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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Introduction to Satellite Communications
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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 ?
Meet the Instructors
Laurent FranckProfessor
IMT Atlantique, on leave to Airbus Defence & Space as of September 1st, 2017
Tarik BenaddiAssociate Professor
IMT Atlantique
Julien FassonAssociate Professor
INPT/ENSEEIHT
Nathalie ThomasAssociate professor
INPT/ENSEEIHT
Marie-Laure BoucheretProfessor
INPT/ENSEEIHT
-Subsequently, we will look at the variety of services
that may exist in relation with communication satellites.
We will also see how each of these services can benefit
from the strengths I previously mentioned.
Giving honor to whom honor is due, let us start with television
and radio broadcasting. The principle is very simple.
You install a satellite dish, approximately 60 cm in diameter,
outside your home, you install a terminal inside.
Said terminal will give you access to the TV channels,
with or without a subscription depending on the offers.
From there, you can access thousands of TV and radio channels.
Surprisingly, and unlike the other services we will look at,
this service is unidirectional, communication is one-way only.
The direction of this communication goes from the teleport, the place
where the TV programs are grouped and sent to the satellite, to your home.
The second service, which has to do with television,
is satellite news gathering. Its principle is extremely simple.
A reporter, who is out in the field working on a story,
uses satellite means, often installed in a vehicle with a control room,
to send his news report directly to the studio
where it can be broadcast. This is often seen in news programs,
where the news anchor is in the studio,
the reporter is out in the field, and there is a slight delay
between the moment the anchor asks a question,
and the reporter's answer. And you can then be certain
that satellite means are being used between the two.
Another type of service is telephony. This is the age of mobile telephony.
It is exactly the same for satellite telephony.
In that case the terminal also looks like a mobile phone,
like the one you have in your pocket, with your mobile phone subscription.
It just has a slightly larger antenna, and lets you call
from anywhere on Earth, especially from places
where, of course, there is no 3G coverage.
The fourth service, which is somehow linked to telephony services,
is known as backhauling or trunking.
Imagine a situation in which a catastrophe has happened,
and we want to restore terrestrial mobile telephone services,
where the catastrophe took place. What we will do is set up
a 3G receiver antenna, and the entire traffic passing through this antenna
will be connected to the core network precisely by using a telephone link,
a satellite link. This principle is called backhauling,
reconnecting an isolated cell to the core network
using a satellite link. It can also be used for services
other than telephony, for instance for data links,
in particular to connect two companies using a satellite,
and this particular use is then called data trunking.
Finally, let us talk about another very popular service,
Internet access via satellite. It is quite naturally derived
from the deployment of ADSL on terrestrial areas,
but wherever population density is not high enough,
deployment of heavy terrestrial infrastructures such as fiber optic
is not profitable enough for operators and in that case satellite solutions
are starting to become interesting. The principle is extremely simple,
same as for television, you will install a satellite dish outside.
Inside you will install a box, which looks very much like an ADSL box
except that it is a satellite box, and this satellite box
will enable you to access the Internet,
and it will also enable you to use voice over IP telephony.
So when I said that it looked like an ADSL box,
it provides the exact same services. What is interesting is the evolution
of satellite Internet access. Ten years ago, it was necessary
to keep a phone line in order to send data to the Internet,
while receiving data via satellite. But that is a thing of the past,
and nowadays it can be entirely done via satellite.
And the reason for this technological evolution is precisely
the evolution of the technology behind communication satellites
which allow for increasing bandwidth, making this service
extremely affordable for the user. When I say affordable,
a standard subscription will cost you 20 euros per month,
for a 2-gigabyte monthly data allowance.
Then there is another service, which is something of a catch-all service,
which is data exchange. It covers everything
that is not Internet access, television or telephony,
so, for example, telemedicine.
Telemedicine is shown in this illustration.
On the left, you have a telemedicine suitcase, which allows you
to diagnose a patient in a remote location.
You will of course have a telephone communication
with the practitioner on the other end of the line,
you can film the patient, but you can also take measurements
such as the heart rate, the blood oxygen saturation,
or the blood sugar levels, and all these measurements will be sent,
via satellite, to the triage doctor on the other end, here on the right,
who will enable the diagnosis to be established.
This is called telemedicine, and in areas with poor access
to medical facilities, it is something extremely important.
Finally we have a service called data collection.
The principle of data collection is to have the satellite function
as some sort of vacuum cleaner from space, where it will retrieve
data that are on Earth. The simplest example consists
in emergency beacons, that we often hear about
at the time of single-handed sailing races for example,
such as the Vendée Globe. The principle is
to have a small beacon, which is activated either automatically,
or manually by the skipper, and which will send a distress signal.
This distress signal will be captured by the satellite,
forwarded to a data processing center,
so that the person in distress can be located.
These beacons are often improperly called Argos beacons,
they are actually Cospas-Sarsat beacons.
Argos beacons use a similar technology,
but are used to follow marine animals, for example,
and to study their lifestyle, migration patterns, and so on.
Data collection services have lately been experiencing renewed interest,
and two reasons for this have been identified.
The first one is the Internet of Things,
which is beginning to develop, and the second reason
is intermachine communication, also called machine to machine.
Understanding this principle of intermachine communication
is extremely simple. Nearby is the Canal du Midi,
which is a remarkable work of engineering.
It is possible to control the water flows that are released into the canal
from the various supply reservoirs. These water flows are controlled
using gates. Machine to machine will enable
automatic operation of these gates, and will enable, depending
on rainfall conditions for instance, to automatically and remotely
control these gates, to say "a bit more", "a bit less", and so on.
This is a typical use of machine to machine.
In order to control machines that are remotely located,
we need satellite means.
In this table, I have tried to summarize and to classify
these different services. In order to classify them,
we will notably use three categories of services,
which are notions found in regulations.
The first one is called BSS, they are the services
that are strongly based on broadcast. The second category of services
is what we call FSS, services in which the terminals are fixed.
And of course, the third category are services using mobile terminals,
called MSS, and we can see that each service can be classified
into one category or another. From a regulatory perspective,
regarding the frequencies that we will be able to use,
regarding the tolerance to interference that will be accepted,
this will be very important.
In this table, I have tried to summarize how each service
will benefit from the strengths of the satellite.
Clearly, all services will benefit from two major features, which are
global coverage, and resistance to terrestrial events.
Several "plusses" indicate that the economic model of this service
is really built around this advantage of the satellite.
For television, it will be the capacity to send
to all users within coverage a very high-speed flow
containing the various television and radio programs.
For Internet access, backhauling, and satellite news gathering,
it is really the capacity to send data from anywhere around the globe.
And especially for backhauling and trunking, as they are often used
as backup solutions, there is a little "plus" for the notion of resistance
with respect to terrestrial events, that is to say they do not rely
on the existence of terrestrial infrastructure.
Finally, for data collection, it is the possibility to collect data
anywhere on Earth.
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