An indoor positioning system is a system to locate objects or people inside a
building using radio waves, magnetic fields, acoustic signals, or other
sensory information collected by mobile devices. There are several commercial
systems on the market, but there is no standard for an IPS system.
IPS systems use different technologies, including distance measurement to nearby
anchor nodes, magnetic positioning, dead reckoning. They either actively locate
mobile devices and tags or provide ambient location or environmental
context for devices to get sensed. The localized nature of an IPS has resulted
in design fragmentation, with systems making use of various optical, radio, or
even acoustic technologies. System designs must take into account
that at least three independent measurements are needed to unambiguously
find a location. For smoothing to compensate for stochastic errors there
must be a sound method for reducing the error budget significantly. The system
might include information from other systems to cope for physical ambiguity
and to enable error compensation. Applicability and precision
Due to the signal attenuation caused by construction materials, the satellite
based Global Positioning System loses significant 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. Promising direction
radiofrequency positioning error correction opened by the use of
alternative sources of navigational information, such as inertial
measurement unit, monocular camera Simultaneous localization and mapping
and WiFi SLAM. Integration of data from various navigation systems with
different physical principles can increase the accuracy and robustness of
the overall solution. 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 little success. Many vendors do not
even tangle with the term accuracy Relation to GPS
Global navigation satellite systems are generally not suitable to establish
indoor locations, since microwaves will be attenuated and scattered by roofs,
walls and other objects. However, in order to make positioning signals
ubiquitous, integration between GPS and indoor positioning can be made.,
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 through a
mobile phone. However, proper coverage for the
required four satellites to locate a receiver is not achieved with all
current designs 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
Despite the name, most current IPS systems are so coarse that they cannot
be used to detect the orientation or direction of an object.
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 itinerant sequence of jumps.
Identification and segregation In most applications the population of
targets is larger than just one. Hence the IPS must serve a proper specific
identification for each observed target and must be capable to segregate and
separate the targets individually within the group. An IPS must be able to
identify the entities being tracked, despite the "non-interesting" neighbors.
Depending on the design, either a sensor network must know from which tag it has
received information, or a locating device must be able to identify the
targets directly. Non-radio technologies
Non-radio technologies can be used for positioning without using the existing
wireless infrastructure. This can provide increased accuracy at the
expense of costly equipment and installations.
= Magnetic positioning= Magnetic positioning can offer
pedestrians with smartphones an indoor accuracy of 1–2 meters with 90%
confidence level, without using the additional wireless infrastructure for
positioning. Magnetic positioning is based on the iron inside buildings that
create local variations in the Earth's magnetic field. Un-optimized compass
chips inside smartphones can sense and record these magnetic variations to map
indoor locations. = Inertial measurements=
Pedestrian dead reckoning and other approaches for positioning of
pedestrians propose an inertial measurement unit carried by the
pedestrian either by measuring steps indirectly 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. The actual position estimation
can be found as the maximum of a 2-d probability distribution which is
recomputed at each step taking into account the noise model of all the
sensors involved and the constraints posed by walls and furniture.
Wireless technologies Any wireless technology can be used for
locating. Many different systems take advantage of existing wireless
infrastructure for indoor positioning. There are three primary system topology
options for hardware and software configuration, network-based,
terminal-based, and terminal-assisted. Positioning accuracy can be increased at
the expense of wireless infrastructure equipment and installations.
= Wi-Fi-based positioning system= Wi-Fi positioning system is used where
GPS is inadequate. The localization technique used for positioning with
wireless access points is based on measuring the intensity of the received
signal and the method of "fingerprinting". Typical parameters
useful to geolocate the WiFi hotspot or wireless access point include the SSID
and the MAC address of the access point. The accuracy depends on the number of
positions that have been entered into the database. The possible signal
fluctuations that may occur can increase errors and inaccuracies in the path of
the user. Anyplace is a free and open-source Wi-Fi positioning system
that allows anybody to rapidly map indoor spaces and that won several
awards for its location accuracy. = Bluetooth=
According to the Bluetooth Special Interest Group, Bluetooth is all about
proximity, not about exact location. Bluetooth was not intended to offer a
pinned location like GPS, however is known as a geo-fence or micro-fence
solution which makes it an indoor proximity solution, not an indoor
positioning solution. Micromapping and indoor mapping has been linked to
Bluetooth and to the Bluetooth LE based iBeacon promoted by Apple Inc..
Large-scale indoor positioning system based on iBeacons has been implemented
and applied in practice. = 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 identification systems, which do not report the signal strengths
and various distances of single tags or of a bulk 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 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 multiple sensors and overlapping reach.
= Angle of arrival= Angle of arrival is the angle from which
a signal arrives at a receiver. AoA is usually determined by measuring the time
difference of arrival 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 and a known base line to find the location relative to two
anchor transmitters. = Time of arrival=
Time of arrival is the amount of time a signal takes to propagate from
transmitter to receiver. Because the signal propagation rate is constant and
known the travel time of a signal can be used to directly calculate distance.
Multiple measurements can be combined with trilateration and multilateration
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. The accuracy of the TOA based methods
often suffers from massive multipath conditions in indoor localization, which
is caused by the reflection and diffraction of the RF signal from
objects in the environment. However, it is possible to reduce the effect of
multipath by applying temporal or spatial sparsity based techniques.
= Received signal strength indication= Received signal strength indication 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, 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 affect 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. = Others=
Radio frequency identification: passive tags are very cost-effective, but do not
support any metrics Ultrawide band: reduced interference
with other devices Infrared: previously included in most
mobile devices Gen2IR
Visible light communication: can use existing lighting systems
Ultrasound: 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
neighbor. This technique requires a comprehensive on-site survey and will be
inaccurate with any significant change in the environment.
= 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:
Trilateration Triangulation
Advanced systems combine more accurate physical models with statistical
procedures: Bayesian statistical analysis
Kalman filtering. Uses
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 reality School campus
Guided tours of museums Shopping malls.
Store navigation Warehouses
Airports, bus, train and subway stations Parking lots.
Targeted advertising Social networking.
Hospitals Hotels.
Tourism. Sports.
Other public building maps. See also
Automatic vehicle location Bluetooth SMART
Ekahau Site Survey Fuzzy locating system
Internet of Things GSM localization
Navizon Near field communication
Pointr Real-time locating system
Robotic mapping Sensor Fusion
Skyhook Wireless References
External links EZ Localization
Micromapping in OpenStreetMap Indoor Mapping in OpenStreetMap
indoor navigation sdk for mobile apps from indoo.rs