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EE5404 Introduction 1 Satellite Communications Satellite Communications Chen, Zhi Ning Chen, Zhi Ning Contacts: e-mail: [email protected] URL: http://www.icr.a-star.edu.sg/~chenzn

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EE5404 Introduction 1

Satellite CommunicationsSatellite Communications

Chen, Zhi NingChen, Zhi Ning

Contacts:e-mail: [email protected]: http://www.icr.a-star.edu.sg/~chenzn

EE5404 Introduction 2

About This Course:About This Course:Introduction to satellite communication systems

Description of satellite system /Types of orbitsSatellite launchers / Radio regulations Various satellite applications

Link analysis, propagation and interferenceCalculation of link budget using G/T, C/N ratio, EIRP Effects of various propagation phenomenon like rain, ionosphere Terrestrial and satellites interference

Earth station technologyEarth Station design/ Antenna RF sub-system / Communication sub-system Network interface/ Monitoring and control

Satellite communication payloadMission and characteristics Conventional, multibeam and regenerative transponder Antenna coverage

EE5404 Introduction 3

To discuss the important issues of SCS at a system level.

Target & Main Reference BooksTarget & Main Reference Books

To learn the elements of satellite communication systems (SCS)To master the basic principle of the relevant designs of SCS

[1] Satellite Communication Systems[1] Satellite Communication Systems-Systems, Techniques and Technology(3rd Edition) By G. Maral & M. BousquetNovember 2000, John Wiley & Sons

[2] Digital Satellite Communications[2] Digital Satellite Communications(2nd Edition) By Tri T. Ha1990, McGRAW-HILL

[3] Satellite Communications[3] Satellite Communications(3rd Edition) By D. Roddy2001, McGRAW-HILL

[4] Satellite Communication Systems Engineering[4] Satellite Communication Systems Engineering(2nd Edition)By W. L. Pritchard, H. G. Suyderhoud, & R. A. Nelson1993, P T R Prentice Hall

EE5404 Introduction 4

Contents Contents

Introduction to satellite communication systems

Satellite orbits (Geostationary Orbit)

Propagation and Antennas

Link analysis and interference

Earth station technology

Satellite communication payload

Satellite communication techniques

Satellite multiple access techniques

Emerging satellite technologies

EE5404 Introduction 5

1 Introduction

1.1 Satellite Communication Systems & Applicationsbasic elements and applications

1.2 Some Issues in System Design

EE5404 Introduction 6

1.1 Satellite Communication Systems & ApplicationsAn SCS is a type of wireless communication systems.

Features:•Providing coverage over large geographical areas•Resulting in interconnectivity between various communication resources•Realising seamless coverage to combine satellite mobile communication systems with terrestrial mobile systems

It is important to note the common and different characteristics between the SCS and other wireless communication systems.

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TechnologyTechnologySystemSystem

Ground segment

Spacesegment

Basic SystemsBasic Systems

Different from other terrestrial wireless communication systems, the SCS basically comprises Space and Ground segments. The communication will be built up between the space and ground segments.The characteristics of each segment depend on their applications such as fixed, mobile or direct broadcasting systems.With the missile technology, the space segments can be sent to a proper position in space. To reduce sizes of the segments, especially the space segments, the segments are made by microwave technology.The microwave technology also allows the use of high frequency to lower path losses.

missile microwave+

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Basic SystemsBasic Systems

EarthStation

uplink

downlink

Telemetry Tracking and Command (TT&C)To control satellite and monitor satellite’s performance.

Main satellite services:•Fixed satellite service, FSS•Mobile satellite service, MSS•Direct broadcast system, DBS

Satellite

TT&CGroundStation

A typical FSS system

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Aircraft

Ship

Basic SystemsBasic Systems

Mobile Satellite System (MSS)In an MSS, the ground segments consist several types of mobile terminals, which can communicate each other directly and via a satellite. Also, they can be connected to fixed telecommunication networks through a satellite.Usually, the MSS can be categorized into three classes: maritime, aeronautical and land.

Satellite

Gateway

Fixed Network

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Direct Broadcast System (DBS)A large earth station transmits the programmes to a high-power satellite. The latter broadcast the programmes to small terminals on the earth. Community

Reception

Direct-to-homeReception

Basic SystemsBasic Systems

satellite

Gateway

ProgramSource

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Basic ElementsBasic Elements

Space SegmentSpace Segment

Geostationary orbit is 35,786km over equator. The satellites orbiting the Earth in such an orbit rotate in unison with the Earth.They appear almost stationary to the users on the Earth. So, this minimizes the operational requirements of earth stations by simplifying tracking systems of ground terminals.

Molniya Orbit

Ground SegmentGround Segment

Any satellite communication system consists of at least one satellite and several terminals on the earth. The basic elements include the satellite, earth stations, and the orbit, where the satellite is moving on.

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Basic ElementsBasic Elements

Space Space Segment

Receiving signals from an earth stationChanging frequency of the carrierAmplifying the signals Transmitting the signals back to other earth stations

Segment Satellites

Payloads

Platform

receiving antennastransmitting antennas all the electronic equipment

Electric power supplyTemperature ControlAltitude and orbit controlPropulsion equipmentTT&C equipment

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VSAT: very small aperture terminals

Basic Elements

Ground Ground SegmentSegment

Terrestrial Networks

All Earth Stations

Basic ElementsConnecting the end-users to earth stations

Transmitting signals to satellites Receiving signals from satellitesChanging frequencies of the signals

FSS: several kinds of fixed earth stationslarge station(11-30m antennas) or VSAT (1-3m antennas)

MSS: several kinds of mobile terminals connected to the fixed telecommunication networks via fixed earth stations (maritime, aeronautical, and land base)

EarthStations OF

DBS: gateways plus small terminals with 30-100cm antennas

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Basic ElementsBasic Elements

EarthStation

HPAup-converter modulator

feedsystem

basebandprocessing

LNA down-converter

de-modulator

trackingsystem

drivemotors

interface

from/toterrestrialsystems

A typical earth station usually include the elements used in any wireless communication systems.They are roughly classed into two parts, transmitting and receiving parts.

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1.2 Some Issues in System Design

SystemDesign

Selection of

radio frequency

Link Design

SignalQuality

•Application•Propagation•Technology•Regulation•Spectrum•Modulation•Coding•...

To be discussed

Multipoint DataTransmission

Network Services

Voice, data,video

CostTechnology

network

SatelliteBroadcasting

Network

DataCollectionNetwork

The target of system design is the high signal quality. The important issues include kinds of services, cost of system, status of technology, network in use. The most important consideration is the selection of the radio frequency. The selection of the RF is strongly dependent on these factors.

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Frequency Allocations for SatelliteFrequency Allocations for SatelliteElectromagnetic Spectrum for RF

Frequency Wavelength, m Designation 3 Hz-30 kHz 108-104 Very low frequency (VLF) 30 -300 kHz 104-103 Low frequency (LF) 0.3 -3 MHz 103-102 Medium frequency (MF) 3 -30 MHz 102-10 High frequency (HF) 30 -300 MHz 10-1 Very high frequency (VHF) 0.3 -3 GHz 1-10-1 Ultra high frequency (UHF) 3 -30 GHz 10-1-10-2 Super high frequency (SHF) 30 -300 GHz 10-2-10-3 Extremely high frequency (EHF) 100 -1000 GHz 3×10-5-3×10-9 Infrared, visible light, ultraviolet

This is electromagnetic frequency spectrum. Of them, the bands of 3-300GHz is used for various radio applications, such as radar and communications.

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Frequency Allocations for SatelliteFrequency Allocations for SatelliteFrequency spectrum for Satellite Communications

Band Frequency range, G H zL 1-2S 2-4C 4-8X 8-12

Ku 12-18K 18-27

Ka 27-40M illimeter 40-300

Particularly, these frequency bands are allocated for satellite systems.

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Frequency for uplink is always higher than frequency for downlink! Why?

Frequency Allocations for SatelliteFrequency Allocations for Satellite

Frequency Allocations for Satellite Services

FSS- C band: ~6 GHz uplink , ~4 GHz downlink - INTELSAT- X band: ~ 8 GHz uplink , ~7 GHz downlink- government- Ku band: ~ 14 GHz uplink , ~12 GHz downlink- EUTELSAT, Telecom I & II -INTELSAT- Ka Band: ~ 30 GHz uplink , ~20 GHz downlink- experimental- Each allotment consists of an orbital position/bandwidth in the bands mentioned/service areaVSAT – Very Small Aperture Terminals (C and Ku band)

MSS-L band ~ 1.6 GHz uplink, ~1.5 GHz downlink for the mobiles -Ku band for Network Control Centre and Hubs.

DBS- Ku band: ~12 GHz downlink

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International Organizations for International Organizations for Satellite Communications Satellite Communications

International Telecommunication Union (ITU)- United Nations (UN) organization for telecommunications

CCIR= International Radiocommunications Consultative CommitteeCCITT= International Telegraph and Telephone Consultative Committee

Technical & Operational matters, produce Reports & Recommendations.

WRAC= World & Regional Administrative Radio ConferencesDiscuss certain topics and carry out total & partial revision of the administrative regulations like Radiocommunications Regulations (RR)

IFB= International Frequency Registration BoardRegister frequency assignments to radio stations given by the countries and verify that the they conforms to the international frequency assignments

ITU divided the Earth into 3 regions for frequency allocation1. Region 1- Europe, Africa, ex-Soviet Union, Mongolia2. Region 2- North & South America, Greenland3. Region 3- Asia(excluding region 1 Areas), Australia & South West Pacific (Singapore)

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Conclusions Conclusions

•Brief introduction of SCS•Basic elements of SCS•Main applications of SCS•Allocations of frequency for satellite•International organizations for SCS

We just snapshot the satellite communication systems and their main applications. Compared to other wireless communication systems, the key features of the SCS are theirradio link and operation frequency. Therefore, the system design strongly depends on the link design. In the following lectures, we are going to discuss the issues related to the link design.

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GPSGPSGlobal Positioning System!Global Positioning System!

What is GPS?

Why GPS?

How does GPS work?….

EE5404 Introduction 22

What is GPS?

The GPS is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations.

GPS uses these "man-made stars" as reference points to calculate positions accurate to a matter of meters. In fact, with advanced forms of GPS you can make measurements to better than a centimeter!

In a sense it's like giving every square meter on the planet a unique address.

GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. And that makes the technology accessible to virtually everyone.

These days GPS is finding its way into cars, boats, planes, construction equipment, movie making gear, farm machinery, even laptop computers. Soon GPS will become almost as basic as the telephone. Indeed, it just may become a universal utility.

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Why GPS?

Trying to figure out where you are and where you're going is probably one of man's oldest pastimes.

Navigation and positioning are crucial to so many activities and yet the process has always been quite cumbersome.

Over the years all kinds of technologies have tried to simplify the task but every one has had some disadvantage.

The result is the Global Positioning System, a system that's changed navigation forever

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How does GPS work?

Here's how GPS works in five logical steps:

1.The basis of GPS is "triangulation" from satellites.

2.To "triangulate," a GPS receiver measures distance using the travel time of radio signals.

3.To measure travel time, GPS needs very accurate timing which it achieves with some tricks.

4.Along with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the secret.

5.Finally you must correct for any delays the signal experiences as it travels through the atmosphere.

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How does GPS work?

Improbable as it may seem, the whole idea behind GPS is to use satellites in space as reference points for locations here on earth. That's right, by very, very accurately measuring our distance from three satellites we can " triangulate " our position anywhere on earth. Forget for a moment how our receiver measures this distance. We'll get to that later. First consider how distance measurements from three satellites can pinpoint you in space.

Suppose we measure our distance from a satellite and find it to be 11,000 miles. Knowing that we're 11,000 miles from a particular satellite narrows down all the possible locations we could be in the whole universe to the surface of a sphere that is centered on this satellite and has a radius of 11,000 miles.

Next, say we measure our distance to a second satellite and find out that it's 12,000 miles away. That tells us that we're not only on the first sphere but we're also on a sphere that's 12,000 miles from the second satellite. Or in other words, we're somewhere on the circle where these two spheres intersect. If we then make a measurement from a third satellite and find that we're 13,000 miles from that one, that narrows our position down even further, to the two points where the 13,000 mile sphere cuts through the circle that's the intersection of the first two spheres. So by ranging from three satellites we can narrow our position to just two points in space.

EE5404 Introduction 26

How does GPS work?

To decide which one is our true location we could make a fourth measurement. But usually one of the two points is a ridiculous answer (either too far from Earth or moving at an impossible velocity) and can be rejected without a measurement. A fourth measurement does come in very handy for another reason however, but we'll tell you about that later.

Next we'll see how the system measures distances to satellites.

1.Position is calculated from distance measurements (ranges) to satellites.

2.Mathematically we need four satellite ranges to determine exact position.

3.Three ranges are enough if we reject ridiculous answers or use other tricks.

4.Another range is required for technical reasons to be discussed later.

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Web sites related to GPS:

http://www.trimble.com/index.htm

http://www.allgps.com/

… …

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Problems:

•Describe basic elements and functions of a satellite communications system,

such as fixed, mobile and direct broadcast system.

•What are the important considerations in the design of satellite

communication systems?

•Describe the GPS.