Ultra-reliable and low-latency communication (URLLC) is one of the main service categories in the fifth-generation communication systems, which lays the foundation for emerging data-exploring video applications with strict end-to-end latency requirement. Unmanned aerial vehicle (UAV) enabled radio access network (UAV-RAN) is an effective architecture to improve the wireless coverage. Combining wireless caching with UAV-RAN is one of the key driving forces to reduce the burden of wireless traffic, provide resilient coverage and reduce the delay in heterogeneous URLLC networks. In this paper, a collaborative caching strategy is proposed for UAV-RANs. First, a scalable video coding (SVC)-based video library is presented to provide users with videos of different perceptual qualities, and the popularity of different definition videos is also analyzed. Then, we propose a heterogeneous network where UAVs within a distance from based station (BS) can be provided with error-free data and UAVs at several stop points can provide data service to users while BS can offer all users data service. Next, an SVC-based two-tier cooperative caching model is proposed, where BS and UAVs store different video encoded files on the basis of caching matrix. Finally, the energy consumption of UAV and the caching hit probability (CHPro) are analyzed, and the optimal caching matrix is obtained via the maximization of CHPro. The maximization problem is proved to be NP hard, and we propose a two-step solution based on the simulated annealing algorithm. Considering URLLC, the average service delay is also analyzed and proved that the proposed strategy is efficient in reducing delay. Simulation results demonstrate that the collaborative caching strategy is more suitable for the UAV-RANs with a skew video popularity library and an ultra-dense user distribution. Compared with other contrasting schemes, the proposed collaborative caching strategy can achieve quasi-optimal performance.

超可靠和低延迟通信（URLLC）是第五代通信系统中的主要服务类别之一，为具有严格的端到端延迟要求的新兴数据探索视频应​​用奠定了基础。支持无人飞行器（UAV）的无线电接入网（UAV-RAN）是提高无线覆盖范围的有效架构。将无线缓存与UAV-RAN相结合是减少无线流量负担，提供弹性覆盖并减少异构URLLC网络中延迟的关键驱动力之一。本文提出了一种针对UAV-RAN的协同缓存策略。首先，提出了一种基于可伸缩视频编码（SVC）的视频库，以向用户提供不同感知质量的视频，并且还分析了不同清晰度视频的受欢迎程度。然后，我们提出一种异构网络，其中可以向距基站（BS）一定距离的无人机提供无差错数据，并且在几个停靠点的无人机可以为用户提供数据服务，而基站可以为所有用户提供数据服务。接下来，提出了一种基于SVC的两层协作缓存模型，其中BS和UAV基于缓存矩阵存储不同的视频编码文件。最后，分析了无人机的能耗和缓存命中率（CHPro），并通过最大化CHPro获得了最优缓存矩阵。证明了最大化问题是NP难的，我们在模拟退火算法的基础上提出了两步法。考虑URLLC，对平均业务时延进行了分析，证明了该策略在降低时延方面是有效的。仿真结果表明，协作式缓存策略更适合带有偏爱视频流行度库和超密集用户分布的UAV-RAN。与其他对比方案相比，本文提出的协同缓存策略可以达到准最佳性能。