  We study an urban wireless network in which cache-enabled UAV-Access points
(UAV-APs) and UAV-Base stations (UAV-BSs) are deployed to provide higher
throughput and ad-hoc coverage to users on the ground. The cache-enabled
UAV-APs route the user data to the core network via either terrestrial base
stations (TBSs) or backhaul-enabled UAV-BSs through an xHaul link. First, we
derive the association probabilities in the access and xHaul links.
Interestingly, we show that to maximize the line-of-sight (LoS) unmanned aerial
vehicle (UAV) association, densifying the UAV deployment may not be beneficial
after a threshold. Then, we obtain the signal to interference noise ratio
(SINR) coverage probability of the typical user in the access link and the
tagged UAV-AP in the xHaul link, respectively. The SINR coverage analysis is
employed to characterize the successful content delivery probability by jointly
considering the probability of successful access and xHaul transmissions and
successful cache-hit probability. We numerically optimize the distribution of
frequency resources between the access and the xHaul links to maximize the
successful content delivery to the users. For a given storage capacity at the
UAVs, our study prescribes the network operator optimal bandwidth partitioning
factors and dimensioning rules concerning the deployment of the UAV-APs.
