# Unmanned Autonomous Intelligent System in 6G Non-Terrestrial Network
## 2 Non-Terrestrial Networks in 5G/6G
### The Role of UAVs in NTNs  
In sixth-generation (6G) communication networks, space-air-ground-sea integrated networks will satisfy communication demands around the globe, whether in deserts, mountains, or islands. In contrast to common network users like cell phones and other portable devices, UAIS have faced great challenges in terms of network connectivity, throughput, and reliability since platforms such as robots, self-driving cars, or unmanned boats might be unevenly distributed in remote areas and in high-speed maneuvers, which demand flexible and ubiquitous network coverage. In this case, few existing ground network infrastructure is available for the urgent demand for a task-critical and time-sensitive network using conventional terrestrial methods. Considering this challenge, it is beneficial to employ non-terrestrial infrastructures, including satellites and unmanned aerial vehicles (UAVs), HAPS, and LAPS, for wide-area communication coverage for UAIS.  
In particular, NTN is a flexible means to provide on-demand coverage for machines and adapt to the nature of the uneven distribution of UAIS in practical fields; thus, the architecture of the NTN should be designed within a cell-free architecture [24]. In addition, driven by the requirements of time-sensitive missions of UAIS, massive data generated from UAIS must be processed as quickly as possible. Therefore, non-terrestrial communications-based multi-access edge computing is essential and requires the help of UAVs to build high-speed links between UAIS users and UAVs [25; 26; 27]. Depending on the role of UAIS platforms in NTNs, the architecture of NTNs can be defined as follows:  
1. UAV platform as an NTN user: In this use case, UAV platforms are utilized as network users in an NTN architecture, which is a primary form of UAIS in NTNs. For instance, UAVs and satellites can be considered as NTN users serviced by other platforms.
2. UAV platform as an NTN relay: In this use case, UAVs are considered mobile relays for scenarios in which direct links cannot be achieved due to geographic obstacles or extended communication ranges.
3. UAV platform as an NTN base station: In this case, UAVs are equipped with base stations for connectivity coverage. Sometimes, UAV platforms with abundant payload capabilities are further utilized for multi-edge computing.  
Figure 2: The illustration of 3 GPP NTN network architecture [22].  
Unmanned aerial vehicles (UAVs) are ideal operation platforms for flying base stations, relays, access points and other non-terrestrial communication infrastructure, which fully leverage the advantages of the high maneuverability and flexibility of the platform. Therefore, UAVs are preferred when performing network coverage missions in dangerous or communication-congested areas where reliable communication does not exist or has been corrupted. In the past, UAV-based systems have been designed and used for military operations and disaster rescue applications. Such applications include surveillance, inspection, personnel searches, and dangerous situation alerts. Nowadays, UAVs have evolved into platforms for non-terrestrial network coverage for ubiquitous network applications supporting the communication demand of users in various applications. With the constant innovations in the domain of mobile communications, UAV NTN communication coverage for UAIS on the ground, in the air or in the ocean is drawing much attention. Advancements in NTN communications hold potential driving factors for supporting UAIS with low-latency, high-bandwidth and multi-access edge computing in complex environments [28; 29].