Communications satellites today – Satellites at our service

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Communications satellites today

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How is a satellite built? How do they fly? How do they communicate and how does the network operate? You will get all the answers in this course from teachers and researchers from three schools associated with Institut Mines-Télécom. The course is made of : teaching videos, equipment demonstrations and simulation programs. They will guide you through the discovery of satellite communications. Professionals in the space field will share there vocation for this scientific and technical sector. Have you ever wanted to know more about transponders, the geostationary orbit, QPSK modulation, channel coding, link budget, TCP over large bandwdith x delay product links ? This course is for you! This course is available in English: French-speaking lecturers with English subtitles and fully translated contents (slides, practices). This MOOC is supported by the Patrick and Lina Drahi Foundation.

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From the lesson

Satellites at our service

This module provides an introduction to satellite communications. Why using satellites ? What sort of communication services ? How much does it cost ?

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-I was saying at the beginning of this sequence, in the introduction, that we could ask ourselves questions such as: “How many communications satellites are there currently and what are their communication capacities?” To answer the first question, there are currently a little over 400 satellites up in the air, about 20 of which launched in 2014. This is for geostationary satellites. This answer does not really bring anything. The interesting part is that this profusion of geostationary satellites in the air has an extremely important impact on their design. We will see this later on. Regarding the communications capacity, if I take as an example the KA-SAT satellite, an outlandish name but this is how it is called, its communication capacity is 70 gigabits per second, which is a lot. It is the equivalent of about one million simultaneous phone calls. It is a lot, but keep in mind that these one million phone calls has to be shared by all the satellite users. There are not only geostationary satellites. There are others, such as the one on the left of the illustration, which fly at an altitude just under 1 000 km and which also provide communications services. The Iridium satellite is illustrated here. It allows us to make phone calls from anywhere on Earth. It is an extremely popular service among extreme explorers. The right-hand side illustration shows a phone working with such a satellite. Talking about constellations, let us not forget O3b: “other 3 billion”. This constellation has been initiated by the billionaire Greg Wyler and is supported by companies such as Google or HSBC. The idea behind this constellation is to provide communication services in areas which are traditionally neglected by land-based network infrastructures. On this illustration, the orangey red zone represents the coverage of this constellation. Finally, we should talk about recent announcements made by Google, again, and SpaceX, again, since they decided to massively invest in the development of satellites to support the deployment of the Internet where it is currently lacking.

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