Enhancing the reliability of wireless communication networks is critical in emergency situations, important communication missions, freight, and agriculture in order to make systems autonomous while keeping a high level of energy efficiency. Therefore, the use of unmanned aerial vehicles (UAVs), commonly known as drones, has increasingly been the subject of research over the past few years, owing to their autonomy, flexibility, and broad range of applications. Indeed, UAVs have been considered for various applications, including military, surveillance and monitoring, telecommunications, delivery of medical supplies, and rescue operations. The use of UAVs is ever increasing, and some reports suggest that more than 29 million UAVs are expected to be put into use in 2021.

With the ongoing development of smart cities, 5G, Internet of Things (IoT), and artificial intelligence, UAV communication is expected to become more robust, stable, and reliable. Recently, significant interest has arisen in integrating UAVs into cellular networks, for example, 5G networks. On one hand, UAVs with their own missions could be connected to cellular networks as new aerial users by exploiting advanced cellular technologies and the almost ubiquitous accessibility of cellular networks. However, dedicated UAVs could also be deployed as aerial base stations (BSs), access points (APs), or relays to assist 5G and other terrestrial wireless communications from the sky, leading to another paradigm known as UAV-assisted communications.

The aim of this Special Issue is to gather research focusing on key theoretical and practical design issues of UAV communication scenarios. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Channel modeling for UAV-ground communications
• Channel modeling for UAV-UAV communications
• Interference mitigation in UAV communications
• UAV channel estimation and pilot decontamination
• Physical layer security and techniques in wireless networks with UAV multi-access Edge Computing (MEC) with UAV communications
• Non-orthogonal multiple access (NOMA) for UAV Communications
• Massive multiple-input and multiple-output (MIMO)/millimeter wave communications for cellular-connected UAVs
• 3D aerial base station placement
• Online/offline and machine learning based UAV trajectory optimization
• Joint trajectory design and resource allocation for UAV-assisted wireless communication
• Energy-efficient UAV communications