The 5G ecosystem is radically shifting Information and Communication Technologies (ICT) towards a system directly tailored and optimised to support vertical markets and services. In order to design and implement the ambitious 5G network, Satellite Communications (SatCom) have been recognised as a promising solution to extend and complement terrestrial networks in unserved or under-served areas, as reflected by recent commercial and standardisation endeavours. Within 3GPP, this is reflected in the novel Study Item on Non-Terrestrial Networks to introduce 5G (New Radio, as per 3GPP nomenclature) technologies in SatCom. However, typical satellite channel impairments, as large path losses, delays, and Doppler shifts, pose severe challenges to the realisation of a satellite-based 5G network. In this paper, we thoroughly review the standardisation process performed within 3GPP from Rel. 15 to the present, discussing the different technologies and the related system architectures and interfaces. Based on these discussions, we assess the impact of the satellite channel characteristics on the major physical and medium access control layers, i.e., Downlink Synchronisation, Random Access, and Hybrid Automatic Repeat reQuest. A set of potential solutions to the identified shortcomings is finally discussed.

5G生态系统正在将信息和通信技术（ICT）朝着直接定制和优化以支持垂直市场和服务的系统转变。为了设计和实施雄心勃勃的5G网络，卫星通信（SatCom）已被公认为是一种有前途的解决方案，可以在无服务或服务不足的地区扩展和补充地面网络，最近的商业和标准化努力都反映了这一点。在3GPP内，这反映在关于“非地面网络”的新研究项目中，以在SatCom中引入5G（根据3GPP命名法为新无线电）。但是，典型的卫星信道损害（如较大的路径损耗，延迟和多普勒频移）对实现基于卫星的5G网络构成了严峻挑战。在本文中，我们将彻底审查Rel在3GPP中执行的标准化过程。到现在为止的图15，讨论了不同的技术以及相关的系统架构和接口。基于这些讨论，我们评估了卫星信道特性对主要物理和媒体访问控制层的影响，即，下行链路同步，随机访问和混合自动重复请求。最后讨论了针对已发现缺点的一组潜在解决方案。