2 research outputs found
Fundamental Rate Limits of UAV-Enabled Multiple Access Channel with Trajectory Optimization
This paper studies an unmanned aerial vehicle (UAV)-enabled multiple access
channel (MAC), in which multiple ground users transmit individual messages to a
mobile UAV in the sky. We consider a linear topology scenario, where these
users locate in a straight line and the UAV flies at a fixed altitude above the
line connecting them. Under this setup, we jointly optimize the one-dimensional
(1D) UAV trajectory and wireless resource allocation to reveal the fundamental
rate limits of the UAV-enabled MAC, under the users' individual maximum power
constraints and the UAV's maximum flight speed constraints. First, we consider
the capacity-achieving non-orthogonal multiple access (NOMA) transmission with
successive interference cancellation (SIC) at the UAV receiver. In this case,
we characterize the capacity region by maximizing the average sum-rate of users
subject to rate profile constraints. To optimally solve this highly non-convex
problem, we transform the original speed-constrained trajectory optimization
problem into a speed-free problem that is optimally solvable via the Lagrange
dual decomposition. It is rigorously proved that the optimal 1D trajectory
solution follows the successive hover-and-fly (SHF) structure. Next, we
consider two orthogonal multiple access (OMA) transmission schemes, i.e.,
frequency-division multiple access (FDMA) and time-division multiple access
(TDMA). We maximize the achievable rate regions in the two cases by jointly
optimizing the 1D trajectory design and wireless resource (frequency/time)
allocation. It is shown that the optimal trajectory solutions still follow the
SHF structure but with different hovering locations. Finally, numerical results
show that the proposed optimal trajectory designs achieve considerable rate
gains over other benchmark schemes, and the capacity region achieved by NOMA
significantly outperforms the rate regions by FDMA and TDMA.Comment: To appear in IEEE Transactions on Wireless Communication
Secrecy Transmission in Large-Scale UAV-Enabled Wireless Networks
This paper considers the secrecy transmission in a large-scale unmanned
aerial vehicle (UAV)-enabled wireless network, in which a set of UAVs in the
sky transmit confidential information to their respective legitimate receivers
on the ground, in the presence of another set of randomly distributed
suspicious ground eavesdroppers. We assume that the horizontal locations of
legitimate receivers and eavesdroppers are distributed as two independent
homogeneous Possion point processes (PPPs), and each of the UAVs is positioned
exactly above its corresponding legitimate receiver for efficient secrecy
communication. Furthermore, we consider an elevation-angle-dependent
line-of-sight (LoS)/non-LoS (NLoS) path-loss model for air-to-ground (A2G)
wireless channels and employ the wiretap code for secrecy transmission. Under
such setups, we first characterize the secrecy communication performance (in
terms of the connection probability, secrecy outage probability, and secrecy
transmission capacity) in mathematically tractable forms, and accordingly
optimize the system configurations (i.e., the wiretap code rates and UAV
positioning altitude) to maximize the secrecy transmission capacity, subject to
a maximum secrecy outage probability constraint. Next, we propose to use the
secrecy guard zone technique for further secrecy protection, and analyze the
correspondingly achieved secrecy communication performance. Finally, we present
numerical results to validate the theoretical analysis. It is shown that the
employment of secrecy guard zone significantly improves the secrecy
transmission capacity of this network, and the desirable guard zone radius
generally decreases monotonically as the UAVs' and/or the eavesdroppers'
densities increase.Comment: 16 pages, 11 figures. Accepted for publication in the IEEE
Transactions on Communications. It overlaps with the former version
(arXiv:1902.00836