# Reinforcement Learning-Based Routing Protocols in Flying Ad Hoc Networks (FANET): A Review
## 7 Discussion
Moreover, local data, such as the speed and spatial information of UAVs, are more dynamic and expire \begin{table}
\begin{tabular}{c c c} \hline \hline
**Scheme** & **Flat** & **Hierarchical** \\ \hline DQN-VR [67] & \(\times\) & \(\checkmark\) \\ \hline QTAR [68] & \(\checkmark\) & \(\times\) \\ \hline TQNGPSR [69] & \(\checkmark\) & \(\times\) \\ \hline QMR [70] & \(\checkmark\) & \(\times\) \\ \hline QGeo [71] & \(\checkmark\) & \(\times\) \\ \hline QSRP [72] & \(\checkmark\) & \(\times\) \\ \hline QLGR [73] & \(\checkmark\) & \(\times\) \\ \hline FEQ-routing-SA [74] & \(\checkmark\) & \(\times\) \\ \hline Q-FANET [75] & \(\checkmark\) & \(\times\) \\ \hline PPMAC+RLSRP [76] & \(\checkmark\) & \(\times\) \\ \hline PARRoT [77] & \(\checkmark\) & \(\times\) \\ \hline QFL-MOR [78] & \(\checkmark\) & \(\times\) \\ \hline
3 DQ [79] & \(\checkmark\) & \(\times\) \\ \hline ICRA [80] & \(\times\) & \(\checkmark\) \\ \hline TARRAQ [81] & \(\checkmark\) & \(\times\) \\ \hline \hline \end{tabular}
\end{table} 
Table 29: Comparison of RL-based routing methods based on network topology. quickly. Therefore, they must be updated at shorter time intervals. The central controller is responsible for collecting global data and performs the RL-based routing process based on both local and global data. This has improved the performance of this method compared to QSRP. In ICRA, a central controller computes clustering parameters. However, the clustering process is performed by UAVs in the network in a distributed manner. Finally, Table 32 compares different routing methods in terms of the data dissemination process. Broadcast is the most common process used by almost all routing methods. For example, most RL-based routing methods broadcast hello messages to obtain local \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scheme** & **Greedy** & **Store-Carry-Forward** & **Route Discovery** \\ \hline DQN-VR [67] & \(\times\) & \(\times\) & ✓ \\ \hline QTAR [68] & \(\times\) & \(\times\) & ✓ \\ \hline TQNGPSR [69] & ✓ & \(\times\) & \(\times\) \\ \hline QMR [70] & \(\times\) & \(\times\) & ✓ \\ \hline QGeo [71] & \(\times\) & \(\times\) & ✓ \\ \hline QSRP [72] & \(\times\) & \(\times\) & ✓ \\ \hline QLGR [73] & ✓ & \(\times\) & \(\times\) \\ \hline FEQ-routing-SA [74] & \(\times\) & \(\times\) & ✓ \\ \hline Q-FANET [75] & \(\times\) & \(\times\) & ✓ \\ \hline PPMAC+RLSRP [76] & ✓ & \(\times\) & \(\times\) \\ \hline PARRoT [77] & ✓ & \(\times\) & \(\times\) \\ \hline QFL-MOR [78] & \(\times\) & \(\times\) & ✓ \\ \hline
3 DQ [79] & ✓ & ✓ & \(\times\) \\ \hline ICRA [80] & ✓ & \(\times\) & \(\times\) \\ \hline TARRAQ [81] & \(\times\) & \(\times\) & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 31: Comparison of RL-based routing methods based on the routing process. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Scheme** & **Centralized** & **Distributed** \\ \hline DQN-VR [67] & ✓ & ✓ \\ \hline QTAR [68] & \(\times\) & ✓ \\ \hline TQNGPSR [69] & \(\times\) & ✓ \\ \hline QMR [70] & \(\times\) & ✓ \\ \hline QGeo [71] & \(\times\) & ✓ \\ \hline QSRP [72] & ✓ & \(\times\) \\ \hline QLGR [73] & \(\times\) & ✓ \\ \hline FEQ-routing-SA [74] & \(\times\) & ✓ \\ \hline Q-FANET [75] & \(\times\) & ✓ \\ \hline PPMAC+RLSRP [76] & \(\times\) & ✓ \\ \hline PARRoT [77] & \(\times\) & ✓ \\ \hline QFL-MOR [78] & \(\times\) & ✓ \\ \hline
3 DQ [79] & \(\times\) & ✓ \\ \hline ICRA [80] & ✓ & ✓ \\ \hline TARRAQ [81] & \(\times\) & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 30: Comparison of RL-based routing methods based on data delivery technique. information. The most important disadvantage of this technique is high energy and bandwidth consumption. It also imposes a lot of communication overhead on the network. In QTAR, QMR, QGeo, QLGR, QSRP, and TARRAQ, researchers have introduced techniques for adjusting the hello broadcast interval to reduce the routing overhead. However, this issue still requires a lot of research.