At present (year 2023), approximately 2,500 satellites are currently orbiting the Earth. This number is expected to reach 50,000 satellites (that is, 20 times growth) for the next 10 years, thanks to the recent advances concerning launching satellites at low cost and with high probability of success. In this sense, it is expected that next years the world will witness a massive increase in mobile connectivity thanks to the combination of 5G deployments and satellites, building the so-called Space-Terrestrial Integrated Network (STIN), thanks to the emergence of Non-Terrestrial Networks (NTNs). This document overviews the foundations of satellite communications as a short tutorial for those interested in research and development on Space-Terrestrial Integrated Networks (STIN) and Non-Terrestrial Networks (NTN) for supporting 5G in remote areas.

翻译：截至2023年，约有2500颗卫星在地球轨道上运行。得益于近年来低成本高成功率卫星发射技术的进步，预计未来十年卫星数量将增至5万颗（即增长20倍）。在此背景下，随着5G部署与卫星的结合，以及非地面网络（NTN）的兴起，预计未来几年全球移动连接将迎来大规模增长，从而构建所谓的星地融合网络（STIN）。本文档作为面向星地融合网络（STIN）与非地面网络（NTN）研究与开发人员的入门教程，概述了卫星通信的基础知识，旨在支持偏远地区的5G应用。