WHAT IS RTLS
By term "Real Time Locating System" are called systems for monitoring of location and tracking of assets /
goods / people in real-time using a small electronic devices - active RTLS tags. This technology
is designed for positioning objects mainly inside buildings, where appropriate, within the
premises or campuses. These systems typically achieve accuracy in the order of meters, some even in
the tens of centimeters. From the technological point of view we talk about the active RFID technology.
RTLS SYSTEM TOPOLOGY
Each RTLS system is based on the existence of radio wireless infrastructure. The signal must be
available wherever the RTLS should work. Tags transmit data through the wireless infrastructure to location server,
which is capable to determine the current position of the tag out of captured data. These data about the current position,
but also about the routes of tag movement in time, are provided to applications that may use the information about the position
of tracked objects in real time.
RTLS SYSTEM BREAKDOWN BY USE OF INFRASTRUCTURE
On the world market there is a range of RTLS systems, which can be
divided according to use wireless infrastructure or used frequency:
A.) Proprietary systems use for their activities special dedicated wireless infrastructure.
astrukturu. Used are in particular the frequency 433 MHz, 860 / 900 MHz and 2.4 GHz.
B.) Systems using a standardized infrastructure:
- ZigBee (2,4GHz)
- UWB (Ultra Wide Band)
- WiFi (802.11 b/g/n ) (2,4GHz)
Disadvantages of using a dedicated proprietary wireless infrastructure result just from its dedicated purpose.
It is necessary to build, pay, and maintain the infrastructure that will serve only for a single application - RTLS.
The advantage of RTLS systems based on standard wireless infrastructure, especially WiFi, is their infrastructure
universality and multiservice function. WiFi network is universal, it is possible to operate on it many applications, it is
cheap and it provides security on the desired level.
WIFI RTLS ADVANTAGES
Wireless WiFi networking technology has undergone stormy development over the last few years. Since the
original products used to have the data throughput in the hundreds of kbps, the current state-of-the-art technology might
have the throughput up to 300 Mbps in 802.11n standard. Similarly, security of wireless networks has passed through
significant developments as well. The initial products did not address this aspect too much, the latest technology available
offers the most modern and most powerful tools such as WPA2, which addresses as secure access to the wireless network
(user and access point authentication, often using RADIUS server), as well as its own secure communication over the network.
Strong encryption mechanism AES-CCMP are widely used. Modern WiFi network can be reliably secured on the required level.
WiFi networks have become an accepted and widely used standard for flexible wireless network
connectivity. Their big advantage is versatility, the possibility of operating a range of
applications. Last but not least advantage are the low costs of investment.
METHODS OF DETERMINING THE POSITIONS
To determine the location of the object, there is quite a lot of methods. Many of the methods use
mutual correlation of time needed to overcome the distance between the receiver / transmitter, such as
TOA (Time of Arrival). The disadvantage of this method is the need for time synchronization on
the receiver and transmitter, which has a dramatic impact on accuracy. This disadvantage can be eliminated by using the method
TDoA (Difrerece Time of Arrival), based not on absolute values of the time,
but on the differences between neighboring transmitters. This method is used also in GPS. Methods
working with time are generally suitable for outdoor premises with a minimum of reflections and with direct
visibility from the transmitter to the receiver.
Another method is the RSSI (Received Signal Strength Indication). The method is based on radio
signal strength measurements of visible access points. It uses the dependence of signal strength on
the distance from the transmitter. This method is suitable for systems operating inside buildings.
