Contents I. Introduction
The steady increase of commercial UAV applications and the resulting traffic density in the lower airspace are addressed in a defined set of regulations in the so-called U-space, envisaging the integration of UAV monitoring in mobile radio services (5G and beyond). To realize sufficient security against misuse or incorrect use by timely detection of potentially hazardous situations, this cooperative UAV traffic monitoring system needs to be extended by independent airspace surveillance using radar sensing and radio location, ensuring a trust-but-verify (TBV) framework. The trend in this field is towards making efficient use of the radio resources for UAV monitoring by extension of existing mobile radio networks in terms of ISAC away from cost-intensive, stand-alone surveillance systems that also lack the flexibility and low-level accessibility needed for researching novel localization algorithms. Therefore, these commercial solutions are not considered as viable options for an experimental measurement system in this work. With this paper, we will propose a distributed radio sensor network with nanosecond-level synchronization accuracy, which allows to investigate and develop algorithms for radar and emitter localization of cooperative and non-cooperative UAVs. The proposed testbed is modular, tailored for easy deployment and low operational expense and only comprises COTS devices, to encourage replication in the academic radio frequency (RF) community. Recent studies similar to our approach propose software defined radio (SDR)-based systems for radar-only [1] – [3] and emitter-only localization [4], [5]. Additionally, a comparatively light-weight stand-alone measurement unit tailored for the use at commercial transport UAVs with a centimeter-level real-time kinematic (RTK)-based positioning will be introduced enhancing another recent work that makes use of a relatively heavy-weight UAV-mounted transmitter in an SDR-based channel sounder [6]. Furthermore, we will explain the individual testbed modules and essential integration steps in detail needed to achieve the aforementioned performance and accuracies. We will validate the testbed’s performance exemplarily in a real-world measurement campaign addressing the potential of ISAC for large-scale surveillance in a 16 km2 urban area and small-scale monitoring at a rooftop of a building. The focus of this publication will be the measurement system itself and not the measurement results.
