TECHNOLOGIES OF RTLS POSITIONING
Indoor positioning systems (IPS) use sensors and communication technologies to determine the location of indoor objects. In comparison with GPS technology where the positioning accuracy for commercial purposes is within 5 meters, indoor positioning technologies have to demonstrate more accurate results. For example, merchandisers using navigation technologies identify the shelf in the store where the goods are located. This way customers get precise information and are glad with their purchases.
Take a closer look at the overview of positioning technologies:
|Infrared Light||57 cm – 2.3 m||Room|| Equipment cost: high
Maintenance charge: low
|Medium price||Susceptibility to sunlight|
|VLC||10 cm||Building||Equipment cost: high
Maintenance charge: low
|Affordable price, robustness||Expensive equipment|
|Ultrasonic||1 cm – 2 m||Room||High costs||High-level positioning accuracy||Expensiveness|
|Wi-Fi||within 5 m||Building||Low equipment and maintenance costs||Low price, average positioning accuracy||vulnerability while connecting access points|
|iBeacon||30 cm – several meters||Building||Low cost||Low cost, the high-level positioning accuracy||Equipment check-out is a must in course of installation|
|ZigBee||25 cm||Building||Equipment cost: low
Maintenance charge: high
|The already-done (existing) Zigbee infrastructure can be used||Special equipment is required, positioning accuracy depends on environment and physical factors|
|RFID||1-5 m||Room||Equipment cost: high
Maintenance charge: low
|Extremely low prices while using passive equipment for large-volume performance||Low-level positioning accuracy|
|UWB||15 cm||Building||High costs||High-level positioning accuracy||Expensiveness|
|Passive technologies without signal coding|
|Earth magnetic field||2-5 m||Low cost||Infrastructure is not required, average positioning accuracy||Geo-map data-binding is required|
|Automated (computer) vision||from 1 cm to several meters||Low cost||Affordable prices||Susceptibility to illumination, confidentiality|
|Inert sensors of the smartphone||up to 2-3 m||Low cost||Affordable costs, available geolocation data privacy||Low-level accuracy|
Spheres of Application of Indoor Positioning Systems
Each light bulb has its own flicker degree. Thus, the receiving sensor attains light and compares it with the light modulation of the encoded circuits. It means that VCL technologies allow determining the location of the user with such a sensor. The most common receiver nowadays is a mobile phone with a camera that can specify the frequency level of light flickering. Famous vendors who offer various solutions based on visible light communication technology are Philips, Gelighting, and ByteLight.
Also, by determining the direction of radiation, the object movement trajectory can be found. The accuracy of positioning is within 3 cm. An example of this technology is the Cricket passive system where the user 's wearable tag acts as a receiver and the emitter is mounted on the ceiling. The Ultrasonic technology is vulnerable due to the numerous active labels tags at the moment. It affects the performance of the positioning system. Nevertheless, Schweinzer and Syafrudin managed to achieve an accuracy of 1 cm.
The accurate location of the walls and floor was taken into account in the coordinate calculation algorithm. The classic of the positioning genre on WIFI is considered Freeloc where clients used a mobile app. But on account of the fact that all the phones differed in signal level, this positioning model had unideal accuracy. A commercially successful project by Ekahau found market acceptance due to the excellent WIFI accuracy within 3 meters. The user has to wear a wristband with a WIFI receiver. Location data is sent periodically to the server.
There are two UWB measurement methods used in RTLS systems: Time of Arrival (ToA) and Time Difference of Arrival (TDOA). IPS for the UWB technology runs on 4 fixed UWB anchors (readers). Mobile user location is calculated using triangulation algorithms using the TDoA method between receiver and transmitter. Position accuracy is up to 1 meter at 528 MHz. It is worth nothing that the efficient UWB technology model has limitations: the spectrum of radio emission is very small - interference with signals of WiFi, cellular communication; UWB equipment calibration complexities take place – e.g. time-consuming process; data network limits - all readers must be synchronized with a stable real-time IP network. Flagship UWB solution developers are considered Redpoint positioning; DecaWave; Zebra.
A Bluetooth-oriented positioning system according to the Feldmann method uses triangulation on the RSSI signal and positioning accuracy of 2-3 meters. The accuracy is affected by signal distortions because the signal fidelity is severely reduced under some factors. For example, a user is located between the receiver, transmitters, the directional angle of the BLE signal. The commercial use of the iBeacon technology model was offered by Apple. The focal length by signal level is possible at distances up to 50 cm, from 50 cm to 2-5 meters, and 2-5 meters to 30 meters. Accuracy also depends on physical parameters and possible barriers. Bluetooth signals have not got stable measurements. So, the developers of iBeacon-based RTLS systems use fingerprint methods to improve the level of signal fidelity and positioning.
There are numerous spheres of RFID application: safety sector, object tracking (people and equipment), baggage movement monitoring at the airport, logistics (warehouses), etc. RFID is extremely effective in case it is necessary to track object movements at checkpoints rather than on a permanent basis. LANDMARC (Location Identification based on Dynamic Area RFID Calibration) is a pioneer model in RFID systems. This positioning technology is based on principles of intensity of emitted signal from tag to antenna using the algorithm of the nearest neighbor k-NN. The nearest neighbor is used for the LANDMARC model. The accuracy of the method is up to 1 meter. The key vulnerability of RFID technology for RTLS positioning provision is delays. The SeSaMoNet offered an alternative method - a mobile RFID reader and stationary RFID tags. The technology was used to work on the street. The principle is similar to iBeacon technology, but with another accuracy showing - to 25 cm.
One more variation of RFID is NFC (Near field communication) technology. NFC modules are built into many user phones. The NFC model requires two-way communication between reader and emitter. NFC technology is used in payment systems, and can be implemented for efficient area control while the tracking of the objects’ movement is needed (both people and equipment can be monitored this way).
In the localization phase, the user takes a picture of the environment and downloads it to the server. The server runs a SURF algorithm that compares a user’s photo with the reference image in the database. Once the photo is identified, the user 's location can be estimated accurately. Developers assure that the average accuracy can be up to 1.3 meters. The vulnerability of the system takes place when the video or photo content has the low-grade resolution. The SignPost system is used for indoor positioning and works together with Barcode 2D. The smartphone camera scans barcodes in constant mode. This project with an active smartphone camera approach was launched by Microsoft EasyLiving. It was used for personnel tracking and visual interaction of people on behavioral factors. The application of the indoor positioning system based on computer (automated) vision is widely used in offices, business centers, shopping centers, etc.