I. Introduction
Unmanned aerial vehicles (UAV) have gained more interests in the research and consumer community in recent years [2]. The global UAV market is growing rapidly nowadays and estimated to reach USD 25 billion by 2027 [3]. Thereby, these flying machines are widely used for civilian, commercial and military applications in areas such as industrial inspection [4], environmental mapping [5] or payload carrying [6]. In the latter case, Joby Aviation [7], who acquired the former air taxi division of Uber, is an interesting development. They are currently further developing their self-controlled heavy-duty electric vertical takeoff and landing (VTOL) aircrafts for the purpose of transporting human passengers. Compared to these large-scale use cases, recent years showcased evergrowing possibilities of use cases with small UAVs. Here, Amazon Prime Air [8] is a noteworthy example, where Amazon deploys a fleet of autonomous drones to deliver lightweight items, whereby the availability and integrity of exact positioning feedback information become essential for safety purposes.