# 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
Like transparent payload architecture, the access link to UEs is provided by an RN for non-direct access to 5G UEs. In addition to eMBB, this architecture can also support mMTC and some uRRLC satellite use cases. Like transparent satellite payload, this approach also uses the same NR air interfaces between satellite and 5G-UE, and 5G-RN. In addition, Reference [6] presents the survey results on a large constellation of LEO satellites or a constellation of MEO satellites interfacing with a private or public central virtual data center (VDC) through a Ground Station Network (GSN). The GSN collects data from satellites and deposits data into a VDC through a public or private Cloud. Routers, servers, and storages are required to transport, route, store, and process the data collected from coming from the GSN. Interested users of the satellite data that want to obtain the data have two options. The first option is to lease the GSN from ground station providers. The second option is to build their own antennas and GSN. The interested users need to access the Cloud (data center) to get the desired satellite data. An example of a typical leased GSN is the Amazon Web Service (AWS) GSN, which is launched by Amazon [7]. The AWS-GSN provides GSN services available today in US-West-2 (Oregon) and US-East-2 (Ohio) to communicate with LEO and MEO satellites. This is performed using either reservation or on-demand scheduling. Figure 3 illustrates a Cloud-based GSN service solution reducing the data access delay. Figure 3: Cloud-Based GSN Service Solution for Large Satellite Constellation. Figure 2: SATIs5 Architectures for (**a**) Transparent and (**b**) Regenerative Satellite Payloads. References [8, 9] provide an excellent overview of 5G-NTN (also known as 3 GPP-NTN) and related SATis5 architectures and associated technical challenges. As pointed out in [8], the \"next generation RAN\" (NG-RAN) (also known as 5G-RAN) supports the splitting of gNB into two separate units, namely, the \"central unit\" (CU) and \"distributed unit\" (DU). As defined in the 3 GPP standard and specification, the higher-layer protocol stack for the \"New Radio\" (NR) (also known as 5G Radio) is divided into two control planes, namely,  
* User plane (UP): This plane is for managing data transmission;
* Control Plane (CP): This plane is responsible for the control of the signaling mechanism. Table 1 provides a list of 3 GPP-NTN Technical Reports extracted from [8]. As pointed out in 5G-NTN standards and specifications, for NTN, the main impact on the UP comes from the long propagation delays. The delays can cause a potential impact on the \"medium access control\" (MAC) layer, \"radio link control\" (RLC) in the Physical (PHY) layer, and packet data convergence protocol (PDCP). The MAC, RLC, and PDCP were modified for 5G-NTN. Reference [8] provides an excellent summary of 3 GPP NTN work and related technical reports. Key 3 GPP-NTN technical reports related to SATis5 interfaces shown in Figure 2 are provided in Table 1. It should be noted that (i) the technical reports presented in Table 1 were released during 2018-2019, and (ii) only reports related to Figure 2 were extracted from [8]. The impacts of satellite channel characteristics on PHY and MAC layers have been analyzed and presented in [9]. The channel characteristics associated with transmitted waveforms and procedures for eMBB and mMTC-NB-IoT applications were investigated in [9]. [9] also identified and discussed the technical challenges associated with PHY/MAC procedures, including random access, timing advance, and hybrid automatic repeat request. To analyze PHY/MAC layers, [9] has decomposed the two 5G-NTN integration