# Ultra Reliable UAV Communication Using Altitude and Cooperation Diversity

## TL;DR

This paper develops a comprehensive framework for analyzing and optimizing air-to-ground UAV communication links, incorporating altitude-dependent factors and cooperative relaying to enhance network reliability.

## Contribution

It introduces a unified analysis framework that includes height-dependent path loss and small-scale fading, deriving optimal UAV heights and outage probability bounds for cooperative networks.

## Key findings

- Optimal UAV height minimizes outage probability.
- Adding relays does not change optimal UAV placement.
- Framework unifies ground and air-to-ground channel models.

## Abstract

The use of unmanned aerial vehicles (UAVs) that serve as aerial base stations is expected to become predominant in the next decade. However, in order for this technology to unfold its full potential it is necessary to develop a fundamental understanding of the distinctive features of air-to-ground (A2G) links. As a contribution in this direction, this paper proposes a generic framework for the analysis and optimization of the A2G systems. In contrast to the existing literature, this framework incorporates both height-dependent path loss exponent and small-scale fading, and unifies a widely used ground-to-ground channel model with that of A2G for analysis of large-scale wireless networks. We derive analytical expressions for the optimal UAV height that minimizes the outage probability of a given A2G link. Moreover, our framework allows us to derive a height-dependent closed-form expression and a tight lower bound for the outage probability of an \textit{A2G cooperative communication} network. Our results suggest that the optimal location of the UAVs with respect to the ground nodes does not change by the inclusion of ground relays. This enables interesting insights in the deployment of future A2G networks, as the system reliability could be adjusted dynamically by adding relaying nodes without requiring changes in the position of the corresponding UAVs.