Commonly used unmanned aerial vehicle (UAV) platforms rely on the use of global navigation satellite system (GNSS) receivers for navigation. To enable the autonomous navigation of cooperative UAVs in GNSS-denied environments, the use of an ultra-wideband (UWB) positioning system is proposed. This paper discusses the design and evaluation of a practical and cooperative UWB positioning system using newly available integrated radio frequency hardware and antennas. Constellation-aware parameters, as well as other effects like antenna characteristics, are taken into consideration. A non-line-of-sight rejection is implemented based on the ratio of the first path compared to the power of the cumulated channel impulse response. An experiment covering a range of positions and orientations is conducted to gain a broad, representative set of results to assess the system accuracy in real-life usage. In a first experiment the system performance achieves a root-mean-square error of under 10 cm in the horizontal plane and under 20 cm in the three-dimensional space with a probability of 95 %. A GNSS emulation system is implemented to evaluate the real-time in-flight use of the UWB positioning system on an experimental UAV carrier. A proof of concept is given that the GNSS emulation may be used with commercially available UAV platforms to augment those systems with indoor navigation capabilities.

Ultra-wideband wireless positioning technologies based on IEEE 802.15.4a have gained attention for various use cases requiring highly precise localization. Multi-rotor unmanned aerial vehicle (UAV) systems provide several sensors for stabilization and navigation. However, absolute indoor positioning poses a problem for autonomous robotic systems. The specific challenge addressed in this paper is enabling novel applications with autonomous UAV systems through tight integration with scalable and precise receiver-side time-difference of arrival (TDOA) based ultra-wideband (UWB) indoor localization. For the in-depth validation of the proposed approach, several experiments are performed. One proves the repeatability of the proposed method by following a predefined trajectory ten times achieving close to optical motion-capture based control performance, with a 3rd quartile of the alignment error lower than 10 cm. Another experiment addresses the simultaneous flight of three UAVs in close proximity and delivers an analysis of the real-time capabilities which in turn proves the multi-user scalability. The last experiment demonstrates a user-interactive application of the proposed approach in a logistics environment. A video along with the raw samples, reference data and processed positions of the aforementioned experiments is provided alongside this work.

IEEE 802.15.4a Ultra-wideband based wireless positioning has recently gained attention for precise localization. However, the multi-user scalability of those, mostly two-way ranging based, approaches is not considered. Due to the exchange of multiple frames per ranging, two-way ranging has significant downsides in terms of scalability. This paper proposes and validates a novel approach for a multi-user time-difference of arrival based localization system using wireless clock synchronization. The system accuracy is assessed using a complex experiment, covering robotic movement and an optical reference system for comparable results. It is shown, that the accuracies achievable by time-difference of arrival positioning with wireless clock synchronization are comparable to similar two-way ranging based approaches. All raw samples, reference data and processed positions are provided alongside this work.

Current developments in unmanned aerial vehicle technology hold great potential for productive deployment in industrial cyber-physical systems. While autonomous flight in outdoor environments is achieved using global navigation satellite systems, dedicated precise wireless localization is a promising candidate to enable indoor navigation. However, equipping large industrial areas with wireless localization is possible, but providing the required coverage may not be economical. Therefore, this work aims to augment and fuse state of the art ultra-wideband localization with monocular simultaneous localization and mapping to enable autonomous flight in areas not covered by wireless localization. For the in-depth validation of the proposed approach, two experiments are performed: the first one is providing an extensive experimental analysis of the accuracy of different localization methods for drones, whereas the second experiment is showing that precise waypoint flight in areas not covered by wireless localization is feasible, lowering the threshold for integration of drone-based cyber-physical systems in current industrial environments.

Ultra-wideband localization has become a key solution for a variety of industrial applications and recently challenged a significant amount of research. Most of the current research however, focusses primarily on the analysis of the localization accuracy of one or few mobile users in well-defined system environments. This work aims to analyze the interdependency of various system performance criteria, in particular multi-user scalability, real-time capability and energy efficiency of time of arrival based wireless localization. We provide an overview by comparing the predominant system topologies and develop analytical models validated by experiments to evaluate the individual trade-offs. Furthermore, we provide an implementation proposal and in-depth evaluation of emerging time-difference of arrival scheduled channel access to allow for reliable, highly scalable and energy efficient localization enabling a paradigm shift for many industrial applications. We could show that compared to the most commonly used schemes, the number of users and the energy consumption can be improved by orders of magnitude.

Wireless positioning based on IEEE 802.15.4a has recently gained attention for precise localization. However, the multi-user scalability of those, mostly two-way ranging based, approaches is not considered. Due to the exchange of multiple frames per ranging, two-way ranging has significant downsides in terms of scalability. This paper proposes and validates a novel multi-user time-difference of arrival based localization approach using wireless clock synchronization to overcome the limitations of two-way ranging based positioning. The clock characteristics of the individual nodes are experimentally analyzed and the requirements and constraints for wireless clock synchronization are elaborated based on the experiments. The results show, that a clock synchronization rate of around 1 Hz is sufficient to achieve accuracies in the decimeter range. Experiments analyzing the multi-user capabilities of the system are conducted, highlighting the specific properties of multi-user access in the proposed time-difference of arrival based localization. The experiments show, that the system is capable of scaling gracefully under heavy load. However, clock synchronization suffers as it is degrading equally. Therefore, a novel approach is proposed and evaluated to prioritize the wireless clock synchronization to ensure load independent positioning accuracy. It is shown, that the proposed approach is capable of ensuring a synchronization receive ratio of around 90% independent of the system load.