Indoor Positioning System
Encyclopedia
An indoor positioning system (IPS) is a term used for a network of devices used to wirelessly locate objects or people inside a building. Generally the products offered under this term do not comply with the International standard ISO/IEC 24730 on real-time locating system
s (RTLS). There is currently no de facto standard for an IPS systems design, so deployment has been slow. Nevertheless, there are several commercial systems on the market.
Instead of using satellites, an IPS relies on nearby anchors (nodes with a known position), which either actively locate tags or provide environmental context for devices to sense. The localized nature of an IPS has resulted in design fragmentation, with systems making use of various optical, radio
, or even acoustic
technologies.
caused by construction materials, the satellite based Global Positioning System
(GPS) loses significantly power indoors affecting the required coverage for receivers by at least four satellites. In addition, the multiple reflections at surfaces cause multi-path propagation serving for uncontrollable errors. These very same effects are degrading all known solutions for indoor locating which uses electromagnetic waves from indoor transmitters to indoor receivers. A bundle of physical and mathematical methods is applied to compensate for these problems.
With detailed reading in the marketing documents and even in the specifications served by many of the IPS vendors, the interested customer will look for details on precision, reproducibility and other terms for quality of function with poor success. Many vendors do not tangle the term accuracy with the slightest comment.
s (GPS
or GNSS) are generally not suitable to establish indoor locations, since microwaves will be attenuated and scattered by roofs, walls and other objects.
Currently, GNSS receivers are becoming more and more sensitive due to ceaseless progress in chip technology and processing power. High Sensitivity GNSS
receivers are able to receive satellite signals in most indoor environments and attempts to determine the 3D position indoors have been successful. Besides increasing the sensitivity of the receivers, the technique of A-GPS
is used, where the almanac and other information are transferred though a mobile phone.
However, proper coverage for the required for satellites to locate a receiver is not achieved with all current designs (2008-11) for indoor operations. Beyond, the average error budget for GNSS systems normally is much larger than the confinements, in which the locating shall be performed.
of an object, not including the detection of the orientation
or direction
of that object. All known indoor positioning systems (IPS) neither affects nor detects a direction nor offers the option to change the position. Also other various systems titled as e.g. local positioning system and so on do not offer other but detecting an object in a certain known fixed
location, report a measured location or just report the presence of the object in such location.
(RFID) systems, which do not report the signal strengths and various distances of single tags or of a pulk of tags and do not renew any before known location coordinates of the sensor or current location of any tags. Operability of such approaches requires some narrow passage to prevent from passing by out of range.
(AoA) is the angle from which a signal arrives at a receiver. AoA is usually determined by measuring the time difference of arrival (TDOA) between multiple antennas in a sensor array. In other receivers, it is determined by an array of highly directional sensors—the angle can be determined by which sensor received the signal. AoA is usually used with triangulation
to find the location relative to two anchor transmitters.
(ToA, also time of flight) is the amount of time a signal takes to propagate from transmitter to receiver. Because the signal propagation rate is constant and known (ignoring differences in mediums) the travel time of a signal can be used to directly calculate distance. Multiple measurements can be combined with trilateration
to find a location. This is the technique used by GPS. Systems which use ToA, generally require a complicated synchronization mechanism to maintain a reliable source of time for sensors (though this can be avoided in carefully designed systems by using repeaters to establish coupling).
(RSSI) is a measurement of the power level received by sensor. Because radio waves propagate according to the inverse-square law
, distance can be approximated based on the relationship between transmitted and received signal strength (the transmission strength is a constant based on the equipment being used), as long as no other errors contribute to faulty results. The inside of buildings is not free space, so accuracy is significantly impacted by reflection and absorption from walls. Non-stationary objects such as doors, furniture, and people can pose an even greater problem, as they can effect the signal strength in dynamic, unpredictable ways.
A lot of systems use enhanced Wi-Fi
infrastructure to provide location information. None of these systems serves for proper operation with any infrastructure as is. Unfortunately, Wi-Fi signal strength measurements are extremely noisy
, so there is ongoing research focused on making more accurate systems by using statistics to filter out the inaccurate input data. Wi-Fi Positioning Systems
are sometimes used outdoors as a supplement to GPS on mobile devices, where only few erratic reflections disturb the results.
carried by the pedestrian either by measuring steps indirectly (step counting) or in a foot mounted approach, sometimes referring to maps or other additional sensors to constrain the inherent sensor drift encountered with inertial navigation.
Inertial measures generally cover the differentials of motion, hence the location gets determined with integrating and thus requires integration constants to provide results.
. This technique requires a comprehensive on-site survey and will be inaccurate with any significant change in the environment (due to moving persons or moved objects).
Advanced systems combine more accurate physical models with statistical procedures:
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...
s (RTLS). There is currently no de facto standard for an IPS systems design, so deployment has been slow. Nevertheless, there are several commercial systems on the market.
Instead of using satellites, an IPS relies on nearby anchors (nodes with a known position), which either actively locate tags or provide environmental context for devices to sense. The localized nature of an IPS has resulted in design fragmentation, with systems making use of various optical, radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
, or even acoustic
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...
technologies.
Systems designs
Systems design shall take into account, that unambiguous locating service requires at least three independent measures per target. For smoothing to compensate for stochastic errors there must be a mathematical over-determination that allows for reducing the error budget. Otherwise the system must include information from other systems to cope for physical ambiguity and to enable error compensation.Applicability and precision
Due to the signal attenuationAttenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
caused by construction materials, the satellite based Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) loses significantly power indoors affecting the required coverage for receivers by at least four satellites. In addition, the multiple reflections at surfaces cause multi-path propagation serving for uncontrollable errors. These very same effects are degrading all known solutions for indoor locating which uses electromagnetic waves from indoor transmitters to indoor receivers. A bundle of physical and mathematical methods is applied to compensate for these problems.
With detailed reading in the marketing documents and even in the specifications served by many of the IPS vendors, the interested customer will look for details on precision, reproducibility and other terms for quality of function with poor success. Many vendors do not tangle the term accuracy with the slightest comment.
Relation to GPS
Global navigation satellite systemGlobal Navigation Satellite System
A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location to within a few metres using time signals transmitted along a line-of-sight by radio from...
s (GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
or GNSS) are generally not suitable to establish indoor locations, since microwaves will be attenuated and scattered by roofs, walls and other objects.
Currently, GNSS receivers are becoming more and more sensitive due to ceaseless progress in chip technology and processing power. High Sensitivity GNSS
High Sensitivity GPS
High Sensitivity GPS receivers use large banks of correlators and digital signal processing to search for GPS signals very quickly. This results in very fast times to first fix when the signals are at their normal levels, for example outdoors...
receivers are able to receive satellite signals in most indoor environments and attempts to determine the 3D position indoors have been successful. Besides increasing the sensitivity of the receivers, the technique of A-GPS
Assisted GPS
Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system which can, under certain conditions, improve the startup performance, or time-to-first-fix of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones as its development was accelerated by...
is used, where the almanac and other information are transferred though a mobile phone.
However, proper coverage for the required for satellites to locate a receiver is not achieved with all current designs (2008-11) for indoor operations. Beyond, the average error budget for GNSS systems normally is much larger than the confinements, in which the locating shall be performed.
Locating and positioning
In contrast to the common title suggesting that a position may be affected by a system, this assumption is not correct: Despite naming, most of the IPS do not position an object, but just detect locationLocation (geography)
The terms location and place in geography are used to identify a point or an area on the Earth's surface or elsewhere. The term 'location' generally implies a higher degree of can certainty than "place" which often has an ambiguous boundary relying more on human/social attributes of place identity...
of an object, not including the detection of the orientation
Orientation (geometry)
In geometry the orientation, angular position, or attitude of an object such as a line, plane or rigid body is part of the description of how it is placed in the space it is in....
or direction
Relative direction
The most common relative directions are left, right, forward, backward, up, and down. No absolute direction corresponds to any of the relative directions. This is a consequence of the translational invariance of the laws of physics: nature, loosely speaking, behaves the same no matter what...
of that object. All known indoor positioning systems (IPS) neither affects nor detects a direction nor offers the option to change the position. Also other various systems titled as e.g. local positioning system and so on do not offer other but detecting an object in a certain known fixed
location, report a measured location or just report the presence of the object in such location.
Locating and tracking
One of the methods to thrive for sufficient operational suitability is tracking, whether a sequence of locations determined form a trajectory from the first to the most actual location. Statistical methods then serve for smoothing the locations determined in a track resembling the physical capabilities of the object to move. This smoothing must be applied, when a target moves and also for a resident target, to compensate erratic measures. Otherwise the single resident location or even the followed trajectory would compose of an irritant sequence of jumps.Identification and segregation
In many applications the population of targets is larger than just one. Hence the IPS must serve a proper identification for each observed target and must be capable to segregate the targets in a pulk. The fiction of pulk identification does not serve such quality. An IPS must be able to identify the entities being tracked despite the not interesting neighbors. Depending on the design, either a sensor network must know what tag it has received information from, or a locating device must be able to identify the targets directly.Wireless technologies
Any wireless technology can be used for locating, so many systems take advantage of existing infrastructure. Others provide increased accuracy at the expense of costly equipment and installations.Choke point concepts
Simple concept of location indexing and presence reporting for tagged objects, uses known sensor identification only. This is usually the case with passive radio frequency identificationRadio 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...
(RFID) systems, which do not report the signal strengths and various distances of single tags or of a pulk of tags and do not renew any before known location coordinates of the sensor or current location of any tags. Operability of such approaches requires some narrow passage to prevent from passing by out of range.
Grid concepts
Instead of long range measurement, a dense network of low-range receivers may be arranged, e.g. in a grid pattern for economy, throughout the space being observed. Due to the low range, a tagged entity will be identified by only a few close, networked receivers. An identified tag must be within range of the identifying reader, allowing a rough approximation of the tag location. Advanced systems combine visual coverage with a camera grid with the wireless coverage for the rough location.Long range sensor concepts
Most systems use a continuous physical measurement (such as angle and distance or distance only) along with the identification data in one combined signal. Reach by these sensors mostly covers an entire floor, or an aisle or just a single room. Short reach solutions get applied with a bunch of sensors and overlapping reach.Angle of arrival
Angle of arrivalAngle 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) is the angle from which a signal arrives at a receiver. AoA is usually determined by measuring the time difference of arrival (TDOA) between multiple antennas in a sensor array. In other receivers, it is determined by an array of highly directional sensors—the angle can be determined by which sensor received the signal. AoA is usually used with 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...
to find the location relative to two anchor transmitters.
Time of arrival
Time of arrivalTime 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, also time of flight) is the amount of time a signal takes to propagate from transmitter to receiver. Because the signal propagation rate is constant and known (ignoring differences in mediums) the travel time of a signal can be used to directly calculate distance. Multiple measurements can be combined with 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...
to find a location. This is the technique used by GPS. Systems which use ToA, generally require a complicated synchronization mechanism to maintain a reliable source of time for sensors (though this can be avoided in carefully designed systems by using repeaters to establish coupling).
Received signal strength indication
Received signal strength indicationReceived signal strength indication
In telecommunications, received signal strength indicator is a measurement of the power present in a received radio signal.RSSI is a generic radio receiver technology metric, which is usually invisible to the user of the device containing the receiver, but is directly known to users of wireless...
(RSSI) is a measurement of the power level received by sensor. Because radio waves propagate according to the inverse-square law
Inverse-square law
In physics, an inverse-square law is any physical law stating that a specified physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity....
, distance can be approximated based on the relationship between transmitted and received signal strength (the transmission strength is a constant based on the equipment being used), as long as no other errors contribute to faulty results. The inside of buildings is not free space, so accuracy is significantly impacted by reflection and absorption from walls. Non-stationary objects such as doors, furniture, and people can pose an even greater problem, as they can effect the signal strength in dynamic, unpredictable ways.
A lot of systems use enhanced Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
infrastructure to provide location information. None of these systems serves for proper operation with any infrastructure as is. Unfortunately, Wi-Fi signal strength measurements are extremely noisy
Noise
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
, so there is ongoing research focused on making more accurate systems by using statistics to filter out the inaccurate input data. Wi-Fi Positioning Systems
Wi-Fi Positioning System
Wi-Fi-based positioning system emerged as an idea that can solve the positioning in certain situations , taking advantage of the rapid growth of wireless access points in urban areas...
are sometimes used outdoors as a supplement to GPS on mobile devices, where only few erratic reflections disturb the results.
Inertial measurements
Other approaches for positioning of pedestrians propose an inertial measurement unitInertial measurement unit
An inertial measurement unit, or IMU, is an electronic device that measures and reports on a craft's velocity, orientation, and gravitational forces, using a combination of accelerometers and gyroscopes. IMUs are typically used to maneuver aircraft, including UAVs, among many others, and...
carried by the pedestrian either by measuring steps indirectly (step counting) or in a foot mounted approach, sometimes referring to maps or other additional sensors to constrain the inherent sensor drift encountered with inertial navigation.
Inertial measures generally cover the differentials of motion, hence the location gets determined with integrating and thus requires integration constants to provide results.
Others
- Radio frequency identificationRadio Frequency IdentificationRadio-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...
(RFID): passive tags are very cost-effective, but do not support any metrics - Ultrawide band (UWB): reduced interference with other devices
- InfraredInfraredInfrared 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): previously included in most mobile devices - Visible light communication (VLC): can use existing lighting systems
- UltrasoundUltrasoundUltrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
: waves move very slowly, which results in much higher accuracy
Mathematics
Once sensor data has been collected, an IPS tries to determine the location from which the received transmission was most likely collected. The data from a single sensor is generally ambiguous and must be resolved by a series of statistical procedures to combine several sensor input streams.Empirical method
One way to determine position is to match the data from the unknown location with a large set of known locations using an algorithm such as k-nearest neighborK-nearest neighbor algorithm
In pattern recognition, the k-nearest neighbor algorithm is a method for classifying objects based on closest training examples in the feature space. k-NN is a type of instance-based learning, or lazy learning where the function is only approximated locally and all computation is deferred until...
. This technique requires a comprehensive on-site survey and will be inaccurate with any significant change in the environment (due to moving persons or moved objects).
Mathematical modeling
Location will be calculated mathematically by approximating signal propagation and finding angles and / or distance. Inverse trigonometry will then be used to determine location:- 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...
(distance from anchors) - 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...
(angle to anchors)
Advanced systems combine more accurate physical models with statistical procedures:
- Bayesian statistical analysis (probabilistic model)
- Kalman filterKalman filterIn statistics, the Kalman filter is a mathematical method named after Rudolf E. Kálmán. Its purpose is to use measurements observed over time, containing noise and other inaccuracies, and produce values that tend to be closer to the true values of the measurements and their associated calculated...
ing (for estimating proper value streams under noise conditions).
Systems offered
‘’Life cycle of many vendors is extremely short or never exceeds the laboratory stage. The following names are not checked for actual offers.’’Industry
Business
- Inventory Tracking (usually for forklifts and vehicles)
- Healthcare Management (tagging of patients, staff, and equipment)
Consumer
The major consumer benefit of indoor positioning is the expansion of location-aware mobile computing indoors. As mobile devices become ubiquitous, contextual awareness for applications has become a priority for developers. Most applications currently rely on GPS, however, and function poorly indoors. Applications benefiting from indoor location include:- Augmented realityAugmented realityAugmented reality is a live, direct or indirect, view of a physical, real-world environment whose elements are augmented by computer-generated sensory input such as sound, video, graphics or GPS data. It is related to a more general concept called mediated reality, in which a view of reality is...
- Guided tours of museums
- Mall and airport maps
- Store navigation
- Targeted advertisingTargeted advertisingTargeted advertising is a type of advertising whereby advertisements are placed so as to reach consumers based on various traits such as demographics, purchase history, or observed behavior....
- Social networking
See also
- Real-time locating systemReal-time locating systemReal-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) - Fuzzy locating systemFuzzy locating systemFuzzy locating is a rough but reliable method based on appropriate measuring technology for estimating a location of an object. The concept of precise or ‘’crisp locating’’ is replaced with respect to the operational requirements and the economic viability...
- RFID