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 attached to objects or worn by people, and in most RTLS, fixed reference points receive wireless signals from tags to determine their location. Examples of real-time locating systems include tracking automobiles through an assembly line, locating pallets of merchandise in a warehouse, or finding medical equipment in a hospital. The physical layer of RTLS technology is often

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the ...

(RF) communication. Some systems use optical (usually

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

) or acoustic (usually

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 ...

) technology with, or in place of, RF. RTLS tags and fixed reference points can be

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, receivers, or both, resulting in numerous possible technology combinations. RTLS are a form of local positioning system and do not usually refer to

GPS The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...

or to

mobile phone tracking Mobile phone tracking is a process for identifying the location of a mobile phone, whether stationary or moving. Localization may be effected by a number of technologies, such as the multilateration of radio signals between (several) cell towers ...

. Location information usually does not include speed, direction, or spatial orientation.

Origin

The term RTLS was created (circa 1998) at the ID EXPO trade show by Tim Harrington (WhereNet), Jay Werb (PinPoint), and Bert Moore (Automatic Identification Manufacturers, Inc., AIM). It was created to describe and differentiate an

emerging technology Emerging technologies are technologies whose development, practical applications, or both are still largely unrealized. These technologies are generally new but also include older technologies finding new applications. Emerging technologies ar ...

that not only provided the automatic identification capabilities of active RFID tags, but also added the ability to view the location on a computer screen. It was at this show that the first examples of a commercial radio based RTLS system were shown by PinPoint and WhereNet. Although this capability had been utilized previously by military and government agencies, the technology had been too expensive for commercial purposes. In the early 1990s, the first commercial RTLS were installed at three healthcare facilities in the United States and were based on the transmission and decoding of

infrared light Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...

signals from actively transmitting tags. Since then, new technology has emerged that also enables RTLS to be applied to passive tag applications.

Locating concepts

RTLS are generally used in indoor and/or confined areas, such as buildings, and do not provide global coverage like

. RTLS tags are affixed to mobile items to be tracked or managed. RTLS reference points, which can be either transmitters or receivers, are spaced throughout a building (or similar area of interest) to provide the desired tag coverage. In most cases, the more RTLS reference points that are installed, the better the location accuracy, until the technology limitations are reached. A number of disparate system designs are all referred to as "real-time locating systems". Two primary system design elements are locating at choke points and locating in relative coordinates.

Locating at choke points

The simplest form of

choke point In military strategy, a choke point (or chokepoint) is a geographical feature on land such as a valley, defile or bridge, or maritime passage through a critical waterway such as a strait, which an armed force is forced to pass through in order ...

locating is where short range ID signals from a moving tag are received by a single fixed reader in a sensory network, thus indicating the location coincidence of reader and tag. Alternately, a choke point identifier can be received by the moving tag and then relayed, usually via a second wireless channel, to a location processor. Accuracy is usually defined by the sphere spanned with the reach of the choke point transmitter or receiver. The use of directional antennas, or technologies such as infrared or ultrasound that are blocked by room partitions, can support choke points of various geometries.

Locating in relative coordinates

ID signals from a tag are received by a multiplicity of readers in a

sensory network A sensor grid integrates wireless sensor networks with grid computing concepts to enable real-time data collection and the sharing of computational and storage resources for sensor data processing and management. It is an enabling technology for bu ...

, and a position is estimated using one or more locating algorithms, such as

trilateration 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 e ...

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 e ...

, or triangulation. Equivalently, ID signals from several RTLS reference points can be received by a tag and relayed back to a location processor. Localization with multiple reference points requires that distances between reference points in the sensory network be known in order to precisely locate a tag, and the determination of distances is called

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 ...

. Another way to calculate relative location is via mobile tags communicating with one another. The tag(s) will then relay this information to a location processor.

Location accuracy

RF trilateration uses estimated ranges from multiple receivers to estimate the location of a tag. RF triangulation uses the angles at which the RF signals arrive at multiple receivers to estimate the location of a tag. Many obstructions, such as walls or furniture, can distort the estimated range and angle readings leading to varied qualities of location estimate. Estimation-based locating is often measured in accuracy for a given distance, such as 90% accurate for 10-meter range. Some systems use locating technologies that can't pass through walls, such as infrared or ultrasound. These require line of sight (or near line of sight) to communicate properly. As a result, they tend to be more accurate in indoor environments.

Applications

RTLS can be used in numerous logistical or operational areas to: * locate and manage assets within a facility, such as finding a misplaced tool cart in a

warehouse A warehouse is a building for storing goods. Warehouses are used by manufacturers, importers, exporters, wholesalers, transport businesses, customs, etc. They are usually large plain buildings in industrial parks on the outskirts of cities ...

or medical equipment in a hospital * create notifications when an object moves, such as an alert if a tool cart left the facility * combine identity of multiple items placed in a single location, such as on a pallet * locate customers, for example in a restaurant, for delivery of food or service * maintain proper staffing levels of operational areas, such as ensuring guards are in the proper locations in a

correctional facility In criminal justice, particularly in North America, correction, corrections, and correctional, are umbrella terms describing a variety of functions typically carried out by government agencies, and involving the punishment, treatment, and s ...

* quickly and automatically account for all staff after or during an emergency evacuation * Toronto General Hospital is looking at RTLS to reduce quarantine times after an infectious disease outbreak. After a recent

SARS Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''seve ...

outbreak, 1% of all staff were quarantined. With RTLS, they would have more accurate data regarding who had been exposed to the virus, potentially reducing the need for quarantines. * aid in process improvement efforts by automatically tracking and time stamping the progress of people or assets through a process, such as following a patient's emergency room wait time, time spent in the operating room, and total time until discharge * help in healthcare provision through staff and patient monitoring and delivering the right equipment for use in certain situations as the technology eliminates long hours of storing manual reports, calling, locating staff and equipment * aid in acute care capacity management through clinical-care locating * provide

Wayfinding Wayfinding (or way-finding) encompasses all of the ways in which people (and animals) orient themselves in physical space and navigate from place to place. Wayfinding software is a self-service computer program that helps users to find a location, ...

for guests in a facility, like hospitals and stadiums * prevent

Child abduction Child abduction or child theft is the unauthorized removal of a minor (a child under the age of legal adulthood) from the custody of the child's natural parents or legally appointed guardians. The term ''child abduction'' includes two lega ...

by sounding alerts or alarms if an infant leaves the boundary of a hospital's Birthing center

Privacy concerns

RTLS may be seen as a threat to privacy when used to determine the location of people. The newly declared human right of informational self-determination gives the right to prevent one's identity and personal data from being disclosed to others and also covers disclosure of locality, though this does not generally apply to the

workplace A workplace is a location where someone works, for their employer or themselves, a place of employment. Such a place can range from a home office to a large office building or factory. For industrialized societies, the workplace is one of th ...

. Several prominent labor unions have spoken out against the use of RTLS systems to track workers, calling them "the beginning of Big Brother" and "an

invasion of privacy The right to privacy is an element of various legal traditions that intends to restrain governmental and private actions that threaten the privacy of individuals. Over 150 national constitutions mention the right to privacy. On 10 December 194 ...

". Current location-tracking technologies can be used to pinpoint users of mobile devices in several ways. First, service providers have access to network-based and handset-based technologies that can locate a phone for emergency purposes. Second, historical location can frequently be discerned from service provider records. Thirdly, other devices such as Wi-Fi hotspots or IMSI catchers can be used to track nearby mobile devices in real time. Finally, hybrid positioning systems combine different methods in an attempt to overcome each individual method's shortcomings.

Types of technologies used

There is a wide variety of systems concepts and designs to provide real-time locating. * Active

radio frequency identification 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 electrom ...

(Active RFID) * Active radio frequency identification - infrared hybrid (Active RFID-IR) *

Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

(IR) * Optical locating * Low-frequency signpost identification * Semi-active radio frequency identification (semi-active RFID) * Passive RFID RTLS locating via steerable phased array antennae * Radio beacon * Ultrasound Identification (US-ID) * Ultrasonic ranging (US-RTLS) *

Ultra-wideband Ultra-wideband (UWB, ultra wideband, ultra-wide band and ultraband) is a radio technology that can use a very low energy level for short-range, high-bandwidth communications over a large portion of the radio spectrum. UWB has traditional applicati ...

(UWB) * Wide-over-narrow band *

Wireless local area network A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office buildi ...

(WLAN, Wi-Fi) *

Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is limi ...

* Clustering in noisy ambience * Bivalent systems A general model for selection of the best solution for a locating problem has been constructed at the Radboud University of Nijmegen. Many of these references do not comply with the definitions given in international standardization with ISO/IEC 19762-5 and ISO/IEC 24730-1. However, some aspects of real-time performance are served and aspects of locating are addressed in context of absolute coordinates.

Ranging and angulating

Depending on the physical technology used, at least one and often some combination of ranging and/or angulating methods are used to determine location: *

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 ...

(AoA) * Angle of departure (AoD) (e.g., Bluetooth direction finding features a mobile-centric RTLS architecture - see US 7376428 B1) *

Line of sight The line of sight, also known as visual axis or sightline (also sight line), is an imaginary line between a viewer/observer/ spectator's eye(s) and a subject of interest, or their relative direction. The subject may be any definable object taken ...

(LoS) *

Time of arrival 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 diff ...

(ToA) *

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 e ...

(Time difference of arrival) (TDoA) *

Time of flight Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a w ...

(ToF) * Two-way ranging (TWR) according to Nanotron's patents * Symmetrical double-sided two-way ranging (SDS-TWR) * Near-field electromagnetic ranging (NFER)

Errors and accuracy

Real-time locating is affected by a variety of errors. Many of the major reasons relate to the physics of the locating system, and may not be reduced by improving the technical equipment. ;None or no direct response Many RTLS systems require direct and clear line of sight visibility. For those systems, where there is no visibility from mobile tags to fixed nodes there will be no result or a non valid result from locating engine. This applies to satellite locating as well as other RTLS systems such as angle of arrival and time of arrival. Fingerprinting is a way to overcome the visibility issue: If the locations in the tracking area contain distinct measurement fingerprints, line of sight is not necessarily needed. For example, if each location contains a unique combination of signal strength readings from transmitters, the location system will function properly. This is true, for example, with some Wi-Fi based RTLS solutions. However, having distinct signal strength fingerprints in each location typically requires a fairly high saturation of transmitters. ;False location The measured location may appear entirely faulty. This is a generally result of simple operational models to compensate for the plurality of error sources. It proves impossible to serve proper location after ignoring the errors. ;Locating backlog ''Real time'' is no registered branding and has no inherent quality. A variety of offers sails under this term. As motion causes location changes, inevitably the latency time to compute a new location may be dominant with regard to motion. Either an RTLS system that requires waiting for new results is not worth the money or the operational concept that asks for faster location updates does not comply with the chosen system's approach. ;Temporary location error Location will never be reported ''exactly'', as the term ''real-time'' and the term ''precision'' directly contradict in aspects of measurement theory as well as the term ''precision'' and the term ''cost'' contradict in aspects of economy. That is no exclusion of precision, but the limitations with higher speed are inevitable. ;Steady location error Recognizing a reported location steadily apart from physical presence generally indicates the problem of insufficient over-determination and missing of visibility along at least one link from resident anchors to mobile transponders. Such effect is caused also by insufficient concepts to compensate for calibration needs. ;Location jitter Noise from various sources has an erratic influence on stability of results. The aim to provide a steady appearance increases the latency contradicting to real time requirements. ;Location jump As objects containing mass have limitations to jump, such effects are mostly beyond physical reality. Jumps of reported location not visible with the object itself generally indicate improper modeling with the location engine. Such effect is caused by changing dominance of various secondary responses. ;Location creep Location of residing objects gets reported moving, as soon as the measures taken are biased by secondary path reflections with increasing weight over time. Such effect is caused by simple averaging and the effect indicates insufficient discrimination of first echoes.

Standards

ISO/IEC

The basic issues of RTLS are standardized by the

International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Art ...

and the International Electrotechnical Commission under the ISO/IEC 24730 series. In this series of standards, the basic standard ISO/IEC 24730-1 identifies the terms describing a form of RTLS used by a set of vendors but does not encompass the full scope of RTLS technology. Currently several standards are published: * ISO/IEC 19762-5:2008 Information technology — Automatic identification and data capture (AIDC) techniques — Harmonized vocabulary—Part 5: Locating systems * ISO/IEC 24730-1:2014 Information technology — Real-time locating systems (RTLS) — Part 1: Application programming interface (API) * ISO/IEC 24730-2:2012 Information technology — Real time locating systems (RTLS) — Part 2: Direct Sequence Spread Spectrum (DSSS) 2,4 GHz air interface protocol * ISO/IEC 24730-5:2010 Information technology — Real-time locating systems (RTLS) — Part 5: Chirp spread spectrum (CSS) at 2,4 GHz air interface * ISO/IEC 24730-21:2012 Information technology — Real time locating systems (RTLS) — Part 21: Direct Sequence Spread Spectrum (DSSS) 2,4 GHz air interface protocol: Transmitters operating with a single spread code and employing a DBPSK data encoding and BPSK spreading scheme * ISO/IEC 24730-22:2012 Information technology — Real time locating systems (RTLS) — Part 22: Direct Sequence Spread Spectrum (DSSS) 2,4 GHz air interface protocol: Transmitters operating with multiple spread codes and employing a QPSK data encoding and Walsh offset QPSK (WOQPSK) spreading scheme * ISO/IEC 24730-61:2013 Information technology — Real time locating systems (RTLS) — Part 61: Low rate pulse repetition frequency Ultra Wide Band (UWB) air interface * ISO/IEC 24730-62:2013 Information technology — Real time locating systems (RTLS) — Part 62: High rate pulse repetition frequency Ultra Wide Band (UWB) air interface These standards do not stipulate any special method of computing locations, nor the method of measuring locations. This may be defined in specifications for trilateration, triangulation, or any hybrid approaches to trigonometric computing for planar or spherical models of a terrestrial area.

INCITS

INCITS The InterNational Committee for Information Technology Standards (INCITS), (pronounced "insights"), is an ANSI-accredited standards development organization composed of Information technology developers. It was formerly known as the X3 and NCITS. ...

371.1:2003, Information Technology - Real Time Locating Systems (RTLS) - Part 1: 2.4 GHz Air Interface Protocol * INCITS 371.2:2003, Information Technology - Real Time Locating Systems (RTLS) - Part 2: 433-MHz Air Interface Protocol * INCITS 371.3:2003, Information Technology - Real Time Locating Systems (RTLS) - Part 3: Application Programming Interface

Limitations and further discussion

In RTLS application in the healthcare industry, various studies were issued discussing the limitations of the currently adopted RTLS. Currently used technologies RFID, Wi-fi, UWB, all RFID based are hazardous in the sense of interference with sensitive equipment. A study carried out by Dr Erik Jan van Lieshout of the Academic Medical Centre of the University of Amsterdam published in ''JAMA'' (''Journal of the American Medical Equipment'') claimed "RFID and UWB could shut down equipment patients rely on" as "RFID caused interference in 34 of the 123 tests they performed". The first Bluetooth RTLS provider in the medical industry is supporting this in their article: "The fact that RFID cannot be used near sensitive equipment should in itself be a red flag to the medical industry". The RFID Journal responded to this study not negating it rather explaining real-case solution: "The Purdue study showed no effect when ultrahigh-frequency (UHF) systems were kept at a reasonable distance from medical equipment. So placing readers in utility rooms, near elevators and above doors between hospital wings or departments to track assets is not a problem". However the case of ”keeping at a reasonable distance” might be still an open question for the RTLS technology adopters and providers in medical facilities. In many applications it is very difficult and at the same time important to make a proper choice among various communication technologies (e.g., RFID, WiFi, etc.) which RTLS may include. Wrong design decisions made at early stages can lead to catastrophic results for the system and a significant loss of money for fixing and redesign. To solve this problem a special methodology for RTLS design space exploration was developed. It consists of such steps as modelling, requirements specification, and verification into a single efficient process.