## 3 Results and Discussion
### Telecommunications Analysis and Applied Results  
The throughput of the 4G network is not symmetrical, having less available throughput in the upstream channel than in the downstream channel. In the case of streaming video transmission, the limiting factor is the throughput in the upstream channel, from the drone to the ground points. The standard specifies a maximum of 100 Mbps in the downstream channel and 50 Mbps in the upstream channel. However, since these transmission systems share the medium with several users, the actual throughput that we are going to obtain will depend on factors such as the load of the network at that time and the interference caused by such. In practice, we found a range from very low rates to peaks of 15 Mbps. Taking as an example a 720 p video at 30 fps, the calculation of the storage needs, in MB, assuming 3 colors per pixel and 8 bits per color and a 1:125 compression rate for one minute of video can be calculated as follows (Equation (1)):  
\[C=\Delta c\cdot\Delta r\cdot fps\cdot Nb\cdot\lambda\cdot t\cdot CCR \tag{1}\]  
where \(C\) is the storage need in MB, \(\Delta c\) is the number of columns, \(\Delta r\) is the number of rows, _fps_ is the frames-per-second rate, \(Nb\) is the number of bits resolution of each color band, \(\lambda\) is the number of bands per pixel, and \(CCR\) is the Code Compression rate. One minute of video will require approximately 40 MB of memory. Therefore, a bandwidth of at least 5 Mbps will be necessary to transmit this video in streaming with the appropriate quality. Taking as an example a video in 4 K quality and 30 fps, one minute of video will require approximately 170 MB of memory. We consider that a bandwidth of at least 25 Mbps will be necessary to transmit this video in streaming. This is a high consumption of data, which makes it unaffordable for common users, but with the upcoming 5G technology this scenario can change, as noticed in [41]. Latency can be the most critical point, especially in first person view (FPV) video, which must be below 250 ms following the current regulations in most European countries [42]. Depending on the position of the VPN root servers, the latency can reach 100 ms only due to the system architecture. This, added to the latency of the electronics (between 30 ms and 50 ms) and the one introduced by the 4G network, can in some cases cause problems for the video in real time (UDP protocol). In practice, our tests show that although there are some small micro-cuts, the quality of the FPV is good enough at a resolution of 720 p and 30 fps and the latency is under the 250 ms requirement. However, this value is very volatile and dependent on the signal quality. These results agree with the possibilities described in [9] and further developed in [5; 10]. Figure 6: Example of EXO Data logical scheme. Links description. Link A: FPV, telemetry and HD video (optional). Link B: FPV (optional), telemetry and HD video. Link C: CV processed HD video, telemetry insights and Data Base storage. Link D: Telemetry and FPV requests (optional). The major concern is the 4G network telecommunication feasibility for such applications, especially the link cuts due to sporadic coverage losses. We carried out theorical and practical experiments to demonstrate its feasibility. Typical antennas deployed for the 4G network have vertical radiation patterns with half-power beam widths that are around \(7^{\circ}\). The antennas are subjected to both mechanical and electrical inclinations (tilt) to get them to focus on the coverage area and avoid overreaching with neighboring stations. We made a trigonometric approach, in order to estimate the gain of the antenna as a function of the horizontal distance from the drone to the base station. The vertical angles between drone and antenna, are set between \(5^{\circ}\) and \(20^{\circ}\) (taking into consideration the tilt, \(5^{\circ}\) is considered the maximum of the secondary lobe and \(20^{\circ}\) is considered out of the secondary lobe).