination service (article 1.40) *Radiolocation service (article 1.48) **

Radiolocation-satellite service 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 ...

(article 1.49) The ''radiolocation service'' distinguishes basically *

Radiolocation mobile station 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 ...

land-mobile, air-mobile, sea-mobile (article 1.89) * Radiolocation land station (article 1.90)

Examples

Radar antenna.jpg, Bundesarchiv Bild 101I-356-1845-08, Frankreich, Radar an der Kanalküste.jpg, Cavalierairforcestationparcs.jpg, APAR.jpg, File:Boeing E-3 Sentry 090512-F-7550B-902.jpg, File:Radar TRML-3D.jpg,

Satellites

Radiolocation-satellite service (short: RLSS) is – according to ''Article 1.49'' of the International Telecommunication Union´s (ITU)

(RR) – defined as ''«A radiodetermination-satellite service used for the purpose of radiolocation. This (radiocommunication) service may also include the feeder links necessary for its operation''.» The ''radiolocation-satellite service'' distinguishes basically *Earth radio stations *Feeder links and *Space radio stations For example military radar sensors in earth satellites operate in the ''radiolocation-satellite service'' n this service. ;Examples of

radio station Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio ...

s in the ''radiolocation-satellite service'' : ORS-2.jpg, NRO Lacrosse.jpg, Космос-954.jpg,

Frequency allocation

The allocation of radio frequencies is provided according to ''Article 5'' of the ITU Radio Regulations (edition 2012). In order to improve harmonisation in spectrum utilisation, the majority of service-allocations stipulated in this document were incorporated in national Tables of Frequency Allocations and Utilisations which is within the responsibility of the appropriate national administration. The allocation might be primary, secondary, exclusive, and shared. ; Example of

frequency allocation Frequency allocation (or spectrum allocation or spectrum management) is the allocation and regulation of the electromagnetic spectrum into radio frequency bands, normally done by governments in most countries. Because radio propagation does ...

Stations

Land station

A radiolocation land station is – according to ''article 1.90'' of the International Telecommunication Union's (ITU)

ITU Radio Regulations The ITU Radio Regulations (short: RR) is a basic document of the International Telecommunication Union (ITU) that regulates on law of nations scale radiocommunication services and the utilisation of radio frequencies. It is the supplementatio ...

(RR) – defined as "a

radiolocation service 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 ...

not intended to be used while in motion." Each ''radiolocation station'' shall be classified by the '' radiocommunication service'' in which it operates permanently or temporarily. In accordance with ''ITU Radio Regulations'' (article 1) this type of ''radio station'' might be classified as follows:
Radiodetermination station (article 1.86) of the radiodetermination service (article 1.40 ) *

Radionavigation mobile station Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination. The basic principles ar ...

(article 1.87) of the radionavigation service (article 1.42) * Radionavigation land station (article 1.88) of the radionavigation service *

(article 1.89) of the radiolocation service (article 1.48) *Radiolocation land station ;Selection ''radiolocation land stations'': 2012-08 FuMG 65 Funkmessgeraet Wuerzburg Riese anagoria 01.JPG, German Radar Wurzburg Riese (FuMG 65) Radar antenna.jpg, ARPA Long-Range Tracking and Instrumentation Radar (ALTAIR) 14a-WFF Radar.png, NASA Wallops Flight Facility Radar Antenna radar L-band TAR Finland.JPG, Antenna radar L band TAR Finland C-band Radar-dish Antenna.jpg, 50 Feet dish Antenna of a 3 kW C band Radar FPS-108 Cobra Dane.jpg, Intelligence-gathering phased array radar FPS-108 COBRA DANE Cavalierairforcestationparcs.jpg, Phased array radar AN/FPQ-16 PARCS Lägern - Hochwacht - Skyguide 20100524 17-29-30 ShiftN.jpg, Skyguide radar, Hochwacht in Boppelsen on Lägern (Switzerland)

Mobile station

Radiolocation mobile station is – according to ''article 1.89'' of the International Telecommunication Union´s (ITU)

(RR)ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.89, definition: ''radiolocation mobile station'' – defined as "A

intended to be used while in motion or during halts at unspecified points." Each ''radiolocation station'' shall be classified by the '' radiocommunication service'' in which it operates permanently or temporarily. In accordance with ''ITU Radio Regulations'' (article 1) this type of ''radio station'' might be classified as follows:
Radiodetermination station (article 1.86) of the radiodetermination service (article 1.40 ) *

(article 1.87) of the radionavigation service (article 1.42) * Radionavigation land station (article 1.88) of the radionavigation service *Radiolocation mobile station ;Selection ''radiolocation mobile stations'': Radar TRML-3D.jpg, Radar PRV-17 2009 G2.jpg, RAAF radar.jpg, Luer1.jpg, MIM-104 Patriot Radar unit (JASDF).jpg, Nike Hercules IFC radars.JPG, Nike Hercules IFC radars LOPAR and the tracking radars (MTR, TTR, TRR) f.l.t.r. APAR.jpg, Mark 68 director containing SPG-53.jpg, Weapon control radar Sbx underway.jpg, ME-110G-2 at RAF Hendon.jpg,