# 5G-NR Physical Layer-Based Solutions to Support High Mobility in 6G Non-Terrestrial Networks
## 3 Overview of Non-Terrestrial Networks  
The 3 GPP TR 38.811 [1] describes the deployment scenarios, channel models for NTN, and the regions with significant NR interface effects. This TR also specifies the NTN deployment scenarios and system features (such as architecture, altitude, and orbit). TR 38.821 [10] addresses a variety of prerequisites and adjustments that allow the NR protocol to function in NTN, with a focus on satellite access. A network based on UAS and including HAPs may be a remarkable example of non-terrestrial access with a lower delay/Doppler value and fluctuation rate [2]. The objectives of this initiative include performance evaluation of 5G-NR in a few deployment scenarios (LEO satellite), gathering potential effects on the physical layer, defining solutions for them, solutions for 5G-NR associated with layers 2 and 3, solutions for the RAN architecture, and related technologies [30]. The 3 GPP TR 22.822 [29] standard enables service continuity between terrestrial NG-RAN and NTN-based NG-RAN owned or covered by an operator agreement. This TR aims to define service delivery use cases for addressing NTN-based access component integration into the 5G system, as well as new services and requirements (i.e., setup, configuration, maintenance, and regulation).  
The 3 GPP TR 28.808 [30] describes the major challenges of a 5G network with integrated satellite components, such as business roles, services, management, and orchestration. This scenario investigates potential solutions, aspires to simplify the integration of satellite technology into present business models, and considers the management and orchestration parts of current 5G networks. Adapting 5G-NR for satellite communications was considered in [10] based on Release 15 of the NR specifications. The authors in [10; 11] emphasized the issues with connected mode and idle mode mobility and NR-specific network design components in both LEO and GEO-based NTN systems, focusing on the physical layer and user plane characteristics. The network, or elements of a network, that have a base station or transmission equipment relay node as a payload on board an airborne or spaceborne spacecraft are referred to as non-terrestrial networks. Satellites are classified as spaceborne vehicles based on their orbital heights [2], which range from 400 km to 2000 km for low earth orbit (LEO), 2000 km to 35,786 km for medium earth orbit (MEO), and 35,786 km for geostationary earth orbit (GEO). GEO [3] are geosynchronous orbits with a zero angular inclination to the equator. The non-terrestrial network scenarios and use cases are shown in Figure 1. The range of terrestrial and non-terrestrial networks is shown in Figure 1, along with the different colored vectors for the different use cases and their communication between the core network to satellite, HAPS/UAVs, and drones with the terrestrial networks, such as high-speed trains, as a high-mobility application scenario as well as communication between rural, urban, and remote areas and the NTN.  
Figure 1: Non-terrestrial network scenario and use cases.