Ch-1 Sat Com Introduction

7/29/2019 Ch-1 Sat Com Introduction

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Satellite CommunicationIntroductory Lecture


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Overview

Satellite technology has progressed tremendouslyover the last 50 years since Arthur C. Clarke firstproposed its idea in 1945 in his article in WirelessWorld.

Today, satellite systems can provide a variety ofservices including broadband communications,audio/video distribution networks, maritimenavigation, worldwide customer service andsupport as well as military command and control.

Satellite systems are also expected to play an

important role in the emerging 4G globalinfrastructure providing the wide area coveragenecessary for the realization of the OptimallyConnected Anywhere, Anytime vision that drivesthe growth of modern telecom industry.


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Course Objectives

This course aims to:

Provide a broad overview of the status of digitalsatellite communications.

Discuss main physical, architectural and

networking issues of satellite systems. Provide in-depth understanding of modern

modulation, coding and multiple access schemes.

Review the state of the art in open research areas

such as speech and video coding, satellitenetworking, internet over satellite and satellitepersonal communications.

Highlight trends and future directions of satellitecommunication


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Course Pre-requisites

Principles of digital communications

Telecom systems design


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Section 1: The SATCOM Industry

System Design Issues

An Overview of Satellite Communications Examples of current military and commercial systems. Satellite orbits and transponder characteristics (LEO, MEO,

GEO)

Traffic Connectivity: Mesh, Hub-Spoke, Point-to-Point,Broadcast

Basic satellite transmission theory Impairments of the Satellite Channel: Weather and Doppler

effects, Channel models. Communications Link Calculations: Definition of EIRP, Noise

temperature and G/T ratio, Eb/No. Transponder gain and SFD.

Link Budget Calculations. Down-link requirements. Design ofsatellite links to achieve a specified performance.

Earth Station Antenna types: Pointing/Tracking. Smallantennas at Ku band. FCC-Intelsat-ITU antenna requirementsand EIRP density limitations.

Brief introduction to implementation issues: LNA, Up/downconverters, oscillator phase noise.


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Section 2: Elements of Transponder

Design The Baseband

Physical Layer of the Transponder TheBaseband System

Introduction to the theory of DigitalCommunications: Modulation, Equalization andFEC Digital Modulation Techniques: BPSK, QPSK, Nyquist

signal shaping. Overview of Bandwidth Efficient Modulation (BEM)

Techniques: M-ary PSK, Trellis Coded 8PSK, QAM. PSK Receiver Implementation issues: Carrier recovery,

phase slips, differential coding. Overview of Forward Error Correction (FEC):

Standard FEC types (Block and ConvolutionCoding schemes, Viterbi Decoding), Coding Gain,Concatenated coding, Turbo coding.


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Section 3: Multiple Access Issues

Spread Spectrum Techniques: Military andcommercial use of spread-spectrum. Direct-Sequence PN, Frequency-Hop and CDMAsystems.

Principles of Multiple Access Communications Multiplexing & Multiple Access FDD/TDD, FDMA, TDMA

Concepts of Random Access: ALOHA, CSMA

Multiple Access Techniques: FDMA, TDMA, CDMA.DAMA and Bandwidth-on-Demand (BoD).

TDMA Networks: Time Slots, Preambles,Suitability for DAMA and BoD.


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Section 4: SATCOM Networks and

Services Satellite Communication Systems &

Networks Characteristics of IP and TCP/UDP over

satellite: Unicast and Multicast. Need for

Performance Enhancing Proxy (PEP) techniques.

VSAT Networks and their systemcharacteristics.

DVB standards and MF-TDMA

The Future of SATCOM SATCOMs role in the emerging 4G Information

and Communications (ICT) infrastructure.


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Pioneers in Satellite

Communication Konstantin Tsiolkovsky (1857 - 1935)

Russian visionary of space flight First described the multi-stage rocket as means of achieving orbit. Link: The life of Konstantin Eduardovitch Tsiolkovsky

Hermann Noordung (1892 - 1929)Postulated the geostationary orbit. Link: The Problem of Space Travel: The Rocket Motor

Arthur C. Clarke (1917 19 March 2008)Postulated the entire concept of international satellitetelecommunications from geostationary satellite orbit

including coverage, power, services, solar eclipse. Link: "Wireless World" (1945)
http://www.informatics.org/museum/tsiol.htmlhttp://www.hq.nasa.gov/office/pao/History/SP-4026/cover.htmlhttp://www.lsi.usp.br/~rbianchi/clarke/ACC.ETRelaysFull.htmlhttp://www.lsi.usp.br/~rbianchi/clarke/ACC.ETRelaysFull.htmlhttp://www.hq.nasa.gov/office/pao/History/SP-4026/cover.htmlhttp://www.informatics.org/museum/tsiol.htmlhttp://www.informatics.org/museum/tsiol.html


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Satellite History Calendar 1957

October 4, 1957: - First satellite - the Russian Sputnik 01 First living creature in space: Sputnik 02

1958 First American satellite: Explorer 01 First telecommunication satellite: This satellite broadcast a taped message: Score

1959 First meteorology satellite: Explorer 07

1960

First successful passive satellite: Echo 1 First successful active satellite: Courier 1B First NASA satellite: Explorer 08

April 12, 1961: - First man in space 1962

First telephone communication & TV broadcast via satellite: Echo 1 First telecommunication satellite, first real-time active, AT&T: Telstar 1 First Canadian satellite: Alouette 1 On 7th June 1962 at 7:53p the two-stage rocket; Rehbar-I was successfully launched from

Sonmiani Rocket Range. It carried a payload of 80 pounds of sodium and soared to about 130km into the atmosphere. With the launching of Rehbar-I, Pakistan had the honour ofbecoming the third country in Asia and the tenth in the world to conduct such a launchingafter USA, USSR, UK, France, Sweden, Italy, Canada, Japan and Israel.

Rehbar-II followed a successful launch on 9th June 1962 1963

Real-time active: Telstar 2 1964

Creation of Intelsat First geostationary satellite, second satellite in stationary orbit: Syncom 3 First Italian satellite: San Marco 1


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Intelsat 1 becomes first commercial comsat: Early Bird First real-time active for USSR: Molniya 1A

1967 First geostationary meteorology payload: ATS 3

1968 First European satellite: ESRO 2B

July 21, 1969: - First man on the moon

1970

First Japanese satellite: Ohsumi First Chinese satellite: Dong Fang Hong 01

1971 First UK launched satellite: Prospero ITU-WARC for Space Telecommunications INTELSAT IV Launched INTERSPUTNIK - Soviet Union equivalent of INTELSAT formed

1974 First direct broadcasting satellite: ATS 6

1976 MARISAT - First civil maritime communications satellite service started

1977 EUTELSAT - European regional satellite ITU-WARC for Space Telecommunications in the Satellite Service

1979 Creation of Inmarsat


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INTELSAT V launched - 3 axis stabilized satellite built by Ford Aerospace 1983

ECS (EUTELSAT 1) launched - built by European consortium supervised by ESA 1984

UK's UNISAT TV DBS satellite project abandoned First satellite repaired in orbit by the shuttle: SMM

1985 First Brazilian satellite: Brazilsat A1 First Mexican satellite: Morelos 1

1988 First Luxemburg satellite: Astra 1A

1989 INTELSAT VI - one of the last big "spinners" built by Hughes Creation of Panamsat - Begins Service On 16 July 1990, Pakistan launched its first experimental satellite, BADR-I from China

1990 IRIDIUM, TRITIUM, ODYSSEY and GLOBALSTAR S-PCN projects proposed - CDMA designs

more popular EUTELSAT II

1992 OLYMPUS finally launched - large European development satellite with Ka-band, DBTV and Ku-

band SS/TDMA payloads - fails within 3 years 1993

INMARSAT II - 39 dBW EIRP global beam mobile satellite - built by Hughes/British Aerospace 1994

INTELSAT VIII launched - first INTELSAT satellite built to a contractor's design Hughes describe SPACEWAY design DirecTV begins Direct Broadcast to Home

1995 Panamsat - First private company to provide global satellite services.


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INMARSAT III launched - first of the multibeam mobile satellites (built by GE/Marconi) Echostar begins Diresct Broadcast Service

1997 IRIDIUM launches first test satellites ITU-WRC'97

1999 AceS launch first of the L-band MSS Super-GSOs - built by Lockheed Martin Iridium Bankruptcy - the first major failure?

2000 Globalstar begins service Thuraya launch L-band MSS Super-GSO

2001 XM Satellite Radio begins service Pakistans 2nd Satellite, BADR-B was launched on 10 Dec 2001 at 9:15a from Baikonour

Cosmodrome, Kazakistan 2002

Sirius Satellite Radio begins service Paksat-1, was deployed at 38 degrees E orbital slot in December 2002, Paksat-1, was

deployed at 38 degrees E orbital slot in December 2002 2004

Teledesic network planned to start operation 2005

Intelsat and Panamsat Merge VUSat OSCAR-52 (HAMSAT) Launched

2006 CubeSat-OSCAR 56 (Cute-1.7) Launched K7RR-Sat launched by California Politechnic University

2007 Prism was launched by University of Tokyo

2008 COMPASS-1; a project of Aachen University was launched from Satish Dawan Space Center,

India. It failed to achieve orbit.


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base station

or gateway

Classical satellite systems

Inter Satellite Link

(ISL)Mobile User

Link (MUL) Gateway Link

(GWL)

footprint

small cells

(spotbeams)

User data

PSTNISDN GSM

GWL

MUL

PSTN: Public Switched

Telephone Network


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Intelsat

INTELSAT is the original "Inter-governmental Satelliteorganization". It once owned and operated most of theWorld's satellites used for international communications,and still maintains a substantial fleet of satellites.

INTELSAT is moving towards "privatization", with increasingcompetition from commercial operators (e.g. Panamsat,

Loral Skynet, etc.). INTELSAT Timeline: Interim organization formed in 1964 by 11 countries

Permanent structure formed in 1973

Commercial "spin-off", New Skies Satellites in 1998

Full "privatization" by April 2001 INTELSAT has 143 members and signatories listed here.
http://www.satcom.co.uk/Tables/im.asphttp://www.satcom.co.uk/Tables/im.asp


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Intelsat Structure


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Eutelsat

Permanent General Secretariat opened September 1978 Intergovernmental Conference adopted definitive statutes with 26

members on 14 May 1982 Definitive organization entered into force on 1 September 1985

General Secretariat -> Executive Organ

Executive Council -> EUTELSAT Board of Signatories

Secretary General -> Director General

Current DG is Giuliano Berretta Currently almost 50 members Moving towards "privatization" Limited company owning and controlling of all assets and activities

Also a "residual" intergovernmental organization which will ensure thatbasic principles of pan-European coverage, universal service, non-discrimination and fair competition are observed by the company


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Eutelsat Structure


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Communication Satellite

A Communication Satellite can belooked upon as a large microwaverepeater

It contains several transponderswhich listens to some portion ofspectrum, amplifies the incomingsignal and broadcasts it in anotherfrequency to avoid interference withincoming signals.


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Motivation to use Satellites


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Source: Union of Concerned Scientists [www.ucsusa.org]

Satellite Missions


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Satellite Microwave Transmission

Satellites can relay signals over along distance

Geostationary Satellites

Remain above the equator at a height ofabout 22300 miles (geosynchronousorbits)

Travel around the earth in exactly thesame time, the earth takes to rotate


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Satellite System Elements


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Space Segment

Satellite Launching Phase

Transfer Orbit Phase

Deployment

Operation TT&C - Tracking Telemetry and

Command Station

SSC - Satellite Control Center, a.k.a.: OCC - Operations Control Center

SCF - Satellite Control Facility

Retirement Phase


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Ground Segment

Collection of facilities, Users and Applications

Earth Station = Satellite Communication Station(Fixed or Mobile)


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Satellite Uplink and Downlink

Downlink The link from a satellite down to one or more

ground stations or receivers

Uplink The link from a ground station up to a satellite.

Some companies sell uplink and downlinkservices to

television stations, corporations, and to othertelecommunication carriers.

A company can specialize in providing uplinks,downlinks, or both.


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Satellite Uplink and Downlink


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Source: Cryptome [Cryptome.org]

When using a satellite for longdistance communications, thesatellite acts as a repeater.

An earth station transmits thesignal up to the satellite(uplink), which in turnretransmits it to the receivingearth station (downlink).

Different frequencies are usedfor uplink/downlink.

Satellite Communication


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Satellite Transmission Links

Earth stations Communicate bysending signals to the satellite on anuplink

The satellite then repeats thosesignals on a downlink

The broadcast nature of downlink

makes it attractive for services suchas the distribution of TV programs


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Direct to User Services

One way Service (Broadcasting) Two way Service (Communication)


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Satellite Signals

Used to transmit signals and dataover long distances

Weather forecasting

Television broadcasting

Internet communication

Global Positioning Systems


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Satellite Transmission Bands

Frequency Band Downlink Uplink

C 3,700-4,200 MHz 5,925-6,425 MHz

Ku 11.7-12.2 GHz 14.0-14.5 GHz

Ka 17.7-21.2 GHz 27.5-31.0 GHz

The C band is the most frequently used. The Ka and Ku bands are reserved

exclusively for satellite communication but are subject to rain attenuation


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Types of Satellite Orbits

Based on the inclination, i, over the equatorialplane:

Equatorial Orbits above Earths equator (i=0)

Polar Orbits pass over both poles (i=90) Other orbits called inclined orbits (0


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Types of Satellite based Networks

Based on the Satellite Altitude

GEO Geostationary Orbits

36000 Km = 22300 Miles, equatorial, High latency

MEO Medium Earth Orbits High bandwidth, High power, High latency

LEO Low Earth Orbits

Low power, Low latency, More Satellites, SmallFootprint

VSAT

Very Small Aperture Satellites

Private WANs


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Source: Federation of American Scientists [www.fas.org]

Satellite Orbits

Geosynchronous Orbit(GEO): 36,000 km aboveEarth, includes commercialand military communicationssatellites, satellites providing

early warning of ballisticmissile launch.

Medium Earth Orbit (MEO):from 5000 to 15000 km,they include navigationsatellites (GPS, Galileo,

Glonass). Low Earth Orbit (LEO): from

500 to 1000 km above Earth,includes military intelligencesatellites, weather satellites.


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Satellite Orbits


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GEO - Geostationary Orbit

In the equatorial plane

Orbital Period = 23 h 56 m 4.091 s= 1 sidereal day*

Satellite appears to be stationary over any pointon equator: Earth Rotates at same speed as Satellite Radius of Orbit r = Orbital Height + Radius of Earth

Avg. Radius of Earth = 6378.14 Km

3 Satellites can cover the earth (120 apart)


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NGSO - Non Geostationary Orbits

Orbit should avoidVan Allen radiationbelts: Region of charged

particles that cancause damage tosatellite

Occur at ~2000-4000 km and ~13000-25000 km


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LEO - Low Earth Orbits

Circular or inclined orbit with < 1400 kmaltitude Satellite travels across sky from horizon to

horizon in 5 - 15 minutes => needs handoff

Earth stations must track satellite or haveOmni directional antennas

Large constellation of satellites is needed forcontinuous communication (66 satellitesneeded to cover earth)

Requires complex architecture

Requires tracking at ground


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HEO - Highly Elliptical Orbits

HEOs (i = 63.4) are suitable toprovide coverage at high latitudes(including North Pole in thenorthern hemisphere)

Depending on selected orbit (e.g.Molniya, Tundra, etc.) two orthree satellites are sufficient forcontinuous time coverage of theservice area.

All traffic must be periodicallytransferred from the settingsatellite to the rising satellite(Satellite Handover)


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Source: Union of Concerned Scientists [www.ucsusa.org]

Satellite Orbits


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Why Satellites remain in Orbits


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Advantages of Satellite

Communication Can reach over large geographical area Flexible (if transparent transponders) Easy to install new circuits Circuit costs independent of distance

Broadcast possibilities Temporary applications (restoration) Niche applications Mobile applications (especially "fill-in") Terrestrial network "by-pass" Provision of service to remote or underdeveloped

areas User has control over own network 1-for-N multipoint standby possibilities


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Disadvantages of Satellite

Communication

Large up front capital costs (spacesegment and launch)

Terrestrial break even distanceexpanding (now approx. size ofEurope)

Interference and propagation delay

Congestion of frequencies and orbits


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When to use Satellites

When the unique features of satellite communicationsmake it attractive

When the costs are lower than terrestrial routing When it is the only solution Examples:

Communications to ships and aircraft (especially safetycommunications) TV services - contribution links, direct to cable head, direct

to home Data services - private networks Overload traffic Delaying terrestrial investments 1 for N diversity Special events


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When to use Terrestrial

PSTN - satellite is becoming increasinglyuneconomic for most trunk telephony routes

but, there are still good reasons to usesatellites for telephony such as: thin routes,diversity, very long distance traffic and remote

locations. Land mobile/personal communications - in

urban areas of developed countries newterrestrial infrastructure is likely to dominate(e.g. GSM, etc.)

but, satellite can provide fill-in as terrestrialnetworks are implemented, also provide similarservices in rural areas and underdevelopedcountries

F B d All t d t th


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Frequency Bands Allocated to the

FSS Frequency bands are allocated to different services at World

Radio-communication Conferences (WRCs).

Allocations are set out in Article S5 of the ITU RadioRegulations.

It is important to note that (with a few exceptions) bands

are generally allocated to more than one radio services.

CONSTRAINTS Bands have traditionally been divided into commercial" and

"government/military" bands, although this is not reflected inthe Radio Regulations and is becoming less clear-cut as"commercial" operators move to utilize "government" bands.


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Earths atmosphere

Source: All about GPS [www.kowoma.de]


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Atmospheric Losses

Different types of atmospheric losses candisturb radio wave transmission in satellitesystems:

Atmospheric absorption

Atmospheric attenuation

Traveling ionospheric disturbances


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Atmospheric Absorption

Energy absorption by atmosphericgases, which varies with the frequencyof the radio waves.

Two absorption peaks are observed (for90 elevation angle): 22.3 GHz from resonance absorption in

water vapour (H2O) 60 GHz from resonance absorption in

oxygen (O2)

For other elevation angles: [AA] = [AA]90 cosec

Source: Satellite Communications, Dennis Roddy, McGraw-Hill


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Atmospheric Attenuation

Rain is the main cause of atmospheric attenuation(hail, ice and snow have little effect on attenuationbecause of their low water content).

Total attenuation from rain can be determined by:

A = L [dB] where [dB/km] is called the specific attenuation, and

can be calculated from specific attenuation coefficients intabular form that can be found in a number ofpublications

where L [km] is the effective path length of the signalthrough the rain; note that this differs from the geometricpath length due to fluctuations in the rain density.


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Traveling Ionospheric Disturbances

Traveling ionospheric disturbances are cloudsof electrons in the ionosphere that provokeradio signal fluctuations which can only bedetermined on a statistical basis.

The disturbances of major concern are:

Scintillation; Polarisation rotation.

Scintillations are variations in the amplitude,phase, polarisation, or angle of arrival of radiowaves, caused by irregularities in theionosphere which change over time.

The main effect of scintillations is fading of thesignal.


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What is Polarisation?

Polarisation is the property of electromagneticwaves that describes the direction of thetransverse electric field.

Since electromagnetic waves consist of an

electric and a magnetic field vibrating at rightangles to each other.

it is necessary to adopt a convention todetermine the polarisation of the signal.

Conventionally, the magnetic field is ignored andthe plane of the electric field is used.


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Types of Polarisation

Linear Polarisation(horizontal or vertical):

the two orthogonalcomponents of theelectric field are in phase;

The direction of the line in

the plane depends on therelative amplitudes of thetwo components.

Circular Polarisation:

The two components areexactly 90 out of phase

and have exactly thesame amplitude.

Elliptical Polarisation:

All other cases.

Linear Polarisation Circular Polarisation Elliptical Polarisation


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Satellite Communications

Alternating vertical andhorizontal polarisation iswidely used on satellitecommunications

This reduces interferencebetween programs on thesame frequency bandtransmitted from adjacentsatellites (One uses vertical,the next horizontal, and soon)

Allows for reduced angularseparation between thesatellites. Information Resources for Telecommunication Professionals

[www.mlesat.com]

Documents

Ch-1 Sat Com Introduction