  Internet of Things (IoT) involves sensors for monitoring and wireless
networks for efficient communication. However, resource-constrained IoT devices
and limitations in existing wireless technologies hinder its full potential.
Integrating Unmanned Aerial Vehicles (UAVs) into IoT networks can address some
challenges by expanding its' coverage, providing security, and bringing
computing closer to IoT devices. Nevertheless, effective data collection in
UAV-assisted IoT networks is hampered by factors, including dynamic UAV
behavior, environmental variables, connectivity instability, and security
considerations. In this survey, we first explore UAV-based IoT networks,
focusing on communication and networking aspects. Next, we cover various
UAV-based data collection methods their advantages and disadvantages, followed
by a discussion on performance metrics for data collection. As this article
primarily emphasizes reliable and efficient data collection in UAV-assisted IoT
networks, we briefly discuss existing research on data accuracy and
consistency, network connectivity, and data security and privacy to provide
insights into reliable data collection. Additionally, we discuss efficient data
collection strategies in UAV-based IoT networks, covering trajectory and path
planning, collision avoidance, sensor network clustering, data aggregation, UAV
swarm formations, and artificial intelligence for optimization. We also present
two use cases of UAVs as a service for enhancing data collection reliability
and efficiency. Finally, we discuss future challenges in data collection for
UAV-assisted IoT networks.
