Review of 5G NTN Standards Development and Technical Challenges for Satellite Integration With the 5G Network

As the 3rd Generation Partnership Project (3GPP) is discussing the integration of satellite networks into 5G New Radio (NR) and the mega-constellation low-Earth orbit (LEO) satellites are being deployed, communication satellites are gaining momentum for technical and economic success. Ultimate integration of satellites will be able to provide immense payoff for 5G networks, including global coverage extension and 3-D mobility enhancement. This article begins with an overview of the current status of 5G nonterrestrial network (NTN) standardization and state-of-the-art satellite networks, such as high-throughput satellites (HTS), LEO networks, and satellite-terrestrial heterogeneous networks. Technical impediments for realizing orthogonal frequency-division multiplexing (OFDM)-based satellite communications are presented, including channel nonlinearity, long propagation delay, and satellite mobility. We then suggest future engineering directions for network architecture, management/operation, and user terminal design. Options of network architectures are explained in terms of relay nodes between satellites and user terminals, satellite altitudes, and on-board processing. Hand-over, cell pattern generation, and resource allocation are discussed to improve network management and operation. Primary physical layer issues for user equipment terminal design, including antennas, channel models, timing advance, frequency offset, timing relationships, and hybrid automatic repeat requests (HARQs), are discussed.