## 11 Conclusions  
Multi-UAV systems are of great interest to the scientific community because they represent a wide range of opportunities. Their usefulness in the industrial sector is no longer in doubt. They are an effective means for carrying out complex missions that require several types of UAVs. The question of the implementation of a multi-UAV system is a subject that involves two major challenges: technical-functional and legal/ethical. At the technical-functional level, the multi-UAV system must ensure interoperability between these components and maintain a level of autonomy that allows it to make collective decisions without human intervention. Using multi-UAVs for highly mobile network and wide-area missions is a challenging task because the UAVs must not move too far away from each other to avoid signal loss, which is not often the case. In addition, there are constraints related to the system infrastructure, the communication architecture, and the routing protocol. From a legal/ethical point of view, it is very important to consider people's privacy and safety, as well as to implement rigorously the regulations that guarantee the responsible use of multi-UAV systems. \begin{table}
\begin{tabular}{p{71.1 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Category** & **Article** & **Regulation** \\ \hline \multirow{4}{*}{UAV categories} & Article 3 & Uncrewed aircraft systems operational categories \\  & Article 4 & The UAS operational category “open” \\  & Article 5 & The UAS operational category “special” \\  & Article 6 & The UAS operating category “requiring approval” \\ \hline \multirow{4}{*}{Operational requirements} & Article 7 & Rules and procedures for the operation of UAS \\  & Article 8 & Rules and procedures related to the competency of long-distance pilots \\  & Article 10 & Rules and procedures related to the airworthiness of UAS \\ \hline \multirow{4}{*}{Risk classes} & Article 11 & Rules for operational risk assessment \\  & Article 12 & Operating license for the “special” category \\  & Article 14 & Registration of the UAS operator and UAS subject to licensing \\ \hline \multirow{2}{*}{Long distance flight} & Article 13 & Cross-border operation or operation outside of the state of registration \\  & Article 15 & Operating conditions for UAS geographic areas \\ \hline \multicolumn{2}{p{71.1 pt}}{Privacy policy} & Article 19 & Security information \\ \hline \multicolumn{2}{p{71.1 pt}}{} & European Union regulation 2019/947 of 24 May 2019 ([[https://eur-lex.europa.eu/legal-content/EN/AUTO/?uri=CELEX:02019R0947-20220404](https://eur-lex.europa.eu/legal-content/EN/AUTO/?uri=CELEX:02019R0947-20220404)]([https://eur-lex.europa.eu/legal-content/EN/AUTO/?uri=CELEX:02019R0947-20220404](https://eur-lex.europa.eu/legal-content/EN/AUTO/?uri=CELEX:02019R0947-20220404)), accessed on 15 March 2023). \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Most important regulations on the use of UAVs for setting up a swarm. Many scientific contributions have already explored countermeasures to these concerns; nevertheless, certain areas, such as mathematical modeling, the comparative study of communication architectures as well as routing protocols, and decision-making roadmap concerns, have yet to be addressed. With the growing interest in self-organizing swarms, these four challenges cannot be ignored. For this reason, this review paper offers a thorough investigation of the challenges associated with deploying an autonomous multi-UAV system that integrates collaborative actions, as well as the complexity of the collaborative target detection problem in distributed environments. It is an NP-Hard problem [58], which results in challenges related to the balancing of workloads in the swarm and the minimization of the path costs to reach targets.