  In this paper, the problem of unmanned aerial vehicle (UAV) deployment, power
allocation, and bandwidth allocation is investigated for a UAV-assisted
wireless system operating at terahertz (THz) frequencies. In the studied model,
one UAV can service ground users using the THz frequency band. However, the
highly uncertain THz channel will introduce new challenges to the UAV location,
user power, and bandwidth allocation optimization problems. Therefore, it is
necessary to design a novel framework to deploy UAVs in the THz wireless
systems. This problem is formally posed as an optimization problem whose goal
is to minimize the total delays of the uplink and downlink transmissions
between the UAV and the ground users by jointly optimizing the deployment of
the UAV, the transmit power and the bandwidth of each user. The communication
delay is crucial for emergency communications. To tackle this nonconvex delay
minimization problem, an alternating algorithm is proposed while iteratively
solving three subproblems: location optimization subproblem, power control
subproblem, and bandwidth allocation subproblem. Simulation results show that
the proposed algorithm can reduce the transmission delay by up to $59.3\%$,
$49.8\%$ and $75.5\%$ respectively compared to baseline algorithms that
optimize only UAV location, bandwidth allocation or transmit power control.
