IEEE - Aerospace and Electronic Systems - August 2022 - 33

Schwung and Lunze
influence of different communication models on the estimate
is compared in detail in [31]. In [32], the uncertainty
about the trajectory of the obstacle results only from an
uncertain speed profile along the planned path. This uncertainty
is modeled by Bezier surfaces. In [33], the uncertainty
about the trajectory is approximated using lines and
arcs. A random change of both the path and the speed profile
is not considered in either paper. The collision avoidance
results in this article are comparable to the results
in [32] and [33] in terms of the deviation of the avoidance
trajectory from the initial trajectory as well as the smoothness
of the replanning. Furthermore, with the method presented
in this article the collision avoidance can be
guaranteed despite the uncertainties about the trajectory of
the obstacle are larger due to possible changes of both
path and speed profile. Since the information between the
UAVs is solely communicated, the avoidance manoeuvre
in case of packet losses is more aggressive compared to
the methods in [32] and [33].
REFERENCES
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CONCLUSION
This article has proposed a method for the cooperative
control oftwo UAVs. The functions ofthe objects are subdivided
into a stand-on object and a give-way object,
which are connected by an unreliable communication network.
While the stand-on object changes its movement in
response to appearing obstacles, the give-way object has
to ensure the collision avoidance by an appropriate change
of its trajectory. It utilizes a control unit, which contains a
prediction unit to include all possible future positions of
the stand-on object in a set. An event generator indicates
whenever communication must be invoked and the trajectory
of the give-way object must be changed. A delay estimator
generates online an estimate of the time delay of the
communicated data using a two-state Markov model.
The function associated with the objects can be
changed according to the situation. An object that has to
change its trajectory due to obstacles is the stand-on
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The estimation method is evaluated and it is proven
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unit guarantees collision avoidance even in the presence
of network uncertainties. A maximum separation
between the objects can be satisfied with a given probability.
Furthermore, the communication flow of the method
is illustrated.
A simulation study shows that with the method the
control aims are achieved despite the occurrence of time
delays and packet losses with satisfaction of the objects
dynamic constraints.
AUGUST 2022
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IEEE A&E SYSTEMS MAGAZINE
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