Independent systems

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Из курса от партнера Institut Mines-Télécom

Introduction to Satellite Communications

181 оценки

Institut Mines-Télécom

Introduction to Satellite Communications

181 оценки

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.

Из урока

Networking and services

This module explains how services such as voice, television and Internet access are provided by means of communications satellites.

Independent systems5:10

Globalstar vs Iridium7:12

Interconnection with mobile telephony networks5:51

Voice over IP6:13

Going further: Impact of a satellite link on QoS10:19

Познакомьтесь с преподавателями

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

-We have seen what interconnection and interoperability are

by using IP in the first instance.

Then I talked about a key service for satellite, television.

I will now deal with another key service, telephony.

I split this sequence in three main parts.

The first part will talk about independent systems,

that is to say systems designed for telephony.

We will then see how we can interconnect telephone networks

with other telephone or terrestrial networks.

Eventually, I will tackle voice over IP, Internet Protocol.

Voice is the other name given to telephony in networks.

This is the evolution I have already mentionned in sequences 1 and 2.

Let us start with independent systems: the ones aiming at

providing voice services. We have to analyze the needs

for voice services. I mentioned these needs at the beginning of this lesson:

calling from anywhere to anywhere. The satellite coverage is important

since we can imagine a system covering the whole Earth

allowing us to call from anywhere to anywhere.

It can be used for niche applications that I already explained.

For example a mother working on an oil rig who wants to call her family

in the evening can use satellites. But also general-public applications.

In this case it is slightly more difficult.

We will see that independent systems will first want to offer

to all users the ability to give calls.

In the middle and at the end of the '90s, there is a kind of big boom

in the terrestrial networks of mobile telecommunications for private users.

At the beginning of the '90s, it only existed analog systems

and mobile telephony was dedicated to a professional use.

All at once, with 2G, that is to say GSM,

systems opened themselves to the general public,

mainly in cities where there was a large public.

In France, it was first France Télécom with Itineris.

Then came SFR, Bouygues.

Per-minute billing has been replaced by progressive flat rates

with 2 hours of telecommunications for example.

There was a huge boom at the end of the '90s, in 1999 for example,

with the "Millénium" contract which is a good example

of the change in contracts. More and more users from the general public

use mobile telephony services, mainly in covered zones such as cities.

At the same time, at the beginning ofÏthe '90s,

satellites want to offer this telephony

where terrestrial systems have not really advanced yet

since there are large uncovered zones called "white zones".

They want to compete with terrestrial infrastructures quite fast

at the beginning of the '90s. Projects are launched

to try and offer telephony to the general public via satellites.

First, which satellite system must we choose?

To choose a satellite system, we must first look

on what communication quality depends.

This communication quality is called "Quality of Service", QoS.

For telephony, we must first know how to measure it.

It is rather complicated. One solution is to use MOS.

MOS means Mean Opinion Score. It is a subjective value.

We ask users to grade the quality of their call.

They use their phone, listen to a conversation, maybe talk,

and grade it from 1, the worst, to 5, the best.

This is quite expensive because measures need to be made,

it is quite subjective, it takes time and money.

So today we tend not to use MOS to assess communications

but automatic algorithms that work instead.

Regarding satellites, the propagation delay has an impact

on user interactivity, as the jitter also may.

I will explain jitter in the "going further" episode

about QoS at the end of this part. You are welcome to watch it

if you wish to learn more about quality of service.

In fact, to solve these issues, to reduce the delay for example,

we will rather use LEOs. The big project of these times

will be to use LEOs in order to provide telephony.

They have a small coverage compared to geostationary satellites

so you waste less when sending from one person to another,

which is the standard usage of telephony.

But constellations will have to be designed to cover the whole world.

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