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The unmanned aerial vehicles (UAVs) serving as the aerial base stations (ABSs) has emerged as a promising approach to improve the coverage and capacity in the 5G network. In this article, cache-enabled vertical heterogeneous network (VHetNet) is analyzed with the aid of the stochastic geometry approach. The cache-enabled VHetNet framework consisting of ABSs equipped with caches and terrestrial base station (TBSs) is proposed. In the proposed framework, the probabilistic caching strategy is adopted for ABSs and the content-centric association scheme is designed within the cache area with the cache serving radius. Based on the proposed framework, the system performance in terms of the coverage probability and the average rate are analyzed by ignoring the thermal noise under the general channel model incorporating both line-ofsight (LoS) /non-line-of-sight (NLoS) path loss and Nakagami-m fading. The theoretical analysis is verified via the Monte Carlo simulations and the impact of the network parameters on the system performance is analyzed. The simulation results show that there exits the optimal ABSs density, ABSs altitude and cache serving radius to maximize the system performance. Increasing the density of the ABSs deployed at higher altitude may decrease system performance. ABSs with higher density has the smaller optimal cache serving radius. The probabilistic caching strategy outperforms the benchmark caching strategies containing the most popular caching strategy and the random caching strategy.INDEX TERMS Vertical heterogeneous network, UAV, cache, stochastic geometry.

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Caching in the cellular networks has been proposed as a promising technology for reducing the content delivery latency and backhaul cost. Since the backhaul capacity is limited in the practical scenario, the network performance analysis of base station (BS) caching should address the effects of the limited backhaul. This paper investigates the energy efficiency of the cache-enabled cellular networks with the limited backhaul based on the stochastic geometry method. First, the successful content delivery probability (SCDP), which depends on the successful access delivery probability, successful backhaul delivery probability, and cache hit ratio, is analyzed under the limited backhaul. Based on the obtained SCDP results, we derive the analytical expressions of throughput, power consumption, and energy efficiency for various scenes including the general case, the interference-limited case, and the mean load approximation case. The accuracy of theoretical analysis is verified by the Monte Carlo simulation. The simulation results show that BS caching can dramatically improve energy efficiency when the content popularity is skewed, the content library size is small, and the backhaul capacity is relatively small. Furthermore, it is confirmed that there exists an optimal BS density which maximizes the energy efficiency of the cache-enabled cellular networks.

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