TWR BASED LOCATIONING
The RTLS systems based on TWR scheme benefits from idea that no time synchronization is needed between the UWB devices. On the other way such feature limits scalability of RTLS system since the TWR process is applied gradually with all the Anchors within the system. Furthermore the Tags need to be aware about the address range of the Anchors to gradually poll all the available Anchors. This situation is depicted in figure below.
To calculate location of one Tag, it needs to launch TWR process with all the Anchors in system. Therefore length of time slot required to finish all TWR procedures depends accordingly on the number of Anchors in the RTLS system. According to the number of Tags operating in RTLS system, the appropriate number of time slots needs to be reserved within one refresh rate. According to this assumption it is obvious that number of the operating Tags and battery life is limited by required refresh rate and number of the Anchors in the system. Generally the battery life of Tag that reaches several hours or days must be considered when planning application.