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.

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