## 3 System Model
### Link Stability Model  
In order to find targets quickly in the search phase, high mobility is one of the major challenges of the UAV routing protocol, and leads to frequent topology changes or communication link interruptions. For the sake of reducing packet loss due to the rapid movement of nodes, we propose a link-stability evaluation indicator. Each node records its own location information during the last five hello moments and stores the location sequence in the hello packet header. A node \(i\) receives the location sequence \(\mathbf{L}_{j}=\left[L_{j}(t_{1}),L_{j}(t_{2}),L_{j}(t_{3}),L_{j}(t_{4}),L_{j}(t_{ 5})\right]\) from its neighbor node \(j\). The distance between node \(i\) and its neighbor node \(j\) at time \(t_{1}\) can be calculated as follows  
\[D_{ij}(t_{1})=\sqrt{\left(L_{i}^{x}(t_{1})-L_{j}^{x}(t_{1})\right)^{2}+\left( L_{i}^{y}(t_{1})-L_{j}^{y}(t_{1})\right)^{2}} \tag{1}\]  
where \(\left(L_{i}^{x}(t_{1}),L_{i}^{y}(t_{1})\right)\), \(\left(L_{i}^{x}(t_{1}),L_{j}^{y}(t_{1})\right)\) are the coordinates of the nodes \(i\) and \(j\) at time \(t_{1}\), respectively. Hence, the distance sequence between \(i\) and \(j\) during the last five hello intervals is expressed as \(\mathbf{D}_{ij}=\left[D_{ij}(t_{1}),D_{ij}(t_{2}),D_{ij}(t_{3}),D_{ij}(t_{4}),D_{ ij}(t_{5})\right]\). Then, in accordance with the variance of \(\mathbf{D}_{ij}\), the link change extent between \(i\) and \(j\) over a period of time can be evaluated.Then, we can estimate link stability \(LS_{ij}\), which is given by  
\[LS_{ij}=D\big{(}\mathbf{D}_{ij}\big{)}=\mathbb{E}\big{(}\mathbf{D}_{ij} ^{2}\big{)}-\mathbb{E}\big{(}\mathbf{D}_{ij}\big{)}^{2}=\sum_{t}^{t_{5}}\frac{D_{ ij}^{2}(t_{a})}{5}-\left(\sum_{t}^{t_{5}}\frac{D_{ij}(t_{a})}{5}\right)^{2},u=\{1,2,3,4,5\} \tag{2}\]  
where \(\mathbb{E}\big{(}\mathbf{D}_{ij}^{2}\big{)}\) and \(\mathbb{E}\big{(}\mathbf{D}_{ij}\big{)}^{2}\) are the expected distance and the expected square of the distance, respectively. \(D\big{(}\mathbf{D}_{ij}\big{)}\) is the variance of \(\mathbf{D}_{ij}\). If the variance is equal to zero, the link between nodes \(i\) and \(j\) is strictly stable during the last five hello intervals. The smaller \(\mathbf{D}_{ij}\) is, the more stable the link is.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Routing** \\ **Protocol** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Energy Man-** \\ **agement** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Link** \\ **Attribute** \\ **Perception** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Load** \\ **Balance** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Exploration** \\ **Balance** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Quick** \\ **Adaptation** \\ **to High-** \\ **Dynamic** \\ **Scenarios** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Adaptation** \\ **to** \\ **to** **Large-Scale** \\ **Networks** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Network** \\ **Application** \\ **Application** \\ \end{tabular} } \\ \hline GPSR [11] & \(\times\) & \(\times\) & \(\times\) & \(\times\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & MANET \\ QGEO [39] & \(\times\) & \(\checkmark\) & \(\times\) & \(\checkmark\) & \(\times\) & \(\times\) & Mobile robot \\  & & & & & & & networks \\ QNGPSR [42] & \(\times\) & \(\times\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & UANET \\ TQNGPSR [43] & \(\times\) & \(\times\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & UANET \\ FEQSAI [41] & \(\checkmark\) & \(\checkmark\) & \(\times\) & \(\checkmark\) & \(\checkmark\) & \(\times\) & FANET \\ DSEGR & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) & UANET \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of different routing protocols.