# Routing Protocols for UAV-Aided Wireless Sensor Networks
## 2 Communication Technologies for UAWSNs
#### UAV Deployment in Fifth-Generation (5G) Technology  
Recently, due to the significant deployment of Internet of things (IoT), UAV-aided IoT (UAIoT) was studied in industrial and academic research. In UAIoT, UAV is able to access the IoT ground network directly or via the machine-to-machine gateway. Furthermore, using the fifth-generation (5G) technology in IoT enhances the efficiency and coverage of UAIoT communication. In Reference [31], the authors introduced a case study on the application of UAVs along with traditional cellular infrastructures in future systems such as 5G networks. The authors investigated the compatibility of UAVs with the traditional cellular infrastructures to enable high data rate requirements, which may improve the energy efficiency for the 5G and beyond systems. Furthermore, the authors in Reference [31] presented UAV channel modeling, path planning for UAV networks, and finally routing for UAVs in disaster-resilient networks. In addition, the authors introduced the concept of using cognitive radio as an enabling technology for using UAVs in 5G networks.  
In Reference [32], the authors presented a comprehensive survey on UAV communication toward 5G wireless networks. The authors described the network architecture and essential background of the space-air-ground integrated networks. In addition, the authors presented UAV-based swarm networks, which are multi-UAV networks that provide ubiquitous connectivity to ground users.  
There are some technical challenges for the integration of UAVs in currently deployed 5G networks, which include channel characterization, path planning for UAVs, energy charging efficiency, and the integration of UAVs and IoT systems. Channel estimation and modeling are essential to determine the number of UAVs to coverage, the optimal altitude of UAVs, and the communication fairness between UAVs and ground users. The deployment of UAVs in city areas needs to consider the path loss. UAVs are operated by mostly limited battery power and, thus, the operation of UAVs is constrained by their limited onboard power. For this reason, it is essential to consume power judiciously to fulfill both flight and communication. In UAWSNs, an optimal flight path is essential for data collection. A single UAV can be enough for data collection. However, to provide communication facilities for the ground users, a multi-UAV network needs to be considered.  
Limited energy is the bottleneck in UAV networks. However, recent developments in battery technology such as lithium-ion and hydrogen fuel cell batteries perform well for long-time UAV flight. Moreover, energy harvesting can be used to extend the UAV flight duration by utilizing green energy such as solar energy. Novel energy delivering technologies such as wireless power transfer can be smart solutions to enhance the charging efficiency. Due to the unique UAV features such as rapid mobility, fast deployment, easy programmability, and scalability, UAVs can be applied to future IoT systems and UAIoT can be a promising solution to realize the framework of future IoT systems. The 5G network technology can play a vital role in efficient UAIoT communication.