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Payload: repeater

Course video 43 of 126

This module describes the overall architecture of a satellite communications system, discusses the concept of orbit and what are the typical sub-systems of a satellite

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.

查看授课大纲

教学方

Laurent Franck
Professor
Tarik Benaddi
Associate Professor
Julien Fasson
Associate Professor
Nathalie Thomas
Associate professor
Marie-Laure Boucheret
Professor

脚本

-The role of the transponder is to take the signal

from the reception antenna, to amplify it

and to retransmit it to the transmission antenna,

knowing that these two antennas can be the same.

So it looks like a relay

and this is exactly what the transponder is.

It is a simple space relay.

This type of architecture, in which the transponder is just a relay,

is called a transparent satellite.

This illustration shows the pathway of a signal

coming from a reception antenna.

This signal, represented by a multicolored frequency band,

reaches the receiver.

It will be amplified a first time and enter the input multiplexer.

The latter will split the signal in narrower frequency bands.

The reason for this split is mainly technical.

Amplifiers, also called transponders, that are next on the signal's pathway

are more efficient and cheaper if they work

on a small portion of the signal, that is to say a small frequency band.

But even with this trick, amplifiers represent the two thirds

of the manufacturing cost of the payload.

They will amplify the signal by a factor of 100 000

then the signal will be recombined by the output multiplexer

to be sent to the transmission antenna.

Here is how a transponder operates.

I omitted an important technical feature on purpose.

Let us see what it is about.

This feature is about frequency usage. In order to avoid any interferences,

frequencies used for the uplink and the downlink are not the same.

Mobile phones work exactly according to the same principle.

In geostationary telecommunication satellites,

we use either the Ku frequency band or the Ka frequency band.

Ku and Ka are just names given to frequency values

to make it simpler. At least it simplifies our lives.

The illustrated table shows the frequencies used

for the uplink and the downlink depending on the Ku or Ka band.

Ku or Ka is a design choice when the satellite is manufactured.

As an order of magnitude, when we talk about 10 GHz,

this frequency is 100 times higher than a 100-MHz FM station.

Since we do not use the same frequencies

to go up to the satellite or down, we need to change the payload's design

in order to do what is called frequency conversion.

As we will see in more details next week,

frequency conversion does not change at all the transported information.

As an example, even when people have different voices,

more or less high-pitched, they can understand each other.

In that case, when the uplink is converted to the downlink,

we will have a deeper voice. This conversion is done in two steps.

In the receiver, we convert the uplink frequency

to a much lower intermediate frequency.

The reason once again is to facilitate electronic operation.

Then, just before the amplifier,

we convert it into the downlink frequency.

The architecture of the transponder represented here is still very simple.

If you want to know what a more complex architecture looks like,

do not hesitate to watch the "Going Further" episode.

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