IEEE - Aerospace and Electronic Systems - August 2022 - 20

Feature Article:
DOI. No. 10.1109/MAES.2022.3176595
Cooperative Control of UAVs Over an Unreliable
Communication Network
Michael Schwung andJan Lunze , Ruhr University Bochum, 44801 Bochum,
Germany
INTRODUCTION
MOTIVATION AND OBJECTIVES
This article proposes a cooperative control method for
autonomous objects that are connected by an unreliable
communication network. The aim is to plan the collision
avoiding trajectories for the objects based on local data
and communicated information. The method has to cope
with an uncertain movement of nearby objects and
delayed or lost data packets during the communication.
Motivated by the increasing number of autonomously
moving objects, such as unmanned aerial vehicles (UAVs)
or cars, which are connected over a communication network,
it is desirable to develop a method with which the
objects are able to fulfill different tasks such as
surveillance of areas,
rescue missions,
communication relay over aerial base stations, or
merging of vehicle platoons.
The method should be applicable to various types of
objects with as few changes as possible and it should enable
the objects to perform tasks individually or as a group.
This article considers two autonomous quadrotors in
the scenario illustrated in Figure 1. Both objects move on
trajectories from their start points SA;S, SA;G to their end
points SB;S, SB;G on which they should satisfy the requirement
s sðtÞs on their distance. This article considers
the situation that one of the objects faces an obstacle and
changes its trajectory accordingly. In this situation, the
UAVs act with the following functional associations. The
Author's current address: M. Schwung and J. Lunze Ruhr
University Bochum, 44801 Bochum Germany (e-mail:
michael.schwung@rub.de, lunze@atp.rub.de).Manuscript
received 25 June 2021, revised 14 April 2022; accepted 13
May 2022, and ready for publication 17 May 2022.
Review handled byMauro De Sanctis.
0885-8985/22/$26.00 ß 2022 IEEE
20
first object is called the stand-on object PS, because it
stays on its new trajectory to avoid an obstacle (see
Figure 1). As a reaction, the second object is called the
give-way object
PG because it has to change its locally
planned trajectory so as to keep the distance between the
UAVs inside the required interval sðtÞ2½s;s. To this
aim, the objectPG has to fulfill the following three control
tasks.
1) Plan the trajectory to maintain the distance sðtÞ2
½s;s between the objects and monitor the distance
sðtÞ continuously.
2) Follow the planned trajectory.
3) Compensate external disturbances, e.g., influence of
wind.
Due to the complexity of the problem, this article
focuses on a method to satisfy the first control task, while
it uses the methods developed in [1] to fulfill the other two
control tasks. The quadrotors are equipped with sensors to
measure their own position, speed, and acceleration. Furthermore,
in [1] a two-degrees-of-freedom controller was
developed for the UAVs that ensures exact trajectory following
and compensation of external disturbances. Hence,
this article focusses on a method to plan an appropriate
trajectory for the give-way object and assumes that the
UAVs follow this trajectory with reasonable tolerance.
For planning the trajectory, the object is supposed to
use only locally measured and communicated information.
To reduce the communication effort, communication
should only be invoked whenever the uncertainty of the
local data violates a threshold. The idea to this communication
scheme is inspired by the idea of event-based control
known in the control literature.
As a prerequisite for the planning of suitable trajectories,
the main challenges of the method to be developed
concern the estimation of the properties of the unreliable
communication channel to invoke communication appropriately
and the estimation of the uncertain movement of
the object
PS, which can change its trajectory due to new
obstacles pO;i, ði ¼ 1; ... ;NÞ appearing in a set PO on its
trajectory.
IEEE A&E SYSTEMS MAGAZINE
AUGUST 2022
https://orcid.org/0000-0002-8420-737X https://orcid.org/0000-0002-8108-1628
IEEE - Aerospace and Electronic Systems - August 2022

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