# Machine-Learning-Enabled Intrusion Detection System for Cellular Connected UAV Networks
## 2 Background and Related Works
### Satellite Architecture
The 4G network uses frequencies lower than 6 GHz, while 5G uses frequencies from low-band, 600 MHz, to mid-band, and to very high frequencies between 30 GHz to 300 GHz, and they differ from country to country [32]. These low-band frequencies have high 5G coverage and are suitable for rural areas. These high frequencies have great advantages, the most important of which is high capacity and throughput. In comparison to 5G, 4G cells  
Figure 3: 5G System with a satellite backhaul. transmit data covering the cell area, which is a waste of both energy and cell power, while 5G cell transmits only small beams in the direction of users only [33]. Furthermore, much smaller antennas are installed in 5G because of shorter wavelengths while still supplying directional control. In terrestrial mobile networks, one BS can effectively be equipped with even more directional antennas for supporting over 1000 additional devices per square meter in comparison with 4G. Thus, many more users can use 5G with enhanced Mobile Broad Band (eMBB), high precision, and very low latency. Moreover, 5G networks can easily receive the required type of data and switch to a lower power when lower rates are needed, and then it switches to a higher-powered mode [34]. A 5G satellite network can be based on a constellation of one or multiple satellites. The satellites are placed in LEO in order to permit connectivity of users, which have constrained RF and energy capabilities. The constellation of satellites may provide a continuous service, with a satellite covering any user with a continuous global coverage. The satellites that are not within range of a ground station can use ISL to communicate (via indirect means) to the ground station. When a UE moves from one static tracking area to another, the tracking area is updated. A Heterogeneous Space and Terrestrial Integrated Networks (H-STIN) architecture has been proposed according to advancement procedure of the UAV, mobile networks, and satellite network [7]. The integration of UAVs into cellular networks provides significant advantages with several applications and use cases. With the new paradigm of integrating UAVs with cellular networks, UAVs can be used in two categories. In one category, UAVs can be used as aerial users where the UAVs use the cellular network for connectivity also known as cellular-connected UAVs. The second category is that UAVs can be used as aerial platforms for communication, i.e., UAVs can be used as cellular BS or relays, to provide extended communication to the terrestrial networks and users, known as UAV-assisted wireless communication [35]. In Release 17, there is a 5G enhancement for UAVs to provide extended service to mobile users by using on-board UAV access nodes (UxNB). The UxNB provides extended coverage in scenarios such as natural disasters, temporary coverage for mobile users, and other emergency situations [36]. With the help of on-board UxNB access nodes, the UAV can act as either a base station, where it is connected with the 5G core network, or as a relay, where the UAV is connected with the terrestrial BS to provide extended coverage, as shown in Figure 5. The telecommunications community has acknowledged the importance of providing communication support to low-altitude UAVs in achieving beyond-LoS control and developing a secure communication network. Only terrestrial or satellite communication cannot satisfy the connectivity issues for terrestrial, aerial vehicles,  
Figure 4: Multi-connectivity architecture with terrestrial, NGSO satellite, and GEO satellite RANs. and mobile devices. 5G communication needs to have non-terrestrial support such as integration of satellite system to enhance its communication range and provide guaranteed service. The satellite enhances the 5G system by providing satellite access to allow a radio coverage extension to the terrestrial networks, as well as extension to other 5G terrestrial networks through a roaming agreement.