Real-time locating system - AbsoluteAstronomy.com

Real-time locating systems (RTLS) 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 typically refers to systems that provide passive or active (automatic) collection of location information.

Location information usually does not include speed, direction, or spatial orientation. These additional measurements would be part of a navigation, maneuvering or positioning system.

Origin

The term RTLS was created (circa 1998) to describe an emerging technology that not only provided the Automatic Identification capabilities of active RFID tags, but added the ability to see the physical location of the tagged asset on a computer screen. Although this capability had been utilized previously by military and government agencies, the technology had been too expensive for commercial purposes.

By the early 1990s, commercialization began at two healthcare facilities in the United States (Foote Hospital

Foote Hospital

Allegiance Health is a community-owned and locally-governed health system located in Jackson in the U.S. state of Michigan. It was founded in 1918 as Foote Hospital when a local citizen, Mrs. Ida Foote, donated land for construction of the new hospital in honor of her late husband, W.A...

in Jackson, MI and Broward Children's Hospital

Broward Health

Broward Health, formerly the North Broward Hospital District, is one of the 10 largest health systems in the U.S. Located in Broward County, Florida, Broward Health has the county’s first certified stroke center and only liver transplant program...

in Pompano Beach, FL). These early adopters are attributed to real-time locating industry innovator Precision Tracking (Versus Technology, Inc.) and were based on the transmission and decoding of infrared light signals from actively transmitting tags.

System designs

RTLS excludes passive RFID indexing (radio frequency transponder indexers) and Cellnet base station segment locators (location-based service

Location-based service

A Location-Based Service is an information or entertainment service, accessible with mobile devices through the mobile network and utilizing the ability to make use of the geographical position of the mobile device....

s) from the scope of the ISO/IEC

International Electrotechnical Commission

The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

approach to RTLS standardization as well as all beacon

Beacon

A beacon is an intentionally conspicuous device designed to attract attention to a specific location.Beacons can also be combined with semaphoric or other indicators to provide important information, such as the status of an airport, by the colour and rotational pattern of its airport beacon, or of...

systems, that ping

Ping

Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol network and to measure the round-trip time for messages sent from the originating host to a destination computer...

without request.
RTLS systems apply typically in confined areas, where the required reference points would be equipped with wireless anchor nodes.

Operation

For RTLS to function, the location of tagged items must be determined either by a central processor or by an embedded mobile computing facility. Locating is generally accomplished in one of the following ways

1. ID signals from nodes are identifiable to a single reader in a sensory network thus indicating the coincidence of reader and nodes.
2. ID signals from nodes are picked up by a multiplicity of readers in a sensory network and a position is estimated using one or more locating algorithms
3. Location signals from signposts with identifiers are transmitted to the moving nodes and are then relayed, usually via a second wireless channel, to a location processor.
4. Mobile nodes communicate with each other and perform metering distances.

Examples one (1) and three (3) have much of the same characteristics. They typically require that a node be assigned at a time to a single reader/signpost. Separation from overlapping readers/signposts is roughly provided by RSSI or Physical Space Division (walls/floors/ceilings). Readers/signposts are often associated with highly stable location boundaries (i.e. a room or room division). In these examples, locations are listed as "Current Location" or "Last Known Location."

Example two (2) requires that distances between nodes in the sensory network be determined in order to precisely locate a node. In this instance, the determination of the location is called Localization. The location is calculated through Trilateration

Trilateration

In 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...

or Multilateration

Multilateration

Multilateration 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...

from the determined distance between the nodes or through Triangulation

Triangulation

In 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...

from the determined angles between nodes. The determination of distances is called 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...

Application

RTLS serves in operational areas for logistics and other services,as for example stock grounds or storehouses, and for servicing areas in clinics and industrial plants. Tasks done by a RTLS include:

to combine identity and location of any type of items or objects
to combine identity of items with location of lifter placing the items
to ensure permanent availability of proper information about temporary placement
to support notification of placing of items
to prove proper manning of operational areas
to prove consequent evacuation of endangered areas
to make marshalling staff dispensable

ISO/IEC

The basic issues of RTLS are standardized by the International Organization for Standardization

International Organization for Standardization

The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

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 or under discussion:

ISO/IEC FDIS 19762-5 Information technology AIDC techniques — Harmonized vocabulary, Part 5 — Locating systems
ISO/IEC 24730-1:2006 Information technology real-time locating systems (RTLS) Part 1: Application program interface (published).
ISO/IEC 24730-2:2006 Information technology real-time locating systems (RTLS) Part 2: 2,4 GHz Air interface protocol (published, WhereNet/Zebra approach).
ISO/IEC WD 24730-5 Information technology real-time locating systems (RTLS) Part 5: (drafted ISO/IEC standard out for balloting in 2008, Nanotron approach).

The other proposals ISO/IEC 24730-3 and ISO/IEC 24730-4 had never left the stage of intention. For copies of these documents see references.

These standards do not stipulate any special method of computing locations, nor the method of measuring locations. This may be defined in specifications for triangulation

Triangulation

or any hybrid approaches to trigonometric computing for planar or spherical models of a terrestrial area.

ANSI standards

ANS/INCITS 371: Information Technology – Real-Time Locating Systems (RTLS).

Ranging

Ranging, as a special term for measuring distance, is the prerequisite for locating. Measuring a bearing angle, i.e. angulating is the other alternative.

Determining the distance may be either a non cooperative scanning process, as with RADAR

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

or LIDAR

LIDAR

LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...

, or a cooperative direct distance measuring process, as with RTLS. A scanned beam may form an overall image as a model of the whole scene. In all other cases the image of the scene is rather selective.

The following step is extracting the distance information from the scanned image. Direct distance measurement with a single beam targets only the object to be measured, for example, with a laser. This method requires additional information about the direction of the beam. The remaining method is omni-directional transmission with a signal containing an address code. Only the addressed object responds to the request. The time required for the signal to reach the object can be used to calculate the distance. After completing the distance measurement, the location may be computed.

There are two different principles when measuring travel time of radio waves:

Trilateration
Trilateration
In 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...

derives the travel time of a radio signal from a metering unit, and measures and computes the distance with the relation of light speed in vacuum, the (Time of arrival
Time of arrival
Time 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...

concept).

Triangulation
Triangulation
In 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...

derives the travel time of a pair of synchronous radio signals from a metering unit with two transmitters, and measures and computes the difference of distance with the relation of light speed in vacuum as an angle versus the baseline of the two transmitters (TDOA time difference of arrival concept).

All the terms named here just apply to measurement concepts. All information about location is for services applied to mobile or portable or otherwise transportable objects. Location information may be relevant for managing interaction of persons with services as well.

Angle of arrival
Angle of arrival
Angle of arrival measurement is a method for determining the direction of propagation of a radio-frequency wave incident on an antenna array...

(AoA)
Line-of-sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

(LoS)
Time of arrival
Time of arrival
Time 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...

(ToA)
Multilateration
Multilateration
Multilateration 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...

(Time difference of arrival) (TDoA)
Time-of-flight
Time-of-flight
Time of flight describes a variety of methods that measure the time that it takes for an object, particle or acoustic, electromagnetic or other wave to travel a distance through a medium...

(ToF)
Two-way ranging (TWR) according to Nanotron’s patents
Symmetrical Double Sided – Two Way Ranging (SDS-TWR)
Near-field electromagnetic ranging
Near-field electromagnetic ranging
Near-field electromagnetic ranging refers to any radio technology employing the near-field properties of radio waves as a Real Time Location System .-Overview:...

(NFER)

Privacy concerns

RTLS may be seen a threat to privacy, if applied to persons, either directly or parasitically. The requirement therefore is to describe the purpose and the conditions of operation to those affected and to advertise for expressed agreement. Recent adjustment of jurisdiction leads to more careful assessment of needs and options. The newly declared human right of informational self-determination :de:Informationelle Selbstbestimmung, i.e. to prevent one's identity and personal data from disclosure to others, covers disclosure of locality as well. Base of discussion is very similar to disclosure of personal data for passing immigration at US airports: Balancing threat and burden http://www.hasbrouck.org/articles/PNR.html.

Types of technologies used

There is a wide variety of systems concepts and designs to provide real-time locating. A good choice is listed in RTLS for Dummies by Ajay Malik (Wiley 2009).
Methods include:

Active radio frequency identification
Radio Frequency Identification
Radio-frequency identification is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, attached to an object, through a reader for the purpose of identifying and tracking the object. Some RFID tags can be read from several meters away and beyond the...

(Active RFID)
Active radio frequency identification - infrared hybrid (Active RFID-IR)
Infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

(IR)
Optical locating,
Low-frequency signpost identification
Semi-active radio frequency identification (semi-active RFID)
Radio beacon,
Ultrasound Identification
Ultrasound Identification
Ultrasound Identification is a real-time locating system or indoor positioning system technology used to automatically determine and identify the location of objects with room accuracy....

(US-ID)
Ultrasonic ranging (US-RTLS)
Ultra-wideband
Ultra-wideband
Ultra-wideband is a radio technology that can be used at very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging...

(UWB)
Wide-over-narrow band
Wireless Local Area Network (WLAN, Wi-Fi)
Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...

,
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.

Locating concepts

A lot of systems concepts sails under the label of real-time locating systems. However the qualification of these approaches is very different and offers a wide variation of cost-to-benefit ratio.

Locating at choke points

There is class of most simple locating which applies no physical measurement at all, but just communicates at coincidence of transceiver and transponder as long as communication may happen. Then locating collapses to simple application of RFID technologies according to the equivalent standard. This is the only option to apply passive RFID tags for locating. Then the reach of the RFID reader determines the choke point. Hence accuracy is defined by the sphere spanned with the reach of the reader. The concept does not serve for discrimination of direction on passage, unless the reader is enhanced with a two distant antenna inputs to determine a sequence of activation and deactivation of the pair of antennae.

Locating in relative coordinates

Many references describe locating at relative coordinates. Such coordinates may be radial distances compared with reference to known locations and no angular directions. There is no exact metrics required, unless the relation to the reference points is intelligible. This is a valuable support for many operational needs, whereas the precision of the term RTLS is widely diluted to arbitrary interpretation. Such solutions may be referred as fuzzy locating.

Locating in absolute coordinates

The high precision of satellite navigation systems led to some snugness in setting the requirements for locating of objects. generally the determining of absolute coordinates is the most challenging approach. Such solutions may be referred as crisp locating. The difference to the qualities of relative coordinates may be easily understood with indoor sensor operations, where satellites are not commonly available for referring to global coordinates and when always a multiplicity of errors applies. The most challenging problem with modern modulation concepts still is multi-path propagation, which causes ambiguous results of erratic measurement.

A sound escape from electromagnetics and surface effects is found with ultra short pulse communications, as with UWB

UWB

UWB may refer to:* Ultra-wideband, a very wide band radio technologyIn education:* University of West Bohemia, Czech Republic* University of Washington, Bothell, United States...

indoor approaches. However, many such concepts often do not serve results for the paid price when the targets move. This may be assessed by the vast number of publications and the very small references on installed solutions

Locating in contiguity

A newer approach for locating defines a location just as the contiguous ambience of the person looking for something to be located. That is very similar to choke point locating. However, the accuracy may be much better tuned, as the reach is not influenced by the steady illumination of the tag with the reader, but just by the tuned transmission power level of an active RFID tag as an itermittent beacon

Beacon

.

This is the easy option to apply graded active RFID tags for economised locating. Then the reach of the RFID receiver determines the base point. Hence operational suitability is defined by the algorithm for varying the minimum reach of transmission of the beacon. Solutions are available as very simple electronic leash

Electronic leash

Electronic leash is a concept offered from various vendors in various functional shapes and physical designs. It is usually a miniature wireless appliance that extends the concept of a key pager, adding the feature of adjustable distance sensitivity and an option of a multiplicity of identity codes...

es or in more complex designs. A very common application is with electronic wireless lock

Wireless lock

Wireless lock is a protection concept for authenticated LAN or WLAN network clients offered from various vendors in various functional shapes and physical designs...

solutions. More advanced applications combine the tag operation with autonomously operating software agent

Software agent

In computer science, a software agent is a piece of software that acts for a user or other program in a relationship of agency, which derives from the Latin agere : an agreement to act on one's behalf...

s, e.g. in smartphone

Smartphone

A smartphone is a high-end mobile phone built on a mobile computing platform, with more advanced computing ability and connectivity than a contemporary feature phone. The first smartphones were devices that mainly combined the functions of a personal digital assistant and a mobile phone or camera...

s for monitoring manually controlled systems and services.

Erratic effects in locating systems

Real-time locating is affected by a variety of errors. The major reasons are physical and may not be reduced by improving the technical equipment. The only escape is mathematical intelligence to improve.

None or no direct response

Many RTLS systems have a very mundane requirement: they require direct and clear wireless visibility. For those systems, where there is no visibility on the path from mobile tags to resident 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 systems 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.

External links

Literature

Indoor Geolocation Using Wireless Local Area Networks (Berichte Aus Der Informatik), Michael Wallbaum (2006)
Local Positioning Systems: LBS applications and services, Krzysztof Kolodziej & Hjelm Johan, CRC Press Inc (2006)

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Origin

System designs

Operation

Application

ISO/IEC

ANSI standards

Ranging

Privacy concerns

Types of technologies used

Locating concepts

Locating at choke points

Locating in relative coordinates

Locating in absolute coordinates

Locating in contiguity

Erratic effects in locating systems

See also

External links

Literature