## 4 Summary and Lessons Learned

Table 1: Deployment of multiple UAVs. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multirow{2}{*}{**Objective**} & \multirow{2}{*}{**Algorithm/Analysis**} & \multicolumn{4}{c}{**Design Considerations of UAV Networks**} \\ \cline{5-8}  & & & **UAV Altitude** & **Environment/Scenario** & **Channel Model** \\ \hline \multicolumn{8}{c}{Use Case 1: UAV BS} \\ \hline
[38] & \begin{tabular}{c} Maximize the number \\ of covered users \\ \end{tabular} & \
\begin{tabular}{c} Circle placement \\ problem (2D placement) \\ \end{tabular} & Find an optimal altitude & - &
\begin{tabular}{c} Air-to-ground channel \\ model [61] \\ \end{tabular} \\ \hline
[39] & \begin{tabular}{c} Maximize the number \\ of covered users \\ \end{tabular} & \begin{tabular}{c} Bisection/interior point \\ method \\ \end{tabular} & Find an optimal altitude & \
\begin{tabular}{c} Urban, suburban, dense \\ urban, High-rise urban \\ \end{tabular} &
\begin{tabular}{c} Air-to-ground channel \\ model [61] \\ \end{tabular} \\ \hline
[40] & \begin{tabular}{c} Improve the spectral \\ efficiency \\ \end{tabular} & \
\begin{tabular}{c} Propose algorithm to \\ autonomously control \\ the repositioning of \\ UAV \\ \end{tabular} & Fixed & - &
\begin{tabular}{c} Air-to-ground channel \\ model [61] \\ \end{tabular} \\ \hline
[41] & \begin{tabular}{c} Minimize the transmit \\ power \\ \end{tabular} & \begin{tabular}{c} Solve the non-convex \\ problem by considering \\ two practical cases \\ \end{tabular} & \
\begin{tabular}{c} Numerically search an \\ optimal altitude \\ \end{tabular} & High-rise building &
\begin{tabular}{c} Outdoor-Indoor path \\ loss model in [71] \\ \end{tabular} \\ \hline
[18] & \begin{tabular}{c} Optimize the sum-rate \\ capacity or transmit \\ power gain \\ \end{tabular} & \
\begin{tabular}{c} Propose altitude \\ dependent performance \\ evaluation model \\ \end{tabular} & Find an optimal altitude & - &
\begin{tabular}{c} \# dependent Rician \\ fading and pathloss \\ exponent model \\ \end{tabular} \\ \hline
[44] & \begin{tabular}{c} Maximize the network \\ throughput \\ \end{tabular} & \
\begin{tabular}{c} Power control and time \\ allocation algorithm \\ \end{tabular} & Fixed & Disaster &
\begin{tabular}{c} Air-to-ground channel \\ model [61] and Rician \\ fading \\ \end{tabular} \\ \hline
[45] & \begin{tabular}{c} Maximize the network \\ throughput \\ \end{tabular} & \begin{tabular}{c} UAV deployment and \\ time allocation \\ algorithm \\ \end{tabular} & Find an optimal altitude & \
\begin{tabular}{c} No terrestrial wireless \\ network \\ \end{tabular} &
\begin{tabular}{c} Air-to-ground channel \\ model [61] and Rician \\ radio \\ \end{tabular} \\ \hline
[46] & \begin{tabular}{c} Maximize total number \\ of served users and \\ sum-rates \\ \end{tabular} & \
\begin{tabular}{c} Exhaustive search to \\ find 3D location of UAV \\ \end{tabular} & Find an optimal altitude & Urban &
\begin{tabular}{c} Air-to-ground channel \\ model [61] \\ \end{tabular} \\ \hline
[47] & \begin{tabular}{c} Maximize the sum-rates \\ \end{tabular} & \
\begin{tabular}{c} Genetic algorithm and \\ successive convex \\ approximation \\ \end{tabular} & Fixed & Two way relay system &
\begin{tabular}{c} Air-to-ground channel \\ model [61] \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Deployment of single UAV.