  In this article, we investigate the content distribution in the hotspot area,
whose traffic is offloaded by the combination of the unmanned aerial vehicle
(UAV) communication and edge caching. In cache-enabling UAV-assisted cellular
networks, the network deployment and resource allocation are vital for quality
of experience (QoE) of users with content distribution applications. We
formulate a joint optimization problem of UAV deployment, caching placement and
user association for maximizing QoE of users, which is evaluated by mean
opinion score (MOS). To solve this challenging problem, we decompose the
optimization problem into three sub-problems. Specifically, we propose a swap
matching based UAV deployment algorithm, then obtain the near-optimal caching
placement and user association by greedy algorithm and Lagrange dual,
respectively. Finally, we propose a low complexity iterative algorithm for the
joint UAV deployment, caching placement and user association optimization,
which achieves good computational complexity-optimality tradeoff. Simulation
results reveal that: i) the MOS of the proposed algorithm approaches that of
the exhaustive search method and converges within several iterations; and ii)
compared with the benchmark algorithms, the proposed algorithm achieves better
performance in terms of MOS, content access delay and backhaul traffic
offloading.
