Journal of Communications and Information Networks, Vol.3, No.4, Dec. 2018
DOI: 10.1007/s41650-018-0040-3 Research paper
Placement Optimization for UAV-Enabled Wireless
Networks with Multi-Hop Backhauls
Peiming Li, Jie Xu
Abstract—Unmanned aerial vehicles (UAVs) have
emerged as a promising solution to provide wireless data
access for ground users in various applications (e.g.,
in emergency situations). This paper considers a UAV-
enabled wireless network, in which multiple UAVs are
deployed as aerial base stations to serve users distributed
on the ground. Different from prior works that ignore
UAVs’ backhaul connections, we practically consider that
these UAVs are connected to the core network through a
ground gateway node via rate-limited multi-hop wireless
backhauls. We also consider that the air-to-ground access
links from UAVs to users and the air-to-air backhaul links
among UAVs are operated over orthogonal frequency
bands. Under this setup, we aim to maximize the common
(or minimum) throughput among all the ground users
in the downlink of this network subject to the flow
conservation constraints at the UAVs, by optimizing the
UAVs’ deployment locations, jointly with the bandwidth
and power allocation of both the access and backhaul
links. However, the common throughput maximization
is a non-convex optimization problem that is difficult
to be solved optimally. To tackle this issue, we use the
techniques of alternating optimization and successive
convex programming to obtain a locally optimal solu-
tion. Numerical results show that the proposed design
significantly improves the common throughput among all
ground users as compared to other benchmark schemes.
Keywords—UAV, wireless networks, multi-hop back-
hauls, deployment optimization, bandwidth and power al-
location
Manuscript received Sept. 13, 2018; revised Nov. 30, 2018; accepted Dec.
10, 2018. This work was supported by the National Natural Science Founda-
tion of China (No. 61871137). The associate editor coordinating the review
of this paper and approving it for publication was W. Zhang.
P. M. Li, J. Xu. School of Information Engineering, Guangdong
University of Technology, Guangzhou 510006, China (e-mail: peimin-
glee@outlook.com; jiexu@gdut.edu.cn).
Part of this paper was presented at the IEEE International Conference on
Communication Systems (ICCS), Chengdu, China, Dec. 19-21, 2018
[1]
.
I. INTRODUCTION
U
nmanned aerial vehicles (UAVs), also known as (a.k.a.)
drones, have found a wide range of applications in, e.g.,
cargo delivery, aerial inspection, precision agriculture, and
traffic monitoring. Among others, employing UAVs as aerial
communication platforms to assist terrestrial wireless commu-
nications has recently emerged as one of the key technologies
for the fifth-generation (5G) cellular networks, which has at-
tracted a lot of interests from both academia and industry
[2,3]
.
On the one hand, UAVs can be used as aerial base stations
(BSs) to provide basic wireless data access for remote ar-
eas and in emergency situations (e.g., after natural disasters),
as well as to enhance the network capacity in terrestrial hot
spots
[4-8]
. On the other hand, UAVs can be utilized as aerial re-
lays to help far-apart ground users exchange information
[9,10]
,
and as access points in the sky for information dissemina-
tion and data collection with ground nodes (e.g., sensors and
actuators in Internet-of-Things networks)
[11]
. Besides wire-
less communications, UAVs can also serve as aerial plat-
forms for wireless power transfer (WPT)
[12,13]
, wireless pow-
ered communication networks (WPCN)
[14]
, and mobile edge
computing (MEC)
[15]
. In the industry, various companies
have launched their UAV-assisted wireless communication
projects, and some preliminary prototypes include Facebook’s
Aquila and Nokia’s flying-cell (F-Cell).
As compared to conventional terrestrial wireless communi-
cations, UAV-assisted wireless communications have the fol-
lowing advantages. First, UAV-enabled aerial communica-
tion platforms can be quickly deployed on demand, and thus
are cost-effective and suitable for emergency scenarios, e.g.,
when the terrestrial wireless infrastructures are damaged on
account of natural disasters. Next, the air-to-ground (A2G)
wireless channels between UAVs and ground nodes gener-
ally have much stronger line-of-sight (LoS) links than conven-
tional ground-to-ground (G2G) wireless channels; as a result,
the aerial BSs are expected to provide better wireless cover-
age and higher communication throughput than ground BSs.
Furthermore, due to the fully controllable mobility in three-
dimensional (3D) airspace, UAVs can adaptively change their
locations over time for reducing the distances with intended
ground users, so as to further improve the communication per-
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