## 4 UAV Communication Network and Technology
### Communication Protocols in UAV Networks
It can be concluded that although the current LTE network can provide the minimum requirements for the drone's mobile connectivity, further improvements are needed to enhance the aerial coverage, eliminate interference, and reduce network latency. * 5G Network  
Similar to LTE, 5G technology is also considered for UAV network communications when bit rates higher than 2.4 Gbps are required. UAV-enabled communications have several promising advantages, such as facilitating on-demand deployment, high flexibility in network reconfiguration, and enabling long-range LoS communication links. In some cases, UAVs act as 5G radio stations (also known as APs) to extend the coverage of 5G networks to ground users, especially for sensitive applications such as public safety and disaster management [71; 72]. In [73], a swarm of UAVs is connected to a cellular network, enabling the UAVs to autonomously coordinate their activities and cooperate to complete a given task. This study  
Figure 22: UAV-enabled WiFi Direct network architecture to improve throughput, device connectivity, and energy efficiency in 3D space and constrained areas with boundaries. focuses on the problem of cooperative and communication-aware UAV channel scheduling for data transmission from a set of target points of interest (PoIs) to a cellular base station (BS). A novel cooperative multi-hop communication model based on the Mode 4 C-V2X (Cellular-Vehicle-to-Everything) cellular side-link (PC5) air interface is presented for efficient UAV data flow scheduling in the swarm. The model design aims to optimize cellular communication over UAV-to-UAV (U2U) and UAV-to-Infrastructure (U2I) links through a novel interference-aware scheduling approach, thereby envisioning a novel mobile UAV-to-Everything (C-U2X) communication model (Figure 23). The extensive simulation results demonstrate that the proposed distributed algorithm can extend the coverage of mobile infrastructure while improving multipoint communication by automatically adapting to network conditions. In [74], the authors present how UAV BSs and drone UEs can be integrated into 5G systems. The authors highlight important open issues in the standardization process, either through the adoption of existing standards or by providing modifications towards further improvements that could realize the vision of 5G-enabled UAVs. * 6G Network  
The demand for higher throughput and a larger number of devices never stops, and 6G is on its way to serve these requirements. 6G, the next generation of wireless communications, is expected to provide intelligent, secure, reliable, and unlimited connectivity at speeds 100 times faster than 5G [75]. Hence, the diverse requirements of UAV networks, such as low latency, reliability, and energy efficiency, will be better served by 6G networks, and airborne nodes will be an integral part of 6G networks. In addition, network intelligence is envisioned as a key feature of 6G, which can support a variety of applications. In [76], the authors consider a network of unmanned aerial vehicles (UAVs) over a cellular network, where UAVs act as aerial users to collect various sensor data and send the collected data to the transmission destination over cellular links. Different UAVs have different communication requirements due to their sensing applications, thus requiring a more flexible communication solution. To address this issue, the authors propose a UAV-to-Everything (U2X) network. It allows UAVs to adapt their communication mode according to the requirements of their sensing applications. A mobile UAV network typically consists of a BS, multiple UAVs, and multiple ground UEs. UAVs collect data from sensing targets and transmit the collected data to the BS or ground UEs to support various applications (Figure 24). Sensing tasks are performed in two steps: UAV sensing and UAV transmission. The authors consider the use of U2X communication in the UAV mobile Internet, enabling UAVs to support multiple sensing applications at high transmission rates.