# Unmanned Autonomous Intelligent System in 6G Non-Terrestrial Network
## 4 Application of UAV-Aided Non-Terrestrial Networks in UAIS
### 1.2.1. **USV-assisted maritime communications**  
The limited flight duration time and inability to operate in adverse weather conditions severely impacted the usability of UAVs in maritime communication. With its long endurance and all-weather operation capability, USV is a promising solution for providing three-dimensional and ubiquitous network coverage for oceanic operations in maritime NTNs. The use of USVs for maritime communication is a promising research area that can be integrated with UAV non-terrestrial networks to expand communication coverage for unmanned maritime platforms. In contrast to ground or air communications, maritime communications advancements are far from satisfactory in achieving ubiquitous wireless connectivity. USV with autonomous maneuverability and self-determination abilities offer a promising solution for extending oceanic network connectivity and improving quality of service.  
In [175], a novel method is introduced for mobile relaying assisted by USVs to demonstrate the application of utilizing USVs in maritime non-terrestrial wireless communications. On the other hand, USVs can be utilized for data collection purposes to collect seabed-based data, in support of the underwater internet of things (UIoT) [176; 177]. Ref. [178] utilized MIoT for maritime transportation systems. However, in [179], by combining the satellite network and USV-assisted wireless communication, a hybrid communication scheme was proposed to maximize the communication throughput and coverage.  
The recent advancement of NTN in maritime are summarized in Table 5. However, maritime NTN communications are still in the early stages of research, and several problems still need further investigation in the field of maritime communication applications, which include maritime channel conditions, maritime mobile edge computing, data security, and UAV-USV-satellite communication coordination [179]. For instance, MIoT is a vital issue in maritime information exchange and is worth in-depth investigation.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Literature** & **Topics** & **Contributions** & **NTN Communication Type** \\ \hline
[162] & Multi-USV Control &
\begin{tabular}{c} An integrated communication framework for \\ terrestrial, sea and HAP for multi-USV control. \\ \end{tabular} & HAP–USV \\ \hline
[164] & Multi-USV Communication &
\begin{tabular}{c} Multi-USV group communication scheme with \\ nested topology \\ \end{tabular} & USV–USV \\ \hline
[166] & USV Formation Control &
\begin{tabular}{c} Cooperative communication framework design \\ considering varying topology \\ \end{tabular} & UAV–USV \\ \hline
[167] & USV Formation Control &
\begin{tabular}{c} Event-triggered formation controller for lower \\ communication power consumption \\ \end{tabular} & UAV–USV \\ \hline
[168] & USV Formation Control &
\begin{tabular}{c} Dynamic event-triggered control scheme for \\ fixed time formation consensus. \\ \end{tabular} & UAV–USV \\ \hline \hline \end{tabular}
\end{table}
Table 5. Summary of previous work concerning USV in NTN communication.