  We consider the relaying application of unmanned aerial vehicles (UAVs), in
which UAVs are placed between two transceivers (TRs) to increase the throughput
of the system. Instead of studying the placement of UAVs as pursued in existing
literature, we focus on investigating the placement of a jammer or a major
source of interference on the ground to effectively degrade the performance of
the system, which is measured by the maximum achievable data rate of
transmission between the TRs. We demonstrate that the optimal placement of the
jammer is in general a non-convex optimization problem, for which obtaining the
solution directly is intractable. Afterward, using the inherent characteristics
of the signal-to-interference ratio (SIR) expressions, we propose a tractable
approach to find the optimal position of the jammer. Based on the proposed
approach, we investigate the optimal positioning of the jammer in both dual-hop
and multi-hop UAV relaying settings. Numerical simulations are provided to
evaluate the performance of our proposed method.
