Semester

Summer

Date of Graduation

2022

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Matthew Valenti

Committee Co-Chair

Xi Yu

Committee Member

Xi Yu

Committee Member

Xin Li

Abstract

Recently, there has been a rapid increase in the use of air-assisted communications involv-
ing the use of airborne platforms such as unmanned aerial vehicles (UAVs). In air-assisted
networks, the UAVs can act like base stations in a traditional cellular network as long as an
appropriate backhaul is available. Alternatively, the UAVs could serve as relays, for instance,
connecting two ground-based users who are within range of the UAV. UAVs have the benefit
of being deployed and reconfigured rapidly and on demand.
Meanwhile, there has been a trend towards the use of higher and higher frequencies,
including those in millimeter-wave and terahertz bands or even free-space optical communi-
cations. Such bands have the benefits of large available bandwidths, relatively little inter-
ference, and enhanced security due to spatial isolation. However, such bands are also prone
to blocking in the environment, with even relatively small obstacles causing the signal to
be blocked and the link unable to be closed. For such systems, successful communication
requires a reliable line-of-sight (LoS) link.
When using LoS based communications, air-assisted communications is a good solution
because the UAVs can be deployed sufficiently high that the ground user will likely have a
line of sight or can be maneuvered to create LoS links as needed. This thesis explores the
use of air-assisted communications in cluttered environments with randomized obstructions
that may block the LoS between the ground user and the air platform. The key challenge
is identifying blockages that are taller than a position-dependent critical height that could
block the LoS of the ground-to-air link. The approach taken is to leverage tools from stochas-
tic geometry in general, and Poisson point processes in particular, to derive a closed-form
analytical expression for the probability of obtaining a LoS path in certain environments
characterized as Poisson forests. An inhomogeneous Poisson point Process is used to ac-
count for the distance-dependence of the critical height, and the LoS probability is the void
probability of this process. The UAV is assumed to be located at a fixed height, and its
horizontal distance to the ground user could either be fixed or random. Results are verified
through simulation.

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