Satellite Communications
Course Title
Satellites Communications
By: Lecturer. Elmustafa Sayed Ali Ahmed
Electrical and Electronics engineering Dept.
E-mail: elmustafasayed@gmail.com
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Satellite Communications
Course outlines
Lecture 1: Introduction To satellites.
Lecture 2: Keplers laws.
Lecture 3: Orbits and satellite coverage areas.
Lecture 4: Radio Link Analysis.
Lecture 5: Earth stations segment.
Lecture 6: satellite station segment.
Lecture 7: Satellites systems Modulation and accessing.
Lecture 8: Impairments of the Satellite link Communication.
Lecture 9: Interference in Satellite systems.
Lecture 10: Noise and rain effect in satellite link.
Lecture 11: Link budget of satellite system.
Lecture 12: VSAT.
Lecture 13: Advanced Topics.
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Satellite Communications
Lecture 1
Introduction
The use of the satellite systems in communication is very much a fact of everyday
life, as is evidenced by many homes which are equipped with antennas and dishes
used for reception of the satellite television. Satellite carry a large amount of data
and telephone traffic in addition to TV signals. Satellites also may use for remote
sensing, examples being the detection of water pollution, monitoring and
reporting the weather condition.
For 10,000 years (or 20,000 or since man was first able to lift his eyes upward)
he has wondered about questions such as "What holds the sun up in the sky?",
"Why doesn't the moon fall on us?", and "How do they (the sun and the moon)
return from the far west back to the far east to rise again each day?" Most of the
answers which men put for in those years we now classify as superstition,
mythology, or pagan religion. It is only in the last 300 years that we have
developed a scientific description of how those bodies travel. Our description of
course is based on fundamental laws put forth by the English genius Sir Isaac
Newton in the late 17th century.
The first of Newton's laws, which was a logical extension of earlier work by
Johannes Kepler, proposed that every bit of matter in the universe attracts every
other bit of matter with a force that is proportional to the product of their masses
and inversely proportional to the square of the distance between the two bits. That
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Satellite Communications
is, larger masses attract more strongly and the attraction gets weaker as the bodies
are moved farther apart. Newton's law of gravity means that the sun pulls on the
earth (and every other planet for that matter) and the earth pulls on the sun.
Furthermore, since both are quite large (by our standards at least) the force must
also be quite large. The question that almost every student asks is, "If the sun and
the planets are pulling on each other with such a large force, why don't the planets
fall into the sun?" The answer is simply
THEY ARE! The Earth, Mars, Venus, Jupiter and Saturn are continuously
falling into the Sun. The Moon is continuously falling into the Earth.
Our salvation is that they are also moving "sideways" with a sufficiently large
velocity that by the time the earth has fallen the 93,000,000 miles to the sun it
has also moved "sideways" about 93,000,000 miles - far enough to miss the sun.
By the time the moon has fallen the 240,000 miles to the earth, it has moved
sideways about 240,000 miles - far enough to miss the earth. This process is
repeated continuously as the earth (and all the other planets) make their
apparently unending trips around the sun and the moon makes its trips around the
earth. A planet, or any other body, which finds itself at any distance from the sun
with no "sideways" velocity will quickly fall without missing the sun, will be
drawn into the sun's interior, only our sideways motion (physicists call it our
"angular velocity) saves us. The same of course is true for the moon, which
would fall to earth but for its angular velocity. That means earth and other planets
moves around the sun by this phenomenon .This is illustrated in the drawing
below, figure (1).
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Figure (1): The Earth Orbits the Sun with Angular Velocity.
Selective Communications Satellite History
1945 Arthur C. Clarke Article: "Extra-Terrestrial Relays"
1955 John R. Pierce Article: "Orbital Radio Relays"
1956 First Trans-Atlantic Telephone Cable: TAT-1
1957 Sputnik: Russia launches the first earth satellite.
1960 1st Successful DELTA Launch Vehicle
1960 AT&T applies to FCC for experimental satellite communications
license
1961 Formal start of TELSTAR, RELAY, and SYNCOM Programs
1962 TELSTAR and RELAY launched
1962 Communications Satellite Act (U.S.)
1963 SYNCOM launched
1964 INTELSAT formed
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Satellite Communications
1965 COMSAT's EARLY BIRD: 1st commercial communications
satellite
1969 INTELSAT-III series provides global coverage
1972 ANIK: 1st Domestic Communications Satellite (Canada)
1974 WESTAR: 1st U.S. Domestic Communications Satellite
1975 INTELSAT-IVA: 1st use of dual-polarization
1975 RCA SATCOM: 1st operational body-stabilized comm. satellite
1976 MARISAT: 1st mobile communications satellite
1976 PALAPA: 3rd country (Indonesia) to launch domestic comm.
satellite
1979 INMARSAT formed.
1988 TAT-8: 1st Fiber-Optic Trans-Atlantic telephone cable.
Satellite definition and background
Satellite is a space craft that carries many communications equipments and
operation systems to support huge coverage to the earth. Supporting many types
of applications in very commutation fields.
For many years, such a velocity was unthinkable and the artificial satellite
remained a dream. Eventually, however, the technology (rocket engines,
guidance systems) caught up with the concept, largely as a result of weapons
research started by the Germans during the Second World War.
Finally, in 1957, the first artificial satellite, called Sputnik, was launched by the
Soviets. Consisting of little more than a spherical case with a radio transmitter, it
caused quite a stir. Americans were fascinated listening to the "beep. Beep. Beep"
of Sputnik appear and then fade out as it came overhead every 90 minutes. It was
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also quite frightening to think of the Soviets circling overhead in as much as they
were their mortal enemies. After Sputnik, it was only a few years before the U.S.
launched its own satellite; the Soviets launched Yuri Gagarin, the first man to
orbit the earth; and the U.S. launched John Glenn, the first American in orbit.
Every communications satellite in its simplest form -whether low earth or
geosynchronous- involves the transmission of information from an originating
ground station to the satellite (the uplink), followed by a retransmission of the
information from the satellite back to the ground (the downlink). The downlink
may either be to a select number of ground stations or it may be broadcast to
everyone in a large area.
Hence the satellite must have a receiver and a receive antenna, a transmitter and
a transmit antenna, some method for connecting the uplink to the downlink for
retransmission, and prime electrical power to run all of the electronics. The exact
nature of these components will differ, depending on the orbit and the system
architecture, but every communications satellite must have these basic
components. This is illustrated in figure (2).
Figure (2): Basic Components of a Communications Satellite Link.
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Frequency allocations for satellite services
Allocating frequency to the satellite services is a complicated process which
requires international coordination and planning. This is organized by the
international telecommunication union (ITU). To facilitate frequency planning
the world is divided into three regions;
Region 1: Europe, Africa, and what was formally the soviet union, Mongolia.
Region 2: north and South America and Greenland.
Region 3: Asia, Australia, and south west pacific.
Within this region frequency bands are allocated to various satellite services,
some of the services provided by the satellite are;
Fixed satellite services (FSS).
Broadcasting satellite services (BSS).
Mobile satellite services (MSS).
Navigation satellite services (NSS).
Metrological satellite services.
Fixed satellite service, FSS, which provides links for existing telephone
networks as well as transmitting television signals to cable companies in
order to redistribute over cable systems.
Broad-casting satellite service, BSS, those are intended mainly for direct
broad cast to home, sometimes referred to as direct broad cast satellite
service, DBS, and might be known as direct to home, DTH.
Mobile satellite services, MSS, those include land mobile, maritime
mobile and aeronautical mobile.
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Navigational satellite services, NSS, those include the global positioning
systems.
Meteorological satellite services, MSS, those are intended for the
meteorological satellite services, MSS, often provide a search and reuse
service.
Electromagnetic Frequency Band
Frequency range
3Hz 30 kHz
Band Designation
VLF (Very Low Frequency)
30 kHz 300 kHz
LF (Low Frequency)
300 kHz 3MHz
MF (Medium Frequency)
3MHz 30MHz
HF (High Frequency)
30MHz 300MHz
VHF (Very High Frequency)
300MHz 3GHz
UHF (Ultra High Frequency)
3GHz 30GHz
SHF (Super High Frequency)
30GHz 300GHz
EHF (Extremely High Frequency)
Satellite Frequency Band
Frequency range, GHz
0.1-0.3
0.3-1.0
1.0-2.0
2.0-4.0
4.0-8.0
8.0-12.0
12.0-18.0
18.0-24.0
24.0-40.0
40.0-100.0
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Band Designation
VHF
UHF
L
S
C
X
Ku
K
Ka
mm
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Satellite Applications
To provide general over view of satellite systems there are three types of
application:
The largest international system, Intelsat.
The domestic satellite system in the US, Domsat.
United Sates national oceanographic and atmospheric administration,
NOAA.
Intelsat
INTELSAT is a name derived from International Telecommunication
Satellite, the organization was established to handle the myriad of technical and
administrative problems associated with worldwide telecommunication systems.
it has over 140 member countries , they start with early bird satellite in 1965
currying number of voice channels , it cover three regions , Atlantic ocean region
(AOR) , Indian ocean region (IOR), and pacific ocean region (POR). The
satellites are positioned in a geostationary orbit. They have many versions of
satellites such as Intel I, II, and III, to V, VA, and VB.
US domsats
Domsat is an approbation of domestic satellite used to provide many
communication services, such as voice, data, and video transmitting within
country. In US all domsats are situated in geostationary orbit, it carries large
amount of commercial telecommunication traffic.
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Polar orbiting satellite (NOAA)
This satellites are cover north and south polar regions of earth. Such example
used this orbit is US experience with weather satellites which has led to the use
of relatively low orbit, ranging in altitude between 800 to 900 km , compared
with geo of 36000km. In US the national oceanic and atmospheric administrator
(NOAA) operate the weather satellites.
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Satellite Communications
Lecture 2
Keplers laws
Satellite is an object launched to orbit earth or another celestial body, in other
words it is celestial body that orbits a planet as well as it might be considered as
a secondary planet, which revolves about another planet. The artificial satellite is
a man-made object that orbits around the earth.
Orbit is the path of a celestial body or an artificial satellite as it revolves around
another body, it is said to be a one complete revolution of such a body, also, it is
the path of a body in a field of force surrounding another body.
Satellites are said to be spacecraft that orbits the earth following the same laws
that govern the motion of planets. Early, Johanne Kepler was able to drive
empirically three laws describing planetary motion. This laws are used to explain
the motion of the satellites around the earth.
Keplers First Law
States that the path followed by the satellite around the primary will be an
ellipse. The center of mass of the two-body system is termed the barycenter and
is always centered on one of the foci. In our case and because of the enormous
difference between the masses of the earth and the satellite the center of mass
coincides with the center of the earth which itself is at one of the foci. The
eccentricity and semi major axis are two of the orbital parameters specified for
satellites orbiting the earth.
= (2 2 )
Where a = semi major axis of ellipse,
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b= semi minor axis, e= eccentricity, e varies between zero and one [0 < e < 1]. If
e= 0 the orbit is circular, if e=1 the satellite will circulate randomly
Shows the foci F1, F2, the semi major axis a, and the semi major axis b, of an eclipse.
Keplers Second Law
Keplers second law states that for equal time intervals the satellite will sweep
out equal areas in its orbital plane, focused at the barycenter. Assume the satellite
travel distances S1 and S2 meters in 1 second then areas A1 and A2 will be equal.
If V1 and V2 are assumed to be an average velocities of two areas, and because
of the equal areas law, it follows that the velocity at S2 is less than that at S1. An
important sequence of this is that the satellite takes longer to travel a given
distance when it is farther away from earth.
Illustrates Keplers second law
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Keplers Third Law
Keplers third law states that the square of the periodic time of orbit is
proportional to the cube of the mean distance between the two bodies. The mean
distance is equal to the semi major axis, a. The law can be denoted by
a3 = /n2
Where n = the mean motion of satellite in rad/sec, = the earths geocentric
gravitational constant and equal to 3.986005 x 1014 m3/S2.
This law is applied only to the ideal situation of a satellite orbiting a perfectly
spherical earth of uniform mass with no perturbing forces acting but if there is the
orbital period will be given by P= 2/n. The importance of this third law is that it
shows that there is a fixed relationship between period and size.
example
Calculate the radius of the circular orbit for which the period is one day.
Solution
The mean motion in rad/ day is given by:
n= 2/ 1 day
n= 7.272*10-5 rad/sec
Earth gravitational constant is: = 3.986005*1014 m3. sec -2
Kepler third law;
a=
1/3
2
a= 42241 km
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