  Reliable positioning services are extremely important for users and devices
in mountainous environments as it enables a variety of location-based
applications. However, in such environments, the service reliability of
conventional wireless positioning technologies is often disappointing. Frequent
non-line-of-sight (NLoS) propagation and poor geometry of available anchor
nodes are two significant challenges. Due to the high maneuverability and
flexible deployment of unmanned aerial vehicles (UAVs), UAV-enabled positioning
could be a promising solution to these challenges. Compared with satellites and
terrestrial base stations, UAVs are capable of flying to places where both the
propagation conditions and geometry are favorable for positioning. The eventual
aim of this research project is to design a novel UAV-enabled positioning
system that uses a low-altitude UAV platform to provide highly reliable
services for ground users in mountainous environments. In this article, we
introduce the recent progress made in the first phase of our project, including
the following. First, the structure of the proposed system and the positioning
method used are determined after comprehensive consideration of various
factors. Utilizing the digital elevation model of the realistic terrain, we
then establish a geometry-based NLoS probability model so that the NLoS
propagation can be treated as a type of fault during the reliability analysis.
Most importantly, a reliability prediction method and the corresponding metric
are developed to evaluate the system's ability to provide reliable positioning
services. At the end of this article, we also propose a voting-based method for
improving the service reliability. Numerical results demonstrate the tremendous
potential of the proposed system in reliable positioning.
