# A Review of SATis5: Perspectives on Commercial and Defense 5G SATCOM Integration
## 2 An Overview of 5G Terrestrial and Non-Terrestrial Networks  
The overview of 5G-NT and 5G-NTN presented in this section is derived from [1, 2, 3, 4, 5]. These references provide a summary of current 5G standards and specifications with an excellent description of the following pertinent 5G technology features:  
* Extreme broadband speed using \"enhanced mobile broadband\" (eMBB) and millimeter-wave technologies'
* Massive multiple-input and multiple-output antenna array and state-of-the-art beam-forming technologies'
* \"Massive machine-type communications\" (mMTC) for consumer and industrial Internet-of-Thing (IoT), and industry 4.0 \"mission-critical machine-to-machine\" (MC-M2M)\"
* \"Ultra-reliable and ultralow latency communications\" (uRLLC) for \"vehicle-to-vehicle\" (V2V) and \"vehicle-to-infrastructure\" (V2I) communications and autonomous driving'
* Non-terrestrial network (NTN) for communication systems that are to be integrated into the 5G systems and networks, including satellites, UAVs, and/or HAPs. This review focuses on the 5G-NTN using GEO/LEO satellites. An overview of current work on \"IoT and UAV integration in 5G hybrid terrestrial-and-satellite networks\" is also provided in Section 4.  
Two key technological advances in 5G networks are the \"virtualization of network functions\" (VNFs) and the use of end-to-end \"5G Slices\" technologies (see Section 4.6). The VNF and 5G Slices technologies allow the 5G network to provide services with a specified quality of service (QoS). As indicated in [2], at a high level, the newly developed 5G network incorporated these technologies has the following three key components:  
* gNB: is defined as gNodeB, which is the 3 GPP standard terminology for a 5G wireless base station that transmits and receives communications between the user equipment (UE) and the mobile network;
* NGC: also known as Next-Generation Core Network (NGCN), which is the 3 GPP standard terminology for 5G wireless next-generation core network. As defined by 3 GPP, the NGC is part of the 5G network providing services to mobile subscribers through the \"radio access network\" (RAN). It is also the gateway to other networks, for instance to the public switched telephone or to public clouds;* RAN: RAN is the 3 GPP standard terminology that is defined as a network that is part of the 5G network that connects (i) UE to other parts of a mobile network via a radio connection, and (ii) UE to the core network.  
Figure 1 depicts an enhanced 5G-TN architecture for multicasting and broadcasting services [4]. The CDN and Nx (e.g., N1, N2, N3,..., Nx) shown in Figure 1 is the Content Delivery Network (or content provider such as the Internet) and the Nx is the Xth interface specified in 3 GPP interface specifications, respectively.  
The 5G-NTN standard specification allows for integrating non-terrestrial networks such as satellites, UAVs, or/and HAPs. This review focuses on the integration of satellite systems, such as GEO and LEO satellites, into 5G terrestrial cellular networks overcoming the range limitation of existing cellular networks. This 5G-NTN architecture is also defined as SATis5 architecture allowing GEO/LEO satellite systems to expand their current services beyond satellite TV, satellite communications, and internet services. Reference [5] discusses 5G-NTN roles addressing (i) the last-mile problem in the terrestrial 5G networks, (ii) coverages for communications-on-the-move (COTM) for moving user-terminals over a large area such as ships at sea or cars driving across the US, and (iii) potential backup of the terrestrial network improving 5G network resiliency.