Caching to the Sky: Proactive Deployment of Cache-enabled SBSs for Cellular-Connected UAVs

Enhancing LTE support for aerial users has become the study focus of recent 3rd Generation Partnership Project (3GPP) standardizations due to their high maneuverability and flexibility for on-demand deployment. A question arises: how to serve aerial users using LTE network deployments with base station (BS) antennas targeting terrestrial coverage. In this paper, the potential enhancement for supporting aerial users at high altitudes using coordinated multi-point (CoMP) transmission is envisaged. A network of clustered cache-enabled small base stations (SBSs) serving aerial users is considered, wherein a requested content by the aerial user is cooperatively transmitted from ground catering SBSs within certain collaboration distance. Using stochastic geometry, an upper bound expression on the coverage probability as a function of the system parameters is derived. The effect of different system parameters such as collaboration distance and content availability on the achievable performance is investigated. Results reveal that, with the antennas tilted downwards, the coverage probability of high-altitude aerial user is upper bounded by that of a ground user regardless of the transmission scheme. Moreover, it is shown that for low signal to interference plus noise ratio (SINR) threshold, the CoMP transmission improves the coverage probability for aerial users from 10% to 70% for a collaboration distance 200m.