Carrier transmission

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來自 Institut Mines-Télécom 的課程

Introduction to Satellite Communications

256 個評分

Institut Mines-Télécom

Introduction to Satellite Communications

256 個評分

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.

從本節課中

Digital communications

This module discusses the basics of information transmission

Introduction3:43

Bit rate / symbol rate2:15

Concept of frequency1:48

Bandwidth occupied by the signal3:45

Bandwidth / rate relation3:32

Carrier transmission2:56

與講師見面

Laurent Franck
Professor
IMT Atlantique, on leave to Airbus Defence & Space as of September 1st, 2017
Tarik Benaddi
Associate Professor
IMT Atlantique
Julien Fasson
Associate Professor
INPT/ENSEEIHT
Nathalie Thomas
Associate professor
INPT/ENSEEIHT
Marie-Laure Boucheret
Professor
INPT/ENSEEIHT

-Last step of this sequence on the formation of the signal.

We previously saw that the role of the modulator

within the transmitter was to build a signal

adapted to the propagation channel to be crossed.

First, it will build it

according to the available bandwidth in the channel.

Then, it has to transport the spectrum of the generated signal

in the band it has been allocated within the propagation channel.

For this kind of transmission,

we talk about a carrier frequency transmission

because we use a carrier wave

which carries the message in the allocated band.

It will carry it in one of its parameters:

amplitude, phase, frequency. This wave is sinusoidal

and its frequency is called the carrier frequency.

It corresponds to the central frequency

of the allocated band in the propagation channel.

Let us get back to the FM radio example.

I kept the France Info example with a central frequency of 105.5 MHz

and a certain band available around it.

When it builds its signal, France Info creates a signal with a band used

that is compatible with the available band

that has been reserved in the propagation channel

and corresponding to FM broadcasting.

Once this is done, this spectrum needs to be carried

in the band allocated to France Info.

We talk about carrier frequency transmission

and for this purpose we use this sinusoidal wave

called a carrier wave.

It is not always mandatory to perform a carrier frequency transmission.

For example, in the case of a transmission

between two computers using a cable, the propagation channel is dedicated

so the signal does not need to be transported

in a certain allocated band.

In that case, we keep the signal within a low-frequency spectrum.

All signals are generated within a low-frequency spectrum.

Then we carry them in the allocated band or not.

When we do not carry the signal spectrum in the allocated band,

we talk about a baseband transmission.

Regarding satellite transmissions,

the space used to transmit is the free space.

Of course, we will always perform a carrier frequency transmission.

We will see it later on.

We always have an allocated frequency space.

We have to first generate the signal with a low-frequency spectrum,

then transport this spectrum in the band that was reserved for us.

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