# A Review of SATis5: Perspectives on Commercial and Defense 5G SATCOM Integration
## 3 Survey of Existing 5G Satellite Integration (SATis5) and Associated Challenges
### Overview of Current Proposed SATis5 Roadmaps  
Ref. [10] analyzes the four SATis5 architectures described in Section 3.1 and proposes roadmaps for 5G integrated commercial SATCOM systems. The analysis is focused on three key SATis5 areas, including:  
* Adaptation of Satellite Networks in 5G Architecture: Reference [10] has analyzed the NR air interface design and multi-user transmission for 5G-TN and recommended the adaptation of the terrestrial system in satellite networks;
* Mobility Management, Routing Control, and Load Balance: [10, 11] analyzed mobility management, routing control, and load balance associated with intra-satellite, inter-satellite, and inter-access handovers. Based on the analysis, [10] recommended approach for optimizing signaling overhead of handover assuring service continuity;
* Optical-Electric-Mixed Switching Network: [10] conducted research on 5G requirements for multiple service types along with large-scale on-board switching with high rates. [10] also pointed out the need for a switching system that is compatible with different SATCOM and terrestrial links.
* Based on the analysis of the above three key SATis5 areas, [10] has proposed SATis5 roadmaps that include the following three phases:
* Short-Term Phase--SATis5 Serving as Backhaul Links: This phase focuses on the non-direct satellite links architecture. The integrated SATCOM architecture provides backhaul links for short-term 5G-RAN and gNB base stations expanding 5G networks coverage to rural and suburban areas, or emergency services. Figure 6 illustrates a strawman SATis5 architecture for a satellite backhaul network [10]. Section 6 below provides a discussion on the NR air interfaces required at the satellite, gateway, and remote nodes. Note that 5G gNodeB (also known as gNB) at the remote node is very similar to terrestrial gNB located in the metropolitan areas, except that the gNB functions in remote areas are less complex than in metropolitan areas.
* Mid-Term Phase--SATis5 with Satellite Integrated 5G-NGC networks: This intermediate phase supports both direct and non-direct satellite links providing a unified Satellite-5G-NGC network integrated with satellite gateway, 5G-gNB base stations and terrestrial data network. The unified Satellite-5G-NGC automatically selects either satellite or terrestrial networks, depending on the required Quality of Services (QoS) and network availability, providing 5G services for users as required. Figure 7 describes a strawman SATis5 architecture for the intermediate phase. Discussion on the NR air interface is provided in Section 6 below.
* Long-Term Phase--The integration of 5G-UE-Satellite and NR-Satellite Air Interface: The final phase is the full integration of the 5G-UE-Satellite and NR-Satellite air interfaces. As indicated in [10], the satellite and 5G-TN can (i) adopt the same architecture with similar switching techniques and transmission technologies, and (ii) revise existing air interface protocols of the satellite access networks adapting the satellite-terrestrial wireless environment. Note that the 5G terrestrial networks use existing air interface protocols without changing the current 3 GPP/5G-UE air interface protocol stack. Discussion of the NR air interface along with an outlook for long-term SATis5 architecture is provided in Section 6.