# Flying Ad Hoc Networks: A New Domain for Network Communications
## 2 State of the Art
### Results  
We conducted three sets of experiments whose description and results are explained as follows. The first set of experiments aimed to get the best configuration of the antennas for the WiFi as an isolated device, i.e., the most appropriate orientation in order to achieve the highest signal power. This was done for the 2.4 GHz band and the 5 GHz band, which corresponded to the U2U and U2G links, respectively, as shown in Figure 1.  
To obtain the radiation pattern as accurately as possible, three planes were studied, depicted in Figure 11 as X Plane, Y Plane, and Z Plane. Within each plane, both vertical and horizontal polarizations were studied. Figure 12 depicts a detailed example of a measurement and represents how the WiFi  
Figure 10: Experimental testbed elements (DUT \(\equiv\) Device Under Test \(\equiv\) UAV + WiFi device). \begin{table}
\begin{tabular}{c c} \hline
**Device or Parameter** & **Configuration** \\ \hline TX Antennas (Antenna Gain 2.4/5 GHz) & ARS-NT5B (5/5 dBi), APA-M25 (8/10 dBi) \\ RX Antenna (Antenna Gain 2.4/5 GHz) & HF906 (10/11 dBi) \\ Distance between TX and RX Antennas & 3 m \\ Traffic Generator & Iperf v2.0.9 (TCP default configuration) \\ Center Frequency & 2.462/5.210 GHz \\ Transmitted BW & 40/40 MHz \\ Captured BW & 20/20 MHz \\ TX Power & 20/20 dBm \\ \hline \end{tabular}
\end{table} 
Table 5: Summary of parameters and characteristics of the test bed. Figure 9: UAV and WiFi device. appeared on each spatial cut (X, Y, and Z planes). The regions of interest for the U2U and U2G links are also highlighted in green and yellow colors in Figure 12, respectively. These regions of interest were used to select the best configuration of the antennas considering a specific scenario. Particularly, we assumed that for communications among UAVs (U2U links), the regions of interest should be located in the same horizontal plane (\(\pm 45^{\circ}\)). Therefore, the region of interest for communication among UAVs corresponds to the complete X plane plus two areas of \(90^{\circ}\) (from \(45^{\circ}\) to \(135^{\circ}\) and from \(-45^{\circ}\) to \(-135^{\circ}\)) seen from the Y and Z planes as shown in Figure 12. On the other hand, we set the region of interest for U2G communications as a \(90^{\circ}\) coverage (from \(135^{\circ}\) to \(-135^{\circ}\)) in Y and Z planes from the UAV to the ground. Therefore, the optimal antenna configuration was such that the maximum power was obtained in the so-defined regions of interest. Please observe that for another type of network deployment, e.g., in case of a satellite-aided UAV communication, the region of interest for the UAV-satellite link would be different, being maybe interested in that case in using the antennas configuration that would maximize power transmission in Y and Z planes with an angle of \(90^{\circ}\) (from \(-45^{\circ}\) to \(45^{\circ}\)). After carrying out this first set of experiments, the best antenna configuration that we observed is shown in Figure 13. The corresponding radiation pattern is depicted in Figure 14 for the 2.4 GHz band and in Figure 15 for the 5 GHz band. For example, note that with the configuration shown in Figure 13 we obtained the maximum power transmitted in the region of interest defined for the Y plane (from \(135^{\circ}\) to \(-135^{\circ}\)). These results could be considered as expected given that to optimize the U2G link, the power must be transmitted from the UAV downwards, and this is achieved by orienting the antennas towards the nadir. In addition, if the antennas rotate 90 degrees between them, we have polarization diversity and, therefore, we avoid a situation of crossed polarization between the receiving antenna and any of the transmitting antennas at the same time. Another important feature  
Figure 11: Planes under study.