## 1 Introduction  
The dimensions of new and integrated technologies are evolving and providing convenience to users by providing services anytime and anywhere [1]. The Internet of Things (IoT) network is a combination of connected devices, either heterogeneous or homogeneous, that have the power of sensing and processing, and are equipped with data transmission and network capabilities [2]. There are various features and characteristics of IoT networks that make them different from other networks. IoT networks are used in industries, homes, education, transportation, and smart grids [3]. IoT devices are interacting with human interventions and are equipped with different routing and communication standards. The automated actions are performed and data is transmitted back to the central backbone devices. Different standards are involved in IoT networks including IEEE 802.11 (WLAN), IEEE 802.15.1 (Bluetooth), IEEE 802.15.4 (ZigBee), and IPv4 and 6 [4, 5]. Routing is one of the challenges in IoT networks due to the unique features of devicesand networks [6]. The deployment of devices or nodes makes this network more complex and unpredictable. The heterogeneous nature of networks makes them distinct in terms of resources. Besides these challenges, congested networks, especially in the ground area, sports stadiums, or traffic jam situations are observed. In addition, the continued disconnection, interference, delay, and overhead issues degrade the networks' performance. To overcome these issues, other solutions such as Unmanned Aerial Vehicles (UAVs) are used to facilitate IoT networks to collect the data from the ground and forward them toward the decision center [7]. The UAVs' nodes are providing coverage facilities for environmental monitoring, industrial accident plant safety, and dust from environments in civilian sectors. These networks are also providing services for luggage, medicine, and food deliveries. The UAVs networks are more feasible and convenient for disaster areas where emergency medicine distribution or other important materials need to be delivered. Another use of these applications is providing surveillance targeting and enemy monitoring at border areas. The most popular application of UAVs is for goods and product delivery in urban and rural areas. The UAVs' nodes are equipped with embedded software, sensors, transmitters, memory, and processing capabilities [1]. Routing protocols play a significant role in data transmission between UAVs and IoT networks. The used routing protocols are classified and divided into different categories such as a mesh-based protocol, a tree-based protocol, and hybrid or topology-based routing protocols. Tree-based routing protocols are further classified into source-rooted and core-rooted-based routing protocols. Some other types of routing protocols are topology-based, position-based, and hierarchical-based routing protocols [8]. UAVs have unique properties, such as dynamic topologies, high mobility, and mobility. In high mobility, the performance of the tree-primarily based routing is degraded compared with the mesh routing protocols. The mesh-based protocols are used to keep and manage the control messages that cause routing overhead and result in weak efficiency. In source-based routing, the data packets from the intermediate node need to keep the updated information. The disadvantage of source-based routing is the network overhead. In source-based routing, the bandwidth utilizes because each packet represents the entire route in its header but the routing table size increases in the network. The next stage of routing is forwarding the data toward the destination by using hop-by-hop routing. Figure 1 shows a UAV's architecture and components. Figure 1: UAVs’ Architecture. Many routing protocols have been designed for UAVs and most of them are not efficient and cause more overhead and delay. In UAVs' networks, the existing routing protocols are not compatible.