  The use of Millimeter-wave (mmWave) spectrum in cellular communications has
recently attracted growing interest to support the expected massive increase in
traffic demands. However, the high path-loss at mmWave frequencies poses severe
challenges. In this paper, we analyze the potential coverage gains of using
unmanned aerial vehicles (UAVs), as hovering relays, in integrated access and
backhaul (IAB) mmWave cellular scenarios. Specifically, we utilize the WinProp
software package, which employs ray tracing methodology, to study the
propagation characteristics of outdoor mmWave channels at 30 and 60 GHz
frequency bands in a Manhattan-like environment. In doing so, we propose the
implementation of amplify-and-forward (AF) and decode-and-forward (DF) relaying
mechanisms in the WinProp software. We show how the 3D deployment of UAVs can
be defined based on the coverage ray tracing maps at access and backhaul links.
Furthermore, we propose an adaptive UAV transmission power for the AF relaying.
We demonstrate, with the aid of ray tracing simulations, the performance gains
of the proposed relaying modes in terms of downlink coverage, and the received
signal to interference and noise ratio (SINR).
