Satellite communication (a tutorial)

Tutorial
Satellite Communication
By
Kamran Ahmed
(kamrahmed@excite.com)

Course Contents
•

Overview of Satellite Systems

•

Orbits & Launching Methods

•

Orbital Mechanics

•

Orbital Perturbations

•

Satellite Visibility

•

Radio Wave Propagation

•

Polarization

•

Antenna

•

Link Budget

•

Interference

•

Channel Characterization

1.

Overview of Satellite Systems

Contents
•
•
•
•
•
•
•
•
•
•
•

What is satellite communication
The Origin of Satellite
Elements of Satellite Communication
Key input data
Early Satellite Systems
System Design Considerations
Major Problems for Satellite
Limitation for Satellites
Advantages of Satellite
Different Applications
Frequency Allocation & Regulatory Aspects

What is Satellite Communication…
• A communication satellite is basically an
electronic communication package placed in orbit
whose prime objective is to initiate or assist
another through space.
• Satellite communication is one of the most
impressive spin-offs from the space programs and
has made a major contribution to the pattern of
international communication.
• The information transferred most often
correspondence to voice (telephone), video
(Television) and digital data.

Cont...
• Communication satellite are off-course
only one means of telecommunication
transmission. The traditional means
include copper wire and microwave pointto-point links. Newer techniques involves
use of optics either point-to-point infrared
or fiber optics. Point-to-point radio system
such as short wave radio may also be used.

The origin of satellite
• The concept of using object in space to reflect signals for
communication was proved by Naval Research Lab in
Washington D.C. when it use the Moon to establish a
very low data rate link between Washington and Hawaii
in late 1940’s.
• Russian started the Space age by successfully launching
SPUTNIK the first artificial spacecraft to orbit the earth,
which transmitted telemetry information for 21 days in
Oct. 1957.
• The American followed by launching an experimental
satellite EXPLORER In 1958.
• In 1960 two satellite were deployed “Echo” & “Courier”
• In 1963 first GSO “Syncom”
• The first commercial GSO (Intelsat & Molnya) in 1965
these provides video (Television) and voice (Telephone)
for their audience

Elements of Satellite
Communications
• The basic elements of a communication satellite
service are divided between;

• Space Segment
• Ground Segment
• The space segment consist of the spacecraft &
launch mechanism and ground segment
comprises the earth station and network control
center of entire satellite system.

Satellite Communications System

Uplink

IDU

Down Link

RFT

RFT

IDU

RF
Transmit Earth Station

Receive Earth
Station

Concept
Transponder

downlink

downlink
uplink

uplink

IRRADIUM

Earth station (site A)

Earth station(site B)

Propagation Delay

Single Hop 270 ms

Double Hop 540 ms

Ground Station _ Anatomy

Indoor Unit
(IDU)

IFL

70/140
MHz

Antenna
Sub-System

Outdoor Unit
(ODU)
C/Ku

Satellite Services
•
•
•
•

The ITU has grouped the satellite services in to three main
groups
Fixed Satellite Services (FSS)
Broadcast Satellite Services (BSS)
Mobile Satellite services (MSS)

Space Segment
• Space segment consist of a satellite in
suitable orbit.
• Space segment classified on the basis of
orbit;
–
–
–
–

LEO
MEO
HEO
GEO & GSO

Ground Segment
• The ground segment of each service has
distinct characteristics.
• Services like;
• FSS
• BSS
• MSS
– Maritime, Aeronautical & Land base

• DBS
• Etc.

Satellite Footprints
Satellite beam their signals in a straight path to the earth. The
satellite focus these microwaves signals onto the specified
portions of the earth’s surface to most effectively use the
limited power of their transponders. These focused signals
create unique beam patterns called “footprints.”
Types of footprints:
– Global beam footprint
– Hemispheric Beam Footprint
– Zone Beam Footprint

Key Input Data...
Bands:
C-Band (
Ku-Band (

Beams:
Global ( )
Hemi ( )
Zone ( )
Spot (
)

)
)

National and Regional Systems

1
2
3
4
5

Anik, Canada
Morelos, Mexico
Panamsat, Americas
Brasilsat, Brazil
Eutelsat, Europe

6
7
8
9
10

Telecom, France
Kopernikus, Germany
Italsat, Italy
Arabsat, Arab League
Insat, India

11
12
13
14

Asiasat, East Asia
CS, Japan
Palapa, Indonesia
Aussat, Australia

Early Satellites
Satellite

Launching Date

Country/Organization

Type

Height (miles)

RELAY

1962

USA/RCA & NASA

Active Duplex

SYNCOM

1963

USA/NASA

Active Duplex

MOLNIYA

1965

U.S.S.R

Active Duplex

High altitude
elliptical

First Soviet communication satellite
used a high altitude elliptical orbit.

EARLY
BIRD

1965

INTELSAT/COMSAT

Active

Geostationary

First commercial communication
satellite; served the Atlantic ocean
region; capacity to carry 240 voice
channels

INTELSAT 2

1966

INTELSAT/COMSAT

Active

Geostationary

First multiple access commercial
satellite with multidestination
capability

INTELSAT 3

1968

INTELSAT/COMSAT

Active

Geostationary

3 generation designed to carry 1200
voice circuits

942-5303

Comments
4.2/1.7 GHz satellite designed to
carry telephone signals.

Geostationary First Geostationary communication
satellite used to transmit television
signals from the Tokyo Olympics.

Early Satellites
Satellite

Launching Date

Explorer

1958

ECHO


Type

Height (miles)

Comments

USA/NASA

Broadcast

110 to 920

Very short life; Noted for
re-broadcasting an on-board
taped message from president
Eisnhour

1960

USA/NASA

Passive

1000

100-Foot diameter plastic balloon
with an aluminum coating which
reflect radio signals

COURIER

1960

Department of defense

Store & Repeat

600-700

TELSTAR

1962

USA/AT&T

Active Duplex

682-4030

First radio repeater satellite. It
accepted and stored upto 360,000
teletype words as it passed
overhead and then broadcast to
ground stations further along the
orbit; only operated for 17 days.
First satellite to receive and transmit
simultaneously; Operated in 4/6
GHz band

Early Satellites
Satellite

Launching Date


Type

Height (miles)

Comments

INTELSAT 4

1971

INTELSAT/COMSAT

Active

Geostationary

COMSAT’s 4th generation;
designed to carry 6000 voice
circuits.

ANIK 1

1972

Canada/Telesat

Active

Geostationary

World’s first domestic satellite; 5000
voice circuits capacity.

WESTAR

1974

USA/Western Union

Active

Geostationary

First US domestic satellite

Early Satellites
•
•
•
•

US Navy bounced messages off the moon
ECHO 1 “balloon” satellite - passive
ECHO 2 - 2nd passive satellite
All subsequent satellites used active
communications

Early Satellites
• Relay
– 4000 miles orbit

• Telstar
– Allowed live transmission across the Atlantic

• Syncom 2
– First Geosynchronous satellite

TELSTAR

•

Picture from NASA

SYNCOM 2

•

Picture from NASA

System Design Consideration
•
•
•
•

Services or Application
Selection of RF Band
Finance
Further technical design considerations are:– Optimal modulation, coding scheme, type of service,
permitted earth station size and complexity, shape of
service area, landing rights, state of prevailing
technology related both to spacecraft and ground
station.

Major problems for satellite
• Positioning in orbit in-term of Frequency
& Orbit Selection
• Stability
• Power
• Communications
• Harsh environment
• Interference Problem

Limitation of Satellites
• High initial investment
• New investment require in Ground
Segment
• Short life time
• Spectrum crowding
• Regulatory aspects (landing rights etc.)
• Launch vehicle reliability

Advantages of Satellite
•
•
•
•
•
•

Wide band capability
Wide area coverage readily possible
Distance-insensitive costs
Counter inflationary cost history
All user have same access possibilities
Point to point, point to multipoint (broadcast)
and multipoint to point (data collection) are all
possible
• Inherently suited for mobile application.
• Compatible with all new technologies
• Service directly to the users premises

Applications
• Communication
(truncking call)
• Teleconference
• Telemedicine
• TV Broadcasting
• Data communication
• Telemetry(TEC,
remote sensing etc)

•
•
•
•

Weather telecast
Navigation
GPS
Security/Calamity
monitoring
• Standard Time
• Military
• Remote Sensing

Frequency Allocations &
Regulatory Aspects
• Frequency bands for satellite services are shared with terrestrial
services.
• Satellite signal strength is constrained to avoid interference by it
to others.
• Thus a large antenna and sensitive receiver are needed at the earth
station.
• Frequency sharing techniques are an important study area.
• Many satellites have to share a limited frequency band (and
limited orbital arc) thus coordination in frequency and orbital
location is important.
• Frequency allocation are done by international agreements

The Frequency Spectrum and Typical Applications

Power
Systems

102
AC

104

GPSMobil
Glonass
Mittel GalileoFunk
Sat
Welle
Mikro TV
TV
Sun
Welle
IR Lamp
AM UKW
Studio

106
Broadcast

108

1010
Microwave

1012

1014

Infrared

1016
Ultraviolett

X-Rays

1018

1020 Hz
X-Ray

Radio Frequency Bands
Band Number
4
5
6
7
8
9
10
11

Band Name

Frequency Range

Metric Subdivision

VLF, Very low frequency
LF, Low frequency
MF, Medium frequency
HF, High frequency
VHF, Very high frequency
UHF, Ultra high frequency
SHF, Super high frequency
EHF, Extra high frequency

3-30 KHz
30-300 KHz
300-3000 KHz
3-30 MHz
30-300 MHz
300-3000 MHz
3-30 GHz
30-300 GHz

Myriametric waves
Kilometric waves
Hectometric waves
Decametric waves
Metric waves
Decimetric waves
Centimetric waves
Decimillimetric waves

Satellite Operating Frequency Bands
Frequency Range (GHz)
0.39-1.55
1.55-5.2
3.9-6.2
5.2-10.9
10.9-36.0
15.35-17.25
18.3-31.0

Band
L
S
C
X
K
Ku
Ka

Category
MSS
FSS & BSS
FSS
Military
FSS & BSS
FSS & BSS
FSS

Frequency Allocation and Regulatory
Aspects
•

Domestic
e.g. Federal communication Commission (FCC)
National Telecommunication and Information Administration
(NITA)
In Pakistan, PTA (Pakistan Telecommunication Authority)

•

International
International Telecommunication Union (ITU)
– Formed in 1932 from the International Telegraph Union
– Consists of over 150 members nations
– World Administrative Radio Conference (WARC)
– International Radio Consultative Committee (CCIR)
consists of 13 study groups.

ITU Regions
ITU divides the surface area of the earth into three regions for the
purpose of frequency allocation
•

Region 1: Pacific Ocean Region
North and South America
Greenland

•

Region 2: Atlantic Ocean Region
Europe
Africa
Middle East
Central Asia

ITU Regions (Continued)
•

Region 3: Indian Ocean Region
Pakistan, India, Sub-continent , South East Asia &
Australia

Frequency Allocations to Satellite Services

International Telecommunications Union
Examples of Satellite Radio Services:
-

Fixed Satellite Service

FSS

-

Mobile Satellite Service

MSS

-

Broadcast Satellite Service BSS

-

Radio Navigation Sat. Serv. RNSS

-

Radio location Sat. Service RSS

-

Space Operation Service

-...

Earth observation Sat. Serv. ESS

In total more than 18 radio services

SOS

Artikel S5 der Radio Regulations
Region 1

Region 2

Region 3

19.7 - 20.1 GHz
FIXED-SATELLITE
(space-to-earth)

19.7 - 20.1 GHz
FIXED-SATELLITE
(space-to-earth)

19.7 - 20.1 GHz
FIXED-SATELLITE
(space-to-earth)

Mobile-Satellite
(space-to-earth)

MOBILE-SATELLITE Mobile-Satellite
(space-to-earth)
(space-to-earth)

S5.524

S5.524, S5.525, S5.526 S5.524
S5.527, S5.528, S5.529

A license is required by every operator in order to
operate a satellite system nationally; a licence may
only be acquired if:
- the operator can show that he has a contract with
the system owner to be his service provider
- the frequencies for the system have been cleared /
coordinated / notified
- that system is fully registered with the ITU
-the operator has workers registered as operators
A licence will be cancelled if:
- there are no more registered operators to work the
system
- the service provider has breached ‘data protection
laws’

2.

Orbits and Launching Methods

Contents
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Different Types of orbit
Satellite Orbits & Relative Periods
GEO
View & Coverage from GEO
Some GEO
Characteristics of GEO
Transfer Orbit
C & Ku Bands Satellites in Orbit
Mega LEO, MEO, HEO & GEO Projects
The Future
Broadband LEO
Launching
Launch Vehicle
Summary of Launchers
Types of Launches

Different Types of Orbits
• Circular orbits are simplest
• Inclined orbits are useful for coverage of
equatorial regions
• Elliptical orbits can be used to give quasi
stationary behaviour viewed from earth
– using 3 or 4 satellites

• Orbit changes can be used to extend the
life of satellites

Cont…
Several types
• LEOs - Low Earth Orbit
• MEOs - Medium Earth Orbit
• HEOs – Highly Elliptical Orbit
• GSO - Geostationary Earth Orbit

LEO
•
•
•
•
•
•
•

Low Earth Orbit
200-3,000 km
High orbit speed
Many satellites
Predominately mobile
Iridium, Globalstar
(space shuttle orbit)

MEO
•
•
•
•
•
•

Medium Earth Orbit
6,000 – 12,000km
New generation
About 12 satellites
Voice and mobile
ICO (Odyssey), Orbcomm,
Ellipso
Ellipso

HEOs: Molnya and Tundra
Molnya
Period
Apogee
Perigee
Inclination

Tundra

12 h
39 500 km
1 000 km
63.4°

24 h
46 300 km
25 300 km
63.4°

Satellite Orbits and Periods
Height
of Orbit1
(km)

Period
Cell
of Orbit Diameter
(h)
(km)

200
700
1000
1 414
10 000
20 000
35 786

1.5
1.6
1.8
1.9
5.8
11.9
24.0

1

3 154
5 720
6 719
7 806
14 935
16 922
18 100

Visible
Numbers
Part of Earth of Satellite
%
*
1.5
5.0
6.8
9.1
30.5
37.9
42.4

above the surface of the earth

*minimum necessary for 0° elevation and 0 redundancy

66
20
15
11
4
3
3

Duration of
Over flight
(min)
7
14
18
22
130
300
24 h/d

GEOs
• Originally proposed by Arthur C. Clarke
• Circular orbits above the equator
• Angular separation about 2 degrees allows 180 satellites
• Orbital height above the earth about 23000
miles/35786.16km
• Round trip time to satellite about 0.24
seconds

GEOs (2)
• GEO satellites require more power for
communications
• The signal to noise ratio for GEOs is worse
because of the distances involved
• A few GEOs can cover most of the surface
of the earth
• Note that polar regions cannot be “seen”
by GEOs

GEOs (3)
• Since they appear stationary, GEOs do not
require tracking
• GEOs are good for broadcasting to wide
areas
• Currently 329 GEO are in orbit
(ref: web site provided by Johnston)

The original vision
• 1945 Arthur C Clark envisaged
“extraterrestrial relays”
• # of Satellites: 03
• Period:
23 h 56 min 4.091 s
• Height:
36 000 km above
equator
• Speed of flight: 3.074 km/s

and then..
• 1957 Sputnik
• a rush of experimental satellites in many
orbits
• Intelsat 1965 – 1st commercial GEO service
• over 800 objects registered so far

GEO - geostationary earth orbit
• characterised by:
– delay (echo) ~0.5sec return
– high power
– 5-7 years life

•
•
•
•

global and spot beams
C and K band (4-6Ghz and 12-14Ghz)
2 – 3o spacing
Currently more than 200 GEO satellites in
operation

Earth coverage with 2 spacecraft
90

70

50

30

10

-10

-30

-50

-70

-90
-170

-150

-130

-110

-90

-70

-50

-30

-10

10

30

50

70

90

110

130

Coverage of the inhabited world except for Polynesia

150

170

190

some GEO’s above us
•
•
•
•
•
•

Optus * 3
AsiaSat * 3
PAS
*2
Intelsat * 7
Inmarsat * 2
Palapa * 2
and others

Some Service Providers:
Netspeed Austar Optus Telstra iHug
Newskies MediaSat NTL Heartland Xantic
Stratos

Characteristics of a Geostationary Satellite
Orbit
•
•
•
•
•
•

Eccentricity (e)
0
Inclination of the orbital plane (i)
0º
Period (T)
23h 56m 4s
Semi-major axis (a)
42164 km
Satellite altitude(R)
35786 km
Satellite velocity (Vs)
3075 m/s
µ=Gme=3.986x1014 m3/s2

F=GMm/r2

T=2π√ a3/µ

e=c/a

V= µ(2/r-1/a) m/s

The GEO
Elevation , distance to the satellite
Ro

ζ

ε

d
pRo

Kgrav

= m Me G / r2

Kzent

= m r ω 2, = m v2 / r

Angular velocity ω = 2π / T, T Period, v velocity
Kgrav = Kzent und
m Me g / r2 = m r ω 2

bzw.

Me g / r2

= r ω2

r 3 = Me g T2 / ( 2π )2
The period T of the circular orbit (r in km, m = 398 601.8 km3/s2) is
────
──────
T = 2 π √ r 3 / m = 9.952 10-3 √ r 3 / km in Seconds
p = 6.611

The GEO
Ro

ζ

ε

d
pRo

∆lon = LongitudeE/S - LongitudeSatellite
∆lat = LatitudeE/S - LatitudeSatellite
Space angle α: cos( α ) = cos ( ∆lon ) * cos( ∆lat )
───────────────────────────────────────

Distance d:

d = Ro √ 6.6112 – 2 * 6.611 * cos α + 1

Elevation ε:

sin( ε ) = [ 6.6112 Ro2 – Ro2 – d2 ) / ( 2 Ro d ) ]

Test: α = 81.3°
α = 0°

d = 41680 km and ε = 0°
d = 35787 km and ε = 90°

The inclination (1)
.
)

The inclination: orbit remains geosynchroneous,
24 h; satellite moves North/South;
inclination builds up 0.8°/year if
not corrected contiuously

T

ne
d pla
ne
incli
he

The equatorial plane

The inclination (2)
.
)

After 18 years some 15° of inclination will have built up;
ne
now the inclination reverses and decreases by 0.8°/year;
d pla
ine
satellites with <15° inclination are geostationary by law. The incl

The equatorial plane

C-Band satellites in GEO

Legende
im Orbit
im Bau
ITU Appl.
Legend
on orbit
under constr
ITU Appl.
(1995)

Ku-Band satellites in GEO

Legende
im Orbit
im Bau
ITU Appl.
Legend
on orbit
under constr
ITU Appl.
(1995)

C and Ku-Band satellites in America

Comparison Chart
Features

GEO

MEO

LEO

Heig ht
(km’s )
Time per
Orbit (hrs )
Speed
(kms / hr)
Time
delay
(ms )
Time in
s ite of
Gatew ay
Satellites
f or Global
Coverag e

3 6 ,0 0 0

200-3000

24

6 ,0 0 0 1 2 ,0 0 0
5-12

1 1 ,0 0 0

1 9 ,0 0 0

2 7 ,0 0 0

250

80

10

Alw ays

2 - 4 hrs

< 1 5 min

3

10-12

50-70

1 .5

Mega LEOs, MEOs, HEOs,
and GEOs
1
2
3
4
5
6
7
8
9
10
11

TELEDESIC of microSoft with 288 LEOs at Ka-Band
V-Band Supplement of TELEDESIC/microSoft with 72 LEOs im Q-Band
GS-40 of Globalstar LP with 80 LEOs at Q-Band
M-Star of Mororola with 72 LEOs at Q-Band
LEO ONE of LEO ONE Corp. with 48 LEOs at Q-Band
ORBLINK of Orblink LLC with 7 MEOs in Q-Band
SkyBridge of ALCATEL witt 64 LEOs and 9 GEOs in Ku-Band
WEST of MATRA with 10 MEOs and 12 GEOs in Ka-Band
GESN of TRW with 15 MEOs and 4 GEOs in Q-Band
CELESTRI of Motorola MOT with 63 LEOs and 10 GEOs in Ka-Band
SpaceWay of Hughes Communications with 20 LEOs and 16 GEOs in KaBand

12 StarLynx of Hughes Communications with 20 MEOs and 4 GEOs in Q-Band
13 DenAli Telecom LLC PenTriad in HEO im Ku-, Ka-, V- and W-Band

The Future
• given current-generation LEO’s and
MEO’s are predominately used for mobile
voice and low-speed data services (MPSS)
– good voice coverage for remote regions
– adjunct to GSM mobile networks ~ Globalstar

the future
• continual development in VSAT (GEO)
technology
– bandwidth gains
– multiple services = choice

• Broadband LEOs
– Teledesic
•
•
•
•

fixed and transportable terminals
64k – 2M – and above (Gb)
288 satellites
2005 launch??

– SkyBridge
• 80 satellites
• 2004

what is SkyBridge?
• SkyBridge is an Alcatel controlled company planning to
establish a constellation of 80 satellites to provide
broadband data communications direct to business &
residential premises.
• Satellites are Low Earth Orbit (LEO) at an altitude of
1500 km
• offers “last mile” broadband access from 2004
– no long-haul trunking capability - connects users to
terrestrial gateway
• System cost is approx US$4.8bn

broadband LEO – low latency
36 000 km

1 500 km

GEO : 500ms
Astrolink
Intelsat
Spaceway
LEO : 30ms
SkyBridge
Teledesic

LEO round-trip propagation time
comparable to terrestrial

Launching
Step 1: satellite is released in the Low Earth Orbit by launch
vehicle (click on the picture below)

Step 2:

The Payload Assist Module (PAM) rocket fires to place the

satellite into the geostationary transfer orbit (GTO)

Launching (Continued)
Step 3: Several days after the satellite gets into the GTO the
Apogee Kick Motor (AKM) fires to put the satellite into a
nearly circular orbit.

Launching (Continued)
Step 4: Orbital Adjustment by firing the AKM to achieve a circular
geosynchronus orbit. (click on the picture below)

Launch Vehicles
Launch
Vehicles

Atlas II

Country

USA

Delta II

Proton

Long

H-2

March-3
USA

Gross
Weight
Boast to
GTO

Ariane-4

Europe

460 t

3636 Kg

1,819 Kg

2,200 Kg

Russia

680 t

2,000 Kg

China

JAPAN

202 t

260 T

650 Kg

2,200 kG

At the Equator

equator

11 day travel, 3 days on site, 9 days back
1. and 2. stage fueled on launch site; 3. stage and satellite fueled in Long Beach

Sea Launch

Lift-Off!
Up to 6 t

3000 m deep water
Commander is
5 km away for launch

The Launch Service Alliance

ArianeSpace, Boeing Launch Services, and Mitsubishi Heavy Industries
↪ mutual backup to mitigate schedule risks, range issues, etc.

Summary of Launchers
International Launch Services, ILS
Lockheed Martin, USA,
Khrunichev, RUS, Energia, RUS
Atlas-IIARlo, Proton-Mhi
Baikonur Launch Site

Types of Launches

The Evolution:

Land Launch
since the 60ies

Sea Launch
since the 90ies

Rail Launch
since the 70ies

Air Launch
since the 80ies

Anatomy of a Satellite
A communication satellite consists of the following subsystems:
• Antenna_For receiving and transmitting signals.
• Transponder_It contains the electronics for receiving the
signals, amplifying them, changing their frequency and
retransmitting them.
• Power Generation and conditioning subsystem_For creating
power and converting the generated power into a usable form
to operate the satellite.
• Command and Telemetry_For transmitting data about the
satellite (status, health etc.) to the earth and receiving
commands from earth.
• Thrust subsystem_For making the adjustments to the satellite
orbital position and altitude.
• Stabilization subsystem_For keeping the satellite antennas
pointing in exactly the right direction.

Common Abbreviations
Orbits:
GEO = Geostationary Earth Orbit
HEO = Highly inclined Elliptical Orbit
MEO = Medium altitude Earth Orbit
LEO = Low altitude Earth Orbit
IGSO = Inclined Geo-Synchroneous Orbit
HAP = High Altitude Platform
Services:
BIG = Voice Telephony
Super = Voice telephony into mobiles from GEO
Little = Data only, typically store and forward
Mega = Mega-bit/s services
DBS = Direct Broadcast satellite television Service
Dab = Digital Audio Broadcast satellite service
Nav = Navigation service

glossary
GEO – geostationary earth orbit – 36,000km
MEO – Medium earth orbit – 6-12,000km
LEO – Low earth orbit – 200-3,000km
Broadcast – One to many simultaneous
transmission, usually associated with older
style analogue transmission
Multicast – In communications networks, to
transmit a message to multiple recipients at
the same time. Multicast is a one-to-many
transmission similar to broadcasting, except
that multicasting means sending to specific
groups, whereas broadcasting implies
sending to everybody. When sending large
volumes of data, multicast saves
considerable bandwidth, because the bulk
of the data is transmitted once from its
source through major backbones and is
multiplied, or distributed out, at switching
points closer to the end users.
2-way – Infers forward and reverse transmission
via the satellite, usually but not always
asymmetric, i.e. high-speed download from
the satellite and low speed from client to
the satellite
latency – The time between initiating a request for
data and the beginning of the actual data
transfer. A GEO satellite has a latency of
approx 256ms resulting in a round trip
delay of about half a second (echo)

IP – Internet Protocol – the language of the
Internet. The protocol stack is referred to
as TCP / IP
Fixed – refers to a satellite receiver being
attached as a permanent mounting, as
opposed to tracking.
Mobile – Refers to a mobile satellite receiver
such as a personal communicator or
mobile phone. Usually associated with
LEO and MEO services.
Broadband – high speed transmission. The
threshold is arguable, but is construed as
being faster than dial-up ~ 64kbps and
upwards. Some conventions suggest the
threshold starts at 1.5 or 2Mbps.
Orbit – The path of a celestial body or an artificial
satellite as it revolves around another
body.
One complete revolution of such a body
VSAT– Very small aperture terminal, refers to a
small-dish service using a GEO satellite
and a large central hub, usually 6 metres
plus.
DTH – Direct to home. A service bypassing
normal terrestrial infrastructure such as a
satellite TV receiver. As opposed to
community satellite service where local
distribution from a satellite receiver is done
by cable, radio or other means.

Contents
•
•
•
•
•
•
•
•
•
•
•

Kepler’s Laws
Orbital Elements
Epoch
Orbital Inclination
Right Ascension of Ascending Node
(R.A.A.N.)
Argument of Perigee
Eccentricity
Mean Motion
Mean Anomaly
Drag (optional)
Apogee & Perigee Heights

Kepler’s Laws
• LAW 1: The orbit of a planet about the Sun is an
ellipse with the Sun's center of mass at one focus
LAW 2: A line joining a planet and the Sun
sweeps out equal areas in equal intervals of time
• LAW 3: The squares of the periods of the planets
are proportional to the cubes of their semi-major
axes

Kepler’s First Law
• LAW 1: The orbit of a planet about the
Sun is an ellipse with the Sun's center of
mass at one focus.

This is the equation for an ellipse:

Cont….
• Earth’s orbit has an eccentricity of 0.017
(nearly circular)
• Pluto’s orbit has an eccentricity of 0.248
(the largest in our solar system)
• Satellites also follow Kepler’s 1st Law
– But Earth can replace sun at Focus

Kepler’s Second Law
• LAW 2: A line joining a planet and the
Sun sweeps out equal areas in equal
intervals of time

Cont…
• So… Satellites go faster at Perigee than at
Apogee
• Reason: conservation of specific
mechanical energy;
i.e., З = KE + PE

Kepler’s Third Law
LAW 3:
The period of an orbit depends on the
altitude of the orbit
OR
The square of the period is proportional
to the cube of its mean distance from
primary focus
• T a2 / T b2 = R a3 / R b3

Cont…
• Low Earth orbit: 90 minutes
– 186 miles, 17,684 mph

• Geosychronous: 24 hours
– 22,236 miles, 6,857 mph

• Moon: 28 days (one month)
– 238,330 miles, 2,259 mph

Orbital Elements
• The classic 'Keplerians' are the seven
mathematical values which determine
a spacecraft's orbit around the Earth.
• In practice there are additional values
which are required because the Earth
isn't a perfect sphere, and other
anomalies.

Cont…
• Seven numbers are required to define a satellite
orbit. This set of seven numbers is called the
satellite orbital elements, or sometimes
"Keplerian" elements (after Johann Kepler [15711630]), or just elements
• These numbers define an ellipse, orient it about
the earth, and place the satellite on the ellipse at a
particular time.
• In the Keplerian model, satellites orbit in an
ellipse of constant shape and orientation. The
Earth is at one focus of the ellipse, not the center
(unless the orbit ellipse is actually a perfect circle)

Cont…
The basic orbital elements are...
1. Epoch
2. Orbital Inclination
3. Right Ascension of Ascending Node (R.A.A.N.)
4. Argument of Perigee
5. Eccentricity
6. Mean Motion
7. Mean Anomaly
8. Drag (optional)
Note:Satellite keplerians are also distributed by NASA in a format called the NASA twoline format.

Epoch
• [aka "Epoch Time" or "T0"]
• A set of orbital elements is a snapshot, at a
particular time, of the orbit of a satellite. Epoch is
simply a number which specifies the time at which
the snapshot was taken
Orbital Inclination
• [aka "Inclination" or "I0"]
• The orbit ellipse lies in a plane known as the
orbital plane. The orbital plane always goes
through the center of the earth, but may be tilted
any angle relative to the equator. Inclination is the
angle between the orbital plane and the equatorial
plane. By convention, inclination is a number
between 0 and 180 degrees.

Right Ascension of Ascending Node
• [aka "RAAN" or "RA of Node" or “RAAN", and
occasionally called "Longitude of Ascending
Node"]
• Right ascension is another fancy word for an
angle, in this case, an angle measured in the
equatorial plane from a reference point in the sky
where right ascension is defined to be zero.
Astronomers call this point the vernal equinox.
• Finally, "right ascension of ascending node" is an
angle, measured at the center of the earth, from the
vernal equinox to the ascending node.

Apogee & Perigee

A few words about elliptical orbits... The
point where the satellite is closest to the
earth is called perigee, although it's
sometimes called periapsis or perifocus.
We'll call it perigee. The point where the
satellite is farthest from earth is called
apogee (aka apoapsis, or apifocus).

Argument of Perigee
• If we draw a line from perigee to apogee, this line
is called the line-of-apsides
(Sometimes the line-of-apsides is called the major-axis of the ellipse)

• The line-of-apsides passes through the center of
the earth. We've already identified another line
passing through the center of the earth: the line of
nodes. The angle between these two lines is called
the argument of perigee
• Where any two lines intersect, they form two
supplementary angles, so to be specific, we say
that argument of perigee is the angle (measured at
the center of the earth) from the ascending node to
perigee.

Cont…
• In simple words the polar angle locating
the perigee point of a satellite in the orbital
plane; drawn between the ascending node,
geocenter and perigee and measured from
ascending node in direction of satellite
motion.

Eccentricity
• [aka "ecce" or "E0" or "e"]
• Eccentricity tells us the "shape" of the ellipse.
When e=0, the ellipse is a circle. When e is very
near 1, the ellipse is very long and skinny.
Mean Motion
• [aka "N0"] (related to "orbit period" and
"semimajor-axis")
• Now we need to know the "size" of the orbit
ellipse. In other words, how far away is the
satellite?

• Kepler's third law of orbital motion gives us a precise
relationship between the speed of the satellite and its
distance from the earth. Satellites that are close to the earth
orbit very quickly. Satellites far away orbit slowly. This
means that we could accomplish the same thing by
specifying either the speed at which the satellite is moving,
or its distance from the earth!
• Satellites in circular orbits travel at a constant speed.
Simple. We just specify that speed, and we're done.
Satellites in non-circular (i.e., eccentricity > 0) orbits move
faster when they are closer to the earth, and slower when
they are farther away. The common practice is to average
the speed. You could call this number "average speed", but
astronomers call it the "Mean Motion". Mean Motion is
usually given in units of revolutions per day

• In this context, a revolution or period is defined as
the time from one perigee to the next.
• Sometimes "orbit period" is specified as an orbital
element instead of Mean Motion. Period is simply
the reciprocal of Mean Motion. A satellite with a
Mean Motion of 2 revs per day, for example, has a
period of 12 hours.
• Sometimes semi-major-axis (SMA) is specified
instead of Mean Motion. SMA is one-half the
length (measured the long way) of the orbit
ellipse, and is directly related to mean motion by a
simple equation.
• Typically, satellites have Mean Motions in the
range of 1 rev/day to about 16 rev/day

Mean Anomaly
• [aka "M0" or "MA" or "Phase"]
• Now that we have the size, shape, and orientation
of the orbit firmly established, the only thing left
to do is specify where exactly the satellite is on
this orbit ellipse at some particular time.
• Anomaly is yet another astronomer-word for
angle. Mean anomaly is simply an angle that
marches uniformly in time from 0 to 360 degrees
during one revolution. It is defined to be 0 degrees
at perigee, and therefore is 180 degrees at apogee.

Drag
• [aka "N1"]
• Drag caused by the earth's atmosphere causes
satellites to spiral downward. As they spiral
downward, they speed up. The Drag orbital
element simply tells us the rate at which Mean
Motion is changing due to drag or other related
effects. Precisely, Drag is one half the first time
derivative of Mean Motion.
• Its units are revolutions per day per day. It is
typically a very small number. Common values for
low-earth-orbiting satellites are on the order of
10^-4. Common values for high-orbiting satellites
are on the order of 10^-7 or smaller.

Kepler Orbital Parameters
(Kepler Elements)
• Ω – right ascension of ascending node
• i – inclination of orbital plane
• ω – argument of perigee
• a – semimajor axis of orbital ellipse
• e – numerical eccentricity of ellipse
• T0 – epoch of perigee passage
Ref:
www.amsat.org/amsat/keps/kepmodel.html#argp
www.amsat.org/amsat/ftp/keps/current/amsat.all

Contents
•
•
•
•
•
•
•
•
•
•

Orbital perturbations
Types of Orbital Perturbations
The Non-Spherical Earth
Atmospheric Disturbances
Solar Radiation & Solar Winds
Third Body Interaction
Attitude Perturbations
Aerodynamic Pressure
Solar Pressure
Earth Magnetic Field

Orbital perturbations
• In this chapter we will discuss the most
important disturbances. This is necessary to
do because we want to know the lifetime of
the satellite before it will tumble down to
earth.
• We will also see how the orbit changes due
to the different disturbances.
• One important thing to remember is that
these calculations are for a cause to do the
predicted orbit and lifetime more accurate.

Types of Orbital Perturbations
• There are two types of Orbital
Perturbations

– gravitational, when considering third body
interaction and the non-spherical shape of
the earth.
– non-gravitational like atmospheric drag,
solar-radiation pressure and tidal friction.

• These can also be classified as conservative or
non-conservative disturbances forces. Where
conservative forces depends only on the position,
while non-conservative forces depends on both
position and velocity.

The Non-Spherical Earth
• The earth is far away from perfectly
spherical.
• One depends on the rotation, making the
radius from center of the earth to the
equator larger than from the center of the
earth to the poles.
–
–
–

Gravitation potential
Gravity harmonics
Force approach

Atmospheric Disturbances
• Although the atmosphere is almost empty you
have to consider it. This is the most
important disturbance, because it is the main
cause in determining the lifetime of the
satellite.
• The drag that can be calculated is an
empirical function based on Cd which is a
constant depending on the shape of the body.
• The also necessary density of the atmosphere
depends on some different environmental
factors such as the activity of the sun. The
major part of the atmosphere below 1000 km
consists of O2, N2, and He.

• The minor representative parts are O3, CO2,
H2, NO,electrons, and both positive and
negative ions.
• The difficulty to determine the density is
because of the chemical reactions especially
photochemical reactions. These are driven by
the sunlight, and therefore the activity of the
sun is important.
• The other chemical reaction in the
atmosphere is diffusion. The minor
constituents are controlled by photochemical

• In this case we use a mean value of the
density.

CD is the drag coefficient depending on the shape and
surface but the best value is given in an actual test
flight. But the value for a sphere is 2.2 and for a
cylinder it is 3.0. Usually 2.2 is considered to give a
conservative result.

Solar radiation and solar wind
• Solar radiation is all kind of electromagnetic
field emitted by the sun, from X-rays to radio
waves.
• The solar wind consists of particles emitted
by the sun, mainly ionized nuclei and
electrons.
• Because of the charged particles in the solar
wind it does not penetrate the magnetopause,
except at the magnetic poles. The
magnetopause starts about 10 earth radii
from the center of the earth (Re = 8371) km.
Therefore, the sun is more or less active. It
has an activity cycle of 22 years between two

• Therefore the solar pressure is also not
constant, but it fluctuate by <1%. The
pressure is, P0 = 4.7 ·10-6 [Pa]. The
perturbing forces can be calculated by:

• The effect due to the solar radiation
pressure is, for a LEO, not that big.
• The aerodynamic drag has a more
disturbing effect. But at altitudes above
1000 km and an orbit close to the
ecliptic plane it has a more distinct
effect.

Third body interaction
• How do the other planets disturb the
satellite?

Attitude Perturbations
• The disturbance in orientation or
attitude is important to look at
because we want to keep the
orientation so it can perform the tasks
• Here we consider the atmospherically
drag, the solar pressure and the
magnetic disturbance.

• Aerodynamic Pressure

– The pressure due to the atmosphere affects
the satellite, although one often think of
space as a vacuum it has, or at least the
environment where the satellite operates,
has some kind of atmosphere. If the center
of pressure of the body is different from the
center of mass, the pressure acts on the
body and the resultant of the forces is not
through the center of mass and there are a
torque due to the atmosphere. The force on
a differential area can be expressed by;

Solar Pressure
• Just like the pressure from the
atmosphere a torque due to solar
pressure act on the satellite. The
pressure of the the sun and the
difference of the center of pressure and
the center of mass causes a torque on
the satellite. The force on a differential
area can be described with;

The total torque can be found in the same way as for
the atmospheric torque.

Earth Magnetic Field
• The magnetic field of the earth has two ways
of disturbing the satellite. The first is when
the satellite rotates in a magnetic field. The
magnetic field induces eddy currents in the
shell and due to the resistance of the shell it
produces heat. The energy it takes to
produce the heat is taken from the rotational
energy but the effects are very small. In this
case when we have a short life cycle of the
satellite we do not have to take this aspect
in our calculations. The torques due to eddy
currents are;

• where ke is a constant depending on the
satellite’s geometry (see table) and
conductivity, B is the vector of the
magnetic strength of the earth

Contents
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•
•
•
•

When are satellites visible?
Factors Affecting the satellite visibility
Orbit & Attitude Inclination
Earth Shadow
Ground Track
Other factors

Limit of Visibility
• When Are Satellites Visible?
• Whether or not a satellite is visible to a
given observer is dependent upon many
factors such as observer location, time
of day, satellite altitude, and sky
condition. Knowing these details may aid
an observer in determining the most
favorable times for sightings and is most
certainly necessary

Factors Affecting Satellite Visibility
• Orbit Altitude And Inclination
• Earth's Shadow
• Ground Track
• Other Factors

Orbit Altitude & Inclination
•
•
•
•

GEO
MEO
LEO
HEO

Earth's Shadow
• The Earth's shadow must also be
considered. When eclipsed, a
satellite is naturally not visible.
Such events are dependent upon
the satellite's altitude, inclination,
the time of year, and the
observer's location

Ground Track
• Precession Of course it is not simply a question of
watching for a given satellite at the same time each
night. Few satellites have an orbital period which is a
simple fraction of one day, the geostationary satellites
being the obvious exception. The orbital period is
dictated by the satellite's altitude. The higher the
altitude, the further it has to travel around the Earth
and the longer it thus takes. Satellites in low Earth orbit
complete one orbit in around 90 minutes, whereas at
geostationary altitudes (about 36,000 km) one orbit
takes 24 hours.
• Many satellites in low Earth orbit go through a similar
cycle of visibility. The cycle varies with orbital
inclination, altitude, and observer location.

Other Factors
• satellite suffers greater air resistance
the lower its orbit. This bleeds off the
orbital energy, lowering the orbit yet
further as the satellite begins to brush
the upper atmosphere at perigee.
• The forces on the satellite due to the
Earth (and Moon, Sun, etc.) vary
throughout its orbit giving rise to
continual change in the orbit.

Contents
• Introduction
• Atmospheric Losses
–
–
–
–
–
–
–

Beam-spreading Loss
Polarization Loss
Rayleigh fading
Scintillation Loss
Free-space loss
Weather Loss
Doppler Effect

• Rain Attenuation
• Ionospheric Losses

Introduction
• This section discusses the basic effects of the
propagation anomalies as they influence the
communication satellite system performance
• The greatest difference between the bands
above 10 GHz and those between 1 and 10 Ghz
• The 1-10 GHZ range is already extensively
used by both terrestrial microwave and satellite
services.although the noise level and
attenuation are lower than the higher
frequencies, the potential for interference from
terrestrial point-to-point services has limited
earth station locations.

• Above 10GHz the rain attenuation increases,
but the chances of interference with other
services are minimum.
• At certain wavelengths signals encounter
absorption bands due to atmospheric
components (like water vapor and oxygen)
within the range of 1-10 GHz
• Frequencies above 30GHz have been
underutilized, there is spectrum available,
especially for services that do not pass through
the atmosphere like ISL(Inter Satellite Link)

• The fundamental equation for the free-space
position of the slant range losses(Lrange) is;
Lrange = (4Π S/λ )2
where;
S= Slant Range in m
λ =Wavelength in m

•

At 6GHz the slant range attenuation is about
200db

Atmospheric Losses
• In satellite communications, atmospheric
losses results from the absorption of the
Earth-satellite or satellite-Earth signals as
they pass through the Earth's atmosphere.
The value of the atmospheric loss is
strongly dependent on frequency.

Atmospheric Losses
– Beam-spreading Loss
– Polarization Loss
– Rayleigh fading
– Scintillation Loss
– Free-space loss
– Weather Loss
– Doppler Effect

Beam-spreading loss
• In satellite communications, beamspreading loss results from the spreading of
the earth-satellite signals as they pass
through the Earth's atmosphere

Scintillation loss
• In satellite communications, scintillation
loss results from rapid variations in the
signal’s amplitude and phase due to
changes in the refractive index of the
Earth's atmosphere.

Polarization loss
• In satellite communications, polarization
loss results from a rotation of the
polarization of the signal as it passes

Rayleigh Fading
• Rayleigh fading is fading in a satellite
communications channel due to the interference
caused to the main signal by the same signal
arriving over many different paths, resulting in
out-of-phase components incident at the receiver.
• Rayleigh fading occurs commonly in wireless
communications channels, including satellite
communications channels.

Free Space Losses
• In satellite communications, free-space loss is the
major loss suffered by signals in traveling over
the Earth-satellite path. The loss is inversely
proportional to the square of the distance traveled
and inversely proportional to the square of the
frequency used. That is, as the distance is doubled
the received power is reduced by a factor of four.
Similarly, as the frequency is doubled the received
power is reduced by a factor of four.
• Free-space loss for geo-stationary satellite
communications satellites varies between 190-210
dB depending on the frequency used

Weather Losses
• In satellite communications, weather loss
results from attenuation of the Earthsatellite signals by hydrometers as they pass

Brightness Temperature of the Earth

14 GHz (ESA/EUTELSAT-Modell)

Doppler Effect
• The Doppler effect in satellite communications is
the change in frequency of an electromagnetic
signal that results from the relative speed of the
satellite and the Earth terminal. When the
orbital parameters of a satellite are known,
Doppler shift can be used to determine the
position of the Earth terminal. When an Earth
terminal's position is known, Doppler shift can
be used to estimate the orbital parameters of a
satellite. When the satellite (or the Earth station)
is moving quickly, the Doppler effect is an
important consideration in satellite
communications

Atmospheric and Rain Attenuation

Rain Attenuation
• Rain is predominant loss element below
60GHz.
• Fog is shown has attenuation 0.1 g /m3
• The total link attenuation is the sum of the
losses due to slant range , the atmosphere,
precipitation and any additional losses(such
as scintillation etc.)

Climatic Zones

A: is extremely dry climate, . . . P: extremely humid climate

Climatic Zones
A
C

C
D

K
E
H

K
E

M

E

P H

H
P
H

E
E

C
D

K

K

P

D

N

C
E

P

H
D

E

F

P
N
E

F

D
M
K

A

Atmospheric and Rain Attenuation
20 mm/h

Rain Attenuation
10 mm/h
100

Equatorial
Latitudes

Additional Attenuation
in dB

10

100

10

Ionospheric
Delay

1

Atmosph.
Attenuation

Medium
Latitudes

1


5
GHz

Frequency in GHz

Ionospheric Losses
• Al lower frequencies (e.g 1.5 and 2.5 GHz)
ionospheric effect may be encountered,
particularly scintillation.
• The magnitude of these losses vary
considerably with the time of day and the
sunspot activity level (the affect the
ionosphere).

Ionospheric Losses
• All radio waves propagated over ionospheric paths
undergo energy losses before arriving at the receiving
site. As we discussed earlier, absorption in the
ionosphere and lower atmospheric levels account for
a large part of these energy losses.
• There are two other types of losses that also
significantly affect the ionospheric propagation of
radio waves. These losses are known as ground
reflection loss and free space loss.
• The combined effects of absorption, ground
reflection loss, and free space loss account for most of
the energy losses of radio transmissions propagated
by the ionosphere

Contents
•
•
•
•
•
•
•
•

Polarization
Types of Polarization
Antenna polarization
Manual Polarization Switching
Polarization of satellite signals
Depolarization
Cross polarization discrimination
Ionospheric depolarization, rain & ice
depolarization
• XPD and Co-Polar Attenuation
• Ionospheric Effect

Polarization
• The polarization of an electromagnetic wave
is defined as the orientation of the electric
field vector. Recall that the electric field
vector is perpendicular to both the direction
of travel and the magnetic field vector.
• The polarization is described by the
geometric figure traced by the electric field
vector upon a stationary plane perpendicular
to the direction of propagation, as the wave
travels through that plane.

Cont…
• Polarization is also describe as the "direction of
vibration" on the radio wave.
• It depends the orientation of elements of an antenna,
when you set elements vertical, it generates verticalpolarized radio wave similarly when you set as
horizontal, it generates horizontal-polarized.
• In the case of YAGI antenna, the direction of
Electronic-Field is same as the direction of its
elements.
• Radio stations have to set as a same direction of
polarization for communication each other.

Types of Polarization
• An electromagnetic wave is frequently composed of
(or can be broken down into) two orthogonal. This
may be due to the arrangement of power input leads
to various points on a flat antenna, or due to an
interaction of active elements in an array, or many
other reasons.
• The geometric figure traced by the sum of the electric
field vectors over time is, in general, an ellipse as
shown in Figure 2. Under certain conditions the
ellipse may collapse into a straight line, in which case
the polarization is called linear.

Cont…
• In the other extreme, when the two components are
of equal magnitude and 900 out of phase, the ellipse
will become circular as shown in Figure 3. Thus linear
and circular polarization are the two special cases of
elliptical polarization. Linear polarization may be
further classified as being vertical, horizontal, or
slant.

Cont…
• Polarization makes the beam more concentrated
• FSS satellites use horizontal and vertical
polarization, whereas DBS satellites use left- and
right-hand circular polarization
• To use the channels that are available for satellite
broadcast as efficiently as possible, both horizontal
and vertical polarization (and left- and right-hand
circular polarization) can be applied simultaneously
per channel or frequency. In such cases the
frequency of one of the two is slightly altered, to
prevent possible interference

Cont…
• Horizontal and vertical transmissions will therefore
not interfere with each another because they are
differently polarized. This means twice as many
programs can be transmitted per satellite
• Consequently, via one and (almost) the same
frequency the satellite can broadcast both a
horizontal and a vertical polarized signal (H and V), or
a left- and right-hand circular polarized signal (LH
and RH).

Radio stations have to set as a same direction
of polarization for communication each other.
• When you try to hear the vertical-polarized
wave with horizontal- polarized antenna,
what will be happened? A theory tells it is
impossible to receive. In fact, although it is
possible, It becomes very difficult (very weak
less than -20dB ). This is due to:– The radio waves do not travels with pure-polarized
condition, and
– There is no real antenna that has pure-polarized
character. Anyway, you should to adjust the
polarization for better communication.

Is Circular Polarization better choice for
satellite?
• Circular-polarization (CP) is another choice when
you could not decide the polarization of your
choice.
• CP is the special style of polarization, the
direction of Electric-Field rotates one times par
one cycle.
• The CP antenna can receive both horizontal and
vertical polarized radio wave, even in the
direction of slant-polarized.
• CP is very popular technique for satellite
communication both commercial and amateur
satellite systems.

Antenna Polarization
• Table 1 shows the theoretical ratio of power
transmitted between antennas of different
polarization. These ratios are seldom fully
achieved due to effects such as reflection,
refraction, and other wave interactions, so
some practical ratios are also included.

Cont…
• The sense of antenna polarization is defined from a
viewer positioned behind an antenna looking in the
direction of propagation. The polarization is specified
as a transmitting, not receiving antenna regardless of
intended use.
• We frequently use "hand rules" to describe the sense
of polarization. The sense is defined by which hand
would be used in order to point that thumb in the
direction of propagation and point the fingers of the
same hand in the direction of rotation of the E field
vector.

Cont…
• For example, referring to Figure 4, if your thumb is
pointed in the direction of propagation and the
rotation is counterclockwise looking in the direction of
travel, then you have left hand circular polarization.
• The polarization of a linearly polarized horn antenna
can be directly determined by the orientation of the
feed probe, which is in the direction of the E-field.

Cont…
• In general, a flat surface or sphere will reflect a
linearly polarized wave with the same polarization as
received. A horizontally polarized wave may get
extended range because of water and land surface
reflections, but signal cancellation will probably result
in "holes" in coverage. Reflections will reverse the
sense of circular polarization.

Cont…
• For a linearly polarized antenna, the radiation
pattern is taken both for a co-polarized and cross
polarized response.
• The polarization quality is expressed by the ratio
of these two responses. The ratio between the
responses must typically be great (30 dB or
greater) for an application such as cross
polarized jamming
• For general applications, the ratio indicates
system power loss due to polarization mismatch.
• For circularly polarized antennas, radiation
patterns are usually taken with a rotating linearly
polarized reference antenna.

Manual Polarization Switching
• The CP antenna reduces QSB so it might be better
for comfortable operation, but the CP antenna is
bigger and more complicated than the simple linearpolarized antenna. Also the big and complicated
antenna will be expensive. 3dB loss will be a problem
with some limited conditions.
• There is another choice. Setup a pair of
vertical/Horizontal polarized independent antenna
and switch them at your shack. You select where
either is better during its pass. This is the theory of
"Divercity" reception

Polarization of satellite signal
• Applied for geo-stationary satellites
• “Horizontal”polarization = parallel to the
equatorial plane
• “Vertical”polarization = parallel to the Earth's axis
• Polarization angle at earth station

–
–
–
–
–

r = local gravity direction
k = the direction of the wave propagation
p = unit polarization vector
f = k x r, normal to the reference plane
x = the angle between the reference plane
(r and k) and the polarization vector

Depolarization
• The electric field E1 is depolarized after going
through a depolarizing medium.
• The result is, as shown in the figure, an
orthogonal (E12) component may be
generated.
• E11 is called the co-polar component and E12
is called the cross-polar component.
• This phenomenon can cause interference.

Cross-Polarization Discrimination (XPD)
• One measure to quantify the effects of
polarization is called the cross-polarization
discrimination (XPD)

Cross-polarization discrimination
observations - rain depolarization
• Looking at XPD as a function of the co-polar
attenuation (A), it can be concluded that:
– XPD degrades at a given co-polar attenuation as
the frequency decreases
– XPD degrades with increasing co-polar attenuation
– XPD for the Vertical Polarization wave is better
than that for Horizontal Polarization
– XPD for the Vertical Polarization and the Horizontal
Polarization waves are better that the Circular
Polarization

XPD and co-polar attenuation A

θ -> the elevation angle in
degrees
τ −> the polarization tilt angle
τ = 45 for circular polarization

Ionospheric effects
• Faraday’s effects
– The rotation of a linearly polarized
wave due to the earth’s magnetic
field is called the Faraday’s
effect. It is proportional to the
1/f2 factor.

• Ionospheric scintillation
– Due to the refractive index
variations in the ionosphere caused
by local concentrations of
ionization. It is also proportional
to the 1/f2 factor.

Contents
•
•
•
•
•
•
•
•
•

Antenna
Some Basic Definitions
Radiation Parameters
Radiation Patterns
Types of Radiation Patterns
Antenna Radiation Pattern Nulls & Lobes
Antenna Beamwidth
Types of Ground Station Antenna used in SatCom
Types of Space Segment Antenna used in SatCom

Antenna
• Antennas form a very important element in communication
system, either terrestrial or extra terrestrial, depending on the
mission type and requirements
• "That part of a transmitting or receiving system which is
designed to radiate or to receive electromagnetic waves".
• we use antennas to overcome our inability to lay a physical
interconnection between two remote locations or an antenna
can also be viewed as a transitional structure (transducer)
between free-space and a transmission line (such as a coaxial
line).
• Antennas cannot add power, instead they can only focus and
shape the radiated power in space e.g. it enhances the power
in some wanted directions and suppresses the power in other
directions

Some Basic Definitions
• Suppose we have an antenna
located at the origin of a spherical
co-ordinate system, further
assume that the antenna is
transmitting and the observations
are made for a very large distance;
• Let Po (Watts) be the accepted
power in the antenna and Pr
(Watts) be the radiated power,
then the radiating efficiency ή as;

• ή = Pr / Po

z
θ
Ant
Location

ç
z

r

P

y

Radiation Intensity
• We define Radiation Intensity f (θ,Ф) or Θ(θ,Ф)
(watts/steradians)
Pr =
• The Average radiation intensity is;
Θavg = Pr / 4π

Antenna Directivity
(Measure of the focusing property of an antenna)
•

•

"The directivity of an antenna is defined as the ratio of the radiation
intensity in a given direction from the antenna, to the radiation
intensity averaged over all directions.
This average radiation intensity is equal to the total power of the
antenna divided by (4 pi). If the direction is not specified, the
directivity refers to the direction of maximum radiation intensity".

D (θ,Ф) = {Θ(θ,Ф) / Θavg}
or
D (θ,Ф) = 4π {Θ(θ,Ф) / Pr}
≈ θ is the elevation angle
≈ φ is the azimuth

•

where D is the directivity. Generally D > 1, except in the case of an
isotropic antenna for which D = 1. An antenna with directivity D
>> 1 is called a directive antenna.

Gain (Measure of Directivity)
• The Gain G(θ,ф) is the ability to concentrate the power
accepted by the antenna in a particular direction. It is
related to the Directivity and Power Radiation efficiency
or in other words Power Radiation Intensity as follow;
G(θ,ф)= ή D(θ,ф)
for loss less antenna ή =1

G(θ,ф)=4π{Θ(θ,Ф) / Pr}
• With respect to the antenna's
dimensions,
G= ή{4πA / λ2}
A is the aperture area of the antenna
λ is the wavelength of the operational
frequency
η is the antenna efficiency (usually between

Cont…
• Basically there are only two types of antennas:
• dipole antenna (Hertzian)
• vertical antenna (Marconi)

• All antennas can be broken down to one of
these types (although some say that there is
only one - the dipole)
• In addition to this we have a theoretical
perfect antenna (non-existent) that radiates
equally in all directions with 100% efficiency.
This antenna is called an isotropic radiator.

Gain presented as 3D gain

The gain can also be presented as a 3D gain.
The radius of the spheroid is proportional to
the antenna gain.

Gain in theory
• Since all real antennas will radiate more in
some directions than in others, you can say
that gain is the amount of power you can
reach in one direction at the expense of the
power lost in the others. When talking about
gain it is always the main lobe that is
discussed
• Gain may be expressed as dBi or dBd. The
first is gain compared to the isotropic radiator
and the second gain is compared to a halfwave dipole in free space (0 dBd=2.15 dBi)

Power Density
• The power density P(θ,ф) is related to
radiation intensity as follows;
P(θ,ф)= {Θ(θ,Ф) / r2}
or
P(θ,ф)= {G(θ,Ф) Po/ 4πr2}
• The factor Po/ 4πr2 represent the power
density that results if the power accepted by
the antenna were radiated by loss-less
isotropic antenna

Equivalent Isotopic Radiated Power
(EIRP)
• The maximum power flux density at some distance
“r” from a transmitting antenna of gain “G” is;

• An isotropic radiator with input power equal to GPS
would produce the same flux density. Hence,

Antenna Effective Area
• Measure of the effective absorption area
presented by an antenna to an incident plane
wave.
• Depends on the antenna gain and wavelength

λ
2
Ae =
G (ϑ , ϕ ) [m ]
4π
2

• Aperture efficiency: ηa = Ae / A

A: physical area of antenna’s aperture, (m2)

Transmission losses
• Free Space Transmission [FSL]
– More to follow

• Feeder Losses [RFL]
– Between the receive antenna and the
receive proper

• Antenna Misalignment Losses [AML]
• Fixed Atmospheric & Ionospheric
Losses
– Absorption losses
– Depolarization losses

Power transfer between two antennas
• For two antennas in free space separated by large
distance R
• The received power is equal to a product of
power density of the incident wave and the
effective aperture area of the receiving antennas
Pr = PAe
or
Pr = {(GtPtGrλ2) / (16π2R2)}

Antenna Bandwidth
•

•

•

•

The bandwidth of an antenna is defined as ”The range of
frequencies within which the performance of the antenna, with
respect to some characteristic, conforms to a specified standard”.
The reason for this qualitative definition is that all the antenna
parameters are changed with frequency and the importance of the
different parameters as gain, return loss, beamwidth, side-lobe
level etc. much depends on the application.
For example, the bandwidth of an antenna for gain (-1dB from the
maximum) is defined as

where fU is the upper frequency, fL is the lower frequency, and fC is
the center frequency. Another example is the bandwidth related to
the mismatch loss defined by the SWR .

Reciprocity
•

•

ALL the major properties of a linear passive antenna are identical whether it
is used in transmit or receive mode. There is only one exception to this rule
called "reciprocity", and that is when the antenna contains magnetically
biased magnetic materials such as ferrites with resonantly rotating electron
spin systems.
The physical reason for reciprocity is that the only difference between
outgoing and incoming waves lies in the arrow of time. Since the
electromagnetic equations are invariant except for the signs of magnetic
fields and currents, under time reversal, there can be no difference between
transmit and receive mode in the physical current and field distributions.
However, if we have a magnet providing a steady bias field, under time
reversed conditions we would have to reverse the direction of this bias field.
But for incoming and outgoing waves, the bias field direction remains the
same. Thus it is possible for the system to be non-reciprocal.

Cont…
• Of course, antennas containing amplifiers, or diodes,
or spark gaps, may well not be reciprocal for obvious
reasons. Also, practical antenna installations having
metal-oxide-metal contacts, "rusty bolts", dry
soldered joints and other electrical contact
imperfections are also likely to behave differently
under transmit and receive modes of operation

• Radiation Pattern measurement
– Graphical representation of the field magnitude at
a fixed distance from an antenna as a function of
direction i.e. angular variation of the test antennas
radiation.

• Gain measurement
– Absolute measurement that gives the angular
variation of the test antenna’s radiation. Needed to
fully characterize the radiation properties of the
test antenna.

• Polarization
– Defined as the polarization of the electromagnetic
wave radiated by the antenna along a vector
originating the antenna along the primary
direction of propagation. The direction of the
oscillating electrical field vector i.e. orientation of
the E-filed.
– Four basic types of polarization
Vertical-, horizontal-linear polarization and Lefthand elliptical, Right-hand elliptical polarization.

Radiation Pattern
• Radiation pattern
characteristics/parameters:
–
–
–
–
–
–

Half-power beam width
Main lobe
Side lobes
Antenna directivity
Gain function
Boresight (Direction
of maximum gain)
– Polarization
– Distortion
– XPD(cross polarization

Radiation Pattern
• Antenna radiation pattern is three-dimensional, but is
needed to describe them as two-dimensional paper. The most
popular technique is to record signal level along great circle
or conical cuts through the radiation pattern. In other words,
one angular coordinate is held fixed, while the other is varies.
• Radiation Pattern = Radiation Intensity as function of the
azimuth/ elevation angles
or
In different words when power radiation intensity and power
density are presented as relative scale, they are referred to as
antenna radiation pattern.
• A family of such two-dimensional patterns then can be used
to describe the complete three dimensional patterns
• The main lobe of the radiation pattern is in the direction of
maximum gain

Types of Radiation Pattern
• There are many types of antenna
radiation patterns, most common are;
• Omnidirectional (azimuthal plane)
beam
• Pencil beam
• Fan beam
• Shaped beam

Omnidirectional Antenna and Coverage
Patterns
The Omnidirectional beam is most popular in
communication and broadcast applications. The
azimuthal pattern is circular, but the elevation pattern
will have some directivity to increase the gain in the
horizontal directions

Pencil Beam
Pencil beam is applied to a highly directive antenna
pattern consisting of a major lobe contained with in it
cone of small solid angle. Usually the beam is circularly
symmetric about the direction of peak intensity

Fan Beam
A fan beam is narrows in one direction and wide
in the other. A typical use of a fan beam would
be in search or surveillance radar

Shaped Beam
Shaped beams are also used in search and surveillance

Cont…
•

•
•

•

Radiation patterns generally defined as the far field power or field
strength produced by the antenna as a function of the direction
(Azimuth and elevation) measured from the antenna position. The
behavior of the fields is changed with the distance from the antenna,
and generally three regions are defined:
Reactive near-field region - The region in the space immediately
surrounding the antenna in which the reactive field dominated the
radiating field (d <λ/(2π)).
Radiating near-field region - Beyond the former region and for which
d <2D2/ λ where r is the distance from the antenna, D is the largest
dimension of the antenna and λ is the wavelength. This region is
called also Fresnel region. In this region the radiating field begins to
dominate.
Far-field region - Beyond this region, the reactive field become
negligible and also the radial part of the fields. This region is called
also Fraunhofer region.
– Generally measurements are taken in the far field region. In case of
large planar antennas it is more convenient to make near field
measurements and to calculate the far field.

Antenna Radiation Pattern Lobes and Nulls
• A radiation lobe can be defined as a portion of
radiation pattern bounded by regions of relatively
weak radiation intensity. The main lobe is a high
radiating energy region. Other lobes are called
sidelobes, and the lobe radiating in the counter
direction to the desired radiation direction is called
back lobe. Regions for which the radiation is very
weak are called nulls.

Antenna Beamwidth.
• Antenna beamwidth is defined as the angle θ
between half power points on the main
beam. In case that we have a power pattern
in [dB] units, it means that we measure the
angle between two 3dB points.

Measuring E and H field of antenna

Half-power beam width
• It is the angular beam width
at 3 dB. It can be
approximated as,

• D is the antenna's diameter.
∀ λ is the operational
wavelength.

Short Dipole in Free Space FF
1

H

V
Relative Gain

1
-1
0
0

90

180

270

360

Degrees

Horizontal plane: GVi /GVimax = 1
Vertical plane: GHi /GHimax = |sin θ|

Elements of Radiation Pattern
Main lobe
Emax

•
•
Emax /√2
•
Nulls
•

Sidelobes

-180

0
Beamwidth

Gain
Beam width
Nulls (positions)
Side-lobe levels
180 (envelope)
• Front-to-back ratio

Antenna Mask (Example 1)
0

-10
-15

180

120

60

0

-60

-120

-20
-180

Isotropic gain, dB

-5

• Typical
relative
directivitymask of
receiving
antenna (Yagi
ant., TV dcm
waves)

Azimith angle, degrees
[CCIR doc. 11/645, 17-Oct 1989)

Antenna Mask (Example 2)
0

0dB

RR/1998 APS30 Fig.9
-10

Relative gain (dB)

COPOLAR
-20

-3dB

Phi0/2
Phi

-30

-40

CROSSPOLAR

-50
0.1

1

10

100

Phi/Phi0

Reference pattern for co-polar and cross-polar components for satellite
transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz)

Types of Ground Antennas Used
in Satellite Missions

• Different satellite missions have different allotted frequency slots
by ITU, each slot behaves differently between ground and earth
segment in terms of dispersion, attenuation and noise accumulation
• Generally at frequencies below 1GHz, TTT&C are running, the
antenna may then be arrays of dipoles, helices and yagi-uda arrays,
such type of antenna systems have wider beamwidth and medium
gain. Deploying them in an array pattern results in increased gain
and fanned and shaped beams thus enabling them for comparatively
easy tracking
• At frequencies above 1GHz the electromagnetic waves become
highly directional but more susceptible to attenuation, fading and
dispersion, therefore, horn and parabolic antennas are most
commonly used. The most popular and widely used are the aperture
antennas given bellow;

• Axially Symmetric Fed Antenna
– This is the most common type of antennas found on roof tops or
back yards of homes. They come in different configurations.
Axis symmetric point focus feed. Front feed and Vortex feed

• Cassegrain Feed Antenna
– The second common configuration used particularly in large
antennas is the Cassegrain antenna. Here the feed is located at the
vertex of the parabolid and illuminates a hyperbolic shaped subreflector located at the focal area. The benefit here is that the
electronics is located at a more accessible part of the antenna but
with some sacrifice in sidelobe level because of the blockage .

• Gregorian Feed Antenna
– In Gregorian configuration the feed is at the focal
point of an ellipse and the elliptical sub-reflector at its
other focus. With this configuration there is an
improvement in the far-outside lobe level

• Offset Aperture Antennas
– These configurations indicate that the feed are on
axis . The same generic types may also be used with
offset feeds. The removal of feed from a collimated
beam improves the side lobe level and has better
effect of reducing mutual interference from adjacent
satellites.

Crossed Yagi antennas for circular polarisation
and
right-handed and left-handed helical antennas

Cassegrain Feed Antenna

Comparison between the measured
antenna gain pattern and the predicted
one for small offaxis angles

Front Fed Antenna

A Front-Fed Offset Reflector Antenna with
Multiple-Feed Horns (Courtesy Alenia Spazio)

Satellite Antennas
• The physical dimensions of the spacecraft and the availability of
limited power restrict use of large antennas.
• Medium gain antennas are used instead which include modified
parabolic antennas for large area coverage
• In LEO missions, the satellite may be two axis stabilized, the
rotation being on the axis with largest inertia, the antenna gain
pattern may not remain uniform when received at the ground station.
Therefore, a rotating antenna whose rotation is in the opposite
direction of the satellite rotation is used, such type of antenna is
called “Despun antenna”
• Circular polarization may employed for TT&C purposes or image
transmission like weather satellite
• Helical antennas are used for circularly polarized EM wave pattern,
these antennas has larger beamwidth, therefore, tracking by the
ground station becomes easier

Satellite Antennas
• In GEO satellites, DVB and VSAT applications are dominant
• In broadcast services satellite has to cover larger area , linearly
polarized array antennas are used. For broadcast services the
transmitting antennas may consist of array of Horn Antennas, Helical
Antennas or Disk-on-Rod Antennas. Power beam form the antennas
can be steered to cover specific area on the earth’s surface by
switching on or off different antennas from the array on the satellite.

18 dBi X-band pyramidal horn antenna

Contents
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Introduction
General Architecture
Signal Power Calculation
EIRP
Noise Calculation
Thermal Noise
Effective Temperature
Noise Temperature
G/T
Link Analysis
Eb/No
Carrier Parameters
BER
Rain Attenuation and Margin

Introduction
Overall design of a complete satellite communications
system involves many complex trade-offs to obtain a costeffective solutions
Factors which dominate are
–Downlink EIRP, G/T and SFD of Satellite
–Earth Station Antenna
–Frequency
–Interference

General Architecture
EIRP down

Uplink

Downlink

G/T & SFD

Uplink Path Loss
Rain Attenuation

Downlink Path Loss
Rain Attenuation

EIRP Up

Gt

G/T ES

Pt

HPA / Transceiver

LNA / LNB

Transmit Earth Station
– Antenna Gain
– Power of Amplifier

Uplink
– Path Loss
– Rain Attenuation

Satellite
– G/T
– EIRP
– SFD

(Equivalent Isotropic Radiated Power)
(Saturated Flux Density)

– Amplifier Characteristic

Downlink
– Path Loss

Receiving Earth Station
– Antenna Gain
– LNA /LNB Noise Temperature
– Other Equipment

Antenna Gain
G = η (Π * d / λ) 2 [dBi]
Where,
λ=C/f,
C = Speed of light
f = frequency of interest
η = efficiency of antenna (%),
d = diameter of antenna (m)

Antenna Beam width
θ 3dB = 70 * C / df
Where,
C= 3x108 m/s (Velocity of Light)

[degrees]

EIRP
Is the effective radiated power from the
transmitting side and is the product of the
antenna gain and the transmitting power,
expressed as

EIRP = Gt + Pt –Lf
Where,
Lf is the Feed Losses

[dB]

Signal Power (Pr)
Pr = EIRP – Path Loss + Gr (sat)
[dB]
Where,
Path Loss = (4ΠD / λ) 2
D is the Slant Range (m)

Thermal Noise
Is the noise of a system generated by the random
movement of electronics, expressed as
Noise Power = KTB
Where,
K= (-228.6 dBJ/K)
T= Equivalent Noise Temperature (K)
B= Noise Bandwidth of a receiver

Te = T1 + (T2/G1)
Where,
T1= Temperature of LNA
T2= Temperature of D/C
G1= Gain of LNA

Noise Temperature
Ts = Tant / Lf+(1-1/Lf)Tf
Where ,
Tant = Temperature of antenna
Lf = Feed Losses
Tf = Feed Temperature

Tsys = Ts + Te
•
•
•

Being a first stage in the receiving chain, LNA is the
major factor for the System Temperature Calculation
Lower the noise figure of LNA lower the system
temperature
Antenna temperature depends on the elevation angle
from the earth station to satellite

G/T (Gain to System Noise Temperature)
– This is the Figure of merit of any receiving
system
– It is the ratio of gain of the system and
system noise temperature

G/T = G-10log (Tsys)

[dB/K]

Link Analysis
C/N Uplink
(C/N)u = (EIRP)e-(Path Loss)u+(G/T)sat-K-Noise BW

[dB]

C/N Downlink
(C/N)d = (EIRP)sat-(Path Loss)d+(G/T)e-K-Noise BW

[dB]

C/N Total
(C/N)T-1 = (C/N)u-1 + (C/N)d-1 + [C/I)IM-1 + [C/I]adj-1 + [C/I]xp-1

[dB]

Eb/No (Energy per bit per Noise Power Density)
– Is the performance criterion for any desire
BER
– It is the measure at the input to the
receiver
– Is used as the basic measure of how
strong the signal is
– Directly related to the amount of power
transmitted from the uplink station
Eb/No = (C/N)T + Noise BW – Information
Rate

Carrier Parameters
• Solution - Carrier Performance:
– Eb/No Threshold
– Bit Error Rate (BER)

Bit Error Rate (BER)
– Why is it used? - To represent the amount of errors
occurring in a transmission
- To express the link quality
– What is it?
- BER is an equipment characteristic
- BER is directly related to Eb/No
- BER improves as the Eb/No
gets larger

P = 1/2 e -Eb/No

(with P = Probability of error)

Carrier Parameters
• Performance:
– Application specific
• Digital voice links:
– BER threshold 10-3
• Data links:
- BER threshold: 10-4

Carrier Parameters
• Performance:
– Typical Eb/No values for different FEC

Eb/No for
FEC 1/2 (dB)

Eb/No for
FEC 3/4 (dB)

Eb/No for
FEC 7/8 (dB)

BER

6.5
7.1
7.6
9.9

8.0
8.7
9.2
11.0

9.1
9.7
10.4
12.1

10-6
10-7
10-8
10-10

Rain Attenuation
• Performance - Rain Attenuation:
– Availability
TO

• Rain Margins
– Typically 99.60 % for Ku-Band
– Typically 99.96 % for C-Band
E/S

• Performance - Additional Margins:
– Adjacent Satellite Interference (ASI)
– Interference Margins

SA

L
TE

E
LIT

Summary; Transmission Parameter for Link Budgets

C

= 10 log (c) in dBW

c = 100.1 C in W

N

= 10 log (n) in dBW

n = 100.1 N in W

C-N

= C - N in dB

EIRP = P + G - V in dBW
PL

= FD + AD + RD in dB

G-T

= G - T in dBi/K

N

= T + K + B in dBW

C ‑N
[dB]

= EIRP ‑ PL + G‑T K
‑ B
[dBW] [dB] [dBi/K] [dBWs/K] [dBHz]

Cont...
EIRP = P + G - V in dBW, Equivalent Isotropic Radiated Power
G-T

= G - T in dBi/K, Figure of Merit

PL

= FD + AD + RD in dB, Pathlosses

N

= T + K + B in dBW,Noise Power.
= No + B; No Noise Power Density dBW/Hz

C-N = C - N in dB, Signal to Noise Ratio
Eb-No =Energy per bit to noise power density, in dB
BER = Bit Error Rate, e.g.: 10-5

Contents
•
•
•
•
•
•
•
•
•
•
•
•
•

Interference in Satellites
Interference Types
Sources of Interference
Causes of Interference
FM Interference
Cross Polarization Interference
Digital & CW Interference
Intermodulation Interference
Raised Noise Floor
Spikes & Unknown
Adjacent Satellite Interference
Adjacent Transponder Interference
Co-Channel Interference

Interference in Satellite
• Interference is mainly concern on;
– Interference Type
– Sources of Interference
– Causes of Interference

Interference
Interference Type:
• Digital
• Spike
• Cross Polarization
• TDMA
• FM TV
• Intermodulation
• Unknown

Interference
Source of Interference:
•Neighboring Customer
•Adjacent Satellite
•Self-Customer
•Opposite Polarization
•Others
External Factors:

40.22%

Internal Factors:

59.78%

Interference
Causes of Interference:
•Human Error:

29.89%

•Equipment Error:

21.74%

•Adjacent Satellite:

16.85%

•Customer Cooperation:

8.15%

•Others:

23.37%

Internal Factors:

59.78%

Types of Interference
•
•
•
•
•
•
•
•
•

FM
Cross Polarization
Digital
CW
Intermodulation
Raised Noise Floor
TV/FM
TDMA
Spikes & Unknown

FM Interference
I

Base band

IF

Up converter

70 MHz

RF

HPA

6 GHz
FM signal:88 MHz to 108 MHz

70 MHz

6 GHz

FM Radio Signal

FM Interference
II
f (MHz)
70

f (MHz)
88

108

90

+

f (MHz)
70

IF

90

f (GHz)
6.0

RF

6.09

FM Interference
III
Source:
•

Terrestrial FM Radio Broadcast

•

Introduced at the IF level of the Earth Station

FM Interference
IV
Cause:
• Poor Connection between BB and RF
equipment, so FM broadcast is induced into
the system and eventually transmitted to the
satellite.
• Poor quality accessory between BB and RF
• Poor grounding system

FM Interference
V
Prevention:
•
•
•
•

Select accessories with standard specifications
Good Earth Station installation
Good grounding system
Coordinate with PCNS to perform UAT and
interference checking when a new station is
installed

Cross Polarization Interfrence
Source:
• If XPD level of an uplink antenna is less than
30 dB, antenna will transmit both vertical and
horizontal polarizations
• Therefore, cross pole will occur at the other
satellite or transponder with opposite pole and
will interfere the existing carrier

Cause:
• Poor antenna pointing
• Poor cross pole isolation
• Sudden change in the antenna pointing due to
mistake or storm
• Carrier uplink without performing proper UAT
with PCNS

Prevention:
• Do not uplink the carrier without
performing UAT with PCNS
• DO not uplink un-modulated carrier for
UAT before PCNS’s directions
• Perform Regular Preventive maintenance

Source:
• Earth Station Equipment

Cause:
• Transmission of wrong carrier frequency by the
user
• Unauthorized access
• Uplink CW for UAT before calling PCNS
• Equipment malfunction

Prevention:
• Verify U/L frequency before transponder
access
• Do not uplink un-modulated carrier (CW)
before PCNS directions
• Perform UAT
• Request PCNS if customer wants to uplink a
new carrier for special purpose at some vacant
slot
• Perform Preventive Maintenance periodically

Description:
• If more than one carrier are transmitted by a
single HPA, mixing or Intermodulation (IM)
processes take place
• This results in Intermodulation products which are
displaced from the carriers at multiples of the difference
frequencies
• The power level of the Intermodulation products are
dependent on the relative power level of the carrier and
the linearity of TWTA or SSPA

Description:
• The frequencies of the Intermodulation products are:

– 2f1-f2
– 2f2-f1

f1: frequency of carrier #1
f2: frequency of carrier #2

• It can occur at both E/S and Satellite

Cause:
• U/L power level of the each carrier is set so high that
the Intermodulation occurs
• U/L power level is increased without considering the
the possibility of intermodulation
• Increasing the U/L power without informing PCNS

How does it affects
• It reduces the Eb/No of your carrier using at the
same frequency
• May raise the Noise Floor of some slots
• Existing uplink power at E/S would be used more
than normal
• Therefore, you have to replace new RFT to get
more power when you would want to put new
carriers into it

Prevention:
• Verify the link budget of the station transmitting
more than one carrier before transponder access
• Aggregate input back-off for HPA or RFT at E/S
must be defined and informed to up linker
• Do not increase U/L power without informing
PCNS
• Do not operate with overused power

Raised Noise Floor
Source:
• Earth Station Equipment

Raised Noise Floor
Cause:
• E/S equipment configuration was not set up
properly
• The gain of U/L equipment such as U/C or HPA
was not set suitably
• The U/L power is too high

Raised Noise Floor
Prevention:
• Use good E/S setup
• Set suitable gain of E/S equipment
• Do not increase the U/L power without informing
PCNS
• Verify uplink noise level at the output of HPA
before transponder access

Spike and Unknown
Description:
• Unpredictable Frequency, Bandwidth, Time
• Some of them may occur at out of assigned
transponder

Spike and Unknown
Cause:
• Most of them are caused by the U/L equipment
error (both base band and RF equipment)
• It does not affect all carriers transmitted by itself

Spike and Unknown
Investigation:
• Only RF equipment such as U/C, HPA, Transceiver
needs turning off
• Turning of Base band equipment such as Modem,
Exciter, Modulator cannot prove the source of
interference

Spike and Unknown
Prevention:
• Perform Preventive Maintenance periodically
• Operate all U/L equipment under suitable conditions as
directed by operational manual of the equipment
• Find out root cause if it disappeared with unknown reason
or equipment reset in order to perform prevention

• Co-Channel Interference
Wanted Carrier

T x p 1 2 /1 2

T x p 2 2 /2 2

Unwanted Carrier

• TWTA Intermodulation
Wanted Carrier

Unwanted Carrier

…

T x p 1 2 /1 2

...

Transponder Parameters
• Intermodulation (IM)
– What is it?
– Why does it exist?

- Potential source of noise
- Different signals are sent
simultaneously

– How is it avoidable? - By reducing the
saturation E.I.R.P.
E.I.R.P.Operation = E.I.R.P.Saturation - OBO

• Adjacent Satellite Interference (ASI)
SATELLITE SPACING

SATELLITE ANTENNA

WANTED SIGNALS
UNWANTED SIGNALS

RADIO LINK

• Adjacent Transponder Interference
(Multipath)
1 -2

3 -4

R C V R

1 -2

S SP A

1 -2

IM U X

1 -2

. . .

S M
3 -4

S SP A

3 -4

3 -4

W H

. . .
S a te llite d is h

1 -2
O M U X
3 -4
W H

S a t e llit e d is h

S a te llite d is h
S a te llite d is h

• Satellite:
– Co-Channel Interference
– TWTA Intermodulation
– Adjacent Satellite
Interference
– Adjacent Transponder
Interference - “Multipath”

• Path Losses:
– Up link thermal Noise
– Down link thermal Noise

• Earth Station:
– HPA Intermodulation

• Outside:
– Sun Interference
– Terrestrial Interference

Contents
•
•
•
•
•
•
•
•
•
•
•

The sequence of signal processing and transmission
Multiplexing & Multiple Access
FDMA
TDMA
CDMA
Comparison in TDMA, FDMA & CDMA
Channel Coding & Modulation
Channel Reservation
Channel Coding
Modulation Techniques
The Baseband Eye Pattern

The Sequence of Signal Processing and Transmission
Transmission
Frequency Conversion
Modulation
Interleaver
Channel Coding
Multiplexing
Encryption
Source Coding
Digitization

Demodulation
De-Interleaving
Channel Decoding
Demultiplexing
Decryption
Source Decoding
Display

Signal processing and transmission
Digitisation

higher reliability, low cost, less susceptible to

Source Coding

to reduce bit rate for transmission

Encryption

for communications privacy

Multiplexing

for efficient transmission of multiple channels

ChannelCoding

for error free transmission

Interleaving

for robust error correction

Modulation

imparting baseband information to a carrier


to operate at radio frequencies

noise,

Multiplexing and Multiple
Access
• For the majority of data communications that take
place, there is a requirement for several users to share
a common channel resource at the same time.
• For multiple users to be able to share a common
resource in a managed and effective way requires
some form of access protocol that defines when or
how the sharing is to take place and the means by
which messages from individual users are to be
identified upon receipt. These sharing process come to
be known as multiplexing and multiple access in digital
communications.

Multiple Access and Multiplexing
•

Multiple Access:is the ability for several earth
stations to transmit their respective carriers
simultaneously into the same satellite
transponder

•

Multiplexing:is the reversible operation of
combining several information-bearing signals
to form a single, more complex signal.

Multiple Access and Multiplexing

Multiple Access
at radio frequency

Multiplexing
at baseband

TDMA

-

TDM

FDMA

-

FDM

CDMA

-

CDM

FDMA
• Used extensively in the early
telephone and wireless multiuser communication systems
• If a channel, such as a cable,
has a transmission bandwidth
W Hz, and individual users
require B Hz to achieve their
required information rate,
then the channel in theory
should be able to support W/B
users
• Near-Far problem

Frequency Division Multiple Access; FDMA

Uplink

Downlink

Guard
Band
...
f1

f2

f3.....

fM

f1

f2

f3

fM

Frequency

TDMA
• The basic principle behind time division multiplexing is
that the user has access to a modem operating at a
rate several times that required to support his own
data throughput, such that he can send his
information in a time slot that is shorter than his own
message transaction. Other users can then be
assigned similar time slots on the same channel.
Clearly if the data rate on the channel is
w bits/second, and each individual user requires only
b bits/second, then the system can support
w/b simultaneous users.
• In TDM systems, users are assigned a time slot for the
duration of their call whether they require it or not.

TDMA

TDMA

Near – Far Effect in TDMA

Example of a TDMA system
• The GSM digital cellular system is a very good
example of a TDMA

Time Division Multiple Access; TDMA

Upli
nk

Downlink
Guard
Time
...

t1

t2

t3.....

tM

t1

T2

t3

tM

Time

Time Division Multiplexing

...
burst1

to Joe

burst2

to Bill

burst3

to Tim

a coherent stream of data

burstn

to who?

Time Division Multiple Access; TDMA

Satellite communication (a tutorial)

Satellite communication (a tutorial)

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