# Flying Ad Hoc Networks: A New Domain for Network Communications
## 2 State of the Art
### Positioning Protocols  
Coverage in a given area is a classic problem in wireless telecommunication networks. Widely studied, most recent proposals use evolutionary algorithms [38], integer linear programming [39], or greedy algorithms [40] (among others) to plan the best location of base stations and cellular systems. However, these solutions do not lead to an optimal deployment in FANETs due to their unique characteristics. As a consequence, original methods have been presented for optimal positioning of UAV nodes in FANETs, whose objective is either to offer coverage at ground level or to increase the capacity of traditional mobile networks [15; 41] or MANETs [42]. The proposed taxonomy is hence divided into two categories: height-based positioning and network-based positioning. * Height-based positioning. First, there are several studies that analyze the impact of the height of the UAV node on the achieved coverage. In Reference [43], the optimal position of a UAV node that maximizes coverage through a mathematical model is obtained. The channel model on which they based their study contains statistical parameters for the urban environment defined by the International Telecommunication Union (ITU). Thus, their results included a formula to obtain the optimal altitude based on the maximum allowable losses, and some additional statistical parameters. [PERSON] et al. [44] extended the work done in Reference [43]. They obtained the optimum height where to place a UAV to offer the maximum coverage area with the minimum transmitted power. In addition, they studied the use of two UAVs to provide coverage in two scenarios, namely, interference-free and full interference between both UAVs. In the first scenario, the height and distance between UAVs was calculated for optimal deployment in an area. In the second scenario, the existence of interference did not allow full coverage of the entire area, but the results showed the existence of an optimal separation between both UAVs, which provided the highest proportion of coverage area. Nevertheless, the authors used a theoretical channel model, without relying on any of the existing channel models for the U2G communication channel. Similarly, the authors in Reference [45] also investigated the optimal height of a UAV to provide coverage. In this case, they considered that the channel presented path loss and scattering. Particularly, they employed a Rician fading model with dependence on the elevation angle. They showed that there is an optimal position that maximizes the coverage area and presented the lowest losses. * Network-based positioning. Regarding the control of nodes positioning, there are a large number of studies. As an example, the deployment of a network with FW-UAV is evaluated in [46]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Class** & **Ref** & **Mobility Model** & **RW/FW UAV** & **Applications** \\ \hline \multirow{4}{*}{Pure Randomized} & [21] & RW & RW & \multirow{4}{*}{Environmental sensing/Traffic and urban Monitoring} \\  & [17] & RWP & RW & \\  & [22] & RD & RW & \\  & [23] & MG & RW & \\ \hline \multirow{4}{*}{Time-Dependent} & [24] & BSA & RW & \multirow{4}{*}{Environmental sensing/Search and rescue} \\  & [25] & GM & RW & \\  & [26] & EGM & RW/FW & \\  & [27] & 3D-GM & RW/FW & \\  & [19] & ST & RW/FW & \\ \hline \multirow{2}{*}{Path-Planned} & [28] & SRCM & RW & \multirow{2}{*}{Agricultural management/Traffic and urban Monitoring} \\  & [18] & PPKZM & RW/FW & \\ \hline \multirow{4}{*}{Group} & [35] & ECR & RW & \multirow{4}{*}{Environmental sensing/Search and rescue} \\  & [31] & PSMM & RW/FW & \\  & [32] & RPGM & RW & \\  & [21] & CLMN & RW & \\  & [21] & NC & RW & \\  & [21] & PBS & RW/FW & \\ \hline Hybrid & [34] & H3 MP & RW & Surveillance/Search and rescue \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The taxonomy of mobility models, the adequate type of UAV, and examples of their applications. These nodes cannot remain static in a point, but they must be flying over a point.