# 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 SATis5 Architectures  
Reference [6] provides a good survey of SATCOM in the new space era where 5G communication networks provide seamless integration between the 5G-TN and 5G-NTN. Figure 1: Enhanced 5G System Architecture for Terrestrial Multicasting and Broadcasting Network [4]. The 5G-NTN includes satellites in GEO, MEO, LEO, and very LEO (VLEO), along with both HAPs and \"low altitude platforms\" (LAPs). Reference [6] has also defined three SATis5 use cases, namely:  
* eMBB Satellite Use Case: Backhauling and Tower Feed (BATF): As defined in [6], the satellite provides a matching role by backhauling the traffic load from the edge of the 5G network or broadcasting the popular content to the edge. This matching role optimizes the overall operation of the 5G network infrastructure. Trucking and Head-End Feed (THEF): This use case allows a satellite to directly connect to 5G UEs in remote areas where terrestrial infrastructure is not available. Hybrid Multiplay (HYMP): This use case employs a satellite system to allow 5G service into home/office premises in underserved areas using the proposed 3 GPP hybrid terrestrial-satellite broadband connections. Communications on-the-Move (COTM): For this use case, a satellite system is used to provide (i) direct connectivity to COTM platforms (e.g., aircraft, UAV, vehicles (boats, etc.) or (ii) complementary connectivity to COTM platforms supporting 5G services. * mMTC Satellite Use Case: Wide area IoT services: IoT devices distributed over a wide area and reporting information to or controlled by a central server. Typical SATCOM applications include: Government: Monitoring of oil/gas pipeline status, border, Earthquakes, remote road alerts, etc. ; Aerospace and Defense: Fleet management, space asset tracking, etc. ; Education: Monitoring and tracking student work, faculty and staff management, etc. ; Farming/Agriculture: Farm management, livestock management, etc. Local area IoT services: IoT devices are used to collect local data and report to the central server. Typical applications include a smart grid sub-system (advanced metering) or services for onboard moving platforms, e.g., a container onboard a vessel, a truck, or a train. * uRLLC Satellite Use Case: As indicated in [6], 3 GPP for satellite integration, the SATCOM services require 99.99% link availability, lower than 1 ms communication link delay, and package error rate (PER) of \(10^{-5}\) for communication link reliability. Typical uRLLC satellite applications include autonomous driving, remote surgery, factory automation, etc. In addition, [6] provides a description of two key SATis5 architecture approaches for integrating satellite(s) with 5G networks using 5G-NTN standards and specifications, namely:
* 5G-NTN SATis5 Architecture with Transparent Satellite Payloads: The Satellite provides direct or non-direct access to UEs on the ground, i.e., connectivity between the satellite and UEs. For non-direct access, the connectivity would be through a base station (BS), which is a Relay Node (RN) on the ground. 3 GPP has provided standards and specifications for the RN and associated air interface for the communication link between gNB and the RN. This architecture can support a satellite use case for eMBB. Figure 2a illustrates this architectural approach. This approach uses the new radio (NR) air interfaces between satellite and 5G-UE, and 5G-RN. * SATis5 Architecture with Regenerative Satellite Payloads: As shown in Figure 2b, the 5G wireless BS' (gNB) functionalities would be performed by the satellite and thus improve round-trip time (RTT) communications significantly. In addition, regenerative satellite payload would also allow for an inter-satellite link (ISL). The ISL can be used to relay information from the satellites to the ground stations for managing the hand over mechanism for a large LEO satellite constellation. This architecture option also provides direct or non-direct access to UEs on the ground.