## 4 UAV Communication Network and Technology
### Communication Protocols in UAV Networks
The core of the system is a fully distributed mobility algorithm that periodically updates the UAV structure to adapt to the movements of the ground nodes. LoRaUAV has been successfully deployed in NS-3, and its performance has been evaluated in wild-land firefighting scenarios using packet reception ratio (PRR) and end-to-end delay as key performance metrics. The Connection Maintenance and Resumption (CRM) and Motion Prediction (MP) mechanisms implemented in LoRaUAV effectively improve PRR, with the only drawback being higher latency affecting a small percentage of packets due to buffering delays and disconnections. A UAV-enabled WiFi Direct network architecture (depicted in Figure 22) to improve throughput, device connectivity, and energy efficiency in 3D space and constrained areas with boundaries is proposed in [66]. In this, a UAV equipped with a WiFi Direct group owner (GO) device, called a Soft-AP, is deployed in the network to serve a set of WiFi stations. The authors proposed to use a simpler but more efficient algorithm for optimal UAV placement. The proposed algorithm dynamically places the UAV in the network to reduce the distance between the GO and the client devices. The expected benefits of the proposed scheme are to maintain the connectivity of the client devices. This aims to increase the overall network throughput and improve energy efficiency. Real simulations are performed with NS-3 to validate the claimed benefits of the proposed scheme. The simulation results showed large improvements of 23% in client connectivity, 54% in network throughput, and 33% in energy consumption when using a single UAV, compared to the case of a fixed or randomly moving GO. * LTE  
Traditionally, UAVs operate on licensed radio frequency bands (2.4 GHz), where the UAV's operating range is limited to the LoS range. Therefore, to fully exploit the potential of UAV devices, it is necessary to establish beyond line-of-sight (BVLoS) connectivity [67]. Recent years have seen an increase in the use of terrestrial LTE networks to provide connectivity to UAVs. LTE systems provide airborne connectivity beyond the LoS communication range for UAVs. In [68], LTE is used for scenarios where UAVs operate as a BS transmitting in the downlink (DL) or a UE transmitting in the uplink (UL). The paper highlights that current LTE networks require significant modifications for the seamless integration of LTE-enabled UAVs. The most notable drawback to using LTE and other cellular systems is the need to register the drone transmitter with the service provider. It increases operating costs and limits drone operations to areas covered by the service provider. In [69], the authors performed a comprehensive quality of service analysis taking into account the throughput, packet loss rate, and latency provided for the integration of LTE and UAV through simulation. The simulation layout of UAV-GCS communication over an LTE network was implemented at Cranfield University. The UAV flew in a schematic diagram along the runway of Cranfield Airport. The research results can help design a UAV system using LTE to transmit 1080p video with low latency. In addition, the simulation results also showed that the UAV altitude greatly affects communication performance. At low altitudes (25 m), the signal is more disturbed, especially in Urban Micro (UMi) environments due to the shielding from buildings. At 100 m altitude, the performance improved significantly, and further improvements were made possible by adjusting LTE parameters. In [70], the authors developed a prototype LTE-based control system for small UAVs at low altitudes and studied the feasibility and performance of the drone's mobile connectivity at different altitudes, with measurement parameters such as delay, handover, and signal strength. The measurement results showed that when the flight altitude from the ground increased to 170 m, the received signal power and signal quality level decreased by 20 dBm and 10 dB, respectively. The downlink data rate decreased by 70%, and the latency increased to 94 ms.