# 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
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**3 GPP Study Item/Objective** & **Responsible Group** & **Technical Report** & **Release** \\ \hline RP-190710: Study on solutions for NR to support NTNs & & & \\ Objective: study a set of necessary features enabling NR & RAN1, RAN2, RAN3 & TR 38.821 & 16 \\ support for NTN. & & & \\ RP-201256: Solutions for NR to support NTNs & & & \\ Objective: specify the enhancements identified for NR & & & \\ NTN with a focus on LEO and GEO and implicit & RAN1, RAN2, RAN3, RAN4 & N/A & 17 \\ compatibility to support HAP station and & & & \\ air-to-ground scenarios. & & & \\ SP-180326: Integration of satellite access in 5G & & & \\ Objective: specify stage 1 requirements. & & & \\ P-191335: Integration of satellite systems in the & & & \\
5G architecture & & & \\ Objective: produce normative specifications based on the & & & \\ conclusions identified in TR 23.737 (see below) & & & \\ SP-181253: Study on architecture aspects for using satellite & & & \\ access in 5G & & & \\ Objective: identify key issues of satellite integration in 5G & & & \\ system architecture and provide solutions for direct & & & \\ satellite access and satellite backhaul. & & & \\ CP-202244: Core Network and Terminal (CT) aspects of & & & \\
5 GC architecture for satellite networks & & & \\ Objective of study phase: study the issues related to & & & \\ Public Land Mobile Network (PLMN) selection and & & & \\ propose solutions. & & & \\ Objective of normative phase: support Stage 2 & & & \\ requirements, and satellite access requirements and & & & \\ solutions for PLMN selection & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Related 3 GPP-NTN Technical Reports (Extracted from [8]). architectures shown in Figure 2 into four architectures, called A1, A2, A3, and A4. They are defined as follows:  
* A1: SATis5 Architecture for Direct User Access Link with Transparent Satellite Payload (PL);
* A2: SATis5 Architecture for Non-Direct User Access with Transparent Satellite PL;
* A3: SATis5 Architecture for Direct User Access Link with Regenerative Satellite PL;
* A4: SATis5 Architecture for Non-Direct User Access with Regenerative Satellite PL. Table 2 provides a summary of the four possible SATis5 architectures listed above. Reference [10] provides an excellent description of four SATis5 architecture options and associated air interface and related standards presented in Table 2. The air-interface and related standards presented in [10] were derived from recent 2018-2019 3 GPP-NTN study results. These results are also in the same time frame as the 3 GPP-NTN technical reports presented in Table 1. [10] discusses the NR air interface and standards to support 3 GPP-NTN with a focus on the above four SATis5 architecture options. Additionally, [10] provides an architecture diagram for transparent and regenerative satellite payloads with single hop and multiple hops. The hops pass through satellite payloads with and without on-board processing for direct and non-direct access to UEs, respectively. Figures 4 and 5 illustrate the concept of single-hop multiple-hop associated with the above four SATis5 options. Figure 4a,b show a single-hop transparent satellite payload for direct access and non-direct access to 5G-UE, respectively. Figure 5a,b describe a single-hop and multiple-hop for regenerative satellite payload for direct access to 5G-UEs, respectively. As shown in Figure 5b for SATis5 A4 with non-direct access, the generative satellite payload is required to perform either fully or partly gNB functions depending on the development cost trade-off study for on-board processing at the satellite payload vs. ground processing at the RN nodes. A summary of the design features associated with the four SATis5 architectures is derived from [10] and shown in Table 3. Many of the UE air interface and SATis5 Gateway features have been identified in the 3 GPP study report. For the LEO satellite use case with a large satellite constellation, their handovers between satellites and 5G UEs are very complicated.