## 2 Related Works  
Recently, plenty of studies have been conducted to investigate the performance of existing 4G/LTE networks for UAV operations. One of the most precise and significant studies was performed by the 3 rd Generation Partnership Project (3 GPP), as reported in [17] and summarized in [19]. 3 GPP formed a team in the \"Radio Access Network studyingEnhanced LTE Support for Aerial Vehicles\" and performed numerous flight tests and simulations to evaluate the use of 4G LTE as a potential communication solution for UAV operation. Accordingly, the researchers verified the system performance level and identified the density of supportable heights, speeds, and UAVs. In addition, air-to-ground channel models were developed for different scenarios, and performance-enhancing solutions were studied for interference detection and mitigation, handover, and positioning. In addition, some recent works in [13; 15; 20; 21] investigated the performance of cellular-connected drones in simulation environments under different flight heights and drone speed scenarios. Accordingly, different measurement metrics were considered, including signal-to-interference plus noise ratio (SINR), RSRP, and HO. The results showed that the probability of LoS communication links increases by increasing the flight altitude, which, on the one hand, reduces the destructive effects such as penetration loss and shadowing and, on the other hand, enhances the inter-cell interference level, especially on the uplink. In addition, the papers demonstrated how drones are served by BS antennas' sidelobes and revealed the issue of HO when drones move to the BS antenna sidelobe nulls. However, the conducted studies were limited to simulation results and therefore did not fully reflect real-world scenarios' technical challenges and constraints. Other research works, such as [12; 13], performed field measurements to investigate the performance of cellular-connected drones in different scenarios. The performance of drone connectivity in an LTE network was investigated in terms of coverage, data-rate, interference, and latency. Results showed that existing LTE networks could provide communication links for low-altitude drones. However, the results were limited to specific scenarios, such as remote or rural environments. The authors in [22] performed a set of aerial drive tests in a suburban area to investigate the performance of LTE for UAV communications. It was found that the existing LTE network can provide aerial coverage under some circumstances, which mainly depends on the position of the UAV to the BS. The authors in [23] conducted a measurement campaign in the 4G network and the result evaluation shows the weakness of the existing cellular networks in providing areal coverage, compared to terrestrial applications. In addition, the authors proposed a long-range multi-link communication system for UAVs, in which the developed communication module leverages multiple LTE modems and networks together with a multipath transmission control protocol for multi-link aggregation. The results show that the pro-posed system can considerably increase the communication link availability in maritime scenarios and provide smooth handover between different networks. Besides performance evaluation, recently, the topic of UAV-to-BSs channel modeling has attracted the attention of researchers and, thereby, plenty of works have been conducted on this domain. For instance, ref. [24] reviewed the recently developed state-of-the-art air-to-ground channel models for different wireless communication technologies, including cellular-connected UAVs. Meanwhile, ref. [25] developed an empirical channel model for the UAV-to-BS scenario based on path loss and shadowing effects in the LTE network. The results showed that the path loss exponents decrease by increasing the flight height. The research findings also revealed the need for a height-based channel model for describing the propagation channel between UAVs and BSs.