Tallinn University of Technology

Taavi Laadung the PhD student of Thomas Johann Seebecki department of electronics will defend his PhD thesis August 21, 2023 starting at 11:00 (Tallinn time) „Active-Passive Two-Way Ranging Protocol for Positioning Systems“. The defence takes place in room U02-208 (Ehitajate tee 5) and in MS Teams.

An essential component of the seamless functioning of modern society has become various location-based services — whether it's the daily positioning of different means of transportation, parcels, or even people themselves. Obtaining timely location information simplifies and accelerates our daily lives in many ways. Typically when people think of technical tools for obtaining location data, they inevitably think of Global Navigation Satellite System (GNSS), the most famous of which is the GPS (Global Positioning System), introduced by the American military and now also widely used in the civilian world.

Due to the fact that GNSSs determine location by emitting radio-frequency electromagnetic waves from orbiting satellites, their primary area of use is outdoors, as indoors these systems tend to lose their accuracy or even cease to work altogether. However, in industries such as manufacturing and warehousing, where activities mainly take place indoors, there is still a need to precisely determine the locations of objects, equipment, or individuals to optimize work processes, for example.

As a result, indoor positioning systems based on various technologies have gained popularity in recent years. In the realm of indoor positioning, Ultra-Wideband (UWB) technology stands out as one of the most promising. The strength of UWB is evident in four aspects: 1. radio waves can penetrate through most of the materials found indoors; 2. UWB uses very low transmit power, so it doesn't interfere with other existing radio communication systems; 3. since the UWB signal is wideband, the effects of multipath effects are decreased – reflected signal paths in a propagation environment can be effectively distinguished from one another; 4. thanks to its high temporal resolution, UWB signals can be used to accurately measure distances (or their differences).

UWB positioning is primarily performed in two ways: by measuring the differences in signal arrival times (Time Difference of Arrival, TDoA) or the absolute propagation time of the signal (Time of Flight, ToF). Both methods have their own advantages and disadvantages. In TDoA, the temporal use of the radio spectrum is minimized, but the infrastructure devices require very precise synchronization, which is challenging in real conditions. In ToF, multiple packet transmissions are used to mitigate the need for precise synchronization, while consequently increasing radio spectrum usage.

In the doctoral thesis titled "Active-Passive Two-Way Ranging Protocol for Positioning Systems", the generalized Active-Passive Two-Way Ranging (AP-TWR) protocol has been proposed and further developed. The development of the protocol essentially addresses the limitations of the two previously described positioning methods. As a result, it eliminates the need for synchronization, reduces radio spectrum utilization, and increases ranging accuracy. Ultimately, the usage of AP-TWR manifests as a more error-resistant, air time and energy-efficient, and accurate indoor positioning system.

Although the proposed AP-TWR protocol was tested using UWB technology within the scope of this doctoral thesis, its use is not limited to just UWB — AP-TWR can also be applied in other technologies. As a practical outcome of the work, the AP-TWR protocol has been implemented in the Eliko UWB RTLS indoor positioning system developed by OÜ Eliko Tehnoloogia Arenduskeskus, in Tallinn, Estonia.

The thesis is published in the Digital Collection of TalTech Library.


  • Professor Dr Muhammad Mahtab Alam
  • Professor Dr Yannick Le Moullec
  • Dr Sander Ulp


  • Professor  Dr Elena Simona Lohan (Tampere Ülikool)
  • Dr Ahmed Zoha (Glasgow Ülikool)

Follow public defense in MS Teams

Meeting ID: 321 929 217 974
Passcode: CeRW7E