# Towards a Connected Sky: Performance of Beamforming with Down-tilted Antennas for Ground and UAV User Co-existence

## TL;DR

This paper investigates the performance of beamforming with down-tilted antennas in cellular systems supporting both ground users and aerial users like UAVs, analyzing how system parameters affect content delivery success.

## Contribution

It introduces a model for simultaneous content delivery to aerial and ground users using massive MIMO and conjugate beamforming, deriving success probability as a function of system parameters.

## Key findings

- Down-tilt angles create a tradeoff when UAV altitude is below BS height.
- For UAVs above BS height, larger down-tilt angles improve performance for both UAVs and ground users.
- Optimal antenna tilt depends on UAV altitude relative to BS height.

## Abstract

Providing connectivity to aerial users such as cellular connected unmanned aerial vehicles is a key challenge for future cellular systems. In this paper, the use of conjugate beamforming for simultaneous content delivery to an AU coexisting with multiple ground users is investigated. In particular, a content delivery network of uniformly distributed massive MIMO enabled ground base stations serving both aerial and ground users through spatial multiplexing is considered. For this model, the successful content delivery probability is derived as a function of the system parameters. The effects of various system parameters such as antenna down-tilt angle, AU altitude, number of scheduled users, and number of antennas on the achievable performance are then investigated. Results reveal that whenever the AU altitude is below the BS height, the antennas down-tilt angles yield an inherent tradeoff between the performance of the AU and the GUs. However, if the AU altitude exceeds the BS height, down-tilting the BS antennas with a considerably large angle improves the performance of both the AU and the GUs.